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Sample records for cdte crystals grown

  1. GROWTH KINETICS, CRYSTAL STRUCTURE, AND MORPHOLOGY OF OMVPE-GROWN HOMOEPITAXIAL CdTe

    OpenAIRE

    Snyder, D.; Sides, P.; Ko, E.; Mahajan, S.

    1991-01-01

    The growth rate, crystal structure, morphology, and electronic properties of homoepitaxial CdTe grown by OMVPE in an impinging jet reactor were investigated. Under operating conditions where surface reactions controlled the rate, the deposition rate depended on the diethyltelluride partial pressure to the .8 power and on the dimethylcadmium partial pressure to the .2 power, approximately. Cadmium was easily adsorbed and was ubiquitous on the surface during deposition ; tellurium was relativel...

  2. Photoluminescence of CdTe Crystals Grown by Physical Vapor Transport

    Science.gov (United States)

    Palosz, W.; Grasza, K.; Boyd, P. R.; Cui, Y.; Wright, G.; Roy, U. N.; Burger, A.

    2002-01-01

    High quality CdTe crystals with resistivities higher than 10(exp 8) omega cm were grown by the physical vapor transport technique. Indium, Aluminum, and the transition metal Scandium were introduced at the nominal level of about 6 ppm to the source material. Low-temperature photoluminescence (PL) has been employed to identify the origins of PL emissions of the crystals. The emission peaks at 1.584 eV and 1.581 eV were found only in the In-doped crystal. The result suggests that the luminescence line at 1.584 eV is associated with Cd-vacancy/indium complex. The intensity of the broadband centered at 1.43 eV decreases strongly with introduction of Sc.

  3. Photoluminescence of CdTe Crystals Grown by Contactless PVT Method

    Science.gov (United States)

    Palosz, W.; Grasza, K.; Cui, Y.; Wright, G.; Roy, U. N.; Burger, A.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    High quality CdTe crystals with resistivities higher than 10(exp 8) Omega cm were grown by the 'contactless' PVT (physical vapor transport) technique. Group III elements In and Al, and the transition metal Sc were introduced at the nominal level of about 6 ppm to the source material. Low-temperature photoluminescence (PL) has been employed to identify the origins of PL emissions of the crystals. It was found that the emission peaks at 1.584 eV and 1.581 eV exist only in the In-doped crystal. The result suggests that the luminescence line at 1.584 eV is associated with Cd-vacancy/indium complex. The intensity of the broadband centered at 1.43 eV decreases dramatically with introduction of Sc.

  4. Photoluminescence of CdTe Crystals Grown by Physical-Vapor Transport

    Science.gov (United States)

    Palosz, W.; Grasza, K.; Boyd, P. R.; Cui, Y.; Wright, G.; Roy, U. N.; Burger, A.

    2003-01-01

    High-quality CdTe crystals with resistivities higher than 10(exp 8) omega cm were grown by the physical-vapor transport (PVT) technique. Indium, aluminum, and the transition-metal scandium were introduced at the nominal level of about 6 ppm to the source material. Low-temperature photoluminescence (PL) has been employed to identify the origins of PL emissions of the crystals. The emission peaks at 1.584 eV and 1.581 eV were found only in the In-doped crystal. The result suggests that the luminescence line at 1.584 eV is associated with Cd-vacancy/In complex. The intensity of the broadband centered at 1.43 eV decreases strongly with introduction of Sc.

  5. Crystal Growth and Characterization of CdTe Grown by Vertical Gradient Freeze

    Science.gov (United States)

    Su, Ching-Hua; Lehoczky, S. L.; Raghothamachar, B.; Dudley, M.

    2007-01-01

    In this study, crystals of CdTe were grown from melts by the unseeded vertical gradient freeze method. The quality of grown crystal were studied by various characterization techniques including Synchrotron White Beam X-ray Topography (SWBXT), chemical analysis by glow discharge mass spectroscopy (GDMS), low temperature photoluminescence (PL), and Hall measurements. The SWBXT images from various angles show nearly strain-free grains, grains with inhomogeneous strains, as well as twinning nucleated in the shoulder region of the boule. The GDMS chemical analysis shows the contamination of Ga at a level of 3900 ppb, atomic. The low temperature PL measurement exhibits the characteristic emissions of a Ga-doped sample. The Hall measurements show a resistivity of 1 x l0(exp 7) ohm-cm at room temperature to 3 x 10(exp 9) ohm-cm at 78K with the respective hole and electron concentration of 1.7 x 10(exp 9) cm(exp -3) and 3.9 x 10(exp 7) cm(exp -3) at room temperature.

  6. Evolution of transport properties along a semi-insulating CdTe crystal grown by vertical gradient freeze method

    International Nuclear Information System (INIS)

    The evolution of transport properties along a chlorine-doped CdTe crystal grown by the gradient freeze (GF) method has been investigated by time of flight (TOF) measurement. Drift mobilities as high as 1100 cm2/(Vs) and 80 cm2/(Vs) for electrons and holes, respectively, are measured at the initial part of the grown crystal, and were found to decrease with increasing solidified fraction (g). On the other hand, the specific resistivity increases with increasing g. These behaviors can be understood as the dopant (Cl) concentration variation due to segregation during growth. The change in γ-detection properties between crystals having different g is demonstrated. (author)

  7. Research into the electrical property variation of undoped CdTe and ZnTe crystals grown under Te-rich conditions

    International Nuclear Information System (INIS)

    Highlights: • Conductivity type and resistivity of undoped Te-rich ZnTe and CdTe are different. • Tei and VZn as the dominant defects account for the p-type low resistivity ZnTe. • TeCd as the principle defect leading to the light n-type high resistivity CdTe. • DAP and eA peaks dominate the luminescence with their intensities anti-correlated. - Abstract: Both undoped ZnTe and CdTe bulk single crystals are grown under Te-saturated conditions from the solution and melt, respectively. To give an insight into the variation of the electrical properties, the defects structures in both tellurides are discussed. According to the actual growth velocities and the entire cooling history, tellurium interstitials (Tei) and Zinc vacancies (VZn) are proposed as the dominant grown-in defects, account for the low resistivity of p-type ZnTe. However, relatively high pulling rates and slow cooling-down processes result in tellurium anti-sites (TeCd) as the principle grown-in defects, leading to the high resistivity of light n-type CdTe. Further low-temperature (8.6 K) photoluminescence spectra of both tellurides are obtained. The donor–acceptor pair (DAP) and recombination of free electron to neutral acceptor (eA) dominate the luminescence, however, with their intensities are anti-correlated. eA is superior to DAP in undoped Te-rich ZnTe, suggests a high concentration of Tei or VZn. On the contrary, DAP is the principal emission for undoped Te-rich CdTe. In addition, V-line is clearly identified in undoped Te-rich ZnTe, which possibly associated with VZn or close Frenkel pair VZn–Zni

  8. Characterisation of vapour phase grown CdTe and (Cd,Zn)Te for detector applications

    CERN Document Server

    Fiederle, M; Rogalla, M; Meinhardt, J; Ludwig, J; Runge, K; Benz, W

    1999-01-01

    The growth of CdTe from the vapour phase offers several improvements in crystal quality and homogeneity. CdTe and (Cd, Zn)Te were grown by the modified Markov technique. The transport properties and the detector performance are given and compared to melt grown material. (author)

  9. Preparation and properties of evaporated CdTe films compared with single crystal CdTe

    Science.gov (United States)

    Bube, R. H.

    The hot wall vacuum deposition system is discussed and is is good temperature tracking between the furnace core and the CdTe source itself are indicated. Homojunction cells prepared by HWVE deposition of n-CdTe on p-CdTe substrates show no significant change in dark or light properties after open circuit storage for the next 9 months. CdTe single crystal boules were grown with P, As and Cs impurity. For P impurity it appears that the segregation coefficient is close to unity, that the value of hole density is controlled by the P, and that growth with excess Cd gives slightly higher values of hole density than growth with excess Te. CdTe:As crystals appear similar to CdTe:P crystals.

  10. Single-Crystal CdTe Homojunction Structures for Solar Cell Applications

    Science.gov (United States)

    Su, Peng-Yu; Dahal, Rajendra; Wang, Gwo-Ching; Zhang, Shengbai; Lu, Toh-Ming; Bhat, Ishwara B.

    2015-09-01

    We report two different CdTe homojunction solar cell structures. Single-crystal CdTe homojunction solar cells were grown on GaAs single-crystal substrates by metalorganic chemical vapor deposition. Arsenic and iodine were used as dopants for p-type and n-type CdTe, respectively. Another homojunction solar cell structure was fabricated by growing n-type CdTe directly on bulk p-type CdTe single-crystal substrates. The electrical properties of the different layers were characterized by Hall measurements. When arsine was used as arsenic source, the highest hole concentration was ~6 × 1016 cm-3 and the activation efficiency was ~3%. Very abrupt arsenic doping profiles were observed by secondary ion mass spectrometry. For n-type CdTe with a growth temperature of 250°C and a high Cd/Te ratio the electron concentration was ~4.5 × 1016 cm-3. Because of the 300 nm thick n-type CdTe layer, the short circuit current of the solar cell grown on the bulk CdTe substrate was less than 10 mA/cm2. The open circuit voltage of the device was 0.86 V. According to a prediction based on measurement of short circuit current density ( J sc) as a function of open circuit voltage ( V oc), an open circuit voltage of 0.92 V could be achieved by growing CdTe solar cells on bulk CdTe substrates.

  11. MBE-Grown CdTe Layers on GaAs with In-assisted Thermal Deoxidation

    Science.gov (United States)

    Arı, Ozan; Bilgilisoy, Elif; Ozceri, Elif; Selamet, Yusuf

    2016-03-01

    Molecular beam epitaxy (MBE) growth of thin (˜2 μm) CdTe layers characterized by high crystal quality and low defect density on lattice mismatched substrates, such as GaAs and Si, has thus far been difficult to achieve. In this work, we report the effects of in situ thermal deoxidation under In and As4 overpressure prior to the CdTe growth on epiready GaAs(211)B wafers, aiming to enhance CdTe crystal quality. Thermally deoxidized GaAs samples were analyzed using in situ reflection high energy electron diffraction, along with ex situ x-ray photo-electron spectroscopy (XPS) and atomic force microscopy. MBE-grown CdTe layers were characterized using x-ray diffraction (XRD) and Everson-type wet chemical defect decoration etching. We found that In-assisted desorption allowed for easier surface preparation and resulted in a smoother surface compared to As-assisted surface preparation. By applying In-assisted thermal deoxidation to GaAs substrates prior to the CdTe growth, we have obtained single crystal CdTe films with a CdTe(422) XRD rocking curve with a full-width half-maximum value of 130.8 arc-s and etch pit density of 4 × 106 cm-2 for 2.54 μm thickness. We confirmed, by XPS analysis, no In contamination on the thermally deoxidized surface.

  12. Photoluminescence of CdTe nanocrystals grown by pulsed laser ablation on a template of Si nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Guillen-Cervantes, A.; Silva-Lopez, H.; Becerril-Silva, M.; Arias-Ceron, J.S.; Campos-Gonzalez, E.; Zelaya-Angel, O. [CINVESTAV-IPN, Physics Department, Apdo. Postal 14-740, Mexico (Mexico); Medina-Torres, A.C. [Escuela Superior de Fisica y Matematicas del IPN, Mexico (Mexico)

    2014-11-12

    CdTe nanocrystals were grown on eroded Si (111) substrates at room temperature by pulsed laser ablation. Before growth, Si substrates were subjected to different erosion time in order to investigate the effect on the CdTe samples. The erosion process consists of exposition to a pulsed high-voltage electric arc. The surface consequence of the erosion process consists of Si nanoparticles which acted as a template for the growth of CdTe nanocrystals. CdTe samples were studied by X-ray diffraction (XRD), room temperature photoluminescence (RT PL) and high-resolution transmission electron microscopy (HRTEM). CdTe nanocrystals grew in the stable cubic phase, according to XRD spectra. A strong visible emission was detected in photoluminescence (PL) experiments. The PL signal was centered at 540 nm (∝2.34 eV). With the effective mass approximation, the size of the CdTe crystals was estimated around 3.5 nm. HRTEM images corroborated the physical characteristics of CdTe nanocrystals. These results could be useful for the development of CdTe optoelectronic devices. (orig.)

  13. Photoluminescence of CdTe nanocrystals grown by pulsed laser ablation on a template of Si nanoparticles

    International Nuclear Information System (INIS)

    CdTe nanocrystals were grown on eroded Si (111) substrates at room temperature by pulsed laser ablation. Before growth, Si substrates were subjected to different erosion time in order to investigate the effect on the CdTe samples. The erosion process consists of exposition to a pulsed high-voltage electric arc. The surface consequence of the erosion process consists of Si nanoparticles which acted as a template for the growth of CdTe nanocrystals. CdTe samples were studied by X-ray diffraction (XRD), room temperature photoluminescence (RT PL) and high-resolution transmission electron microscopy (HRTEM). CdTe nanocrystals grew in the stable cubic phase, according to XRD spectra. A strong visible emission was detected in photoluminescence (PL) experiments. The PL signal was centered at 540 nm (∝2.34 eV). With the effective mass approximation, the size of the CdTe crystals was estimated around 3.5 nm. HRTEM images corroborated the physical characteristics of CdTe nanocrystals. These results could be useful for the development of CdTe optoelectronic devices. (orig.)

  14. Characterization of CdTe, (Cd,Zn)Te, and Cd(Te,Se) single crystals by transmission electron microscopy

    Science.gov (United States)

    Rai, R. S.; Mahajan, S.; McDevitt, S.; Johnson, C. J.

    1991-10-01

    CdTe, (Cd,Zn)Te, and Cd(Te,Se) crystals grown by the Bridgman technique have been characterized by transmission electron microscopy. Results indicate that the Te precipitates are seen in all the crystals, but their density and size are lowest and largest in the case of Cd(Te,Se) crystals. In addition, dislocations, stacking faults, and microtwins are observed in as-grown CdTe, (Cd,Zn)Te, and Cd(Te,Se) crystals. Arguments have been developed to rationalize these observations and their ramifications on crystal perfection are discussed.

  15. Device Fabrication using Crystalline CdTe and CdTe Ternary Alloys Grown by MBE

    Energy Technology Data Exchange (ETDEWEB)

    Zaunbrecher, Katherine; Burst, James; Seyedmohammadi, Shahram; Malik, Roger; Li, Jian V.; Gessert, Timothy A.; Barnes, Teresa

    2015-06-14

    We fabricated epitaxial CdTe:In/CdTe:As homojunction and CdZnTe/CdTe and CdMgTe/CdTe heterojunction devices grown on bulk CdTe substrates in order to study the fundamental device physics of CdTe solar cells. Selection of emitter-layer alloys was based on passivation studies using double heterostructures as well as band alignment. Initial results show significant device integration challenges, including low dopant activation, high resistivity substrates and the development of low-resistance contacts. To date, the highest open-circuit voltage is 715 mV in a CdZnTe/CdTe heterojunction following anneal, while the highest fill factor of 52% was attained in an annealed CdTe homojunction. In general, all currentvoltage measurements show high series resistance, capacitancevoltages measurements show variable doping, and quantum efficiency measurements show low collection. Ongoing work includes overcoming the high resistance in these devices and addressing other possible device limitations such as non-optimum junction depth, interface recombination, and reduced bulk lifetime due to structural defects.

  16. Research on single-crystal CdTe solar cells

    Science.gov (United States)

    Borrego, J. M.; Ghandhi, S. K.

    1987-10-01

    This report outlines two years of work on the growth and characterization of single-crystal CdTe layers, to explore their potential for high-efficiency solar cells. It was demonstrated that high-quality layers can be grown by organometallic vapor phase epitaxy (OMVPE), whose photoluminescence peak has a FWHM of 5.8 MeV, the lowest value for them yet achieved. CdTe layers were extrinsically doped both n- and p-type with indium and arsenic, respectively. The doping level achieved for p-type is the highest yet reported in the literature, achieved for the first time in an OMVPE system. A hole lifetime of 2.0 microns was measured. In the n-type material, five deep levels were isolated; their capture cross section, energy level, and concentration were determined. A thermodynamic analysis was made to identify their defect character. Both Schottky and p-n junction devices were produced on these layers. The diode characteristics were superior to those of GaAs so this is a potentially superior material for solar cells.

  17. Crystal Growth of CdTe by Gradient Freeze in Universal Multizone Crystallizator (UMC)

    Science.gov (United States)

    Su, Ching-Hua; Lehoczky, S. L.; Li, C.; Knuteson, D.; Raghothamachar, B.; Dudley, M.; Szoke, J.; Barczy, P.

    2004-01-01

    In the case of unsealed melt growth of an array of II-VI compounds, namely, CdTe, CdZnTe and ZnSe, there is a tremendous amount of experimental data describing the correlations between melt conditions and crystal quality. The results imply that the crystallinity quality can be improved if the melt was markedly superheated or long-time held before growth. It is speculated that after high superheating the associated complex dissociate and the spontaneous nucleation is retarded. In this study, crystals of CdTe were grown from melts which have undergone different thermal history by the unseeded gradient freeze method using the Universal Multizone Crystallizator (UMC). The effects of melt conditions on the quality of grown crystal were studied by various characterization techniques, including Synchrotron White Beam X-ray Topography (SWSXT), infrared microscopy, chemical analysis by glow discharge mass spectroscopy (GDMS), electrical conductivity and Hall measurements.

  18. HgTe and CdTe epitaxial layers and HgTe–CdTe superlattices grown by laser molecular beam epitaxy

    OpenAIRE

    Cheung, J. T.; Niizawa, G.; Moyle, J.; Ong, N. P.; Paine, B. M.; Vreeland, T., Jr.

    1986-01-01

    CdTe and HgTe epilayers and HgTe/CdTe superlattices have been grown by laser molecular beam epitaxy (laser MBE) on CdTe substrates. The power density of the laser radiation used to evaporate source materials was found to be a very important growth parameter. The superlattice structures have been characterized by helium ion backscattering spectrometry, x-ray double crystal diffractometry, and low temperature electrical transport measurements. Results indicate good crystallinity and very strong...

  19. Ultra low density of CdTe quantum dots grown by MBE

    OpenAIRE

    Kobak, J.; Rousset, J. -G.; Rudniewski, R.; Janik, E.; S\\lupiński; Kossacki, P.; Golnik, A.; Pacuski, W.

    2012-01-01

    This work presents methods of controlling the density of self-assembled CdTe quantum dots (QDs) grown by molecular beam epitaxy. Two approaches are discussed: increasing the deposition temperature of CdTe and the reduction of CdTe layer thickness. Photoluminescence (PL) measurements at low temperature confirms that both methods can be used for significant reduction of QDs density from 1010QD/cm2 to 107-108QD/cm2. For very low QDs density, identification of all QDs lines observed in the spectr...

  20. Properties of CdTe nanocrystalline thin films grown on different substrates by low temperature sputtering

    Institute of Scientific and Technical Information of China (English)

    Chen Huimin; Guo Fuqiang; Zhang Baohua

    2009-01-01

    CdTe nanocrystalline thin films have been prepared on glass, Si and Al2O3 substrates by radio-frequency magnetron sputtering at liquid nitrogen temperature. The crystal structure and morphology of the films were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The XRD examinations revealed that CdTe films on glass and Si had a better crystal quality and higher preferential orientation along the (111) plane than the Al2O3. FESEM observations revealed a continuous and dense morphology of CdTe films on glass and Si substrates. Optical properties of nanocrystalline CdTe films deposited on glass substrates for different deposited times were studied.

  1. Melt growth of CdTe crystals and transmission electron microscopic investigations of their grain boundaries

    Energy Technology Data Exchange (ETDEWEB)

    Sabinina, I.V.; Gutakovski, A.K.; Milenov, T.I.; Lyakh, N.N.; Sidorov, Y.G.; Gospodinov, M.M. (Inst. of Semiconductor Physics, Academy of Sciences of the USSR (Siberian Branch), Novosibirsk (USSR) Inst. of Solid State Physics, Bulgarian Academy of Sciences, Sofia (Bulgaria))

    1991-01-01

    Transmission electron microscopy investigations are carried out on CdTe crystals grown in quartz ampoules in a temperature region (1020-1091degC) near to the melting point of 1092degC, by travelling heater method in quasi-closed and in sealed (at 0.135 Pa) volume, and by the Bridgman method from nearly stoichiometric melts. An original method for preparation of CdTe thin foil is reported. Two types of grain boundaries are observed: high-angle misoriented grain boundaries (more than ten degrees misorientation between adjacent grains) and low-angle misoriented grain boundaries (less than one degree misorientation between adjacent sub-grain). Both dislocations with Burgers vector b=a/6<112> and b=a/2<110> are present. (orig.).

  2. Growth and characterization of CdTe single crystals for radiation detectors

    CERN Document Server

    Funaki, M; Satoh, K; Ohno, R

    1999-01-01

    To improve the productivity of CdTe radiation detectors, the crystal growth by traveling heater method (THM) as well as the quality of the fabricated detectors were investigated. In the THM growth, optimization of the solvent volume was found to be essential because it affects the shape of the growth interface. The use of the slightly tilted seed from B was also effective to limit the generation of twins having different directions. Single-crystal (1 1 1) wafers, larger than 30x30 mm sup 2 were successfully obtained from a grown crystal of 50 mm diameter. Pt/CdTe/Pt detectors of dimensions 4x4x2 mm sup 3 , fabricated from the whole crystal ingot, showed an energy resolution (FWHM of 122 keV peak from a sup 5 sup 7 Co source) between 6% and 8%. Similarly, Pt/CdTe/In detectors of dimensions 2x2x0.5 mm sup 3 showed a resolution better than 3%. These characteristics encourage the practical applications of various types of CdTe detectors.

  3. CdTe and CdZnTe crystals for room temperature gamma-ray detectors

    CERN Document Server

    Franc, J; Belas, E; Grill, R; Hlidek, P; Moravec, P; Bok, J B

    1999-01-01

    CdTe(Cl) detectors from CdTe single crystals, grown by the Bridgman method from Te-rich melt, were fabricated. The quality of the detectors was tested with sup 5 sup 7 Co and sup 2 sup 4 sup 1 Am sources. In the sup 5 sup 7 Co spectrum low noise is demonstrated by the presence of a 14 keV peak and good resolution approx 7 keV (FWHM) evident from the separation of 122 and 136 keV peaks. A review is given of the state-of-the-art properties of (CdZn)Te single crystals prepared for substrates in the Institute of Physics of Charles University. The quality of samples is tested by measurements of the diffusion length of minority carriers, from which the mobility-lifetime product is evaluated. (author)

  4. Impact of extended defects on recombination in CdTe heterostructures grown by molecular beam epitaxy

    Science.gov (United States)

    Zaunbrecher, Katherine N.; Kuciauskas, Darius; Swartz, Craig H.; Dippo, Pat; Edirisooriya, Madhavie; Ogedengbe, Olanrewaju S.; Sohal, Sandeep; Hancock, Bobby L.; LeBlanc, Elizabeth G.; Jayathilaka, Pathiraja A. R. D.; Barnes, Teresa M.; Myers, Thomas H.

    2016-08-01

    Heterostructures with CdTe and CdTe1-xSex (x ˜ 0.01) absorbers between two wider-band-gap Cd1-xMgxTe barriers (x ˜ 0.25-0.3) were grown by molecular beam epitaxy to study carrier generation and recombination in bulk materials with passivated interfaces. Using a combination of confocal photoluminescence (PL), time-resolved PL, and low-temperature PL emission spectroscopy, two extended defect types were identified and the impact of these defects on charge-carrier recombination was analyzed. The dominant defects identified by confocal PL were dislocations in samples grown on (211)B CdTe substrates and crystallographic twinning-related defects in samples on (100)-oriented InSb substrates. Low-temperature PL shows that twin-related defects have a zero-phonon energy of 1.460 eV and a Huang-Rhys factor of 1.50, while dislocation-dominated samples have a 1.473-eV zero-phonon energy and a Huang-Rhys factor of 1.22. The charge carrier diffusion length near both types of defects is ˜6 μm, suggesting that recombination is limited by diffusion dynamics. For heterostructures with a low concentration of extended defects, the bulk lifetime was determined to be 2.2 μs with an interface recombination velocity of 160 cm/s and an estimated radiative lifetime of 91 μs.

  5. Impact of extended defects on recombination in CdTe heterostructures grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Zaunbrecher, Katherine N. [Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA; National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Kuciauskas, Darius [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Swartz, Craig H. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Dippo, Pat [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Edirisooriya, Madhavie [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Ogedengbe, Olanrewaju S. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Sohal, Sandeep [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Hancock, Bobby L. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; LeBlanc, Elizabeth G. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Jayathilaka, Pathiraja A. R. D. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA; Barnes, Teresa M. [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Myers, Thomas H. [Materials Science, Engineering and Commercialization Program, Texas State University, San Marcos, Texas 78666, USA

    2016-08-29

    Heterostructures with CdTe and CdTe 1-xSex (x ~ 0.01) absorbers between two wider-band-gap Cd1-xMgxTe barriers (x ~ 0.25-0.3) were grown by molecular beam epitaxy to study carrier generation and recombination in bulk materials with passivated interfaces. Using a combination of confocal photoluminescence (PL), time-resolved PL, and low-temperature PL emission spectroscopy, two extended defect types were identified and the impact of these defects on charge-carrier recombination was analyzed. The dominant defects identified by confocal PL were dislocations in samples grown on (211)B CdTe substrates and crystallographic twinning-related defects in samples on (100)-oriented InSb substrates. Low-temperature PL shows that twin-related defects have a zero-phonon energy of 1.460 eV and a Huang-Rhys factor of 1.50, while dislocation-dominated samples have a 1.473-eV zero-phonon energy and a Huang-Rhys factor of 1.22. The charge carrier diffusion length near both types of defects is ~6 um, suggesting that recombination is limited by diffusion dynamics. For heterostructures with a low concentration of extended defects, the bulk lifetime was determined to be 2.2 us with an interface recombination velocity of 160 cm/s and an estimated radiative lifetime of 91 us.

  6. Characterization of CdTe, HgTe, and Hg1-xCdxTe grown by chemical beam epitaxy

    Science.gov (United States)

    Wagner, B. K.; Rajavel, D.; Benz, R. G.; Summers, C. J.

    1991-10-01

    Detailed characterization of chemical beam epitaxially (CBE) grown CdTe and Hg1-xCdxTe layers are reported. These characterizations include photoluminescence, infrared transmission, energy dispersive x-ray analysis, and variable temperature (10-300 K) Hall effect and resistivity measurements. The results indicate that high quality HgCdTe layers can be grown by CBE.

  7. SEM, EDS, PL and absorbance study of CdTe thin films grown by CSS method

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Torres, M.E.; Silva-Gonzalez, R.; Gracia-Jimenez, J.M. [Instituto de Fisica, BUAP, Apdo. Postal J-48, San Manuel, 72570 Puebla, Pue. (Mexico); Casarrubias-Segura, G. [CIE- UNAM, 62580 Temixco, Morelos (Mexico)

    2006-09-22

    Oxygen-doped CdTe films were grown on conducting glass substrates by the close spaced sublimation (CSS) method and characterized using SEM, EDS, photoluminescence (PL) and absorbance. A significant change in the polycrystalline morphology is observed when the oxygen proportion is increased in the deposition atmosphere. The EDS analysis showed that all samples are nonstoichiometric with excess Te. The PL spectra show emission bands associated with Te vacancies (V{sub Te}), whose intensities decrease as the oxygen proportion in the CSS chamber is increased. The oxygen impurities occupy Te vacancies and modify the surfaces states, improving the nonradiative process. (author)

  8. Vapor-phase epitaxial growth of thick single crystal CdTe on Si substrate for X-ray, gamma ray spectroscopic detector development

    Energy Technology Data Exchange (ETDEWEB)

    Niraula, Madan; Yasuda, Kazuhito; Yamashita, Hayate; Wajima, Yuto; Tsukamoto, Yudai; Matsumoto, Masahiko; Suzuki, Yuta; Takai, Noriaki; Tsukamoto, Yuki; Agata, Yasunori [Nagoya Institute of Technology, Graduate School of Engineering, Gokiso, Showa, Nagoya 466-8555 (Japan)

    2014-07-15

    We investigated MOVPE growth conditions to grow large-area and thick single crystal CdTe layers with uniform material properties directly on (211) Si substrates to develop nuclear radiation detectors. We found that group VI/II precursor flow-ratio as well as rapid thermal annealing performed by interrupting the growth at the initial stage has marked influence on the crystal quality. By using a VI/II precursor ratio of 3.0, and a 900 C anneal performed in flowing hydrogen, we were able to achieve 1-sq inch sized thick single crystal CdTe that showed uniform material properties and high crystal quality throughout the wafer. We further demonstrated that the grown crystals were suitable for fabricating nuclear radiation detector. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Position-sensitive CdTe detector using improved crystal growth method

    Science.gov (United States)

    1988-09-01

    The feasibility of developing a position-sensitive CdTe detector array for astronomical observations in the hard X-ray, soft gamma ray region is demonstrated. In principle, it was possible to improve the resolution capability for imaging measurements in this region by orders of magnitude over what is now possible through the use of CdTe detector arrays. The objective was to show that CdTe crystals of the quality, size and uniformity required for this application can be obtained with a new high pressure growth technique. The approach was to fabricate, characterize and analyze a 100 element square array and several single-element detectors using crystals from the new growth process. Results show that detectors fabricated from transversely sliced, 7 cm diameter wafers of CdTe exhibit efficient counting capability and a high degree of uniformity over their entire areas. A 100 element square array of 1 sq mm detectors was fabricated and operated.

  10. CdTe and HgI2 crystals and detectors: present state and future

    International Nuclear Information System (INIS)

    After recalling the main properties of CdTe and HgI2 crystals from which the characteristics of these detectors will arise, the fabrication cycle is analysed at its various stages. The results at present achieved on CdTe and HgI2 detectors are analysed with a number of concrete applications in view such as medium power (0-200 keV) X and γ spectrometry, localisation of γ photons and solid ionisation chambers

  11. Chemical structure of microcrystalline CdTe films grown by RF sputtering

    Science.gov (United States)

    Hernández-Calderón, I.; Jiménez-Sandoval, S.; Peña, J. L.; Sailer, V.

    1990-01-01

    We have applied X-ray photoemission and Auger spectroscopy techniques to the study of the stoichiometric properties of CdTe thin films grown by RF sputtering. The microcrystalline films were deposited on glass substrates held at temperatures between 50 and 200°C. They contain a mixture of the cubic (zinc-blende) and hexagonal (wurtzite) phases which are nearly stoichiometric. By using bulk and surface sensitive photoemission geometries it is shown that a tellurium oxide overlayer is always formed after exposure to air. A simple calculation shows that this overlayer is at most 10 Å thick. Cadmium seems to be insensitive to the presence of oxygen, as demonstrated by the absence of shifted Cd peaks in the X-ray spectra. It is shown that the low kinetic energy features in the Auger spectra ( oxide overlayer and contamination.

  12. Transmission electron microscopy study of CdTe(111) grown on GaAs(100) by molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Reno, J.L.; Carr, M.J.; Gourley, P.L. (Sandia National Laboratory, Albuquerque, New Mexico 87185 (USA))

    1990-05-01

    We have used transmission electron microscopy to investigate CdTe(111) grown on GaAs(100) by molecular-beam epitaxy. The loop structure previously observed by photoluminescence microscopy has been identified as the boundary between twinned microcrystallites that extend from the CdTe/GaAs interface to the CdTe surface. When viewed along the growth axis, these boundaries between the columnar twins appear as loops and segments. Surface roughness of the GaAs substrate contributes to the initial growth of twinned material. This leads to competitive growth between the twins and the creation of the observed columnar twins.

  13. Energy Band Gap, Intrinsic Carrier Concentration and Fermi Level of CdTe Bulk Crystal between 304 K and 1067 K

    Science.gov (United States)

    Su, Ching-Hua

    2007-01-01

    Optical transmission measurements were performed on CdTe bulk single crystal. It was found that when a sliced and polished CdTe wafer was used, a white film started to develop when the sample was heated above 530 K and the sample became opaque. Therefore, a bulk crystal of CdTe was first grown in the window area by physical vapor transport; the optical transmission was then measured and from which the energy band gap was derived between 304 and 1067 K. The band gaps of CdTe can be fit well as a function of temperature using the Varshini expression: Eg (e V) = 1.5860 - 5.9117xl0(exp -4) T(sup 2)/(T + 160). Using the band gap data, the high temperature electron-hole equilibrium was calculated numerically by assuming the Kane's conduction band structure and a heavy-hole parabolic valance band. The calculated intrinsic carrier concentrations agree well with the experimental data reported previously. The calculated intrinsic Fermi levels between 270 and 1200 K were also presented.

  14. Mechanism of the high X-ray sensitivity of single-crystal CdTe detectors

    International Nuclear Information System (INIS)

    One investigated into the effect of germanium amorphous impurities on X-ray sensitivity and on other features of single-crystals. One investigated into CdTe heat-stable crystals. One proposes a model of a local rearrangement of crystalline lattice near GeCd impurity atom. High X-ray sensitivity of CdTe doped by Ge impurity (doping levels = 3.0x1015 cm-3) is explained by difference of mobility of electrons and holes under ambipolar X-ray conductivity. The optimal impurity-defect composition of p-CdTe crystals serving as high-sensitive active elements of X-ray detectors is characterized by presence of GeCd, VCd defects and of VTe-Tei Frenkel pairs

  15. Effects of heat treatment on diffusion of Cu atoms into CdTe single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Soo, Y. L. [Department of Physics, State University of New York at Buffalo, Amherst, New York 14260 (United States); Huang, S. [Department of Physics, State University of New York at Buffalo, Amherst, New York 14260 (United States); Kim, S. [Department of Physics, State University of New York at Buffalo, Amherst, New York 14260 (United States); Kioseoglou, G. [Department of Physics, State University of New York at Buffalo, Amherst, New York 14260 (United States); Kao, Y. H. [Department of Physics, State University of New York at Buffalo, Amherst, New York 14260 (United States); Compaan, A. D. [Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606 (United States); Grecu, D. [Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606 (United States); Albin, D. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States)

    2000-06-19

    Angular dependence of x-ray fluorescence and x-ray absorption fine structure techniques have been used to study the diffusion of Cu atoms into the photovoltaic material CdTe. Depth profile, effective valency, and local structure of Cu atoms in a Cu-doped single crystal of CdTe were investigated before and after a second heat treatment. Enhanced Cu diffusion into the CdTe single crystal was observed as a result of heating at a moderate temperature around 200 degree sign C, resulting in a redistribution of the Cu impurities through a broader depth profile. Some of the Cu atoms are believed either to form small complexes with Te or occupy interstitial sites in the host but accompanied by a large local lattice distortion while others substitute for Cd on the cation sites. The results thus demonstrate that these nondestructive x-ray characterization methods are useful for probing microstructural changes in CdTe photovoltaic materials/devices in which some Cu-containing compounds are used as back contacts. (c) 2000 American Institute of Physics.

  16. Optical characterization of epitaxial single crystal CdTe thin films on Al{sub 2}O{sub 3} (0001) substrates

    Energy Technology Data Exchange (ETDEWEB)

    Jovanovic, S.M.; Devenyi, G.A., E-mail: devenyga@mcmaster.ca; Jarvis, V.M.; Meinander, K.; Haapamaki, C.M.; Kuyanov, P.; Gerber, M.; LaPierre, R.R.; Preston, J.S.

    2014-11-03

    The optoelectronic properties of single crystal CdTe thin films were investigated by photoluminescence spectroscopy, photoreflectance spectroscopy and variable angle spectroscopic ellipsometry. The room temperature bandgap was measured to be 1.51 eV and was consistent between spectroscopic measurements and previously reported values. Breadth of bandgap emission was consistent with high quality material. Low temperature photoluminescence spectra indicated a dominant emission consistent with bound excitons. Emissions corresponding to self-compensation defects, doping and contaminants were not found. Variable angle spectroscopic ellipsometry measurements over the near-UV to infrared range demonstrated sharp resonance peaks. All spectroscopic measurements indicate high quality thin film material of comparable or better quality than bulk CdTe. - Highlights: • High quality epitaxial CdTe thin films were grown. • Two dimensional X-ray diffraction characterization confirmed single crystal material. • Photoluminescence indicated low defect density when compared to bulk single crystals. • Optical characterization indicated the presence of room temperature excitons.

  17. Nonresonant four wave mixing in photorefractive CdTe crystals using a picosecond parametric generator

    OpenAIRE

    Jarasiunas, Kestutis; Gudelis, Vytautas; Delaye, Philippe; Roosen, Gérald

    1998-01-01

    We demonstrate that a parametrically pumped picosecond laser has enough coherence and energy to write transient phase gratings at nonresonant interaction, thus allowing a study of time-resolved carrier transport in CdTe crystals to be made. Autocorrelation trace of light diffraction efficiency on transient grating allowed us to measure a coherence length of the parametric generator. Carrier diffusion, recombination, and drift in light-created internal space-charge ~SC! electric fields have be...

  18. Crystal growth of CdTe in space and thermal field effects on mass flux and morphology

    Science.gov (United States)

    Wiedemeier, H.

    1988-01-01

    The primary, long-range goals are the development of vapor phase crystal growth experiments, and the growth of technologically useful crystals in space. The necessary ground-based studies include measurements of the effects of temperature variations on the mass flux and crystal morphology in vapor-solid growth processes. For in-situ mass flux measurements dynamic microbalance techniques will be employed. Crystal growth procedures and equipment will be developed to be compatible with microgravity conditions and flight requirements. Emphasis was placed on the further development of crystal growth and the investigation of relevant transport properties of CdTe. The dependence of the mass flux on source temperature was experimentally established. The CdTe synthesis and pretreatment procedures are being developed that yield considerable improvements in mass transport rates, and mass fluxes which are independent of the amount of source material. A higher degree of stoichiometric control of CdTe than before was achieved during this period of investigation. Based on this, a CdTe crystal growth experiment, employing physical vapor transport, yielded very promising results. Optical microscopy and X-ray diffraction studies revealed that the boule contained several large sized crystal grains of a high degree of crystallinity. Further characterization studies of CdTe crystals are in progress. The reaction chamber, furnace dimensions, and ampoule location of the dynamic microbalance system were modified in order to minimize radiation effects on the balance performance.

  19. Growth of CdTe films on GaAs by ionized cluster beam epitaxy

    Science.gov (United States)

    Tang, H. P.; Feng, J. Y.; Fan, Y. D.; Li, H. D.

    1991-06-01

    Stoichiometric epitaxial films of CdTe were grown on (100)GaAs substrates by ionized cluster beam (ICB) epitaxy. Streaky RHEED patterns indicated good crystallinity and surface flatness of the epitaxial CdTe films. CdTe(100) orientation was obtained when the substrate preheating temperature was 480°C, while CdTe growth inboth (100) and (111) orientations occured when the substrate preheating temperature was above 550°C. The characteristics of the ICB growth process were investigated and the cluster-involving growth behavior has been evidenced. When sufficient clusters were generated in the deposition beam under adequate source vapor pressures, the crystalline quality of the resulting CdTe epilayers improved significantly with the increase of kinetic energy of the CdTe clusters. The best CdTe epilayer obtained exhibited a CdTe(400) double crystal rocking curve (DCRC) having a FWHM of 630 arc sec.

  20. Growth of CdTe films on GaAs by ionized cluster beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Tang, H.P.; Feng, J.Y.; Fan, Y.D.; Li, H.D. (Dept. of Materials Science and Engineering, Tsinghua Univ., Beijing (China))

    1991-06-01

    Stoichiometric epitaxial films of CdTe were grown on (100)GaAs substrates by ionized cluster beam (ICB) epitaxy. Streaky RHEED patterns indicated good crystallinity and surface flatness of the epitaxial CdTe films. CdTe(100) orientation was obtained when the substrate preheating temperature was 480degC, while CdTe growth in both (100) and (111) orientations occurred when the substrate preheating temperature was above 550degC. The characteristics of the ICB growth process were investigated and the cluster-involving growth behavior has been evidenced. When sufficient clusters were generated in the deposition beam under adequate source vapor pressures, the crystalline quality of the resulting CdTe epilayers improved significantly with the increase of kinetic energy of the CdTe clusters. The best CdTe epilayer obtained exhibited a CdTe(400) double crystal rocking curve (DCRC) having a FWHM of 630 arc sec. (orig.).

  1. Orientation of CdTe epitaxial films on GaAs(100) grown by vacuum evaporation

    Energy Technology Data Exchange (ETDEWEB)

    Houng Mauphon; Fu Shenli; Jenq Fenqlin (Dept. of Electrical Engineering, National Cheng-Kung Univ., Tainan (Taiwan)); Chen Jiannruey (Dept. of Materials Science and Engineering, National Tsing Hua Univ., Hsinchu (Taiwan))

    1991-08-15

    The growth of (100)- and (111)-oriented CdTe epitaxial layers on (100)-oriented GaAs substrates were investigated. Ar{sup +} plasma bombardment was used to remove the surface oxide layer, while preheating the substrate before evaporation was performed to deplete arsenic on the GaAs substrate surface. Results indicate that the CdTe(100) will grow on GaAs(100) with an oxide layer remaining on the surface. For the GaAs(100) substrate with the oxide layer removed by plasma bombardment, CdTe(100) will grow on the arsenic-depleted GaAs substrate, while CdTe(111) will grow on the GaAs substrate without arsenic depletion. A model is proposed that a tellurium-rich surface is formed on the arsenic-depleted GaAs surface through Ga-Te bonding on which the CdTe(100) will grow, whereas CdTe(111) will grow on a tellurium-poor surface. The photoluminescence investigation conforms to our proposed model. (orig.).

  2. A photoluminescence comparison of CdTe thin films grown by molecular-beam epitaxy, metalorganic chemical vapor deposition, and sputtering in ultrahigh vacuum

    Science.gov (United States)

    Feng, Z. C.; Bevan, M. J.; Krishnaswamy, S. V.; Choyke, W. J.

    1988-09-01

    High perfection CdTe thin films have been grown on (001) InSb and CdTe substrates by molecular-beam epitaxy, metalorganic chemical vapor deposition (MOCVD), and sputtering in ultrahigh vacuum techniques. The quality of the as-grown CdTe films are characterized by 2-K photoluminescence. The spectra show strong and sharp exciton transitions and weak 1.40-1.50-eV defect-related bands. Radiative defect densities of lower than 0.002 are realized. High-resolution spectroscopy shows that the full width at half maximum of the principal bound exciton lines is about 0.1 meV. Such small ρ values and narrow photoluminescence lines have not been previously reported. The largest luminescence efficiency is observed for MOCVD-CdTe films grown on CdTe substrates. A variety of impurities appear to be responsible for the observed radiative transitions in these three kinds of CdTe films. We attempt to assign the observed impurity related lines by a comparison with ``known'' impurities in bulk CdTe spectra given in the literature.

  3. Photoluminescence and photoelectric properties of CdTe crystals doped with Er atoms

    International Nuclear Information System (INIS)

    The low-temperature photoluminescence (PL) and photodiffusion spectra of CdTe crystals doped with Er atoms were measured. The most intensive and narrow line in the PL spectrum is A°X-line which is caused by the emission of an exciton bound to a neutral center associated with Na residual impurity. The presence of Na atoms in CdTe:Er crystals is supported by observation of recombination between electrons of the conduction band and acceptor levels associated with these impurity atoms. Other PL bands caused by optical transition with participation of donor–acceptor pairs (DAP) are also observed. It is shown that in this case P acceptor centers and donors caused by the presence of Al atoms situated in the Cd sites take part in the recombination process. The PL bands associated with recombination of DAP which include the complex acceptor centers do not appear in the PL spectra. Our findings indicate a high optical quality of the crystals. Thus, they provide a way to improve structural properties of CdTe crystals using the ability of rare earth (RE) elements to react with residual impurities in semiconductor materials. This is a result of the manifestation of so-called “cleaning” process of the semiconductor materials by their doping with RE elements. - Highlights: • The photoluminescence (PL) and photoelectric properties of CdTe:Er crystals were studied. • The PL exciton (A°X)-line and exciton reflection band is very narrow (about 1 meV). • The broad PL bands are due to the recombination of DAPs and (e,A) transitions. • The nature and energy levels of donor and acceptor levels in CdTe:Er were found. • It was shown that Na and P atoms are the residual impurities in the investigated crystals. • The results provide a way to improve the optical properties of CdTe by RE doping

  4. Redetermination of Ba2CdTe3 from single-crystal X-ray data

    Directory of Open Access Journals (Sweden)

    Min Yang

    2012-10-01

    Full Text Available The previous structure determination of the title compound, dibarium tritelluridocadmate, was based on powder X-ray diffraction data [Wang & DiSalvo (1999. J. Solid State Chem. 148, 464–467]. In the current redetermination from single-crystal X-ray data, all atoms were refined with anisotropic displacement parameters. The previous structure report is generally confirmed, but with some differences in bond lengths. Ba2CdTe3 is isotypic with Ba2MX3 (M = Mn, Cd; X = S, Se and features 1∞[CdTe2/2Te2/1]4− chains of corner-sharing CdTe4 tetrahedra running parallel [010]. The two Ba2+ cations are located between the chains, both within distorted monocapped trigonal–prismatic coordination polyhedra. All atoms in the structure are located on a mirror plane.

  5. Physical properties of Bi doped CdTe thin films grown by CSVT and their influence on the CdS/CdTe solar cells PV-properties

    Energy Technology Data Exchange (ETDEWEB)

    Vigil-Galan, O. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico)]. E-mail: osvaldo@esfm.ipn.mx; Sanchez-Meza, E. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Ruiz, C.M. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Madrid 28049 (Spain); Sastre-Hernandez, J. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Morales-Acevedo, A. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); CINVESTAV-IPN, Electrical Engineering Department, Av. IPN No2508, C. P. 07360, Mexico, D. F. (Mexico); Cruz-Gandarilla, F. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Aguilar-Hernandez, J. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Saucedo, E. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Madrid 28049 (Spain); Contreras-Puente, G. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Bermudez, V. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Madrid 28049 (Spain)

    2007-05-31

    The physical properties of Bi doped CdTe films, grown on glass substrates by the Closed Space Transport Vapour (CSVT) method, from different Bi doped CdTe powders are presented. The CdTe:Bi films were characterized using Photoluminescence, Hall effect, X-Ray diffraction, SEM and Photoconductivity measurements. Moreover, CdS/CdTe:Bi solar cells were made and their characteristics like short circuit current density (J {sub sc}), open circuit voltage (V {sub OC}), fill factor (FF) and efficiency ({eta}) were determined. These devices were fabricated from Bi doped CdTe layers deposited on CdS with the same growth conditions than those used for the single CdTe:Bi layers. A correlation between the CdS/CdTe:Bi solar cell characteristics and the physical properties of the Bi doped CdTe thin films are presented and discussed.

  6. Thermal behaviour of strontium tartrate single crystals grown in gel

    Indian Academy of Sciences (India)

    M H Rahimkutty; K Rajendra Babu; K Sreedharan Pillai; M R Sudarsana Kumar; C M K Nair

    2001-04-01

    Thermal behaviour of strontium tartrate crystals grown with the aid of sodium metasilicate gel is investigated using thermogravimetry (TG) and differential thermal analysis (DTA). Effect of magnetic field and dopant (Pb)2+ on the crystal stability is also studied using thermal analysis. This study reveals that water molecules are locked up in the lattice with different strengths in the grown crystals.

  7. Post-growth, In doping of CdTe single crystals via vapor phase

    Science.gov (United States)

    Lyahovitskaya, Vera; Kaplan, Larissa; Goswami, Jaydeb; Cahen, David

    1999-02-01

    We have developed a new, efficient method to dope bulk single crystals of CdTe by In, via gas phase diffusion, using In 4Te 3 as the source. Doping was carried out on crystals of very high resistivity (>5 MΩ cm), following annealing in the temperature range of 350-1000°C. Resulting crystals showed n-type conductivity with a free carrier concentration in the range of 10 15-10 18 cm -3 and carrier mobility of 100-750 cm 2/(V s), depending on the annealing temperature and time, and on the cooling conditions. Incorporation of In was found to be a function of annealing time and temperature only. Up to 650°C, the In and the free electron concentrations are roughly the same.

  8. CdTe nBn photodetectors with ZnTe barrier layer grown on InSb substrates

    Science.gov (United States)

    He, Zhao-Yu; Campbell, Calli M.; Lassise, Maxwell B.; Lin, Zhi-Yuan; Becker, Jacob J.; Zhao, Yuan; Boccard, Mathieu; Holman, Zachary; Zhang, Yong-Hang

    2016-09-01

    We have demonstrated an 820 nm cutoff CdTe nBn photodetector with ZnTe barrier layer grown on an InSb substrate. At room temperature, under a bias of -0.1 V, the photodetector shows Johnson and shot noise limited specific detectivity (D*) of 3 × 1013 cm Hz1/2/W at a wavelength of 800 nm and 2 × 1012 cm Hz1/2/W at 200 nm. The D* is optimized by using a top contact design of ITO/undoped-CdTe. This device not only possesses nBn advantageous characteristics, such as generation-recombination dark current suppression and voltage-bias-addressed two-color photodetection, but also offers features including responsivity enhancements by deep-depletion and by using a heterostructure ZnTe barrier layer. In addition, this device provides a platform to study nBn device physics at room temperature, which will help us to understand more sophisticated properties of infrared nBn photodetectors that may possess a large band-to-band tunneling current at a high voltage bias, because this current is greatly suppressed in the large-bandgap CdTe nBn photodetector.

  9. Nonresonant four-wave mixing in photorefractive CdTe crystals using a picosecond parametric generator

    Science.gov (United States)

    JarašiÅ«nas, Kestutis; Gudelis, Vytautas; Delaye, Philippe; Roosen, Gerald

    1998-11-01

    We demonstrate that a parametrically pumped picosecond laser has enough coherence and energy to write transient phase gratings at nonresonant interaction, thus allowing a study of time-resolved carrier transport in CdTe crystals to be made. Autocorrelation trace of light diffraction efficiency on transient grating allowed us to measure a coherence length of the parametric generator. Carrier diffusion, recombination, and drift in light-created internal space-charge (SC) electric fields have been studied in vanadium or germanium doped semi-insulating CdTe crystals by nonresonant four-wave mixing technique at 940 nm wavelength. It was found that modification of the deep level charge state in CdTe:V by As codoping has changed the sign of majority carriers, responsible for the creation of SC field. Dynamics of free carrier grating decay in CdTe:Ge revealed an electron-governed very fast initial grating decay which develops with time into the double-exponential hole-governed grating decay. Time-resolved transient grating technique described in this article provides a powerful tool for investigation of the role of deep traps in photorefractive semiconductors and optimization of their photoelectric properties in a required temporal and spectral range.

  10. Analysis of rocking curve width and bound exciton linewidth of MOCVD grown CdTe layers in relation with substrate type and crystalline orientation

    Science.gov (United States)

    Tromson-Carli, A.; Svob, L.; Marfaing, Y.; Druilhe, R.; Desjonqueres, F.; Triboulet, R.

    1991-12-01

    X-ray double diffraction and photoluminescence experiments were performed on a series of CdTe layers grown by MOVPE on CdTe, CdZnTe and GaAs substrates. Some correlation appears between the measured rocking curve widths and impurity-bound exciton linewidth. To analyze these results, a model relating the exciton linewidth to the average strain induced by an array of random dislocations has been developed. It appears that X-ray diffraction is also sensitive to non-random dislocation configurations which do not affect luminescence linewidth.

  11. Determination of CdTe bulk carrier lifetime and interface recombination velocity of CdTe/MgCdTe double heterostructures grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    The bulk Shockley-Read-Hall carrier lifetime of CdTe and interface recombination velocity at the CdTe/Mg0.24Cd0.76Te heterointerface are estimated to be around 0.5 μs and (4.7 ± 0.4) × 102 cm/s, respectively, using time-resolved photoluminescence (PL) measurements. Four CdTe/MgCdTe double heterostructures (DHs) with varying CdTe layer thicknesses were grown on nearly lattice-matched InSb (001) substrates using molecular beam epitaxy. The longest lifetime of 179 ns is observed in the DH with a 2 μm thick CdTe layer. It is also shown that the photon recycling effect has a strong influence on the bulk radiative lifetime, and the reabsorption process affects the measured PL spectrum shape and intensity

  12. NONLINEAR OPTICS: Energy exchange between optical waves due to self-diffraction by photorefractive gratings in a CdTe crystal

    Science.gov (United States)

    Borshch, A. A.; Brodin, M. S.; Burin, O. M.; Volkov, V. I.; Kukhtarev, N. V.; Semenets, T. I.; Smereka, Z. N.

    1990-07-01

    Theoretical and experimental investigations were made of a photorefractive nonlinearity of CdTe semiconductor crystals. Photorefractive gratings were formed in undoped CdTe and used to provide efficient energy exchange between nanosecond pulsed light beams (λ approx 1.06 μm) characterized by an exchange gain of ~ 0.13 cm - 1.

  13. The effects of annealing on the distributions of deep and shallow states in CdTe single crystals

    International Nuclear Information System (INIS)

    Schottky barrier capacitance and DLTS techniques have been employed to study the shallow- and deep-state distributions in bulk-grown CdTe crystals following an annealing treatment designed to convert the samples from semi-insulating to n-type conductivity. Although the annealing conditions (saturated Cd vapour at 800 deg. C) were chosen to ensure that homogeneity was achieved at the annealing temperature, substantial non-uniformities were observed in the test samples at room temperature. Although n-type conductivity was successfully achieved, this was restricted to a near-surface channel with a width of ∼50 μm for undoped samples and >400 μm for In-doped samples. These results can be attributed to diffusion and self-compensation processes occurring during cool-down following the anneal, but the DLTS measurements yield no evidence for the generation of new levels arising from these processes. The existing states (with energy levels in the detectable range from ∼0.2 to ∼0.9 eV below the conduction band) are found to be non-uniformly distributed as a function of depth below the surface, the form of the actual depth profiles being very similar to the corresponding free carrier concentration profile. (author)

  14. Automatic Control System for the High Pressure CdTe Crystal Growth Furnace

    Directory of Open Access Journals (Sweden)

    Petr Praus

    2006-08-01

    Full Text Available CdTe and (CdZnTe bulk single crystals have been widely used as substrates for MBE and LPE epitaxy of infrared (HgCdTe as well as gamma- and X-ray detectors. The Cd1-xZnxTe (x = 0.04-0.1 single crystals with diameter up to 100 mm and height at most 40 mm were prepared in our laboratory in a vertical arrangement by gradual cooling of the melt (the Vertical Gradient Freezing method. Achievement of excellent crystal quality required full control of Cd pressure during the growth process and application of high Cd pressures (up to 4 bar at growth temperature. An electronic control system was designed to control both temperature and internal pressure of two zones CZT crystal growth furnace by using two high performance PID controllers/setpoint programmers. Two wire current loop serial communication bus was used for the data exchange and computer control of the furnace electronics setup. Control software was written to supervise the crystal growth process and to collect all important data and parameters.

  15. Orientational domains in metalorganic chemical vapor deposited CdTe(111) film on cube-textured Ni

    International Nuclear Information System (INIS)

    CdTe thin film was grown by metal organic chemical vapor deposition on cube-textured Ni substrate. The microstructures of the CdTe film and Ni substrate were studied using transmission electron microscopy (TEM) lattice imaging in cross sectional. The orientational relationships of multiple hetereoepitaxial domains in the CdTe film were examined by TEM diffraction. The observed epitaxy is [111]CdTe//[001]Ni. The adjacent domains in CdTe film have a 30° rotation with respect to each other as inferred by the observed different diffraction patterns obtained from different zone axes. The high resolution lattice imaging shows that lamellar twins dominate within each domain. Our results are compared with CdTe(111) film epitaxially grown on Si(001) substrate by molecular beam epitaxy reported in the literature. - Highlights: ► Epitaxial CdTe film grew on textured Ni at 350 °C despite of a large lattice mismatch. ► Epitaxial relationship is CdTe(111) parallel to Ni(001). ► 30° CdTe orientation domains inferred from transmission electron microscopy patterns ► Local inclined angle between CdTe and Ni at the interface is due to vertical mismatch. ► Single crystal-like epitaxial semiconductors can be grown on low cost metal sheet

  16. Temperature dependent electroreflectance study of CdTe solar cells

    International Nuclear Information System (INIS)

    Cadmium telluride is a promising material for large scale photovoltaic applications. In this paper we study CdS/CdTe heterojunction solar cells with electroreflectance spectroscopy. Both CdS and CdTe layers in solar cells were grown sequentially without intermediate processing by the close-space sublimation method. Electroreflectance measurements were performed in the temperature range of T = 100–300 K. Two solar cells were investigated with conversion efficiencies of 4.1% and 9.6%. The main focus in this work was to study the temperature dependent behavior of the broadening parameter and the bandgap energy of CdTe thin film in solar cells. Room temperature bandgap values of CdTe were Eg = 1.499 eV and Eg = 1.481 eV for higher and lower efficiency solar cells, respectively. Measured bandgap energies are lower than for single crystal CdTe. The formation of CdTe1−xSx solid solution layer on the surface of CdTe is proposed as a possible cause of lower bandgap energies. - Highlights: ► Temperature dependent electroreflectance measurements of CdS/CdTe solar cells ► Investigation of junction properties between CdS and CdTe ► Formation of CdTe1− xSx solid solution layer in the junction area

  17. Improving surface smoothness and photoluminescence of CdTe(1 1 1)A on Si(1 1 1) substrates grown by molecular beam epitaxy using Mn atoms

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jyh-Shyang, E-mail: jswang@cycu.edu.tw [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Center for Nano-Technology, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Tsai, Yu-Hsuan; Chen, Chang-Wei; Dai, Zi-Yuan; Tong, Shih-Chang [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Yang, Chu-Shou [Graduate Institute of Electro-Optical Engineering, Tatung University, Taipei 10452, Taiwan (China); Wu, Chih-Hung [Institute of Nuclear Energy Research, Longtan 32546, Taiwan (China); Yuan, Chi-Tsu; Shen, Ji-Lin [Department of Physics, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China); Center for Nano-Technology, Chung Yuan Christian University, Chung-Li 32023, Taiwan (China)

    2014-04-01

    Highlights: • CdTe(1 1 1)A epilayers were grown on Si(1 1 1) substrates by molecular beam epitaxy. • We report an enhanced growth using Mn atoms. • The significant improvements in surface quality and optical properties were found. - Abstract: This work demonstrates an improvement of the molecular beam epitaxial growth of CdTe(1 1 1)A epilayer on Si(1 1 1) substrates using Mn atoms. The reflection high-energy electron diffraction patterns show that the involvement of some Mn atoms in the growth of CdTe(1 1 1)A is even more effective than the use of a buffer layer with a smooth surface for forming good CdTe(1 1 1)A epilayers. 10 K Photoluminescence spectra show that the incorporation of only 2% Mn significantly reduced the intensity of defect-related emissions and considerably increased the integral intensity of exciton-related emissions by a large factor of about 400.

  18. Material analysis of the CZT crystal grown for a radiation detector

    Science.gov (United States)

    Kim, Han Soo; Jeong, Manhee; Kim, Young Soo; Kim, Dong Jin; Choi, Hyo Jeong

    2015-01-01

    Room-temperature semiconductor radiation detectors, such as CdZnTe (CZT) and CdTe detectors, are being developed and grown worldwide owing to their high performances as a gamma-ray detector. A 2″ CZT ingot was grown using a 6-zone low-pressure (LP) Bridgman furnace at the Korea Atomic Energy Research Institute (KAERI). To increase the resistivity, indium (In) was doped at 5 ppm and 7 ppm, respectively. Material analysis results obtained by using inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffractometry (XRD), and an infrared (IR) scope system were compared with the I-V results with respect to the location on the grown ingots and doping concentration. A (1,1,1) orientation and 1.41 × 1011 Ω·cm resistivity were measured in the middle part of the ingot. In addition, Te inclusions were also homogeneously shown. The variation in the I-V characteristics with respect to the preparation conditions of the crystals was also addressed.

  19. Thermal lensing and frequency chirp in a heated CdTe modulator crystal and its effects on laser radar performance

    Science.gov (United States)

    Eng, R. S.; Kachelmyer, A. L.; Harris, N. W.

    1991-08-01

    The effects of optical and microwave heatings and thermally-induced birefringence in a CdTe modulator crystal on the performance of a linear FM CO2 laser radar are examined. This is conducted in terms of reductions in beam Strehl ratio and dynamic ranges of the Doppler shift and range for given optical and microwave powers. An analysis of the thermal lenses generated by these heatings is presented.

  20. Synthesis and characterization of gel-grown cobalt tartrate crystals

    Indian Academy of Sciences (India)

    V M Athivanan; M Haris; T Prasanyaa; M Amgalan

    2014-03-01

    Crystals of cobalt tartrate are grown from the gel using chemical reaction method. The functional groups are found from Fourier transform infrared spectroscopy (FTIR). The OH stretching mode owing to water, carbonyl group, CH stretching modes and metal–oxygen stretching are identified. The unit cell dimensions, interaxial angles and unit cell volume are found from powder X-ray diffraction studies (XRD) which show the orthorhombic nature of the crystal. The magnetic study is used to find the magnetic susceptibility and magnetic moment of the grown crystal. It reveals the magnetic nature of the crystal. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are done to find the thermal properties of the crystal which manifest the water of hydration in the crystal. The variation of dielectric constant with respect to the applied frequency shows the polarization property of the crystal. The AC conductivity is increased proportionally with increase in frequency. The reverse nature is found for the AC resistivity. The nature of the composition of the crystals affects the dielectric properties.

  1. Growth of CdTe: Al films

    International Nuclear Information System (INIS)

    CdTe: AI films were grown by the close space vapor transport technique combined with free evaporation (CSVT-FE). The Aluminum (Al) evaporation was made by two kinds of sources: one made of graphite and the other of tantalum. The films were deposited on glass substrates. The Al source temperature was varied maintaining the CdTe source temperature fixed as well as the substrate temperature. The films were characterized by x-ray energy dispersive analysis (EDAX), x-ray diffraction and optical transmission. The results showed for the films grown with the graphite source for Al evaporation, the Al did not incorporate in the CdTe matrix, at least to the level of EDAX sensitivity; they maintained the same crystal structure and band gap. For the samples grown with the tantalum source, we were able to incorporate the Al. The x-ray diffraction patterns show that the films have a crystal structure that depends on Al concentration. They were cubic up to 2.16 at. % Al concentration; for 19.65 at. % we found a mixed phase; for Al concentration higher than 21 at. % the films were amorphous. For samples with cubic structure it was found that the lattice parameter decreases and the band gap increases with Al concentration. (Author)

  2. Structural and optical properties of Cu-doped CdTe films with hexagonal phase grown by pulsed laser deposition

    OpenAIRE

    F. de Moure-Flores; J. G. Quiñones-Galván; A. Guillén-Cervantes; Santoyo-Salazar, J.; A. Hernández-Hernández; Olvera, M. de la L.; M. Zapata-Torres; Meléndez-Lira, M.

    2012-01-01

    Cu-doped CdTe thin films were prepared by pulsed laser deposition on Corning glass substrates using powders as target. Films were deposited at substrate temperatures ranging from 100 to 300 °C. The X-ray diffraction shows that both the Cu-doping and the increase in the substrate temperature promote the presence of the hexagonal CdTe phase. For a substrate temperature of 300 °C a CdTe:Cu film with hexagonal phase was obtained. Raman and EDS analysis indicate that the films grew with an excess ...

  3. Positron trapping in vacancies in indium doped CdTe crystals

    Science.gov (United States)

    Gély-Sykes, C.; Corbel, C.; Triboulet, R.

    1991-10-01

    In weakly n-type CdTe(In) crystals grown by the travelling heater method, positrons annihilate in vacancy-type defects with a lifetime of 320 ± 4 ps. The concentration of these native defects varies with the concentration of indium and electron in agreement with the model of self-compensation where the indium donors are compensated by indium-vacancy complexes. These defects are assumed to be (V CdIn) - complexes. The positron trapping in these complexes disappears at low temperature. This phenomenon is attributed to competing trapping of positrons by negative ions which are either residual impurities or intrinsic defects.

  4. Kinetic and interface studies for MOCVD CdTe and HgCdTe epilayers grown on GaAs substrates

    Science.gov (United States)

    Rui-wu, Peng; Fei, Xu; Yong-qing, Ding

    1991-12-01

    The growth rates of CdTe and CMT on GaAs and on CdTe/GaAs substrates were studied as a function of temperature and gas composition. A Langmuir-Hinshelwood model for surface reaction control region is proposed. The CdTe/GaAs interface was examined by X-ray double crystal diffraction, laser Raman spectroscopy and transmission electron microscopy (TEM). A defect layer was observed at CdTe/GaAs interface. The relationship between the interface qualities and electrical properties of the CMT overlayers was discussed.

  5. Electrical properties of Schottky diodes based on high-resistance CdTe crystals

    International Nuclear Information System (INIS)

    Measurement of the Schottky barrier height on the CdTe monocrystals alloyed with the Cl, Br, J during the growth process is carried out through the method of chemical transport reactions. Verification of the efficiency of the proposed F(V) function modification with the purpose of determining the Me(In, Sn)-p-CdTe diodes parameters is accomplished. The Schottky barriers with the current transmission diffusion mechanism perspective for developing high-efficiency semiconducting detectors of nuclear radiation are created on the basis of the method for the gas-phase growth of the semiinsulating CdTe monocrystals

  6. Spectral response of THM grown CdZnTe crystals

    DEFF Research Database (Denmark)

    Chen, H.; Awadalla, S.A.; Harris, F.;

    2008-01-01

    The spectral response of several crystals grown by the Traveling Heater Method (THM) were investigated. An energy resolution of 0.98% for a Pseudo Frisch-Grid of 4 × 4 × 9 mm3 and 2.1% FWHM for a coplanar-grid of size 11 × 11 × 5 mm3 were measured using 137Cs-662 keV. In addition a 4% FWHM at 122...

  7. Concentration of uncompensated impurities as a key parameter of CdTe and CdZnTe crystals for Schottky diode x/γ-ray detectors

    International Nuclear Information System (INIS)

    In this paper we report on the strong impact of the concentration of uncompensated impurities on the detection efficiency of CdTe and Cd0.9Zn0.1Te Schottky diodes. The results of our study explain the observed poor detection properties of some Cd0.9Zn0.1Te detectors with resistivity and lifetime of carriers comparable to those of good CdTe detectors. We show that the concentration of uncompensated impurities in a highly efficient CdTe Schottky diode detector is several orders of magnitude higher than that of a CdZnTe, which does not register the gamma spectra of commonly used isotopes (59–662 keV) by using photoelectric measurements. The significant difference of the concentration of uncompensated impurities between CdTe and Cd0.9Zn0.1Te crystals is confirmed by our study of the temperature change of the resistivity and of the Fermi level energy. The degree of compensation of the donor complex, responsible for the electrical conductivity of the material, is much lower in the CdTe crystal compared to that in the Cd0.9Zn0.1Te crystal. The calculations of the detection efficiency of x/γ-radiation by a Schottky diode result in a dependence on the concentration of uncompensated impurities described by a curve with a pronounced maximum. The position of this maximum occurs at a concentration of uncompensated impurities which ranges from 3 × 1010 to 3 × 1012 cm−3 depending on the registered photon energy of x/γ-rays and on the lifetime of the charge carriers. Our measurements and calculations lead to the conclusion that the concentration of uncompensated impurities in this range is a necessary condition for the effective operation of x- and γ-ray Schottky diode detectors based on CdTe and Cd1−xZnxTe crystals

  8. Temperature dependent electroreflectance study of CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Raadik, T., E-mail: taavi.raadik@ttu.ee [Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn (Estonia); Krustok, J.; Josepson, R.; Hiie, J. [Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn (Estonia); Potlog, T.; Spalatu, N. [Moldova State University, A. Mateevici str. 60, MD-2009 Chisinau (Moldova, Republic of)

    2013-05-01

    Cadmium telluride is a promising material for large scale photovoltaic applications. In this paper we study CdS/CdTe heterojunction solar cells with electroreflectance spectroscopy. Both CdS and CdTe layers in solar cells were grown sequentially without intermediate processing by the close-space sublimation method. Electroreflectance measurements were performed in the temperature range of T = 100–300 K. Two solar cells were investigated with conversion efficiencies of 4.1% and 9.6%. The main focus in this work was to study the temperature dependent behavior of the broadening parameter and the bandgap energy of CdTe thin film in solar cells. Room temperature bandgap values of CdTe were E{sub g} = 1.499 eV and E{sub g} = 1.481 eV for higher and lower efficiency solar cells, respectively. Measured bandgap energies are lower than for single crystal CdTe. The formation of CdTe{sub 1−x}S{sub x} solid solution layer on the surface of CdTe is proposed as a possible cause of lower bandgap energies. - Highlights: ► Temperature dependent electroreflectance measurements of CdS/CdTe solar cells ► Investigation of junction properties between CdS and CdTe ► Formation of CdTe{sub 1−} {sub x}S{sub x} solid solution layer in the junction area.

  9. Towards defect-free epitaxial CdTe and MgCdTe layers grown on InSb (001) substrates

    Science.gov (United States)

    Lu, Jing; DiNezza, Michael J.; Zhao, Xin-Hao; Liu, Shi; Zhang, Yong-Hang; Kovacs, Andras; Dunin-Borkowski, Rafal E.; Smith, David J.

    2016-04-01

    A series of three CdTe/MgxCd1-xTe (x~0.24) double heterostructures grown by molecular beam epitaxy on InSb (001) substrates at temperatures in the range of 235-295 °C have been studied using conventional and advanced electron microscopy techniques. Defect analysis based on bright-field electron micrographs indicates that the structure grown at 265 °C has the best structural quality of the series, while structures grown at 30 °C lower or higher temperature show highly defective morphology. Geometric phase analysis of the CdTe/InSb interface for the sample grown at 265 °C reveals minimal interfacial elastic strain, and there is no visible evidence of interfacial defect formation in aberration-corrected electron micrographs of this particular sample. Such high quality CdTe epitaxial layers should provide the basis for applications such as photo-detectors and multi-junction solar cells.

  10. Growth of CdTe: Al films; Crecimiento de peliculas de CdTe: Al

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez A, M.; Zapata T, M. [CICATA-IPN, 89600 Altamira, Tamaulipas (Mexico); Melendez L, M. [CINVESTAV-IPN, A.P. 14-740, 07000 Mexico D.F. (Mexico); Pena, J.L. [CINVESTAV-IPN, A.P. 73 Cordemex, 97310 Merida, Yucatan (Mexico)

    2006-07-01

    CdTe: AI films were grown by the close space vapor transport technique combined with free evaporation (CSVT-FE). The Aluminum (Al) evaporation was made by two kinds of sources: one made of graphite and the other of tantalum. The films were deposited on glass substrates. The Al source temperature was varied maintaining the CdTe source temperature fixed as well as the substrate temperature. The films were characterized by x-ray energy dispersive analysis (EDAX), x-ray diffraction and optical transmission. The results showed for the films grown with the graphite source for Al evaporation, the Al did not incorporate in the CdTe matrix, at least to the level of EDAX sensitivity; they maintained the same crystal structure and band gap. For the samples grown with the tantalum source, we were able to incorporate the Al. The x-ray diffraction patterns show that the films have a crystal structure that depends on Al concentration. They were cubic up to 2.16 at. % Al concentration; for 19.65 at. % we found a mixed phase; for Al concentration higher than 21 at. % the films were amorphous. For samples with cubic structure it was found that the lattice parameter decreases and the band gap increases with Al concentration. (Author)

  11. The relationship between electrical and structural characteristics of CdTe and CdMnTe layers grown on InSb

    Science.gov (United States)

    Ashenford, D.; Hogg, J. H. C.; Lunn, B.; Scott, C. G.

    1991-06-01

    CdTe and CdMnTe layers with thickness in the range 1-2 μm have been grown by MBE on (001) InSb substrates. Measurements of the free-carrier concentration as a function of depth through these layers have revealed non-unformities attributed to the presence of extended defects arising from the relief of lattice strain resulting from the epilayer-substrate lattice mismatch. Evidence for the existence of such structural non-uniformity has been provided by DCXRD rocking curve measurements. Detailed analysis of these curves also indicates the presence of a thin interfacial layer of a different phase. The use of an excess Cd flux during growth has been found to lead to increased and more uniform carrier densities in both undoped and In doped layers.

  12. Structural analysis of an epitaxial layer of CdTe on GaAs by the multidirectional channeling technique

    Energy Technology Data Exchange (ETDEWEB)

    Wielunski, L.S. (CSIRO Div. of Applied Physics, Lucas Heights Research Labs., Menai, NSW (Australia)); Kwietniak, M.S.; Pain, G.N. (Telecom Australia Research Labs., Clayton, Victoria (Australia)); Rossouw, C.J. (CSIRO Div. of Materials Science and Tech., Clayton, Victoria (Australia))

    1990-01-01

    Multidirectional RBS channeling analysis is used to identify the crystal orientation of a MOCVD-grown CdTe layer on a (100) GaAs substrate. Results show that the CdTe has a (111) orientation. However, from channeling in different axial directions and a rotational angular scan around the <111> axis, it is deduced that the CdTe layer is multiply twinned about this axis. Cross-sectional electron microscopy has revealed the twins to be 180deg rotational twins. (orig.).

  13. InP Bulk Crystals Grown from Various Stoichiometric Melt

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    InP crystal was grown from stoichiometric or non-stoichiometric melt, including P-rich and In-rich condition by the P-injection synthesis LEC method. Owing to the non-stoichiometric condition, there are many pores in the tail of the P-rich ingot. Samples were characterized by high speed photoluminescence mapping and E.P.D. mapping. The perfection (dislocation, stoichiometry and uniformity) of these samples were studied and compared. The PL peak intensity standard deviation of the 4-inch InP wafer is higher. The EPDs around the pores are higher than the other regions. Besides the stress releasing, the pores and the high concentration of dislocations around them are the leading factors causing the inhomogeneity of the wafer. By adjusting the thermal field and ensuring the chemical stoichiometry, InP crystals of larger diameters and better performance can be developed.

  14. Strain reduction in selectively grown CdTe by MBE on nanopatterned silicon on insulator (SOI) substrates

    OpenAIRE

    Bommena, R.; Seldrum, T.; Samain, Louise; Sporken, R.; Sivananthan, S.; S. R. J. Brueck

    2008-01-01

    Silicon-based substrates for the epitaxy of HgCdTe are an attractive low-cost choice for monolithic integration of infrared detectors with mature Si technology and high yield. However, progress in heteroepitaxy of CdTe/Si (for subsequent growth of HgCdTe) is limited by the high lattice and thermal mismatch, which creates strain at the heterointerface that results in a high density of dislocations. Previously we have reported on theoretical modeling of strain partitioning between CdTe and Si o...

  15. Analysis of Phase Separation in Czochralski Grown Single Crystal Ilmenite

    Science.gov (United States)

    Wilkins, R.; Powell, Kirk St. A.; Loregnard, Kieron R.; Lin, Sy-Chyi; Muthusami, Jayakumar; Zhou, Feng; Pandey, R. K.; Brown, Geoff; Hawley, M. E.

    1998-01-01

    Ilmenite (FeTiOs) is a wide bandgap semiconductor with an energy gap of 2.58 eV. Ilmenite has properties suited for radiation tolerant applications, as well as a variety of other electronic applications. Single crystal ilmenite has been grown from the melt using the Czochralski method. Growth conditions have a profound effect on the microstructure of the samples. Here we present data from a variety of analytical techniques which indicate that some grown crystals exhibit distinct phase separation during growth. This phase separation is apparent for both post-growth annealed and unannealed samples. Under optical microscopy, there appear two distinct areas forming a matrix with an array of dots on order of 5 pm diameter. While appearing bright in the optical micrograph, atomic force microscope (AFM) shows the dots to be shallow pits on the surface. Magnetic force microscope (MFM) shows the dots to be magnetic. Phase identification via electron microprobe analysis (EMPA) indicates two major phases in the unannealed samples and four in the annealed samples, where the dots appear to be almost pure iron. This is consistent with micrographs taken with a scanning probe microscope used in the magnetic force mode. Samples that do not exhibit the phase separation have little or no discernible magnetic structure detectable by the MFM.

  16. RF sputtering deposition of CdTe on GaAs substrate

    Science.gov (United States)

    Adamiec, Krzysztof; Rutkowski, Jaroslaw; Bednarek, S.; Michalski, E.

    1997-06-01

    The fabrication of HgCdTe IR detectors demands high-quality CdTe or CdZnTe substrates. Bulk CdTe tends to twin, therefore large single crystals are generally not available. This problem could be circumvented by growing CdTe epilayers on an alternative large area substrate. Several studies have been made on the growth of CdTe on different substrates such as InSb, GaAs, Si and sapphire by MOCVD and MBE techniques. We report the initial results for the growth of CdTe buffer films on GaAs (100) substrates by sputter epitaxy. This crystal was chosen as the substrate material because of its transparency to IR radiation and availability as large area wafers with high structural perfection. Epitaxial films of CdTe were deposited in a sputtering system with a base pressure of 2 X 10-4 Pa. The GaAs substrate was degreased, etched in standard solution, and mounted immediately on a cooper substrate holder in the system. The substrates were ion etched in the sputtering system to remove surface oxide. The CdTe films were deposited in a wide substrate temperature range from 50 to 450 degrees C. Film thickness ranged from 0.1 to 5 micrometers , and deposition rates from 1 to 5 micrometers /h. The orientations and crystalline quality epitaxial films were characterized by x-ray diffraction. The surface morphology and the cross section of the gown CdTe layers were investigated by Nomarski interference contrast microscope. The optical and the electrical properties of the epitaxial films were investigated too. Structural characterization reveals that crystalline quality is a function of temperature of substrates. The single-crystals films grown at 300 degrees C on GaAs showed a best surface morphology.

  17. Crystal growth and characterization of γ-glycine grown from potassium fluoride for photonic applications

    Science.gov (United States)

    Dillip, G. R.; Raghavaiah, P.; Mallikarjuna, K.; Reddy, C. Madhukar; Bhagavannarayana, G.; Kumar, V. Ramesh; Raju, B. Deva Prasad

    2011-09-01

    Single crystals of γ-glycine, an organic nonlinear optical material have been synthesized in the presence of potassium fluoride (KF) by slow evaporation technique at ambient temperature. The size of the grown crystal is up to the dimension of 12 mm × 10 mm × 8 mm. The γ-phase was confirmed by single crystal X-ray diffraction, powder XRD and the FTIR analysis. Optical absorption spectrum reveals that the grown crystal has good optical transparency in the entire visible region with an energy band gap of 5.09 eV, which is an essential requirement for a nonlinear optical crystal. Thermal stability of the grown γ-glycine crystal was determined using the thermo gravimetric and differential thermal analyses. The NLO activity of γ-glycine was confirmed by the Kurtz powder technique using Nd:YAG laser and the grown crystal exhibits high relative conversion efficiency when compared to potassium dihydrogen phosphate (KDP).

  18. Lattice constant and hardness of InSb:Bi bulk crystals grown by vertical directional solidification

    Science.gov (United States)

    Maske, Dilip; Deshpande, Manisha; Choudhary, Rashmi; Gadkari, Dattatray

    2016-05-01

    Ingots of the Bi doped InSb (InSb1-xBix) bulk semiconductor crystals were grown by specially designed Vertical Directional Solidification (VDS) technique. Substrates of seven crystals grown with various composition values of x (0 ≤ x 0.05.

  19. Development of single crystal CdTe solar cell for terrestrial application, adapted for use in optical concentrators

    Energy Technology Data Exchange (ETDEWEB)

    Jaeger, H.; Fuessl, B.; Seipp, E.; Thiel, R.

    1981-01-01

    During the first phase of the contract most of the work was done in order to optimize the most important structural elements of the solar cells, which were produced on the base of crystalline CdTe. Two approaches in development of such cells were made. In the first, n-CdTe crystals were covered with a p-type heterolayer as a window for sunlight; ZnTe was evaporated as a p-type layer. In the second, p-CdTe crystals were covered with a n-type heterolayer as a window. Here, CdS evaporation layers and indium-tin-oxide (ITO) sputtered layers were applied. Within the first approach the realization of ZnTe-layers simultaneously highly conductive and transparent was tried by using numerous dopants. Success finally was attained in July. Within the second approach, the development of p-CdTe/n-CdS solar cells, the resistances of the ohmic contacts on the back of the p-CdTe wafers were a major problem. We found some ways of preparing ohmic contacts of acceptable contact resistance, but an ideal problem solution is lacking still. We found a dependence of the contact resistance on the p-CdTe doping concentration. Solar cells made from p-CdTe crystals covered with nn/sup +/-CdS attained on open circuit voltage of 655 mV and a short circuit current density of 13,8 mA/cm/sup 2/ in a 100 mW/cm/sup 2/ light. Assuming a sufficiently low series resistance we expect an efficiency of about 6 percent. Besides the /sup +/-CdS layers n/sup +/-ITO-layers (indium-tin-oxide) were deposited on p-CdTe by sputtering. These cells exhibit a short circuit density a little higher but a lower open circuit voltage than the heterosolarcells with n/sup +/-CdS.

  20. Optical, mechanical and thermal characterization of l-threonine single crystals grown in dimethyl urea solution

    Science.gov (United States)

    Shanthi, A.; Krishnan, C.; Selvarajan, P.

    2013-09-01

    An organic material of a noncentrosymmetric l-threonine single crystal was grown in a dimethyl urea solution using the slow evaporation method. The grown crystal was transparent and colorless, with a size of about 20 × 7 × 4 mm3, obtained within a period of 10 days. The grown crystal was subjected to various studies, such as x-ray diffraction (XRD), Fourier transform infrared (FTIR), microhardness, ultraviolet-visible (UV-Vis) transmittance, thermogravimetric analysis and differential thermal analysis (TGA/DTA) and second harmonic generation (SHG). l-threonine crystals grown in a dimethyl urea solution show relative SHG efficiency of 0.92 times that of potassium dihydrogen phosphate. The functional groups of the crystals have been confirmed by FTIR analysis. The mechanical strength of the crystal was estimated by the Vickers hardness test. The lattice parameters of the grown crystal were determined by single crystal XRD and powder XRD studies, and the diffraction peaks were indexed. A UV-Vis spectrum was recorded in the wavelength range of 200-1100 nm to find the suitability of the crystal for nonlinear optical applications. The thermal stability of l-threonine crystal grown in dimethyl urea was checked using the TGA/DTA analysis.

  1. Characterization of the native defects in HgTe, CdTe, Hg1-x, CdxTe by positron annihilation: evidence of native vacancies

    International Nuclear Information System (INIS)

    Direct evidence of native vacancies is found in as-grown CdxHg1-xTe single crystals prepared by the travelling heating method (THM). The vacancies have characteristics depending on the annealing undergone by the crystals after their growth and on the conduction type in the crystals. In as-grown CdTe and Cd0.7Hg0.3Te (THM), native vacancies are found in n-type materials. In as-grown HgTe and Cd0.2Hg0.8Te (THM), native vacancies are found in p materials. They disappear after stoechiometric annealings in which the crystals are converted n-type. From the positron lifetime at the vacancies, 320±4 ps, one can show that the native vacancies are metallic vacancies VCd in CdTe, VHg in HgTe, VHg or/and VCd in CdxHg1-xTe alloys. The concentration of the metallic vacancies is estimated in as-grown crystals. In as-grown p-type CdTe and Cd0.7Hg0.3Te (THM), in as-grown then subsequently p-type annealed HgTe and Cd0.2Hg0.8Te (THM), vacancy type defects are also found giving rise to lifetime of about 290 ps. These defects are also found in crystals grown by Bridgman method. The nature of these defects is discussed. The In doping effects on the metallic vacancies have been studied. It is shown that In addition increases the concentration of metallic vacancies in CdTe (In) (THM). Vacancy-In complexes appear for In concentrations of the order or above 1017 cm-3. These complexes disappear after decompensating annealings and only the metallic vacancies survive. Small vacancies clusters of two or three vacancies are found after deformation at room temperature in CdTe (Mn) (THM)

  2. Improved spectrometric performance of CdTe radiation detectors in a p-i -n design

    OpenAIRE

    Niraula, Madan; Mochizuki, Daisuke; Aoki, Toru; Hatanaka, Yoshinori; Tomita, Yasuhiro; Nihashi, Tokuaki; ニラウラ, マダン

    1999-01-01

    CdTe radiation detectors were fabricated using a p-i-n design and a significant improvement in the spectral properties was obtained during room temperature operation. An iodine doped n-CdTe layer was grown on the Te faces of the (111) oriented high resistivity CdTe crystals at the low substrate temperature of 150°C. An aluminum electrode was evaporated on the n-CdTe side for the n-type contact, while a gold electrode on the opposite side acted as the p-type contact. Very low leakage currents,...

  3. Neutron irradiation of Czochralski and temperature gradient technique grown YAG crystals

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Chengyong [Faculty of Scinece, Ningbo University, Ningbo 315211 (China)]. E-mail: Jiangchengyong@nbu.edu.cn

    2006-03-01

    Absorption, fluorescence and thermoluminescence spectra are presented for 1.5-MeV neutron-irradiated YAG crystals grown by Czochralski (CZ) and temperature gradient technique (TGT). F{sup +} centers were formed in both YAG samples and valence of iron impurities in TGT-grown YAG crystals switched from divalent to trivalent after neutron irradiation. At 350 and 300 deg. C thermoluminescence was observed in CZ-grown and TGT-grown YAG crystals, respectively, and assigned to irradiation-induced color centers. Calculated with the initial elevation method, thermoluminescence trap depths of the 350 deg. C band and of the 300 deg. C band are 0.379 and 0.768 eV, respectively. The significant difference in thermoluminescence intensities between CZ- and TGT-grown YAG crystals is associated with the irradiation-induced color centers and quenching effect of Fe{sup 3+} ions.

  4. Surface studies on as-grown (111) faces of sodium bromate crystals

    Indian Academy of Sciences (India)

    K Kishan Rao; V Surender

    2001-12-01

    Single crystals of sodium bromate are grown at various supersaturations ranging from 3% to 8%. Surface studies have been carried out on as-grown and etched (111) faces of these crystals. Typical and systematically oriented growth hillocks are observed almost on all the faces. Further dislocation studies are made to understand the growth history of these crystals. These studies suggest that the crystals grow by 2D-growth mechanism. In addition to this, studies are also conducted on the formation of overgrowths and inclusions in these crystals.

  5. Low-temperature structure of rubrene single crystals grown by vapor transport

    NARCIS (Netherlands)

    Jurchescu, OD; Meetsma, A; Palstra, TTM; Jurchescu, Oana D.

    2006-01-01

    We report the crystal structure of rubrene, C42H28 (5,6,11,12-tetraphenyltetracene), in the temperature interval 100-300 K. The crystals are grown by physical vapor transport in an open system. The crystal structure is orthorhombic over the entire temperature range.

  6. Effects of various deposition times and RF powers on CdTe thin film growth using magnetron sputtering

    Science.gov (United States)

    Ghorannevis, Z.; Akbarnejad, E.; Ghoranneviss, M.

    2016-04-01

    Cadmium telluride (CdTe) is a p-type II-VI compound semiconductor, which is an active component for producing photovoltaic solar cells in the form of thin films, due to its desirable physical properties. In this study, CdTe film was deposited using the radio frequency (RF) magnetron sputtering system onto a glass substrate. To improve the properties of the CdTe film, effects of two experimental parameters of deposition time and RF power were investigated on the physical properties of the CdTe films. X-ray Diffraction (XRD), atomic force microscopy (AFM) and spectrophotometer were used to study the structural, morphological and optical properties of the CdTe samples grown at different experimental conditions, respectively. Our results suggest that film properties strongly depend on the experimental parameters and by optimizing these parameters, it is possible to tune the desired structural, morphological and optical properties. From XRD data, it is found that increasing the deposition time and RF power leads to increasing the crystallinity as well as the crystal sizes of the grown film, and all the films represent zinc blende cubic structure. Roughness values given from AFM images suggest increasing the roughness of the CdTe films by increasing the RF power and deposition times. Finally, optical investigations reveal increasing the film band gaps by increasing the RF power and the deposition time.

  7. Effects of various deposition times and RF powers on CdTe thin film growth using magnetron sputtering

    Science.gov (United States)

    Ghorannevis, Z.; Akbarnejad, E.; Ghoranneviss, M.

    2016-09-01

    Cadmium telluride (CdTe) is a p-type II-VI compound semiconductor, which is an active component for producing photovoltaic solar cells in the form of thin films, due to its desirable physical properties. In this study, CdTe film was deposited using the radio frequency (RF) magnetron sputtering system onto a glass substrate. To improve the properties of the CdTe film, effects of two experimental parameters of deposition time and RF power were investigated on the physical properties of the CdTe films. X-ray Diffraction (XRD), atomic force microscopy (AFM) and spectrophotometer were used to study the structural, morphological and optical properties of the CdTe samples grown at different experimental conditions, respectively. Our results suggest that film properties strongly depend on the experimental parameters and by optimizing these parameters, it is possible to tune the desired structural, morphological and optical properties. From XRD data, it is found that increasing the deposition time and RF power leads to increasing the crystallinity as well as the crystal sizes of the grown film, and all the films represent zinc blende cubic structure. Roughness values given from AFM images suggest increasing the roughness of the CdTe films by increasing the RF power and deposition times. Finally, optical investigations reveal increasing the film band gaps by increasing the RF power and the deposition time.

  8. Characterization of CdTe films with in situ CdCl{sub 2} treatment grown by a simple vapor phase deposition technique

    Energy Technology Data Exchange (ETDEWEB)

    Rios Flores, Araceli, E-mail: arios@mda.cinvestav.mx [Applied Physics Department, CINVESTAV-IPN Merida, C.P. 97310 Merida, Yucatan (Mexico); Castro-Rodriguez, R.; Pena, J.L. [Applied Physics Department, CINVESTAV-IPN Merida, C.P. 97310 Merida, Yucatan (Mexico); Romeo, N.; Bosio, A. [Dipartimento di fisica, Universita di Parma, Campus Universitario, Parco Area delle Scienza, 43100 Parma (Italy)

    2009-05-15

    A unique vapor phase deposition (VPD) technique was designed and built to achieve in situ CdCl{sub 2} treatment of CdTe film. The substrate temperature was 400 deg. C, and the temperature of CdTe mixture with CdCl{sub 2} source was 500 deg. C. The structural and morphological properties of CdTe have been studied as a function of wt.% CdCl{sub 2} concentration by using X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). XRD measurements show that the presence of CdCl{sub 2} vapor induces (1 1 1)-oriented growth in the CdTe film. SEM measurements have shown enhance growth of grains, in the presence of CdCl{sub 2}. From AFM the roughness of the films showed a heavy dependence on CdCl{sub 2} concentration. In the presence of 4% CdCl{sub 2} concentration, the CdTe films roughness has a root mean square (rms) value of about 275 A. This value is about 831 A for the non-treated CdTe films.

  9. Electrical and Optical Properties of Bulk ZnO Single Crystal Grown by Flux Bridgman Method

    Institute of Scientific and Technical Information of China (English)

    LI Xin-Hua; XU Jia-Yue; JIN Min; SHEN Hui; LI Xiao-Min

    2006-01-01

    Zinc oxide (ZnO) single crystals are grown by the modified vertical Bridgman method using a PbF2 flux. Themaximum size of the as-grown ZnO crystal is about φ25 mm× 5mm. The transmittance of the as-grown ZnOcrystal is more than 70% in the range of 600-800nm and the optical band gap is estimated to be 3.21 eV. Thephotoluminescence spectrum indicates that the as-grown ZnO crystal has a very low concentration of nativedefects and is much closed to its stoichiometry. The electrical measurement exhibits that the ZnO crystal haslow electrical resistivity of 0.02394Ωcm-1 and a high carrier concentration of 2.10 × 1018 cm-3

  10. Nucleation studies and characterization of potassium thiocyanate added KDP crystals grown by seed rotation technique

    Energy Technology Data Exchange (ETDEWEB)

    Dhanaraj, P.V. [Centre for Crystal Growth, SSN College of Engineering, Kalavakkam 603 110 (India); Rajesh, N.P., E-mail: rajeshnp@ssn.edu.i [Centre for Crystal Growth, SSN College of Engineering, Kalavakkam 603 110 (India); Mahadevan, C.K. [Physics Research Centre, S.T. Hindu College, Nagercoil 629 002 (India); Bhagavannarayana, G. [C.G.C. Section, National Physical Laboratory, New Delhi 110 012 (India)

    2009-08-01

    The effect of the addition of potassium thiocyanate on potassium dihydrogen phosphate (KDP) crystals, grown from aqueous solution by the temperature lowering method using a microcontroller based seed rotation technique has been studied. As part of nucleation studies, metastable zone width, induction period and crystal growth rate of additive added KDP are determined and analyzed with the pure system. Dielectric measurements were carried out on pure and doped crystals at various temperatures ranging from 313 to 423 K and compared. The crystalline perfection of the grown crystal was studied by the high resolution X-ray diffraction analysis. The crystal grown from additive added solution was subjected to structural, optical transmission, second harmonic generation and hardness studies and the effect of additive on pure system is investigated.

  11. Growth, characterization and dielectric property studies of gel grown barium succinate single crystals

    Indian Academy of Sciences (India)

    M P Binitha; P P Pradyumnan

    2014-05-01

    Single crystals of barium succinate (BaC4H4O4) were grown in silica gel medium using controlled chemical reaction method. Plate-like single crystals of size up to 3 × 2 × 0.2 mm3 was obtained. Single crystal X-ray diffraction (XRD) studies confirmed that structure of the title compound is tetragonal. Powder X-ray diffraction (PXRD) pattern of the grown crystal and the Fourier transform infrared (FT–IR) spectrum in the range 400–4000 cm-1 are recorded. The vibrational bands corresponding to different functional groups are assigned. Thermal stability of the grown crystals is confirmed by differential scanning calorimetry (DSC). Dielectric constant and dielectric loss have been calculated and discussed as a function of frequency at different temperatures.

  12. Photoluminescence study of Cu diffusion in CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Grecu, D.; Compaan, A.D. [Department of Physics, University of Toledo, Toledo, Ohio (United States)

    1999-03-01

    We report changes in the photoluminescence spectra associated with the diffusion of Cu in CdTe thin films used in CdTe/CdS solar cells. Films grown by vapor transport deposition and radio-frequency sputtering as well as single crystal CdTe were included in the study. The main effects of Cu diffusion appear to be the quenching of a donor-acceptor transition associated with Cd vacancies and the increase in intensity of a lower energy broad-band transition. The PL is subsequently used to explore the effects of electric fields on Cu diffusion. The role of Te as a diffusion barrier for Cu is investigated. {copyright} {ital 1999 American Institute of Physics.}

  13. Growth and characterization of gel grown pure and mixed iron–manganese levo-tartrate crystals

    Indian Academy of Sciences (India)

    S J Joshi; B B Parekh; K D Vohra; M J Joshi

    2006-06-01

    Several applications of iron tartrate and manganese tartrate compounds are reported in the literature. In the present investigation, we have grown pure and mixed iron (II)–manganese levo-tartrate crystals by single diffusion gel growth technique. Crystals with spherulitic morphology were harvested. The colouration of the crystals changed from black to pinkish brown upon increasing the content of manganese in the crystals. The crystals were characterized by FTIR spectroscopy, powder XRD, TGA, VSM and dielectric study. Crystal structures of different mixed crystals were studied. From TGA it was observed that on heating the hydrated crystals became anhydrous and then converted into oxides. Paramagnetic nature of the crystals was revealed from VSM study. The variation of the dielectric constant with frequency was studied. The results are discussed.

  14. Creating standard resistors based on germanium and silicon single crystals grown under microgravity conditions

    Science.gov (United States)

    Kartavykh, A. V.; Rakov, V. V.

    2006-11-01

    Requirements on the creation of standard resistors (SRs), which are necessary for the calibration of microprobe complexes used for the diagnostics of electrical homogeneity of single crystal semiconductors, are considered. SR prototypes have been created based on Sb-doped Ge single crystals grown by float zone melting under microgravity conditions aboard the Photon series satellites, in which the inhomogeneity of the resistivity distribution does not exceed 1%. The main factors influencing the homogeneity of doping for Ge and Si crystals grown from melt under orbital flight conditions are formulated; methods for the optimization of this technological process are described.

  15. Molecular-beam epitaxy of CdTe on large area Si(100)

    Science.gov (United States)

    Sporken, R.; Lange, M. D.; Faurie, J. P.; Petruzzello, J.

    1991-10-01

    We have grown CdTe directly on 2- and 5-in. diam Si(100) by molecular-beam epitaxy and characterized the layers by in situ reflection high-energy electron diffraction, double crystal x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and low-temperature photoluminescence. The films are up to 10-μm thick and mirror-like over their entire surface. Even on 5-in. diam wafers, the structural and thickness uniformity is excellent. Two domains, oriented 90° apart, are observed in the CdTe films on oriented Si(100) substrates, whereas single-domain films are grown on Si(100) titled 6° or 8° toward [011]. The layers on misoriented substrates have better morphology than those on oriented Si(100), and the substrate tilt also eliminates twinning in the CdTe layers. First attempts to grow HgCdTe on Si(100 with a CdTe buffer layer have produced up to 10-μm thick layers with cutoff wavelengths between 5 and 10-μm and with an average full width at half-maximum of the double-crystal x-ray diffraction peaks of 200 arc s.

  16. Effect of Crucibles on Qualities of Self-Seeded Aluminium Nitride Crystals Grown by Sublimation

    Institute of Scientific and Technical Information of China (English)

    HAN Qi-Feng; WANG Yu-Qi; DUAN Cheng-Hong; QIU Kai; JI Chang-Jian; LI Xin-Hua; ZHONG Fei; YIN Zhi-Jun; CAO Xian-Cun; ZHOU Xiu-Ju

    2007-01-01

    Self-seeded aluminium nitride (AIN)crystals are grown in tungsten and hot pressed boron nitride(HPBN)crucibles With different shapes by a sublimation method.The qualities of the AIN crystals are characterized by high-resolution transmission electronic microscopy(HRTEM),scanning electron microscopy(SEM)and MicroRaman spectroscopy.The results indicate that the better quality crystals can be collected in.conical tungsten crucible.

  17. Challenges in p-type Doping of CdTe

    Science.gov (United States)

    McCoy, Jedidiah; Swain, Santosh; Lynn, Kelvin

    We have made progress in defect identification of arsenic and phosphorous doped CdTe to understand the self-compensation mechanism which will help improve minority bulk carrier lifetime and net acceptor density. Combining previous measurements of un-doped CdTe, we performed a systematic comparison of defects between different types of crystals and confirmed the defects impacting the doping efficiency. CdTe bulk crystals have been grown via vertical Bridgman based melt growth technique with varying arsenic and phosphorous dopant schemes to attain p-type material. Furnace temperature profiles were varied to influence dopant solubility. Large carrier densities have been reproducibly obtained from these boules indicating successful incorporation of dopants into the lattice. However, these values are orders of magnitude lower than theoretical solubility values. Infrared Microscopy has revealed a plethora of geometrically abnormal second phase defects and X-ray Fluorescence has been used to identify the elemental composition of these defects. We believe that dopants become incorporated into these second phase defects as Cd compounds which act to inhibit dopant solubility in the lattice.

  18. Identification of Ag-acceptor related photoluminescence in $^{111}\\!$Ag doped CdTe

    CERN Document Server

    Hamann, J; Deicher, M; Filz, T; Ostheimer, V; Schmitz, C; Wolf, H; Wichert, T

    1998-01-01

    Bridgman-grown, nominally undoped CdTe crystals were doped with Ag by implanting radioactive $^{111}\\!$Ag. Photoluminescence spectra of the crystals show a donor-acceptor pair (DAP) line at 1.491 eV. The decrease of the intensity of this line with a half life of T$_{1/2}$=(7.2$\\pm$0.4) d is in good agreement with the half life of the $\\beta\\!^{-}$-decay of $^{111}\\!$Ag to $^{111}\\!$Cd of 7.45 d. This decrease is not caused by the aging behavior of Ag which was reported in the literature. The data show that the involved acceptor defect contains exactly one Ag atom and confirm the earlier assignment of the acceptor to the AgCd defect. Based on the DAP line at 1.491 eV, the spectra did not reveal a contamination of the CdTe crystals by stable Ag.

  19. A naturally grown three-dimensional nonlinear photonic crystal

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Tianxiang; Lu, Dazhi; Yu, Haohai, E-mail: haohaiyu@sdu.edu.cn; Zhang, Huaijin, E-mail: huaijinzhang@sdu.edu.cn; Wang, Jiyang [State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan 250100 (China); Zhang, Yong, E-mail: zhangyong@nju.edu.cn [National Laboratory of Solid State Microstructures, School of Physics, and College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093 (China)

    2016-02-01

    Nonlinear frequency conversion via three-dimensional (3D) quasi-phase matching (QPM) process is experimentally realized based on a Ba{sub 0.77}Ca{sub 0.23}TiO{sub 3} (BCT) crystal. The ferroelectric domains in BCT crystal are observed, and the results reveal that the antiparallel domains distribute in three dimensions and can provide 3D reciprocal lattice vectors for QPM processes. Broadband petal-like second-harmonic patterns are achieved, which are well consistent with the theoretical quasi-cubic model of 3D nonlinear photonic crystals. Our work not only promotes the development of QPM technique but also builds a platform for 3D nonlinear optics and quantum optics.

  20. Optical and electrical properties of SnS semiconductor crystals grown by physical vapor deposition technique

    International Nuclear Information System (INIS)

    Tin sulfide (SnS) is a material of interest for use as an absorber in low cost solar cells. Single crystals of SnS were grown by the physical vapor deposition technique. The grown crystals were characterized to evaluate the composition, structure, morphology, electrical and optical properties using appropriate techniques. The composition analysis indicated that the crystals were nearly stoichiometric with Sn-to-S atomic percent ratio of 1.02. Study of their morphology revealed the layered type growth mechanism with low surface roughness. The grown crystals had orthorhombic structure with (0 4 0) orientation. They exhibited an indirect optical band gap of 1.06 eV and direct band gap of 1.21 eV with high absorption coefficient (up to 103 cm-1) above the fundamental absorption edge. The grown crystals were of p-type with an electrical resistivity of 120 Ω cm and carrier concentration 1.52x1015 cm-3. Analysis of optical absorption and diffuse reflectance spectra showed the presence of a wide absorption band in the wavelength range 300-1200 nm, which closely matches with a significant part of solar radiation spectrum. The obtained results were discussed to assess the suitability of the SnS crystal for the fabrication of optoelectronic devices.

  1. Thermoelastic stresses in SiC single crystals grown by the physical vapor transport method

    Institute of Scientific and Technical Information of China (English)

    Zibing Zhang; Jing Lu; Qisheng Chen; V.Prasad

    2006-01-01

    A finite element-based thermoelastic anisotropic stress model for hexagonal silicon carbide polytype is developed for the calculation of thermal stresses in SiC crystals grown by the physical vapor transport method.The composite structure of the growing SiC crystal and graphite lid is considered in the model.The thermal expansion match between the crucible lid and SiC crystal is studied for the first time.The influence of thermal stress on the dislocation density and crystal quality iS discussed.

  2. Morphology and fluorescence spectra of rubrene single crystals grown by physical vapor transport

    Energy Technology Data Exchange (ETDEWEB)

    Zeng Xionghui [Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084 (China); Zhang Deqiang [Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084 (China); Duan Lian [Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084 (China); Wang Liduo [Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084 (China); Dong Guifang [Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084 (China); Qiu Yong [Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084 (China)]. E-mail: qiuy@mail.tsinghua.edu.cn

    2007-05-15

    Rubrene single crystals with pentagon, hexagon, lath-like, and needle-like shape were grown by physical vapor transport. The morphology of surface and transect of rubrene crystals was characterized by optical microscope, atomic force microscope and scanning electron microscope. Monolayers and layer-like structures were observed on the rubrene crystal surface and in the interior of single crystals, respectively. Size and quality of rubrene crystals could be controlled by tuning growth parameters including source temperature, deposition temperature, and growth time. Compared with the emission peak at 555 nm of rubrene solution with the concentration of 10{sup -5} M, the emission peak of rubrene single crystals is at 649 nm with a shift of 94 nm. Hexagon etching pits with typical ladder-like structure were also observed on the (1 0 0) crystal plane and the density of dislocation lines is about 10{sup 3} cm{sup -2}.

  3. Simulation studies and spectroscopic measurements of a position sensitive detector based on pixelated CdTe crystals

    OpenAIRE

    Karafasoulis, K.; Zachariadou, K.; Seferlis, S.; Kaissas, I.; Lambropoulos, C.; Loukas, D; Potiriadis, C.

    2010-01-01

    Simulation studies and spectroscopic measurements are presented regarding the development of a pixel multilayer CdTe detector under development in the context of the COCAE project. The instrument will be used for the localization and identification of radioactive sources and radioactively contaminated spots. For the localization task the Compton effect is exploited. The detector response under different radiation fields as well as the overall efficiency of the detector has been evaluated. Spe...

  4. Shock-produced vapor-grown crystals in the Yanzhuang meteorite

    Institute of Scientific and Technical Information of China (English)

    谢先德; 陈鸣

    1997-01-01

    Vapor-grown crystals intimately related to shock metamorphism of meteorites were found in the Yanzhuang (H6) chondrite which had been heavily impacted in the space. These crystals include: (i) subhedral low-Ca pyroxene occurring on the wall of the pores within a silicate melt pocket that experienced a shock temperature higher than 1 500℃, (ii)Fe-Ni needle-whiskers (taenite) occurring in the cracks in the partially melted chondritic facies that experienced a shock temperature of 850-1 300℃ , (iii) troilite with abundant microholes occurring in the cracks in the brecciated facies and the lightly deformed chondritic facies that experienced a shock temperature lower than 850℃ . The occurrence and mineralogical features of vapor-grown crystals show that vaporization of minerals could be produced in heavily impacted meteorites and that a small amount of crystals could be deposited in situ from vapor plus-

  5. Structural features of Ge(Ga) single crystals grown under conditions simulating the microgravity perturbation factors

    Energy Technology Data Exchange (ETDEWEB)

    Prokhorov, I.A.; Strelov, V.I.; Zakharov, B.G. [Space Materials Science Research Centre of the Crystallography Institute, RAS, Akademicheskaya 8, 248640 Kaluga (Russian Federation); Shul' pina, I.L.; Ratnikov, V.V. [Ioffe Physico-Technical Institute, RAS, Politekhnicheskaya 26, 194021 St. Petersburg (Russian Federation)

    2005-04-01

    Peculiarities of the real structure of Ge(Ga) single crystals grown under external mechanical perturbations of the crystallization process simulating actual microgravity environment aboard spacecrafts were investigated by X-ray topography and diffractometry methods, etching analysis and spreading resistance measurements. The applied perturbations included vibrations and variations of growth facility orientation with respect to the direction of gravity force. It has been shown that microinhomogeneity of the crystals grown is defined not only by formation of dopant growth striations at peculiar vibrational perturbations of a melt, but also by specific features of dislocation structure of crystals related with the formation of small angle boundaries, slip bands and other inhomogeneities in dislocation distribution. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. Second harmonic generation studies in L-alanine single crystals grown from solution

    International Nuclear Information System (INIS)

    Single crystals of L-alanine of dimensions 2×1.1×0.5 cm3 were grown by evaporation method using deionised water as a solvent. The morphology of the grown crystals had (1 2 0) and (0 1 1) as their prominent faces. UV–vis-near IR spectrum shows the transparency range of L-alanine crystal available for frequency doubling from 250 to 1400 nm. Phase-matched second harmonic generation was observed in L-alanine sample by using 7 ns Q-switched Nd:YAG laser with OPO set up. In the present work, phase matching was achieved by angle and wavelength tuning. The angular and spectral phase-matching bandwidths were determined experimentally for a 1.5 mm thick L-alanine crystal and the results have been compared with their theoretical results. Further the possible reasons for the broadening of SHG spectrum have been discussed

  7. Electrical conductivity measurements on gel grown KDP crystals added with urea and thiourea

    Indian Academy of Sciences (India)

    M Priya; C M Padma; T H Freeda; C Mahadevan; C Balasingh

    2001-10-01

    Pure and impurity added (with urea and thiourea) KDP single crystals were grown by the gel method using silica gels. Electrical conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 30 to 140°C by the conventional two-probe method. The present study shows that the conductivity in KDP crystals, for both the impurities considered, increases with the increase in impurity concentration and temperature. Activation energies were also determined and reported.

  8. A pipeline for structure determination of in vivo-grown crystals using in cellulo diffraction

    OpenAIRE

    Boudes, Marion; Garriga, Damià; Fryga, Andrew; Caradoc-Davies, Tom; Coulibaly, Fasséli

    2016-01-01

    While structure determination from micrometre-sized crystals used to represent a challenge, serial X-ray crystallography on microfocus beamlines at synchrotron and free-electron laser facilities greatly facilitates this process today for microcrystals and nanocrystals. In addition to typical microcrystals of purified recombinant protein, these advances have enabled the analysis of microcrystals produced inside living cells. Here, a pipeline where crystals are grown in insect cells, sorted by ...

  9. Electro-Plating and Characterisation of CdTe Thin Films Using CdCl2 as the Cadmium Source

    Directory of Open Access Journals (Sweden)

    Nor A. Abdul-Manaf

    2015-09-01

    Full Text Available Cadmium telluride (CdTe thin films have been successfully prepared from an aqueous electrolyte bath containing cadmium chloride (CdCl2·H2O and tellurium dioxide (TeO2 using an electrodeposition technique. The structural, electrical, morphological and optical properties of these thin films have been characterised using X-ray diffraction (XRD, Raman spectroscopy, optical profilometry, DC current-voltage (I-V measurements, photoelectrochemical (PEC cell measurement, scanning electron microscopy (SEM, atomic force microscopy (AFM and UV-Vis spectrophotometry. It is observed that the best cathodic potential is 698 mV with respect to standard calomel electrode (SCE in a three electrode system. Structural analysis using XRD shows polycrystalline crystal structure in the as-deposited CdTe thin films and the peaks intensity increase after CdCl2 treatment. PEC cell measurements show the possibility of growing p-, i- and n-type CdTe layers by varying the growth potential during electrodeposition. The electrical resistivity of the as-deposited layers are in the order of 104 Ω·cm. SEM and AFM show that the CdCl2 treated samples are more roughness and have larger grain size when compared to CdTe grown by CdSO4 precursor. Results obtained from the optical absorption reveal that the bandgap of as-deposited CdTe (1.48–1.52 eV reduce to (1.45–1.49 eV after CdCl2 treatment. Full characterisation of this material is providing new information on crucial CdCl2 treatment of CdTe thin films due to its built-in CdCl2 treatment during the material growth. The work is progressing to fabricate solar cells with this material and compare with CdTe thin films grown by conventional sulphate precursors.

  10. Growth and fabrication method of CdTe and its performance as a radiation detector

    Science.gov (United States)

    Choi, Hyojeong; Jeong, Manhee; Kim, Han Soo; Kim, Young Soo; Ha, Jang Ho; Chai, Jong-Seo

    2015-01-01

    A CdTe crystal ingot doped with 2000 ppm of Cl was grown by using the low-pressure Bridgman (LPB) method at the Korea Atomic Energy Research Institute (KAERI). A Semiconductor detector as a radiation detection sensor with a size of 7 (W) × 6.5 (D) × 2 (H) mm3 was fabricated from the CdTe ingot. In addition, the properties of the CdTe sample were observed through four kinds of experiments to analyze its performance. The resistivity was obtained as 1.41 × 1010 Ωcm by using a Keithley 6517A high-precision electrometer. The mobility-lifetime products for electrons and holes were 3.137 × 10-4 cm2/V and 4.868 × 10-5 cm2/V, respectively. Finally, we achieved a 16.8% energy resolution at 59.5 keV for the 241Am gamma-ray source. The CdTe semiconductor detector grown at KAERI has a performance good enough to detect low-energy gamma-rays.

  11. Growth and study of some gel grown group II single crystals of iodate

    Indian Academy of Sciences (India)

    Sharda J Shitole; K B Saraf

    2001-10-01

    Single crystals of calcium iodate and barium iodate were grown by simple gel technique by single diffusion method. The optimum conditions were established by varying various parameters such as pH of gel solution, gel concentration, gel setting time, concentration of the reactants etc. Crystals having different morphologies and habits were obtained. Prismatic, dendritic crystals of barium iodate and prismatic, needle shaped, hopper crystals of calcium iodate were obtained. Some of them were transparent, some transluscent, and few others were opaque. Both the crystals were studied using XRD, FT-IR, and thermal analysis. The crystals were doped by iron impurity. The effect of doping was studied using IR spectroscopy and thermal analysis.

  12. Formamide adsorption and habit changes of alkali halide crystals grown from solutions

    NARCIS (Netherlands)

    Radenovic, N.; Enckevort, W.J.P. van; Vlieg, E.

    2004-01-01

    The possibility to obtain {111} surfaces on NaCl crystals grown from pure water solutions was investigated in order to verify some early observations. Repeating the same experiments as reported by Kern in 1953 (Bull. Soc. Fr. Mineral Cristallogr. 76 (1953) 391) followed by detailed examination using

  13. Optical characteristics of ZnO single crystal grown by the hydrothermal method

    Energy Technology Data Exchange (ETDEWEB)

    Chen, G. Z.; Yin, J. G., E-mail: gzhchen@siom.ac.cn, E-mail: yjg@siom.ac.cn; Zhang, L. H.; Zhang, P. X.; Wang, X. Y.; Liu, Y. C. [Chinese Academy of Sciences, Key Laboratory of High Power Laser Materials, Shanghai Institute of Optics and Fine Mechanics (China); Zhang, C. L. [Guilin Research Institute of Geology for Mineral Resources (China); Gu, S. L. [Nanjing University, Department of Physics (China); Hang, Y., E-mail: yhang@siom.ac.cn [Chinese Academy of Sciences, Key Laboratory of High Power Laser Materials, Shanghai Institute of Optics and Fine Mechanics (China)

    2015-12-15

    ZnO single crystals have been grown by the hydrothermal method. Raman scattering and Photoluminescence spectroscopy (PL) have been used to study samples of ZnO that were unannealed or annealed in different ambient gases. It is suggested that the green emission may originate from defects related to copper in our samples.

  14. Studies on bulk growth, structural and microstructural characterization of 4-aminobenzophenone single crystal grown from vertical Bridgman technique

    Indian Academy of Sciences (India)

    S P Prabhakaran; R Ramesh Babu; G Bhagavannarayana; K Ramamurthi

    2014-02-01

    Bulk single crystal of 4-aminobenzophenone with a size of 25 mm dia. and 35 mm length has been grown by vertical Bridgman technique. The crystal system of the grown crystal was confirmed by X-ray diffraction analysis. Crystalline perfection was analysed by high resolution X-ray diffraction studies. Chemical etching was carried out for the first time in 4-aminobenzophenone single crystal to study the defects presented in the grown crystal and the growth mechanism involved. Several organic etchants were employed with different etching time to select suitable etchant for studying dislocation pattern and other structural defects existing in the grown crystal. Etch patterns such as spirals and striations observed for the selective etchants provide considerable information on growth mechanism of the crystal.

  15. CdTe and related compounds: physics, defects, hetero- and nano-structures, crystal growth, surfaces and applications

    CERN Document Server

    Triboulet, Robert

    Almost thirty years after the remarkable monograph of K. Zanio and the numerous conferences and articles dedicated since that time to CdTe and CdZnTe, after all the significant progresses in that field and the increasing interest in these materials for several extremely attractive industrial applications, such as nuclear detectors and solar cells, the edition of a new enriched and updated monograph dedicated to these two very topical II-VI semiconductor compounds, covering all their most prominent, modern and fundamental aspects, seemed very relevant and useful.

  16. Different Shapes of Nano-ZnO Crystals Grown in Catalyst-Free DC Plasma

    Institute of Scientific and Technical Information of China (English)

    HUO Chunqing; ZHANG Yuefei; LIU Fuping; CHEN Qiang; MENG Yuedong

    2009-01-01

    Nano-ZnO crystals grown in hollow-cathode discharge (HCD) driven by direct current (DC) power on p-silicon (100) substrates were presented.With Ar as the diluted gas,O_2 as the reactive gas and high purity zinc powder as the metallic source,the nano-ZnO structure was grown in a catalyst-free process.The crystal ZnO morphology was measured by scanning electron microscopy (SEM).Photoluminescence (PL) spectroscopy was employed to evaluate the crystal nano-ZnO's properties.Effect of several parameters,such as the temperature,O_2 ratio,deposition time and polarity during nanostructure growth,was also investigated.

  17. Photoluminescence characteristics of Pb-doped, molecular-beam-epitaxy grown ZnSe crystal layers

    International Nuclear Information System (INIS)

    The characteristic green photoluminescence emission and related phenomena in Pb-doped, molecular-beam-epitaxy (MBE)-grown ZnSe crystal layers were investigated to explore the nature of the center responsible for the green emission. The intensity of the green emission showed a distinct nonlinear dependence on excitation intensity. Pb-diffused polycrystalline ZnSe was similarly examined for comparison. The characteristic green emission has been observed only in MBE-grown ZnSe crystal layers with moderate Pb doping. The results of the investigations on the growth conditions, luminescence, and related properties of the ZnSe crystal layers suggest that the green emission is due to isolated Pb replacing Zn and surrounded with regular ZnSe lattice with a high perfection

  18. Anomalous effects of dopant distribution in Ge single crystals grown by FZ-technique aboard spacecrafts

    Science.gov (United States)

    Kartavykh, A. V.; Kopeliovich, E. S.; Mil'vidskii, M. G.; Rakov, V. V.

    1999-09-01

    The gallium distribution in nine germanium single crystals, all grown with similar heat conditions using the floating zone (FZ) method aboard five unmanned "Photon" spacecrafts (SC), from melts doped from 1×10 18 to 1×10 20 at/cm 3 are studied. For the first time, the strong anomalous concentration dependence of the distribution coefficient (from 0.16 to 0.089, respectively), having no "earth" analogue, was revealed experimentally as a result of comparative studies of space-grown and reference crystals. It also was shown, that the revealed dependence can completely define the longitudinal dopant distribution profile in a single crystal. The hypothesis of the nature of the observed effect was proposed, which consists of an intensification of the mixing processes in the heavily doped molten zone, restricted by free surface, caused by an increase of the surface-active impurity content in reduced gravity.

  19. Thermal, FT–IR and dielectric studies of gel grown sodium oxalate single crystals

    Indian Academy of Sciences (India)

    B B Parekh; P M Vyas; Sonal R Vasant; M J Joshi

    2008-04-01

    Oxalic acid metabolism is important in humans, animals and plants. The effect of oxalic acid sodium salt is widely studied in living body. The growth of sodium oxalate single crystals by gel growth is reported, which can be used to mimic the growth of crystals in vivo. The grown single crystals are colourless, transparent and prismatic. The crystals have been characterized by thermogravimetric analysis, FT–IR spectroscopy and dielectric response at various frequencies of applied field. The crystals become anhydrous at 129.3°C. Coats and Redfern relation is applied to evaluate the kinetic and thermodynamic parameters of dehydration. The dielectric study suggests very less variation of dielectric constant with frequency of applied field in the range of 1 kHz–1 MHz. The nature of variation of imaginary part of complex permittivity, dielectric loss and a.c. resistivity with applied frequency has been reported.

  20. Structural and optical properties of LiKB{sub 4}O{sub 7} single crystals grown by Czochralski technique

    Energy Technology Data Exchange (ETDEWEB)

    Sukumar, M. [Crystal Growth and Thin Film Laboratory, Department of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu (India); Babu, R. Ramesh, E-mail: rampap2k@yahoo.co.in [Crystal Growth and Thin Film Laboratory, Department of Physics, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu (India); Ramamurthi, K. [Crystal Growth and Thin Film Laboratory, Department of Physics and Nanotechnology, Faculty of Engineering and Technology, SRM University, Kattankulathur 603 203, Tamil Nadu (India); Bhagavannarayana, G. [Crystal Growth and Crystallography Section, National Physical Laboratory, Krishnan Marg, New Delhi 110 012 (India)

    2015-06-15

    One of the alkali metal borates, lithium potassium borate (LiKB{sub 4}O{sub 7}) single crystal, was grown following two different micro step pulling movements employing the modified crystal puller. The influence of two different micro step pulling movements on the crystalline nature, optical properties and micro morphology of the grown LiKB{sub 4}O{sub 7} crystal was investigated by high resolution X-ray diffraction (HRXRD) analysis and birefringence interferometry and chemical etching techniques, respectively. HRXRD studies revealed that the crystalline perfection of the grown crystals is reasonably good. Interferometric images showed that the crystal grown under higher micro step pulling movement has very less number of scattering centers. The etching studies revealed that the crystal grown under higher micro steps pulling movement contains relatively low level dislocation density. - Graphical abstract: Diffraction curve recorded for LiKB{sub 4}O{sub 7} crystal from (a) top portion and (b) bottom portion. - Highlights: • LiKB{sub 4}O{sub 7} crystal was grown under two different micro stepping movements by the crystal puller. • Crystalline nature, optical properties and micro morphology of LiKB{sub 4}O{sub 7} were investigated. • The micro stepping pull movement reduces the dislocation density during the growth of LiKB{sub 4}O{sub 7} crystals.

  1. Optical investigations on Tb3+ doped L-Histidine hydrochloride mono hydrate single crystals grown by low temperature solution techniques

    Science.gov (United States)

    Rajyalakshmi, S.; Ramachandra Rao, K.; Brahmaji, B.; Samatha, K.; Visweswara Rao, T. K.; Bhagavannarayana, G.

    2016-04-01

    The potential nonlinear optical material of Terbium (Tb3+) ion doped L-Histidine hydrochloride monohydrate (LHHC) single crystals were successfully grown. Tb3+:LHHC crystals of 7 mm × 5 mm × 3 mm and 59 mm length and 15 mm diameter have been grown by the slow solvent evaporation and Sankaranarayanan-Ramasamy (SR) techniques respectively. The grown crystals were characterized by single crystal X-ray diffraction analysis to confirm the crystalline structure and morphology. High resolution X-ray diffraction (HRXRD) studies revealed that the SR grown sample shows relatively good crystalline nature with 9″ full-width at half-maximum (FWHM) for the diffraction curve. Functional groups were identified by Fourier transform infra-red spectroscopy (FTIR). The optical transparency and band gaps of grown crystals were measured by UV-Vis spectroscopy. Thermogravimetric and differential thermal analysis (TG/DTA) studies reveal that the crystal was thermally stable up to 155 °C in SR grown crystal. Surface morphology of the growth plane was observed using scanning electron microscopy (SEM). The incorporation of Tb ion was estimated by EDAX. The frequency-dependent dielectric properties of the crystals were carried out for different temperatures. Vickers hardness study carried out on (1 0 0) face at room temperature shows increased hardness of the SR method grown crystal. Second harmonic generation efficiency of SEST and SR grown crystals are 3.2 and 3.5 times greater than that of pure KDP. The Photoluminescence (PL) studies of Tb3+ ions result from the radiative intra-configurational f-f transitions that occur from the 5D4 excited state to the 7Fj (j = 6, 5, 4, 3) ground states. The decay curve of the 5D4 level of emission was observed with a long life time of 319.2041 μs for the SR grown Tb3+:LHHC crystal.

  2. Crystalline perfection and optical properties of rapid grown KH2PO4 crystal with chromate additive

    Indian Academy of Sciences (India)

    Jianxu Ding; Bing Liu; Shenglai Wang; Xiaoming Mu; Shengjun Zhu; Guangxia Liu; Wenjie Liu; Yun Sun; Lin Liu; Duanliang Wang

    2013-10-01

    Potassium dihydrogen phosphate (KDP) crystals were grown in the presence of a series of chromate (CrO$^{2-}_{4}$) additive concentrations via rapid growth method. CrO$^{2-}_{4}$ made KDP crystals were coloured by yellowgreen, suggesting CrO$^{2-}_{4}$ had entered into the crystal lattice. The elemental analysis indicated that Cr element in KDP crystal was at ppm level. High resolution X-ray diffraction data revealed that the crystalline perfection of these as-grown KDP crystals was destroyed after CrO$^{2-}_{4}$ entered into crystal lattice, embedded in the full width at half maximum was broadened and satellite peaks appeared. Additionally, the extinction ratio was decreased with rise of CrO$^{2-}_{4}$ concentration. CrO$^{2-}_{4}$ introduced two absorption peaks centred at 360 and 280 nm and enhanced the intrinsic absorption near 220 nm, which were at the same band positions compared with the CrO$^{2-}_{4}$ or HCrO$^{-}_{4}$ transmittance spectra. Additionally, CrO$^{2-}_{4}$ could increase the size of light scattering, which was attributed to the point defects and microscopic defects by the replacement by CrO$^{2-}_{4}$ at PO$^{3-}_{4}$ position.

  3. Characterization of bulk hexagonal boron nitride single crystals grown by the metal flux technique

    Science.gov (United States)

    Edgar, J. H.; Hoffman, T. B.; Clubine, B.; Currie, M.; Du, X. Z.; Lin, J. Y.; Jiang, H. X.

    2014-10-01

    The optical and physical properties of hexagonal boron nitride single crystals grown from a molten metal solution are reported. The hBN crystals were grown by precipitation from a nickel-chromium flux with a boron nitride source, by slowly cooling from 1500 °C at 2-4 °C/h under a nitrogen flow at atmospheric pressure. The hBN crystals formed on the surface of the flux with an apparent crystal size up to 1-2 mm in diameter. Individual grains were as large as 100-200 μm across. Typically, the flakes removed from the metal were 6-20 μm thick. Optical absorption measurements suggest a bandgap of 5.8 eV by neglecting the binding energy of excitons in hBN. The highest energy photoluminescence peak was at 5.75 eV at room temperature. The hBN crystals typically had a pit density of 5×106 cm-2 after etching in a molten eutectic mixture of potassium hydroxide and sodium hydroxide. The quality of these crystals suggests they are suitable as substrates for two dimensional materials such as graphene and gallium nitride based devices.

  4. Characterization of electrochemical photovoltaic cells using polycrystalline CdSe and CdTe electrodes grown by a liquid metal-vapor reaction

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Z.; Cinquino, M.; Lawrence, M.F. (Laboratories for Inorganic Materials, Department of Chemistry and Biochemistry, Concordia University, 1455 De Maisonneuve Bld. West, Montreal, Quebec, Canada H3G 1M8 (CA))

    1991-06-01

    Polycrystalline CdSe and CdTe layers were fabricated by putting liquid Cd in contact with Se or Te vapors under constant Ar flow. The crystalline structure, surface properties, and semiconducting properties of these materials have been determined. Both materials were found to be {ital n}-type semiconductors. The results show that, under the proper experimental conditions, the liquid metal-vapor reaction enables the synthesis of polycrystalline CdSe photoelectrodes with a 6.9% energy conversion efficiency when used in an electrochemical photovoltaic cell under 80 mW/cm{sup 2} of white light illumination. This efficiency rates amongst the highest ones measured under similar conditions using polycrystalline CdSe. These CdSe layers have a majority charge carrier density of {ital N}{sub {ital D}}=2.6{times}10{sup 17} cm{sup {minus}3} and possess a highly textured surface which is assumed to be mainly responsible for the high photovoltaic efficiency. The highly textured CdTe samples obtained by this process, however, show a photovoltaic conversion efficiency of only 0.2%, and this is seen to be mainly due to their high majority charge carrier density of {ital N}{sub {ital D}}=7.8{times}10{sup 19} cm{sup {minus}3}.

  5. Characterization of electrochemical photovoltaic cells using polycrystalline CdSe and CdTe electrodes grown by a liquid metal-vapor reaction

    International Nuclear Information System (INIS)

    Polycrystalline CdSe and CdTe layers were fabricated by putting liquid Cd in contact with Se or Te vapors under constant Ar flow. The crystalline structure, surface properties, and semiconducting properties of these materials have been determined. Both materials were found to be n-type semiconductors. The results show that, under the proper experimental conditions, the liquid metal-vapor reaction enables the synthesis of polycrystalline CdSe photoelectrodes with a 6.9% energy conversion efficiency when used in an electrochemical photovoltaic cell under 80 mW/cm2 of white light illumination. This efficiency rates amongst the highest ones measured under similar conditions using polycrystalline CdSe. These CdSe layers have a majority charge carrier density of ND=2.6x1017 cm-3 and possess a highly textured surface which is assumed to be mainly responsible for the high photovoltaic efficiency. The highly textured CdTe samples obtained by this process, however, show a photovoltaic conversion efficiency of only 0.2%, and this is seen to be mainly due to their high majority charge carrier density of ND=7.8x1019 cm-3

  6. PENINGKATAN KUALITAS FILM TIPIS CdTe SEBAGAI ABSORBER SEL SURYA DENGAN MENGGUNAKAN DOPING TEMBAGA (Cu

    Directory of Open Access Journals (Sweden)

    P. Marwoto

    2012-12-01

    Full Text Available Film tipis CdTe dengan doping tembaga (Cu berkonsenterasi 2% telah berhasil ditumbuhkan di atas substrat Indium Tin Oxide (ITO dengan metode dc magnetron sputtering. Penelitian ini dilakukan untuk mengetahui pengaruh doping Cu(2% terhadap struktur morfologi, struktur kristal, fotoluminisensi dan resistivitas listrik film CdTe. Citra morfologi Scanning Electron Microscopy (SEM dan hasil analisis struktur dengan X-Ray Diffraction (XRD menunjukkan bahwa film CdTe:Cu(2% mempunyai citra permukaan dan struktur kristal yang lebih sempurna dibandingkan film CdTe tanpa doping. Hasil analisis spektrometer fotoluminisensi menunjukkan bahwa film CdTe dan CdTe(2% mempunyai puncak fotoluminisensi pada tiga panjang gelombang yang identik yaitu 685 nm (1,81 eV, 725 nm (1,71 eV dan 740 nm (1,67 eV. Film CdTe dengan doping Cu(2% memiliki intensitas puncak fotoluminisensi yang lebih tajam pada pita energi 1,81 eV dibandingkan dengan film CdTe tanpa doping. Pengukuran arus dan tegangan (I-V menunjukkan bahwa pemberian doping Cu(2% dapat menurunkan resistivitas film dari 8,40x109 Ωcm menjadi 6,92x105 Ωcm. Sebagai absorber sel surya, kualitas film tipis CdTe telah berhasil ditingkatkan dengan pemberian doping Cu(2%.CdTe:Cu(2% thin film has been successfully grown on Indium Tin Oxide (ITO substrates by using dc magnetron sputtering. This study was carried out in order to investigate the effect of Cu(2% doping on the morphologycal structure, crystal structure, photoluminesence, and resistivity of CdTe thin film. Scanning Electron Microscopy (SEM  images and X-Ray Diffraction (XRD results showed that CdTe:Cu(2% thin film has morphologycal and crystal structures more perfect than undoped CdTe film. Photoluminesence spectroscopy results showed that CdTe and CdTe:Cu(2% thin films have luminesence peak at three identical wevelength regions i.e. 685 nm (1.81 eV, 725 nm (1.71 eV and 740 nm (1.67 eV however CdTe:Cu(2% film shows sharper photoluminescence peak at band

  7. Growth, spectral, structural and mechanical properties of struvite crystal grown in presence of sodium fluoride

    Indian Academy of Sciences (India)

    K Suguna; M Thenmozhi; C Sekar

    2012-08-01

    Struvite or magnesium ammonium phosphate hexahydrate (MAP) is one of the components of urinary stone. Struvite stones are commonly found in women. It forms in human beings as a result of urinary tract infection with urea splitting organisms. These stones can grow rapidly forming “staghorn-calculi”, which is a painful urological disorder. Therefore, it is of prime importance to study the growth and inhibition of struvite crystals. The growth inhibition effect of struvite crystals in sodium metasilicate (SMS) gel in the presence of sodium fluoride has been carried out. Crystals obtained have been analysed by powder and single crystal XRD, SEM–EDX, FTIR and TG–DTA. The results show that the presence of fluoride significantly affects struvite crystal growth and the characteristics of the crystallites produced. The mechanical property of the grown crystals has been investigated by Vickers microhardness testing. Work hardening coefficient was found to be >1.6 for both pure and doped samples which suggests that the crystal belongs to the family of soft material. Presence of sodium fluoride further softened the crystal.

  8. Simulation studies and spectroscopic measurements of a position sensitive detector based on pixelated CdTe crystals

    CERN Document Server

    Karafasoulis, K; Seferlis, S; Kaissas, I; Lambropoulos, C; Loukas, D; Potiriadis, C

    2010-01-01

    Simulation studies and spectroscopic measurements are presented regarding the development of a pixel multilayer CdTe detector under development in the context of the COCAE project. The instrument will be used for the localization and identification of radioactive sources and radioactively contaminated spots. For the localization task the Compton effect is exploited. The detector response under different radiation fields as well as the overall efficiency of the detector has been evaluated. Spectroscopic measurements have been performed to evaluate the energy resolution of the detector. The efficiency of the event reconstruction has been studied in a wide range of initial photon energies by exploiting the detector's angular resolution measure distribution. Furthermore, the ability of the COCAE detector to localize radioactive sources has been investigated.

  9. Characterization of L-ascorbic acid single crystals grown from solution with different solvents

    Energy Technology Data Exchange (ETDEWEB)

    Srinivasan, K.; Vanitha Devi, K. [Crystal Growth Laboratory, Department of Physics, School of Physical Sciences, Bharathiar University, Coimbatore-641 046, Tamil Nadu (India)

    2010-09-15

    Single crystals of L-ascorbic acid, popularly known as vitamin-C, were grown from solutions with different solvents and solvent combinations by low temperature solution growth methods. The suitability of different solvents and solvent combinations such as acetone, ethanol, methanol, isopropyl alcohol, water, water + acetone (1:1), water + ethanol (3:1), water + isopropyl alcohol (3:1) and isopropyl alcohol + methanol (1:1) for crystal growth of L-ascorbic acid was found out by assessing the solubility and crystallization behaviours. Solubility of L-ascorbic acid in selected solvents and solvent combinations in a range of temperatures was determined by gravimetric method. Solution prepared with water, water + acetone (1:1), water + ethanol (3:1) and water + isopropyl alcohol (3:1) were yielded crystals with tabular, columnar and prismatic habits and their morphologies were evaluated by goniometry. Grown single crystals were characterized with various instrumental techniques such as powder X-ray diffraction, Fourier infrared spectroscopy, optical transmittance study, differential scanning calorimetry and second harmonic generation studies. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. A pipeline for structure determination of in vivo-grown crystals using in cellulo diffraction.

    Science.gov (United States)

    Boudes, Marion; Garriga, Damià; Fryga, Andrew; Caradoc-Davies, Tom; Coulibaly, Fasséli

    2016-04-01

    While structure determination from micrometre-sized crystals used to represent a challenge, serial X-ray crystallography on microfocus beamlines at synchrotron and free-electron laser facilities greatly facilitates this process today for microcrystals and nanocrystals. In addition to typical microcrystals of purified recombinant protein, these advances have enabled the analysis of microcrystals produced inside living cells. Here, a pipeline where crystals are grown in insect cells, sorted by flow cytometry and directly analysed by X-ray diffraction is presented and applied to in vivo-grown crystals of the recombinant CPV1 polyhedrin. When compared with the analysis of purified crystals, in cellulo diffraction produces data of better quality and a gain of ∼0.35 Å in resolution for comparable beamtime usage. Importantly, crystals within cells are readily derivatized with gold and iodine compounds through the cellular membrane. Using the multiple isomorphous replacement method, a near-complete model was autobuilt from 2.7 Å resolution data. Thus, in favourable cases, an in cellulo pipeline can replace the complete workflow of structure determination without compromising the quality of the resulting model. In addition to its efficiency, this approach maintains the protein in a cellular context throughout the analysis, which reduces the risk of disrupting transient or labile interactions in protein-protein or protein-ligand complexes. PMID:27050136

  11. Optical characteristics of C{sub 60} single crystals grown in microgravity conditions

    Energy Technology Data Exchange (ETDEWEB)

    Steinman, E.A.; Avdeev, S.V.; Efimov, V.B. [and others

    2000-05-01

    This work is devoted to the growing and characterization of perfect C{sub 60} single crystals with the aim of further understanding of the physical properties of this material related to the low energy excited states which determine in a considerable degree its electronic properties, which, in turn, are important for its possible application. Here the authors present several characterization techniques based on optical properties of C{sub 60} crystals and the first results of the investigation of the C{sub 60} samples grown at the orbital space station MIR.

  12. Electrical conductivity measurements on gel grown KDP crystals added with some ammonium compounds

    Indian Academy of Sciences (India)

    T H Freeda; C Mahadevan

    2000-08-01

    Pure and impurity added [with NH4Cl, NH4NO3, NH4H2PO4, (NH4)2CO3 and (NH4)2SO4] KDP single crystals were grown by the gel method using silica gels. Electrical conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 28 to 140°C by the conventional two-probe method. The present study shows that the conductivity in KDP crystals, for all the five dopants considered, increases with the increase in impurity concentration and temperature. Activation energies were also determined and reported.

  13. Synthesis and characterization of germanium monosulphide (GeS) single crystals grown using different transporting agents

    Indian Academy of Sciences (India)

    G K Solanki; Dipika B Patel; Sandip Unadkat; M K Agarwal

    2010-05-01

    This paper reports the growth of germanium monosulphide (GeS) single crystals by vapour phase technique using different transporting agents. The single crystallinity and composition of the grown crystals have been verified by transmission electron microscopy (TEM) and energy dispersive analysis of X-rays (EDAX) respectively. Resistivity measurements have been carried out in different temperature ranges. Transport parameters, e.g. resistivity, Hall coefficient, carrier concentration and mobility have been measured at varying magnetic fields. All the experimental results have been explained.

  14. The mechanism of Marangoni convection influence on dopant distribution in Ge space-grown single crystals

    Science.gov (United States)

    Artemyev, V. K.; Folomeev, V. I.; Ginkin, V. P.; Kartavykh, A. V.; Mil'vidskii, M. G.; Rakov, V. V.

    2001-02-01

    A direct numerical simulation of heat mass transfer processes in the melt under the influence of surface tension forces on free surfaces during germanium crystal growth by the floating zone (FZ) method under microgravity conditions is performed. Development in time, and interaction between thermal and solutal kinds of Marangoni convection in the molten zone taking into account the temperature dependence of melt viscosity are analyzed. The obtained results explain anomalous distributions of Ga dopant in Ge single crystals grown aboard Russian Photon series spacecrafts (SC).

  15. Characterization of large cadmium zinc telluride crystals grown by traveling heater method

    DEFF Research Database (Denmark)

    Chen, H.; Awadalla, S.A.; Iniewski, K.;

    2008-01-01

    The focus of this paper is to evaluate thick, 20 X 20 X 10 and 10 X 10 X 10 mm(3), cadmium zinc telluride (CZT), Cd0.9Zn0.1Te, crystals grown using the traveling heater method (THIM). The phenomenal spectral performance and small size and low concentration of Te inclusions/precipitates of these c......The focus of this paper is to evaluate thick, 20 X 20 X 10 and 10 X 10 X 10 mm(3), cadmium zinc telluride (CZT), Cd0.9Zn0.1Te, crystals grown using the traveling heater method (THIM). The phenomenal spectral performance and small size and low concentration of Te inclusions...

  16. Epitaxial gamma-iron silicide grown on single-crystal Si. A summary of Moessbauer results

    Energy Technology Data Exchange (ETDEWEB)

    Desimoni, J.; Sanchez, F.H

    1998-08-15

    Metastable {gamma}-FeSi{sub 2} grown on or into single-crystals of silicon can be produced by different techniques as molecular beam epitaxy, and ion implantation followed by ion beam induced epitaxial crystallisation. In these investigations, Moessbauer effect has been used to provide short range order information about the system. We present here a summary of these results, which will be compared and discussed.

  17. Properties of boron-doped epitaxial diamond layers grown on (110) oriented single crystal substrates

    OpenAIRE

    Mortet, Vincent; Pernot, J.; Jomard, F.; Soltani, A; Remes, Zdenek; Barjon, Julien; D'Haen, J; Haenen, Ken

    2015-01-01

    Boron doped diamond layers have been grown on (110) single crystal diamond substrates with B/C ratios up to 20 ppm in the gas phase. The surface of the diamond layers observed by scanning electron microscopy consists of (100) and (113) micro-facets. Fourier Transform Photocurrent Spectroscopy indicates substitutional boron incorporation. Electrical properties were measured using Hall effect from 150 to 1000 K. Secondary ion mass spectrometry analyses are consistent with the high incorporation...

  18. Control of surface and bulk crystalline quality in single crystal diamond grown by chemical vapour deposition

    OpenAIRE

    Friel, I.; Clewes, S L; Dhillon, H. K.; Perkins, N.; Twitchen, D. J.; Scarsbrook, G. A.

    2009-01-01

    In order to improve the performance of existing technologies based on single crystal diamond grown by chemical vapour deposition (CVD), and to open up new technologies in fields such as quantum computing or solid state and semiconductor disc lasers, control over surface and bulk crystalline quality is of great importance. Inductively coupled plasma (ICP) etching using an Ar/Cl gas mixture is demonstrated to remove sub-surface damage of mechanically processed surfaces, whilst maintaining macro...

  19. Optical and electrical properties of ZrSe3 single crystals grown by chemical vapour transport technique

    Indian Academy of Sciences (India)

    Kaushik Patel; Jagdish Prajapati; Rajiv Vaidya; S G Patel

    2005-08-01

    Single crystals of the lamellar compound, ZrSe3, were grown by chemical vapour transport technique using iodine as a transporting agent. The grown crystals were characterized with the help of energy dispersive analysis by X-ray (EDAX), which gave confirmation about the stoichiometry. The optical band gap measurement of as grown crystals was carried out with the help of optical absorption spectra in the range 700–1450 nm. The indirect as well as direct band gap of ZrSe3 were found to be 1.1 eV and 1.47 eV, respectively. The resistivity of the as grown crystals was measured using van der Pauw method. The Hall parameters of the grown crystals were determined at room temperature from Hall effect measurements. Electrical resistivity measurements were performed on this crystal in the temperature range 303–423 K. The crystals were found to exhibit semiconducting nature in this range. The activation energy and anisotropy measurements were carried out for this crystal. Pressure dependence of electrical resistance was studied using Bridgman opposed anvils set up up to 8 GPa. The semiconducting nature of ZrSe3 single crystal was inferred from the graph of resistance vs pressure. The results obtained are discussed in detail.

  20. Study of crystalline perfection and thermal analysis of zinc cadmium thiocyanate single crystals grown in silica gel

    Energy Technology Data Exchange (ETDEWEB)

    Nisha Santha Kumari, P. [Department of Physics, Auxilium College, Vellore (India); Kalainathan, S. [School of Science and Humanities, VIT University, Vellore (India); Bhagavannarayana, G. [Materials Characterization Division, National Physical Laboratory, New Delhi (India)

    2008-03-15

    Zinc cadmium thiocyanate ZnCd(SCN){sub 4} abbreviated as ZCTC is a bimetallic thiocyanate complex that exhibits excellent nonlinear optical property. Single crystals of ZCTC have been grown in silica gel by the process of diffusion. Colorless transparent crystals of size 12 mm x 2 mm x 1.3 mm have been obtained. High resolution X-ray diffraction study was carried out to investigate the crystalline perfection of the grown crystal and the quality of the crystal was found to be quite good. Thermal stability of the grown crystal was investigated by thermogravimetric and differential thermal analyses. Fourier Transform Infrared spectrum was recorded to confirm the functional groups. Microhardness of the crystal is also studied. Being a nonlinear optical material, a comparative study of its second harmonic generation efficiency with urea has been made. (copyright 2007 WILEY -VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. Structural, optical and dielectric studies on solution-grown semi-organic L-histidine tetrafluoroborate single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Raj, S. Gokul [Department of Physics, Presidency College, Chepauk, Chennai 600005 (India); Kumar, G. Ramesh [Department of Physics, Presidency College, Chepauk, Chennai 600005 (India); Mohan, R. [Department of Physics, Presidency College, Chepauk, Chennai 600005 (India); Pandi, S. [Department of Physics, Presidency College, Chepauk, Chennai 600005 (India); Jayavel, R. [Crystal Growth Centre, Anna University, Sardar Patel Road, Chennai 600025 (India)]. E-mail: rjvel@annauniv.edu

    2005-03-15

    L-Histidine tetrafluoroborate (L-HFB) is a highly transparent monoclinic crystal with favourable properties of efficient frequency conversion. Single crystals have been grown successfully by a slow evaporation method. The solubility of the L-HFB crystal is very high in water when compared to other solvents like acetone or methanol. In this study, L-HFB crystals were grown from aqueous solution. The grown crystals have been subjected to X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), second harmonic generation and ultraviolet-visible spectral analyses. Thermogravimetric and differential scanning calorimetry analyses have been performed to study the thermal stability of the crystal. Capacitance and dielectric loss measurements were carried out and the dielectric constant was calculated at room temperature in the frequency range 1 kHz-40 MHz. The dielectric constant at room temperature remains constant for the entire frequency range.

  2. A comparative study of pure and potassium doped cadmium mercury thiocyanate single crystals grown in silica gel

    Energy Technology Data Exchange (ETDEWEB)

    Kumari, P.N.S. [Department of Physics, Auxilium College, Vellore (India); Margaret, M.B. [Department of Physics, Arignar Anna Govt. College for Women, Walajapet (India); Kalainathan, S. [School of Science and Humanities, VIT University, Vellore (India)

    2009-02-15

    Pure and potassium doped cadmium mercury thiocyanate single crystals have been obtained from silica gel by the process of diffusion. The X-ray diffraction studies reveal the crystal lattice of both pure and doped crystals to be tetragonal. The crystalline perfection of the grown crystals were investigated by high resolution X-ray diffraction analysis and the quality of the crystals are found to be extremely good. Transmission and Fourier transform infrared spectra were recorded for the grown crystals. The TG/DTA analyses show that the crystals are highly thermally stable. The mechanical strength of the crystals were studied by Vickers microhardness test and a study of their second harmonic generation efficiency in comparison with urea has been made by performing Kurtz powder test. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Growth and characterization of CdTe absorbers on GaAs by MBE for high concentration PV solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Ari, Ozan; Polat, Mustafa; Selamet, Yusuf [Department of Physics, Izmir Institute of Technology, Izmir 35430 (Turkey); Karakaya, Merve [Department of Material Science and Engineering, Izmir Institute of Technology, Izmir 35430 (Turkey)

    2015-11-15

    CdTe based II-VI absorbers are promising candidates for high concentration PV solar cells with an ideal band gap for AM1.5 solar radiation. In this study, we propose single crystal CdTe absorbers grown on GaAs substrates with a molecular beam epitaxy (MBE) which is a clean deposition technology. We show that high quality CdTe absorber layers can be grown with full width half maximum of X-ray diffraction rocking curves (XRD RC) as low as 227 arc-seconds with 0.5% thickness uniformity that a 2 μm layer is capable of absorbing 99% of AM1.5 solar radiation. Bandgap of the CdTe absorber is found as 1.483 eV from spetroscopic ellipsometry (SE) measurements. Also, high absorption coefficient is calculated from the results, which is ∝5 x 10{sup 5}cm{sup -1} in solar radiation spectrum. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Growth and characterization of CdTe absorbers on GaAs by MBE for high concentration PV solar cells

    International Nuclear Information System (INIS)

    CdTe based II-VI absorbers are promising candidates for high concentration PV solar cells with an ideal band gap for AM1.5 solar radiation. In this study, we propose single crystal CdTe absorbers grown on GaAs substrates with a molecular beam epitaxy (MBE) which is a clean deposition technology. We show that high quality CdTe absorber layers can be grown with full width half maximum of X-ray diffraction rocking curves (XRD RC) as low as 227 arc-seconds with 0.5% thickness uniformity that a 2 μm layer is capable of absorbing 99% of AM1.5 solar radiation. Bandgap of the CdTe absorber is found as 1.483 eV from spetroscopic ellipsometry (SE) measurements. Also, high absorption coefficient is calculated from the results, which is ∝5 x 105cm-1 in solar radiation spectrum. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  5. Thermal characteristics of pure and substituted gel grown Gd-molybdate crystals

    Indian Academy of Sciences (India)

    Vinay Hangloo; K K Bamzai; P N Kotru; M L Koul

    2004-10-01

    Polycrystalline spherulitic crystals of pure Gd-heptamolybdate and single and twinned crystals of substituted Gd–Ba-molybdate were grown by using gel encapsulation technique. The thermal behaviour of these crystals was studied using the thermoanalytical techniques, which included TG, DTA and DSC. Thermal analysis suggests decomposition of the materials in one or more than one stages. Results obtained on application of TG based models viz. Horowitz–Metzger, Coats–Redfern and Piloyan–Novikova, are reported. According to the results of the kinetics of thermal decomposition, the random nucleation model is shown to be the one that is relevant to the decomposition of single rare earth (Gd) containing material and contracting sphere to the decomposition of the substituted (Gd–Ba) one. The kinetic parameters viz. the order of reaction, frequency factor and energy of activation using above-mentioned models, are computed and shown to bear reasonably good agreement.

  6. Thermal kinetic and dielectric parameters of acenaphthene crystal grown by vertical Bridgman technique

    Science.gov (United States)

    Karuppusamy, S.; Dinesh Babu, K.; Nirmal Kumar, V.; Gopalakrishnan, R.

    2016-05-01

    The bulk acenaphthene crystal was grown in a single-wall ampoule by vertical Bridgman technique. X-ray diffraction analysis confirmed the orthorhombic crystal system of title compound with space group Pcm21. Thermal behavior of compound was studied using thermogravimetry—differential scanning calorimetry analysis. Thermal kinetic parameters like activation energy, frequency factor, Avrami exponent, reaction rate and degree of conversion were calculated using Kissingers and Ozawa methods under non-isothermal condition for acenaphthene crystal and reported for the first time. The calculated thermal kinetic parameters are presented. Dielectric studies were performed to calculate the dielectric parameters such as dielectric constant, dielectric loss, AC conductivity, and activation energy from Arrhenius plot.

  7. Dislocation Analysis for Large-sized Sapphire Single Crystal Grown by SAPMAC Method

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In this paper, large-sized sapphire (Φ230×210 mm, 27.5 kg) was grown by SAPMAC method (sapphire growth technique with micro-pulling and shoulder-expanding at the cooled center). Dislocation peculiarity in large sapphire boule (0001) basal plane was investigated by chemical etching, scanning electron microscopy and X-ray topography method. The triangular dislocation etch pit measured is 7.6×101~8.0×102 cm-2, in which relative high-density dislocations were generated at both initial and final stages of crystal growth. The analysis of single-crystal X-ray topography shows that there are no apparent sub-grain boundaries; the dislocation lines are isolated and straight. Finally, the origins of low-density dislocation in sapphire crystal are discussed by numerical analysis method.

  8. Studies on the Properties of ZnO Crystal Plane Grown by the Innovated Hydrothermal Method

    Institute of Scientific and Technical Information of China (English)

    WANG Yong-Hao; CHEN Da-Gui; LI Wei; HUANG Jia-Kui; WANG Guo-Hong; LIN Zhang; HUANG Feng

    2008-01-01

    ZnO single crystals were grown by the innovated hydrothermal method. The crystal surfaces were polished, and then studied by atom force microscope (AFM) and wet-chemical etching (WCE). It was found that the Zn polar plane was smoother than O polar plane under the same polishing conditions. The etch pit density of Zn polar plane is 4.3×103 cm-2,which is consistent with the previous report, while the density of etch pit of O polar plane is more than 103 cm-2. After annealing treatment, the density of etch pit of Zn plane reduces to 5.8×102 cm-2 and is superior to the current report. This investigation reveals that the high quality ZnO single crystals with fine Zn polar plane can be obtained by the innovated hydrothermal method.

  9. The unoccupied electronic structure characterization of hydrothermally grown ThO{sub 2} single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Kelly, T.D.; Petrosky, J.C.; McClory, J.W. [Department of Engineering Physics, Air Force Institute of Technology, WPAFB, OH (United States); Turner, D. [Oak Ridge Institute for Science and Education, Oak Ridge, TN (United States); Mann, J.M. [Sensors Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH (United States); Kolis, J.W. [Department of Chemistry and Center for Optical Materials Science and Engineering Technologies (COMSET), Clemson University, Clemson, SC (United States); Zhang, Xin; Dowben, P.A. [Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, NE (United States)

    2014-03-15

    Single crystals of thorium dioxide ThO{sub 2}, grown by the hydrothermal growth technique, have been investigated by ultraviolet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IPES), and L{sub 3}, M{sub 3}, M{sub 4}, and M{sub 5} X-ray absorption near edge spectroscopy (XANES). The experimental band gap for large single crystals has been determined to be 6 eV to 7 eV, from UPS and IPES, in line with expectations. The combined UPS and IPES, place the Fermi level near the conduction band minimum, making these crystals n-type, with extensive band tailing, suggesting an optical gap in the region of 4.8 eV for excitations from occupied to unoccupied edge states. Hybridization between the Th 6d/5f bands with O 2p is strongly implicated. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. A three-dimensional computational analysis of the influence of magnetic field on the growth of CdTe single crystals by the traveling heater method

    International Nuclear Information System (INIS)

    A three-dimensional numerical simulation for the THM (Travelling Heater Method) growth of CdTe single crystals under an applied (vertical) static magnetic field was carried out. The effect of magnetic field intensity on the transport structures (fluid flow, concentration and temperature fields) in the liquid solution was investigated. Numerical results show that the transport structures in the liquid solution exhibit three, distinct behavior at different field intensity levels. There is a critical magnetic field level, about 8.0 kGauss, below which the applied magnetic field is very beneficial; suppresses the convection and leads to more uniform concentration and temperature distributions and flatter growth interfaces for a prolonged and stable growth. It appears that the field intensity of 8.0 kGauss is the optimum level for which the convection was suppressed to a minimum and the growth interface was the flattest. At field higher levels, the flow structures first show a transitional behaviour and then become very strong and unstable. The computed flow and temperature fields indicate that higher magnetic field levels may in deed lead to unstable transport structures in growth experiments. (author)

  11. GaN grown on (1 1 1) single crystal diamond substrate by molecular beam epitaxy

    Science.gov (United States)

    Dussaigne, A.; Malinverni, M.; Martin, D.; Castiglia, A.; Grandjean, N.

    2009-10-01

    GaN epilayers are grown on (1 1 1) oriented single crystal diamond substrate by ammonia-source molecular beam epitaxy. Each step of the growth is monitored in situ by reflection high energy electron diffraction. It is found that a two-dimensional epitaxial wurtzite GaN film is obtained. The surface morphology is smooth: the rms roughness is as low as 1.3 nm for 2×2 μm 2 scan. Photoluminescence measurements reveal pretty good optical properties. The GaN band edge is centred at 3.469 eV with a linewidth of 5 meV. These results demonstrate that GaN heteroepitaxially grown on diamond opens new rooms for high power electronic applications.

  12. Thermoelectric properties of Tl-doped PbTeSe crystals grown by directional solidification

    Science.gov (United States)

    Su, Ching-Hua

    2016-04-01

    Three Tl-doped PbTe and two Tl-doped PbTeSe crystals were grown by vertical un-seeded directional solidification method. Among them, two Tl-doped PbTe ingots, with starting composition of (Pb0.99Tl0.01)Te, were grown under Pb or Te pressure over the melt provided by a Pb or Te reservoir, respectively, whereas another ingot, with starting composition of (Pb0.98Tl0.02)Te, was grown under Te overpressure. Two Tl-doped PbTeSe crystals, with starting composition of (Pb0.98Tl0.02)(Te0.85Se0.15) and (Pb0.96Tl0.04)(Te0.85Se0.15), were grown without any over-pressure. Disk-shaped samples were sliced at different locations along the growth axis and their thermal conductivities were determined from thermal diffusivity, density, and heat capacity measurements. The electrical conductivity and Seebeck coefficient were simultaneously measured as a function of temperature for each disk sample. The Figure of Merit for the thermoelectric application, zT, was calculated from these properties from room temperature to about 640 °C. The Tl-doped PbTeSe samples have the highest zT value of 1.63 at temperature range of 425 to 475 °C, comparing to 1.13 at 410 °C for the Tl-doped PbTe samples. By substituting 15% of the Te atoms in the Tl-doped PbTe by Se atoms, the Figure of Merit of PbTeSe was enhanced by reducing the thermal conductivity about 26% and, at the same time, increasing the electrical conductivity by 43%.

  13. Effect of impurities and stress on the damage distributions of rapidly grown KDP crystals

    International Nuclear Information System (INIS)

    Development of high damage threshold, 50 cm, rapidly grown KF*P frequency triplers for operation of the National Ignition Facility (NIF) in the 14 J/cm2, 351 nm, 3 ns regime requires a thorough understanding of how the crystal growth parameters and technologies affect laser induced damage. Of particular importance is determining the effect of ionic impurities (e.g. Cr3+, Fe3+, Al3+) which may be introduced in widely varying concentrations via starting salts. In addition, organic particulates can contaminate the solution as leachants from growth platforms or via mechanical ablation. Mechanical stresses in the crystals may also play a strong role in the laser-induced damage distribution (LIDD), particularly in the cases of large boules where hydrodynamic forces in the growth tank may be quite high. WE have developed a dedicated, automated damage test system with diagnostic capabilities specifically designed for measured time resolved bulk damage onset and evolution. The data obtained make it possible to construct characteristic damage threshold distributions for each sample. Test results obtained for a variety of KDP samples grown from high purity starting salts and individually doped with Lucite and Teflon, iron, chromium, and aluminium show that the LIDD drops with increasing contamination content. The results also show that solution filtration leads to increased damage performance for undoped crystals but is not solely responsibility for producing the high LIDDs required by the NIF. The highest LIDD measured on a rapidly grown sample indicate that it is possible to produce high damage threshold material using ultrahigh purity, recrystallized starting salts, continuous filtration and a platform designed to minimize internal stress during growth

  14. Lattice variation and thermal parameters of gel grown KDP crystals added with some ammonium compounds

    Indian Academy of Sciences (India)

    T H Freeda; C Mahadevan

    2001-10-01

    Pure and impurity added (with NH4Cl, NH4NO3, NH4H2PO4, and (NH4)2SO4) KDP single crystals were grown by the gel method using silica gels. X-ray diffraction data were collected for powder samples and used for the estimation of lattice variation and thermal parameters like Debye–Waller factor, mean-square amplitude of vibration, Debye temperature and Debye frequency. The thermal parameters do not vary in a particular order with respect to impurity concentration. The results obtained are reported and discussed.

  15. Low-temperature quantum transport in CVD-grown single crystal graphene

    OpenAIRE

    Xiang, Shaohua; Miseikis, Vaidotas; Planat, Luca; Guiducci, Stefano; Roddaro, Stefano; Coletti, Camilla; Beltram, Fabio; Heun, Stefan

    2016-01-01

    Chemical vapor deposition (CVD) has been proposed for large-scale graphene synthesis for practical applications. However, the inferior electronic properties of CVD graphene are one of the key problems to be solved. In this study, we present a detailed study on the electronic properties of high-quality single crystal monolayer graphene. The graphene is grown by CVD on copper using a cold-wall reactor and then transferred to Si/SiO2. Our low-temperature magneto-transport data demonstrate that t...

  16. Crystal Structure and Optical Properties of Nanocrystalline InN/Si Grown at Low Temperature

    International Nuclear Information System (INIS)

    Nanocrystalline InN films on Si(111) have been successfully grown by RF reactive magnetron sputtering in different N2:Ar gas ratio in ambient temperature. The X-ray diffraction results indicate that the layers consist of hexagonal InN nano crystals. The phonon characteristics in InN thin films as well as the InN films quality are found to be dependent on the growth conditions from comparison of the results. The best nanocrystalline InN films with highly c-axis preferred orientation were attained when the deposition gas ratio of N2:Ar was 50:50. (author)

  17. Microstructural Characterization of CdZnTe(CZT) Crystal Ingot Grown by Bridgman Method at KAERI

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kyu Hong; Kim, Han Soo; Ha, Jang Ho; Kim, Young Soo; Choi, Hyo Jeong [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2012-05-15

    Cd{sub 1-x}Zn{sub x}Te crystal is an important wide band-gap IIVI compound semiconductor which is one of the most attractive radiation materials for room temperature detector, especially for gamma rays. However, the electrical and radiation detection properties of CZT crystal vary widely. They have been attributed to several metallurgical defects such as dislocation, grain- and twin-boundary, Cd vacancy, and secondary phase (Te inclusion and precipitation, etc.). They act as trapping sites of carriers, and significantly degrade the detector's performance. To reduce these defects, doping elements such as Indium is applied. That method compensates Cd vacancies. In this study, 1 inch-diameter In-doped CdZnTe ingots were grown by Vertical Bridgman Method. We conducted several microstructural analyses such as Xray diffraction, edge-pit density (EPD), and ICP-MS analysis

  18. Entrapment of Inclusions in Diamond Crystals Grown from Fe-Ni-C System

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Diamond single crystals grown from Fe-Ni-C system at high temperature-high pressure (HPHT) usually contain inclusions related to the metallic catalyst. During the diamond growth, the metallic inclusions are trapped by the growth front or are formed through reaction between the contaminants trapped in the diamond. In the present paper, the metallic inclusions related to the catalyst were systematically examined by transmission electron microscopy (TEM). The chemical composition and crystal structure of the metallic inclusions were for the first time determined by selected area electron diffraction pattern (SADP) combined with energy dispersive X-ray spectrometry (EDS). It is shown that the inclusions are mainly composed of orthorhombic FeSi2, fcc (FeNi)23C6, and orthorhombic Fe3C,hexagonal Ni3C.

  19. Study of gel grown mixed crystals of BaCa(1–)(IO3)4

    Indian Academy of Sciences (India)

    S L Garud; N K Mahajan; K B Saraf

    2009-04-01

    The growth of mixed crystals of BaCa1–(IO3)4 were carried out with simple gel method. The effect of various parameters such as pH of gel solution, gel concentration, gel setting time, concentration of reactants on the growth was studied. Crystals having different morphologies and habits were obtained. The grown crystals were characterized by XRD, FT–IR, EDAX, TGA, DTA and DSC.

  20. Fabrication and performance of p-i-n CdTe radiation detectors

    International Nuclear Information System (INIS)

    We report on the fabrication and performance of CdTe radiation detectors in a new p-i-n structure which helps to reduce the leakage current to a minimum level. Chlorine-doped single-crystal CdTe substrates having resistivity in the order of 109 Ω cm were used in this study. Iodine-doped n-type CdTe layers were grown homoepitaxially on one face of each crystals using the hydrogen plasma-radical-assisted metalorganic chemical vapor deposition technique at low substrate temperature of 150 deg. C. Indium electrode was evaporated on the n-CdTe side while a gold electrode on the opposite side acted as a p-type contact. Detectors thus fabricated exhibited low leakage current (below 0.4 nA/mm2 at 250 V applied reverse bias for the best one) and good performance at room temperature. Spectral response of the detectors showed improved energy resolution for Am-241, Co-57, and Cs-137 radioisotopes. Detectors were further tested with X-ray photons of different intensities for their potential application in imaging systems and promising responses were obtained

  1. GaAs/Ge crystals grown on Si substrates patterned down to the micron scale

    Energy Technology Data Exchange (ETDEWEB)

    Taboada, A. G., E-mail: gonzalez@phys.ethz.ch; Kreiliger, T.; Falub, C. V.; Känel, H. von [Laboratory for Solid State Physics, ETH Zürich, Otto-Stern-Weg. 1, CH-8093 Zürich (Switzerland); Meduňa, M. [Department of Condensed Matter Physics, Masaryk University, Kotlářská 2, CZ-61137 Brno (Czech Republic); CEITEC, Masaryk University Kamenice 5, CZ-60177 Brno (Czech Republic); Salvalaglio, M.; Miglio, L. [L-NESS, Department of Materials Science, Università di Milano-Bicocca, Via R. Cozzi 55, I-20125 Milano (Italy); Isa, F. [Laboratory for Solid State Physics, ETH Zürich, Otto-Stern-Weg. 1, CH-8093 Zürich (Switzerland); L-NESS and Department of Physics, Politecnico di Milano, via Anzani 42, I-22100 Como (Italy); Barthazy Meier, E.; Müller, E. [Scientific Center for Optical and Electron Microscopy (ScopeM), ETH Zürich, Auguste-Piccard-Hof 1, CH-8093 Zürich (Switzerland); Isella, G. [L-NESS and Department of Physics, Politecnico di Milano, via Anzani 42, I-22100 Como (Italy)

    2016-02-07

    Monolithic integration of III-V compounds into high density Si integrated circuits is a key technological challenge for the next generation of optoelectronic devices. In this work, we report on the metal organic vapor phase epitaxy growth of strain-free GaAs crystals on Si substrates patterned down to the micron scale. The differences in thermal expansion coefficient and lattice parameter are adapted by a 2-μm-thick intermediate Ge layer grown by low-energy plasma enhanced chemical vapor deposition. The GaAs crystals evolve during growth towards a pyramidal shape, with lateral facets composed of (111) planes and an apex formed by (137) and (001) surfaces. The influence of the anisotropic GaAs growth kinetics on the final morphology is highlighted by means of scanning and transmission electron microscopy measurements. The effect of the Si pattern geometry, substrate orientation, and crystal aspect ratio on the GaAs structural properties was investigated by means of high resolution X-ray diffraction. The thermal strain relaxation process of GaAs crystals with different aspect ratio is discussed within the framework of linear elasticity theory by Finite Element Method simulations based on realistic geometries extracted from cross-sectional scanning electron microscopy images.

  2. Dielectric properties of highly resistive GaN crystals grown by ammonothermal method at microwave frequencies

    Directory of Open Access Journals (Sweden)

    Jerzy Krupka

    2016-03-01

    Full Text Available Permittivity, the dielectric loss tangent and conductivity of semi-insulating Gallium Nitride crystals have been measured as functions of frequency from 10 GHz to 50 GHz and temperature from 295 to 560 K employing quasi TE0np mode dielectric resonator technique. Crystals were grown using ammonothermal method. Two kinds of doping were used to obtain high resistivity crystals; one with deep acceptors in form of transition metal ions, and the other with shallow Mg acceptors. The sample compensated with transition metal ions exhibited semi-insulating behavior in the whole temperature range. The sample doped with Mg acceptors remained semi-insulating up to 390 K. At temperatures exceeding 390 K the conductivity term in the total dielectric loss tangent of Mg compensated sample becomes dominant and it increases exponentially with activation energy of 1.14 eV. It has been proved that ammonothermal method with appropriate doping allows growth of high quality, temperature stable semi-insulating GaN crystals.

  3. Growth and characterization of cerium lanthanum oxalate crystals grown in hydro-silica gel

    Energy Technology Data Exchange (ETDEWEB)

    John, M.V.; Ittyachen, M.A. [Mahatma Gandhi Univ., Kerala (India). School of Pure and Applied Physics

    2001-07-01

    Single crystals of mixed cerium lanthanum oxalate (CLO) are grown by gel method. Over the hydrosilica gel prepared by mixing oxalic acid and sodium meta silicate, a mixture of aqueous solutions of cerium nitrate and lanthanum nitrate are poured gently. Cerium and lanthanum ions diffuse into the gel and react with oxalic acid to give colorless, transparent cerium lanthanum oxalate crystals with in a few days. Different growth parameters give crystals of various dimensions. Infrared (IR) spectrum confirms the presence of water molecules and carboxylic acid. X-ray diffraction (XRD) pattern of these samples reveals the crystalline nature. Diffraction peaks are indexed. Unit cell parameters are determined. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) data support the presence of 9 H{sub 2}O molecules attached to the CLO crystal lattice which are lost around 200 C as revealed by the endotherm record. Exothermic peak around 350 C-425 C shows the release of CO and CO{sub 2}. Elemental analysis done by energy dispersive X-ray fluorescence analysis (EDXRF) for the mixed rare earth compound is almost in good agreement with experimental and theoretical values. (orig.)

  4. Influence of the pulling rate on the properties of ZnGeP2 crystal grown by vertical Bridgman method

    Science.gov (United States)

    Shen, Liang; Wu, Dong

    2016-07-01

    Zinc-germanium diphosphide (ZGP) crystals (15 mm in diameter and 65 mm in length) were successfully grown by the modified vertical Bridgman method on seeds at different pulling rates (0.5 mm/h and 0.75 mm/h) in order to study the defect generation during crystal growth. At the different positions (the onset, middle and end) in single crystals, their properties of ZGP crystals were investigated by X-ray diffraction, etching technique and optical transmission spectra. The results indicate that the increase in the pulling rate deteriorates the crystal quality at the onset part of the single crystals. The etch pit density (EPD) and the full width at half maximum (FWHM) of the X-ray rocking curves increase, while the optical transmittance decreases with increasing pulling rate. However, the increase in the pulling rate hardly influences the crystal quality at the middle and end part of the single crystals.

  5. Homogeneity and variation of donor doping in Verneuil-grown SrTiO3:Nb single crystals

    Science.gov (United States)

    Rodenbücher, C.; Luysberg, M.; Schwedt, A.; Havel, V.; Gunkel, F.; Mayer, J.; Waser, R.

    2016-08-01

    The homogeneity of Verneuil-grown SrTiO3:Nb crystals was investigated. Due to the fast crystal growth process, inhomogeneities in the donor dopant distribution and variation in the dislocation density are expected to occur. In fact, for some crystals optical studies show variations in the density of Ti3+ states on the microscale and a cluster-like surface conductivity was reported in tip-induced resistive switching studies. However, our investigations by TEM, EDX mapping, and 3D atom probe reveal that the Nb donors are distributed in a statistically random manner, indicating that there is clearly no inhomogeneity on the macro-, micro-, and nanoscale in high quality Verneuil-grown crystals. In consequence, the electronic transport in the bulk of donor-doped crystals is homogeneous and it is not significantly channelled by extended defects such as dislocations which justifies using this material, for example, as electronically conducting substrate for epitaxial oxide film growth.

  6. Towards a greater understanding of hydrothermally grown garnets and sesquioxide crystals for laser applications

    Science.gov (United States)

    Moore, Cheryl Ann

    The hydrothermal method of crystal growth offers many benefits over traditional melt-based techniques such as lower temperature requirements relieving detrimental high temperature effects such as stress fracturing and a closed-environment, which limits impurities. The continued study of this type of growth including hydrothermal epitaxy is crucial in our world of constant miniaturization. Presented in this thesis is the hydrothermal growth of crystals of LuAG and Lu2O3 doped with a variety of dopants. Their room-temperature and cryogenic absorption spectra are also presented. Much like Nature uses heat, pressure, water and a nutrient-rich feedstock we have used this hydrothermal technique to produce synthetic crystals of grossular, Ca3Al2(SiO4)3, a naturally occurring garnet as well as other aluminosilicates related to grossular, including a new type of vesuvianite. Other garnets important to the laser industry have also been grown using the hydrothermal technique, such as yttrium aluminum garnet (YAG), lutetium aluminum garnet (LuAG) and the related sesquioxide Lu2O3, (lutetia). The growth and characteristics of Yb-doped lutetia and LuAG, Nd-doped lutetia, and Dy-doped lutetia and YAG are presented herein. These laser crystals have been analyzed by high-resolution absorption spectroscopy at room temperature as well as 250K, 200K, 150K and 80K and absorption coefficients are presented. A coprecipitation technique common in the ceramics field has been adapted for use creating precursors for hydrothermal crystal growth, including phase-pure polycrystalline anorthite and phase-pure gehlenite. Coprecipitation has also been utilized to gain greater control of dopants to create pre-doped feedstocks used for the growth of laser crystal. The versatility of the hydrothermal growth method is also highlighted in a novel epitaxial technique, core growth, which coats the internal surfaces of a seed crystal as well as external surfaces. This can result in multifunctional

  7. High-temperature treatment of In-doped CZT crystals grown by the high-pressure Bridgman method

    Energy Technology Data Exchange (ETDEWEB)

    Bolotnikov A.; Fochuk, P.; Nakonechnyi, I.; Kopach, O.; Verzhak, Ye.; Panchuk, O.; Komar, V.; Terzin, I.; Kutnij, V.; Rybka, A.; Nykoniuk, Ye.; Camarda, G.C.; Cui, Y.; Hossain, A.; Kim, K.H.; Yang, G.; James, R.B.

    2012-08-12

    We evaluated the effect of high-temperature treatment of Cd0.9Zn0.1Te:In single crystals using Hall-effect measurements, medium- and high-temperature annealing under various deviations from stoichiometry, and infra-red (IR) transmission microscopy Annealing at ~730 K sharply increased the electrical conductivity (by ~1-2 orders-of-magnitude). Plots of the temperature- and cadmium-pressure dependences of the electrical conductivity, carrier concentration, and mobility were obtained. Treating previously annealed Cd-samples under a Te overpressure at 1070 K allowed us to restore their resistance to its initial high values. The main difference in comparing this material with CdTe was its lowered electron density. We explained our results within the framework of Kröger’s theory of quasi-chemical reactions between point defects in solids.

  8. Laser characteristics of TGT-grown Nd,Y-codoped:SrF2 single crystal

    Science.gov (United States)

    Jelínek, Michal; Kubeček, Václav; Su, Liangbi; Jiang, Dapeng; Ma, Fengkai; Zhang, Qian; Cao, Yuexin; Xu, Jun

    2014-05-01

    In this contribution we present spectroscopic and laser properties of TGT (temperature gradient technique) grown Nd,Y:SrF2 crystals with neodymium concentration of 0.4, 0.65 and 0.8 at.%. The absorption cross-section, fluorescence spectra and fluorescence decay time were measured. For the laser experiments, the noncoated crystal samples 3.5 or 5 mm thick were pumped by a 796 nm laser diode matching the Nd:SrF2 absorption peak. Several output couplers with reflectivity ranging from 70 to 98 % at the generated wavelength were tested. In the pulsed pumping regime (pulseduration 2 ms, frequency 10 Hz), the maximum average output power of 75 mW was obtained with the slope efficiency as high as 48 % and the optical-to-optical efficiency of 42 % with respect to the absorbed pump power. The output beam spatial profile was nearly Gaussian in both axes, oscillations started at the wavelength of 1057 nm. At higher pumping levels, the second emission line at 1050 nm appears corresponding to our fluorescence measurements. Wavelength tuning using birefringent filter from 1048 to 1070 nm is probably given by crystal-field splitting of the 4F3/2 manifold in Nd3+. True-CW laser operation was also successfully obtained at lower pumping level with the maximum output power of 90 mW using output coupler reflectivity of 98 %.

  9. Inline atmospheric pressure metal-organic chemical vapour deposition for thin film CdTe solar cells

    International Nuclear Information System (INIS)

    A detailed study has been undertaken to assess the deposition of CdTe for thin film devices via an inline atmospheric pressure metal-organic chemical vapour deposition (AP-MOCVD) reactor. The precursors for CdTe synthesis were released from a showerhead assembly normal to a transparent conductive oxide (TCO)/glass substrate, previously coated with a CdZnS window layer using a conventional batch AP-MOCVD reactor with horizontal flow delivery. Under a simulated illumination with air mass coefficient 1.5 (AM1.5), the initial best cell conversion efficiency (11.2%) for such hybrid cells was comparable to a reference device efficiency (∼ 13%), grown entirely in the AP-MOCVD batch reactor. The performance and structure of the hybrid and conventional devices are compared for spectral response, CdTe grain morphology and crystal structure. These preliminary results reported on the transfer from a batch to an inline AP-MOCVD reactor which holds a good potential for the large-scale production of thin film photovoltaics devices and related materials. - Highlights: • Inline metal-organic chemical vapour deposition (MOCVD) used to grow CdTe films • Desired dopant profiles in CdTe:As achieved with inline MOCVD reactor • Initial conversion efficiency of 11.2% was comparable to batch devices (∼ 13%). • Inline MOCVD holds a good potential for large-scale thin film photovoltaics production

  10. Molecular beam epitaxy of CdTe and HgCdTe on large-area Si(100)

    Science.gov (United States)

    Sporken, R.; Lange, M. D.; Faurie, Jean-Pierre

    1991-09-01

    The current status of molecular beam epitaxy (MBE) of CdTe and HgCdTe on Si(100) is reviewed. CdTe and HgCdTe grow in the (111)B orientation on Si(100); monocrystalline films with two domains are obtained on most nominal Si(100) substrates, single domain films are grown on misoriented substrates and on nominal Si(100) preheated to 900-950 degree(s)C. Double-crystal x-ray rocking curves (DCRCs) with full-width at half-maximum (FWHM) as low as 110 arcsec are reported for HgCdTe on silicon; these layers are n-type, and electron mobilities higher than 5 X 104 cm2V-2s-1 are measured at 23 K for x equals 0.26. Excellent thickness and composition uniformity is obtained: standard deviation of the CdTe thickness 0.4% of the average thickness on 2-in. and 2.3% on 5-in., standard deviation of the Cd concentration in the HgCdTe layers 0.6% of the average concentration on 3-in. and 2.4% on 5-in. First results regarding growth of CdTe on patterned Si substrates are also reported.

  11. Thermoluminescence of Al2O3 crystals grown by temperature gradient techniques

    Institute of Scientific and Technical Information of China (English)

    CHEN Wei; SONG PingXin; DONG YongJun; ZHANG YingJiu; HUA Wei

    2013-01-01

    Color center concentrations of the Al2O3 crystal grown by temperature gradient techniques were calculated from Gaussian fits to absorption spectra.The concentrations for F-and F+-centers at 204,232,and 255 nm were determined to be 1.361×1017,0.098×1017,and 0.325×1017cm-3,respectively.Studies have shown that the thermoluminescence (TL) glow curve exhibits a prominent 450 K peak that matches well the first-order fitting curve.The thermal activation energy E and frequency factor s of the trap were determined to be 0.94456±0.00545 eV and 5.8703×1011 s-1.With this theoretical analysis,a simple one-trap/one-center TL model is presented to provide a theoretical explanation of the TL process.

  12. Reduction in the crystal defect density of Zn Se layers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lopez L, M.; Perez C, A.; Luyo A, J.; Melendez L, M.; Tamura, M. [Departamento de Fisica, Centro de Investigacion y de Estudios Avanzados del instituto politecnico Nacional, A.P. 14-740, 07000 Mexico D.F. (Mexico); Mendez G, V.H.; Vidal, M.A. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, 78000 San Luis Potosi (Mexico)

    2000-07-01

    We present a study of the molecular beam epitaxial (MBE) grown of Zn Se layers on Ga-As and Si substrates. For the growth on GaAs substrates we investigated the effects of introducing buffer layers of Al{sub x}Ga{sub 1-x} As and In{sub x}Ga{sub 1-x} As with x = 0.01. Moreover, an analysis by secondary ion mass spectroscopy revealed that the use of AlGaAs buffer layers effectively suppress the Ga segregation onto the Zn Se layers surface. On the other hand, for the growth of Zn Se on Si substrates, we achieved a significant improvement in the crystal quality of Zn Se by irradiating the Si substrates with plasma of nitrogen prior to the growth. (Author)

  13. Reduction in the crystal defect density of Zn Se layers grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    We present a study of the molecular beam epitaxial (MBE) grown of Zn Se layers on Ga-As and Si substrates. For the growth on GaAs substrates we investigated the effects of introducing buffer layers of AlxGa1-x As and InxGa1-x As with x = 0.01. Moreover, an analysis by secondary ion mass spectroscopy revealed that the use of AlGaAs buffer layers effectively suppress the Ga segregation onto the Zn Se layers surface. On the other hand, for the growth of Zn Se on Si substrates, we achieved a significant improvement in the crystal quality of Zn Se by irradiating the Si substrates with plasma of nitrogen prior to the growth. (Author)

  14. CdTe and Cd sub 1 sub - sub x Zn sub x Te for nuclear detectors: facts and fictions

    CERN Document Server

    Fougeres, P; Hageali, M; Koebel, J M; Regal, R

    1999-01-01

    Both CdTe and Cd sub 1 sub - sub x Zn sub x Te (CZT) can be considered from their physical properties as very good materials for room temperature X- and gamma-rays detection. However, despite years of intense material research, no significant advance has been made to help one to choose between both semiconductors. This paper reviews a few facts about CdTe and CZT to attempt to draw a real comparison between both. THM-CdTe and HPB-CZT have been grown and characterized in Strasbourg. Crystal growth, alloying effects, transport properties and defects are reviewed on the basis of our results and the published ones. The results show that it is still very difficult to claim which one is the best.

  15. Catalytic growth of CdTe nanowires by closed space sublimation method

    International Nuclear Information System (INIS)

    CdTe nano-/micro-structures with various morphologies were grown by using the closed space sublimation (CSS) method on a sapphire substrate by Au-catalyzed vapor–liquid–solid (VLS) mechanism. Length, diameter, and morphology of the CdTe nano-/micro-structures depended on the growth time and temperature gradient between the substrate and powdered CdTe source. Scanning electron microscopy images showed that an Au catalyst droplet existed at the tips of CdTe nanowires, which confirms that CdTe nanowires were grown by an Au-catalyzed VLS mechanism. Also, we observed that the two-dimensional CdTe film layer initially formed before the growth of the CdTe nano-/micro-wires. The optical and structural properties of CdTe nano-/micro-structures were characterized by X-ray diffraction technique and micro-Raman spectroscopy. Our study demonstrates that diverse CdTe nano-/micro-structures can be fabricated by using Au-catalyzed VLS growth process in a simple CSS chamber by controlling the temperature gradient and growth time. - Highlights: • We demonstrated CdTe nanowires using closed space sublimation method. • Au-catalyst droplets at the tips confirmed vapor–liquid–solid mechanism. • Diameters and lengths increased with increasing temperature gradient and time

  16. Growth of CdTe thin films on graphene by close-spaced sublimation method

    International Nuclear Information System (INIS)

    CdTe thin films grown on bi-layer graphene were demonstrated by using the close-spaced sublimation method, where CdTe was selectively grown on the graphene. The density of the CdTe domains was increased with increasing the number of the defective sites in the graphene, which was controlled by the duration of UV exposure. The CdTe growth rate on the bi-layer graphene electrodes was 400 nm/min with a bandgap energy of 1.45–1.49 eV. Scanning electron microscopy, micro-Raman spectroscopy, micro-photoluminescence, and X-ray diffraction technique were used to confirm the high quality of the CdTe thin films grown on the graphene electrodes

  17. High quality (InNb)0.1Ti0.9O2 single crystal grown using optical floating zone method

    Science.gov (United States)

    Liu, Ziyi; Song, Yongli; Wang, Xianjie; Su, Yantao; Liu, Zhiguo; Sui, Yu

    2016-07-01

    A crack-free (InNb)0.1Ti0.9O2 single crystal of 4 mm in diameter and 30 mm in length was successfully grown by the optical floating zone method. The polycrystalline feed and seed rods for growing the (InNb)0.1Ti0.9O2 single crystal were prepared by solid-state reaction method. The oxygen partial pressure significantly affected the crystal quality of the material. As shown in reflecting polarizing microphotographs, crystals grown in air have fewer grain boundaries than those grown in pure oxygen; some air-grown crystals are completely free of grain boundaries. Compared to pure TiO2 crystal, the (Nb+In) co-doped TiO2 crystal required a lower growth rate of 5 mm/h to ensure high quality.

  18. Nanocrystal grain growth and device architectures for high-efficiency CdTe ink-based photovoltaics.

    Science.gov (United States)

    Crisp, Ryan W; Panthani, Matthew G; Rance, William L; Duenow, Joel N; Parilla, Philip A; Callahan, Rebecca; Dabney, Matthew S; Berry, Joseph J; Talapin, Dmitri V; Luther, Joseph M

    2014-09-23

    We study the use of cadmium telluride (CdTe) nanocrystal colloids as a solution-processable "ink" for large-grain CdTe absorber layers in solar cells. The resulting grain structure and solar cell performance depend on the initial nanocrystal size, shape, and crystal structure. We find that inks of predominantly wurtzite tetrapod-shaped nanocrystals with arms ∼5.6 nm in diameter exhibit better device performance compared to inks composed of smaller tetrapods, irregular faceted nanocrystals, or spherical zincblende nanocrystals despite the fact that the final sintered film has a zincblende crystal structure. Five different working device architectures were investigated. The indium tin oxide (ITO)/CdTe/zinc oxide structure leads to our best performing device architecture (with efficiency >11%) compared to others including two structures with a cadmium sulfide (CdS) n-type layer typically used in high efficiency sublimation-grown CdTe solar cells. Moreover, devices without CdS have improved response at short wavelengths.

  19. Nanocrystal grain growth and device architectures for high-efficiency CdTe ink-based photovoltaics.

    Science.gov (United States)

    Crisp, Ryan W; Panthani, Matthew G; Rance, William L; Duenow, Joel N; Parilla, Philip A; Callahan, Rebecca; Dabney, Matthew S; Berry, Joseph J; Talapin, Dmitri V; Luther, Joseph M

    2014-09-23

    We study the use of cadmium telluride (CdTe) nanocrystal colloids as a solution-processable "ink" for large-grain CdTe absorber layers in solar cells. The resulting grain structure and solar cell performance depend on the initial nanocrystal size, shape, and crystal structure. We find that inks of predominantly wurtzite tetrapod-shaped nanocrystals with arms ∼5.6 nm in diameter exhibit better device performance compared to inks composed of smaller tetrapods, irregular faceted nanocrystals, or spherical zincblende nanocrystals despite the fact that the final sintered film has a zincblende crystal structure. Five different working device architectures were investigated. The indium tin oxide (ITO)/CdTe/zinc oxide structure leads to our best performing device architecture (with efficiency >11%) compared to others including two structures with a cadmium sulfide (CdS) n-type layer typically used in high efficiency sublimation-grown CdTe solar cells. Moreover, devices without CdS have improved response at short wavelengths. PMID:25133302

  20. Comparative study of CdTe sources used for deposition of CdTe thin films by close spaced sublimation technique

    OpenAIRE

    Wagner Anacleto Pinheiro; Vivienne Denise Falcão; Leila Rosa de Oliveira Cruz; Carlos Luiz Ferreira

    2006-01-01

    Unlike other thin film deposition techniques, close spaced sublimation (CSS) requires a short source-substrate distance. The kind of source used in this technique strongly affects the control of the deposition parameters, especially the deposition rate. When depositing CdTe thin films by CSS, the most common CdTe sources are: single-crystal or polycrystalline wafers, powders, pellets or pieces, a thick CdTe film deposited onto glass or molybdenum substrate (CdTe source-plate) and a sintered C...

  1. Comparative study of CdTe sources used for deposition of CdTe thin films by close spaced sublimation technique

    Directory of Open Access Journals (Sweden)

    Wagner Anacleto Pinheiro

    2006-03-01

    Full Text Available Unlike other thin film deposition techniques, close spaced sublimation (CSS requires a short source-substrate distance. The kind of source used in this technique strongly affects the control of the deposition parameters, especially the deposition rate. When depositing CdTe thin films by CSS, the most common CdTe sources are: single-crystal or polycrystalline wafers, powders, pellets or pieces, a thick CdTe film deposited onto glass or molybdenum substrate (CdTe source-plate and a sintered CdTe powder. In this work, CdTe thin films were deposited by CSS technique from different CdTe sources: particles, powder, compact powder, a paste made of CdTe and propylene glycol and source-plates (CdTe/Mo and CdTe/glass. The largest deposition rate was achieved when a paste made of CdTe and propylene glycol was used as the source. CdTe source-plates led to lower rates, probably due to the poor heat transmission, caused by the introduction of the plate substrate. The results also showed that compacting the powder the deposition rate increases due to the better thermal contact between powder particles.

  2. Effect of rhodium doping on the growth and characteristics of BaTiO 3 single crystals grown by step-cooling method

    Science.gov (United States)

    Madeswaran, S.; Giridharan, N. V.; Varatharajan, R.; Ravi, G.; Jayavel, R.

    2004-06-01

    Single crystals of Rh-doped BaTiO 3 have been grown by high-temperature solution growth technique. The dopant has significant effect on the growth parameters and crystal properties. Bulk single crystals of dimensions 5×5×4 mm 3 have been grown with optimized growth conditions. Layer growth and vein-like structure patterns, indicative of 2D-nucleation mechanism, have been observed on the grown crystals. The dopant level in the grown crystals was estimated by EDX analysis. The crystals possess tetragonal structure and the tetragonality decreases for higher dopant concentration. Rh doping in BaTiO 3 leads to decrease in dielectric constant and Curie temperature ( Tc) values.

  3. Improvement of Mechanical, Thermal and Optical Properties of Barium Mixed Cobalt Tartrate Hydrate Crystals Grown by Gel Method

    Directory of Open Access Journals (Sweden)

    S. Vanaja

    2015-10-01

    Full Text Available In this present work, CTH and BCTH crystals have been prepared by gel technique by using single diffusion method at room temperature. The as grown crystals were characterized by using XRD, FT-IR, UV, TG / DTA and Micro hardness studies. X-ray powder diffraction results analyzed by using suitable software suggest that a CTH and BCTH crystals belong to cubic crystal system. The unit cell volume is observed to increase with increase in the concentration of barium in cobalt tartrate due to the lattice distortion. The band gap and optical properties have analyzed by UV-Visible spectrum. The functional groups and compound formation of the crystals have been studied by FT-IR spectrum. The mechanical properties of the grown crystals were tested by using Vicker’s microhardness studies. The work hardening coefficient (n was determined to be 3.7 for CTH, 5.3 for BCTH (1 : 1 and 6.4 for BCTH (2 : 1 and the stiffness constants for different loads were calculated and reported. Thermal analysis suggests that pure cobalt tartrate starts decomposing at 73.2 °C whereas the barium mixed cobalt tartrate brings about better thermal stability which increases with an increase in barium concentration.

  4. Microhardness studies on as-grown faces of NaClO3 and NaBrO3 crystals

    Indian Academy of Sciences (India)

    K Kishan Rao; V Surender; B Saritha Rani

    2002-12-01

    Single crystals of NaClO3 and NaBrO3 are grown from their aqueous solutions at a constant temperature of 35°C by slow evaporation by using good quality seed crystals. Systematic microhardness studies are made on as-grown faces of these crystals at various loads. Typical cracks are observed at the corners of the impressions in NaClO3 whereas in addition to the cracks at the corners microcracks also appeared in NaBrO3 crystals around the impressions. The impressions formed in NaBrO3 are not very clear as in NaClO3, a possible mechanism for it is discussed. The work hardening index number () for both these crystals is around 1.6 suggesting that these are moderately harder samples. The hardness studies point out that NaBrO3 is harder than NaClO3 ( ≈ 100 kg/mm2), this could be due to strong inter ionic forces acting between Na–Br in NaBrO3 crystals. Using Gilman’s empirical relation, hardness values are calculated from the values of elastic constants (44) and are found to be close to the experimental results.

  5. Investigation of magnetic property of GdFeO3 single crystal grown in air by optical floating zone technique

    International Nuclear Information System (INIS)

    Highlights: • GdFeO3 single crystals have been grown by OFZ technique in air. • Sample exhibits one order lower coercive field than crystal grown in oxygen. • Bloch 3/2-law holds good for GdFeO3 (B-parameter as 2.69 × 10−5 K−3/2). • The coercivity exhibited sharp dip at 200 and 550 K. • At 550 K pinning of the direction of weak ferromagnetism by AFM ordering vanishes. - Abstract: Single phase Gadolinium orthoferrite (GdFeO3) with orthorhombic perovskite structure was synthesized without any garnet impurities by solid state reaction and subsequently GdFeO3 single crystals were grown by the optical floating zone technique. The temperature dependent magnetization measurement revealed the magnetic phase transition from anti-ferromagnetic ordering to paramagnetic ordering at 670 K. The overlapping of the magnetization measured under zero-field and field cooling condition in the range of 300–20 K signifies that there is no magnetic transition in this temperature range. The hysteresis loop measurements revealed that in comparison to the values reported for the crystal grown in oxygen, the air grown sample exhibits one order lower coercive field (∼75 Oe). The Bloch 3/2-law was found to hold good for GdFeO3 with the value of B-parameter as 2.69 × 10−5 K−3/2. The coercivity exhibited sharp dip at 200 and 550 K. At and above 550 K the ability of the antiferromagnetic ordering to pin the direction of magnetization related to the weak ferromagnetism present in the material vanishes leading to the lowering in the coercivity

  6. Detection of gamma photons using solution-grown single crystals of hybrid lead halide perovskites

    Science.gov (United States)

    Yakunin, Sergii; Dirin, Dmitry N.; Shynkarenko, Yevhen; Morad, Viktoriia; Cherniukh, Ihor; Nazarenko, Olga; Kreil, Dominik; Nauser, Thomas; Kovalenko, Maksym V.

    2016-09-01

    The decay of the majority of radioactive isotopes involves the emission of gamma (γ) photons with energies of ˜50 keV to 10 MeV. Detectors of such hard radiation that are low-cost, highly sensitive and operate at ambient temperatures are desired for numerous applications in defence and medicine, as well as in research. We demonstrate that 0.3-1 cm solution-grown single crystals (SCs) of semiconducting hybrid lead halide perovskites (MAPbI3, FAPbI3 and I-treated MAPbBr3, where MA = methylammonium and FA = formamidinium) can serve as solid-state gamma-detecting materials. This possibility arises from a high charge-carrier mobility-lifetime (μτ) product of 1.0-1.8 × 10-2 cm2 V-1, a low dark carrier density of 109-1011 cm-3 (refs 3,4), a low density of charge traps of 109-1010 cm-3 (refs 4,5) and a high absorptivity of hard radiation by the lead and iodine atoms. We demonstrate the utility of perovskite detectors for testing the radiopurity of medical radiotracer compounds such as 18F-fallypride. Energy-resolved sensing at room temperature is presented using FAPbI3 SCs and an 241Am source.

  7. Properties of Dy 3+-doped PbWO 4 single crystal grown by modified Bridgman method

    Science.gov (United States)

    Huang, Yanlin; Zhu, Wenliang; Feng, Xiqi; Duan, Yong; Man, Zhenyong

    2003-01-01

    Undoped and Dy 3+-doped PbWO 4 single crystals were grown in the same condition by modified Bridgman method. Optical transmittance, X-ray excited luminescence, excitation and emission under UV light, thermoluminescence glow curves and X-ray pulsed excited decays were investigated on Dy 3+:PWO for the first time. Dy 3+-doping has a positive effect similar to that of rare-earth ions La 3+ and Gd 3+, such as improvement of transmittance in the wavelength region of scintillation emission (350-450 nm), compensation of trapping centers that is reflected in the thermoluminescence characteristics and suppression of slow decay component in luminescence kinetics. Analysis of luminescence spectra indicates that energy transfer could take place from the PbWO 4 host to the Dy 3+ ions, followed by characteristic emission line assigned to transition from 4F 9/2 of Dy 3+ ion to lower lying states on basis of the energy level scheme. A tentative concept of energy transfer mechanism is proposed in this paper.

  8. Large-sized SmBCO single crystals with T sub c over 93 K grown in atmospheric ambient by crystal pulling

    CERN Document Server

    Yao Xin; Shiohara, Y

    2003-01-01

    Sm sub 1 sub + sub x Ba sub 2 sub - sub x Cu sub 3 O sub z (SmBCO) single crystals were grown under atmospheric ambient by the top-seeded solution growth method. Inductively coupled plasma results indicate that there is negligible Sm substitution for Ba sites in the grown SmBCO crystals, although they crystallized from different Ba-Cu-O solvents with a wide composition range (Ba/Cu ratio of 0.5-0.6). As a result, these crystals show high superconducting critical transition temperature values (T sub c) of over 93 K with a sharp transition width after oxygenation. A large-sized crystal with an a-b plane of 23 x 22 mm sup 2 and a c-axis of 19 mm was obtained at a high growth rate of nearly 0.13 mm h sup - sup 1. In short, with more controllable thermodynamic parameters, SmBCO single crystals can readily achieve both large size and high superconducting properties. (rapid communication)

  9. Studies on the growth aspects, structural, thermal, dielectric and third order nonlinear optical properties of solution grown 4-methylpyridinium p-nitrophenolate single crystal

    Science.gov (United States)

    Devi, S. Reena; Kalaiyarasi, S.; Zahid, I. MD.; Kumar, R. Mohan

    2016-11-01

    An ionic organic optical crystal of 4-methylpyridinium p-nitrophenolate was grown from methanol by slow evaporation method at ambient temperature. Powder and single crystal X-ray diffraction studies revealed the crystal system and its crystalline perfection. The rocking curve recorded from HRXRD study confirmed the crystal quality. FTIR spectral analysis confirmed the functional groups present in the title compound. UV-visible spectral study revealed the optical window and band gap of grown crystal. The thermal, electrical and surface laser damage threshold properties of harvested crystal were examined by using TGA/DTA, LCR/Impedance Analyzer and Nd:YAG laser system respectively. The third order nonlinear optical property of grown crystal was elucidated by Z-scan technique.

  10. Single crystals of superconducting SmFeAsO{sub 1-x}F{sub y} grown at high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Zhigadlo, N D; Katrych, S; Bukowski, Z; Karpinski, J [Laboratory for Solid State Physics, ETH, 8093 Zuerich (Switzerland); Weyeneth, S [Physik-Institut der Universitaet Zuerich, Winterthurerstrasse 190, 8057 Zuerich (Switzerland); Puzniak, R [Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, 02-668 Warsaw (Poland)], E-mail: zhigadlo@phys.ethz.ch, E-mail: karpinski@phys.ethz.ch

    2008-08-27

    Single crystals of SmFeAsO{sub 1-x}F{sub y} of a size up to 120 x 100 {mu}m{sup 2} have been grown from NaCl/KCl flux at a pressure of 30 kbar and temperature of 1350-1450 deg. C using the cubic anvil high-pressure technique. The superconducting transition temperature of the obtained single crystals varies between 45 and 53 K. Obtained crystals are characterized by a full diamagnetic response in low magnetic fields and by a high critical current density in high magnetic fields. Structural refinement has been performed on the single crystal. Differential thermal analysis investigations at 1 bar Ar pressure show decomposition of SmFeAsO{sub 1-x}F{sub y} at 1302 deg. C. (fast track communication)

  11. Analysis of CZT crystals and detectors grown in Russia and the Ukraine by high-pressure Bridgman methods

    Energy Technology Data Exchange (ETDEWEB)

    H. Hermon; M. Schieber; R. B. James; E. Y. Lee; N. Yang; A. J. Antolak; D. H. Morse; C. Hackett; E. Tarver; N. N. P. Kolesnikov; Yu N. Ivanov; V. Komar; M. S. Goorsky; H. Yoon

    2000-01-10

    Sandia National Laboratories (SNL) is leading an effort to evaluate vertical high pressure Bridgman (VHPB) Cd{sub 1-x}Zn{sub x}Te (CZT) crystals grown in the former Soviet Union (FSU) (Ukraine and Russia), in order to study the parameters limiting the crystal quality and the radiation detector performance. The stoichiometry of the CZT crystals, with 0.04 < x < 0.25, has been determined by methods such as proton-induced X-ray emission (PIXE), X-ray diffraction (XRD), microprobe analysis and laser ablation ICP mass spectroscopy (LA-ICP/MS). Other methods such as triaxial double crystal x-ray diffraction (TADXRD), infrared transmission spectroscopy (IR), atomic force microscopy (AFM), thermoelectric emission spectroscopy (TEES) and laser induced transient charge technique (TCT) were also used to evaluate the material properties. The authors have measured the zinc distribution in a CZT ingot along the axial direction and also its homogeneity. The (Cd+Zn)/Te average ratio measured on the Ukraine crystals was 1.2, compared to the ratio of 0.9-1.06 on the Russian ingots. The IR transmission showed highly decorated grain boundaries with precipitates and hollow bubbles. Microprobe elemental analysis and LA-ICP/MS showed carbon precipitates in the CZT bulk and carbon deposits along grain boundaries. The higher concentration of impurities and the imperfect crystallinity lead to shorter electron and hole lifetimes in the range of 0.5--2 {micro}s and 0.1 {micro}s respectively, compared to 3--20 {micro}s and 1--7 {micro}s measured on US spectrometer grade CZT detectors. These results are consistent with the lower resistivity and worse crystalline perfection of these crystals, compared to US grown CZT. However, recently grown CZT from FSU exhibited better detector performance and good response to alpha particles.

  12. On the Chemistry and Physical Properties of Flux and Floating Zone Grown SmB6 Single Crystals

    Science.gov (United States)

    Phelan, W. A.; Koohpayeh, S. M.; Cottingham, P.; Tutmaher, J. A.; Leiner, J. C.; Lumsden, M. D.; Lavelle, C. M.; Wang, X. P.; Hoffmann, C.; Siegler, M. A.; Haldolaarachchige, N.; Young, D. P.; McQueen, T. M.

    2016-01-01

    Recent theoretical and experimental findings suggest the long-known but not well understood low temperature resistance plateau of SmB6 may originate from protected surface states arising from a topologically non-trivial bulk band structure having strong Kondo hybridization. Yet others have ascribed this feature to impurities, vacancies, and surface reconstructions. Given the typical methods used to prepare SmB6 single crystals, flux and floating-zone procedures, such ascriptions should not be taken lightly. We demonstrate how compositional variations and/or observable amounts of impurities in SmB6 crystals grown using both procedures affect the physical properties. From X-ray diffraction, neutron diffraction, and X-ray computed tomography experiments we observe that natural isotope containing (SmB6) and doubly isotope enriched (154Sm11B6) crystals prepared using aluminum flux contain co-crystallized, epitaxial aluminum. Further, a large, nearly stoichiometric crystal of SmB6 was successfully grown using the float-zone technique; upon continuing the zone melting, samarium vacancies were introduced. These samarium vacancies drastically alter the resistance and plateauing magnitude of the low temperature resistance compared to stoichiometric SmB6. These results highlight that impurities and compositional variations, even at low concentrations, must be considered when collecting/analyzing physical property data of SmB6. Finally, a more accurate samarium-154 coherent neutron scattering length, 8.9(1) fm, is reported. PMID:26892648

  13. Factors affecting stress distribution and displacements in crystals III-V grown by Czochralski method with liquid encapsulation

    International Nuclear Information System (INIS)

    A mathematical model based on the finite element method for calculating temperature and shear stress distributions in III-V crystals grown by LEC technique was developed. The calculated temperature are in good agreements with the experimental measurements. The shear stress distribution was calculated for several environmental conditions. The results showed that the magnitude and the distribution of shear stresses are highly sensitive to the crystal environment, including thickness and temperature distribution in boron oxides and the gas. The shear stress is also strongly influenced by interface curvature and cystals radius. (author)

  14. Characterization of cadmium manganese telluride (Cd1-xMnxTe) crystals grown by floating zone method

    Science.gov (United States)

    Hossain, A.; Gu, G. D.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Gul, R.; Roy, U. N.; Yang, G.; Liu, T.; Zhong, R.; Schneeloch, J.; James, R. B.

    2014-09-01

    Recently, Cadmium Manganese Telluride (CMT) emerged as a promising material for roomtemperature X- and gamma-ray detectors. However, our studies revealed several material defects primarily related to growth processes that are impeding the production of large single crystals with high resistivity and high mobility-lifetime product. In this work, we characterized various defects in materials grown by the floating zone method, including twins, Te inclusions, and dislocations, using our unique facilities. We also fabricated detectors from selected CMT crystals and tested their performance. This paper discusses our detailed findings on the material's properties and the performance of fabricated CMT detectors.

  15. Vertical cavity lasing from melt-grown crystals of cyano-substituted thiophene/phenylene co-oligomer

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, Yosuke; Yanagi, Hisao, E-mail: yanagi@ms.naist.jp [Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan); Goto, Kaname; Yamashita, Kenichi; Yamao, Takeshi; Hotta, Shu [Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585 (Japan); Sasaki, Fumio [Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan)

    2015-10-19

    Vertical-cavity organic lasers are fabricated with melt-grown crystals of a cyano-substituted thiophene-phenylene co-oligomer. Due to lying molecular orientation, surface-emitting lasing is achieved even in the half-cavity crystal grown on a distributed Bragg reflector (DBR) under optical pumping at room temperature. Anticrossing splits in angle-resolved photoluminescence spectra suggest the formation of exciton-polaritons between the cavity photons and the confined Frenkel excitons. By constructing the full-cavity structure sandwiched between the top and bottom DBRs, the lasing threshold is reduced to one order, which is as low as that of the half cavity. Around the threshold, the time profile of the full-cavity emission is collapsed to a pulsed shape accompanied by a finite turn-on delay. We discuss these observed characteristics in terms of a polariton contribution to the conventional photon lasing.

  16. Observation of the vortex-glass and the melting transitions in NdBa2Cu3O7-y single crystals grown by different methods

    International Nuclear Information System (INIS)

    We present the transport and magnetization properties of NBCO single crystals grown by the travelling solvent floating zone (TSFZ) and the self-flux (SF) methods under low O2 partial pressure. The TSFZ-grown crystal shows a continuous transition exhibiting a vortex-glass behaviour in V-I characteristics for H = 1 T. In contrast, a first-order melting transition was observed in the crystal grown by the SF method under 0.03% O2 partial pressure displaying a kink and hysteresis in resistance. The temperature dependent magnetization curves show a change in slope at the melting transition. The V-I characteristics in field for the SF-grown crystal exhibited a characteristic S-shape behaviour at the melting transition. The different behaviour in transport properties between two set of crystals suggests that the presence of twin planes and the substitutional defects play a major role in the observed vortex dynamics. (author)

  17. Detached phenomenon: Its effect on the crystal quality of Ga{sub (1−x)}In{sub x}Sb bulk crystal grown by the VDS technique

    Energy Technology Data Exchange (ETDEWEB)

    Gadkari, Dattatray, E-mail: db.gadkari@gmail.com [Department of Physics, Mithibai College, Mumbai 400056 (India)

    2013-05-15

    Vertical directional solidification (VDS) technique is used on the combined growth principals of the conventional methods since 1994, which leads to the detached growth. For evaluation of the detached growth, five bulk ingots of indium doped gallium–antimonide GaSb:In (In = 0.5, 0.25, 0.15) have been grown – without the seed, without contact to the ampoule wall, without coating and without external pressure. The gap is attributed to compensate the differential thermal dilatation that is grown with the reduced diameter than the diameter of the ampoule. VDS experiments have been proved that the sum of the contact angle and growth angle is large enough to allow detachment without any additional pressure difference under the melt to offset hydrostatic pressure. A meniscus forms at the bottom of the melt, the capillarity effect establishes due to which spontaneous gap could be created by the melt free surface, thus no thermal shear stress and thermo-mechanical stresses at the interface. Detached grown bulk GaSb:In crystals showed superior crystal quality with the highest physical properties and mobility than the crystals grown ever. The axial and radial composition profile of the grown GaSb:In ingots showed variation ≤10%. From the conical region, dislocation density decreases in the growth direction and reaches less than 10{sup 3} cm{sup −2}. - Highlights: ► Detachment: without seed, without ampoule contact, without coating, without external pressure. ► Detached ingot growth samples showed the highest physical properties and the carrier mobility. ► Initial to final transition: in detached growth, dislocations decreases and less than 10{sup 3} cm{sup −2}. ► Detached samples: Raman spectrum shows only TO phonon (110) direction of single orientation. ► Detached ingot: FTIR shows highest transmissions % but decreases on increase doping in samples.

  18. Evidence for graphite-like hexagonal AlN nanosheets epitaxially grown on single crystal Ag(111)

    Science.gov (United States)

    Tsipas, P.; Kassavetis, S.; Tsoutsou, D.; Xenogiannopoulou, E.; Golias, E.; Giamini, S. A.; Grazianetti, C.; Chiappe, D.; Molle, A.; Fanciulli, M.; Dimoulas, A.

    2013-12-01

    Ultrathin (sub-monolayer to 12 monolayers) AlN nanosheets are grown epitaxially by plasma assisted molecular beam epitaxy on Ag(111) single crystals. Electron diffraction and scanning tunneling microscopy provide evidence that AlN on Ag adopts a graphite-like hexagonal structure with a larger lattice constant compared to bulk-like wurtzite AlN. This claim is further supported by ultraviolet photoelectron spectroscopy indicating a reduced energy bandgap as expected for hexagonal AlN.

  19. Homo-epitaxial growth of CdTe by sublimation under low pressure

    Science.gov (United States)

    Yoshioka, Yasushi; Yoda, Hiroki; Kasuga, Masanobu

    1991-12-01

    A new method to obtain a twin-free single crystal of CdTe on a CdTe substrate by sublimation is described. When CdTe(111)A substrates were employed for the homo-epitaxial growth of CdTe, twin crystals were frequently obtained. The substrate of CdTe(211)A and (211)B, however, gave no twins resulting in single crystals of high quality. The difference may come from the existence of many steps, sufficient to suppress two-dimensional nucleation and to promote step flow mechanism. To obtain twin-free films, therefore, a fairly large tilt angle of the substrate from a singular plane and a fairly low supersaturation are essential.

  20. On the morphology of SrCO3 crystals grown at the interface between two immiscible liquids

    Indian Academy of Sciences (India)

    Satyanarayana Reddy; Debabrata Rautaray; S R Sainkar; Murali Sastry

    2003-04-01

    In this paper we report on the growth of strontianite crystals at the interface between an aqueous solution of Sr2+ ions and organic solutions of chloroform and hexane containing fatty acid/fatty amine molecules by reaction with sodium carbonate. When fatty acid was used as an additive at the interface, the crystals grown were self-assembled needle shaped strontianite crystallites branching out from the seed crystal via secondary nucleation. Under identical conditions of supersaturation, the presence of fatty amine molecules at the liquid–liquid interface resulted in needle shaped strontianite crystals with spherical crystallites arranged around central needles. This clearly indicates that the functionality of the head group of the amphiphiles at the liquid–liquid interface affects the morphology of the strontium carbonate crystals formed. The use of interfacial effects such as dielectric discontinuity, polarity and finite solubility of the two solvents etc opens up exciting possibilities for tailoring the morphology of crystals at the liquid–liquid interface and is currently not possible in the more popular crystal growth with similar amphiphiles at the air–water interface.

  1. The distribution of Ga and Sb impurities in Ge-Si crystals grown by the Bridgman method using a feeding rod

    International Nuclear Information System (INIS)

    Gallium- and antimony-doped Ge1-xSix crystals (0 ≤ x ≤ 0.25) have been grown by the improved Bridgman method using a silicon seed and a macrohomogeneous feeding Ge-Si rod of the corresponding composition. The impurity concentration profiles along the grown crystals were determined from Hall measurements. The mathematical problem of impurity distribution along two-component mixed crystals grown from a melt with uniform and graded composition is solved in the Pfann approximation and within the virtual-crystal model for the solid solution. It is shown that the experimental impurity distributions in Ge1-xSix crystals are described well by the data calculated on the assumption of linear change in the impurity segregation coefficient with the crystal composition.

  2. Growth and micro-topographical studies of gel grown cholesterol crystals

    Indian Academy of Sciences (India)

    Anit Elizabeth; Cyriac Joseph; M A Ittyachen

    2001-08-01

    Cholesterol (C27H46O) is the most abundant and best-known steroid in the animal kingdom. The in vitro crystallization of this important biomaterial has been attempted by few researchers. Here we are reporting crystallization of pure cholesterol monohydrate crystals in gel medium. It is found that the morphology of the crystals depends on various parameters. The effect of solvent has been studied in detail. The different morphologies observed are fibrous, needle, platelet, dendrite etc. Micro topographical studies have been made and it is found that the crystals grow, at least in the last stage, by spreading of layers. However, at initial stage microcrystals formed and developed into dendrite or needle forms. These one-dimensional crystals developed into platelets and finally thickened. Further studies reveal that micro impurities play a vital role in the development of these crystals as seen by dissolution figures on the crystals. These crystals are characterized by using the XRD and IR spectroscopic methods.

  3. Strikingly different luminescent properties arising from single crystals grown from solution or from the vapor phase in a diketo-pyrrolo-pyrrole analog

    OpenAIRE

    Imoda, Tomohiko; Mizuguchi, Jin

    2007-01-01

    The title compound di-cyano-pyrrolo-pyrrole (DCPP) is an analog of diketo-pyrrolo-pyrrole (DPP) known as a red pigment on the market. Brilliant orange photoluminescence has been observed in crystals of DCPP recrystallized from solution (crystal I); whereas the luminescence was quite weak in single crystals grown from the vapor phase (crystal II). To elucidate the difference in luminescent properties, a series of structural analysis together with thermal analysis has been carried out on crysta...

  4. Structure of a heterogeneous, glycosylated, lipid-bound, in vivo-grown protein crystal at atomic resolution from the viviparous cockroach Diploptera punctata.

    Science.gov (United States)

    Banerjee, Sanchari; Coussens, Nathan P; Gallat, François-Xavier; Sathyanarayanan, Nitish; Srikanth, Jandhyam; Yagi, Koichiro J; Gray, James S S; Tobe, Stephen S; Stay, Barbara; Chavas, Leonard M G; Ramaswamy, Subramanian

    2016-07-01

    Macromolecular crystals for X-ray diffraction studies are typically grown in vitro from pure and homogeneous samples; however, there are examples of protein crystals that have been identified in vivo. Recent developments in micro-crystallography techniques and the advent of X-ray free-electron lasers have allowed the determination of several protein structures from crystals grown in cellulo. Here, an atomic resolution (1.2 Å) crystal structure is reported of heterogeneous milk proteins grown inside a living organism in their functional niche. These in vivo-grown crystals were isolated from the midgut of an embryo within the only known viviparous cockroach, Diploptera punctata. The milk proteins crystallized in space group P1, and a structure was determined by anomalous dispersion from the native S atoms. The data revealed glycosylated proteins that adopt a lipocalin fold, bind lipids and organize to form a tightly packed crystalline lattice. A single crystal is estimated to contain more than three times the energy of an equivalent mass of dairy milk. This unique storage form of nourishment for developing embryos allows access to a constant supply of complete nutrients. Notably, the crystalline cockroach-milk proteins are highly heterogeneous with respect to amino-acid sequence, glycosylation and bound fatty-acid composition. These data present a unique example of protein heterogeneity within a single in vivo-grown crystal of a natural protein in its native environment at atomic resolution. PMID:27437115

  5. Influence of thickness on physical properties of vacuum evaporated polycrystalline CdTe thin films for solar cell applications

    Science.gov (United States)

    Chander, Subhash; Dhaka, M. S.

    2016-02-01

    This paper presents the influence of thickness on physical properties of polycrystalline CdTe thin films. The thin films of thickness 450 nm, 650 nm and 850 nm were deposited employing thermal vacuum evaporation technique on glass and indium tin oxide (ITO) coated glass substrates. The physical properties of these as-grown thin films were investigated employing the X-ray diffraction (XRD), source meter, UV-Vis spectrophotometer, scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The structural analysis reveals that the films have zinc-blende cubic structure and polycrystalline in nature with preferred orientation (111). The structural parameters like lattice constant, interplanar spacing, grain size, strain, dislocation density and number of crystallites per unit area are calculated. The average grain size and optical band gap are found in the range 15.16-21.22 nm and 1.44-1.63 eV respectively and observed to decrease with thickness. The current-voltage characteristics show that the electrical conductivity is observed to decrease with thickness. The surface morphology shows that films are free from crystal defects like pin holes and voids as well as homogeneous and uniform. The EDS patterns show the presence of cadmium and tellurium elements in the as grown films. The experimental results reveal that the film thickness plays significant role on the physical properties of as-grown CdTe thin films and higher thickness may be used as absorber layer to solar cells applications.

  6. On the bulk β-Ga2O3 single crystals grown by the Czochralski method

    Science.gov (United States)

    Galazka, Zbigniew; Irmscher, Klaus; Uecker, Reinhard; Bertram, Rainer; Pietsch, Mike; Kwasniewski, Albert; Naumann, Martin; Schulz, Tobias; Schewski, Robert; Klimm, Detlef; Bickermann, Matthias

    2014-10-01

    The growth of bulkx β-Ga2O3 single crystals by the Czochralski method is reported and discussed in terms of crucial growth conditions and correlated with basic electrical and optical properties of the obtained crystals. β-Ga2O3 crystals have a tendency to a spiral formation due to free carrier absorption in the near infrared (NIR) wavelength range, which hampers radiative heat transfer through the growing crystal. Moderate or low free electron concentrations (crystals with a high crystallized fraction (g≥0.5). The use of a CO2-containing growth atmosphere provides oxygen partial pressures between 0.8 and 4.4×10-2 bar that is sufficient to obtain cylindrical and semiconducting crystals. Doping with Sn increases the free electron concentration in the crystals to high values (~1019 cm-3) that lead to an immediate spiral formation, while doping with Mg (>6 wt ppm) provides insulating crystals with reduced probability of the spiral formation. The estimated Mg equilibrium segregation coefficient across the liquid-solid interface is 0.10-0.12. Annealing of undoped crystals in an oxidizing atmosphere at temperatures ≥1200 °C for 20 h decreases the bulk free electron concentration by about one order of magnitude, while the crystal surface becomes insulating. However, Mg:β-Ga2O3 crystals are insensitive to annealing in both oxygen- and hydrogen-containing atmospheres. The transmittance spectra showed a steep absorption edge at 260 nm and virtually full transparency in the visible and NIR wavelength range for low and moderate free electron concentrations. We also demonstrated the possibility of growing 2 in. diameter β-Ga2O3 single crystals by the Czochralski method. The good crystal quality is evidenced by rocking curve FWHM values of below 50". We noted that most dislocations propagate parallel to (100) plane. Further, we also provide thermal properties of the crystals as a function of temperature.

  7. Synthesis and characterization of calcium iodate, monohydrate crystals grown in silica gel

    International Nuclear Information System (INIS)

    Simple gel technique was used to grow single crystals of calcium iodate, monohydrate, by single diffusion method. For the growth of crystals, the optimum conditions were established. Morphologies and habit faces like prismatic, prismatic pyramidal crystals were obtained. Few crystals were opaque, some were translucent and some good quality transparent crystals were obtained. Doping of Cu+2 and Fe+3 was done, to study the effect on structure, thermal and nonlinear optical properties. Cell parameters were obtained from the X-ray diffractograms. Structural analysis was done by using FT-IR spectroscopy. TGA and DTA techniques were used to carry out thermal analysis. Nonlinear optical properties were studied using SHG measurements.

  8. Growth and Characteristics of Bulk Single Crystals Grown from Solution on Earth and in Microgravity

    Science.gov (United States)

    Aggarwal, M. D.; Batra, A. K.; Lal, R. B.; Penn, Benjamin G.; Frazier, Donald O.

    2011-01-01

    The growth of crystals has been of interest to physicists and engineers for a long time because of their unique properties. Single crystals are utilized in such diverse applications as pharmaceuticals, computers, infrared detectors, frequency measurements, piezoelectric devices, a variety of high technology devices and sensors. Solution crystal growth is one of the important techniques to grow a variety of crystals when the material decomposes at the melting point and a suitable solvent is available to make a saturated solution at a desired temperature. In this chapter an attempt is made to give some fundamentals of growing crystals from solution including improved designs of various crystallizers. Since the same solution crystal growth technique could not be used in microgravity, authors had proposed a new cooled sting technique to grow crystals in space. Authors? experiences of conducting two space shuttle experiments relating to solution crystal growth are also detailed in this work. The complexity of these solution growth experiments to grow crystals in space are discussed. These happen to be some of the early experiments performed in space, and various lessons learned are described. A brief discussion of protein crystal growth that also shares basic principles of solution growth technique is given along with some flight hardware information for its growth in microgravity.

  9. Strain-relief by single dislocation loops in calcite crystals grown on self-assembled monolayers.

    Science.gov (United States)

    Ihli, Johannes; Clark, Jesse N; Côté, Alexander S; Kim, Yi-Yeoun; Schenk, Anna S; Kulak, Alexander N; Comyn, Timothy P; Chammas, Oliver; Harder, Ross J; Duffy, Dorothy M; Robinson, Ian K; Meldrum, Fiona C

    2016-01-01

    Most of our knowledge of dislocation-mediated stress relaxation during epitaxial crystal growth comes from the study of inorganic heterostructures. Here we use Bragg coherent diffraction imaging to investigate a contrasting system, the epitaxial growth of calcite (CaCO3) crystals on organic self-assembled monolayers, where these are widely used as a model for biomineralization processes. The calcite crystals are imaged to simultaneously visualize the crystal morphology and internal strain fields. Our data reveal that each crystal possesses a single dislocation loop that occupies a common position in every crystal. The loops exhibit entirely different geometries to misfit dislocations generated in conventional epitaxial thin films and are suggested to form in response to the stress field, arising from interfacial defects and the nanoscale roughness of the substrate. This work provides unique insight into how self-assembled monolayers control the growth of inorganic crystals and demonstrates important differences as compared with inorganic substrates. PMID:27302863

  10. Effects of Annealing Treatments on Luminescence and Scintillation Properties of Ce:Lu3Al5O12 Crystal Grown by Czochralski Method

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Ce:Lu3Al5O12 single crystals grown in pure N2 atmosphere by Czochralski method were annealed in oxidizing atmosphere (air) and reducing atmosphere (H2+N2), respectively. Effects of annealing treatments on luminescence and scintillation properties of the crystals were investigated. The crystal annealed in air showed the highest luminescence intensity under blue light or vacuum ultraviolet excitation in comparison with that annealed in reducing flux or the as-grown crystal. Under X-ray excitation, crystal annealed in reducing atmosphere had the lowest light yield, and crystal annealed in air had the fastest decay time under 137Cs 662 keV γ-ray excitation. Different annealing treatments resulted in different luminescence and scintillation properties, which might related with oxygen vacancies or defect existing in the crystals.

  11. Material and detector properties of cadmium manganese telluride (Cd1-xMnxTe) crystals grown by the modified floating-zone method

    Science.gov (United States)

    Hossain, A.; Gu, G. D.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Roy, U. N.; Yang, G.; Liu, T.; Zhong, R.; Schneeloch, J.; James, R. B.

    2015-06-01

    We demonstrated the material- and radiation-detection properties of cadmium manganese telluride (Cd1-xMnxTe; x=0.06), a wide-band-gap semiconductor crystal grown by the modified floating-zone method. We investigated the presence of various bulk defects, such as Te inclusions, twins, and dislocations of several as-grown indium-doped Cd1-xMnxTe crystals using different techniques, viz., IR transmission microscopy, and chemical etching. We then fabricated four planar detectors from selected CdMnTe crystals, characterized their electrical properties, and tested their performance as room-temperature X- and gamma-ray detectors. Our experimental results show that CMT crystals grown by the modified floating zone method apparently are free from Te inclusions. However, we still need to optimize our growth parameters to attain high-resistivity, large-volume single-crystal CdMnTe.

  12. Properties of Bi-Te-Sb single crystals grown by the Czochralski method for thermoelectric cooling

    International Nuclear Information System (INIS)

    This paper reports on materials based on Bi, Te, Se, Sb and produced by pressing, extrusion or zone recrystallization that are used usually for the thermoelectric cooling. But by Czochralski method materials have been far less grown. Researches on growing of monocrystalline ingots on the base of combinations Bi-Se-Te and Bi-Sb-Te have been done. Thermoelectric material produced by the Czochralski method does not essentially differ from that one grown by zone recrystallization or Bridgman method

  13. Study of Growth, Structural, Thermal and Nonlinear Optical Properties of Silica Gel Grown Calcium Iodate Monohydrate Crystals

    Directory of Open Access Journals (Sweden)

    Sharda J. Shitole

    2015-12-01

    Full Text Available Single crystals of calcium iodate, monohydrate [Ca (IO32, H2O] were grown by simple gel technique by single and double diffusion method. Morphologies and habit faces like prismatic, prismatic pyramidal, needle shaped, hopper crystals were obtained. Few crystals were opaque, some were translucent and some good quality transparent crystals were obtained. EDAX spectrum verified that crystals are of calcium iodate, monohydrate indeed and was used to find Atomic % and Weight %. Unit cell parameters were obtained from the X-ray diffractogram. The calculated unit cell parameters, β, and‘d’ values are in good agreement with reported ones. Structural analysis was done by using FTIR spectroscopy which confirmed the presence of fundamental infrared frequencies, generally observed in all iodate compounds. Thermal analysis exhibits three steps explicitly on heating the samples. The first step involves dehydration at 5500C, second step shows decomposition at 5800C, and the third step involves again decomposition at 6400C. Powder second harmonic generation experiments exhibit the nonlinear nature of the substance.

  14. Ce-doped LuAG single-crystal fibers grown from the melt for high-energy physics

    CERN Document Server

    Xu, X; Moretti, F; Pauwels, K; Lecoq, P; Auffray, E; Dujardin, C

    2014-01-01

    Under a stationary stable regime undoped and Ce-doped LuAG (Lu3Al5O12) single-crystal fibers were grown by a micro-pulling-down technique. The meniscus length corresponding to the equilibrium state was <200 mu m. Fluctuations in the fiber composition and pulling rate were found to have a significant effect on the properties of the fibers grown. A great improvement in the performance was found in samples containing low Ce concentrations (<= 0.1 at.\\%) and produced using pulling rates <0.5 mm min(-1). Under such conditions a good lateral surface fiber quality was obtained and light propagation was significantly improved. Conversely, a high Ce concentration and a high pulling rate resulted in a strong degradation of the fiber surface quality causing defects to appear and a decrease in light output. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  15. Effects of tellurium concentration on the structure of melt-grown ZnSe crystals

    International Nuclear Information System (INIS)

    It has been shown that isovalent doping by tellurium positively affects the structural perfection of ZnSe crystals related to the completeness of the wurtzite-sphalerite phase transition. The optimum concentration range of tellurium in ZnSe crystals is 0.3-0.6 mass %. X-ray diffraction studies have shown that in ZnSe1-xTex crystals at tellurium concentrations below 0.3 mass % twinning and packing defects occur, while tellurium concentrations above 0.6 mass % lead to formation of tetragonal crystal lattice

  16. Surface structure determinations of crystalline ionic thin films grown on transition metal single crystal surfaces by low energy electron diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, J.G.

    2000-05-01

    The surface structures of NaCl(100), LiF(100) and alpha-MgCl2(0001) adsorbed on various metal single crystals have been determined by low energy electron diffraction (LEED). Thin films of these salts were grown on metal substrates by exposing the heated metal surface to a molecular flux of salt emitted from a Knudsen cell. This method of investigating thin films of insulators (ionic salts) on a conducting substrate (metal) circumvents surface charging problems that plagued bulk studies, thereby allowing the use of electron-based techniques to characterize the surface.

  17. High pressure effect on MoS2 and MoSe2 single crystals grown by CVT method

    Indian Academy of Sciences (India)

    Madhavi Dave; Rajiv Vaidya; S G Patel; A R Jani

    2004-04-01

    Single crystals of MoS2 and MoSe2 were grown by chemical vapour transport method using iodine as a transporting agent and characterized by optical microscopy, energy dispersive analysis (EDAX), X-ray powder diffraction (XRD) and Hall mobility at room temperature. The variation of electrical resistance under pressure was monitored in a Bridgman anvil set-up up to 6.5 GPa to identify occurrence of any structural transition. MoS2 and MoSe2 do not undergo any structural transitions under pressure.

  18. Scintillation properties of μPD-grown Y4Al2O9:Pr (YAM:Pr) crystals

    International Nuclear Information System (INIS)

    Highlights: • YAM:Pr crystals do scintillate and as such deserve further interest. • Fast d–f luminescence of Pr3+ ions appears in X-ray excited spectra. • Two components (24 and 790 ns) constitute scintillation time profiles. - Abstract: Y4Al2O9:Pr (YAM:Pr) crystals have been grown by the micro-pulling-down method and their scintillation properties have been investigated. YAM:0.1%Pr displays a light yield of about 2000 ph/MeV and its scintillation time profile contains a prompt component with a decay time of 23.5 ns and a contribution of 20%. Radioluminescence spectra show both fast d–f and slow f–f praseodymium emissions. Low temperature glow curves are complex, consisting of discrete peaks and broad bands related to quasi-continuous trap distributions. Overall scintillation performance of YAM:Pr deteriorates with increasing praseodymium concentration

  19. GaN Schottky diodes with single-crystal aluminum barriers grown by plasma-assisted molecular beam epitaxy

    Science.gov (United States)

    Tseng, H. Y.; Yang, W. C.; Lee, P. Y.; Lin, C. W.; Cheng, Kai-Yuan; Hsieh, K. C.; Cheng, K. Y.; Hsu, C.-H.

    2016-08-01

    GaN-based Schottky barrier diodes (SBDs) with single-crystal Al barriers grown by plasma-assisted molecular beam epitaxy are fabricated. Examined using in-situ reflection high-energy electron diffractions, ex-situ high-resolution x-ray diffractions, and high-resolution transmission electron microscopy, it is determined that epitaxial Al grows with its [111] axis coincident with the [0001] axis of the GaN substrate without rotation. In fabricated SBDs, a 0.2 V barrier height enhancement and 2 orders of magnitude reduction in leakage current are observed in single crystal Al/GaN SBDs compared to conventional thermal deposited Al/GaN SBDs. The strain induced piezoelectric field is determined to be the major source of the observed device performance enhancements.

  20. Characterization of pure and copper-doped iron tartrate crystals grown in silica gel

    Indian Academy of Sciences (India)

    V Mathivanan; M Haris

    2013-07-01

    Single crystal growth of pure and copper-doped iron tartrate crystals bearing composition Cu Fe(1−) C4H4O6 · H2O, where = 0, 0.07, 0.06, 0.05, 0.04, 0.03, is achieved using gel technique. The elemental analysis has been done using energy-dispersive X-ray analysis (EDAX) spectrum. The characterization studies such as Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), magnetic analysis and thermal analysis have been done for crystals with = 0 for pure iron tartrate and with = 0.05 for copper-mixed iron tartrate crystals. A detailed comparison has been made between pure and doped crystals.

  1. Magnetic properties of high-resistivity CdTeIn and CdTeCl crystals

    International Nuclear Information System (INIS)

    Paper presents the measurement results of magnetic susceptibility χ of CdTe high-resistant single crystals (within 4.2-300 K temperature range) grown from the melt and doped with indium or chlorine. The marked dependent of χ on temperature was determined. Below 50 K temperature all the specimens transit into the paramagnetic state. The detected anomalies are explained by presence of donor-acceptor pairs formed by intrinsic defects with doping impurities and uncontrollable impurities

  2. Superstructure studies in hydrothermal-grown RbBe{sub 2}BO{sub 3}F{sub 2} crystals

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Tao [Beijing Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, P.O. Box 2711, Beijing 100190 (China); University of Chinese Academy of Sciences, Beijing 100039 (China); Liu, Lijuan, E-mail: llj@mail.ipc.ac.cn [Beijing Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, P.O. Box 2711, Beijing 100190 (China); Wang, Xiaoyang [Beijing Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, P.O. Box 2711, Beijing 100190 (China); Zhou, Haitao; He, Xiaoling; Zhang, Changlong [China Nonferrous Metal (Guilin) Geology and Mining Co., Ltd., No. 20 Tieshan Road, Guilin, GuangXi 541004 (China); Chen, Chuangtian [Beijing Center for Crystal Research and Development, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, P.O. Box 2711, Beijing 100190 (China)

    2015-03-15

    Highlights: • Three extra peaks were found in PXRD patterns of hydrothermal RBBF crystals. • A centrosymmetric structure of R3{sup ¯}c was obtained in hydrothermal RBBF crystals. • A stacking fault model of hydrothermal RBBF crystals was proposed. • R32 and R3{sup ¯}c structures co-exist with different weight fractions. - Abstract: Deep-UV nonlinear optical crystal RbBe{sub 2}BO{sub 3}F{sub 2} (RBBF) grown by the hydrothermal method was found to have a centrosymmetric structure of R3{sup ¯}c by powder X-ray diffraction. The structure of R3{sup ¯}c has cell parameters of a = 4.44223(11) Å and c = 39.6696(12) Å in the lattice where the (BO{sub 3}){sup 3−} groups turn 60° along each (Be{sub 2}BO{sub 3}F{sub 2}){sub ∞} layer in the a–b plane and it is double size along the c-axis compared with standard R32 structure. As the examined RBBF shows a very low second harmonic generation capability, a stacking fault model was proposed that the hydrothermal RBBF is nonuniform with a mixture of both R32 and R3{sup ¯}c structures using the DIFFaX program.

  3. Czochralski growth techniques of germanium crystals grown from a melt covered partially or fully by liquid B2O3

    Science.gov (United States)

    Taishi, Toshinori; Hashimoto, Yoshio; Ise, Hideaki; Murao, Yu; Ohsawa, Takayuki; Yonenaga, Ichiro

    2012-12-01

    We propose two unique Czochralski (CZ) techniques for growing germanium (Ge) crystals with an extremely low dislocation density and high interstitial oxygen concentration ([Oi]) using boron oxide (B2O3) and a silica crucible. When a Ge melt is partially covered with liquid B2O3, but only on the outer region of the melt surface, germanium-oxide (GeO2)-related particles forming naturally in the melt are effectively dissolved by the liquid B2O3. The clean central portion of the melt produces dislocation-free undoped or Ga-doped Ge crystals. In addition, Ge crystals with [Oi] up to 6×1017 cm-3 can be grown from a melt fully covered by liquid B2O3 with added GeO2 powder. The reaction and transportation of oxygen atoms during the growth process using B2O3 was investigated, revealing that liquid B2O3 acts like a catalyst without heavy contamination of the growing Ge crystal by B and Si atoms.

  4. Crystallization and semiconductor-metal switching behavior of thin VO2 layers grown by atomic layer deposition

    International Nuclear Information System (INIS)

    Crystalline vanadium dioxide (VO2) thin films were prepared by annealing amorphous VO2 films which were deposited by atomic layer deposition on a SiO2 substrate. A large influence of the oxygen partial pressure in the annealing ambient was observed by means of in-situ X-ray diffraction. In the range between 1 and 10 Pa of oxygen the interesting VO2(R) phase crystallized near 450 °C. Between 2 and 10 Pa of oxygen, metastable VO2(B) was observed as an intermediate crystalline phase before it transformed to VO2(R). Anneals in inert gas did not show any crystallization, while oxygen partial pressures above 10 Pa resulted in oxidation into the higher oxide phase V6O13. Film thickness did not have much effect on the crystallization behavior, but thinner films suffered more from agglomeration during the high-temperature crystallization on the SiO2 substrate. Nevertheless, continuous polycrystalline VO2(R) films were obtained with thicknesses down to 11 nm. In the case where VO2(R) was formed, the semiconductor–metal transition was observed by three complementary techniques. This transition near 68 °C was characterized by X-ray diffraction, showing the transformation of the crystal structure, by spectroscopic ellipsometry, mapping optical changes, and by sheet resistance measurements, showing resistance changes larger than 2 orders of magnitude between the low-temperature semiconducting state and the high-temperature metallic state. - Highlights: • Amorphous VO2 films were grown by atomic layer deposition. • Crystallization was studied by means of in-situ X-ray diffraction (XRD). • The optimal oxygen partial pressure during annealing was found to be around 1 Pa. • Continuous crystalline VO2 layers down to 11 nm thickness were obtained at 450 °C. • XRD, ellipsometry and sheet resistance showed the semiconductor–metal transition

  5. EBIC INVESTIGATIONS OF EXTENDED DEFECTS IN CdTe

    OpenAIRE

    Panin, G.; Yakimov, E.

    1991-01-01

    The EBIC and remote contact EBIC (REBIC) techniques have been used to reveal grain boundaries and precipitates in CdTe crystals and to study their recombination contrast as a function of the electron beam parameters and temperature. The results obtained are discussed taking into account the defect charge state and the recombination properties of their environment.

  6. Selective growth of CdTe on patterned CdTe/Si(211)

    OpenAIRE

    Seldrum, T.; Bommena, R.; Samain, Louise; Sivananthan, S.; Sporken, R.; Dumont, J.

    2008-01-01

    The authors have studied selective growth of cadmium telluride on Si(211) by molecular beam epitaxy (MBE). Patterned substrates were produced by optical lithography of MBE-grown CdTe/As/Si(211). Photoemission microscopy was used as the main tool to study selective growth. This is very powerful because Si or SiO2 can be very easily distinguished from areas covered with even small amounts of CdTe due to contrast from work function differences. It was found that CdTe grows on CdTe without sticki...

  7. Approaches to improve the Voc of CDTE devices: Device modeling and thinner devices, alternative back contacts

    Science.gov (United States)

    Walkons, Curtis J.

    An existing commercial process to develop thin film CdTe superstrate cells with a lifetime tau=1-3 ns results in Voc= 810-850 mV which is 350 mV lower than expected for CdTe with a bandgap EG = 1.5 eV. Voc is limited by 1.) SRH recombination in the space charge region; and 2.) the Cu2Te back contact to CdTe, which, assuming a 0.3 eV CdTe/Cu2Te barrier, exhibits a work function of phi Cu2Te= 5.5 eV compared to the CdTe valence band of Ev,CdTe=5.8 eV. Proposed solutions to develop CdTe devices with increased Voc are: 1.) reduce SRH recombination by thinning the CdTe layer to ≤ 1 mum; and 2.) develop an ohmic contact back contact using a material with phi BC≥5.8 eV. This is consistent with simulations using 1DSCAPS modeling of CdTe/CdS superstrate cells under AM 1.5 conditions. Two types of CdTe devices are presented. The first type of CdTe device utilizes a window/CdTe stack device with an initial 3-9 mum CdTe layer which is then chemically thinned resulting in regions of the CdTe film with thickness less than 1 mum. The CdTe surface was contacted with a liquid junction quinhydrone-Pt (QH-Pt) probe which enables rapid repeatable Voc measurements on CdTe before and after thinning. In four separate experiments, the window/CdTe stack devices with thinned CdTe exhibited a Voc increase of 30-170 mV, which if implemented using a solid state contact could cut the Voc deficit in half. The second type of CdTe device utilizes C61 PCBM as a back contact to the CdTe, selected since PCBM has a valence band maximum energy (VBM) of 5.8 eV. The PCBM films were grown by two different chemistries and the characterization of the film properties and device results are discussed. The device results show that PCBM exhibits a blocking contact with a 0.6 eV Schottky barrier and possible work function of phiPCBM = 5.2 eV.

  8. Characterization and inhibitive study of gel-grown hydroxyapatite crystals at physiological temperature

    Science.gov (United States)

    Parekh, Bharat; Joshi, Mihir; Vaidya, Ashok

    2008-04-01

    Hydroxyapatite is very useful for various biomedical applications, due to its chemical similarity with mineralized bone of human. Hydroxyapatite is also responsible for arthropathy (joint disease). In the present study, the growth of hydroxyapatite crystals was carried out by using single-diffusion gel growth technique in silica hydro gel media, at physiological temperature. The growth of hydroxyapatite crystals under slow and controlled environment in gel medium can be simulated in a simple manner to the growth in human body. The crystals, formed in the Liesegang rings, were characterized by powder XRD, FTIR and dielectric study. The diffusion study is also carried out for the hydroxyapatite crystals using the moving boundary model. The inhibitive influence of various Ayurvedic medicinal plant extracts such as Boswellia serrata gum resin , Tribulus terrestris fruits, Rotula aquatica roots, Boerhaavia diffusa roots and Commiphora wightii, on the growth of hydroxyapatite was studied. Roots of R. aquatica and B. diffusa show some inhibition of the hydroxyapatite crystals in vitro. This preclinical study will be helpful to design the therapy for prevention of hydroxyapatite-based ailments.

  9. Metastable fcc-Fe film epitaxially grown on Cu(100) single-crystal underlayer

    Science.gov (United States)

    Ohtake, Mitsuru; Shimamoto, Kohei; Futamoto, Masaaki

    2013-05-01

    Fe film of 40 nm thickness is prepared on fcc-Cu(100) single-crystal underlayer at room temperature by ultra-high vacuum molecular beam epitaxy. The film growth and the detailed structure are investigated by reflection high-energy electron diffraction, cross-sectional high-resolution transmission electron microscopy (HR-TEM), and x-ray diffraction (XRD). An Fe single-crystal with metastable fcc structure nucleates on the underlayer. The HR-TEM shows that fcc lattice is formed from the Fe/Cu interface up to the film surface. A large number of misfit dislocations are introduced around the Fe/Cu interface due to an accommodation of lattice mismatch. Dislocations exist up to the film near surface. The lattice constant is estimated by XRD to be a = 0.3607 nm. The film shows a ferromagnetic property, which reflects the property of fcc-Fe crystal with high-spin ferromagnetic state.

  10. Thermally activated crystallization of Nb2O5 grown on Pt electrode

    Science.gov (United States)

    Berger, L.; Mähne, H.; Klemm, V.; Leuteritz, A.; Mikolajick, T.; Rafaja, D.

    2012-08-01

    The influence of the local crystallographic orientation of the polycrystalline bottom platinum electrode on the crystallization of niobium pentoxide thin films during their rapid thermal annealing was investigated by X-ray diffraction, X-ray reflectivity and transmission electron microscopy. The Nb2O5 thin films under study were reactively sputtered in a mixed O2/Ar atmosphere and subsequently subjected to the annealing in argon atmosphere at temperatures ranging from 500 ∘C to 700 ∘C. The X-ray diffraction confirmed a transition from the amorphous niobium oxide to the crystalline orthorhombic Nb2O5 for temperatures between 500 ∘C and 600 ∘C. The X-ray reflectivity measurements showed that the crystallization process was accompanied by a continuous increase of the electron density in Nb2O5 and by a rapid increase of the surface roughness at 700 ∘C. It was further observed by transmission electron microscopy that Nb2O5 crystallizes selectively and that the crystalline domains of Nb2O5 possess a strong orientation relationship to the platinum from the bottom electrode. The orientation relationship (bar{1} 1 1)_{Pt} {allel} (bar{1} bar{6}0)_{Nb2O5} was identified as the most beneficial one for crystallization of Nb2O5.

  11. Effects of AIN nucleation layer thickness on crystal quality of AIN grown by plasma-assisted molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    Ren Fan; Hao Zhi-Biao; Hu Jian-Nan; Zhang Chen; Luo Yi

    2010-01-01

    In this paper,the effects of thickness of AIN nucleation layer grown at high temperature on AIN epi-layer crystalline quality are investigated.Crack-free AIN samples with various nucleation thicknesses are grown on sapphire substrates by plasma-assisted molecular beam epitaxy.The AIN crystalline quality is analysed by transmission electron microscope and x-ray diffraction(XRD)rocking curves in both(002)and(102)planes.The surface profiles of nucleation layer with different thicknesses after in-situ annealing are also analysed by atomic force microscope.A critical nucleation thickness for realising high quality AIN films is found.When the nucleation thickness is above a certain value,the(102)XRD full width at half maximum(FWHM)of AIN bulk increases with nucleation thickness increasing,whereas the(002)XRD FWHM shows an opposite trend.These phenomena can be attributed to the characteristics of nucleation islands and the evolution of crystal grains during AIN main layer growth.

  12. Micro structural and dielectric property analysis on hydrothermally grown gadolinium doped SnO2 crystals

    Science.gov (United States)

    Pilakavil, Jaya T.; Pradyumnan, P. P.

    2016-09-01

    A series of SnO2-Gd2O3 mixed oxides were grown in aqueous medium by varying the thermodynamic parameters by hydrothermal method. X ray diffraction data identified tetragonal phases corresponding to tin oxide. The average crystallite size of the samples were between 21 and 31 nm. The morphological studies were conducted using scanning electron microscopy and compositional purity confirmed using energy dispersive spectroscopy. Detailed dielectric studies on the samples were performed in the frequency range 100 Hz-5 MHz, which showed that dielectric constant decreases with frequency in the low frequency range, whereas remains constant at higher frequencies. Impedance analysis is used to explain the effects of grain and grain boundary on transport mechanism of Gd:SnO2 particles synthesised at various pH.

  13. Multiple delta doping of single crystal cubic boron nitride films heteroepitaxially grown on (001)diamonds

    Energy Technology Data Exchange (ETDEWEB)

    Yin, H., E-mail: hyin@jlu.edu.cn [State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012 (China); Ziemann, P. [Institute of Solid State Physics, Ulm University, D-89069 Ulm (Germany)

    2014-06-23

    Phase pure cubic boron nitride (c-BN) films have been epitaxially grown on (001) diamond substrates at 900 °C. The n-type doping of c-BN epitaxial films relies on the sequential growth of nominally undoped (p-) and Si doped (n-) layers with well-controlled thickness (down to several nanometer range) in the concept of multiple delta doping. The existence of nominally undoped c-BN overgrowth separates the Si doped layers, preventing Si dopant segregation that was observed for continuously doped epitaxial c-BN films. This strategy allows doping of c-BN films can be scaled up to multiple numbers of doped layers through atomic level control of the interface in the future electronic devices. Enhanced electronic transport properties with higher hall mobility (10{sup 2} cm{sup 2}/V s) have been demonstrated at room temperature as compared to the normally continuously Si doped c-BN films.

  14. Preparation of CdTe nanocrystal-polymer composite microspheres in aqueous solution by dispersing method

    Institute of Scientific and Technical Information of China (English)

    LI Minjie; WANG Chunlei; HAN Kun; YANG Bai

    2005-01-01

    Highly fluorescent CdTe nanocrystals were synthesized in aqueous solution, and then processible CdTe nanocrystal-polymer composites were fabricated by coating the aqueous nanocrystals with copolymers of styrene and octadecyl-p-vinyl-benzyldimethylammonium chloride (SOV- DAC) directly. A dichloromethane solution of CdTe nano- crystal-polymer composites was dispersed in the aqueous solution of poly (vinyl alcohol) (PVA) generating highly fluorescent microspheres. Experimental parameters such as the concentration of nanocrystal-polymer composites, the concentration of PVA, and stirring speed which had important effect on the preparation of the microspheres were investigated in detail with fluorescent microscope characterization.

  15. Investigation of SR method grown directed KDP single crystal and its characterization by high-resolution X-ray diffractometry (HRXRD), laser damage threshold, dielectric, thermal analysis, optical and hardness studies

    International Nuclear Information System (INIS)

    directed potassium dihydrogen orthophosphate (KDP) single crystal was grown by Sankaranarayanan-Ramasamy (SR) method. The oriented seed crystals were mounted at the bottom of the platform and the size of the crystals were 10 mm diameter, 110 mm height. Two different growths were tried, in one the crystal diameter was the ampoule's inner diameter and in the other the crystal thickness was less than the ampoule diameter. In the first case only the top four pyramidal faces were existing whereas in the second case the top four pyramidal faces and four prismatic faces were existing through out the growth. The crystals were grown using same stoichiometric solution. The results of the two growths are discussed in this paper. The grown crystals were characterized by high-resolution X-ray diffractometry (HRXRD), laser damage threshold, dielectric, thermal analysis, UV-vis spectroscopy and microhardness studies. The HRXRD analysis indicates that the crystalline perfection is excellent without having any very low angle internal structural grain boundaries. Laser damage threshold value has been determined using Nd:glass laser operating at 1054 nm. The damage threshold for the KDP crystal is greater than 4.55 GW cm-2. The dielectric constant was higher and the dielectric loss was less in SR method grown crystal as against conventional method grown crystal. In thermal analysis, the starting of decomposition nature is similar in SR method grown KDP crystal and conventional method grown crystal. The SR method grown KDP has higher transmittance and higher hardness value compared to conventional method grown crystals.

  16. Investigation of SR method grown <0 0 1> directed KDP single crystal and its characterization by high-resolution X-ray diffractometry (HRXRD), laser damage threshold, dielectric, thermal analysis, optical and hardness studies

    Energy Technology Data Exchange (ETDEWEB)

    Balamurugan, S. [Centre for Crystal Growth, SSN College of Engineering, Kalavakkam, Chennai 603 110 (India); Ramasamy, P., E-mail: ramasamyp@ssn.edu.in [Centre for Crystal Growth, SSN College of Engineering, Kalavakkam, Chennai 603 110 (India); Sharma, S.K. [LMDDD, RRCAT, Indore (India); Inkong, Yutthapong; Manyum, Prapun [School of Physics, Institute of Science, Suranaree University of Technology (Thailand)

    2009-10-15

    <0 0 1> directed potassium dihydrogen orthophosphate (KDP) single crystal was grown by Sankaranarayanan-Ramasamy (SR) method. The <0 0 1> oriented seed crystals were mounted at the bottom of the platform and the size of the crystals were 10 mm diameter, 110 mm height. Two different growths were tried, in one the crystal diameter was the ampoule's inner diameter and in the other the crystal thickness was less than the ampoule diameter. In the first case only the top four pyramidal faces were existing whereas in the second case the top four pyramidal faces and four prismatic faces were existing through out the growth. The crystals were grown using same stoichiometric solution. The results of the two growths are discussed in this paper. The grown crystals were characterized by high-resolution X-ray diffractometry (HRXRD), laser damage threshold, dielectric, thermal analysis, UV-vis spectroscopy and microhardness studies. The HRXRD analysis indicates that the crystalline perfection is excellent without having any very low angle internal structural grain boundaries. Laser damage threshold value has been determined using Nd:glass laser operating at 1054 nm. The damage threshold for the KDP crystal is greater than 4.55 GW cm{sup -2}. The dielectric constant was higher and the dielectric loss was less in SR method grown crystal as against conventional method grown crystal. In thermal analysis, the starting of decomposition nature is similar in SR method grown KDP crystal and conventional method grown crystal. The SR method grown KDP has higher transmittance and higher hardness value compared to conventional method grown crystals.

  17. On the doping problem of CdTe films: The bismuth case

    Energy Technology Data Exchange (ETDEWEB)

    Vigil-Galan, O. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico); Brown, M. [Department of Physics and Astronomy, The University of Toledo, 43606 Toledo, OH (United States); Ruiz, C.M. [Depto. Fisica de Materiales, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Vidal-Borbolla, M.A. [Instituto de Investigacion en Comunicacion Optica, Av. Karakorum 1470, Lomas 4a. Secc., 78210 San Luis Potosi, SLP (Mexico); Ramirez-Bon, R. [CINVESTAV-IPN, U. Queretaro, Libramiento Norponiente No. 2000, Fracc. Real de Juriquilla, 76230 Santiago de Queretaro, Qro. (Mexico); Sanchez-Meza, E. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico); Tufino-Velazquez, M. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico)], E-mail: mtufinovel@yahoo.com.mx; Calixto, M. Estela [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico); Compaan, A.D. [Department of Physics and Astronomy, The University of Toledo, 43606 Toledo, OH (United States); Contreras-Puente, G. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico)

    2008-08-30

    The controlled increase of hole concentration is an important issue and still an unsolved problem for polycrystalline CdTe-based solar cells. The typical hole concentration of as-grown CdTe thin-films goes up to 10{sup 13} cm{sup -3}, depending on the specific growth technique. The highest electron concentration obtained for CdS, the suitable window partner material of CdTe, is around 10{sup 15} cm{sup -3}. Thus, the PV-performance of a CdS/CdTe device can be optimized if the hole concentration in CdTe is increased. We have faced up this problem by studying the electrical properties of two types of CdTe films: CdTe films grown by Close Space Vapor Transport using a CdTe:Bi powder as the starting material and CdTe sputtered films doped by implantation with different Bi-doses. Temperature-dependent resistivity and Hall effect measurements and a discussion on the efficiency of both doping processes are presented.

  18. On the doping problem of CdTe films: The bismuth case

    International Nuclear Information System (INIS)

    The controlled increase of hole concentration is an important issue and still an unsolved problem for polycrystalline CdTe-based solar cells. The typical hole concentration of as-grown CdTe thin-films goes up to 1013 cm-3, depending on the specific growth technique. The highest electron concentration obtained for CdS, the suitable window partner material of CdTe, is around 1015 cm-3. Thus, the PV-performance of a CdS/CdTe device can be optimized if the hole concentration in CdTe is increased. We have faced up this problem by studying the electrical properties of two types of CdTe films: CdTe films grown by Close Space Vapor Transport using a CdTe:Bi powder as the starting material and CdTe sputtered films doped by implantation with different Bi-doses. Temperature-dependent resistivity and Hall effect measurements and a discussion on the efficiency of both doping processes are presented

  19. Heteroepitaxy of CdTe on Ge(211)Substrates by Molecular Beam Epitaxy%Ge(211)衬底上分子束外延CdTe薄膜

    Institute of Scientific and Technical Information of China (English)

    李艳辉; 杨春章; 苏栓; 谭英; 高丽华; 赵俊

    2011-01-01

    采用分子束外延在3英寸Ge(211)衬底上生长了10 μm厚的CdTe(211)B薄膜.CdTe表面镜面光亮,3英寸范围厚度平均值9.72 μm,偏差0.3 μm;薄膜晶体质量通过X射线双晶迴摆曲线进行评价,FWHM平均值80.23 arcsec,偏差3.03 arcsec; EPD平均值为4.5×106cm-2.通过研究CdTe薄膜厚度与FWHM和EPD的关系,得到CdTe的理想厚度为8~9 μm.%The 10μm thick CdTe(211)B has been grown by molecular beam epitaxy(MBE) on Ge(211) substrate. The surface morphology of CdTe layers with a diameter of three inches is smooth and mirror-like. The average of thick is 9.72 μm, deviation 0.3 μm; The crystalline quality was measured by an X-ray double-crystal rocking curve, the average is 80.23 arcsec, deviation 3.03 arcsec; The EPD is 4.5 × 106cm -2. We has studied the effects of the thickness onFWHM and EPD for CdTe layer, the optimum thickness of CdTe layer is 8~9 μm.

  20. Growth Stresses in Thermally Grown Oxides on Nickel-Based Single-Crystal Alloys

    Science.gov (United States)

    Rettberg, Luke H.; Laux, Britta; He, Ming Y.; Hovis, David; Heuer, Arthur H.; Pollock, Tresa M.

    2016-03-01

    Growth stresses that develop in α-Al2O3 scale that form during isothermal oxidation of three Ni-based single crystal alloys have been studied to elucidate their role in coating and substrate degradation at elevated temperatures. Piezospectroscopy measurements at room temperature indicate large room temperature compressive stresses in the oxides formed at 1255 K or 1366 K (982 °C or 1093 °C) on the alloys, ranging from a high of 4.8 GPa for René N4 at 1366 K (1093 °C) to a low of 3.8 GPa for René N5 at 1255 K (982 °C). Finite element modeling of each of these systems to account for differences in coefficients of thermal expansion of the oxide and substrate indicates growth strains in the range from 0.21 to 0.44 pct at the oxidation temperature, which is an order of magnitude higher than the growth strains measured in the oxides on intermetallic coatings that are typically applied to these superalloys. The magnitudes of the growth strains do not scale with the parabolic oxidation rate constants measured for the alloys. Significant spatial inhomogeneities in the growth stresses were observed, due to (i) the presence of dendritic segregation and (ii) large carbides in the material that locally disrupts the structure of the oxide scale. The implications of these observations for failure during cyclic oxidation, fatigue cycling, and alloy design are considered.

  1. Dielectric and thermal studies on gel grown strontium tartrate pentahydrate crystals

    Indian Academy of Sciences (India)

    A Firdous; I Quasim; M M Ahmad; P N Kotru

    2010-08-01

    Results of dielectric and thermal studies on strontium tartrate pentahydrate crystals are described. The value of dielectric constant is shown to be independent of temperature till 360 K at all the frequencies (110–700 kHz) of the applied a.c. field. It increases abruptly achieving a peak value of 25.5 at 100 kHz; the peak value being strongly dependent on frequency. In the temperature range, 87 < < 117°C, the value of ' falls suggesting a transition at around 100°C or so. The dielectric constant, ', of the material is shown to be frequency dependent but temperature independent in the pre- or post-c range 87 < < 117°C, suggesting that the contribution towards polarization may be due to ionic or space charge polarization which gets eliminated at higher frequencies. The ferroelectric transition is supported by the results of thermoanalytical studies. It is explained that crystallographic change due to polymorphic phase transition may be occurring in the material, besides the change due to loss of water molecules, which leads to the dielectric anomaly at around 100°C. Coats–Redfern approximation method is applied for obtaining non-isothermal kinetic parameters leading to calculation of activation energies corresponding to three decomposition stages of material in the temperature ranging from 379–1113 K.

  2. Identification of triangular-shaped defects often appeared in hard-sphere crystals grown on a square pattern under gravity by Monte Carlo simulations

    International Nuclear Information System (INIS)

    In this paper, we have successfully identified the triangular-shaped defect structures with stacking fault tetrahedra. These structure often appeared in hard-sphere (HS) crystals grown on a square pattern under gravity. We have, so far, performed Monte Carlo simulations of the HS crystals under gravity. Single stacking faults as observed previously in the HS crystals grown on a flat wall were not seen in the case of square template. Instead, defect structures with triangular appearance in xz- and yz- projections were appreciable. We have identified them by looking layer by layer. Those structures are surrounded by stacking faults along face-centered cubic (fcc) {111}. Also, we see isolated vacancies and vacancy–interstitial pairs, and we have found octahedral structures surrounded by stacking faults along fcc {111}

  3. Investigation on growth and defects of Ho{sup 3+}:BaY{sub 2}F{sub 8} crystals grown by Czochralski method

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Hui [Department of Materials Science, Sichuan University, 610064 Chengdu (China); Southwest Institute of Technical Physics, Chengdu 610041 (China); Guan, Zhouguo [Southwest Institute of Technical Physics, Chengdu 610041 (China); He, Zhiyu, E-mail: hzyscu@163.com [Department of Materials Science, Sichuan University, 610064 Chengdu (China); Huang, Wei [Department of Materials Science, Sichuan University, 610064 Chengdu (China); Zhang, Wei; Niu, Ruihua; Yao, Chao; Yang, Yongqiang; Zhang, Huirong; Zhang, Zhibin [Southwest Institute of Technical Physics, Chengdu 610041 (China)

    2015-11-05

    Large and heavily Ho{sup 3+}-doped BaY{sub 2}F{sub 8} single crystals were grown by the Czochralski method. X-ray powder diffraction was applied to analyze the phase of the crystal samples. Simultaneously, metallographic microscope, scanning electron microscopy and energy dispersive spectrometer were employed to observe and investigate defects in the as grown crystals. Two significant kinds of defects, namely cracking and impurities were discovered in the samples of Ho{sup 3+}:BaY{sub 2}F{sub 8} single crystals. Theoretical analyses suggested that mechanisms concerning the formation of the impurities such as bubbles and inclusions were considered to be closely related to the growth temperature and atmosphere while the former defect was primarily brought by the lattice distortion relating to the thermal stress and the impurities. Based on the results of experiments and theoretical analyses, the parameters of growth process were optimized and a crack free 20 mol% Ho{sup 3+}:BaY{sub 2}F{sub 8}single crystal has been successfully obtained. Furthermore, the UV–Vis-IR (0.2–10 μm) absorption spectra of BaY{sub 2}F{sub 8} single crystal and the crystal heavily doped with Ho{sup 3+} ions (20 mol%) have been investigated at room temperature. - Highlights: • Main reason of cleavages is the crystal lattice distortion caused by the impurities. • Lattice distortion was caused by carbon phases derived from the graphite crucible. • High quality crystal can be obtained by using CF{sub 4} and high purity graphite crucibles. • The crystal exhibits the broader absorption band and larger absorption cross section.

  4. The growth of high quality CdTe on GaAs by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Reno, J.L.; Carr, M.J.; Gourley, P.L. (Sandia National Laboratories, Albuquerque, New Mexico 87185 (US))

    1990-03-01

    We have grown CdTe (111) on oriented and misoriented GaAs (100) and have characterized the layers by photoluminescence microscopy (PLM) and transmission electron microscopy (TEM). Photoluminescence microscopy showed a totally different type of defect structure for the oriented substrate than for the misoriented substrates. The CdTe grown on the misoriented substrates exhibited only threading dislocations. The CdTe grown on oriented GaAs showed fewer threading dislocations but exhibited a random structure of loops. The loop structure observed by PLM has been identified by TEM as the boundary between twinned crystallites which extend from the CdTe/GaAs interface to the CdTe surface. When viewed along the growth axis, these boundaries between the columnar twins appear as loops and segments. Surface roughness of the GaAs substrate contributes to the initial growth of twinned material. This leads to competitive growth between the twins and the creation of the observed columnar twins. We present for the first time the growth of CdTe on patterned GaAs substrates. By growing on oriented GaAs(100) substrates that had been patterned prior to growth with 12 {mu}m mesas, it is possible to grow material on the mesa top that is twin free and has a low dislocation density.

  5. Growth of MgF2 optical crystals and their ionic conductivity in the as-grown state and after partial pyrohydrolysis

    Science.gov (United States)

    Karimov, D. N.; Sorokin, N. I.; Chernov, S. P.; Sobolev, B. P.

    2014-11-01

    MgF2 single crystals have been grown from melt by the Bridgman technique in a fluorinating atmosphere. To control the presence of oxygen impurity, it was first suggested to measure the ionic conductivity in MgF2 crystals by impedance spectroscopy. The characteristics of ionic conductivity of " as grown" (i.e., without thermal treatment) crystals and crystals obtained by commercial vacuum technology practically coincide: the volume conductivity σv = 1.4 × 10-7 S/cm at 773 K and the ion-transport activation energy E a = 1.40 ± 0.05 eV. Annealing MgF2 crystals during electrophysical studies upon heating from 293 to 823 K in vacuum (residual pressure ˜1 Pa) for 4 h led to their partial pyrohydrolisis. The influence of this thermal treatment of MgF2 crystals on their optical transmission is studied in the wavelength range of 115-300 nm.

  6. Investigation of magnetic property of GdFeO{sub 3} single crystal grown in air by optical floating zone technique

    Energy Technology Data Exchange (ETDEWEB)

    Ramesh Babu, P. [Centre for Crystal Growth, School Advance Sciences, VIT University, Vellore, Tamil Nadu (India); Bhaumik, Indranil [Crystal Growth Laboratory, Laser Materials Development and Devices Division, Raja Ramanna Centre for Advanced Technology, Indore (India); Ganesamoorthy, S. [X-ray Scattering and Crystal Growth Section, CMPD, Material Science Group, IGCAR, Kalpakkam, Tamil Nadu (India); Kalainathan, S., E-mail: kalainathan@yahoo.com [Centre for Crystal Growth, School Advance Sciences, VIT University, Vellore, Tamil Nadu (India); Bhatt, R.; Karnal, A.K.; Gupta, P.K. [Crystal Growth Laboratory, Laser Materials Development and Devices Division, Raja Ramanna Centre for Advanced Technology, Indore (India)

    2015-05-15

    Highlights: • GdFeO{sub 3} single crystals have been grown by OFZ technique in air. • Sample exhibits one order lower coercive field than crystal grown in oxygen. • Bloch 3/2-law holds good for GdFeO{sub 3} (B-parameter as 2.69 × 10{sup −5} K{sup −3/2}). • The coercivity exhibited sharp dip at 200 and 550 K. • At 550 K pinning of the direction of weak ferromagnetism by AFM ordering vanishes. - Abstract: Single phase Gadolinium orthoferrite (GdFeO{sub 3}) with orthorhombic perovskite structure was synthesized without any garnet impurities by solid state reaction and subsequently GdFeO{sub 3} single crystals were grown by the optical floating zone technique. The temperature dependent magnetization measurement revealed the magnetic phase transition from anti-ferromagnetic ordering to paramagnetic ordering at 670 K. The overlapping of the magnetization measured under zero-field and field cooling condition in the range of 300–20 K signifies that there is no magnetic transition in this temperature range. The hysteresis loop measurements revealed that in comparison to the values reported for the crystal grown in oxygen, the air grown sample exhibits one order lower coercive field (∼75 Oe). The Bloch 3/2-law was found to hold good for GdFeO{sub 3} with the value of B-parameter as 2.69 × 10{sup −5} K{sup −3/2}. The coercivity exhibited sharp dip at 200 and 550 K. At and above 550 K the ability of the antiferromagnetic ordering to pin the direction of magnetization related to the weak ferromagnetism present in the material vanishes leading to the lowering in the coercivity.

  7. Annealing and surface conduction on Hydrogen peroxide treated bulk melt-grown, single crystal ZnO

    Energy Technology Data Exchange (ETDEWEB)

    Mtangi, W., E-mail: wilbert.mtangi@up.ac.za [University of Pretoria, Physics Department, Pretoria 0002 (South Africa); Nel, J.M.; Auret, F.D.; Chawanda, A.; Diale, M. [University of Pretoria, Physics Department, Pretoria 0002 (South Africa); Nyamhere, C. [Nelson Mandela Metropolitan University, Physics Department, P.O. Box 77000, Port Elizabeth 6031 (South Africa)

    2012-05-15

    We report on the studies carried out on hydrogen peroxide treated melt-grown, bulk single crystal ZnO samples. Results show the existence of two shallow donors in the as-received ZnO samples with energy levels (37.8{+-}0.3) meV that has been suggested as Zn{sub i} related and possibly H-complex related and (54.5{+-}0.9) meV, which has been assigned to an Al-related donor. Annealing studies performed on the hydrogen peroxide treated samples reveal the existence of a conductive channel in the samples in which new energy levels have been observed, Zn vacancies, related to the Group I elements, X{sub Zn}. The surface donor volume concentration of the conductive channel was calculated from a theory developed by Look (2007) . Results indicate an increase in the surface volume concentration with increasing annealing temperature from 60 Multiplication-Sign 10{sup 17} cm{sup -3} at 200 Degree-Sign C to 4.37 Multiplication-Sign 10{sup 18} cm{sup -3} at 800 Degree-Sign C.

  8. Magnetic properties of Cu-flux-grown UCu{sub 2}Si{sub 2} single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Troc, R.; Bukowski, Z. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wroclaw (Poland)

    2006-01-01

    In order to solve a serious problem of understanding the magnetic properties of UCu{sub 2}Si{sub 2}, we have grown single crystals of this compound from Cu-flux. Here we focus primarily on the magnetic behavior of this compound. In contrast to some previous polycrystalline and single-crystalline reports on UCu{sub 2}Si{sub 2} no signs of the transition into antiferromagnetic behavior have been observed below T {sub C}=104(1) K. The magnetic properties of this compound are highly anisotropic, with an easy axis of magnetization along the [001] direction. The saturation moment has been determined at 4.2 K to be 1.55 {mu}{sub B}. In the paramagnetic region the effective moments for the easy and hard directions are both about 3.0 {mu}{sub B}. An extensive discussion of the obtained data, compared to those recently published by Fisk et al. and Matsuda et al., also based on single crystalline materials, has been presented. No an antiferromagnetic phase above T{sub C} has been detected. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Annealing and surface conduction on Hydrogen peroxide treated bulk melt-grown, single crystal ZnO

    International Nuclear Information System (INIS)

    We report on the studies carried out on hydrogen peroxide treated melt-grown, bulk single crystal ZnO samples. Results show the existence of two shallow donors in the as-received ZnO samples with energy levels (37.8±0.3) meV that has been suggested as Zni related and possibly H-complex related and (54.5±0.9) meV, which has been assigned to an Al-related donor. Annealing studies performed on the hydrogen peroxide treated samples reveal the existence of a conductive channel in the samples in which new energy levels have been observed, Zn vacancies, related to the Group I elements, XZn. The surface donor volume concentration of the conductive channel was calculated from a theory developed by Look (2007) . Results indicate an increase in the surface volume concentration with increasing annealing temperature from 60×1017 cm−3 at 200 °C to 4.37×1018 cm-3 at 800 °C.

  10. Growth and characterization of Cu2ZnSn(Sx Se1-x)4 single crystal grown by traveling heater method

    Science.gov (United States)

    Nagaoka, Akira; Katsube, Ryoji; Nakatsuka, Shigeru; Yoshino, Kenji; Taniyama, Tomoyasu; Miyake, Hideto; Kakimoto, Koichi; Scarpulla, Michael A.; Nose, Yoshitaro

    2015-08-01

    High-quality Cu2ZnSn(SxSe1-x)4 (CZTSxSe1-x) single crystals were grown by the traveling heater method (THM), which is an example of a solution growth process. The CZTSxSe1-x solute-Sn solvent pseudobinary system was investigated and the ranges of growth temperature and quantity of solvent were determined for THM growth. The CZTSxSe1-x single crystals were obtained from a 70-80 mol% CZTSxSe1-x solution at growth temperature 900 °C and speed 4-5 mm/day. The structural and compositional analyses of the grown single crystals were carried out by powder X-ray diffraction, Raman spectroscopy and electron probe microanalysis. The grown crystals were kesterite and nearly stoichiometric with slightly Cu-poor and Zn-rich despite the excess Sn used as the solvent. As the sulfur content x increases, the carrier concentration increases slightly but systematically between 2×1017 and 3×1017 cm-3 while the mobility decreases from 35.1 to 10.4 cm2V-1 s-1. These data provide references for the results of characterization on thin film samples as well as giving insight into the defect equilibrium and resulting quantities such as doping and mobility affecting device performance.

  11. Temperature and illumination intensity dependence of photoconductivity in sputter-deposited heteroepitaxial (100)CdTe layers

    Science.gov (United States)

    Das, S. R.; Cook, J. G.; Mukherjee, G.

    1991-06-01

    The photoconductivity behavior and the Hall-effect of sputter-deposited heteroepitaxial (100)CdTe layers grown at temperatures between 300 and 325 C were investigated. The (100)CdTe epilayers were found to be highly photoconductive and exhibited photoconductivity/dark conductivity ratios as high as 1 x 10 to the 6th at around 200 K. Photoconductivity showed a sublinear dependence on the illumination intensity and was higher at higher temperatures. It is shown that the model of Simmons and Taylor (1974) developed to explain photoconductivity in amorphous semiconductors is also applicable to the (100)CdTe epitaxial layers.

  12. Efficient generation of 480 fs electrical pulses on transmission lines by photoconductive switching in metalorganic chemical vapor deposited CdTe

    Science.gov (United States)

    Nuss, Martin C.; Kisker, D. W.; Smith, P. R.; Harvey, T. E.

    1989-01-01

    Electrical pulses of only 480 fs duration have been generated by photoconductive switching in CdTe grown by ultraviolet-enhanced metalorganic chemical vapor deposition (MOCVD). In addition to the extremely fast switching times, MOCVD CdTe also exhibits a high mobility of 180 sq cm/V s and can be grown on almost any substrate, making it ideal for integration into existing circuits and devices.

  13. Optical absorption of Cd sub 1 sub - sub x Co sub x Te single crystals

    CERN Document Server

    Kim, H K; Park, S T; Park, H Y

    1999-01-01

    Cd sub 1 sub - sub x Co sub x Te single crystals were grown by the vertical Bridgman method. We measured the optical absorption in the range from 750 to 3000 nm at room temperature and at 4.8 K. Several absorption bands were detected and assigned to electronic transitions between the splitting energy levels of Co sup 2 sup + sited at the T sub d symmetry of the CdTe host lattice. The crystal-field parameter (Dq), the Racah parameter (B), and the spin-orbit coupling parameter (lambda) were determined. In addition, the band-gap energy was obtained as a function of cobalt composition x.

  14. Strikingly different luminescent properties arising from single crystals grown from solution or from the vapor phase in a diketo-pyrrolo-pyrrole analog

    Science.gov (United States)

    Imoda, Tomohiko; Mizuguchi, Jin

    2007-10-01

    The title compound di-cyano-pyrrolo-pyrrole (DCPP) is an analog of diketo-pyrrolo-pyrrole (DPP) known as a red pigment on the market. Brilliant orange photoluminescence has been observed in crystals of DCPP recrystallized from solution (crystal I); whereas the luminescence was quite weak in single crystals grown from the vapor phase (crystal II). To elucidate the difference in luminescent properties, a series of structural analysis together with thermal analysis has been carried out on crystals I and II at -180 °C, RT, 150 °C, and 200 °C. However, no difference in structure is recognized between crystals I and II within the precision of the x-ray analysis. Nevertheless, a slight difference in sublimation temperature of about 5° is observed between crystals I and II. Since the sublimation temperature depends on the cohesion in the solid state and the cohesion, in turn, governs the extent of lattice vibration (i.e., nonradiative process), a slight difference in sublimation temperature appears to determine the fraction between the radiative and nonradiative processes in crystals I and II.

  15. Optical properties of Ni-doped MgGa{sub 2}O{sub 4} single crystals grown by floating zone method

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, Takenobu, E-mail: takenobu@toyota-ti.ac.j [Research Center for Advanced Photon Technology, Toyota Technological Institute, 2-12-1, Hisakata, Tempaku-ku, Nagoya 468-8511 (Japan); Hughes, Mark; Ohishi, Yasutake [Research Center for Advanced Photon Technology, Toyota Technological Institute, 2-12-1, Hisakata, Tempaku-ku, Nagoya 468-8511 (Japan)

    2010-01-15

    The single crystal growth conditions and spectroscopic characterization of Ni-doped MgGa{sub 2}O{sub 4} with inverse-spinel structure crystal family are described. Single crystals of this material have been grown by floating zone method. Ni-doped MgGa{sub 2}O{sub 4} single crystals have broadband fluorescence in the 1100-1600 nm wavelength range, 1.6 ms room temperature lifetime, 56% quantum efficiency and 1.05x10{sup -21}cm{sup 2} stimulated emission cross section at the emission peak. This new material is very promising for tunable laser applications covering the important optical communication and eye safe wavelength region.

  16. Influence of CdTe thickness on structural and electrical properties of CdTe/CdS solar cells

    International Nuclear Information System (INIS)

    Due to its high scalability and low production cost, CdTe solar cells have shown a very strong potential for large scale energy production. Although the number of modules produced could be limited by tellurium scarcity, it has been reported that reducing CdTe thickness down to 1.5 μm would solve this issue. There are, however, issues to be considered when reducing thickness, such as formation of pinholes, lower crystallization, and different possible effects on material diffusion within the interfaces. In this work, we present the study of CdTe solar cells fabricated by vacuum evaporation with different CdTe thicknesses. Several cells with a CdTe thickness ranging from 0.7 to 6 μm have been fabricated. The deposition process has been optimized accordingly and their physical and electrical properties have been studied. Thin cells show a different electrical behavior in terms of open circuit voltage and fill factor. Efficiencies range from 7% for thin CdTe cells to 13.5% for the standard thickness. - Highlights: ► Ultra thin CdTe absorbers have been prepared and studied. ► Grain size is depending on the CdTe thickness but spread in the grains increases. ► Lattice parameter is reduced only for ultra thin CdTe. ► The band gap reveals an intermixed CdTe absorber. ► The reason for lower efficiency of ultra thin CdTe is explained

  17. Structural characterization of Hg 0.78Cd 0.22Te/CdTe LPE heterostructures grown from Te solutions

    Science.gov (United States)

    Bernardi, S.; Bocchi, C.; Ferrari, C.; Franzosi, P.; Lazzarini, L.

    1991-08-01

    Hg 0.78Cd 0.22Te epilayers have been grown on CdTe substrates by slider liquid phase epitaxy. The crystal quality of the epitaxial material has been studied in as-grown structures and chemically or mechano-chemically prepared bevels using X-ray topography, double crystal diffractometry and transmission electron microscopy. It has been found that the bulk epilayers exhibit a very high crystal quality, as evidenced by the relatively low density of dislocations and the very narrow Bragg peaks. In contrast, a high dislocation and precipitate density and a broadening of the Bragg peak have been detected in the epilayer near the interface. Finally, a Hg decrease in the layer and a corresponding Hg increase in the substrate close to the interface have been observed.

  18. CdTe-Cd1 - xMnxTe multiple quantum well structures grown by pulsed laser evaporation and epitaxy

    Science.gov (United States)

    Dubowski, J. J.; Roth, A. P.; Wasilewski, Z. R.; Rolfe, S. J.

    1991-09-01

    Structural and optical properties of (001) CdTe-Cd1-xMnxTe (x=0.10) multiple quantum well structures grown by pulsed laser evaporation and epitaxy (PLEE) are investigated. The layers are grown on (001) CdZnTe wafers held at a temperature in the range of 210-230 °C. Secondary-ion mass spectroscopy in-depth profiles reveal that highly uniform structures are grown. Numerical analysis of double crystal x-ray diffraction results demonstrates high structural quality of the layers and indicates partial relaxation of the strain in these structures. Low-temperature photoluminescence exhibits excitonic recombinations in the CdTe wells whereas photoluminescence from the Cd1-xMnxTe barriers is not observed. The chemical composition of the barriers deduced from photoluminescence is in excellent agreement with the intended chemical composition set during growth.

  19. Crystal Perfection in GaP Films Heteroepitaxially Grown on GaAs by Low-pressure Metalorganic Chemical Vapor Deposition

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The crystal perfection in GaP epitaxial layers was stuided by the use of double crystal X-ray diffraction,backscattering spectrometry and Raman scattering techniques.GaP films grown on GaAs by low-pressure metalorganic chemical vapor deposition were used as the samples.By means of the morphology and the full-width at half maximum of X-ray diffraction peak for the GaP epilayers,the growth temperature and Ⅴ/Ⅲ ratio were optimized.In addition,the residual stress and strain of a GaP epilayer were calculated,based on Raman scattering measurement.

  20. Synthesis and characterization of BaFe{sub 2}As{sub 2} single crystals grown by in-flux technique

    Energy Technology Data Exchange (ETDEWEB)

    Garitezi, T.M.; Adriano, C.; Rosa, P.F.S.; Bittar, E.M.; Bufaical, L.; Almeida, R.L.; Granado, E.; Pagliuso, P.G., E-mail: thalesmg@ifi.unicamp.br [Universidade Estadual de Campinas (UNICAM), SP (Brazil). Instituto de Fisica Gleb Wataghin; Grant, T; Fisk, Z. [University of California, Irvine, CA (United States); Avila, M.A.; Ribeiro, R.A. [Universidade Federal do ABC (UFABC), Santo Andre, SP (Brazil). Centro de Ciencias Naturais e Humanas; Kuhns, P.L.; Reyes, A.P.; Urbano, R.R. [National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL (United States)

    2013-08-15

    We report a detailed characterization of BaFe{sub 2}As{sub 2} single crystals grown by a metallic In-flux technique, an alternative to well-established growth routes using FeAs self- or Sn-flux. Electrical resistivity, magnetic susceptibility, nuclear magnetic resonance, and energy dispersive spectroscopy measurements showed no evidence of flux incorporation. More importantly, our results demonstrate that BaFe{sub 2}As{sub 2} single crystals grown by In-flux have extremely high quality. To explore the efficiency of the In-flux growth method, we have also prepared nearly optimally doped superconducting samples of Ba(Fe{sub 1} {sub -x} M {sub x} ){sub 2}As{sub 2} (M = Co, Cu, Ni, and Ru). Among other interesting features, this alternative chemical substitution method has led to enhancement of the maximum T{sub c} for most dopings. (author)

  1. Physical vapor deposition of CdTe thin films at low temperature for solar cell applications

    International Nuclear Information System (INIS)

    Cadmium telluride is successfully utilized as an absorber material for thin film solar cells. Industrial production makes use of high substrate temperatures for the deposition of CdTe absorber layers. However, in order to exploit flexible substrates and to simplify the manufacturing process, lower deposition temperatures are beneficial. Based on the phase diagram of CdTe, predictions on the stoichiometry of CdTe thin films grown at low substrate temperatures are made in this work. These predictions were verified experimentally using additional sources of Cd and Te during the deposition of the CdTe thin films at different substrate temperatures. The deposited layers were analyzed with energy-dispersive X-ray spectroscopy. In case of CdTe layers which were deposited at substrate temperatures lower than 200 C without usage of additional sources we found a non-stoichiometric growth of the CdTe layers. The application of the additional sources leads to a stoichiometric growth for substrate temperatures down to 100 C which is a significant reduction of the substrate temperature during deposition.

  2. Polarity determination of epitaxial structures of CdTe on GaAs by channeling techniques

    Energy Technology Data Exchange (ETDEWEB)

    Wielunski, L.S. (CSIRO Div. of Applied Physics, Lucas Heights Research Labs., Menai, NSW (Australia)); Kwietniak, M.S.; Pain, G.N. (Telecom Australia Research Labs., Clayton, Victoria (Australia)); Rossouw, C.J. (CSIRO Div. of Materials Science and Tech., Clayton, Victoria (Australia))

    1990-01-01

    RBS spectra analysis near the (111) planar channeling direction is used for polarity determination of MOCVD-grown epitaxial layers of (111) and (100) CdTe on sapphire and GaAs substrates. Extensive multiple twinning limits the application of RBS channeling analysis for polarity determination. Comparison is made with polarity determination by X-ray diffraction and two electron diffraction techniques. (orig.).

  3. Structural and optical characterization of CdTe quantum dots thin films

    International Nuclear Information System (INIS)

    Highlights: • CdTe QDs are prepared by hot injection method. • Thermally evaporated CdTeQDs thin films were prepared. • Structural characterization and analysis were done. • Optical parameters were studied. - Abstract: Cadmium telluride quantum dots (CdTe QDs) have been synthesized using hot-injection chemical technique. The CdTe QDs thin films were deposited onto optical flat fused quartz substrates using thermal evaporation technique. The CdTe QDs powder and the as deposited films were characterized using X-ray diffraction and high resolution transmission electron microscope (HRTEM). The X-ray analysis shows that both CdTe QDs powder and the as deposited films crystallize in cubic zinc-blende type structure with lattice parameter 6.46 Å and 6.45 Å, respectively. The X-ray calculation shows that the average crystallite size of the as deposited CdTe QDs films varied from 1.1 nm for the powder to 2.3 nm for the thin film. The HRTEM examination of the as deposited films shows that the average particle size vary from 2.5 nm for the powder to 2.7 nm for the thin film. For the as deposited films, the dependence of (αhν)2 on the incident photon energy indicates that the optical transitions within the film are allowed direct with energies observed at Eg1≅2eV and Eg2≅2.3eV which attributed to quantum confinement effect. The optical band gap increases from 1.5 eV for microstructure CdTe to 2 eV for nanostructure quantum dots which corresponding to wavelength(620 nm) so it is a great benefit to use CdTe quantum dots as solar harvesting devices application in solar spectrum region (400–800 nm). Urbach energy is calculated and found to be 360 meV which is higher than microstructure CdTe. The refractive index and refractive index dispersion of the as deposited CdTe QDs film has been calculated from transmission and reflection spectra. It has been found that the refractive index is reduced from (2.66) for microstructure CdTe to be (1.7) for CdTe quantum dots

  4. Tilt growth of CdTe epilayers on sapphire substrates by MOCVD

    Science.gov (United States)

    Ebe, H.; Sawada, A.; Maruyama, K.; Nishijima, Y.; Shinohara, K.; Takigawa, H.

    1991-12-01

    We studied model lattice matching in the growth direction by tilt growth and found that the ratio of the tilt angle of the epilayer (α) to the offset angle of the substrate (θ) had a maximum at α / θ = 0.73, independent of the offset angle. Experimental plots of the ratio versus the full width at half maximum (FWHM) of (333) CdTe rocking curves in double-crystal X-ray diffraction show that the ratio ranges from 0.05 to 0.6 while the FWHM varies from 1100 to 400 arc sec. This result suggests that the lattice inclination orients the lattice structure perpendicular to the CdTe-sapphire heterointerface and that the tilt angle reduces defects such as dislocations and stacking faults. Most epilayers grown on sapphire substrates with offset angles above 3° were confirmed to have a α / θ ratio below 0.2. This suggests that crystal defects may be generated by shearing stress due to large offset angles. Greater defect density lowers the ratio and degrades crystallinity.

  5. Improvement of the sensitivity of CdTe semiconductor detector in the high energy region

    International Nuclear Information System (INIS)

    Cadmium Telluride, CdTe, semiconductor detectors have sufficient band gap energy (1.47 eV) to use at room temperature, and their atomic number are so large (48 and 52) that their photon detection efficiency is more excellent than that of Si or Ge. Recently CdTe crystals have become easily available because of improvements in the crystal growth method. It is a useful X-ray detector, because it has good energy resolution and high efficiency at the full energy peak at less than a few hundred keV of incident photon energy. However, if the incident photon energy become higher, the efficiency of the full energy peak become worse, and it is very difficult to distinguish the full energy peak above 1 MeV, because the mobility of charge carriers in the CdTe crystal is much smaller than in Si and Ge and it is difficult to produce a larger volume element. In order to analyze the energy of several radioisotopes, it is necessary to improve the sensitivity of CdTe detectors in high energy regions. We have previously suggested a multilayered structure of CdTe elements. This paper describes a simulation and experiment to improve the efficiency of the full energy peak in the high energy region above 1 MeV. (author)

  6. Study of fluorination of CdTe surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Sugiyama, Koichi; Mori, Koichi; Miyake, Hideto (Dept. of Electrical Engineering, Mie Univ., Tsu-shi (Japan))

    1991-03-20

    In this paper we deal with fluorination of CdTe(100) single crystals in a 2% fluorine-98% nitrogen atmosphere for different temperatures and times. The fluorination process has been investigated by the use of microscopy, X-ray diffraction, energy-dispersive X-ray microanalysis, X-ray photoelectron spectroscopy and Auger electron spectroscopy measurements. Three temperature regions are found to be distinguished for the fluorination process. The fluorinated layer is mainly composed of CdF{sub 2} crystals, but an intermediate layer is shown to exist beneath the fluoride layer except for fluorination at low temperature. The formation mechanisms of the fluoride and intermediate layers are discussed. (orig.).

  7. Chemical etching of a GaSb crystal incorporated with Mn grown by the Bridgman method under microgravity conditions

    Institute of Scientific and Technical Information of China (English)

    Chen Xiaofeng; Chen Nuofu; Wu Jinliang; Zhang Xiulan; Chai Chunlin; Yu Yude

    2009-01-01

    uring crystal growth can be reflected by the observations of etch pit distribution and other structural defects. Suggestions for improving the space experiment to improve the quality of the crystal are given.

  8. Phosphorus Doping of Polycrystalline CdTe by Diffusion

    Energy Technology Data Exchange (ETDEWEB)

    Colegrove, Eric; Albin, David S.; Guthrey, Harvey; Harvey, Steve; Burst, James; Moutinho, Helio; Farrell, Stuart; Al-Jassim, Mowafak; Metzger, Wyatt K.

    2015-06-14

    Phosphorus diffusion in single crystal and polycrystalline CdTe material is explored using various methods. Dynamic secondary ion mass spectroscopy (SIMS) is used to determine 1D P diffusion profiles. A 2D diffusion model is used to determine the expected cross-sectional distribution of P in CdTe after diffusion anneals. Time of flight SIMS and cross-sectional cathodoluminescence corroborates expected P distributions. Devices fabricated with diffused P exhibit hole concentrations up to low 1015 cm-3, however a subsequent activation anneal enabled hole concentrations greater than 1016 cm-3. CdCl2 treatments and Cu based contacts were also explored in conjunction with the P doping process.

  9. Crystal growth and dielectric property of Na0.5K0.5NbO3 and Mn-doped Na0.5K0.5NbO3 single crystal grown by flux method

    International Nuclear Information System (INIS)

    Potassium sodium niobate (KNN) (K0.5Na0.5) NbO3 single crystal and co-doped (K0.5Na(1-x)0.5 Mnx) NbO3 (where x=.02,.04,06,.) single crystal were grown using a high temperature flux method. The effects of cationic substitution of Mn for Nb in the B sites of perovskite lattice on the structure, phase transition behavior and dielectric properties, X-ray diffraction (XRD) pattern, SEM and EDAX, FTIR, UV-VIS, SPECTRUM, AFM were investigated. (author)

  10. Structural Characterization of Lateral-grown 6H-SiC am-plane Seed Crystals by Hot Wall CVD Epitaxy

    Science.gov (United States)

    Goue, Ouloide Yannick; Raghothamachar, Balaji; Dudley, Michael; Trunek, Andrew J.; Neudeck, Philip G.; Woodworth, Andrew A.; Spry, David J.

    2014-01-01

    The performance of commercially available silicon carbide (SiC) power devices is limited due to inherently high density of screw dislocations (SD), which are necessary for maintaining polytype during boule growth and commercially viable growth rates. The NASA Glenn Research Center (GRC) has recently proposed a new bulk growth process based on axial fiber growth (parallel to the c-axis) followed by lateral expansion (perpendicular to the c-axis) for producing multi-faceted m-plane SiC boules that can potentially produce wafers with as few as one SD per wafer. In order to implement this novel growth technique, the lateral homoepitaxial growth expansion of a SiC fiber without introducing a significant number of additional defects is critical. Lateral expansion is being investigated by hot wall chemical vapor deposition (HWCVD) growth of 6H-SiC am-plane seed crystals (0.8mm x 0.5mm x 15mm) designed to replicate axially grown SiC single crystal fibers. The post-growth crystals exhibit hexagonal morphology with approximately 1500 m (1.5 mm) of total lateral expansion. Preliminary analysis by synchrotron white beam x-ray topography (SWBXT) confirms that the growth was homoepitaxial, matching the polytype of the respective underlying region of the seed crystal. Axial and transverse sections from the as grown crystal samples were characterized in detail by a combination of SWBXT, transmission electron microscopy (TEM) and Raman spectroscopy to map defect types and distribution. X-ray diffraction analysis indicates the seed crystal contained stacking disorders and this appears to have been reproduced in the lateral growth sections. Analysis of the relative intensity for folded transverse acoustic (FTA) and optical (FTO) modes on the Raman spectra indicate the existence of stacking faults. Further, the density of stacking faults is higher in the seed than in the grown crystal. Bundles of dislocations are observed propagating from the seed in m-axis lateral directions

  11. Characteristics of CdTe films and CdTe/CdS solar cells fabricated by photostimulated sublimation

    International Nuclear Information System (INIS)

    Full text : The effect of illumination during the close-spaced sublimation (CSS) growth on composition, structural, electrical, optical and photovoltaic properties of CdTe films and CdTe/CdS solar cells was investigated. Data on comparative study by using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), absorption spectra and conductivity-temperature measurements of CdTe films prepared by CSS method in a dark (CSSD) and under illumination (CSSI) were presented. It is shown that the growth rate of CdTe films under illumination is higher than that for films prepared without illumination. Moreover, the polycrystalline CdTe films of the cubic structure grown by CSSI technology were characterized with larger the grain size as compared to that for films prepared by CSSD

  12. Growth of CdTe on Si(100) surface by ionized cluster beam technique: Experimental and molecular dynamics simulation

    Science.gov (United States)

    Araghi, Houshang; Zabihi, Zabiholah; Nayebi, Payman; Ehsani, Mohammad Mahdi

    2016-10-01

    II-VI semiconductor CdTe was grown on the Si(100) substrate surface by the ionized cluster beam (ICB) technique. In the ICB method, when vapors of solid materials such as CdTe were ejected through a nozzle of a heated crucible into a vacuum region, nanoclusters were created by an adiabatic expansion phenomenon. The clusters thus obtained were partially ionized by electron bombardment and then accelerated onto the silicon substrate at 473 K by high potentials. The cluster size was determined using a retarding field energy analyzer. The results of X-ray diffraction measurements indicate the cubic zinc blende (ZB) crystalline structure of the CdTe thin film on the silicon substrate. The CdTe thin film prepared by the ICB method had high crystalline quality. The microscopic processes involved in the ICB deposition technique, such as impact and coalescence processes, have been studied in detail by molecular dynamics (MD) simulation.

  13. CdTe devices and method of manufacturing same

    Science.gov (United States)

    Gessert, Timothy A.; Noufi, Rommel; Dhere, Ramesh G.; Albin, David S.; Barnes, Teresa; Burst, James; Duenow, Joel N.; Reese, Matthew

    2015-09-29

    A method of producing polycrystalline CdTe materials and devices that incorporate the polycrystalline CdTe materials are provided. In particular, a method of producing polycrystalline p-doped CdTe thin films for use in CdTe solar cells in which the CdTe thin films possess enhanced acceptor densities and minority carrier lifetimes, resulting in enhanced efficiency of the solar cells containing the CdTe material are provided.

  14. A comparison of the X-ray performance of TlBr crystals grown by the Bridgeman-Stockbarger and travelling molten zone methods

    Energy Technology Data Exchange (ETDEWEB)

    Gostilo, V. E-mail: bsi@bsi.lv; Owens, A.; Bavdaz, M.; Lisjutin, I.; Peacock, A.; Sipila, H.; Zatoloka, S

    2003-08-21

    We have investigated at optimal temperature the X-ray detection characteristics of two TlBr crystals by the Traveling Molten Zone (TMZ) technique. The resistivities were typically 1.5x10{sup 10} {omega} cm at room temperature, increasing to (1.1-1.7)x10{sup 12} {omega} cm at -15 deg. C. In the temperature range -0 deg. C to -50 deg. C, both crystals exhibited mobility-lifetime products of {approx}8x10{sup -5} cm{sup 2}V{sup -1} and {approx}1.5x10{sup -5} cm{sup 2}V{sup -1}, for electrons and holes respectively. From these crystals, two detectors were packaged and X-ray metrology carried out. For the best detector, the measured energy resolutions at an operating temperature of -15 deg. C and 500 V bias were 1.0 keV at 5.9 keV; 1.1 at 13.9 keV; 2.5 at 59.54 keV; 3.3 keV at 88 keV; 4 keV at 122 keV and 27.7 keV at 662 keV.A comparative analysis of the characteristics of detectors grown by TMZ to those grown by the Bridgeman-Stockbarger method is given.

  15. A comparison of the X-ray performance of TlBr crystals grown by the Bridgeman-Stockbarger and travelling molten zone methods

    International Nuclear Information System (INIS)

    We have investigated at optimal temperature the X-ray detection characteristics of two TlBr crystals by the Traveling Molten Zone (TMZ) technique. The resistivities were typically 1.5x1010 Ω cm at room temperature, increasing to (1.1-1.7)x1012 Ω cm at -15 deg. C. In the temperature range -0 deg. C to -50 deg. C, both crystals exhibited mobility-lifetime products of ∼8x10-5 cm2V-1 and ∼1.5x10-5 cm2V-1, for electrons and holes respectively. From these crystals, two detectors were packaged and X-ray metrology carried out. For the best detector, the measured energy resolutions at an operating temperature of -15 deg. C and 500 V bias were 1.0 keV at 5.9 keV; 1.1 at 13.9 keV; 2.5 at 59.54 keV; 3.3 keV at 88 keV; 4 keV at 122 keV and 27.7 keV at 662 keV.A comparative analysis of the characteristics of detectors grown by TMZ to those grown by the Bridgeman-Stockbarger method is given

  16. Fabrication of pixelated CdTe and CdZnTe radiation detectors

    International Nuclear Information System (INIS)

    Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) are compound semiconductor characterized by wide semiconducting band gap and high photon stopping power due to its high atomic number and density. The mobility-life time product (μ t product) for holes in the materials is smaller than that for electrons. Hence, the effect of trapping losses is more pronounced on holes than on electrons. The trapping losses for holes limit achievable energy resolutions for planar detectors. In this study, pixelated CdTe detectors and pixelated CdZnTe detectors were fabricated and tested by 662 KeV gamma-rays of 137Cs at room temperature. Electrodes were formed on both sides of CdTe crystals and CdZnTe crystals by vacuum evaporation of gold. For purpose of comparison, a planar CdTe detector and a planar CdZnTe detector were evaluated. Since the pixelated CdTe detectors and the pixelated CdZnTe detectors operated as a single-polarity charge sensing device, the obtained energy resolutions were significantly higher than those for the planar detectors. Further improvement of energy resolutions of the detectors will be achieved by optimizing electrode structures. (M. Suetake)

  17. CdTe deposition by successive ionic layer adsorption and reaction (SILAR) technique onto ZnO nanowires

    International Nuclear Information System (INIS)

    In this study is reported CdTe deposition by Successive Ionic Layer Adsorption and reaction (SILAR) at room temperature onto ZnO nanowires (NWs). The as-deposited CdTe layer exhibits poor crystalline quality and not well defined optical transition which is probably result of its amorphous nature. The implementation of an annealing step and chemical treatment by CdCl2 to the classical SILAR technique improved significantly the CdTe film quality. The XRD analysis showed that the as treated layers are crystallized in the cubic zinc blende structure. The full coverage of ZnO nanowires and thickness of the CdTe shell, composed of small crystallites, was confirmed by STEM and TEM analysis. The layer thickness could be controlled by the number of SILAR cycles. The sharper optical transitions for the annealed and CdCl2 treated heterostructures additionally proves the enhancement of the layer crystalline quality. For comparison CdTe was also deposited by close space sublimation (CSS) method onto ZnO nanowires. It is shown that the SILAR deposited CdTe exhibits equal crystalline and optical properties to that prepared by CSS. These results demonstrate that SILAR technique is more suitable for conformal thin film deposition on nanostructures. CdTe extremely thin film deposited by SILAR method onto ZnO nanowire. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Optical and scintillation properties of Dy{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} and undoped Y{sub 3}Al{sub 5}O{sub 12} crystals grown in reduction atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Seki, Mafuyu; Kurosawa, Shunsuke; Suzuki, Akira; Yamaji, Akihiro; Fujimoto, Yutaka; Wakahara, Shingo; Pejchal, Jan; Yokota, Yuui [Institute of Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); Kochurikhin, Vladimir V. [General Physics Institute, Vavilova St. 38, 119991 Moscow (Russian Federation); Yoshikawa, Akira [Institute of Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); New Industry Creation Hatchery Center, Tohoku University, 6-6-10 Aramaki, Aoba-ku, Sendai, Miyagi 980-8579 (Japan)

    2012-12-15

    Optical and scintillation properties of a 1.0-mol% Dy-doped yttrium aluminium garnet (YAG) grown under N{sub 2} atmosphere and undoped YAG crystals were investigated. Both crystals were grown by the Czochralski process. The one of the undoped YAG crystal was grown in an Ar + H{sub 2} (97:3) reducing atmosphere. Absorption peaks at 352 nm and 366 nm observed in 1.0-mol% Dy-doped YAG originated from 4f-4f transition of Dy{sup 3+}. In addition, the crystal showed sharp emission lines at near 482 nm and 584 nm under 352 nm UV and alpha-ray excitation. The light output of Dy-doped YAG was estimated to be approximately 20,000 photons/(5.5-MeV alpha ray, {sup 241}Am). The scintillation decay time constants for Dy-doped YAG crystal was around 400 ns and 40 ns. Undoped YAG crystals grown under Ar + H{sub 2}(97:3) atmosphere showed absorption and excitation peak at 370 nm. A 400-nm emission peak was observed under 370-nm excitation. The light output of the crystal was also estimated to be 50,000 photons/(5.5-MeV alpha ray). The scintillation decay time constants of the crystal were around 370 ns and 50 ns. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Synthesis, growth, structural, optical, luminescence, surface and HOMO LUMO analysis of 2-[2-(4-cholro-phenyl)-vinyl]-1-methylquinolinium naphthalene-2-sulfonate organic single crystals grown by a slow evaporation technique

    Science.gov (United States)

    Karthigha, S.; Kalainathan, S.; Maheswara Rao, Kunda Uma; Hamada, Fumio; Yamada, Manabu; Kondo, Yoshihiko

    2016-02-01

    Single crystals of 2-[2-(4-cholro-phenyl)-vinyl]-1-methylquinolinium naphthalene-2-sulfonate (4CLNS) were grown by a slow evaporation technique. The formation of molecule was confirmed from 1H NMR and FTIR analysis. The confirmation of crystal structure was done by single crystal XRD and atomic packing of grown crystal was identified. The grown single crystal crystallized in triclinic structure with centrosymmetric space group P-1. The crystalline nature of the synthesised material was recorded by powder XRD. The optical absorption properties of the grown crystals were analyzed by UV-vis spectral studies. The thermal behaviour of the title material has been studied by TG/DTA analysis which revealed the stability of the compound till its melting point 276.7 °C. The third order nonlinear optical property of 4CLNS was investigated in detail by Z scan technique and it confirms that the title crystal is suitable for photonic devices and NLO optical applications. Emissions at 519 nm in green region of the EM spectrum were found by photoluminescence studies. The charge transfer occurring within the molecule is explained by the calculated HOMO and LUMO energies.

  20. Improved structural properties and crystal coherence of superconducting NdBa2Cu3O7-δ films grown by pulsed laser ablation

    Science.gov (United States)

    Abrecht, M.; Ariosa, D.; Schmauder, T.; Saleh, S. A.; Rast, S.; Pavuna, D.

    2000-11-01

    We report on improved structural, crystallographic and electrical properties of epitaxial NdBa2Cu3O7-δ (NBCO) films grown on SrTiO3 by `off-axis' pulsed laser deposition (PLD). Transport and XRD studies show that the c-axis-oriented epitaxial films, with critical temperatures of 90-92 K, are mono phase and single-crystalline. Furthermore, very smooth, almost outgrowth-free surfaces and crystal coherences of up to 0.8 µm (to our knowledge the best value ever reported for high-Tc films) were obtained.

  1. Metal-Semiconductor Field-Effect Transistors Fabricated Using DVT Grown n-MoSe2 Crystals With Cu-Schottky Gates

    Directory of Open Access Journals (Sweden)

    C.K. Sumesh

    2011-01-01

    Full Text Available Metal-semiconductor field-effect transistors (MESFETs based on DVT grown MoSe2 crystals and Cu Schottky gate have been fabricated and studied. When Schottky gate voltage (Vgs changes from 0 to 10 V, the source-drain current (Ids increases exponentially with Vgs and the conductance shows a drastic increase with positive Vgs. The fabricated n-MoSe2 MESFET have a saturated current level of about 100 mA and maximum transconductance of about 53 mA/V. Their results suggest a way of fabricating MESFETs from layered metal dichalcogenide semiconducting materials.

  2. Characterization of CdTe substrates and MOCVD Cd 1- xZn xTe epilayers by Raman, photoluminescence and X-ray diffraction techniques

    Science.gov (United States)

    Levy, M.; Amir, N.; Khanin, E.; Muranevich, A.; Nemirovsky, Y.; Beserman, R.

    1998-05-01

    CdTe substrates and the quality of the Cd 1- xZn xTe ( x⩽0.1) epilayers grown by metalorganic chemical vapor deposition (MOCVD) on CdTe substrates, are characterized by Raman scattering and photoluminescence (PL) as well as by X-ray double-crystal rocking curve (DCRC). At a low temperature the intensity of LO phonon is enhanced wherever there is a structural defect. The defect-induced enhancement is due to a large momentum transfer which enhances the intraband Frolich interaction. In addition, the bound exciton peak intensity measured by PL decreases wherever the LO phonon scattering efficiency increases confirming that the defect is the origin of the above Raman enhancement. The quantitative measure of the structural perfection is related to the ratio between the defect band and excitonic peaks in the PL spectra, and correlates with the X-ray full-width at half-maximum (FWHM) of the layer peak. It is shown that in addition to these parameters, the FWHM of the PL defect band is a useful parameter to determine the quality of the epilayer, and a good correlation is obtained between the different parameters. The effect of growth parameters such as zinc partial pressure in the reactor during growth and the reactor design are studied. The results indicate that crystalline imperfection is caused by lattice mismatch between the CdTe substrate and the CdZnTe epilayer and by the nonuniformity of the zinc composition throughout the layers. The quality of the layers is independent of the reactor volume.

  3. Patterning thick diffused junctions on CdTe

    CERN Document Server

    Kalliopuska, Juha; Sipilä, Heikki; Andersson, Hans; Vähänen, Sami; Eränen, Simo; Tlustos, Lukas

    2009-01-01

    Dividing the detector crystal into discrete pixels enables making an imaging detector, in which the charge collected by each pixel can be read separately. Even if the detector is not meant for imaging, patterns on the crystal surface may be used as guard structures that control and limit the flow of charges in the crystal. This has been exceedingly hard for the detector crystals having thick diffused layers. The paper reports a patterning method of the thick diffused junctions on CdTe. The patterning method of In-diffused pn-junction on CdTe chip is demonstrated by using a diamond blade. The patterning is done by removing material from the pn-junction side of the chip, so that the trenches penetrate the diffused layer. As the trenches extend deeper into the bulk than the junction, the regions separated by the trench are electrically isolated. Electrical characterization results are reported for the strips separated by trenches with various depths. The strip isolation is clearly seen in both measured leakage c...

  4. Second Harmonic Generation in CdTe Plate by Free Electron Laser

    Science.gov (United States)

    Yamauchi, Toshihiko; Kikuzawa, Nobuhiro; Minehara, Eisuke; Nagai, Ryoji; Nishimori, Nobuyuki; Sawamura, Masaru; Hajima, Ryoichi; Shizuma, Toshiyuki; Hayakawa, Takehito

    2000-10-01

    The second harmonic generation (SHG) signal converted from the 22 μm input wavelength of free electron laser (FEL) is observed using a non-birefringent CdTe crystal. The conversion efficiency of SHG is experimentally obtained to be ˜3× 10-5%/(MWcm-2).

  5. Second harmonic generation in CdTe plate by free electron laser

    Energy Technology Data Exchange (ETDEWEB)

    Yamauchi, Toshihiko; Kikuzawa, Nobuhiro; Minehara, Eisuke; Nagai, Ryoji; Nishimori, Nobuyuki; Sawamura, Masaru; Hajima, Ryoichi; Shizuma, Toshiyuki; Hayakawa, Takehito [Division of Advanced Photon Research, Japan Atomic Energy Research Institute, Tokai, Ibaraki (Japan)

    2000-10-01

    The second harmonic generation (SHG) signal converted from the 22 {mu}m input wavelength of free electron laser (FEL) is observed using a non-birefringent CdTe crystal. The conversion efficiency of SHG is experimentally obtained to be {approx}3 x 10{sup -5}% (MWcm{sup -2}). (author)

  6. Raman tensor and domain structure study of single-crystal-like epitaxial films of CaCu3Ti4O12 grown by pulsed laser deposition

    Science.gov (United States)

    Ahlawat, Anju; Mishra, Dileep K.; Sathe, V. G.; Kumar, Ravi; Sharma, T. K.

    2013-01-01

    The local domain structure of a strain free, 150 nm thick, epitaxially grown single crystalline thin film of CaCu3Ti4O12 is probed by polarized Raman spectroscopy. The polarization dependence of the Raman intensities of the observed bands as a function of varying angle between the domain axes and the polarization vector of the scattered laser photon is measured. Theoretical formulations involving the Raman tensor are presented, which enable determination of the domain structure from the observed polarized Raman spectra, and a single-crystal-like domain structure is found. The Raman tensor elements and domain orientation direction were determined by fitting the observed Raman intensities with theoretical calculations and by carrying out Raman mapping of the film. Our data show an absence of twin domain structure and twin domain boundaries in the single-crystal-like epitaxial thin films of CaCu3Ti4O12.

  7. Preparation of Ag Schottky contacts on n-type GaN bulk crystals grown in nitrogen rich atmosphere by the hydride vapor phase epitaxy technique

    Energy Technology Data Exchange (ETDEWEB)

    Stübner, R., E-mail: ronald.stuebner@physik.tu-dresden.de; Kolkovsky, Vl.; Weber, J. [Technische Universität Dresden, 01062 Dresden (Germany); Leibiger, Gunnar; Habel, Frank [Freiberger Compound Materials GmbH, 09599 Freiberg (Germany)

    2014-10-14

    Electrical properties of Schottky contacts on n-type GaN grown in nitrogen rich atmosphere with different N/Ga ratios by hydride vapor phase epitaxy were investigated. We show that tunneling of electrons from the conduction band of GaN to the metal is dominant in our samples. The quality of Schottky contacts does not only depend on surface preparation but also on the growth conditions of the crystals. Schottky contacts on these crystals show an increasing deterioration when higher N/Ga growth ratios are used. We correlate our results with the presence of negatively charged gallium vacancies in the samples. These charges compensate the positively charged donors and lead to a significant increase in series resistance.

  8. Conductive-radiative model for predicting the shape of HgI2 crystal grown in the LTVG furnace

    Science.gov (United States)

    Roux, A.; Fedoseyev, A.; Roux, Bernard

    1992-08-01

    The modeling of heat exchanges in a sealed ampoule in the LTVG (Low Temperature Vapor Growth) furnace is focused upon, in order to compute temperature fields and control the growth of HgI2 crystals from vapor phase at low temperatures. A coupled conductive radiative model was used to determine the shape of the source and the crystal at different equilibrium states (that is, without growth rate). The model involves conductivity anisotropy in the crystal and radiative exchanges between grey and diffuse surfaces (source and crystal interfaces, pyrex walls), which are considered as opaque. Internal buoyancy effect is not taken into account as the pressure inside the ampoule is very small. The source temperature is fixed. For different undercoolings, that is, for different cold finger temperatures, the 'equilibrium' isotherm between the source/gas and crystal/gas interfaces was numerically obtained. This 'equilibrium' isotherm, which is associated with the stop of the growing process, gives a crystal shape. This shape is compared with experimental results given by the ETH-Zurich group. The model would permit a better understanding and control of the future HgI2 crystal growth experiment. The computations are performed using a finite element package (FIDAP).

  9. Improvement of the energy resolution of CdTe detectors by pulse height correction from waveform

    CERN Document Server

    Kikawa, T; Hiraki, T; Nakaya, T

    2011-01-01

    Semiconductor detectors made of CdTe crystal have high gamma-ray detection efficiency and are usable at room temperature. However, the energy resolution of CdTe detectors for MeV gamma-rays is rather poor because of the significant hole trapping effect. We have developed a method to improve the energy resolution by correcting the pulse height using the waveform of the signal and achieved 2.0% (FWHM) energy resolution for 662keV gamma-rays. Best energy resolution was achieved at temperatures between -10 degrees C and 0 degrees C.

  10. Simulation of active-edge pixelated CdTe radiation detectors

    OpenAIRE

    Duarte, DD; Lipp, JD; Schneider, A.; Seller, P; Veale, MC; Wilson, MD; Baker, MA; Sellin, PJ

    2016-01-01

    The edge surfaces of single crystal CdTe play an important role in the electronic properties and performance of this material as an X-ray and γ-ray radiation detector. Edge effects have previously been reported to reduce the spectroscopic performance of the edge pixels in pixelated CdTe radiation detectors without guard bands. A novel Technology Computer Aided Design (TCAD) model based on experimental data has been developed to investigate these effects. The results presented in this paper sh...

  11. Improvement of the energy resolution of CdTe detectors by pulse height correction from waveform

    OpenAIRE

    Kikawa, T.; Ichikawa, A. K.; Hiraki, T.; Nakaya, T.(Kyoto University, Department of Physics, Kyoto, Japan)

    2011-01-01

    Semiconductor detectors made of CdTe crystal have high gamma-ray detection efficiency and are usable at room temperature. However, the energy resolution of CdTe detectors for MeV gamma-rays is rather poor because of the significant hole trapping effect. We have developed a method to improve the energy resolution by correcting the pulse height using the waveform of the signal and achieved 2.0% (FWHM) energy resolution for 662keV gamma-rays. Best energy resolution was achieved at temperatures b...

  12. Negative Thermal Expansion in Zincblende Structure: an EXAFS study of CdTe

    OpenAIRE

    Abd El All, Naglaa Fathy

    2010-01-01

    To gain a deeper insight on the local origin of NTE in zincblende crystals, EXAFS measurements have been performed on CdTe, which has NTE properties intermediate between Ge and CuCl. In this work an accurate evaluation of the bond thermal expansion, parallel and perpendicular MSRDs and distribution asymmetry of the first shell of CdTe has been made, obtaining a good agreement between two different procedures of the data analysis (i) ratio method (ii) FEFF6-FEFFIT method. The values of the rel...

  13. Simulation of active-edge pixelated CdTe radiation detectors

    Science.gov (United States)

    Duarte, D. D.; Lipp, J. D.; Schneider, A.; Seller, P.; Veale, M. C.; Wilson, M. D.; Baker, M. A.; Sellin, P. J.

    2016-01-01

    The edge surfaces of single crystal CdTe play an important role in the electronic properties and performance of this material as an X-ray and γ-ray radiation detector. Edge effects have previously been reported to reduce the spectroscopic performance of the edge pixels in pixelated CdTe radiation detectors without guard bands. A novel Technology Computer Aided Design (TCAD) model based on experimental data has been developed to investigate these effects. The results presented in this paper show how localized low resistivity surfaces modify the internal electric field of CdTe creating potential wells. These result in a reduction of charge collection efficiency of the edge pixels, which compares well with experimental data.

  14. Performance of a new Schottky CdTe detector for hard x-ray spectroscopy

    Science.gov (United States)

    Takahashi, Tadayuki; Hirose, K.; Matsumoto, Chiho; Takizawa, Kyoko; Ohno, Ryouichi; Ozaki, Tsutomu; Mori, Kunishiro; Tomita, Yasuhiro

    1998-07-01

    We report a significant improvement of the spectral properties of a cadmium telluride (CdTe) detector. With the use of a high quality CdTe crystal, we formed a high Schottky barrier for the holes on a CdTe surface using a low work-function metal, indium. For a 2 X 2 mm(superscript 2) detector with a thickness of 0.5 mm the leakage current was measured to be 0.7 nA at room temperature (20 degree(s)C) and 10 pA at -20 degree(s)C for a 400 V bias voltage. The low-leakage current of the detector allows us to operate the detector at a higher bias voltage than previous CdTe detectors. The improved charge collection efficiency and the low-leakage current leads to an energy resolution of 1.1 - 2.5 keV FWHM in the energy range 2 keV to 150 keV at 20 degree(s)C without charge loss correction electronics. We confirmed that once a high electric field of several kV/cm is applied, the Schottky CdTe has a very good energy resolution as well as sufficient stability to be used for practical applications.

  15. Optical and electrical properties of hydrothermally prepared CdTe nanowires

    Science.gov (United States)

    Hadia, N. M. A.; Awad, M. A.; Mohamed, S. H.; Ibrahim, E. M. M.

    2016-10-01

    The hydrothermal process was used to synthesize CdTe nanowires (NWs). Various analytical techniques were used to characterize the obtained NWs. The wire diameters were in the range 35-60 nm, and the lengths were >5 μm. The CdTe NWs had zinc-blende crystal structure. The NWs had high uniformity and high yield. FTIR analysis revealed the presence of the characteristic vibrational spectra of oxygen and hydrogen bounded to Cd and Te in CdTe NWs. The optical band gap value was 2.09 eV. The CdTe NWs showed a strong red emission band centered around 620.3 nm. The conductivity measurements were carried out in the temperature range 300-500 K and in air atmosphere. Two types of conduction mechanisms were observed with activation energies of 0.27 and 0.17 eV at high and low temperature regions, respectively. These results validate the potential of CdTe NWs for optoelectronic applications.

  16. Synthesis of CdTe thin films on flexible metal foil by electrodeposition

    Science.gov (United States)

    Luo, H.; Ma, L. G.; Xie, W. M.; Wei, Z. L.; Gao, K. G.; Zhang, F. M.; Wu, X. S.

    2016-04-01

    CdTe thin films have been deposited onto the Mo foil from aqueous acidic bath via electrodeposition method with water-soluble Na2TeO3 instead of the usually used TeO2. X-ray diffraction studies indicate that the CdTe thin films are crystallized in zinc-blende symmetry. The effect of tellurite concentration on the morphology of the deposited thin film is investigated. In such case, the Cd:Te molar ratios in the films are both stoichiometric at different tellurite concentrations. In addition, the reduction in tellurite concentration leads to the porous thin film and weakens the crystallinity of thin film. The island growth model is used to interpret the growth mechanism of CdTe. The bandgap of the CdTe thin films is assigned to be 1.49 eV from the UV-Vis spectroscopy measurement, which is considered to serve as a promising candidate for the heterojunction solar cells.

  17. Synthesis of CdTe thin films on flexible metal foil by electrodeposition

    Energy Technology Data Exchange (ETDEWEB)

    Luo, H.; Ma, L.G.; Xie, W.M.; Wei, Z.L.; Gao, K.G.; Zhang, F.M.; Wu, X.S. [Nanjing University, Collaborative Innovation Center of Advanced Microstructures, Lab of Solid State Microstructures, School of Physics, Nanjing (China)

    2016-04-15

    CdTe thin films have been deposited onto the Mo foil from aqueous acidic bath via electrodeposition method with water-soluble Na{sub 2}TeO{sub 3} instead of the usually used TeO{sub 2}. X-ray diffraction studies indicate that the CdTe thin films are crystallized in zinc-blende symmetry. The effect of tellurite concentration on the morphology of the deposited thin film is investigated. In such case, the Cd:Te molar ratios in the films are both stoichiometric at different tellurite concentrations. In addition, the reduction in tellurite concentration leads to the porous thin film and weakens the crystallinity of thin film. The island growth model is used to interpret the growth mechanism of CdTe. The bandgap of the CdTe thin films is assigned to be 1.49 eV from the UV-Vis spectroscopy measurement, which is considered to serve as a promising candidate for the heterojunction solar cells. (orig.)

  18. Process design and simulation for optimizing the oxygen concentration in Czochralski-grown single-crystal silicon

    International Nuclear Information System (INIS)

    The highest-concentration impurity in a single-crystal silicon ingot is oxygen, which infiltrates the ingot during growth stage. This oxygen adversely affects the wafer is quality. This study was aimed at finding an optimal design for the Czochralski (Cz) process to enable high-quality and low cost (by reducing power consumption) wafer production by controlling the oxygen concentration in the silicon ingots. In the Cz process, the characteristics of silicon ingots during crystallization are greatly influenced by the design and the configuration of the hot zone, and by crystallization rate. In order to identify process conditions for obtaining an optimal oxygen concentration of 11 - 13 ppma (required for industrial-grade ingots), designed two shield shapes for the hot zone. Furthermore, oxygen concentrations corresponding to these two shapes were compared by evaluating each shape at five different production speeds. In addition, simulations were performed to identify the optimal shield design for industrial applications.

  19. High Efficient Laser Operation of the Nd:KGd(WO4)2 Crystal Grown by Flux Method

    Institute of Scientific and Technical Information of China (English)

    LUO Zun-Du; CHEN Xue-Yuan; TU Chao-Yang; J. J. Romero; J. Garcia Sole

    2000-01-01

    The laser performance of Neodymium-doped potassium gadolinium tungstate (Nd:KGd(WO4)2) crystal was studied by using Ti:Sapphire laser as the pump source. The maximum optical-to-optical efficiencies for the 1.067 and 1.3 μm laser outputs were measured to be 60% and 32.3%, respectively. The internal loss coefficient of the crystal for 1.067 μm laser was estimated to be as low as 0.004 cm-1. The oscillation thresholds at 1.067 and 1.3 μm for different output transmittances are also given.

  20. Epitaxial growth of CdTe oriented thin films, infrared characterization and possible applications to photo-voltaic cells

    OpenAIRE

    Gerbaux, X.; Pianelli, A.; Hadni, A.; Jeanniard, C.; Strimer, P.

    1980-01-01

    The growth of CdTe oriented thin films by the ENSH method - i.e. Epitaxial Nucleation in Sub-microscopic Holes of an intermediate layer closely applied on a bulk single crystal — has been recently described. The CdTe films are generally difficult to detach from the bulk crystal. However free films are needed to study the infrared transmission in the spectral region of high absorption. To get them, the vitreous or amorphous thin intermediate layers are substituted by quite soluble an oriented ...

  1. P-I-N CdTe gamma-ray detectors by liquid phase epitaxy (LPE)

    International Nuclear Information System (INIS)

    A new device concept of CdTe gamma ray detectors has been demonstrated by using p+(HgCdTe)-n(CdTe)-n+(HgCdTe) diode structures. Both p+ and n+-type Hg/sub 0.25/Cd/sub 0.75/Te epilayers were grown by the liquid phase epitaxy (LPE) technique on semi-insulating CdTe sensor elements. The LPE-grown P-I-N structure offers potential advantages for p-n junction formation and ohmic contact over standard ion-implanted diodes or Schottky barrier devices. Detectors with active areas of 2 mm2 were fabricated. Resolutions of 10 keV were obtained for the 122 keV gamma peak of Co57 at room temperature

  2. Laser MBE-grown yttrium iron garnet films on GaN: characterization of the crystal structure and magnetic properties

    Science.gov (United States)

    Kaveev, A. K.; Bursian, V. E.; Gastev, S. V.; Krichevtsov, B. B.; Suturin, S. M.; Volkov, M. P.; Sokolov, N. S.

    2016-07-01

    Yttrium iron garnet (YIG) films were grown on GaN substrates using the laser molecular beam epitaxy method. X-ray diffraction data showed polycrystalline YIG layers without additional structural modifications. The magnetic properties of the YIG films were studied at room temperature with the aid of a vibration sample magnetometer, the magneto-optical Kerr effect and ferromagnetic resonance methods. ‘Easy-plane’-type magnetic anisotropy was found in the films. The gyromagnetic ratio and 4 πMS value were calculated.

  3. Photoluminescence characteristics of ZnTe bulk crystal and ZnTe epilayer grown on GaAs substrate by MOVPE

    Science.gov (United States)

    Lü, Hai-Yan; Mu, Qi; Zhang, Lei; Lü, Yuan-Jie; Ji, Zi-Wu; Feng, Zhi-Hong; Xu, Xian-Gang; Guo, Qi-Xin

    2015-12-01

    Excitation power and temperature-dependent photoluminescence (PL) spectra of the ZnTe epilayer grown on (100) GaAs substrate and ZnTe bulk crystal are investigated. The measurement results show that both the structures are of good structural quality due to their sharp bound excitonic emissions and absence of the deep level structural defect-related emissions. Furthermore, in contrast to the ZnTe bulk crystal, although excitonic emissions for the ZnTe epilayer are somewhat weak, perhaps due to As atoms diffusing from the GaAs substrate into the ZnTe epilayer and/or because of the strain-induced degradation of the crystalline quality of the ZnTe epilayer, neither the donor-acceptor pair (DAP) nor conduction band-acceptor (e-A) emissions are observed in the ZnTe epilayer. This indicates that by further optimizing the growth process it is possible to obtain a high-crystalline quality ZnTe heteroepitaxial layer that is comparable to the ZnTe bulk crystal. Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20120131110006), the Key Science and Technology Program of Shandong Province, China (Grant No. 2013GGX10221), the Key Laboratory of Functional Crystal Materials and Device (Shandong University, Ministry of Education), China (Grant No. JG1401), the National Natural Science Foundation of China (Grant No. 61306113), the Major Research Plan of the National Natural Science Foundation of China (Grant No. 91433112), and the Partnership Project for Fundamental Technology Researches of the Ministry of Education, Culture, Sports, Science and Technology, Japan.

  4. Chemical beam epitaxy of CdTe, HgTe, and HgCdTe

    Energy Technology Data Exchange (ETDEWEB)

    Benz, R.G. II; Wagner, B.K.; Rajavel, D.; Summers, C.J. (Physical Sciences Lab., Georgia Tech Research Inst., Atlanta, GA (USA))

    1991-05-01

    A chemical beam epitaxy (CBE) system has been implemented for the growth of CdTe, HgTe, and their alloys. The system is briefly described. Results on the cracking of the organometallic source gases are presented. Epitaxial layers have been grown from gas sources of diethylcadmium, diisopropyltelluride and Hg vapor, as well as conventional solid sources. Optical and electrical properties are reported, demonstrating the potential of CBE for growing high quality solar cell and infrared detector material. (orig.).

  5. Anisotropy of ionic conduction in single-crystal Li x La(1- x )/3NbO3 solid electrolyte grown by directional solidification

    Science.gov (United States)

    Fujiwara, Yasuyuki; Taishi, Toshinori; Hoshikawa, Keigo; Kohama, Keiichi; Iba, Hideki

    2016-09-01

    The anisotropy of ionic conduction in a solid electrolyte (Li x La(1- x )/3NbO3) was experimentally confirmed for the first time. Ionic conduction measurements were carried out on the (100), (010), (001), (110), (111), and (112) planes of single-crystal ingots of Li x La(1- x )/3NbO3 grown by directional solidification. We found that the ionic conductivity in Li x La(1- x )/3NbO3 with x = 0.08 was 3.6 × 10-4 S cm-1 in the [100] and [010] directions, approximately 10 times higher than that in the [001] direction. Such anisotropy of the ionic conduction is discussed with respect to the characteristic layered structure of Li x La(1- x )/3NbO3.

  6. On linear resistivity from ~1 to 103 K in Sr2RuO4 - δ single crystals grown by flux technique

    Science.gov (United States)

    Berger, H.; Forró, L.; Pavuna, D.

    1998-03-01

    We report transport measurements on single crystals of Sr2RuO4 - δ, grown by the flux technique. The temperature dependence of the Hall coefficient is similar to the one measured in cuprates, and the linear resistivity persists up to ~1000 K, while the superconductivity remains confined below 1 K. This suggests that the linear temperature dependence of resistivity is not an exclusive signature of the anomalous normal state of high-Tc cuprates but rather of layered oxides in general, especially single-layer perovskites, possibly independently of the magnitude of the superconducting temperature. In addition, such Sr2RuO4 - δ may be used as a broad-range thermometer.

  7. X-ray crystal truncation rod scattering from MBE grown (CaF 2-SrF 2)/Si(111) superlattices

    Science.gov (United States)

    Harada, J.; Itoh, Y.; Shimura, T.; Takahashi, I.; Alvarez, J. C.; Sokolov, N. S.

    1994-01-01

    Flouride CaF 2-SrF 2 superlattices (SLs) grown by molecular beam epitaxy have been studied by means of X-ray diffractometry for the first time. The diffraction patterns showed reasonably good crystalline quality of the SLs and a type-B epitaxial relation to the Si(111) substrate. From the analysis of the crystal truncation rod (CTR) profiles, based on the pseudomorphic model, it was obtained that despite the same high temperature (770°C) of formation of the CaF 2/Si(111) interface its structure depended on the growth temperature of the SLs. The shape of the CTR profiles confirmed the existence of the superlattice which consists of one or two monolayer thick SrF 2 layers. Some CaF 2/SrF 2-interface roughness was noticeable.

  8. Optical, scintillation properties and defect study of Gd2Si2O7:Ce single crystal grown by floating zone method

    Science.gov (United States)

    Feng, He; Xu, Wusheng; Ren, Guohao; Yang, Qiuhong; Xie, Jianjun; Xu, Jun; Xu, Jiayue

    2013-02-01

    Single crystal of Gd2Si2O7:Ce (GPS) presenting attractive scintillation performance was grown by the floating zone method. The vacuum ultra-violet (VUV) excitation and emission, ultra-violet (UV) excitation and emission spectra and fluorescent decay time at 77 K and RT were measured and discussed. Relative energy levels of 5d sublevels of Ce3+ in GPS:Ce are detected by the VUV excitation spectrum. The UV emission curve of GPS:1%Ce peaks around 382 nm at 77 K and moves towards longer wavelength direction as temperature increases. Thermally stimulated luminescence (TSL) was employed to investigate the defects in GPS:1%Ce. Energy depths of two traps detected in GPS:1%Ce are 0.64 and 1.00 eV.

  9. Characteristics of TlBr single crystals grown using the vertical Bridgman-Stockbarger method for semiconductor-based radiation detector applications

    Directory of Open Access Journals (Sweden)

    Jin Kim Dong

    2016-06-01

    Full Text Available TlBr single crystals grown using the vertical Bridgman-Stockbarger method were characterized for semiconductor based radiation detector applications. It has been shown that the vertical Bridgman-Stockbarger method is effective to grow high-quality single crystalline ingots of TlBr. The TlBr single crystalline sample, which was located 6 cm from the tip of the ingot, exhibited lower impurity concentration, higher crystalline quality, high enough bandgap (>2.7 eV, and higher resistivity (2.5 × 1011 Ω·cm which enables using the fabricated samples from the middle part of the TlBr ingot for fabricating high performance semiconductor radiation detectors.

  10. 37 W 888-nm-pumped grown-together composite crystal YVO4/Nd:YVO4/YVO4 oscillator at 1342 nm

    Science.gov (United States)

    Zhang, X.-F.; Li, F.-Q.; Zong, N.; Le, X.-Y.; Cui, D.-F.; Xu, Z.-Y.

    2011-07-01

    We report on a continuous-wave Nd:YVO4 oscillator at 1342 nm based on the combination of a grown-together composite crystal YVO4/Nd:YVO4/YVO4 and the 888 nm diode-laser direct pumping for the first time. At the absorbed pump power of 102 W, a maximum average output power of 37.2 W at 1342 nm was obtained, corresponding to an optical-optical conversion efficiency of 36.5% and a high slope efficiency of 63.0%, respectively. To the best of our knowledge, this is the highest output power ever obtained for a 1342 nm Nd:YVO4 oscillator.

  11. Analysis of oxygen shell splitting in hydrothermally grown single crystal ThO{sub 2}(200)

    Energy Technology Data Exchange (ETDEWEB)

    Kelly, T.D.; Petrosky, J.C.; McClory, J.W. [Department of Engineering Physics, Air Force Institute of Technology, 2950 Hobson Way, WPAFB, OH 45433 (United States); Mann, J.M. [Air Force Research Laboratory, Sensors Directorate, Wright-Patterson AFB, OH 45433 (United States); Kolis, J.W. [Department of Chemistry and Center for Optical Materials Science and Engineering Technologies (COMSET), Clemson University, Clemson, SC 29634-0973 (United States)

    2015-11-15

    Single crystals of ThO{sub 2} have been synthesized using hydrothermal growth and studied using the X-ray absorption fine structure (XAFS) technique. The extended X-ray absorption fine structure (EXAFS) has been extracted from the XAFS and analyzed using a novel, computational Latin hypercube sampling method. The methodology not only confirms the expected space group and crystal structure, it also identifies the origin of a previously reported split O shell. Since EXAFS is a local order analysis technique, the O shell splitting is identified as an O atom occupying an interstitial site. This result is significant for examining O{sup 2-} transport in a ThO{sub 2} matrix and corroborating research indicating partial Th 5f occupancy that is similar to hyper-stoichiometric UO{sub 2+x} compounds. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. CdTe solar cells with open-circuit voltage breaking the 1 V barrier

    Science.gov (United States)

    Burst, J. M.; Duenow, J. N.; Albin, D. S.; Colegrove, E.; Reese, M. O.; Aguiar, J. A.; Jiang, C.-S.; Patel, M. K.; Al-Jassim, M. M.; Kuciauskas, D.; Swain, S.; Ablekim, T.; Lynn, K. G.; Metzger, W. K.

    2016-03-01

    CdTe solar cells have the potential to undercut the costs of electricity generated by other technologies, if the open-circuit voltage can be increased beyond 1 V without significant decreases in current. However, in the past decades, the open-circuit voltage has stagnated at around 800-900 mV. This is lower than in GaAs solar cells, even though GaAs has a smaller bandgap; this is because it is more difficult to achieve simultaneously high hole density and lifetime in II-VI materials than in III-V materials. Here, by doping the CdTe with a Group V element, we report lifetimes in single-crystal CdTe that are nearly radiatively limited and comparable to those in GaAs over a hole density range relevant for solar applications. Furthermore, the deposition on CdTe of nanocrystalline CdS layers that form non-ideal heterointerfaces with 10% lattice mismatch impart no damage to the CdTe surface and show excellent junction transport properties. These results enable the fabrication of CdTe solar cells with open-circuit voltage greater than 1 V.

  13. Characterization of vertical Au/β-Ga2O3 single-crystal Schottky photodiodes with MBE-grown high-resistivity epitaxial layer

    Science.gov (United States)

    X, Z. Liu; C, Yue; C, T. Xia; W, L. Zhang

    2016-01-01

    High-resistivity β-Ga2O3 thin films were grown on Si-doped n-type conductive β-Ga2O3 single crystals by molecular beam epitaxy (MBE). Vertical-type Schottky diodes were fabricated, and the electrical properties of the Schottky diodes were studied in this letter. The ideality factor and the series resistance of the Schottky diodes were estimated to be about 1.4 and 4.6× 106 Ω. The ionized donor concentration and the spreading voltage in the Schottky diodes region are about 4 × 1018 cm-3 and 7.6 V, respectively. The ultra-violet (UV) photo-sensitivity of the Schottky diodes was demonstrated by a low-pressure mercury lamp illumination. A photoresponsivity of 1.8 A/W and an external quantum efficiency of 8.7 × 102% were observed at forward bias voltage of 3.8 V, the proper driving voltage of read-out integrated circuit for UV camera. The gain of the Schottky diode was attributed to the existence of a potential barrier in the i-n junction between the MBE-grown highly resistive β-Ga2O3 thin films and the n-type conductive β-Ga2O3 single-crystal substrate. Project supported by the National Nature Science Foundation of China (Grant No. 61223002) the Science and Technology Commission of Shanghai Municipality, China (Grant No. 13111103700), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 2012018530003).

  14. Behaviour of oxygen-related thermal donors in Ge crystals Czochralski-grown from the melt covered fully by B{sub 2}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Taishi, Toshinori [Institute of Carbon Science and Technology, Shinshu University, Wakasato, Nagano 380-8553 (Japan); Hashimoto, Yoshio [Faculty of Engineering, Shinshu University, Wakasato, Nagano 380-8553 (Japan); Ise, Hideaki; Murao, Yu; Ohsawa, Takayuki; Tokumoto, Yuki; Ohno, Yutaka; Yonenaga, Ichiro, E-mail: taishi@shinshu-u.ac.jp [Institute for Materials Research, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577 (Japan)

    2011-02-01

    Oxygen-related thermal donors (OTDs) in oxygen-enriched Czochralski Ge crystals grown from a melt fully covered by B{sub 2}O{sub 3} liquid were investigated by infrared spectroscopy. Interstitially dissolved oxygen concentrations [O{sub i}] and thermal donor concentrations N{sub TD} in Ge specimens annealed at 350 deg. C for 64h and at 550 deg. C for 1h, followed by subsequent fast cooling to room temperature, were measured in comparison with those in as-grown Ge. By annealing at 350 deg. C, an absorption peak developed at 780 cm{sup -1} and the peak height at 855 cm{sup -1} related to [O{sub i}], decreased. The absorption coefficient at 780 cm{sup -1} showed the same correlation to the difference between the total concentration of oxygen atoms and the dissolved oxygen concentration in the annealed specimens. It was found that the number of oxygen atoms forming the OTD increases with increasing annealing time at 350 deg. C.

  15. Ta2O5单晶激光法生长及其介电性质研究%Growth and dielectric properties of Ta2O5 single crystals grown by laser heated pedestal growth technique

    Institute of Scientific and Technical Information of China (English)

    蒋毅坚; Ruyan Guo; A.S.Bhalla

    2008-01-01

    Ta2O5 single crystals have been grown by the laser heated pedestal growth (LHPG) technique up to several centimeters length with diameter of 1.1 mm. The crystal, characterized by X-ray diffraction, dielectric measurement, and thermal expansion analysis, has Htri-Wa2O5 symmetry. Dielectric permittivity, loss tangent along [001] and [110] direction were investigated over the temperature range from -180℃ to 100℃. Large dielectric anisotropy in 2O5 single crystal was observed. At room temperature, the dielectric permittivities (1 MHz) along [001] and [110] are 33.2 and 231.9, respectively. The reason of dielectric enhancement in Ta2O5 crystal grown by LHPG was also discussed.

  16. Characterization of Highly Efficient CdTe Thin Film Solar Cells by Low-Temperature Photoluminescence

    Science.gov (United States)

    Okamoto, Tamotsu; Matsuzaki, Yuichi; Amin, Nowshad; Yamada, Akira; Konagai, Makoto

    1998-07-01

    Highly efficient CdTe thin film solar cells prepared by close-spaced sublimation (CSS) method with a glass/ITO/CdS/CdTe/Cu-doped carbon/Ag structure were characterized by low-temperature photoluminescence (PL) measurement. A broad 1.42 eV band probably due to VCd Cl defect complexes appeared as a result of CdCl2 treatment. CdS/CdTe junction PL revealed that a CdSxTe1-x mixed crystal layer was formed at the CdS/CdTe interface region during the deposition of CdTe by CSS and that CdCl2 treatment promoted the formation of the mixed crystal layer. Furthermore, in the PL spectra of the heat-treated CdTe after screen printing of the Cu-doped carbon electrode, a neutral-acceptor bound exciton (ACu0, X) line at 1.590 eV was observed, suggesting that Cu atoms were incorporated into CdTe as effective acceptors after the heat treatment.

  17. Allyl- iso-propyltelluride, a new MOVPE precursor for CdTe, HgTe and (Hg,Cd)Te

    Science.gov (United States)

    Hails, Janet E.; Cole-Hamilton, David J.; Stevenson, John; Bell, William

    2000-06-01

    The use of allyl- iso-propyltelluride as the tellurium precursor for the growth of CdTe, HgTe and (Hg,Cd)Te by metal organic vapour-phase epitaxy has been investigated. It has proved to be an efficient source of tellurium with growth rates for HgTe and (Hg,Cd)Te of up to 10 μm h -1 at 300°C. The best CdTe was grown at 4.5 μm h -1 under Me 2Cd-rich conditions at 300°C in the presence of Hg vapour.

  18. Influence of Te doping on the dielectric and optical properties of InBi crystals grown by directional freezing

    Institute of Scientific and Technical Information of China (English)

    C.J. Ajayakumar; A.G. Kunjomana

    2014-01-01

    Stoichiometric pure and tellurium (Te) doped indium bismuthide (InBi) were grown using the directional freezing technique in a fabricated furnace. The X-ray diffraction profiles identified the crystallinity and phase composition. The surface topographical features were observed by scanning electron microscopy and atomic force microscopy. The energy dispersive analysis by X-rays was performed to identify the atomic proportion of elements. Studies on the temperature dependence of dielectric constant (ε), loss tangent (tanδ), and AC conductivity (σac) reveal the existence of a ferroelectric phase transition in the doped material at 403 K. When InBi is doped with tellurium (4.04 at%), a band gap of 0.20 eV can be achieved, and this is confirmed using Fourier transform infrared studies. The results thus show the conversion of semimetallic InBi to a semiconductor with the optical properties suitable for use in infrared detectors.

  19. Structural and photoluminescence studies on europium-doped lithium tetraborate (Eu:Li2B4O7) single crystal grown by microtube Czochralski (μT-Cz) technique

    Science.gov (United States)

    A, Kumaresh; R, Arun Kumar; N, Ravikumar; U, Madhusoodanan; B, S. Panigrahi; K, Marimuthu; M, Anuradha

    2016-05-01

    Rare earth europium (Eu3+)-doped lithium tetraborate (Eu:Li2B4O7) crystal is grown from its stoichiometric melt by microtube Czochralski pulling technique (μT-Cz) for the first time. The grown crystals are subjected to powder x-ray diffraction (PXRD) analysis which reveals the tetragonal crystal structure of the crystals. UV-vis-NIR spectral analysis is carried out to study the optical characteristics of the grown crystals. The crystal is transparent in the entire visible region, and the lower cutoff is observed to be at 304 nm. The existence of BO3 and BO4 bonding structure and the molecular associations are analyzed by Fourier transform infrared (FTIR) spectroscopy. The results of excitation and emission-photoluminescence spectra of europium ion incorporated in lithium tetraborate (LTB) single crystal reveal that the observations of peaks at 258, 297, and 318 nm in the excitation spectra and peaks at 579, 591, 597, 613, and 651 nm are observed in the emission spectra. The chromaticity coordinates are calculated from the emission spectra, and the emission intensity of the grown crystal is characterized through a CIE 1931 (Commission International d’Eclairage) color chromaticity diagram. Project supported by the Department of Science and Technology-Science and Engineering Research Board (Grant No. SR/S2/LOP-0012/2011), the Government of India for Awarding Major Research Project, the University Grants Commission-Department of Atomic Research-Consortium for Scientific Research (Grant No. CSR-KN/CSR-63/2014-2015/503), and the Kalpakkam and Indore, India.

  20. Luminescence Dynamics of Cr2+ in CdTe and Cd0.55Mn0.45Te

    Science.gov (United States)

    Bluiett, A.; Hommerich, U.; Seo, J. T.; Shah, R.; Trivedi, S. B.; Kutcher, S. W.; Chen, R. J.; Wang, C. C.; Zong, H.

    2001-04-01

    Cr^2+ in tetrahedrally coordinated CdTe and Cd_0.55Mn_0.45Te crystals are under investigation as potential host materials for tunable, mid-infrared (MIR) lasers. The small crystal field splitting of the free ion energy levels of Cr^2+ induces absorption (1900nm) and stokes shifted emission (2000nm-3000nm) bands in the MIR. Also, the relatively large ionic mass and tetrahedral environment of Cr^2+ in CdTe and Cd_0.55Mn_0.45Te have shown that the luminescence efficiency at room temperature is approximately 72100luminescence lifetime decreases rapidly, which suggest that the effects of nonradiative decay increases. The decay dynamics of Cr^2+ in CdTe and Cd_0.55Mn_0.45Te will be described with the model of Struck and Fonger for the non-radiative decay rate.

  1. Transport and magnetic properties of epitaxial LSMO thin films grown on MgO single-crystal substrates

    Energy Technology Data Exchange (ETDEWEB)

    StrbIk, V; Spankova, M; Benacka, S [Institute of Electrical Engineering, Slovak Academy of Sciences, 9 Dubravska cesta, 841 04 Bratislava (Slovakia); Reiffers, M; Kovac, J, E-mail: elekstrb@savba.s [Institute of Experimental Physics, Slovak Academy of Sciences, 47 Watsonova, 040 01 Kotice (Slovakia)

    2010-04-01

    Thin epitaxial La{sub 0.67}Sr{sub 0.33}MnO{sub 3} (LSMO) films were deposited on single crystal MgO substrates. The electrical transport and magnetic properties of the films in the temperature range 4 - 350 K were investigated and strong correlation between them was registered. Magnetoresistance up to 52 % at temperature T = 256 K and magnetic field B = 5 T was achieved. The results obtained indicate that LSMO films with such properties are suitable for application as 'barrier' layers in superconducting-ferromagnetic-superconducting heterostructures, but optimization of LSMO film thickness is needed.

  2. Investigation of induced recrystallization and stress in close-spaced sublimated and radio-frequency magnetron sputtered CdTe thin films

    Energy Technology Data Exchange (ETDEWEB)

    Moutinho, H.R.; Dhere, R.G.; Al-Jassim, M.M.; Levi, D.H.; Kazmerski, L.L. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States)

    1999-07-01

    We have induced recrystallization of small grain CdTe thin films deposited at low temperatures by close-spaced sublimation (CSS), using a standard CdCl{sub 2} annealing treatment. We also studied the changes in the physical properties of CdTe films deposited by radio-frequency magnetron sputtering after the same post-deposition processing. We demonstrated that the effects of CdCl{sub 2} on the physical properties of CdTe films are similar, and independent of the deposition method. The recrystallization process is linked directly to the grain size and stress in the films. These studies indicated the feasibility of using lower-temperature processes in fabricating efficient CSS CdTe solar cells. We believe that, after the optimization of the parameters of the chemical treatment, these films can attain a quality similar to CSS films grown using current standard conditions. {copyright} {ital 1999 American Vacuum Society.}

  3. Interface reactions in CdTe solar cell processing

    Energy Technology Data Exchange (ETDEWEB)

    Albin, D.; Dhere, R.; Swartzlander-Guest, A. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1998-12-31

    Currently, the best performing CdS/CdTe solar cells use a superstrate structure in which CdTe is deposited on a heated CdS/SnO{sub 2}/Glass substrate. In the close-spaced-sublimation (CSS) process, substrate temperatures in the range 550 C to 620 C are common. Understanding how these high processing temperatures impact reactions at the CdS/CdTe interface in addition to reactions between previously deposited layers is critical. At the SnO{sub 2}/CdS interface the authors have determined that SnO{sub 2} can be susceptible to reduction, particularly in H{sub 2} ambients. Room-temperature sputtered SnO{sub 2} shows the most susceptibility. In contrast, higher growth temperature chemical vapor deposited (CVD) SnO{sub 2} appears to be much more stable. Elimination of unstable SnO{sub 2} layers, and the substitution of thermal treatments for H{sub 2} anneals has produced total-area solar conversion efficiencies of 13.6% using non-optimized SnO{sub 2} substrates and chemical-bath deposited (CBD) CdS. Alloying and interdiffusion at the CdS/CdTe interface was studied using a new lift-off approach which allows enhanced compositional and structural analysis at the interface. Small-grained CdS, grown by a low-temperature CBD process, results in more CdTe{sub 1{minus}x}S{sub x} alloying (x = 12--13%) relative to larger-grained CdS grown by high-temperature CSS (x{approximately}2--3%). Interdiffusion of S and Te at the interface, measured with lift-off samples, appears to be inversely proportional to the amount of oxygen used during the CSS CdTe deposition. The highest efficiency to date using CSS-grown CdS is 10.7% and was accomplished by eliminating oxygen during the CdTe deposition.

  4. Microstructure of (110)-Oriented Epitaxial SrRuO3 Thin Films Grown on Off-Cut Single Crystal YSZ(100) Substrates

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Xinhua [Max-Planck-Institut fur Mikrostrukturphysik, Germany; Lee, Sung Kyun [Max-Planck-Institut fur Mikrostrukturphysik, Germany; Lee, Ho Nyung [ORNL; Hesse, Dietrich [Max-Planck-Institut fur Mikrostrukturphysik, Germany

    2005-01-01

    The microstructure of (1 1 0){sup pc}-oriented epitaxial SrRuO{sub 3} (SRO) thin films grown by pulsed laser deposition on (1 0 0)YSZ (YSZ: yttria-stabilized zirconia) single crystal substrates with a miscut angle of 5{sup o} has been investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The films grow epitaxially with their pseudocubic (1 1 0) plane parallel to the (1 0 0) surface of the YSZ single crystal substrate, and with an in-plane orientation relationship of [{ovr 1} 1 1]{sub SRO}//[0 1 1]{sub YSZ}. Cross-sectional TEM investigations show that the films have a rough, facetted surface. Generally, four different azimuthal domains are present in (1 1 0)SRO films on (1 0 0)YSZ. Their number can be significantly reduced using annealed offcut YSZ substrates before SRO deposition, and this reduction effect is shown to be much stronger on [0 1 1]-miscut (1 0 0)YSZ than on [0 0 1]-miscut ones. Size and morphology of the azimuthal pseudocubic domains and their domain boundaries, as well as of anti-phase domains and their domain boundaries are studied by plan-view and cross-section TEM.

  5. Microstructure of (110)-oriented epitaxial SrRuO{sub 3} thin films grown on off-cut single crystal YSZ(100) substrates

    Energy Technology Data Exchange (ETDEWEB)

    Zhu Xinhua [Max-Planck Institut fuer Mikrostrukturphysik, Weinberg 2, D-06120 Halle (Germany)]. E-mail: xhzhu@mpi-halle.de; Lee, Sung Kyun [Max-Planck Institut fuer Mikrostrukturphysik, Weinberg 2, D-06120 Halle (Germany); Lee, Ho Nyung [Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Hesse, Dietrich [Max-Planck Institut fuer Mikrostrukturphysik, Weinberg 2, D-06120 Halle (Germany)

    2005-04-25

    The microstructure of (110){sup pc}-oriented epitaxial SrRuO{sub 3} (SRO) thin films grown by pulsed laser deposition on (100)YSZ (YSZ: yttria-stabilized zirconia) single crystal substrates with a miscut angle of 5{sup o} has been investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The films grow epitaxially with their pseudocubic (110) plane parallel to the (100) surface of the YSZ single crystal substrate, and with an in-plane orientation relationship of [1-bar 11]{sub SRO}//[011]{sub YSZ}. Cross-sectional TEM investigations show that the films have a rough, facetted surface. Generally, four different azimuthal domains are present in (110)SRO films on (100)YSZ. Their number can be significantly reduced using annealed offcut YSZ substrates before SRO deposition, and this reduction effect is shown to be much stronger on [011]-miscut (100)YSZ than on [001]-miscut ones. Size and morphology of the azimuthal pseudocubic domains and their domain boundaries, as well as of anti-phase domains and their domain boundaries are studied by plan-view and cross-section TEM.

  6. Bioprecipitation of Calcium Carbonate Crystals by Bacteria Isolated from Saline Environments Grown in Culture Media Amended with Seawater and Real Brine

    Science.gov (United States)

    Silva-Castro, G. A.; Uad, I.; Gonzalez-Martinez, A.; Rivadeneyra, A.; Gonzalez-Lopez, J.; Rivadeneyra, M. A.

    2015-01-01

    The precipitation of calcium carbonate and calcium sulphate by isolated bacteria from seawater and real brine obtained in a desalination plant growth in culture media containing seawater and brine as mineral sources has been studied. However, only bioprecipitation was detected when the bacteria were grown in media with added organic matter. Biomineralization process started rapidly, crystal formation taking place in the beginning a few days after inoculation of media; roughly 90% of total cultivated bacteria showed. Six major colonies with carbonate precipitation capacity dominated bacterial community structure cultivated in heterotrophic platable bacteria medium. Taxonomic identification of these six strains through partial 16S rRNA gene sequences showed their affiliation with Gram-positive Bacillus and Virgibacillus genera. These strains were able to form calcium carbonate minerals, which precipitated as calcite and aragonite crystals and showed bacterial fingerprints or bacteria calcification. Also, carbonic anhydrase activity was observed in three of these isolated bacteria. The results of this research suggest that microbiota isolated from sea water and brine is capable of precipitation of carbonate biominerals, which can occur in situ with mediation of organic matter concentrations. Moreover, calcium carbonate precipitation ability of this microbiota could be of importance in bioremediation of CO2 and calcium in certain environments. PMID:26273646

  7. Bioprecipitation of Calcium Carbonate Crystals by Bacteria Isolated from Saline Environments Grown in Culture Media Amended with Seawater and Real Brine

    Directory of Open Access Journals (Sweden)

    G. A. Silva-Castro

    2015-01-01

    Full Text Available The precipitation of calcium carbonate and calcium sulphate by isolated bacteria from seawater and real brine obtained in a desalination plant growth in culture media containing seawater and brine as mineral sources has been studied. However, only bioprecipitation was detected when the bacteria were grown in media with added organic matter. Biomineralization process started rapidly, crystal formation taking place in the beginning a few days after inoculation of media; roughly 90% of total cultivated bacteria showed. Six major colonies with carbonate precipitation capacity dominated bacterial community structure cultivated in heterotrophic platable bacteria medium. Taxonomic identification of these six strains through partial 16S rRNA gene sequences showed their affiliation with Gram-positive Bacillus and Virgibacillus genera. These strains were able to form calcium carbonate minerals, which precipitated as calcite and aragonite crystals and showed bacterial fingerprints or bacteria calcification. Also, carbonic anhydrase activity was observed in three of these isolated bacteria. The results of this research suggest that microbiota isolated from sea water and brine is capable of precipitation of carbonate biominerals, which can occur in situ with mediation of organic matter concentrations. Moreover, calcium carbonate precipitation ability of this microbiota could be of importance in bioremediation of CO2 and calcium in certain environments.

  8. Bioprecipitation of Calcium Carbonate Crystals by Bacteria Isolated from Saline Environments Grown in Culture Media Amended with Seawater and Real Brine.

    Science.gov (United States)

    Silva-Castro, G A; Uad, I; Gonzalez-Martinez, A; Rivadeneyra, A; Gonzalez-Lopez, J; Rivadeneyra, M A

    2015-01-01

    The precipitation of calcium carbonate and calcium sulphate by isolated bacteria from seawater and real brine obtained in a desalination plant growth in culture media containing seawater and brine as mineral sources has been studied. However, only bioprecipitation was detected when the bacteria were grown in media with added organic matter. Biomineralization process started rapidly, crystal formation taking place in the beginning a few days after inoculation of media; roughly 90% of total cultivated bacteria showed. Six major colonies with carbonate precipitation capacity dominated bacterial community structure cultivated in heterotrophic platable bacteria medium. Taxonomic identification of these six strains through partial 16S rRNA gene sequences showed their affiliation with Gram-positive Bacillus and Virgibacillus genera. These strains were able to form calcium carbonate minerals, which precipitated as calcite and aragonite crystals and showed bacterial fingerprints or bacteria calcification. Also, carbonic anhydrase activity was observed in three of these isolated bacteria. The results of this research suggest that microbiota isolated from sea water and brine is capable of precipitation of carbonate biominerals, which can occur in situ with mediation of organic matter concentrations. Moreover, calcium carbonate precipitation ability of this microbiota could be of importance in bioremediation of CO2 and calcium in certain environments. PMID:26273646

  9. Fabrication and characterization of a ZnO X-ray sensor using a high-resistivity ZnO single crystal grown by the hydrothermal method

    International Nuclear Information System (INIS)

    We investigated the X-ray detection capability of a fabricated Pt/ZnO diode using a high-resistivity ZnO single crystal grown by the hydrothermal method. The X-ray sensor consists of a Pt electrode on the Zn-face, an Au/Ti electrode on the O-face and a (0 0 0 1) ZnO substrate with high resistivity. The fabricated X-ray sensor showed ohmic-like characteristics in the measurement of current-applied voltage characteristics. We attributed these ohmic characteristics to degradation of the surface quality of the ZnO substrate caused by handling damage that occurred when carrying out a series of electrical and optical ZnO characterizations. The fabricated X-ray sensor at a bias of 20 V responded to X-rays in current-mode measurement. The sensor current increased linearly with X-ray tube current at 60 keV, and the results showed that sensitivity was approximately 1.5 μC/Gy. We demonstrated that a ZnO single crystal has potential for the development of an X-ray detector.

  10. Microstructure of Co(112-bar 0) epitaxial thin films, grown on MgO(100) single-crystal substrates

    Energy Technology Data Exchange (ETDEWEB)

    Nukaga, Yuri; Ohtake, Mitsuru; Futamoto, Masaaki [Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551 (Japan); Kirino, Fumiyoshi, E-mail: nukaga@futamoto.elect.chuo-u.ac.j [Graduate School of Fine Arts, Tokyo National University of Fine Arts and Music, 12-8 Ueno-koen, Taito-ku, Tokyo 110-8714 (Japan)

    2010-01-01

    Co(112-bar 0) epitaxial thin films with hcp structure were prepared on MgO(100) single-crystal substrates heated at 300 {sup 0}C by ultra high vacuum molecular beam epitaxy. The microstructure is investigated by employing X-ray diffraction and high-resolution transmission electron microscopy. The film consists of two types of domains whose c-axes are rotated around the film normal by 90{sup 0} each other. Stacking faults are observed for the film along the Co[0001] direction. An atomically sharp boundary is recognized between the film and the substrate, where some misfit dislocations are introduced in the film at the Co/MgO interface. Dislocations are also observed in the film up to 15 nm thickness from the interface. Presence of such stacking faults and misfit dislocations seem to relieve the strain caused by the lattice mismatch between the film and the substrate. X-ray diffraction analysis indicates that the out-of-plane and the in-plane lattice spacings of the film are in agreement within 0.5% and 0.1%, respectively, with those of the bulk hcp-Co crystal, suggesting the strain in the film is very small.

  11. Monolayer Single-Crystal 1T'-MoTe2 Grown by Chemical Vapor Deposition Exhibits Weak Antilocalization Effect.

    Science.gov (United States)

    Naylor, Carl H; Parkin, William M; Ping, Jinglei; Gao, Zhaoli; Zhou, Yu Ren; Kim, Youngkuk; Streller, Frank; Carpick, Robert W; Rappe, Andrew M; Drndić, Marija; Kikkawa, James M; Johnson, A T Charlie

    2016-07-13

    Growth of transition metal dichalcogenide (TMD) monolayers is of interest due to their unique electrical and optical properties. Films in the 2H and 1T phases have been widely studied but monolayers of some 1T'-TMDs are predicted to be large-gap quantum spin Hall insulators, suitable for innovative transistor structures that can be switched via a topological phase transition rather than conventional carrier depletion [ Qian et al. Science 2014 , 346 , 1344 - 1347 ]. Here we detail a reproducible method for chemical vapor deposition of monolayer, single-crystal flakes of 1T'-MoTe2. Atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy confirm the composition and structure of MoTe2 flakes. Variable temperature magnetotransport shows weak antilocalization at low temperatures, an effect seen in topological insulators and evidence of strong spin-orbit coupling. Our approach provides a pathway to systematic investigation of monolayer, single-crystal 1T'-MoTe2 and implementation in next-generation nanoelectronic devices. PMID:27223343

  12. The single crystal X-ray structure of β-hematin DMSO solvate grown in the presence of chloroquine, a β-hematin growth-rate inhibitor

    Science.gov (United States)

    Gildenhuys, Johandie; le Roex, Tanya; Egan, Timothy J.; de Villiers, Katherine A.

    2012-01-01

    Single crystals of solvated β-hematin were grown from a DMSO solution containing the antimalarial drug chloroquine, a known inhibitor of β-hematin formation. In addition, a kinetics study employing biomimetic lipid-water emulsion conditions was undertaken to further investigate the effect of chloroquine and quinidine on the formation of β-hematin. Scanning electron microscopy shows that the external morphology of the β-hematin DMSO solvate crystals is almost indistinguishable from that of malaria pigment (hemozoin) and single crystal X-ray diffraction confirms the presence of μ-propionato coordination dimers of iron(III) protoporphyrin IX. The free propionic acid functional groups of adjacent dimers hydrogen bond to included DMSO molecules, rather than forming carboxylic acid dimers. The observed exponential kinetics were modeled using the Avrami equation, with an Avrami constant equal to 1. The decreased rate of β-hematin formation observed at low concentrations of both drugs could be accounted for by assuming a mechanism of drug adsorption to sites on the fastest growing face of β-hematin. This behavior was modeled using the Langmuir isotherm. Higher concentrations of drug resulted in decreased final yields of β-hematin, and an irreversible drug-induced precipitation of iron(III) protoporphyrin IX was postulated to account for this. The model permits determination of the equilibrium adsorption constant (Kads). The values for chloroquine (log Kads = 5.55 ± 0.03) and quinidine (log Kads = 4.92 ± 0.01) suggest that the approach may be useful as a relative probe of the mechanism of action of novel antimalarial compounds. PMID:23253048

  13. Study of Defect Structures in 6H-SiC a/ m-Plane Pseudofiber Crystals Grown by Hot-Wall CVD Epitaxy

    Science.gov (United States)

    Goue, Ouloide Y.; Raghothamachar, Balaji; Yang, Yu; Guo, Jianqiu; Dudley, Michael; Kisslinger, Kim; Trunek, Andrew J.; Neudeck, Philip G.; Spry, David J.; Woodworth, Andrew A.

    2016-04-01

    Structural perfection of silicon carbide (SiC) single crystals is essential to achieve high-performance power devices. A new bulk growth process for SiC proposed by researchers at NASA Glenn Research Center, called large tapered crystal (LTC) growth, based on axial fiber growth followed by lateral expansion, could produce SiC boules with potentially as few as one threading screw dislocation per wafer. In this study, the lateral expansion aspect of LTC growth is addressed through analysis of lateral growth of 6H-SiC a/ m-plane seed crystals by hot-wall chemical vapor deposition. Preliminary synchrotron white-beam x-ray topography (SWBXT) indicates that the as-grown boules match the polytype structure of the underlying seed and have a faceted hexagonal morphology with a strain-free surface marked by steps. SWBXT Laue diffraction patterns of transverse and axial slices of the boules reveal streaks suggesting the existence of stacking faults/polytypes, and this is confirmed by micro-Raman spectroscopy. Transmission x-ray topography of both transverse and axial slices reveals inhomogeneous strains at the seed-epilayer interface and linear features propagating from the seed along the growth direction. Micro-Raman mapping of an axial slice reveals that the seed contains high stacking disorder, while contrast extinction analysis (g· b and g· b× l) of the linear features reveals that these are mostly edge-type basal plane dislocations. Further high-resolution transmission electron microscopy investigation of the seed-homoepilayer interface also reveals nanobands of different SiC polytypes. A model for their formation mechanism is proposed. Finally, the implication of these results for improving the LTC growth process is addressed.

  14. Quantized Nanocrystalline CdTe Thin Films

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Nanocrystalline CdTe thin films were prepared by asymmetric rectangular pulse electrodeposition in organic solution at 110°C. STM image shows a porous network morphology constructed by interconnected spherical CdTe crystallites with a mean diameter of 4.2 nm. A pronounced size quantization was indicated in the action and absorption spectra. Potentials dependence dual conductive behavior was revealed in the photocurrent-potential (I-V) curves.

  15. Chlorine diffusion in CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Sadaiyandi, K.; Ramachandran, K. (School of Physics, Madurai Kamaraj Univ. (India))

    1991-06-01

    The experimental results of chlorine diffusion in CdTe reveal that the dominant mechanism for diffusion is through neutral defect pair such as (V{sub Cd}V{sub Te}){sup *}. Here, theoretical calculations are carried out for all the possible mechanisms such as single vacancy, single interstitial, neutral defect pair, and Frenkel defect pair. The results suggest that the most possible mechanism for Cl diffusion in CdTe is that through neutral defect pair, supporting the experiment. (orig.).

  16. Thin yttrium iron garnet films grown by pulsed laser deposition: Crystal structure, static, and dynamic magnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Sokolov, N. S., E-mail: nsokolov@fl.ioffe.ru; Fedorov, V. V.; Korovin, A. M.; Suturin, S. M.; Baranov, D. A.; Gastev, S. V.; Krichevtsov, B. B.; Bursian, V. E.; Lutsev, L. V. [Ioffe Physical-Technical Institute of Russian Academy of Sciences, St. Petersburg 194021 (Russian Federation); Maksimova, K. Yu.; Grunin, A. I. [Immanuel Kant Baltic Federal University, Kaliningrad 236041 (Russian Federation); Tabuchi, M. [Synchrotron Radiation Research Center, Nagoya University, Nagoya 464-8603 (Japan)

    2016-01-14

    Pulsed laser deposition has been used to grow thin (10–84 nm) epitaxial layers of Yttrium Iron Garnet Y{sub 3}Fe{sub 5}O{sub 12} (YIG) on (111)–oriented Gadolinium Gallium Garnet substrates at different growth conditions. Atomic force microscopy showed flat surface morphology both on micrometer and nanometer scales. X-ray diffraction measurements revealed that the films are coherent with the substrate in the interface plane. The interplane distance in the [111] direction was found to be by 1.2% larger than expected for YIG stoichiometric pseudomorphic film indicating presence of rhombohedral distortion in this direction. Polar Kerr effect and ferromagnetic resonance measurements showed existence of additional magnetic anisotropy, which adds to the demagnetizing field to keep magnetization vector in the film plane. The origin of the magnetic anisotropy is related to the strain in YIG films observed by XRD. Magneto-optical Kerr effect measurements revealed important role of magnetization rotation during magnetization reversal. An unusual fine structure of microwave magnetic resonance spectra has been observed in the film grown at reduced (0.5 mTorr) oxygen pressure. Surface spin wave propagation has been demonstrated in the in-plane magnetized films.

  17. Distributed Bragg reflectors obtained by combining Se and Te compounds: Influence on the luminescence from CdTe quantum dots

    Science.gov (United States)

    Rousset, J.-G.; Kobak, J.; Janik, E.; Parlinska-Wojtan, M.; Slupinski, T.; Golnik, A.; Kossacki, P.; Nawrocki, M.; Pacuski, W.

    2016-05-01

    We report on the optical properties of structures containing self assembled CdTe quantum dots (QDs) combined with Te and Se based distributed Bragg reflectors either in a half cavity geometry with a relatively broad cavity mode or in a full cavity geometry where the cavity mode is much narrower. We show that for both structures the extraction coefficient of the light emitted from the QDs ensemble is enhanced by more than one order of magnitude with respect to the QDs grown on a ZnTe buffer. However, a single QD line broadening is observed and attributed to an unintentional incorporation of Se in the vicinity of the CdTe QDs. We show that postponing the QDs growth for 24 h after the distributed Bragg reflector deposition allows recovering sharp emission lines from individual QDs. This two step growth method is proven to be efficient also for the structures with CdTe QDs containing a single Mn2+ ion.

  18. Calculation of the High-Temperature Point Defects Structure in Te-Rich CdTe

    Science.gov (United States)

    Dai, Shujun; Wang, Tao; Liu, Huimin; He, Yihui; Jie, Wanqi

    2016-06-01

    A thermodynamic equilibrium model for CdTe annealed under Te vapor is established, in which possible point defects and a defect reaction existing in undoped and In-doped Te-rich CdTe crystals are taken into consideration. Independent point defects, such as VCd, Cdi, and Tei, as well as defect complexes, namely TeCd-VCd (B complex), {{Te}}_{{Cd}}^{2 + } - {{V}}_{{Cd}}^{2 - } (D complex), {{In}}_{{Cd}}^{ + } - {{V}}_{{Cd}}^{ - } (A-center) and Tei-VCd (TeCd), are discussed based on the defect chemistry theory. More specially, the mass action law and quasi-chemical equations are used to calculate defects concentration and Fermi level in undoped and doped CdTe crystals with different indium concentrations. It is found that the Fermi level is controlled by a {{V}}_{{Cd}}^{2 - } , TeCd, and B/D-complex in undoped crystal. The concentration of VCd drops down in an obvious manner and that of TeCd rises for doped crystal with increasing [In].

  19. Calculation of the High-Temperature Point Defects Structure in Te-Rich CdTe

    Science.gov (United States)

    Dai, Shujun; Wang, Tao; Liu, Huimin; He, Yihui; Jie, Wanqi

    2016-10-01

    A thermodynamic equilibrium model for CdTe annealed under Te vapor is established, in which possible point defects and a defect reaction existing in undoped and In-doped Te-rich CdTe crystals are taken into consideration. Independent point defects, such as VCd, Cdi, and Tei, as well as defect complexes, namely TeCd-VCd (B complex), {Te}_{{Cd}}^{2 + } - {V}_{{Cd}}^{2 - } (D complex), {In}_{{Cd}}^{ + } - {V}_{{Cd}}^{ - } (A-center) and Tei-VCd (TeCd), are discussed based on the defect chemistry theory. More specially, the mass action law and quasi-chemical equations are used to calculate defects concentration and Fermi level in undoped and doped CdTe crystals with different indium concentrations. It is found that the Fermi level is controlled by a {V}_{{Cd}}^{2 - } , TeCd, and B/D-complex in undoped crystal. The concentration of VCd drops down in an obvious manner and that of TeCd rises for doped crystal with increasing [In].

  20. Flexible CdTe solar cells on polymer films

    Energy Technology Data Exchange (ETDEWEB)

    Tiwari, A.N.; Romeo, A.; Baetzner, D.; Zogg, H. [ETH Swiss Federal Inst. of Technology, Thin Film Physics Group, Zurich (Switzerland)

    2001-07-01

    Lightweight and flexible CdTe/CdS solar cells on polyimide films have been developed in a 'superstrate configuration' where the light is absorbed in CdTe after passing through the polyimide substrate. The average optical transmission of the approximately 10-{mu}m-thin spin-coated polyimide substrate layer is more than {approx}75% for wavelengths above 550 nm. RF magnetron sputtering was used to grow transparent conducting ZnO:Al layers on polyimide films. CdTe/CdS layers were grown by evaporation of compounds, and a CdCl{sub 2} annealing treatment was applied for the recrystallisation and junction activation. Solar cells of 8.6% efficiency with V{sub oc} = 763 mV, I{sub sc} = 20.3 mA/cm{sup 2} and FF = 55.7% were obtained. (Author)

  1. Photo-responsivity characterizations of CdTe films for direct-conversion X-ray detectors

    International Nuclear Information System (INIS)

    We have fabricated and investigated thin, polycrystalline, cadmium-telluride (CdTe) films in order to utilize them for optical switching readout layers in direct-conversion X-ray detectors. The polycrystalline CdTe films are fabricated on ITO glasses by using the physical vapor deposition (PVD) method at a slow deposition rate and a pressure of 10-6 torr. CdTe films with thicknesses of 5 and 20 μm are grown. The electrical and the optical characteristics of the CdTe films are investigated by measuring the dark-current and the photo-current as functions of the applied field under different wavelengths of light. Higher photo-currents are generated at the longer wavelengths of light for the same applied voltage. When a higher electrical field is applied to the 20 μm-thick CdTe film, a higher dark-current, a higher photo-current, a larger number of charges, and a higher quantum efficiency are generated.

  2. Absence of the 90 K structural transition in CuV{sub 2}S{sub 4} crystals grown by chemical vapour transport using TeCl{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Crandles, D A [Department of Physics, Brock University, St Catharines, ON, L2S 3A1 (Canada); Reedyk, M [Department of Physics, Brock University, St Catharines, ON, L2S 3A1 (Canada); Wardlaw, G [Department of Physics, Brock University, St Catharines, ON, L2S 3A1 (Canada); Razavi, F S [Department of Physics, Brock University, St Catharines, ON, L2S 3A1 (Canada); Hagino, T [Department of Materials Science and Engineering, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran, Hokkaido 050-8535 (Japan); Nagata, S [Department of Materials Science and Engineering, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran, Hokkaido 050-8535 (Japan); Shimono, I [Hokkaido Industrial Technology Centre, 379 Kikyo-cho, Hakodate, Hokkaido 041-0801 (Japan); Kremer, R K [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany)

    2005-08-03

    Various physical properties (magnetization, specific heat, optical reflectance, electrical resistivity) of CuV{sub 2}S{sub 4} crystals grown by chemical vapour transport using TeCl{sub 4} as the transporting agent have been measured. The data show slight differences compared to samples grown using different techniques. These differences include the absence of a sharp drop in magnetization and the absence of a peak in the heat capacity near 90 K. These differences suggest that the cubic-tetragonal phase transition near 90 K does not occur in these particular crystals. The reflectance of the same crystals has been studied from (70-20 000 cm{sup -1}) for temperatures between 40 and 300 K and the data are consistent with those for a disordered metal. A high frequency absorption, perhaps an interband transition, has been observed in addition to absorption due to strongly scattered free carriers.

  3. Film Thickness Dependence of Crystal Structure in 100-Oriented Epitaxial Pb(Zr0.65Ti0.35)O3 Films Grown on Single-Crystal Substrates with Different Thermal Expansion Coefficients

    Science.gov (United States)

    Ehara, Yoshitaka; Yasui, Shintaro; Ishii, Koji; Funakubo, Hiroshi

    2012-09-01

    100-oriented epitaxial Pb(Zr0.65Ti0.35)O3 films with various film thicknesses from 0.1 to 3 µm were grown on (100)cSrRuO3 ∥ (100)SrTiO3 and (100)cSrRuO3 ∥ (100)LaNiO3 ∥ (001)CaF2 substrates. The out-of-plane/in-plane lattice parameter ratio of the films on the CaF2 substrates was larger than that on the SrTiO3 substrates up to 1.1 µm film thickness, while (90°-α) (α was defined as the internal tilt angle) was almost 0°. Results of analysis of Raman spectra and piezoresponse images suggest that the 1.1-µm-thick film grown on the (100)cSrRuO3 ∥ (100)LaNiO3 ∥ (001)CaF2 substrate had tetragonal symmetry with a polar-axis orientation. Moreover, the saturation polarization values of the films measured from P-E hysteresis loops correspond to the two Ps values estimated from the thermodynamic theory, assuming the change in the polar direction due to the symmetry change to tetragonal, and from the crystal distortion in tetragonal symmetry. This can be explained by the large compressive stress from the CaF2 substrate having a large thermal expansion coefficient.

  4. Epitaxial bilayer and trilayer heterostructures grown on LaAlO{sub 3} and SrTiO{sub 3}(001) single crystals by laser ablation

    Energy Technology Data Exchange (ETDEWEB)

    Chrzanowski, J.; Meng-Burany, S.; Curzon, A.E.; Irwin, J.C.; Heinrich, B.; Cragg, R.A.; Backhouse, C.; Angus, V.; Habib, F.; Zhou, H.; Fife, A.A. [Dept. of Phys., Simon Fraser Univ., Burnaby, BC (Canada)

    1995-06-01

    High-quality S/I and S/I/S epitaxial heterostructures (S=YBa{sub 2}Cu{sub 3}O{sub x}, l=SrTiO{sub 3}) have been grown in situ on LaAlO{sub 3} and SrTiO{sub 3}(001) single crystals, by the single-chamber pulsed laser deposition technique. YBa{sub 2}Cu{sub 3}O{sub x} and SrTiO{sub 3} layers were deposited sequentially, at a substrate temperature Th=760 degrees C, and an oxygen pressure {rho}{sub (O2)}=300 mTorr. Structural data showed that the SrTiO{sub 3} layer, grown either on a YBCO film or sandwiched by two YBaCuO films, was strained in the (001) plane and exhibited an elongation of the lattice parameter in the (001) direction. This behaviour was consistent with the epitaxial growth of the S/I and S/I/S structures as revealed by the RHEED and ECP patterns. Ion milling in conjunction with AES analysis showed that the thicknesses of the interfacial regions were {<=}35 AA, and resulted from residual roughness of the substrates. The critical temperature (T{sub c}) and critical current density (j{sub c}) of the multilayers at 77 K, as determined by an inductive AC method, were found to be T{sub c}=89.5 and 90.5 K, and j{sub c}=3 and 5x10{sup 6} A cm{sup -2}, for trilayers and bilayers, respectively. (author)

  5. X-ray characterization of the microstructure in a CdTe epitaxial layer

    Energy Technology Data Exchange (ETDEWEB)

    Gao Dachao; Stevenson, A.W.; Wilkins, S.W. (CSIRO Div. of Materials Science and Tech., Clayton, Victoria (Australia)); Pain, G.N. (Telecon Australia Research Labs., Clayton, Victoria (Australia))

    1991-12-10

    High-resolution X-ray diffraction studies of a twinned (anti 1anti 1anti 1) CdTe epilayer on (0001) sapphire substrate were carried out. The structural properties and uniformity of the CdTe epilayer were established from analyses of Lang topographs, double-crystal rocking-curve maps and twin-content maps. Maps of the full width at half-maximum (FWHM) of the rocking curve were taken for two twin species (1 and 2), which relate to each other by a rotation of 180deg about the (anti 1anti 1anti 1) axis. The value of the FWHM varied over the sample from 108 to over 1000 arcs. The twin-content maps were determined over the whole layer, and showed significant variations. Lang topographs were taken using the asymmetric anti 4anti 2anti 2 Bragg reflection for both twins and the results were consistent with the rocking curves. The topographs showed that clusters of dislocations exist in the layer and many of them lie along the (anti 1anti 12) direction parallel to the (anti 1anti 1anti 1) CdTe layer surface with the Burgers vector in the (1anti 10) direction. Evidence of double-positioning twins was found in the CdTe epilayer. It is shown that combinations of rocking-curve maps and topographs give a much more informative characterization than a single-point measurement of the rocking curve. (orig.).

  6. CdTe Quantum Dot/Dye Hybrid System as Photosensitizer for Photodynamic Therapy

    OpenAIRE

    RAKOVICH, YURY; Donegan, John Francis

    2010-01-01

    We have studied the photodynamic properties of novel CdTe quantum dots?methylene blue hybrid photosensitizer. Absorption spectroscopy, photolumines- cence spectroscopy, and fluorescence lifetime imaging of this system reveal efficient charge transfer between nano- crystals and the methylene blue dye. Near-infrared photo- luminescence measurements provide evidence for an increased efficiency of singlet oxygen production by the methylene blue dye. In vitro studies on the...

  7. Optical and scintillation properties of ce-doped (Gd2Y1)Ga2.7Al2.3O12 single crystal grown by Czochralski method

    Science.gov (United States)

    Wang, Chao; Wu, Yuntao; Ding, Dongzhou; Li, Huanying; Chen, Xiaofeng; Shi, Jian; Ren, Guohao

    2016-06-01

    Multicomponent garnets, due to their excellent light yield and energy resolution, become one of the most promising scintillators used for homeland security and nuclear non-proliferation applications. This work focuses on the optimization of Ce-doped (Gd,Y)3(Ga,Al)5O12 scintillators using a combination strategy of pre-screening and scale-up. Ce-doped GdxY1-xGayAl5-yO12 (x=1, 2 and y=2, 2.2, 2.5, 2.7, 3) polycrystalline powders were prepared by high-temperature solid state reaction method. The desired garnet phase in all the samples was confirmed using X-ray diffraction measurement. By comparing the radioluminescence intensity, the highest scintillation efficiency was achieved at a component of Gd2Y1Ga2.7Al2.3O12:Ce powders. A (Gd2Y1)Ga2.7Al2.3O12 doped with 1% Ce single crystal with dimensions of Ø35×40 mm was grown by Czochralski method using a oriented seed. Luminescence and scintillation properties were measured. An optical transmittance of 84% was achieved in the concerned wavelength from 500 to 800 nm. Its 5d-4f emission of Ce3+ is at 530 nm. The light yield of a Ce1%: Gd2Y1Ga2.7Al2.3O12 single crystal slab at a size of 5×5×1 mm3 can reach about 65,000±3000 Ph/MeV along with two decay components of 94 and 615 ns under 137Cs source irradiation.

  8. High compositional homogeneity of CdTe{sub x}Se{sub 1−x} crystals grown by the Bridgman method

    Energy Technology Data Exchange (ETDEWEB)

    Roy, U. N.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Hossain, A.; Tappero, R.; Yang, G.; Gul, R.; James, R. B. [Brookhaven National Laboratory, Upton, New York 11973 (United States); Lee, K.; Lee, W. [Brookhaven National Laboratory, Upton, New York 11973 (United States); Korea University, Seoul 136-103 (Korea, Republic of)

    2015-02-01

    We obtained high-quality CdTe{sub x}Se{sub 1−x} (CdTeSe) crystals from ingots grown by the vertical Bridgman technique. The compositional uniformity of the ingots was evaluated by X-ray fluorescence at BNL’s National Synchrotron Light Source X27A beam line. The compositional homogeneity was highly uniform throughout the ingot, and the effective segregation coefficient of Se was ∼1.0. This high uniformity offers potential opportunity to enhance the yield of the materials for both infrared substrate and radiation-detector applications, so greatly lowering the cost of production and also offering us the prospect to grow large-diameter ingots for use as large-area substrates and for producing higher efficiency gamma-ray detectors. The concentration of secondary phases was found to be much lower, by eight- to ten fold compared to that of conventional Cd{sub x}Zn{sub 1−x}Te (CdZnTe or CZT)

  9. Mapping the 3D distribution of CdSe nanocrystals in highly oriented and nanostructured hybrid P3HT-CdSe films grown by directional epitaxial crystallization.

    Science.gov (United States)

    Roiban, L; Hartmann, L; Fiore, A; Djurado, D; Chandezon, F; Reiss, P; Legrand, J-F; Doyle, S; Brinkmann, M; Ersen, O

    2012-11-21

    Highly oriented and nanostructured hybrid thin films made of regioregular poly(3-hexylthiophene) and colloidal CdSe nanocrystals are prepared by a zone melting method using epitaxial growth on 1,3,5-trichlorobenzene oriented crystals. The structure of the films has been analyzed by X-ray diffraction using synchrotron radiation, electron diffraction and 3D electron tomography to afford a multi-scale structural and morphological description of the highly structured hybrid films. A quantitative analysis of the reconstructed volumes based on electron tomography is used to establish a 3D map of the distribution of the CdSe nanocrystals in the bulk of the films. In particular, the influence of the P3HT-CdSe ratio on the 3D structure of the hybrid layers has been analyzed. In all cases, a bi-layer structure was observed. It is made of a first layer of pure oriented semi-crystalline P3HT grown epitaxially on the TCB substrate and a second P3HT layer containing CdSe nanocrystals uniformly distributed in the amorphous interlamellar zones of the polymer. The thickness of the P3HT layer containing CdSe nanoparticles increases gradually with increasing content of NCs in the films. A growth model is proposed to explain this original transversal organization of CdSe NCs in the oriented matrix of P3HT.

  10. Growth and optical properties of CdTe quantum dots in ZnTe nanowires

    International Nuclear Information System (INIS)

    We report on the formation of optically active CdTe quantum dots in ZnTe nanowires. The CdTe/ZnTe nanostructures have been grown by a gold nanocatalyst assisted molecular beam epitaxy in a vapor-liquid solid growth process. The presence of CdTe insertions in ZnTe nanowire results in the appearance of a strong photoluminescence band in the 2.0 eV-2.25 eV energy range. Spatially resolved photoluminescence measurements reveal that this broad emission consists of several sharp lines with the spectral width of about 2 meV. The large degree of linear polarization of these individual emission lines confirms their nanowire origin, whereas the zero-dimensional confinement is proved by photon correlation spectroscopy.

  11. Effects of Stoichiometry in Undoped CdTe Heteroepilayers on Si

    Energy Technology Data Exchange (ETDEWEB)

    Gessert, Timothy A.; Colegrove, Eric; Stafford, Brian; Gao, Wei; Sivananthan, Siva; Kuciauskas, Darius; Moutinho, Helio; Farrell, Stuart; Barnes, Teresa

    2015-06-14

    Crystalline CdTe layers have been grown heteroepitaxially onto crystalline Si substrates to establish material parameters needed for advanced photovoltaic (PV) device development and related simulation. These studies suggest that additional availability of the intrinsic anion (i.e., Te) during molecular beam epitaxy deposition can improve structural and optoelectronic quality of the epilayer and the interface between Si substrate and the epilayer. This is seen most notably for thin CdTe epitaxial films (<; ~10 micrometers). Although these observations are foundationally important, they are also relevant to envisioned high-performance multijunction II-VI alloy PV devices-where thin layers will be required to achieve production costs aligned with market constraints.

  12. Understanding misfit strain releasing mechanisms via molecular dynamics simulations of CdTe growth on {112}zinc-blende CdS

    Science.gov (United States)

    Zhou, X. W.; Chavez, J. J.; Almeida, S.; Zubia, D.

    2016-07-01

    Molecular dynamics simulations have been used to analyse microstructures of CdTe films grown on {112} surfaces of zinc-blende CdS. Interestingly, CdTe films grow in ⟨331⟩ orientations as opposed to ⟨112⟩ epitaxial orientations. At the CdTe-{331}/CdS-{112} interface, however, there exists an axis that is parallel to the ⟨110⟩ orientation of both CdS and CdTe. It is the direction orthogonal to this ⟨110⟩ that becomes different, being ⟨116⟩ for CdTe and ⟨111⟩ for CdS, respectively. Missing CdTe-{110} planes are found along the ⟨110⟩ axis, suggesting that the misfit strain is released by the conventional misfit dislocation mechanism along this axis. In the orthogonal axis, the misfit strain is found to be more effectively released by the new grain orientation mechanism. Our finding is supported by literature experimental observations of the change of growth direction when Cd0.96Zn0.04Te films are deposited on GaAs. Analyses of energetics clearly demonstrate the cause for the formation of the new orientation, and the insights gained from our studies can help understand the grain structures experimentally observed in lattice mismatched systems.

  13. New development on the control of homoepitaxial and heteroepitaxial growth of CdTe and HgCdTe by MBE

    Energy Technology Data Exchange (ETDEWEB)

    Faurie, J.P.; Sporken, R.; Sivananthan, S.; Lange, M.D. (Microphysics Lab., Physics Dept., Univ. of Illinois at Chicago, IL (USA))

    1991-05-01

    It is reported that rotation twins as well as reflection twins are easily formed in CdTe and HgCdTe grown by MBE in the (111) orientation. Twinning can be avoided by carefully controlling the substrate preparation and by applying very stringent growth conditions, mostly for the stability of Hg pressure and the real surface temperature of the substrate, which is extremely difficult to control when the substrate rotates. A comparison between HgCdTe twinned layers and twin-free layers has shown that electrically active acceptors and high hole mobility are associated with the presence of reflection twins and/or mercury-rich alloy zones due to Hg overpressure during the growth. Twin-free HgCdTe layers can exhibit etch pit density count two orders of magnitude lower than twinned layers. Twin-free CdTe layers have been grown on GaAs and Si substrates. Excellent thickness uniformities have been reported: 0.24% for the standard deviation of a 2-inch diameter CdTe layer grown on GaAs(100) and 2.3% for a 5-inch diameter CdTe grown on Si(100). (orig.).

  14. Heteroepitaxy of CdTe(100) on Si(100) using BaF sub 2 -CaF sub 2 (100) buffer layers

    Energy Technology Data Exchange (ETDEWEB)

    Tiwari, A.N.; Floeder, W.; Blunier, S.; Zogg, H. (AFIF Arbeitsgemeinschaft fuer Industrielle Forschung, Swiss Federal Inst. of Tech., ETH-Hoenggerberg, Zurich (Switzerland)); Proctor, M.J. (Inst. of Micro- and Optoelectronics, EPFL, Lausanne (Switzerland))

    1991-05-01

    Epitaxial CdTe(100) layers have been grown on Si(100) by conventional molecular beam epitaxy (MBE) and photo-assisted MBE (PAMBE) using stacked BaF{sub 2}-CaF{sub 2} as a buffer layer. Two-dimensional (2D) growth of BaF{sub 2}(100) is obtained using a two-temperature growth method. In conventional MBE, CdTe grows 2D for substrate temperatures above 270degC with a 2x1 surface reconstruction indicating a Te-stabilized surface. In PAMBE, 2D growth of CdTe is obtained at lower substrate temperatures ({approx equal}200degC) with 1x1 RHEED patterns indicating that Ar laser illumination induces Te desorption. PAMBE grown layers have superior structural quality than layers grown by conventional MBE. Sb doped CdTe layers grown by PAMBE exhibit a 2x2 surface reconstruction, their 10 K photoluminescence spectra show a single dominant (A{sup 0}, X) peak at 1.588 eV, and resistivities of 10{sup 3} {Omega} cm are measured. (orig.).

  15. Theoretical study of intrinsic defects in CdTe

    Science.gov (United States)

    Menéndez-Proupin, E.; Orellana, W.

    2016-05-01

    The quantum states and thermodynamical properties of the Cd and Te vacancies in CdTe are studied by first principles calculations. It is shown that the band structure of a cubic 64-atoms supercell with a Te vacancy is dramatically different from the band structure of the perfect crystal, suggesting that it cannot be used as model to calculate isolated defects. This flaw is solved modeling the Te vacancy within a cubic 216-atoms supercell. However, even with this large supercell, the 2— charge state relaxes to an incorrect distorted structure. This distortion is driven by partial filling of the conduction band induced by the k-point sampling. The correct structures and formation energies are obtained by relaxation with restriction of system symmetry, followed by band-filling correction to the energy, or by using a larger supercell that allows sampling the Brillouin zone with a single k-point.

  16. Ion-assisted doping of CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Fahrenbruch, A.L.; Chien, K.F.; Kim, D.; Lopez-Otero, A.; Sharps, P.; Bube, R.H. (Dept. of Materials Science and Engineering, Stanford Univ., CA (USA))

    1989-10-15

    The possibility of using ion-assisted doping during growth of p-CdTe films for solar cells has been investigated, to obtain higher doping densities than previously obtained with conventional film deposition processes. For the first time, controlled doping has been demonstrated with low-energy phosphorus ions to obtain hole densities of up to 2 x 10{sup 17} cm{sup -3} in homoepitaxial films deposited by vacuum evaporation on single-crystal CdTe. Solar cells made with these films suggest that ion damage reduces the diffusion length in the most highly doped films and that the active region of such cells must be made with considerably lower doping densities. For polycrystalline films on alumina, preliminary results indicate that the hole densities obtained are not sufficient to overcome grain boundary barrier limited conductivity. (orig.).

  17. Effect of CdCl2 treatment on structural and electronic property of CdTe thin films deposited by magnetron sputtering

    International Nuclear Information System (INIS)

    The structural and electrical properties of the magnetron sputtered CdTe thin films with subsequent CdCl2 solution treatment have been studied with a major focus on the influence of CdCl2 treatment to achieve high quality thin films. In this study, CdTe films with a thickness of 1.5 to 2 μm have been grown using the magnetron sputtering technique on top of glass substrate at an optimized substrate temperature of 250 °C. Aqueous CdCl2 concentration varied from 0.3 mol to 1.2 mol with the annealing temperature from 360 °C to 450 °C. The surface roughness of the films increases with the increase of solution concentration, while it fluctuates with the increase of annealing temperature. The density of nucleation centers and the strain increases for the films treated at 360 °C with 0.3 M to1.2 M while the grain growth of the films reduces. However, these strains are released at higher annealing temperatures, resulting in reduced dislocation densities, structural defects as well as increased crystalline property and grain size. The carrier concentration increases with the increase of treated CdCl2 concentration and subsequent annealing temperature. The highest carrier concentration of 1.05 × 1014/cm3 was found for the CdTe thin films treated with 0.3 M CdCl2 solution followed by an annealing treatment at 420 °C for 20 min. - Highlights: • CdTe thin films are grown as absorption layers in CdTe solar cells by sputtering. • CdTe film quality in terms of structural and electronic properties is examined. • All growth parameters are optimized in the range of 1.5 to 2 μm CdTe films

  18. Effect of CdCl{sub 2} treatment on structural and electronic property of CdTe thin films deposited by magnetron sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Islam, M.A. [Solar Energy Research Institute (SERI), Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor (Malaysia); Hossain, M.S.; Aliyu, M.M. [Department of Electrical, Electronic and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor (Malaysia); Karim, M.R. [Center of Excellence for Research in Engineering Materials (CEREM) College of Engineering, King Saud University, Riyadh, 11421 (Saudi Arabia); Razykov, T.; Sopian, K. [Solar Energy Research Institute (SERI), Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor (Malaysia); Amin, N., E-mail: nowshad@eng.ukm.my [Solar Energy Research Institute (SERI), Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor (Malaysia); Department of Electrical, Electronic and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor (Malaysia); Center of Excellence for Research in Engineering Materials (CEREM) College of Engineering, King Saud University, Riyadh, 11421 (Saudi Arabia)

    2013-11-01

    The structural and electrical properties of the magnetron sputtered CdTe thin films with subsequent CdCl{sub 2} solution treatment have been studied with a major focus on the influence of CdCl{sub 2} treatment to achieve high quality thin films. In this study, CdTe films with a thickness of 1.5 to 2 μm have been grown using the magnetron sputtering technique on top of glass substrate at an optimized substrate temperature of 250 °C. Aqueous CdCl{sub 2} concentration varied from 0.3 mol to 1.2 mol with the annealing temperature from 360 °C to 450 °C. The surface roughness of the films increases with the increase of solution concentration, while it fluctuates with the increase of annealing temperature. The density of nucleation centers and the strain increases for the films treated at 360 °C with 0.3 M to1.2 M while the grain growth of the films reduces. However, these strains are released at higher annealing temperatures, resulting in reduced dislocation densities, structural defects as well as increased crystalline property and grain size. The carrier concentration increases with the increase of treated CdCl{sub 2} concentration and subsequent annealing temperature. The highest carrier concentration of 1.05 × 10{sup 14}/cm{sup 3} was found for the CdTe thin films treated with 0.3 M CdCl{sub 2} solution followed by an annealing treatment at 420 °C for 20 min. - Highlights: • CdTe thin films are grown as absorption layers in CdTe solar cells by sputtering. • CdTe film quality in terms of structural and electronic properties is examined. • All growth parameters are optimized in the range of 1.5 to 2 μm CdTe films.

  19. Grown of CdTe:Eu films by pulsed laser deposition

    OpenAIRE

    M. Zapata-Torres; M. González-Alcudia; Meléndez-Lira, M.; O. Calzadilla Amaya

    2006-01-01

    CdTe:Eu films were grown by the pulsed laser deposition method on glass substrates. The targets were prepared with three different concentrations of Cd, Te and Eu employing CdTe and EuTe powders, homogenized by ball milling. X-ray diffraction measurements showed that the samples grown with a mixture of phases related with the structure of CdTe and EuTe, with a little increase of the lattice parameter. Scanning Electron micrographs revealed that CdTe:Eu films presented a texture similar to sol...

  20. Deep electron traps in CdTe:In films grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Zakrzewski, A.K.; Dobaczewski, L.; Karczewski, G.; Wojtowicz, T.; Kossut, J. [Institute of Physics, Polish Academy of Science, Warsaw (Poland)

    1995-12-31

    N-type indium CdTe grown on n{sup +}-GaAs molecular beam epitaxy has been studied by the standard deep level transient spectroscopy and the isothermal Laplace-transform deep level transient spectroscopy. It was found that the Cd/Te flux ratio strongly influences the deep level transient spectroscopy results. The unusual temperature dependence of the electron emission rate in films grown at nearly stoichiometric conditions may point out that the observed defect is resonant with the conduction band. (author). 5 refs, 1 fig.

  1. Composition dependences of crystal structure and electrical properties of epitaxial Pb(Zr,Ti)O3 films grown on Si and SrTiO3 substrates

    Science.gov (United States)

    Okamoto, Shoji; Okamoto, Satoshi; Yokoyama, Shintaro; Akiyama, Kensuke; Funakubo, Hiroshi

    2016-10-01

    {100}-oriented Pb(Zr x ,Ti1- x )O3 (PZT) thin films of approximately 2 µm thickness and Zr/(Zr + Ti) ratios of 0.39-0.65 were epitaxially grown on (100)cSrRuO3//(100)SrTiO3 (STO) and (100)cSrRuO3//(100)cLaNiO3//(100)CeO2//(100)YSZ//(100)Si (Si) substrates having different thermal expansion coefficients by pulsed metal-organic chemical vapor deposition (MOCVD). The effects of Zr/(Zr + Ti) ratio and type of substrate on the crystal structure and dielectric, ferroelectric and piezoelectric properties of the films were systematically investigated. The X-ray diffraction measurement showed that both films changed from having a tetragonal symmetry to rhombohedral symmetry through the coexisting region with increasing Zr/(Zr + Ti) ratio. This region showed the Zr/(Zr + Ti) ratios of 0.45-0.59 for the films on the STO substrates that were wider than the films on the Si substrates. Saturation polarization values were minimum at approximately Zr/(Zr + Ti) = 0.50 for the films on the STO substrates, and no obvious Zr/(Zr + Ti) ratio dependence was detected in the films on the Si substrates. On the other hand, the maximum field-induced strain values measured by scanning force microscopy at approximately Zr/(Zr + Ti) = 0.50 at 100 kV/cm were about 0.5 and 0.1% in the films on the Si and STO, respectively.

  2. X-ray diffraction study of epitaxial heterostructures of II-VI CdTe and ZnTe semiconductors; Etude par diffraction de rayons X d`heterostructures epitaxiees a base des semi-conducteurs II-VI CdTe et ZnTe

    Energy Technology Data Exchange (ETDEWEB)

    Bouchet-Boudet, N.

    1996-10-07

    This work deals with the structural study of II-VI semiconductor (CdTe and ZnTe) heterostructures by X-ray diffraction and reflectivity. These heterostructures have a high lattice parameter misfit and are grown by Molecular Beam Epitaxy. Two main subjects are developed: the characterization of ZnTe wires, grown by step propagation on a CdTe (001) vicinal surface, and the study of the vertical correlations in Cd{sub 0.8}Zn{sub 0.2}Te / CdTe superlattices and superlattices made of ZnTe fractional layers spaced by CdTe. The growth of organised system is up to date; its aim is to realize quantum boxes (or wires) superlattices which are laterally and vertically ordered. The deformation along the growth axis induced by a ZnTe fractional layer inserted in a CdTe matrix is modelled, in the kinematical approximation, to reproduce the reflectivity measured around the substrate (004) Bragg peak. The lateral periodicity of the wires, deposited on a vicinal surface is a new and difficult subject. Some results are obtained on a vertical superlattice grown on a 1 deg. mis-cut surface. The in-plane and out-of-plane correlation lengths of a Cd{sub 0.8}Zn{sub 0.2}Te / CdTe superlattice are deduced from the diffused scattered intensity measured at grazing incidence. The calculations are made within the `distorted Wave Born Approximation`. The vertical correlation in ZnTe boxes (or wines) superlattices can be measured around Bragg peaks. It is twice bigger in a superlattice grown on a 2 deg. mis-cut substrate than a nominal one. (author). 74 refs.

  3. CdTe and CdZnTe materials for room-temperature X-ray and gamma ray detectors

    Science.gov (United States)

    Eisen, Y.; Shor, A.

    1998-02-01

    Among the semiconductor materials of a wide band gap, CdTe and CdZnTe have attracted most attention as room-temperature X-ray and gamma-ray detectors. Suitable CdTe materials for nuclear detectors and, in particular, for spectrometers, have been developed over the past few decades and are mainly grown via the traveling heater method (THM). However, the manufacture of large homogeneous ingots at relatively low cost has not reached yet a proven stage. Cd 1- xZn xTe (CZT) materials, mainly grown via the high-pressure Bridgman (HPB) technique, possess several advantages over CdTe and appear to better approach the practicality of providing large volume X-ray and gamma-ray detectors at moderate costs. Continuing effort is still underway to improve the characteristics of both CdTe and CZT materials in order to achieve reproducible detectors for either low- and high-energy gamma rays. This review paper is divided into three parts: The first part describes different structural designs of detectors to improve their spectroscopic characteristics. These include hemispherical detectors, coplanar strip-electrode detectors and monolithic, two-dimensional segmented electrode arrays with pad sizes smaller than their thickness. This part will also describe various electronic methods to compensate for the poor charge collection of holes. The second part compares the characteristics of planar CdTe and CZT nuclear detectors containing metal contacts. Characteristics include: charge collection efficiencies for both electrons and holes indicated by the mobility-lifetime product, energy resolutions, leakage currents and robustness in field use. The third part is devoted to field uses of these detectors. Those include: X-ray fluorescent spectrometers, large volume spectrometers and a new generation nuclear gamma camera for medical diagnostics based on room-temperature solid-state spectrometers.

  4. Photoinduced tellurium precipitation in CdTe

    Science.gov (United States)

    Sugai, Shunji

    1991-06-01

    Tellurium precipitation in CdTe is found to be induced by photoirradiation with energy higher than the energy gap at 240 W/sq cm. It is suggested that this photoinduced precipitation is related with the strong electron-phonon interactions, possibly self-trapped excitons. This irreducible tellurium precipitation may cause a serious problem for the life of semiconductor devices.

  5. Characterization measurement of a thick CdTe detector for BNCT-SPECT – Detection efficiency and energy resolution

    International Nuclear Information System (INIS)

    Author's group is carrying out development of BNCT-SPECT with CdTe device, which monitors the therapy effect of BNCT in real-time. From the design calculations, the dimensions were fixed to 1.5×2×30 mm3. For the collimator it was confirmed that it would have a good spatial resolution and simultaneously the number of counts would be acceptably large. After producing the CdTe crystal, the characterization measurement was carried out. For the detection efficiency an excellent agreement between calculation and measurement was obtained. Also, the detector has a very good energy resolution so that gamma-rays of 478 keV and 511 keV could be distinguished in the spectrum. - Highlights: • BNCT-SPECT is developed with CdTe device to estimate therapy effect of BNCT. • By design calculations, CdTe dimensions are determined to be 1.5×2×30 mm3. Collimator length is 10 cm with 2 mm diameter hole. • Producing the crystal, efficiency and energy resolution were measured. • Excellent agreement was obtained between measurement and calculation. Discrimination of 478 keV and 511 keV was confirmed in the spectrum

  6. Structural, thermal, laser damage, photoconductivity, NLO and mechanical properties of modified vertical Bridgman method grown AgGa0.5In0.5Se2 single crystal

    Science.gov (United States)

    Vijayakumar, P.; Ramasamy, P.

    2016-08-01

    AgGa0.5In0.5Se2 single crystal was grown using modified vertical Bridgman method. The structural perfection of the AgGa0.5In0.5Se2 single crystal has been analyzed by high-resolution X-ray diffraction rocking curve measurements. The structural and compositional uniformities of AgGa0.5In0.5Se2 were studied using Raman scattering spectroscopy at room temperature. The FWHM of the Γ1 (W1) and Γ5L (Γ15) measured at different regions of the crystal confirms that the composition throughout its length is fairly uniform. Thermal properties of the as-grown crystal, including specific heat, thermal diffusivity and thermal conductivity have been investigated. The multiple shot surface laser damage threshold value was measured using Nd:YAG laser. Photoconductivity measurements with different temperatures have confirmed the positive photoconducting behavior. Second harmonic generation (SHG) on powder samples has been measured using the Kurtz and Perry technique and the results display that AgGa0.5In0.5Se2 is a phase-matchable NLO material. The hardness behavior has been measured using Vickers micro hardness measurement and the indentation size effect has been observed. The classical Meyer's law, propositional resistance model and modified propositional resistance model have been used to analyse the micro hardness behavior.

  7. Thin-film CdTe photovoltaic cells by laser deposition and rf sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Compaan, A.; Bohn, R.G.; Bhat, A.; Tabory, C.; Shao, M.; Li, Y.; Savage, M.E.; Tsien, L. (Department of Physics and Astronomy, The University of Toledo, Toledo, Ohio 43606 (United States))

    1992-12-01

    Laser-driven physical vapor deposition (LDPVD) and radio-frequency (rf) sputtering have been used to fabricate thin-film solar cells on SnO[sub 2]-coated glass substrates. The laser-ablation process readily permits the use of several target materials in the same vacuum chamber and complete solar cell structures have been fabricated on SnO[sub 2]-coated glass using LDPVD for the CdS, CdTe, and CdCl[sub 2]. To date the best devices ([similar to]9% AM1.5) have been obtained after a post-deposition anneal at 400 [degree]C. In addition, cells have been fabricated with the combination of LDPVD CdS, rf-sputtered CdTe, and LDPVD CdCl[sub 2]. The performance of these cells indicates considerable promise for the potential of rf sputtering for CdTe photovoltaic devices. The physical mechanisms of LDPVD have been studied by transient optical spectroscopy on the laser ablation plume. These measurements have shown that, e.g., Cd is predominantly in the neutral atomic state in the plume but with a large fraction which is highly excited internally ([ge]6 eV) and that the typical neutral Cd translational kinetic energies perpendicular to the target are 20 eV and greater. Quality of as-grown and annealed films has been analyzed by optical absorption. Raman scattering, photoluminescence, electrical conductivity, Hall effect, x-ray diffraction, and SEM/EDS.

  8. Strain relaxation of CdTe on Ge studied by medium energy ion scattering

    Science.gov (United States)

    Pillet, J. C.; Pierre, F.; Jalabert, D.

    2016-10-01

    We have used the medium energy ion scattering (MEIS) technique to assess the strain relaxation in molecular-beam epitaxial (MBE) grown CdTe (2 1 1)/Ge (2 1 1) system. A previous X-ray diffraction study, on 10 samples of the same heterostructure having thicknesses ranging from 25 nm to 10 μm has allowed the measurement of the strain relaxation on a large scale. However, the X-ray diffraction measurements cannot achieve a stress measurement in close proximity to the CdTe/Ge interface at the nanometer scale. Due to the huge lattice misfit between the CdTe and Ge, a high degree of disorder is expected at the interface. The MEIS in channeling mode is a good alternative in order to profile defects with a high depth resolution. For a 21 nm thick CdTe layer, we observed, at the interface, a high density of Cd and/or Te atoms moved from their expected crystallographic positions followed by a rapid recombination of defects. Strain relaxation mechanisms in the vicinity of the interface are discussed

  9. Processing and characterization of large-grain thin-film CdTe

    International Nuclear Information System (INIS)

    Basic material studies addressing the growth and processing of CdTe have resulted in dense, defect-free as-grown CdTe films on 7059 glass with initial grain sizes of ∼0.2 μm. Innovations in postdeposition processing (no CdCl2) have resulted in films with >50 μm grain sizes. Scanning electron microscopy analyses confirm film density while concurrent cathodluminescence reveals a change in the recombination efficiency. Transmission electron microscopy analyses reveal that films grown below 300 degree C are defect-free, while films grown above 300 degree C contain defects. Photoluminescence lifetime measurements reveal a fivefold increase in lifetime following postdeposition processing of these films. These results were correlated with x-ray photoemission measurements of the Te 4d, Cd 4d, and valence band. This indicates that grain boundaries are the main factor limiting lifetimes. Based on these results, we have developed an understanding of the effects of oxygen and grain boundary oxides on postdeposition processing and enhanced grain growth

  10. About the use of photoacoustic spectroscopy for the optical characterization of semiconductor thin films: CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Marin, E.; Calderon, A. [CICATA-IPN, Av. Legaria 694, 11500 Mexico D.F. (Mexico); Vigil G, O.; Sastre, J.; Contreras P, G.; Aguilar H, J. [ESFM-IPN, 07738 Mexico D.F. (Mexico); Saucedo, E.; Ruiz, C.M. [Departamento de Fisica de Materiales, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Madrid (Spain)

    2006-07-01

    CdTe has been used satisfactorily in multiple and diverse technological applications such as detectors of X and gamma rays that operate at room temperature, for digital imagenology of X rays with medical and industrial applications and as active part in CdTe/CdS solar cells. In form of films, CdTe is generally grown with thicknesses ranging between 3 and 15 {mu}m, for which it is difficult to measure, by means of optical techniques, absorption coefficients greater than 10{sup 3} cm{sup -1} because nearly full absorption of light should occur below 800 nm. The exact determination of the optical absorption coefficient in detectors on the basis of CdTe is very important since this parameter determines the absorption length at which 90% of the photons with energies over the forbidden zone of the CdTe will be absorbed by this. In CdS/CdTe polycrystalline solar cells the greater efficiency of conversion have been reported for film thicknesses of 10 mm, however, the optimal value of this parameter depends strongly on the method and the variables of growth. The optical absorption coefficient spectrum can be determined by several methods, often involving several approximations and the knowledge of some minority carrier related electronic parameters that reduce their application in general way. In this work we propose to determine the absorption coefficient in CdTe thin films by photoacoustic spectroscopy (PAS), because this technique allow us to obtain the optical absorption spectra in thicker layers and therefore the study of the influence of the several growth and post-growth processes in the optical properties of this thin films. We measure by PAS the optical-absorption coefficients of CdTe thin films in the spectral region near the fundamental absorption edge ranging from 1.0 to 2.4 eV using an open cell in the transmission configuration. The films were deposited on different substrates by the CSVT-HW (hot wall) technique. In order to study the influence of several

  11. Effect of substrate temperature on photoconductivity in CdTe thin films

    Energy Technology Data Exchange (ETDEWEB)

    Sarmah, K.C.; Das, H.L. (Dept. of Physics, Gauhati Univ., Assam (India))

    1991-03-20

    Thin films of highly pure (99.999%) CdTe grown by vacuum evaporation on glass substrates held at elevated temperatures have been found to be polycrystalline. Within the range from liquid nitrogen temperature to 425 K two distinct conductivity regions both in the dark and under illumination have been observed in all the films having different grain sizes. From lower temperatures to 285 K the conductivity is essentially temperature independent and above 285 K the potential barriers localized at grain boundaries limit the conductivity. (orig.).

  12. Effect of hydrazine hydrate on the luminescence properties of MPA capped CdTe nanocrystals in hot injection method

    International Nuclear Information System (INIS)

    In this research MPA capped CdTe nanocrystals with sizes around 2.7–3.5 nm were grown in aqueous solution. The process was performed through the reaction of NaHTe with MPA and CdCl2 solution in high temperature. The synthesis was carried out in two different states of standard and modified forms. In the modified synthesis, the hydrazine hydrate material was added to the MPA plus CdCl2 solution before injection. The evolution of the nanocrystals size and PL quantum yield was monitored during the heating time for the growth. The results demonstrated that for the standard synthesis the growth rate was slow. The CdTe nanocrystals with high PL quantum yields were achieved in more than 10 h of heating. In contrast for the modified synthesis the growth rate was considerably higher. In this state a band edge emission with PL quantum yield of about 26% was achieved for the MPA capped CdTe nanocrystals in just 2 h of the heating process. - Highlights: • MPA capped CdTe nanocrystals are synthesized without and in presence of hydrazine hydrate. • The growth rate and photoluminescence Q.Y. were investigated and compared for two different states. • The growth rate was considerably faster for the state of applying hydrazine hydrate. • Despite the fast growth in presence of hydrazine hydrate, a proper PL quantum yield was achieved in just 2 h of heating

  13. Optical properties versus growth conditions of CdTe submonolayers inserted in ZnTe quantum wells

    Science.gov (United States)

    Calvo, Vincent; Magnea, Noël; Taliercio, Thierry; Lefebvre, Pierre; Allègre, Jacques; Mathieu, Henry

    1998-12-01

    Standard and piezomodulated optical spectroscopy is performed on ZnTe quantum wells embedding integer and fractional monolayers of CdTe. The samples, grown in a molecular-beam-epitaxy setup on the (001) surface of ZnTe substrates, all basically consist of 120-ML-wide ZnTe/(Zn,Mg)Te quantum wells, and some of them contain five equally spaced full or half-monolayers of CdTe, producing monomolecular islands of CdTe ``buried'' in the wide host ZnTe well. The latter behave as efficient recombination centers for excitons. In order to change the size and the configuration of the islands, various growth parameters have been changed between the different samples, e.g., the growth process (molecular-beam epitaxy of binaries or ternaries, or atomic-layer epitaxy) or the temperature. From spectroscopic measurements, the influence of these parameters is analyzed in detail, in terms of the size of the islands and of their in-plane spacing, or of the vertical correlation between these islands. The internal strain state of the CdTe insertions and the overall photoluminescence efficiency are also studied versus growth conditions.

  14. Study of CdTe(1¯1¯1¯) surface reconstructions by RHEED and XPS

    Science.gov (United States)

    Duszak, R.; Tatarenko, S.; Cibert, J.; Magnéa, N.; Mariette, H.; Saminadayar, K.

    1991-07-01

    The surface and bulk contributions have been distinguished in the angle-resolved X-ray photoemission spectra of Te(3d{5}/{2}) electronic state from the CdTe(1¯1¯1¯) surface with the binding energies Eb1 = 574.0 eV (±0.1 eV) and Eb2 = 572.8 eV (± 0.1 eV), respectively. Several reconstructions, namely (1 × 1), (2 × 2), (2√3 × 2√3)R30° and c(8 × 4) have been observed for the CdTe(1¯1¯1¯) MBE-grown surfaces for different tellurium fluxes as a function of the substrate temperature. The growth of subsequent CdTe(1¯1¯1¯) layers on the reconstructed surfaces was attempted under different conditions such as different tellurium pressure and sample temperature. A correlation between the reconstruction type and the phase of the corresponding RHEED oscillations observed during the growth was found. Bilayer surface representations derived from the "hexagonal ring" model recently proposed for the √19 structure observed on the GaAs(1¯1¯1¯) surface [1] are suggested for the (2 × 2), c(8 × 4) and (2√3 × 2√3)R30° CdTe(1¯1¯1¯) structure

  15. Protein Crystals of Raf Kinase

    Science.gov (United States)

    1995-01-01

    This image shows crystals of the protein raf kinase grown on Earth (photo a) and on USML-2 (photo b). The space-grown crystals are an order of magnitude larger. Principal Investigator: Dan Carter of New Century Pharmaceuticals

  16. Synthesis and Surface Modification of CdTe Nanocrystals

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    CdTe nanocrystals were prepared in aqueous solution via the reaction between Cd2+ and NaHTe in the presence of mercaptoacetic acid. Interactions between CdTe nanocrystals and phenylalanine were formed via electrostatic/coordinate self-assembly. The photoluminescence intensity of CdTe nanocrystals was improved obviously. The interaction mechanism was discussed and was considered to be surface passivation.

  17. CdTe Films Deposited by Closed-space Sublimation

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    CdTe films are prepared by closed-space sublimation technology. Dependence of film crystalline on substrate materials and substrate temperature is investigated. It is found that films exhibit higher crystallinity at substrate temperature higher than 400℃. And the CdTe films deposited on CdS films with higher crystallinity have bigger crystallite and higher uniformity. Treatment with CdCl2 methanol solution promotes the crystallite growth of CdTe films during annealing.

  18. Preparation and Properties of CdTe Polycrystalline Films for Solar Cells

    Institute of Scientific and Technical Information of China (English)

    ZHENG Huajing; ZHANG Jingquan; FENG Lianghuan; ZHENG Jiagui; CAI Wei; LI Bing; CAI Yaping

    2006-01-01

    The structure and characteristics of CdTe thin films are closely dependent on the whole deposition process in close-space sublimation (CSS). The physical mechanism of CSS was analyzed and the temperature distribution in CSS system was measured, and the influences of the increasing-temperature process and pressure on the preliminary nucleus creation were studied. The results indicate: the samples deposited at different pressures have a cubical structure of CdTe and the diffraction peaks of CdS and SnO2∶F. As the atmosphere pressure increases, the crystal size of CdTe decreases, the rate of the transparency of the thin film decreases and the absorption side moves towards the short-wave direction. After a 4-minute depositing process with a substrate temperature of 500 ℃ and a source temperature of 620 ℃, the polycrystalline thin films can be made, so the production of high-quality integrated cell with SnO2:F/CdS/CdTe/Au structure is hopeful.

  19. Optical absorption enhancement of CdTe nanostructures by low-energy nitrogen ion bombardment

    Science.gov (United States)

    Akbarnejad, E.; Ghoranneviss, M.; Mohajerzadeh, S.; Hantehzadeh, M. R.; Asl Soleimani, E.

    2016-02-01

    In this paper we present the fabrication of cadmium telluride (CdTe) nanostructures by means of RF magnetron sputtering followed by low-energy ion implantation and post-thermal treatment. We have thoroughly studied the structural, optical, and morphological properties of these nanostructures. The effects of nitrogen ion bombardment on the structural parameters of CdTe nanostructures such as crystal size, microstrain, and dislocation density have been examined. From x-ray diffractometer (XRD) analysis it could be deduced that N+ ion fluence and annealing treatment helps to form (3 0 0) orientation in the crystalline structure of cadmium-telluride films. Fluctuations in optical properties like the optical band gap and absorption coefficient as a function of N+ ion fluences have been observed. The annealing of the sample irradiated by a dose of 1018 ions cm-2 has led to great enhancement in the optical absorption over a wide range of wavelengths with a thickness of 250 nm. The enhanced absorption is significantly higher than the observed value in the original CdTe layer with a thickness of 3 μm. Surface properties such as structure, grain size and roughness are noticeably affected by varying the nitrogen fluences. It is speculated that nitrogen bombardment and post-annealing treatment results in a smaller optical band gap, which in turn leads to higher absorption. Nitrogen bombardment is found to be a promising method to increase efficiency of thin film solar cells.

  20. Photovoltaic minimodule based on CdTe

    International Nuclear Information System (INIS)

    CdS/CdTe solar cells were fabricated without antireflection coatings by successive growth without intermediate processing from the close space sublimation of CdS and CdTe thin layers on conductive and transparent SnO2/glass substrates. At 300 K and 100 mW/cm2 the following best photoelectric parameters were obtained: Isc= (18-19)mA/cm2 and Voc=(0,80-0,82)V. The conversion efficiency is around 10%. The quantum efficiency (QE) in the 510 nm and 845 nm range of wavelengths is on the order of 80-85%. The minimodule fabricated on the basis of the CdTe cells shows power of 0.45 W, corresponding to a voltage of 3 V, and current of 150 mA. (authors)

  1. Recycling of CdTe photovoltaic waste

    Science.gov (United States)

    Goozner, Robert E.; Long, Mark O.; Drinkard, Jr., William F.

    1999-01-01

    A method for extracting and reclaiming metals from scrap CdTe photovoltaic cells and manufacturing waste by leaching the waste with a leaching solution comprising nitric acid and water, skimming any plastic material from the top of the leaching solution, separating the glass substrate from the liquid leachate and electrolyzing the leachate to separate Cd from Te, wherein the Te is deposits onto a cathode while the Cd remains in solution.

  2. Effect of doping and heat treatment on the mechanical parameters of ZnSe(1-x)Tex crystals grown from the melt

    International Nuclear Information System (INIS)

    The mechanical properties of crystals of ZnSe(1-x)Tex (0 (1-x)Tex crystals varies in a similar manner. It is demonstrated that heat treatment and the presence of interblock boundaries affect the ultimate strength and the cracking resistance of the ZnSe(1-x)Tex crystals. This is an important factor which should be taken into account in mechanical treatment of the materials under investigation.

  3. Thin-film CdTe cells: Reducing the CdTe

    International Nuclear Information System (INIS)

    Polycrystalline thin-film CdTe is currently the dominant thin-film technology in world-wide PV manufacturing. With finite Te resources world-wide, it is appropriate to consider the limits to reducing the thickness of the CdTe layer in these devices. In our laboratory we have emphasized the use of magnetron sputtering for both CdS and CdTe achieving AM1.5 efficiency over 13% on 3 mm soda-lime glass with commercial TCO and 14% on 1 mm aluminosilicate glass. This deposition technique is well suited to good control of very thin layers and yields relatively small grain size which also facilitates high performance with ultra-thin layers. This paper describes our magnetron sputtering studies for fabrication of very thin CdTe cells. Our thinnest cells had CdTe thicknesses of 1 μm, 0.5 μm and 0.3 μm and yielded efficiencies of 12%, 9.7% and 6.8% respectively. With thinner cells Voc, FF and Jsc are reduced. Current-voltage (J-V), temperature dependent J-V (J-V-T) and apparent quantum efficiency (AQE) measurements provide valuable information for understanding and optimizing cell performance. We find that the stability under light soak appears not to depend on CdTe thickness from 2.5 to 0.5 μm. The use of semitransparent back contacts allows the study of bifacial response which is particularly useful in understanding carrier collection in the very thin devices.

  4. Impact of thermal annealing on physical properties of vacuum evaporated polycrystalline CdTe thin films for solar cell applications

    Science.gov (United States)

    Chander, Subhash; Dhaka, M. S.

    2016-06-01

    A study on impact of post-deposition thermal annealing on the physical properties of CdTe thin films is undertaken in this paper. The thin films of thickness 500 nm were grown on ITO and glass substrates employing thermal vacuum evaporation followed by post-deposition thermal annealing in air atmosphere within low temperature range 150-350 °C. These films were subjected to the XRD, UV-Vis NIR spectrophotometer, source meter, SEM coupled with EDS and AFM for structural, optical, electrical and surface topographical analysis respectively. The diffraction patterns reveal that the films are having zinc-blende cubic structure with preferred orientation along (111) and polycrystalline in nature. The crystallographic parameters are calculated and discussed in detail. The optical band gap is found in the range 1.48-1.64 eV and observed to decrease with thermal annealing. The current-voltage characteristics show that the CdTe films exhibit linear ohmic behavior. The SEM studies show that the as-grown films are homogeneous, uniform and free from defects. The AFM studies reveal that the surface roughness of films is observed to increase with annealing. The experimental results reveal that the thermal annealing has significant impact on the physical properties of CdTe thin films and may be used as absorber layer to the CdTe/CdS thin films solar cells.

  5. Study of the spectrometric performances of monolithic CdTe CdZnTe gamma ray detectors

    OpenAIRE

    Gros D'Aillon, Eric

    2005-01-01

    Pixelated monolithic CdTe / CdZnTe semiconductor gamma ray detectors are brought to replace scintillation detectors for medical applications, notably for single photon emission computed tomography (SPECT). In addition to compactness, they present better spectrometric performances: energy resolution, detection efficiency, and spatial resolution. Moreover, the photons depth of interaction in the crystal can be measured. This work aimed in studying experimentally and by simulation the correlatio...

  6. Study and development of new CdTe and CdZnTe detection structures for X and γ imagery

    International Nuclear Information System (INIS)

    The aim of this study is to show the interest of applying cadmium telluride (CdTe) for X- and γ- ray imaging applications, with specific technological (via contact nature) and geometric (via Frisch grids) structures suited for each application. This work is divided into three different but complementary parts: the first part describes a simulation model which allows a better understanding of CdTe based γ- ray detectors. The new feature of this model compared to previous ones, is that it is able to take into account the electric field's non uniform spatial distribution inside the detector s. The results enable us to de-convolute the influence of material and contact parameters on the spectrometric performances (energy resolution and peak/valley ratio) of CdTe based detectors; the second part presents different technological structures deposited upon CdTe, (grown by two different methods, i.e Bridgman and High Pressure Bridgman). These structures were characterised in X- and γ- ray detection; theoretical models are developed which allow a certain insight into the detection properties of each couple (material + contact); the third part deals with new contact geometries which allow a screening effect of the bulk (analogous to the Frisch grid effect in gaseous detectors) resulting in improved energy resolution and peak/valley ratios; encouraging first results on prototypes are presented and discussed. This work has allowed a better understanding of physical behaviour of CdTe based detectors, coupled with advances in technological issues to upgrade the overall performances of these detectors for application in X- and γ- ray imaging. (author)

  7. Giant pyroelectric coefficient determined from the frequency dependence of the pyroelectric signal generated by epitaxial Pb(Zr0.2Ti0.8)O3 layers grown on single crystal SrTiO3 substrates

    Science.gov (United States)

    Botea, M.; Iuga, A.; Pintilie, L.

    2013-12-01

    Epitaxial Pb(Zr0.2Ti0.8)O3 layers of good structural quality were grown on single crystal SrTiO3 substrates. The pyroelectric coefficient was estimated from the signal generated by the ferroelectric film working as a pyroelectric detector in the voltage mode, without pre-poling procedure. The obtained value is as high as 1.9 × 10-3 C/m2 K. The large value is attributed to the presence of 90° ferroelectric domains and to the compressive misfit strain, leading to an enhanced ferroelectric polarization.

  8. Determination of Ring-OSF Position in Czochralski Silicon Single Crystals by Numerical Analysis of Distribution of Grown-in Defects

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A numerical analysis technique that incorporates Voronkov's model were examined and used to estimate the distribution of defects during crystal growth. By comparisons of the distribution of the density of LSTD and the position of R-OSF in non-nitrogen-doped (non-N-doped) and nitrogen-doped (N-doped) silicon crystals, it is found that the results of the numerical analyses agree with practically evaluated data. The observations suggest that the R-OSF nucleus is a VO2 complex that is formed by bonds between oxygen atoms and residual vacancies consumed during the formation of void defects. This suggests that Voronkov's model can be used to accurately predict the generation and growth of defects in silicon crystals. This numerical analysis technique was also found to be an effective method of estimating the distribution of defects in silicon crystals during crystal growth.

  9. Growth of epitaxial CdTe/CdS heterostructures for single crystal thin film solar cell applications

    Energy Technology Data Exchange (ETDEWEB)

    Kessler, K.; Tiwari, A.N.; Blunier, S.; Zogg, H. [Swiss Federal Inst. of Tech., Zuerich (Switzerland). Arbeitsgemeinschaft fuer Industrielle Forschung

    1994-12-31

    Epitaxial CdTe/CdS heterostructures have been grown by molecular beam epitaxy onto BaF{sub 2} covered Si (111) substrates. An epitaxial BaF{sub 2} buffer is used for compatibility reasons, and because of easier dissolution during the lift-off processing. Epitaxy of cubic CdS (111) layers on BaF{sub 2}/Si (111) is achieved; electron channeling patterns exhibit a three-fold symmetry which is a characteristic for cubic crystal structures. The growth kinetics and structural properties of epitaxial CdS and CdTe/CdS have been studied with reflection high energy electron diffraction, Rutherford backscattering spectrometry and X-ray diffraction rocking curve measurements.the full width at half maximum of the (222) CdS and (333) CdTe X-ray peaks are {approximately} 1,150 arc sec for 2.7 and 3.4 {micro}m thick CdS and CdTe layers, respectively. To fabricate CdTe/CdS single crystal thin film solar cells, a lift-off process has been developed to remove the epitaxial layers from the Si substrates.

  10. Homogeneous CdTe quantum dots-carbon nanotubes heterostructures

    International Nuclear Information System (INIS)

    The development of homogeneous CdTe quantum dots-carbon nanotubes heterostructures based on electrostatic interactions has been investigated. We report a simple and reproducible non-covalent functionalization route that can be accomplished at room temperature, to prepare colloidal composites consisting of CdTe nanocrystals deposited onto multi-walled carbon nanotubes (MWCNTs) functionalized with a thin layer of polyelectrolytes by layer-by-layer technique. Specifically, physical adsorption of polyelectrolytes such as poly (4-styrene sulfonate) and poly (diallyldimethylammonium chloride) was used to deagglomerate and disperse MWCNTs, onto which we deposited CdTe quantum dots coated with mercaptopropionic acid (MPA), as surface ligand, via electrostatic interactions. Confirmation of the CdTe quantum dots/carbon nanotubes heterostructures was done by transmission and scanning electron microscopies (TEM and SEM), dynamic-light scattering (DLS) together with absorption, emission, Raman and infrared spectroscopies (UV–vis, PL, Raman and FT-IR). Almost complete quenching of the PL band of the CdTe quantum dots was observed after adsorption on the MWCNTs, presumably through efficient energy transfer process from photoexcited CdTe to MWCNTs. - Highlights: • Highly homogeneous CdTe-carbon nanotubes heterostructures were prepared. • Simple and reproducible non-covalent functionalization route. • CdTe nanocrystals homogeneously deposited onto multi-walled carbon nanotubes. • Efficient energy transfer process from photoexcited CdTe to MWCNTs

  11. Homogeneous CdTe quantum dots-carbon nanotubes heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Vieira, Kayo Oliveira [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil); Bettini, Jefferson [Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, CEP 13083-970, Campinas, SP (Brazil); Ferrari, Jefferson Luis [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil); Schiavon, Marco Antonio, E-mail: schiavon@ufsj.edu.br [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil)

    2015-01-15

    The development of homogeneous CdTe quantum dots-carbon nanotubes heterostructures based on electrostatic interactions has been investigated. We report a simple and reproducible non-covalent functionalization route that can be accomplished at room temperature, to prepare colloidal composites consisting of CdTe nanocrystals deposited onto multi-walled carbon nanotubes (MWCNTs) functionalized with a thin layer of polyelectrolytes by layer-by-layer technique. Specifically, physical adsorption of polyelectrolytes such as poly (4-styrene sulfonate) and poly (diallyldimethylammonium chloride) was used to deagglomerate and disperse MWCNTs, onto which we deposited CdTe quantum dots coated with mercaptopropionic acid (MPA), as surface ligand, via electrostatic interactions. Confirmation of the CdTe quantum dots/carbon nanotubes heterostructures was done by transmission and scanning electron microscopies (TEM and SEM), dynamic-light scattering (DLS) together with absorption, emission, Raman and infrared spectroscopies (UV–vis, PL, Raman and FT-IR). Almost complete quenching of the PL band of the CdTe quantum dots was observed after adsorption on the MWCNTs, presumably through efficient energy transfer process from photoexcited CdTe to MWCNTs. - Highlights: • Highly homogeneous CdTe-carbon nanotubes heterostructures were prepared. • Simple and reproducible non-covalent functionalization route. • CdTe nanocrystals homogeneously deposited onto multi-walled carbon nanotubes. • Efficient energy transfer process from photoexcited CdTe to MWCNTs.

  12. Carbon analysis in CdTe by nuclear activation

    Science.gov (United States)

    Chibani, H.; Stoquert, J. P.; Hage-Ali, M.; Koebel, J. M.; Abdesselam, M.; Siffert, P.

    1991-06-01

    We describe the capabilities of the nuclear reaction 12C(d, n) 13Nlimit→β +13C the measurement of absolute concentrations of C in CdTe by the charged particle activation (CPA) method. This technique is used to determine the segregation coefficient of C introduced as an impurity in CdTe.

  13. A novel visible-light Nd-doped CdTe photocatalyst for degradation of Reactive Red 43:Synthesis, characterization, and photocatalytic properties

    Institute of Scientific and Technical Information of China (English)

    Younes HANIFEHPOUR; Nazanin HAMNABARD; Bamin KHOMAMI; Sang Woo JOO; Bong-Ki MIN; Jae Hak JUNG

    2016-01-01

    Novel high-efficiency visible-light-sensitive Nd-doped CdTe nanoparticles were prepared with various doping concentra-tions of neodymium ion by a facile hydrothermal method. The reaction products were analyzed via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoelectron spectroscopy (XPS), and UV-Vis diffuse re-flectance spectroscopy techniques. Red shift was seen in the absorption band edge peak in the UV-Vis absorbance spectrum with in-creasing Nd content. The XRD and XPS results confirmed that Nd ions successfully replaced Cd atoms and were incorporated into the crystal lattice of CdTe. SEM and TEM images indicated spherical structure and high crystallinity. Even at a very low Nd/CdTe molar ratio of 2 mol.%, Nd doping could greatly enhance the photocatalytic activity of CdTe. The photocatalytic activity of Nd-doped CdTe nanoparticles was evaluated by monitoring the decolorization of RRed 43 in aqueous solution under visible-light irradiation. The color removal efficiency of Nd0.08Cd0.92Te and pure CdTe were 83.14% and 14.32% after 100 min of treatment, respectively. Among different amounts of the doping agent, 8 mol.% Nd indicated the highest decolorization. The presence of radical scavengers such as Cl−, CO32−, SO42−, and buthanol was found to reduce the decolorization efficiency.

  14. Crystal growth of artificial snow

    Science.gov (United States)

    Kimura, S.; Oka, A.; Taki, M.; Kuwano, R.; Ono, H.; Nagura, R.; Narimatsu, Y.; Tanii, J.; Kamimiytat, Y.

    1984-01-01

    Snow crystals were grown onboard the space shuttle during STS-7 and STS-8 to facilitate the investigation of crystal growth under conditions of weightlessness. The experimental design and hardware are described. Space-grown snow crystals were polyhedrons looking like spheres, which were unlike snow crystals produced in experiments on Earth.

  15. Structural properties of Cu2O epitaxial films grown on c-axis single crystal ZnO by magnetron sputtering

    Science.gov (United States)

    Gan, J.; Gorantla, S.; Riise, H. N.; Fjellvâg, Ø. S.; Diplas, S.; Løvvik, O. M.; Svensson, B. G.; Monakhov, E. V.; Gunnæs, A. E.

    2016-04-01

    Epitaxial Cu2O films grown by reactive and ceramic radio frequency magnetron sputtering on single crystalline ZnO (0001) substrates are investigated. The films are grown on both O- and Zn-polar surface of the ZnO substrates. The Cu2O films exhibit a columnar growth manner apart from a ˜5 nm thick CuO interfacial layer. In comparison to the reactively sputtered Cu2O, the ceramic-sputtered films are less strained and appear to contain nanovoids. Irrespective of polarity, the Cu2O grown by reactive sputtering is observed to have (111)Cu2O||(0001)ZnO epitaxial relationship, but in the case of ceramic sputtering the films are found to show additional (110)Cu2O reflections when grown on O-polar surface. The observed CuO interfacial layer can be detrimental for the performance of Cu2O/ZnO heterojunction solar cells reported in the literature.

  16. Multidirectional channeling analysis of epitaxial CdTe layers using an automatic RBS/channeling system

    Energy Technology Data Exchange (ETDEWEB)

    Wielunski, L.S.; Kenny, M.J. [CSIRO, Lindfield, NSW (Australia). Applied Physics Div.

    1993-12-31

    Rutherford Backscattering Spectrometry (RBS) is an ion beam analysis technique used in many fields. The high depth and mass resolution of RBS make this technique very useful in semiconductor material analysis [1]. The use of ion channeling in combination with RBS creates a powerful technique which can provide information about crystal quality and structure in addition to mass and depth resolution [2]. The presence of crystal defects such as interstitial atoms, dislocations or dislocation loops can be detected and profiled [3,4]. Semiconductor materials such as CdTe, HgTe and Hg+xCd{sub 1-x}Te generate considerable interest due to applications as infrared detectors in many technological areas. The present paper demonstrates how automatic RBS and multidirectional channeling analysis can be used to evaluate crystal quality and near surface defects. 6 refs., 1 fig.

  17. Growth and characterization of CdTe single quantum wells confined by Cd 1- xZn xTe alloy and short period CdTe/ZnTe superlattice

    Science.gov (United States)

    Magnea, N.; Lentz, G.; Mariette, H.; Feuillet, G.; Dal'bo, F.; Tuffigo, H.

    1989-02-01

    A comparative study of structural and optical properties of CdTe single quantum wells has been performed. Very efficient CdTe-Cd 1-xZn xTe (x Zn ≤ 0.2) wells have been grown and short period superlattices appear as a promising substitute of the alloy.

  18. Epitaxial single-crystal thin films of MnxTi1-xO2-δ grown on (rutile)TiO2 substrates with pulsed laser deposition: Experiment and theory

    Energy Technology Data Exchange (ETDEWEB)

    Ilton, Eugene S.; Droubay, Timothy C.; Chaka, Anne M.; Kovarik, Libor; Varga, Tamas; Arey, Bruce W.; Kerisit, Sebastien N.

    2015-02-01

    Epitaxial rutile-structured single-crystal MnxTi1-xO2-δ films were synthesized on rutile- (110) and -(001) substrates using pulsed laser deposition. The films were characterized by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and aberration-corrected transmission electron microscopy (ACTEM). Under the present conditions, 400oC and PO2 = 20 mTorr, single crystal epitaxial thin films were grown for x = 0.13, where x is the nominal average mole fraction of Mn. In fact, arbitrarily thick films could be grown with near invariant Mn/Ti concentration profiles from the substrate/film interface to the film surface. In contrast, at x = 0.25, Mn became enriched towards the surface and a secondary nano-scale phase formed which appeared to maintain the basic rutile structure but with enhanced z-contrast in the tunnels, or tetrahedral interstitial sites. Ab initio thermodynamic calculations provided quantitative estimates for the destabilizing effect of expanding the β-MnO2 lattice parameters to those of TiO2-rutile, the stabilizing effect of diluting Mn with increasing Ti concentration, and competing reaction pathways.

  19. Epitaxial single-crystal thin films of MnxTi1 - xO2 - δ grown on (rutile)TiO2 substrates with pulsed laser deposition: Experiment and theory

    Science.gov (United States)

    Ilton, Eugene S.; Droubay, Timothy C.; Chaka, Anne M.; Kovarik, Libor; Varga, Tamas; Arey, Bruce W.; Kerisit, Sebastien N.

    2015-02-01

    Epitaxial rutile-structured single-crystal MnxTi1 - xO2 - δ films were synthesized on rutile- (110) and -(001) substrates using pulsed laser deposition. The films were characterized by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and aberration-corrected transmission electron microscopy (ACTEM). Under the present conditions, 400 °C and PO2 = 20 mTorr, single crystal epitaxial thin films were grown for x = 0.13, where x is the nominal average mole fraction of Mn. In fact, arbitrarily thick films could be grown with near invariant Mn/Ti concentration profiles from the substrate/film interface to the film surface. In contrast, at x = 0.25, Mn became enriched towards the surface and a secondary nano-scale phase formed which appeared to maintain the basic rutile structure but with enhanced z-contrast in the tunnels, or interstitial sites. Ab initio thermodynamic calculations provided quantitative estimates for the destabilizing effect of expanding the β-MnO2 lattice parameters to those of TiO2-rutile, the stabilizing effect of diluting Mn with increasing Ti concentration, and competing reaction pathways for surface oxide formation.

  20. Extended defects in MBE-grown CdTe-based solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Wichrowska, Karolina; Wosinski, Tadeusz; Kret, Slawomir; Chusnutdinow, Sergij; Karczewski, Grzegorz [Institute of Physics, Polish Academy of Sciences, Warsaw (Poland); Rawski, Michal [Analytical Laboratory, Maria Curie-Sklodowska University, Lublin (Poland); Yastrubchak, Oksana [Institute of Physics, Maria Curie-Sklodowska University, Lublin (Poland)

    2015-08-15

    Extended defects in the p -ZnTe/n -CdTe heterojunctions grown by the molecular-beam epitaxy technique on two different substrates, GaAs and CdTe, have been investigated by deep-level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). Four hole traps, called H1 to H4, and one electron trap, called E3, have been revealed in the DLTS spectra measured for the heterojunctions grown on the GaAs substrates. The H1, H3, H4 and E3 traps have been attributed to the electronic states of dislocations on the ground of their logarithmic capture kinetics. The DLTS peaks associated with the H1 and E3 traps were not observed in the DLTS spectra measured for the heterojunction grown on the CdTe substrate. They are most likely associated with threading dislocations generated at the mismatched interface with the GaAs substrate. Cross-sectional TEM images point out that they are dislocations of the 60 -type. In both the types of heterojunctions the H4 trap was observed only under forward-bias filling pulse, suggesting that this trap is associated with the CdTe/ZnTe interface. In addition, TEM images revealed also the presence of intrinsic and extrinsic stacking faults in the CdTe layers, which may considerably affect their electronic properties. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Substrate heating effect on the growth of a CdTe film on an InSb substrate by vacuum evaporation

    Science.gov (United States)

    Jiann-Ruey, Chen; Mau-Phon, Houng; Fenq-Lin, Jenq; Chien-Shyong, Fang; Wan-Sun, Tse

    1991-07-01

    Epitaxial CdTe thin films were grown on the (111) oriented InSb substrate by vacuum evaporation, with the substrate kept at 190-225°C during the film deposition. The chamber pressure during film deposition was at 3.5 × 10-6 mbar. X-ray diffraction was used to determine the film structure, while the full width at half maximum (FWHM) of the X-ray diffraction peak was used to examine the crystallinity of the as-deposited films. The film morphology was observed by the scanning electron microscope (SEM), and the film composition was determined by electron probe microanalysis (EPMA). The film quality was examined by infrared transmission spectroscopy. Results indicate that the quality of the grown CdTe films was improved with the higher substrate temperature during the film deposition.

  2. CdTe ambulatory ventricular function monitor

    International Nuclear Information System (INIS)

    A prototype device consisting of two arrays of CdTe detectors, ECG amplifiers and gate, microprocessor, and tape recorder was devised to record simultaneous ECG and radionuclide blood pool data from the left ventricle for extended periods during normal activity. The device is intended to record information concerning both normal and abnormal physiology of the heart and to permit the evaluation of new pharmaceuticals under everyday conditions. Preliminary results indicate that the device is capable of recording and reading out data from both phantoms and patients

  3. TEM studies of Er sup + - implanted CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Morawiec, J.; Golacki, Z. (Inst. of Physics, Polish Academy of Sciences, Warsaw (Poland))

    1991-01-01

    The structure and the depth distribution of radiation damage caused by erbium implantation (E{sub i}=100 keV, D=5x10{sup 15} cm{sup -2}, T{sub i}=LNT) in <111> cadmium telluride have been investigated by means of planar-view and cross-sectional TEM techniques. It is found that the implantation disturbes the CdTe target up to the depth well-beyond the calculated projected range (that is > or approx.x5R{sub p}). The resulting damage structure consists of well-defined defects: precipitates, stacking faults, dislocation loops, and dislocation networks, which appear to be segregated with depth forming a sequence of homogeneously faulted zones. This characteristical and deep damage is suggested to be formed on dynamic annealing in response to internal stresses (caused by lattice parameter mismatch) which are high enough to produce plastic relaxation with dislocation generation and slip. This study is aimed at describing the ion-implantation-induced damage in single crystal cadmium telluride caused by Er{sup +} ions by means of transmission electron microscopy. (orig.).

  4. CdTe reflection anisotropy line shape fitting

    Energy Technology Data Exchange (ETDEWEB)

    Molina-Contreras, J.R., E-mail: rmolina@correo.ita.mx [Departamento de Ingenieria Electrica y Electronica, Instituto Tecnologico de Aguascalientes, Av. Lopez Mateos 1801 Ote. Fracc. Bona Gens, Aguascalientes, Ags, 20256 (Mexico)

    2010-10-25

    In this paper, an empirical novel plane-wave time dependent ensemble is introduced to fit the RA, the reflectance (R) and the imaginary part of the dielectric function oscillation measured around the E{sub 1} and E{sub 1} + {Delta}{sub 1} transition region in II-VI semiconductors. By applying the new plane-wave time dependent ensemble to the measured spectrum for a (0 0 1) oriented CdTe undoped commercial wafer, crystallized in a zinc-blende structure, a very good agreement was found between the measured spectrum and the fitting. In addition to this, the reliability of the plane-wave time dependent ensemble was probed, by comparing the results with the calculated fitting in terms of a Fourier series and in terms of a six-order polynomial fit. Our analysis suggests, that the experimental oscillation in the line shape of the RA cannot be fitted with a Fourier series using harmonics multiples of the number which dominates the measured RA spectra in the argument of the plane-wave ensemble.

  5. Structural and AC conductivity study of CdTe nanomaterials

    Science.gov (United States)

    Das, Sayantani; Banerjee, Sourish; Sinha, T. P.

    2016-04-01

    Cadmium telluride (CdTe) nanomaterials have been synthesized by soft chemical route using mercapto ethanol as a capping agent. Crystallization temperature of the sample is investigated using differential scanning calorimeter. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to cubic structure with the average particle size of 20 nm. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 313 to 593 K and in a frequency range from 42 Hz to 1.1 MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance (R) and a constant phase element (CPE). Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using modified Cole-Cole equation. The temperature dependence relaxation time is found to obey the Arrhenius law having activation energy ~0.704 eV. The frequency dependent conductivity spectra are found to follow the power law. The frequency dependence ac conductivity is analyzed by power law.

  6. Influence of cerium doping on the dielectric relaxation of Sr{sub 0.75}Ba{sub 0.25}Nb{sub 2}O{sub 6} single crystal grown by the double crucible Stepanov technique

    Energy Technology Data Exchange (ETDEWEB)

    Bhaumik, Indranil, E-mail: neel@rrcat.gov.in [Crystal Growth Laboratory, LMDDD, Raja Ramanna Centre for Advanced Technology, Indore (India); Ganesamoorthy, S. [XS and CGS, CMPD, MSG, Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Bhatt, R. [Crystal Growth Laboratory, LMDDD, Raja Ramanna Centre for Advanced Technology, Indore (India); Subramanian, N. [XS and CGS, CMPD, MSG, Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Karnal, A.K.; Gupta, P.K. [Crystal Growth Laboratory, LMDDD, Raja Ramanna Centre for Advanced Technology, Indore (India); Takekawa, S.; Kitamura, K. [Polar Domain Engineering Group, NIMS, Namiki, Tsukuba (Japan)

    2015-02-05

    Highlights: • Incorporation of Ce in the lattice reduces dielectric maxima in Sr{sub 0.75}Ba{sub 0.25}Nb{sub 2}O{sub 6}. • It increases degree of diffusiveness and lowers the temperature of dielectric maxima. • These are due to introduction of addition random field via created point defects. • Both of the crystals undergo non-debye type relaxation. • VF fitting revealed that attempt frequency reduced by one order on Ce doping. - Abstract: The effect of Ce doping on the dielectric relaxation in Sr{sub 0.75}Ba{sub 0.25}Nb{sub 2}O{sub 6} single crystal grown by double crucible Stepanov technique has been investigated. It has been observed that the incorporation of Ce ion in the lattice reduces the dielectric maxima. It further increases the degree of diffusiveness and lowers the temperature of dielectric maxima as a result of the introduction of additional random field via created point defects. Both the undoped and Ce doped crystals undergo a non-debye type relaxation. Vogel–Fulcher fitting reveals that the attempt frequency reduced by one order of magnitude on Ce doping.

  7. Cu Migration in Polycrystalline CdTe Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Da [Arizona State University; Akis, Richard [Arizona State University; Brinkman, Daniel [Arizona State University; Sankin, Igor [First Solar; Fang, Tian [First Solar; Vasileska, Dragica [Arizona State University; Ringhofer, Christian [Arizona State University

    2014-03-12

    An impurity reaction-diffusion model is applied to Cu defects and related intrinsic defects in polycrystalline CdTe for a better understanding of Cu’s role in the cell level reliability of CdTe PV devices. The simulation yields transient Cu distributions in polycrystalline CdTe during solar cell processing and stressing. Preliminary results for Cu migration using available diffusivity and solubility data show that Cu accumulates near the back contact, a phenomena that is commonly observed in devices after back-contact processing or stress conditions.

  8. Auger relative sensitivivity factors for CdTe oxide

    OpenAIRE

    Bartolo-Pérez, P.; Peña, J. L.; M.H. Farías

    1999-01-01

    The Auger lineshape of Te MNN in measurements of Auger spectra of CdTe oxide films with various degrees of oxidation was analyzed. By using standards from stoichiometric compounds, Auger relative sensitivity factors (RSF´s) of Cd, Te and O for CdTe oxide thin films were obtained. The value of the RFS of oxygen is about constant, 0.27-0.28, for the standard compound, CdO, TeO2 and CdTeO3 (considering the RSF of Cd as 1). However, the obtained RSF of Te changes from 0.69 in CdTe up to 0.87 in C...

  9. Counting efficiency of a CdTe detector

    International Nuclear Information System (INIS)

    The purpose of this work is to obtain some data about the energy dependence of the sensitivity of a CdTe detector in order to use it for a miniature dose rate meter. The intrinsic efficiencies of the CdTe detector were measured for several photon energies between 22 and 835 keV. The results showed the great dependence of the efficiency of the CdTe detector on photon energy, for example, the intrinsic efficiencies for the photons of 122 keV and 835 keV were 71% and 8.7% respectively. Some further problems were also presented and discussed. (author)

  10. Spin dynamics in bulk CdTe at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Nahalkova, P. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Nemec, P. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic)]. E-mail: nemec@karlov.mff.cuni.cz; Sprinzl, D. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Belas, E. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Horodysky, P. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Franc, J. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Hlidek, P. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Maly, P. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic)

    2006-01-25

    In this paper, we report on the room temperature dynamics of spin-polarized carriers in undoped bulk CdTe. Platelets of CdTe with different concentration of preparation-induced dislocations were prepared by combining the mechanical polishing and chemical etching. Using the polarization-resolved pump-probe experiment in transmission geometry, we have observed a systematic decrease of both the signal polarization and the electron spin dephasing time (from 52 to 36 ps) with the increased concentration of defects. We have suggested that the Elliot-Yafet mechanism might be the dominant spin dephasing mechanism in platelets of CdTe at room temperature.

  11. Spin dynamics in bulk CdTe at room temperature

    International Nuclear Information System (INIS)

    In this paper, we report on the room temperature dynamics of spin-polarized carriers in undoped bulk CdTe. Platelets of CdTe with different concentration of preparation-induced dislocations were prepared by combining the mechanical polishing and chemical etching. Using the polarization-resolved pump-probe experiment in transmission geometry, we have observed a systematic decrease of both the signal polarization and the electron spin dephasing time (from 52 to 36 ps) with the increased concentration of defects. We have suggested that the Elliot-Yafet mechanism might be the dominant spin dephasing mechanism in platelets of CdTe at room temperature

  12. Process Development for High Voc CdTe Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Ferekides, C. S.; Morel, D. L.

    2011-05-01

    This is a cumulative and final report for Phases I, II and III of this NREL funded project (subcontract # XXL-5-44205-10). The main research activities of this project focused on the open-circuit voltage of the CdTe thin film solar cells. Although, thin film CdTe continues to be one of the leading materials for large-scale cost-effective production of photovoltaics, the efficiency of the CdTe solar cells have been stagnant for the last few years. This report describes and summarizes the results for this 3-year research project.

  13. Characterization measurement of a thick CdTe detector for BNCT-SPECT - detection efficiency and energy resolution.

    Science.gov (United States)

    Murata, Isao; Nakamura, Soichiro; Manabe, Masanobu; Miyamaru, Hiroyuki; Kato, Itsuro

    2014-06-01

    Author׳s group is carrying out development of BNCT-SPECT with CdTe device, which monitors the therapy effect of BNCT in real-time. From the design calculations, the dimensions were fixed to 1.5×2×30mm(3). For the collimator it was confirmed that it would have a good spatial resolution and simultaneously the number of counts would be acceptably large. After producing the CdTe crystal, the characterization measurement was carried out. For the detection efficiency an excellent agreement between calculation and measurement was obtained. Also, the detector has a very good energy resolution so that gamma-rays of 478keV and 511keV could be distinguished in the spectrum. PMID:24581600

  14. Annealing conditions for intrinsic CdTe

    Science.gov (United States)

    Berding, M. A.

    1999-01-01

    Equilibrium native defect densities in CdTe are calculated from ab initio methods, and compared with experimental results. We find that CdTe is highly compensated p type under tellurium-saturated conditions, with the cadmium vacancy as the dominant acceptor and the tellurium antisite as the compensating donor. This finding is in agreement with recent experiments that find a much larger deviation from stoichiometry than would be predicted by the electrically active defects. Under cadmium-saturated conditions, cadmium interstitials are predicted to dominate and the material is found to be n type. Native defect concentrations and the corresponding carrier concentrations are predicted as a function of processing conditions, and can serve as a guide to postgrowth anneals to manipulate the conductivity of undoped material for applications in x- and γ-ray spectrometers. Furthermore, we show that by choosing appropriate annealing conditions and extrinsic dopants, one can increase the operating efficiency of nuclear spectrometers by reducing the density of specific native defects that produce midgap trapping states.

  15. High efficiency pixellated CdTe detector

    International Nuclear Information System (INIS)

    Position sensitive detectors constructed from compound semiconductors (CdTe, CdZnTe, HgI2) are being developed for a variety of applications where high sensitivity and improved energy resolution are significant advantages over scintillator or gas based systems. We have investigated the possibility of using a CdTe detector array in a SPECT gamma camera that would require a high efficiency at 140 keV. The problem of worsening photopeak efficiencies in thick detectors (due to incomplete charge collection) makes it difficult to maintain a high efficiency which, ironically, is the primary reason for choosing a thicker detector. Recent research has shown that following a simple geometrical design criterion can greatly reduce this deleterious effect. This paper reports on the results from a small prototype pixellated array fabricated using this design. We verify the 'small pixel effect' for a detector thickness and pixel size significantly larger than those used in most other work. A 9-element detector (1 x 1 mm pixels, 4 mm thick) has been fabricated and characterized in terms of energy resolution, peak-to-valley ratio and detection efficiency. Testing of the detector in a fast pulse mode to obtain its high count rate response has also been performed. (orig.)

  16. Conditions for the deposition of CdTe by electrochemical atomic layer epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Gregory, B.W.; Suggs, D.W.; Stickney, J.L. (School of Chemical Sciences, Univ. of Georgia, Athens, GA (US))

    1991-05-01

    In this paper the method of electrochemical atomic layer epitaxy (ECALE) is described. It involves the alternated electrochemical deposition of atomic layers of elements to form compound semiconductors. It is being investigated as a method for forming epitaxial thin films. Presently, it appears that the method is applicable to a wide range of compound semiconductors composed of a metal and one of the following main group elements: S, Se, Te, As, Sb, or Br. Initial studies have involved CdTe deposition. Factors controlling deposit structure and composition are discussed here. Preliminary results which show that ordered electrodeposits of CdTe can be formed by the ECALE method are also presented. Results reported here were obtained with both a polycrystalline Au thin-layer electrochemical cell and a single-crystal Au electrode with faces oriented to the (111), (110), and (100) planes. The single-crystal electrode was contained in a UHV surface analysis instrument with an integral electrochemical cell. Deposits were examined without their exposure to air using LEED and Auger electron spectroscopy. Coverages were determined using coulometry in the thin-layer electrochemical cell.

  17. Structure characterization of Pd/Co/Pd tri-layer films epitaxially grown on MgO single-crystal substrates

    Energy Technology Data Exchange (ETDEWEB)

    Tobari, Kousuke, E-mail: tobari@futamoto.elect.chuo-u.ac.jp; Ohtake, Mitsuru; Nagano, Katsumasa; Futamoto, Masaaki

    2011-09-30

    Pd/Co/Pd tri-layer films were prepared on MgO substrates of (001), (111), and (011) orientations at room temperature by ultra high vacuum rf magnetron sputtering. The detailed film structures around the Co/Pd and the Pd/Co interfaces are investigated by reflection high energy electron diffraction. Pd layers of (001){sub fcc}, (111){sub fcc}, and (011){sub fcc} orientations epitaxially grow on the respective MgO substrates. Strained fcc-Co(001) single-crystal layers are formed on the Pd(001){sub fcc} layers by accommodating the fairly large lattice mismatch between the Co and the Pd layers. On the Co layers,, Pd polycrystalline layers are formed. When Co films are formed on the Pd(111){sub fcc} and the Pd(011){sub fcc} layers, atomic mixing is observed around the Co/Pd interfaces and fcc-CoPd alloy phases are coexisting with Co crystals. The Co crystals formed on the Pd(111){sub fcc} layers consist of hcp(0001) + fcc(111) and Pd(111){sub fcc} epitaxial layers are formed on the Co layers. Co crystals epitaxially grow on the Pd(011){sub fcc} layers with two variants, hcp(11-bar 00) and fcc(111). On the Co layers, Pd(011){sub fcc} epitaxial layers are formed.

  18. Aragonite crystals grown on bones by reaction of CO2 with nanostructured Ca(OH)2 in the presence of collagen. Implications in archaeology and paleontology.

    Science.gov (United States)

    Natali, Irene; Tempesti, Paolo; Carretti, Emiliano; Potenza, Mariangela; Sansoni, Stefania; Baglioni, Piero; Dei, Luigi

    2014-01-21

    The loss of mechanical properties affecting archeological or paleontological bones is often caused by demineralization processes that are similar to those driving the mechanisms leading to osteoporosis. One simple way to harden and to strengthen demineralized bone remains could be the in situ growth of CaCO3 crystals in the aragonite polymorph - metastable at atmospheric pressure -which is known to have very strong mechanical strength in comparison with the stable calcite. In the present study the controlled growth of aragonite crystals was achieved by reaction between atmospheric CO2 and calcium hydroxide nanoparticles in the presence of collagen within the deteriorated bones. In a few days the carbonation of Ca(OH)2 particles led to a mixture of calcite and aragonite, increasing the strength of the mineral network of the bone. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) and Fourier transform infrared (FT-IR) spectrometry showed that aragonite crystallization was achieved. The effect of the aragonite crystal formation on the mechanical properties of the deteriorated bones was investigated by means of X-rays microtomography, helium porosimetry, atomic force microscopy (AFM), and Vickers microhardness techniques. All these data enabled to conclude that the strength of the bones increased of a factor of 50-70% with respect to the untreated bone. These results could have immediate impact for preserving archeological and paleontological bone remains.

  19. The effect on CdS/CdTe solar cell conversion efficiency of the presence of fluorine in the usual CdCl2 treatment of CdTe

    OpenAIRE

    Echendu, O. K.; Dharmadasa, I.

    2015-01-01

    The addition of CdF2 to the CdCl2 solution used in the well-known CdCl2 treatment of CdS/CdTe solar cells has been observed to drastically improve the conversion efficiency of fully fabricated CdS/CdTe solar cells. The observed improvement is as a result of further enhancement of structural and optoelectronic properties of the CdCl2+CdF2-treated CdTe layers compared to the CdCl2-treated CdTe layers. A set of CdS/CdTe samples were grown by electrochemical deposition under different conditions ...

  20. 提拉法生长大尺寸γ-LiAlO2单晶的研究%Study on Large-size γ-LiAlO2 Single Crystal Grown by Czochralski Technique

    Institute of Scientific and Technical Information of China (English)

    彭观良; 邹军; 庄漪; 张涟翰; 周国清; 周圣明; 徐军; 干福熹

    2005-01-01

    由于与GaN晶格失配小(约1.4%),γ-LiAlO2单晶有望成为一种很有希望的CaN外延衬底材料.本文使用提拉法生长出了尺寸达φ45×50mm3的γ-LiAlO2单晶.对该晶体毛坯的各个有代表性的位置作了X射线粉末衍射(XRPD)分析,结果表明仅仅在晶体毛坯的底部生成了一种缺锂相(LiAl5O8).γ-LiAlO2晶体化学稳定性差,在室温时轻微水解.当在空气中于1100℃退火70h,γ-LiAlO2晶体挥发出锂组分,在表面产生缺锂相(LiAl5O8).值得注意的是,在γ-LiAlO2晶体的红外光谱区不存在氢氧根吸收带.%γ-LiAlO2 single crystals were anticipated to act as a promising substrate material for the epitaxy of GaN because of the little lattice misfit ( about 1.4% ) between each other. In the present work, largesize γ-LiAlO2 single crystal with dimension of φ45 × 50mm3 has been grown by Czochralski technique.Various representative positions of the crystal boule were examined using X-ray powder diffraction (XRPD) analysis. Only in the bottom of the crystal boule there produced a kind of lithium-poor phase (LiAl5 O8 ). The γ-LiAlO2 crystal exhibits a poor chemical stability because it hydrolyzes slightly at room temperature. When the γ-LiAlO2 crystal was annealed for 70h at 1100℃ in air-atmosphere, it volatilizes a lithium component, and produces a lithium-poor phase ( LiAl5 O8 ) layer on the surface. It is noteworthy that no hydroxyl absorption band presents in the infrared spectra region of γ-LiAlO2 crystals.

  1. CdTe thin film solar cells produced using a chamberless inline process via metalorganic chemical vapour deposition

    International Nuclear Information System (INIS)

    Cd1−xZnxS and CdTe:As thin films were deposited using a recently developed chamberless inline process via metalorganic chemical vapour deposition (MOCVD) at atmospheric pressure and assessed for fabrication of CdTe photovoltaic (PV) solar cells. Initially, CdS and Cd1−xZnxS coatings were applied onto 15 × 15 cm2 float glass substrates, characterised for their optical properties, and then used as the window layer in CdTe solar cells which were completed in a conventional MOCVD (batch) reactor. Such devices provided best conversion efficiency of 13.6% for Cd0.36Zn0.64S and 10% for CdS which compare favourably to the existing baseline MOCVD (batch reactor) devices. Next, sequential deposition of Cd0.36Zn0.64S and CdTe:As films was realised by the chamberless inline process. The chemical composition of a 1 μm CdTe:As/150 nm Cd0.36Zn0.64S bi-layer was observed via secondary ions mass spectroscopy, which showed that the key elements are uniformly distributed and the As doping level is suitable for CdTe device applications. CdTe solar cells formed using this structure provided a best efficiency of 11.8% which is promising for a reduced absorber thickness of 1.25 μm. The chamberless inline process is non-vacuum, flexible to implement and inherits from the legacy of MOCVD towards doping/alloying and low temperature operation. Thus, MOCVD enabled by the chamberless inline process is shown to be an attractive route for thin film PV applications. - Highlights: • CdS, CdZnS and CdTe thin films grown by a chamberless inline process • The inline films assessed for fabricating CdTe solar cells • 13.6% conversion efficiency obtained for CdZnS/CdTe cells

  2. [Spectral analyzing effects of atmosphere states on the structure and characteristics of CdTe polycrystalline thin films made by close-spaced sublimation].

    Science.gov (United States)

    Zheng, Hua-jing; Zheng, Jia-gui; Feng, Liang-huan; Zhang, Jing-quan; Xie, Er-qing

    2005-07-01

    The structure and characteristics of CdTe thin films are dependent on the working atmosphere states in close-spaced sublimation. In the present paper, CdTe polycrystalline thin films were deposited by CSS in mixture atmosphere of argon and oxygen. The physical mechanism of CSS was analyzed, and the temperature distribution in CSS system was measured. The dependence of preliminary nucleus creation on the atmosphere states (involving component and pressure) was studied. Transparencies were measured and optic energy gaps were calculated. The results show that: (1) The CdTe films deposited in different atmospheres are cubic structure. With increasing oxygen concentration, a increases and reaches the maximum at 6% oxygen concentration, then reduces, and increases again after passing the point at 12% oxygen concentration. Among them, the sample depositing at 9% oxygen concentration is the best. The optic energy gaps are 1.50-1.51 eV for all CdTe films. (2) The samples depositing at different pressures at 9% oxygen concentration are all cubical structure of CdTe, and the diffraction peaks of CdS and SnO2:F still appear. With the gas pressure increasing, the crystal size of CdTe minishes, the transparency of the thin film goes down, and the absorption side shifts to the short-wave direction. (3) The polycrystalline thin films with high quality deposit in 4 minutes under the depositing condition that the substrate temperature is 550 degrees C, and source temperature is 620 degrees C at 9% oxygen concentration. PMID:16241058

  3. Highly Luminescent Hybrid SiO2-Coated CdTe Quantum Dots Retained Initial Photoluminescence Efficiency in Sol-Gel SiO2 Film.

    Science.gov (United States)

    Sun, Hongsheng; Xing, Yugui; Wu, Qinan; Yang, Ping

    2015-02-01

    A highly luminescent silica film was fabricated using tetraethyl orthosilicate (TEOS) and 3-aminopropyltrimethoxysilane (APS) through a controlled sol-gel reaction. The pre-hydrolysis of TEOS and APS which resulted in the mixture of TEOS and APS in a molecular level is a key for the formation of homogenous films. The aminopropyl groups in APS play an important role for obtaining homogeneous film with high photoluminescence (PL). Red-emitting hybrid SiO2-coated CdTe nano-crystals (NCs) were fabricated by a two-step synthesis including a thin SiO2 coating via a sol-gel process and a subsequent refluxing using green-emitting CdTe NCs. The hybrid SiO2-coated CdTe NCs were embedded in a functional SiO2 film via a two-step process including adding the NCs in SiO2 sol with a high viscosity and almost without ethanol and a subsequent spinning coating. The hybrid SiO2-coated CdTe NCs retained their initial PL efficiency (54%) in the film. Being encapsulated with the hybrid NCs in the film, no change on the absorption and PL spectra of red-emitting CdTe NCs (632 nm) was observed. This indicates the hybrid NCs is stable enough during preparation. This phenomenon is ascribed to the controlled sol-gel process and a hybrid SiO2 shell on CdTe NCs. Because these films exhibited high PL efficiency and stability, they will be utilizable for potential applications in many fields. PMID:26353691

  4. On linear resistivity from {proportional_to}1 to 10{sup 3} K in Sr{sub 2}RuO{sub 4-{delta}} single crystals grown by flux technique

    Energy Technology Data Exchange (ETDEWEB)

    Berger, H.; Forro, L.; Pavuna, D. [Ecole Polytechnique Federale, Lausanne (Switzerland). Dept. de Physique

    1998-03-01

    We report transport measurements on single crystals of Sr{sub 2}RuO{sub 4-{delta}}, grown by the flux technique. The temperature dependence of the Hall coefficient is similar to the one measured in cuprates, and the linear resistivity persists up to {proportional_to}1000 K, while the superconductivity remains confined below 1 K. This suggests that the linear temperature dependence of resistivity is not an exclusive signature of the anomalous normal state of high-T{sub c} cuprates but rather of layered oxides in general, especially single-layer perovskites, possibly independently of the magnitude of the superconducting temperature. In addition, such Sr{sub 2}RuO{sub 4-{delta}} may be used as a broad-range thermometer. (orig.). 16 refs.

  5. Conduction mechanism in highly doped β-Ga2O3(\\bar{2}01) single crystals grown by edge-defined film-fed growth method and their Schottky barrier diodes

    Science.gov (United States)

    Oishi, Toshiyuki; Harada, Kazuya; Koga, Yuta; Kasu, Makoto

    2016-03-01

    Edge-defined fed-grown (\\bar{2}01) β-Ga2O3 single crystals with high electron concentration of 3.9 × 1018 cm-3 at 300 K were characterized by Hall effect measurement, and Schottky barrier diodes have been demonstrated. Electron mobility was as high as 74 cm2/(V·s) at 300 K regardless of the high doping concentration. The electron concentration did not change substantially in the low temperature below 160 K. This properties can be explained by the two-band model due to the inter-band conduction. On the Schottky barrier diodes, the rectification characteristics were clearly observed, and the current density of 96.8 A/cm2 at the forward voltage of 1.6 V was obtained.

  6. Extracting Cu Diffusion Parameters in Polycrystalline CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Akis, Richard [Arizona State Univeristy; Brinkman, Daniel [Arizona State Univeristy; Sankin, Igor [First Solar; Fang, Tian [First Solar; Guo, Da [Arizona State Univeristy; Dragica, Vasileska [Arizona State Univeristy; Ringhofer, Christian [Arizona State University

    2014-06-13

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystal-line, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately.

  7. CdTe Solar Cells: The Role of Copper

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Da [Arizona State University; Akis, Richard [Arizona State University; Brinkman, Daniel [Arizona State University; Sankin, Igor [First Solar; Fang, Tian [First Solar; Vasileska, Dragica [Arizona State University; Ringhofer, Christain [Arizona State University

    2014-06-06

    In this work, we report on developing 1D reaction-diffusion solver to understand the kinetics of p-type doping formation in CdTe absorbers and to shine some light on underlying causes of metastabilities observed in CdTe PV devices. Evolution of intrinsic and Cu-related defects in CdTe solar cell has been studied in time-space domain self-consistently with free carrier transport and Poisson equation. Resulting device performance was simulated as a function of Cu diffusion anneal time showing pronounced effect the evolution of associated acceptor and donor states can cause on device characteristics. Although 1D simulation has intrinsic limitations when applied to poly-crystalline films, the results suggest strong potential of the approach in better understanding of the performance and metastabilities of CdTe photovoltaic device.

  8. Modeling Copper Diffusion in Polycrystalline CdTe Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Akis, Richard [Arizona State University; Brinkman, Daniel [Arizona State University; Sankin, Igor [First Solar; Fang, Tian [First Solar; Guo, Da [Arizona State Univeristy; Vasileska, Dragica [Arizona State University; Ringhofer, Christain [Arizona State University

    2014-06-06

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystalline, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately

  9. Radiative and interfacial recombination in CdTe heterostructures

    International Nuclear Information System (INIS)

    Double heterostructures (DH) were produced consisting of a CdTe film between two wide band gap barriers of CdMgTe alloy. A combined method was developed to quantify radiative and non-radiative recombination rates by examining the dependence of photoluminescence (PL) on both excitation intensity and time. The measured PL characteristics, and the interface state density extracted by modeling, indicate that the radiative efficiency of CdMgTe/CdTe DHs is comparable to that of AlGaAs/GaAs DHs, with interface state densities in the low 1010 cm−2 and carrier lifetimes as long as 240 ns. The radiative recombination coefficient of CdTe is found to be near 10−10 cm3s−1. CdTe film growth on bulk CdTe substrates resulted in a homoepitaxial interface layer with a high non-radiative recombination rate

  10. Studies of key technologies for CdTe solar modules

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    In this paper, CdS thin films, which act as the window layer and n-type partner to the p-type CdTe layer, were prepared by chemical bath deposition (CBD). CdTe thin films were deposited by the close-spaced sublimation (CSS) method. To obtain high-quality back contacts, a Te-rich layer was created with chemical etching and back contact materials were applied after CdTe annealing. The results indicate that the ZnTe/ZnTe:Cu complex layers show superior performance over other back contacts. Finally, by using laser scribing and mechanical scribing, the CdTe mini-modules were fabricated, in which a glass/SnO2:F/CdS/CdTe/ZnTe/ZnTe:Cu/Ni solar module with a PWQC-confirmed total-area efficiency of 7.03% (54 cm2) was achieved.

  11. Interaction of porphyrins with CdTe quantum dots

    International Nuclear Information System (INIS)

    Porphyrins may be used as photosensitizers for photodynamic therapy, photocatalysts for organic pollutant dissociation, agents for medical imaging and diagnostics, applications in luminescence and electronics. The detection of porphyrins is significantly important and here the interaction of protoporphyrin-IX (PPIX) with CdTe quantum dots was studied. It was observed that the luminescence of CdTe quantum dots was quenched dramatically in the presence of PPIX. When CdTe quantum dots were embedded into silica layers, almost no quenching by PPIX was observed. This indicates that PPIX may interact and alter CdTe quantum dots and thus quench their luminescence. The oxidation of the stabilizers such as thioglycolic acid (TGA) as well as the nanoparticles by the singlet oxygen generated from PPIX is most likely responsible for the luminescence quenching. The quenching of quantum dot luminescence by porphyrins may provide a new method for photosensitizer detection.

  12. Controlled Synthesis of Nanoscale CdTe Urchins

    Institute of Scientific and Technical Information of China (English)

    BAO Jian; SHEN Yue; SUN Yan; YUE Yang; CHEN Xin; DAI Ning

    2009-01-01

    We presented a simple route to prepare nanoscale CdTe urchins in a tri-n-octylphosphine oxide(TOPO)system.CdTe urchins consisted of a core and several attached arms.The arms were ca.3 nm wide,and their lengths could be controlled with the reaction time.The authors investigated the optical absorption and structural properties of the prepared CdTe.The lengths of the arms could be tuned into CdTe nanourchins,which led to a change in the photophysical properties of the nanoscale CdTe urchins.The results,including transmission electron microscopy(TEM) and absorption spectra,indicated that mesoporous silica and aminopropyltriethoxysilane(APTES) contributed to the formation of nanoscale CdTe urchins.

  13. Compound semiconductor GaAs and CdTe nuclear radiation detectors

    International Nuclear Information System (INIS)

    The preparation technology and characteristics of semi-insulating bulk single crystal GaAs surface-barrier detectors and single crystal CdTe surface-barrier detectors are described. The spectroscopic performance of the detectors for γ-rays from 125I, 241Am and 57Co at room temperature is given. The influence of the magnitude of forward resistive induced by ohmic contacts and of the surface passivation and aging in the fabrication process of surface-barrier detectors on the performance of the detectors is discussed. Finally, the influence of the fabrication technology of ohmic contacts and selected materials, such as Ni-Ge-Au and In-Ge-Ag, on the performance of the detectors is also studied

  14. CdTe Photovoltaics for Sustainable Electricity Generation

    Science.gov (United States)

    Munshi, Amit; Sampath, Walajabad

    2016-04-01

    Thin film CdTe (cadmium telluride) is an important technology in the development of sustainable and affordable electricity generation. More than 10 GW of installations have been carried out using this technology around the globe. It has been demonstrated as a sustainable, green, renewable, affordable and abundant source of electricity. An advanced sublimation tool has been developed that allows highly controlled deposition of CdTe films onto commercial soda lime glass substrates. All deposition and treatment steps can be performed without breaking the vacuum within a single chamber in an inline process that can be conveniently scaled to a commercial process. In addition, an advanced cosublimation source has been developed to allow the deposition of ternary alloys such as Cd x Mg1-x Te to form an electron reflector layer which is expected to address the voltage deficits in current CdTe devices and to achieve very high efficiency. Extensive materials characterization, including but not limited to scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, high resolution transmission electron microscopy and electron back-scatter diffraction, has been performed to get a better understanding of the effects of processing conditions on CdTe thin film photovoltaics. This combined with computer modeling such as density function theory modeling gives a new insight into the mechanism of CdTe photovoltaic function. With all these efforts, CdTe photovoltaics has seen great progress in the last few years. Currently, it has been recorded as the cheapest source of electricity in the USA on a commercial scale, and further improvements are predicted to further reduce the cost while increasing its utilization. Here, we give an overview of the advantages of thin film CdTe photovoltaics as well as a brief review of the challenges that need to be addressed. Some fundamental studies of processing conditions for thin film CdTe are also presented

  15. Electrical properties of single CdTe nanowires

    OpenAIRE

    Elena Matei; Camelia Florica; Andreea Costas; María Eugenia Toimil-Molares; Ionut Enculescu

    2015-01-01

    Ion track, nanoporous membranes were employed as templates for the preparation of CdTe nanowires. For this purpose, electrochemical deposition from a bath containing Cd and Te ions was employed. This process leads to high aspect ratio CdTe nanowires, which were harvested and placed on a substrate with lithographically patterned, interdigitated electrodes. Focused ion beam-induced metallization was used to produce individual nanowires with electrical contacts and electrical measurements were p...

  16. CdTe Photovoltaics for Sustainable Electricity Generation

    Science.gov (United States)

    Munshi, Amit; Sampath, Walajabad

    2016-09-01

    Thin film CdTe (cadmium telluride) is an important technology in the development of sustainable and affordable electricity generation. More than 10 GW of installations have been carried out using this technology around the globe. It has been demonstrated as a sustainable, green, renewable, affordable and abundant source of electricity. An advanced sublimation tool has been developed that allows highly controlled deposition of CdTe films onto commercial soda lime glass substrates. All deposition and treatment steps can be performed without breaking the vacuum within a single chamber in an inline process that can be conveniently scaled to a commercial process. In addition, an advanced cosublimation source has been developed to allow the deposition of ternary alloys such as Cd x Mg1- x Te to form an electron reflector layer which is expected to address the voltage deficits in current CdTe devices and to achieve very high efficiency. Extensive materials characterization, including but not limited to scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, high resolution transmission electron microscopy and electron back-scatter diffraction, has been performed to get a better understanding of the effects of processing conditions on CdTe thin film photovoltaics. This combined with computer modeling such as density function theory modeling gives a new insight into the mechanism of CdTe photovoltaic function. With all these efforts, CdTe photovoltaics has seen great progress in the last few years. Currently, it has been recorded as the cheapest source of electricity in the USA on a commercial scale, and further improvements are predicted to further reduce the cost while increasing its utilization. Here, we give an overview of the advantages of thin film CdTe photovoltaics as well as a brief review of the challenges that need to be addressed. Some fundamental studies of processing conditions for thin film CdTe are also presented

  17. High-quality CdTe films from nanoparticle precursors

    Energy Technology Data Exchange (ETDEWEB)

    Schulz, D.L.; Pehnt, M.; Urgiles, E. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1996-05-01

    In this paper the authors demonstrate that nanoparticulate precursors coupled with spray deposition offers an attractive route into electronic materials with improved smoothness, density, and lower processing temperatures. Employing a metathesis approach, cadmium iodide was reacted with sodium telluride in methanol solvent, resulting in the formation of soluble NaI and insoluble CdTe nanoparticles. After appropriate chemical workup, methanol-capped CdTe colloids were isolated. CdTe thin film formation was achieved by spray depositing the nanoparticle colloids (25-75 {Angstrom} diameter) onto substrates at elevated temperatures (T = 280-440{degrees}C) with no further thermal treatment. These films were characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Cubic CdTe phase formation was observed by XRD, with a contaminant oxide phase also detected. XPS analysis showed that CdTe films produced by this one-step method contained no Na or C and substantial O. AFM gave CdTe grain sizes of {approx}0.1-0.3 {mu}m for film sprayed at 400{degrees}C. A layer-by-layer film growth mechanism proposed for the one-step spray deposition of nanoparticle precursors will be discussed.

  18. Toward epitaxially grown two-dimensional crystal hetero-structures: Single and double MoS2/graphene hetero-structures by chemical vapor depositions

    Science.gov (United States)

    Lin, Meng-Yu; Chang, Chung-En; Wang, Cheng-Hung; Su, Chen-Fung; Chen, Chi; Lee, Si-Chen; Lin, Shih-Yen

    2014-08-01

    Uniform large-size MoS2/graphene hetero-structures fabricated directly on sapphire substrates are demonstrated with layer-number controllability by chemical vapor deposition (CVD). The cross-sectional high-resolution transmission electron microscopy (HRTEM) images provide the direct evidences of layer numbers of MoS2/graphene hetero-structures. Photo-excited electron induced Fermi level shift of the graphene channel are observed on the single MoS2/graphene hetero-structure transistors. Furthermore, double hetero-structures of graphene/MoS2/graphene are achieved by CVD fabrication of graphene layers on top of the MoS2, as confirmed by the cross-sectional HRTEM. These results have paved the possibility of epitaxially grown multi-hetero-structures for practical applications.

  19. Effects of thermal diffuse scattering and surface tilt on diffraction and channeling of fast electrons in CdTe

    International Nuclear Information System (INIS)

    A Bloch-wave model for propagating a fast-electron wave through a noncentrosymmetric crystal for non-normal incidence is discussed, as well as approximations for linearizing the equations. Calculations which simulate /111/ systematic row diffraction conditions in CdTe are used to illustrate how the tilt of the surface with respect to the diffracting planes affects the fast-electron wave function in the crystal. The influence of thermal diffuse scattering (TDS) removes possible ambiguity from the interpretation of ''ALchEmI-type'' experiments [J. C. H. Spence and J. TaftoX, J. Microsc. 130, 147 (1983)] in determining the polarity of noncentrosymmetric crystals. The inclusion of mean and anomalous absorption, using a quantitative Einstein model for TDS, allows direct correlation between theory and experiment for convergent-beam electron diffraction, again allowing direct measurement of crystal polarity

  20. Hydrothermal synthesis of CdTe quantum dots–TiO2–graphene hybrid

    International Nuclear Information System (INIS)

    CdTe–TiO2–graphene nanocomposites were successfully synthesized via a simple and relatively general hydrothermal method. During the hydrothermal environment, GO was reduced to reduced graphene oxide (RGO), accompanying with the anchoring of TiO2 nanoparticles on the surface of RGO. In the following process, CdTe quantum dots (QDs) were then in situ grown on the carbon basal planes. The morphologies and structural properties of the as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and fluorescent spectroscopy. It is hoped that our current work could pave a way towards the fabrication of QDs–TiO2–RGO hybrid materials.

  1. Identification of Ag-acceptors in $^{111}Ag^{111}Cd$ doped ZnTe and CdTe

    CERN Document Server

    Hamann, J; Deicher, M; Filz, T; Lany, S; Ostheimer, V; Strasser, F; Wolf, H; Wichert, T

    2000-01-01

    Nominally undoped ZnTe and CdTe crystals were implanted with radioactive /sup 111/Ag, which decays to /sup 111/Cd, and investigated by photoluminescence spectroscopy (PL). In ZnTe, the PL lines caused by an acceptor level at 121 meV are observed: the principal bound exciton (PBE) line, the donor-acceptor pair (DAP) band, and the two-hole transition lines. In CdTe, the PBE line and the DAP band that correspond to an acceptor level at 108 meV appear. Since the intensities of all these PL lines decrease in good agreement with the half-life of /sup 111/Ag of 178.8 h, both acceptor levels are concluded to be associated with defects containing a single Ag atom. Therefore, the earlier assignments to substitutional Ag on Zn- and Cd-lattice sites in the respective II-VI semiconductors are confirmed. The assignments in the literature of the S/sub 1/, S /sub 2/, and S/sub 3/ lines in ZnTe and the X/sub 1//sup Ag/, X/sub 2 //sup Ag//C/sub 1//sup Ag/, and C/sub 2//sup Ag/ lines in CdTe to Ag- related defect complexes are ...

  2. CdTe Thin Film Solar Cells and Modules Tutorial; NREL (National Renewable Energy Laboratory)

    Energy Technology Data Exchange (ETDEWEB)

    Albin, David S.

    2015-06-13

    This is a tutorial presented at the 42nd IEEE Photovoltaics Specialists Conference to cover the introduction, background, and updates on CdTe cell and module technology, including CdTe cell and module structure and fabrication.

  3. Inclusion free cadmium zinc tellurium and cadmium tellurium crystals and associated growth method

    Science.gov (United States)

    Bolotnikov, Aleskey E.; James, Ralph B.

    2010-07-20

    The present disclosure provides systems and methods for crystal growth of cadmium zinc tellurium (CZT) and cadmium tellurium (CdTe) crystals with an inverted growth reactor chamber. The inverted growth reactor chamber enables growth of single, large, high purity CZT and CdTe crystals that can be used, for example, in X-ray and gamma detection, substrates for infrared detectors, or the like. The inverted growth reactor chamber enables reductions in the presence of Te inclusions, which are recognized as an important limiting factor in using CZT or CdTe as radiation detectors. The inverted growth reactor chamber can be utilized with existing crystal growth techniques such as the Bridgman crystal growth mechanism and the like. In an exemplary embodiment, the inverted growth reactor chamber is a U-shaped ampoule.

  4. Protein Crystal Recombinant Human Insulin

    Science.gov (United States)

    1994-01-01

    The comparison of protein crystal, Recombiant Human Insulin; space-grown (left) and earth-grown (right). On STS-60, Spacehab II indicated that space-grown crystals are larger and of greater optical clarity than their earth-grown counterparts. Recombiant Human Insulin facilitates the incorporation of glucose into cells. In diabetics, there is either a decrease in or complete lack of insulin, thereby leading to several harmful complications. Principal Investigator is Larry DeLucas.

  5. Influence of crystallographic orientation on the magnetic properties of NiFe, Co, and Ni epitaxial fcc films grown on single-crystal substrates

    Science.gov (United States)

    Ohtani, Taiki; Kawai, Tetsuroh; Ohtake, Mitsuru; Futamoto, Masaaki

    2013-08-01

    Ni80Fe20 (at. %), Co, and Ni epitaxial thin films of fcc(100) and fcc(111) orientations are prepared on single-crystal substrates by using an ultra-high-vacuum radio-frequency magnetron sputtering system. The influence of the magnetocrystalline anisotropy on the magnetostriction behavior under in-plane rotating magnetic fields is investigated. Triangular waveforms are observed in the magnetostriction measurements under low rotating fields for films that show four-fold symmetry in the in-plane magnetic anisotropies. The magnetostriction behavior is related to the motion of ninety-degree magnetic domain walls in magnetically unsaturated films. The waveform changes from a triangular to a sinusoidal shape when magnetization saturation is approached under increasing magnetic field. On the other hand, films having almost isotropic in-plane magnetic properties show sinusoidal waveforms even when the films are not magnetically saturated.

  6. High-Mobility AlGaN/GaN Two-Dimensional Electron Gas Heterostructure Grown on (111) Single Crystal Diamond Substrate

    Science.gov (United States)

    Dussaigne, Amélie; Gonschorek, Marcus; Malinverni, Marco; Py, Marcel A.; Martin, Denis; Mouti, Anas; Stadelmann, Pierre; Grandjean, Nicolas

    2010-06-01

    High mobility Al0.28Ga0.72N/GaN two-dimensional electron gas (2DEG) is achieved on (111) oriented single crystal diamond substrate. The surface morphology of the epilayer is free of cracks thanks to the use of an AlN interlayer for strain relaxation. The rms roughness of the sample surface deduced from atomic force microscopy is 0.6 nm for a 2 ×2 µm2 scan area, which indicates an excellent surface morphology. Hall effect measurements reveal a 2DEG with room temperature mobility and sheet carrier density of 750 cm2 V-1 s-1 and 1.4 ×1013 cm-2, respectively. These results compare fairly well with AlGaN/GaN 2DEG characteristics obtained on other substrates like silicon and demonstrate that high power electronics can be developed on diamond substrates with high power dissipation capabilities.

  7. The influence of substrate orientation on the density of silicon nanowires grown on multicrystalline and single crystal substrates by electron cyclotron resonance chemical vapour deposition

    Energy Technology Data Exchange (ETDEWEB)

    Ball, J., E-mail: balljb@lsbu.ac.uk; Reehal, H.S.

    2012-01-31

    The Au catalysed, vapour-liquid-solid growth of Si nanowires on Si substrates of different orientations has been studied using electron cyclotron resonance plasma-assisted chemical vapour deposition (ECRCVD). ECRCVD plasma excitation is found to strongly promote wire growth rate and density with wire diameters in excess of 200 nm under the conditions used. Substrate orientation and nanowire density are strongly correlated. This has been studied using multicrystalline as well as single crystal Si substrates. It is suggested that the Gibbs-Thomson effect can account for the behaviour of wire density with orientation. The application of an RF generated, DC self-bias of - 5 V on the substrate during growth strongly enhances wire density without affecting growth rate or diameter. A tentative model for wire growth has been proposed which is based on an initial incubation/crystallisation step, followed by silicon incorporation at the vapour-liquid interface being rate-limiting.

  8. Pressure cryocooling protein crystals

    Science.gov (United States)

    Kim, Chae Un; Gruner, Sol M.

    2011-10-04

    Preparation of cryocooled protein crystal is provided by use of helium pressurizing and cryocooling to obtain cryocooled protein crystal allowing collection of high resolution data and by heavier noble gas (krypton or xenon) binding followed by helium pressurizing and cryocooling to obtain cryocooled protein crystal for collection of high resolution data and SAD phasing simultaneously. The helium pressurizing is carried out on crystal coated to prevent dehydration or on crystal grown in aqueous solution in a capillary.

  9. A pixellated gamma-camera based on CdTe detectors clinical interests and performances

    CERN Document Server

    Chambron, J; Eclancher, B; Scheiber, C; Siffert, P; Hage-Ali, M; Regal, R; Kazandjian, A; Prat, V; Thomas, S; Warren, S; Matz, R; Jahnke, A; Karman, M; Pszota, A; Németh, L

    2000-01-01

    A mobile gamma camera dedicated to nuclear cardiology, based on a 15 cmx15 cm detection matrix of 2304 CdTe detector elements, 2.83 mmx2.83 mmx2 mm, has been developed with a European Community support to academic and industrial research centres. The intrinsic properties of the semiconductor crystals - low-ionisation energy, high-energy resolution, high attenuation coefficient - are potentially attractive to improve the gamma-camera performances. But their use as gamma detectors for medical imaging at high resolution requires production of high-grade materials and large quantities of sophisticated read-out electronics. The decision was taken to use CdTe rather than CdZnTe, because the manufacturer (Eurorad, France) has a large experience for producing high-grade materials, with a good homogeneity and stability and whose transport properties, characterised by the mobility-lifetime product, are at least 5 times greater than that of CdZnTe. The detector matrix is divided in 9 square units, each unit is composed ...

  10. Recent Progress in CdTe and CdZnTe Detectors

    CERN Document Server

    Takahashi, T; Takahashi, Tadayui; Watanabe, Shin

    2001-01-01

    Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been regarded as promising semiconductor materials for hard X-ray and Gamma-ray detection. The high atomic number of the materials (Z_{Cd} =48, Z_{Te} =52) gives a high quantum efficiency in comparison with Si. The large band-gap energy (Eg ~ 1.5 eV) allows us to operate the detector at room temperature. However, a considerable amount of charge loss in these detectors produces a reduced energy resolution. This problem arises due to the low mobility and short lifetime of holes. Recently, significant improvements have been achieved to improve the spectral properties based on the advances in the production of crystals and in the design of electrodes. In this overview talk, we summarize (1) advantages and disadvantages of CdTe and CdZnTe semiconductor detectors and (2) technique for improving energy resolution and photopeak efficiencies. Applications of these imaging detectors in future hard X-ray and Gamma-ray astronomy missions are briefly discus...

  11. Characterization of CdTe nuclear detectors for gamma radiation spectrometry

    International Nuclear Information System (INIS)

    The crystallography of CdTe is presented. The characterization of CdTe crystals manufactured at LETI was studied using a spectrometry unit, and an experimental study of surface states and contacts was simultaneously undertaken. A manufacturing process was perfected for the detectors: hand polishing and deposit of a drop of conducting lac. Measurements mode on a great number of materials revealed the interest of chlore doping, the polarization phenomenon associated (the polarization is equivalent to a voltage drop and depends on temperature), the effect of surface states and contacts. It was shown that magnesium doping is a failure and the polarization time constant has a value of about 1 msec. An electron time-of-flight experiment was performed in order to measure the mobilities in the sample at normal temperature: the values obtained are: 70-90 cm2/v.sec for holes and 800-1000 cm2/v.sec for electrons. A trapping level was observed at 0.14eV in a Cl- doped sample; trapping parameters were estimated for a few samples

  12. p-i-n CdTe multi-pixel detector for gamma-ray imaging fabricated by excimer laser processing

    International Nuclear Information System (INIS)

    A multi-pixel gamma-ray imaging detector unit, which has a high-energy resolution with room temperature operation, was fabricated using the diode-type CdTe detector. The diode structure was prepared by indium-doped n-type CdTe thin layer formed by excimer laser doping on one-side of high resistivity p-like single crystal CdTe wafer, and a gold electrode as a Shottkey electrode evaporated on the opposite side of the wafer. This diode-detectors showed good diode I-V characteristics with low leakage current. This CdTe detectors were pixelized in the 2mm x 2mm, and the 128 chips (32x4 chips) were mounted on the ceramic printed circuit boards at 3 mm interval with 1 mm gap. The printed circuit boards are directly connected the MCSA-EXI ASIC chip and 128 ch radiation spectrum analyzer systems. When using the Am-241 and the Co-57 as radioisotopes, the spectral response from all the pixels within 4,4 ke V of FWHM at 122 ke V peak of Co-57 for radiation performed at room temperature. The intensities of the peak from pixels were also uniform (Authors)

  13. Luminescence and scintillation properties of rare-earth-doped BaLu{sub 2}F{sub 8} single crystals grown by the micro-pulling-down method

    Energy Technology Data Exchange (ETDEWEB)

    Pejchal, Jan [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Institute of Physics AS CR, Cukrovarnicka 10, Prague 16253 (Czech Republic); Fukuda, Kentaro; Kawaguchi, Noriaki [Tokuyama co., Kasumigaseki 3-chome, Chiyoda-ku, Tokyo 100-8983 (Japan); Futami, Yoshisuke; Yokota, Yuui [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Nikl, Martin; Kral, Robert [Institute of Physics AS CR, Cukrovarnicka 10, Prague 16253 (Czech Republic); Yoshikawa, Akira [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); New Industry Creation Hatchery Center, Tohoku University, 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan)

    2012-12-15

    The BaLu{sub 2}F{sub 8} crystals doped with 1 mol% Tm, Nd and Er were prepared by micro-pulling-down method to study their scintillation and luminescence properties. The unwanted phase transition from orthorhombic structure to monoclinic one, which occurs some 50 C below the melting point, was avoided using Li-flux. No Li-containing secondary phase was observed. Radioluminescence measurements of Nd-doped samples revealed 5d-4f Nd{sup 3+} luminescence situated around 180nm, the intensity of which was comparable with that of the LaF{sub 3}:Nd 8% reference scintillator sample. Further slight enhancement of the Nd{sup 3+} 5d-4f emission was achieved by Tm{sup 3+} co-doping probably due to energy transfer from the Tm{sup 3+} 5d levels to the Nd{sup 3+} ones. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Synchrotron X-ray topographic study on nature of threading mixed dislocations in 4H–SiC crystals grown by PVT method

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Jianqiu; Yang, Yu; Wu, Fangzhen; Sumakeris, Joe; Leonard, Robert; Goue, Ouloide; Raghothamachar, Balaji; Dudley, Michael

    2016-10-01

    Synchrotron X-ray Topography is a powerful technique to study defects structures particularly dislocation configurations in single crystals. Complementing this technique with geometrical and contrast analysis can enhance the efficiency of quantitatively characterizing defects. In this study, the use of Synchrotron White Beam X-ray Topography (SWBXT) to determine the line directions of threading dislocations in 4H–SiC axial slices (sample cut parallel to the growth axis from the boule) is demonstrated. This technique is based on the fact that the projected line directions of dislocations on different reflections are different. Another technique also discussed is the determination of the absolute Burgers vectors of threading mixed dislocations (TMDs) using Synchrotron Monochromatic Beam X-ray Topography (SMBXT). This technique utilizes the fact that the contrast from TMDs varies on SMBXT images as their Burgers vectors change. By comparing observed contrast with the contrast from threading dislocations provided by Ray Tracing Simulations, the Burgers vectors can be determined. Thereafter the distribution of TMDs with different Burgers vectors across the wafer is mapped and investigated.

  15. Widely tunable alloy composition and crystal structure in catalyst-free InGaAs nanowire arrays grown by selective area molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Treu, J., E-mail: Julian.Treu@wsi.tum.de, E-mail: Gregor.Koblmueller@wsi.tum.de; Speckbacher, M.; Saller, K.; Morkötter, S.; Xu, X.; Riedl, H.; Abstreiter, G.; Finley, J. J.; Koblmüller, G., E-mail: Julian.Treu@wsi.tum.de, E-mail: Gregor.Koblmueller@wsi.tum.de [Walter Schottky Institut, Physik Department, Center of Nanotechnology and Nanomaterials, Technische Universität München, Am Coulombwall 4, Garching 85748 (Germany); Döblinger, M. [Department of Chemistry, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, Munich 81377 (Germany)

    2016-02-01

    We delineate the optimized growth parameter space for high-uniformity catalyst-free InGaAs nanowire (NW) arrays on Si over nearly the entire alloy compositional range using selective area molecular beam epitaxy. Under the required high group-V fluxes and V/III ratios, the respective growth windows shift to higher growth temperatures as the Ga-content x(Ga) is tuned from In-rich to Ga-rich InGaAs NWs. Using correlated x-ray diffraction, transmission electron microscopy, and micro-photoluminescence spectroscopy, we identify structural defects to govern luminescence linewidths in In-rich (x(Ga) < 0.4) and Ga-rich (x(Ga) > 0.6) NWs, whereas limitations at intermediate Ga-content (0.4 < x(Ga) < 0.6) are mainly due to compositional inhomogeneities. Most remarkably, the catalyst-free InGaAs NWs exhibit a characteristic transition in crystal structure from wurtzite to zincblende (ZB) dominated phase near x(Ga) ∼ 0.4 that is further reflected in a cross-over from blue-shifted to red-shifted photoluminescence emission relative to the band edge emission of the bulk ZB InGaAs phase.

  16. Electro-optical characterization of Ti/Au–ZnTe Schottky diodes with CdTe quantum dots

    International Nuclear Information System (INIS)

    In this study the electric and optical spectroscopy techniques have been applied to investigate ZnTe (p-type)–Ti/Au Schottky diodes containing a layer of CdTe self-assembled quantum dots (SAQDs). The reference sample was the ZnTe–Ti/Au diode without dots. Both samples were grown by molecular beam epitaxy technique. Raman measurements confirmed the presence of the CdTe layer while the photoluminescence proved that CdTe quantum dots were formed in the investigated structure. The PL spectra reveal the CdTe QD electron-hole recombination energy equal to 2.1 eV at 10 K. Based on the temperature PL measurements the activation energy of PL quenching has been determined to be equal to 22 meV. Further confirmation for the QD formation has been obtained from the C–V characteristics which exhibited a step related to the charge accumulation at the QD states. DLTS spectra for the sample with QDs yield three hole-related signals with apparent activation energies equal to EH1 = 0.16 eV, EH2 = 0.2 eV and EH3 = 0.4 eV. For the reference ZnTe–Ti/Au diode solely single signal was observed of signature close to the level H3 in the QD sample. Detailed characterization of the traps as well as the PL studies lead to the conclusion that the level H2 is related to the defects located close to the QDs created during the growth while the other traps are associated with defects present in the ZnTe bulk material. - Highlights: ► Studied structure: ZnTe (p-type) Schottky diode containing CdTe quantum dots (QDs). ► Experimental methods: Raman, photoluminescence, Deep Level Transient Spectroscopy. ► Raman and PL measurements confirm the presence of QDs in the investigated structure. ► DLTS and Pl data prove creation of defects decorating QD formation.

  17. Large-area single-crystal graphene grown on a recrystallized Cu(111) surface by using a hole-pocket method

    Science.gov (United States)

    Phan, Hoang Danh; Jung, Jaehyuck; Kim, Youngchan; Huynh, Van Ngoc; Lee, Changgu

    2016-07-01

    We describe an efficient chemical vapor deposition (CVD) method for synthesizing graphene with a single crystal orientation on the whole surface of a copper (Cu) foil. We specifically synthesized graphene on the inner surface of a folded Cu foil, on which small holes were made for regulating the permeation and adsorption of the gases used for the synthesis. We compared the results of this method, which we call a ``hole-pocket'' method, with previously developed methods involving traditional synthesis on an open Cu foil and a Cu ``pita-pocket''. From these comparisons, we found the orientation of recrystallized Cu to depend on the shape of the Cu foil. Our hole-pocket method did not require treatment of the Cu surface with a complicated process to reduce the density of nucleation seeds in order to synthesize large hexagonal graphene grains, nor did it require the use of a single-crystalline substrate because methane passing through holes on the upper side of the hole-pocket slowly decomposed into carbon atoms and the control of the evaporation of Cu inside the foil pocket helped induce a transformation of the Cu domains to Cu(111). The current hole-pocket method resulted in domains that were both large, ranging from 2-5 mm in size, and oriented in the same manner. By extending the synthesis time, we were able to obtain continuous large-area films of single-crystalline orientation on the whole surface with dimensions of several centimeters.We describe an efficient chemical vapor deposition (CVD) method for synthesizing graphene with a single crystal orientation on the whole surface of a copper (Cu) foil. We specifically synthesized graphene on the inner surface of a folded Cu foil, on which small holes were made for regulating the permeation and adsorption of the gases used for the synthesis. We compared the results of this method, which we call a ``hole-pocket'' method, with previously developed methods involving traditional synthesis on an open Cu foil and a Cu

  18. Optimization of control parameters of CdZnTe ACRT-Bridgman single crystal growth

    Institute of Scientific and Technical Information of China (English)

    2004-01-01

    [1]Kennedey, J. J., Amirtharaj, P. M., Boyd, P. R. Et al., Growth and characterization of Cd1-xZnxTe and Hg1-yZnyTe, J. Cryst. Growth, 1988, 86: 93-99.[2]Tanaka, A., Masa, Y., Seto, S. et al., Zinc and selenium co-doped CdTe substrates lattice matched to HgCdTe, J. Cryst. Growth, 1989, 94: 166-170.[3]Sen, S., Stanard, J. E., Developments in the bulk growth of Cd1-xZnxTe for substrates, Prog. Crystal Growth and Charact., 1994, 29: 253-273.[4]Azoulay, M., Rotter, S., Gafni, G. et al., Zinc segregation in CdZnTe grown under Cd/Zn partial pressure control, J. Cryst. Growth, 1992, 117: 276-280.[5]Lee, T. S., Lee, S. B., Kim, J. M. et al., Vertical Bridgman techniques to homogenize zinc composition of CdZnTe substrates, J. Electronic Materials, 1995, 24: 1057-1059.[6]Mühlberg, M., Rudolph, P., Genzel, C. Et al., Crystalline and chemical quality of CdTe and Cd1-xZnxTe grown by the Bridgman method in low temperature gradients, J. Cryst. Growth, 1990, 101: 275-280.[7]Cheuvart, P., El-Hanani, U., Schneider, D. et al., CdTe and CdZnTe crystal growth by horizontal Bridgman technique, J. Cryst. Growth, 1990, 101: 270-274.[8]Lu, Y. C., Shiau, J. J., Fiegelson, R. S. et al., Effect of vibrational stirring on the quality of Bridgman-grown CdTe, J. Cryst. Growth, 1990, 102: 807-813.[9]Butler, J. F., Doty, F. P., Apotovsky, B. Et al., γ-ray and X-ray detectors manufactured from Cd1-xZnxTe grown by a high-pressure Bridgman method, Mater. Sci. & Eng. B, 1993, 16: 291-295.[10]Capper, P., The role of accelerated crucible rotation in the growth of Hg1-xCdxTe and CdTe/CdZnTe, Prog. Crystal Growth and Charact., 1994, 28: 1-55.[11]Schulz-Dubois, E. O., Accelerated crucible rotation: hydrodynamics and stirring effect, J. Cryst. Growth, 1971, 12: 81-87.[12]Capper, P., Gosney, J. J. G., Jones, C. L. et al., Fluid flows in tall narrow containers by ACRT, Journal of Electronic Materials, 1986 15(6): 361-370.[13]Distanov, V. E., Kirdyashkin, A

  19. Design of a thin film CdTe solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Meyers, P.V.

    1988-01-15

    Cadmium telluride was originally considered for thin film solar cells because of its optimum band gap, high optical absorption coefficient and ability to be doped. Furthermore, it is a stable compound which can be produced by a wide variety of methods from stable raw materials. As thin film photovoltaics mature, however, it is clear that several more subtle attributes have a significant impact on the viability of commercialization. We discuss the observations which have provided insight and direction to Ametek's CdTe solar cell program. Rather than try to modify the inherent material properties of CdTe, advances have been made by designing a solar cell that exploits existing properties. Specifically, the tendency to self-compensate, which makes low resistance contacting difficult, is turned into an advantage in the n-i-p configuration; the CdTe provides an intrinsic layer with good carrier collection efficiency.

  20. Study of Back Contacts for CdTe Solar Cells

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    ZnTe/ZnTe∶Cu layer is used as a complex back contact. The parameters of CdTe solar cells with and without the complex back contacts are compared. The effects of un-doped layer thickness, doped concentration and post-deposition annealing temperature of the complex layer on solar cells performance are investigated.The results show that ZnTe/ZnTe∶Cu layer can improve back contacts and largely increase the conversion efficiency of CdTe solar cells. Un-doped layer and post-deposition annealing of high temperature can increase open voltage. Using the complex back contact, a small CdTe cell with fill factor of 73.14% and conversion efficiency of 12.93% is obtained.

  1. Resetting the Defect Chemistry in CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Metzger, Wyatt K.; Burst, James; Albin, David; Colegrove, Eric; Moseley, John; Duenow, Joel; Farrell, Stuart; Moutinho, Helio; Reese, Matt; Johnston, Steve; Barnes, Teresa; Perkins, Craig; Guthrey, Harvey; Al-Jassim, Mowafak

    2015-06-14

    CdTe cell efficiencies have increased from 17% to 21% in the past three years and now rival polycrystalline Si [1]. Research is now targeting 25% to displace Si, attain costs less than 40 cents/W, and reach grid parity. Recent efficiency gains have come largely from greater photocurrent. There is still headroom to lower costs and improve performance by increasing open-circuit voltage (Voc) and fill factor. Record-efficiency CdTe cells have been limited to Voc <; 880 mV, whereas GaAs can attain Voc of 1.10 V with a slightly smaller bandgap [2,3]. To overcome this barrier, we seek to understand and increase lifetime and carrier concentration in CdTe. In polycrystalline structures, lifetime can be limited by interface and grain-boundary recombination, and attaining high carrier concentration is complicated by morphology.

  2. Magnetic anisotropy and order structure of L10-FePt(001) single-crystal films grown epitaxially on (001) planes of MgO, SrTiO3, and MgAl2O4 substrates

    Science.gov (United States)

    Hotta, A.; Ono, T.; Hatayama, M.; Tsumura, K.; Kikuchi, N.; Okamoto, S.; Kitakami, O.; Shimatsu, T.

    2014-05-01

    L10-FePt(001) single-crystal films were grown epitaxially on SrTiO3(001), MgAl2O4(001), and MgO(001) substrates. Their uniaxial magnetic anisotropy Ku and the order structure were examined for the film thickness t range of 2-14 nm. All series of films show large Ku of 4 × 107 erg/cm3 in the thickness range higher than 10 nm, with order parameter S of 0.8 and saturation magnetization Ms of 1120 emu/cm3. Ku decreased gradually as t decreased. The Ku reduction was considerable when t decreased from 4 nm to 2 nm. No marked difference in the thickness dependence of Ku was found in any series of films, although the lattice mismatch between FePt and the substrates was markedly different. Ku reduction showed good agreement with the reduction of S for the films on MgAl2O4 and MgO. The Ku ˜ S2 plot showed an almost linear relation, which is in good agreement with theoretical predictions. Transmission electron microscopy images for a FePt film on MgO substrate revealed that the lattice mismatch between FePt(001) and MgO(001) was relaxed in the initial 1 or 2 layers of FePt(001) lattices, which is likely to be true also for two other series of films.

  3. Coal mining applications of CdTe gamma ray sensors

    Energy Technology Data Exchange (ETDEWEB)

    Entine, G.; Tiernan, T.; Waer, P.; Hazlett, T. (Radiation Monitoring Devices, Inc., Watertown, MA (USA))

    1990-01-01

    Cadmium telluride (CdTe) solid-state radiation detectors have been used in the development of instrumentation that improves the efficiency of coal-mining operations by helping to locate coal seams and preventing the mining of high-sulfur coal near the edges of the seam. CdTe detectors were selected for these applications because while they are small and durable, they offer good stopping power, deliver adequate spectral response and operate at low voltage. These CdTe-based instruments have passed the mine-safety standards and are now in operation in the mine. (author).

  4. Advances in CdTe n-i-p photovoltaics

    Energy Technology Data Exchange (ETDEWEB)

    Meyers, P.V. (Ametek Applied Materials Lab., Harleysville, PA (USA))

    1989-10-15

    Development of the CdTe n-i-p solar cell has enabled researchers to produce 11% efficient solar cells while eliminating stability problems associated with a low-resistance back contact. Furthermore, loss analysis indicates that significant increases in efficiency can still be realized through reduction of absorption and reflection and by passivation of recombination centers at the interfaces. Simplifications in the interconnection procedures make the CdTe n-i-p solar module more ''manufacturable''. A submodule with four interconnected cells has been produced. It has an aperture area efficiency over 8% with an area ratio of 0.91. (orig.).

  5. RELAXATION LONGUE DUREE DE LA PHOTOCONDUCTIVITE DANS CdTe

    OpenAIRE

    Zozime, A.; Schröter, W.

    1983-01-01

    Différents aspects des mesures de photoconductivité faites sur des monocristaux de CdTe sont présentés. Les signaux montrent l'existence d'un processus de relaxation de longue durée. Les spectres suivent une loi de variation du type loi d'Urbach. Enfin, le seuil d'énergie correspondant à la limite de détection des signaux mesurés dans CdTe de type n correspond à un niveau profond dans la bande interdite, associé aux dislocations.

  6. Coal mining applications of CdTe gamma ray sensors

    International Nuclear Information System (INIS)

    Cadmium telluride (CdTe) solid-state radiation detectors have been used in the development of instrumentation that improves the efficiency of coal-mining operations by helping to locate coal seams and preventing the mining of high-sulfur coal near the edges of the seam. CdTe detectors were selected for these applications because while they are small and durable, they offer good stopping power, deliver adequate spectral response and operate at low voltage. These CdTe-based instruments have passed the mine-safety standards and are now in operation in the mine. (author)

  7. Electrical properties of single CdTe nanowires

    Directory of Open Access Journals (Sweden)

    Elena Matei

    2015-02-01

    Full Text Available Ion track, nanoporous membranes were employed as templates for the preparation of CdTe nanowires. For this purpose, electrochemical deposition from a bath containing Cd and Te ions was employed. This process leads to high aspect ratio CdTe nanowires, which were harvested and placed on a substrate with lithographically patterned, interdigitated electrodes. Focused ion beam-induced metallization was used to produce individual nanowires with electrical contacts and electrical measurements were performed on these individual nanowires. The influence of a bottom gate was investigated and it was found that surface passivation leads to improved transport properties.

  8. Study and development of new CdTe and CdZnTe detection structures for X and {gamma} imagery; Etude et realisation de nouvelles structures de detection a base de CdTe et CdZnTe pour l`imagerie X et {gamma}

    Energy Technology Data Exchange (ETDEWEB)

    Rosaz, M

    1997-10-24

    The aim of this study is to show the interest of applying cadmium telluride (CdTe) for X- and {gamma}- ray imaging applications, with specific technological (via contact nature) and geometric (via Frisch grids) structures suited for each application. This work is divided into three different but complementary parts: the first part describes a simulation model which allows a better understanding of CdTe based {gamma}- ray detectors. The new feature of this model compared to previous ones, is that it is able to take into account the electric field`s non uniform spatial distribution inside the detector s. The results enable us to de-convolute the influence of material and contact parameters on the spectrometric performances (energy resolution and peak/valley ratio) of CdTe based detectors; the second part presents different technological structures deposited upon CdTe, (grown by two different methods, i.e Bridgman and High Pressure Bridgman). These structures were characterised in X- and {gamma}- ray detection; theoretical models are developed which allow a certain insight into the detection properties of each couple (material + contact); the third part deals with new contact geometries which allow a screening effect of the bulk (analogous to the Frisch grid effect in gaseous detectors) resulting in improved energy resolution and peak/valley ratios; encouraging first results on prototypes are presented and discussed. This work has allowed a better understanding of physical behaviour of CdTe based detectors, coupled with advances in technological issues to upgrade the overall performances of these detectors for application in X- and {gamma}- ray imaging. (author) 93 refs.

  9. Growth, mechanical, thermal and dielectric properties of pure and doped KHP single crystal

    Science.gov (United States)

    M, Lakshmipriya.; Babu, D. Rajan; Vizhi, R. Ezhil

    2015-06-01

    L-Arginine doped potassium hydrogen phthalate and L-Histidine doped potassium hydrogen phthalate single crystals were grown by slow evaporation method at room temperature. The grown crystal crystallizes in orthorhombic system which is confirmed by single crystal XRD analysis. The grown crystals are subjected to thermal, mechanical and dielectric analysis.

  10. Crystallization and crystal properties of squid rhodopsin

    OpenAIRE

    Murakami, Midori; Kitahara, Rei; Gotoh, Toshiaki; Kouyama, Tsutomu

    2007-01-01

    Truncated rhodopsin from the retina of the squid Todarodes pacificus was extracted and crystallized by the sitting-drop vapour-diffusion method. Hexagonal crystals grown in the presence of octylglucoside and ammonium sulfate diffracted to 2.8 Å resolution.

  11. Relations between structural parameters and physical properties in CdTe and Cd0.96Zn0.04Te alloys

    OpenAIRE

    Guergouri, K.; Marfaing, Y.; Triboulet, R.; Tromson-Carli, A.

    1990-01-01

    Electrical measurements and photoluminescence experiments were performed on several CdTe and Cd0.96Zn0.04Te crystals with dislocation density in the range 5 x 104 - 6 × 105 cm-2. The observed variation in electron mobility has been interpreted in terms of scattering on space charge regions surrounding dislocations, a related reduction in the effective volume of the crystals, and excess scattering due to a non ideal alloy behaviour. The linewidth of the acceptor-bound exciton recombination lin...

  12. Radiation induced polarization in CdTe detectors

    Science.gov (United States)

    Vartsky, D.; Goldberg, M.; Eisen, Y.; Shamai, Y.; Dukhan, R.; Siffert, P.; Koebel, J. M.; Regal, R.; Gerber, J.

    1988-01-01

    Polarization induced by irradiation with intense gamma ray sources has been studied in chlorine-compensated CdTe detectors. The influence of several parameters, such as applied field strength, temperature and incident photon flux, on the polarization effect have been investigated. A relationship was found between the degree of polarization, detector efficiency and detector leakage current.

  13. Radiation induced polarization in CdTe detectors

    Energy Technology Data Exchange (ETDEWEB)

    Vartsky, D.; Goldberg, M.; Eisen, Y.; Shamai, Y.; Dukhan, R.; Siffert, P.; Koebel, J.M.; Regal, R.; Gerber, J.

    1988-01-15

    Polarization induced by irradiation with intense gamma ray sources has been studied in chlorine-compensated CdTe detectors. The influence of several parameters, such as applied field strength, temperature and incident photon flux, on the polarization effect have been investigated. A relationship was found between the degree of polarization, detector efficiency and detector leakage current.

  14. Highly luminescent water-soluble CdTe quantum dots

    NARCIS (Netherlands)

    Wuister, SF; Swart, A.N.; van Driel, F; Hickey, SG; Donega, CD; Swart, Ingmar

    2003-01-01

    Colloidal CdTe quantum dots prepared in TOP/DDA (trioctylphosphine/dodecylamine) are transferred into water by the use of aminoethanethiol.HCl (AET) or mercaptopropionic acid (MPA). This results in an increase in the photoluminescence quantum efficiency and a longer exciton lifetime. For the first t

  15. Thermal stability of substitutional ag in CdTe

    NARCIS (Netherlands)

    Jahn, SG; Hofsass, H; Restle, M; Ronning, C; Quintel, H; BharuthRam, K; Wahl, U

    1996-01-01

    The thermal stability of substitutional Ag in CdTe was deduced from lattice location measurements at different temperatures. Substitutional Ag probe atoms were generated via transmutation doping from radioactive Cd isotopes. The lattice sites of Ag isotopes were determined by measuring the channelin

  16. Intracavity CdTe modulators for CO2 lasers.

    Science.gov (United States)

    Kiefer, J. E.; Nussmeier, T. A.; Goodwin, F. E.

    1972-01-01

    The use of cadmium telluride as an electrooptic material for intracavity modulation of CO2 lasers is described. Included are the predicted and measured effects of CdTe intracavity modulators on laser performance. Coupling and frequency modulation are discussed and experimental results compared with theoretically predicted performance for both techniques. Limitations on the frequency response of the two types of modulation are determined.

  17. Electron transient transport in CdTe polycrystalline films

    Science.gov (United States)

    Ramírez-Bon, R.; Sánchez-Sinencio, F.; González de la Cruz, G.; Zelaya, O.

    1991-11-01

    Electron transient currents between coplanar electrodes have been measured in intrinsic polycrystalline films of CdTe, by means of the time of flight technique. The experimental results: electron transient current vs time, transit time vs voltage and the temperature dependence of the electron drift mobility, show features characteristics of dispersive electrical transport similar to that observed in disordered solids.

  18. Applications of CdTe to nuclear medicine. Final report

    International Nuclear Information System (INIS)

    Uses of cadmium telluride (CdTe) nuclear detectors in medicine are briefly described. They include surgical probes and a system for measuring cerebral blood flow in the intensive care unit. Other uses include nuclear dentistry, x-ray exposure control, cardiology, diabetes, and the testing of new pharmaceuticals

  19. Vertically aligned TiO2/(CdS, CdTe, CdSTe) core/shell nanowire array for photoelectrochemical hydrogen generation

    Science.gov (United States)

    Ai, Guanjie; Mo, Rong; Xu, Hang; Chen, Qiong; Yang, Sui; Li, Hongxing; Zhong, Jianxin

    2015-04-01

    Type-II TiO2/CdS, TiO2/CdTe and TiO2/CdSTe heterostructured core/shell nanowire arrays (NWAs) on FTO substrates are synthesized via physical vapor deposition of CdS, CdTe and the alloyed CdSTe layer onto the hydrothermally pre-grown TiO2 NWAs. Their morphologies, microstructures, and optical properties are characterized in detail. As photoanodes for photoelectrochemical (PEC) hydrogen generation, the ternary CdSTe alloy sensitized TiO2 NWAs exhibits a photocurrent density of 4.52 mA cm-2 under 1 sun illumination at 0.4261 V vs. RHE, much higher than that of the TiO2/CdS (2.97 mA cm-2) and TiO2/CdTe (0.46 mA cm-2) electrodes. This highest photocurrent density level of the alloy TiO2/CdSTe electrode is attributed to the broadened light absorption range and enhanced charge separation efficiency according to the optical and electrochemical impedance spectra investigation. Our result implies a promising application of CdSTe sensitized TiO2 photoelectrode in PEC cell and other photoelectronic devices.

  20. Performance of CdTe gamma-ray detectors fabricated in a new M π n design

    Science.gov (United States)

    Niraula, M.; Mochizuki, D.; Aoki, T.; Tomita, Y.; Hatanaka, Y.

    2000-06-01

    CdTe radiation detectors have been fabricated in a new M-π-n structure that provides very effective blocking for the leakage current and, as a result, excellent spectral responses are achieved. An iodine-doped n-CdTe layer was grown on the Te-faces of the (1 1 1)-oriented high-resistivity (˜10 9 Ω cm) ρ-type CdTe wafers at the low substrate temperature of 150°C. An aluminum electrode was evaporated on the n-CdTe side, while a gold electrode was evaporated on the other side. Low leakage current around 60 pA/mm 2 was typically attained for a 0.5 mm thick detector at room-temperature (25°C) for an applied reverse bias of 250 V. Improved charge collection efficiency and spectral responses for different radioisotopes in the energy range of a few tens of keV to several hundreds of keV were obtained due to the application of very large electric fields on the detectors. The performance of the detectors thus fabricated is presented.

  1. Growth of ZnO nanowires through thermal oxidation of metallic zinc films on CdTe substrates

    Energy Technology Data Exchange (ETDEWEB)

    Martinez, O., E-mail: oscar@fmc.uva.es [Optronlab Group, Dpto. Fisica Materia Condensada, Edificio I-D, Universidad de Valladolid, Paseo de Belen 1, 47011, Valladolid (Spain); Hortelano, V.; Jimenez, J. [Optronlab Group, Dpto. Fisica Materia Condensada, Edificio I-D, Universidad de Valladolid, Paseo de Belen 1, 47011, Valladolid (Spain); Plaza, J.L.; Dios, S. de; Olvera, J.; Dieguez, E. [Laboratorio de Crecimiento de Cristales, Departamento de Fisica de Materiales, Facultad de Ciencias, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Fath, R.; Lozano, J.G.; Ben, T.; Gonzalez, D. [Dpto. Ciencia de los Materiales e Ingenieria Metalurgica y Q.I., Facultad de Ciencias, Apdo. 40, 11510 Puerto Real, Cadiz (Spain); Mass, J. [Dpto. de Fisica, Universidad del Norte, Km.5 Via Puerto Colombia, Barranquilla (Colombia)

    2011-04-28

    Research highlights: > ZnO nanowires grown from thermal Zn oxidation. > TEM reveals high quality thin nanowires several microns long. > New phase formation at long oxidation time. > Good spectroscopic properties measured by Raman, Photo and Cathodoluminsecence spectroscopies. - Abstract: <112-bar 0> wurtzite ZnO nanowires (NWs) have been obtained by oxidizing in air at 500 deg. C thermally evaporated Zn metal films deposited onto CdTe substrates. The presence of Cd atoms from the substrate on the ZnO seeding layer and NWs seems to affect the growth of the NWs. The effects of the oxidation time on the structural and optical properties of the NWs are described in detail. It is shown that the NWs density decreases and their length increases when increasing the oxidation time. Thicker Zn layers result in thinner and longer ZnO NWs. Very long oxidation times also lead to the formation of a new CdO phase which is related to the partial destruction and quality reduction of the NWs. The possible process for ZnO NW formation on CdTe substrates is discussed.

  2. A Comparison between TGT and Cz Grown Nd:YAG

    Institute of Scientific and Technical Information of China (English)

    Benxue JIANG; Jun XU; Hong jun LI; Jingya WANG; Guangjun ZHAO

    2006-01-01

    Large sized neodymium-doped Y3Al5O12(Nd:YAG)laser crystals have been grown by temperature gradient technique(TGT)method and compared with Czochralski(Cz)method. The comparison of these two crystal growth methods has been listed. The results showed that the TGT method has many advantages over the Cz method. The concentration distribution of Nd ions in the crystals was determined and the absorption spectra of these crystals have been investigated and compared. The TGT grown highly doped Nd:YAG crystal has a larger absorption FWHM than that of Cz grown Nd:YAG crysral. Highly doped Nd:YAG(~2.8 at. pct)crystals could be obtained by TGT.

  3. Potentiality of photorefractive CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Moisan, J.Y.; Gravey, P.; Picoli, G.; Wolffer, N.; Vieux, V. (Dept. Technologies Appliquees a la Connectique, Centre National d' Etudes des Telecommunications, 22 - Lannion (France))

    1993-01-30

    For optical telecommunication networks, optical switching is now being studied. Different solutions have been proposed (integrated optics, free space switching, etc.), and reconfigurable optical interconnects, based on phase conjugation, should be one interesting method. For example, some results have been obtained with a double-phase conjugated mirror configuration, allowing reconfigurable connection between single-mode optical fibres. These phase-conjugated optics use photorefractive crystals and the first demonstration has been given using Bi[sub 12]TiO[sub 20] photorefractive crystals. In a telecommunication network, semiconductive crystals with a good efficiency in the near-IR wavelength are needed. Our first experiments were carried out with InP:Fe crystals at 1.3 [mu]m. However, it is well known, from published studies, that II-VI materials are, in principle, more interesting for the following reasons. The electro-optic coefficient is higher (and therefore the figure of merit is higher). The solubility of dopants is higher (and therefore the space charge electric field, which modulates the refractive index of the material, may be higher). Next we tested a CdTe:V crystal and, in a two-wave mixing experiment without an external electric field, an amplification gain was observed and a high photosensitivity demonstrated at 1.3 [mu]m. In this paper, we shall describe the photorefractive effect and explain our choice of the CdTe:V crystal, taking into account the parameters of this photorefractive effect and some other parameters required by the applications in the optical beam steering field. Next the results will be given, and finally an optical configuration using phase conjugation will be presented as an example of application. (orig.).

  4. Characterization of CdTe Films Deposited at Various Bath Temperatures and Concentrations Using Electrophoretic Deposition

    Directory of Open Access Journals (Sweden)

    Zulkarnain Zainal

    2012-05-01

    Full Text Available CdTe film was deposited using the electrophoretic deposition technique onto an ITO glass at various bath temperatures. Four batch film compositions were used by mixing 1 to 4 wt% concentration of CdTe powder with 10 mL of a solution of methanol and toluene. X-ray Diffraction analysis showed that the films exhibited polycrystalline nature of zinc-blende structure with the (111 orientation as the most prominent peak. From the Atomic Force Microscopy, the thickness and surface roughness of the CdTe film increased with the increase of CdTe concentration. The optical energy band gap of film decreased with the increase of CdTe concentration, and with the increase of isothermal bath temperature. The film thickness increased with respect to the increase of CdTe concentration and bath temperature, and following, the numerical expression for the film thickness with respect to these two variables has been established.

  5. Characterization of M-π-n CdTe pixel detectors coupled to HEXITEC readout chip

    Science.gov (United States)

    Veale, M. C.; Kalliopuska, J.; Pohjonen, H.; Andersson, H.; Nenonen, S.; Seller, P.; Wilson, M. D.

    2012-01-01

    Segmentation of the anode-side of an M-π-n CdTe diode, where the pn-junction is diffused into the detector bulk, produces large improvements in the spatial and energy resolution of CdTe pixel detectors. It has been shown that this fabrication technique produces very high inter-pixel resistance and low leakage currents are obtained by physical isolation of the pixels of M-π-n CdTe detectors. In this paper the results from M-π-n CdTe detectors stud bonded to a spectroscopic readout ASIC are reported. The CdTe pixel detectors have 250 μm pitch and an area of 5 × 5 mm2 with thicknesses of 1 and 2 mm. The polarization and energy resolution dependence of the M-π-n CdTe detectors as a function of detector thickness are discussed.

  6. First-principles study of roles of Cu and Cl in polycrystalline CdTe

    International Nuclear Information System (INIS)

    Cu and Cl treatments are important processes to achieve high efficiency polycrystalline cadmium telluride (CdTe) solar cells, thus it will be beneficial to understand the roles they play in both bulk CdTe and CdTe grain boundaries (GBs). Using first-principles calculations, we systematically study Cu and Cl-related defects in bulk CdTe. We find that Cl has only a limited effect on improving p-type doping and too much Cl can induce deep traps in bulk CdTe, whereas Cu can enhance p-type doping of bulk CdTe. In the presence of GBs, we find that, in general, Cl and Cu will prefer to stay at GBs, especially for those with Te-Te wrong bonds, in agreement with experimental observations

  7. First-principles study of roles of Cu and Cl in polycrystalline CdTe

    Science.gov (United States)

    Yang, Ji-Hui; Yin, Wan-Jian; Park, Ji-Sang; Metzger, Wyatt; Wei, Su-Huai

    2016-01-01

    Cu and Cl treatments are important processes to achieve high efficiency polycrystalline cadmium telluride (CdTe) solar cells, thus it will be beneficial to understand the roles they play in both bulk CdTe and CdTe grain boundaries (GBs). Using first-principles calculations, we systematically study Cu and Cl-related defects in bulk CdTe. We find that Cl has only a limited effect on improving p-type doping and too much Cl can induce deep traps in bulk CdTe, whereas Cu can enhance p-type doping of bulk CdTe. In the presence of GBs, we find that, in general, Cl and Cu will prefer to stay at GBs, especially for those with Te-Te wrong bonds, in agreement with experimental observations.

  8. First-principles study of roles of Cu and Cl in polycrystalline CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ji-Hui; Park, Ji-Sang; Metzger, Wyatt [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Yin, Wan-Jian [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); College of Physics, Optoelectronics and Energy and Collaborative, Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006 (China); Wei, Su-Huai, E-mail: suhuaiwei@csrc.ac.cn [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Beijing Computational Science Research Center, Beijing 100094 (China)

    2016-01-28

    Cu and Cl treatments are important processes to achieve high efficiency polycrystalline cadmium telluride (CdTe) solar cells, thus it will be beneficial to understand the roles they play in both bulk CdTe and CdTe grain boundaries (GBs). Using first-principles calculations, we systematically study Cu and Cl-related defects in bulk CdTe. We find that Cl has only a limited effect on improving p-type doping and too much Cl can induce deep traps in bulk CdTe, whereas Cu can enhance p-type doping of bulk CdTe. In the presence of GBs, we find that, in general, Cl and Cu will prefer to stay at GBs, especially for those with Te-Te wrong bonds, in agreement with experimental observations.

  9. Furnace design for the mercuric iodide crystal growth for new semiconductor radiation detector

    International Nuclear Information System (INIS)

    Mercuric iodide has been attracted an interest for 40 years due to its efficiency as room temperature detector for X and γ-rays. It is worthy to note that commercial γ-ray detectors such as Ge semiconductor detectors should cool down to liquid nitrogen temperature. Compared to other semiconductor detectors such as CdZnTe and CdTe, mercuric iodide has higher efficiency, lower leakage current and less degradation. In addition, mercuric iodide has useful properties such as large band gap of 2.15 eV, low electron-hole pair creation energy of 4.2 eV, and high atomic number (Hg : 80 and I : 53). However, it is difficult to obtain high quality single crystals and the long term reliability problem in devices so that the applications of α-HgI2 are limited. Mercuric iodide undergoes a structural phase transition from an orthorhombic yellow phase (β-HgI2) to a tetragonal red phase (α-HgI2) at 127 .deg. C. In addition, the melting temperature of HgI2 is 259 .deg. C. Thus, when it grows through a melting method over 259 .deg. C, the β-HgI2 phase can be included in the final crystals in the room temperature. In general, in order to grow α-HgI2single crystals, the operating temperature is below 127 .deg. C. Note that the crystals from the solution method have contamination problems and the crystals from the physical vapor method usually display a higher quality with a well defined structure. A good thing for the physical vapor method is that α-HgI2 has high vapor pressure (∼0.1 Torr at 120 .deg. C) indicating that α-HgI2 can be grown in closed ampoules

  10. Charge collection efficiency and space charge formation in CdTe gamma and X-ray detectors

    Science.gov (United States)

    Matz, R.; Weidner, M.

    1998-02-01

    A new extended model for the charge collection efficiency in CdTe gamma and X ray detectors is presented which allows to derive from apparent experimental gamma spectra of a quasi-monochromatic source, an 241Am source in the present case, not only the μρ products of electrons and holes individually but also the sign, spatial distribution, and temporal evolution of the net space charge accumulated in the detector. Resistive CdTe and CdZnTe as well as CdTe Schottky detectors are studied. While the resistive type is stable in time and exhibits higher μτ products, the Schottky type shows space charge accumulation which approaches saturation after about 1 h at several 10 11 cm -3. This is attributed to efficient majority carrier depletion, Fermi level shift, and trap filling. Resistive detectors thus appear optimized to the needs of gamma spectroscopy even at low bias voltage, while Schottky types need higher bias to overcome the space charge. They are suited to both, gamma spectroscopy and X-ray detection in analog current mode, where they operate more stably due ρo the higher bias. From the point of view of materials characterization, gamma spectroscopy with Schottky detectors probes and reveals the trap density near the Fermi level (several 10 12 cm -3 eV -1). We find a basically homogeneous spatial distribution suggesting the trap origin being in crystal growth rather than surface processing. Capture of photogenerated charges in traps is detrimental for current-mode operation under high X-ray flux because delayed emission from traps limits the detector's ability to respond to fast signal changes.

  11. Charge collection efficiency and space charge formation in CdTe gamma and X-ray detectors

    International Nuclear Information System (INIS)

    A new extended model for the charge collection efficiency in CdTe gamma and X ray detectors is presented which allows to derive from apparent experimental gamma spectra of a quasi-monochromatic source, an 241Am source in the present case, not only the μτ products of electrons and holes individually but also the sign, spatial distribution, and temporal evolution of the net space charge accumulated in the detector. Resistive CdTe and CdZnTe as well as CdTe Schottky detectors are studied. While the resistive type is stable in time and exhibits higher μτ products, the Schottky type shows space charge accumulation which approaches saturation after about 1 h at several 1011 cm-3. This is attributed to efficient majority carrier depletion, Fermi level shift, and trap filling. Resistive detectors thus appear optimized to the needs of gamma spectroscopy even at low bias voltage, while Schottky types need higher bias to overcome the space charge. They are suited to both, gamma spectroscopy and X-ray detection in analog current mode, where they operate more stably due to the higher bias. From the point of view of materials characterization, gamma spectroscopy with Schottky detectors probes and reveals the trap density near the Fermi level (several 1012 cm-3 eV-1). We find a basically homogeneous spatial distribution suggesting the trap origin being in crystal growth rather than surface processing. Capture of photogenerated charges in traps is detrimental for current-mode operation under high X-ray flux because delayed emission from traps limits the detector''s ability to respond to fast signal changes. (orig.)

  12. Growth of semicarbazone of benzophenone single crystals

    Science.gov (United States)

    Vijayan, N.; Ramesh Babu, R.; Gopalakrishnan, R.; Dhanuskodi, S.; Ramasamy, P.

    2002-03-01

    Semicarbazone of benzophenone single crystals have been grown by slow evaporation solution growth technique. The grown crystals have been characterized using XRD, melting point, FT-IR and UV-Vis spectra analyses. The X-ray diffraction analysis reveals that the crystal belongs to the triclinic crystal system and space group P1. From FT-IR studies it is found that the compound possesses both free and hydrogen bonded N-H stretching modes. The hydrogen bonded N-H stretching mode is found to be the major driving force for packing of molecules in the crystals. The transparency of the grown crystals has been confirmed using UV-Vis spectra.

  13. Recrystallization phenomena of solution grown paraffin dendrites

    NARCIS (Netherlands)

    Hollander, F.F.A.; Stasse, O.; Suchtelen, van J.; Enckevort, van W.J.P.

    2001-01-01

    Paraffin crystals were grown from decane solutions using a micro-Bridgman set up for in-situ observation of the morphology at the growth front. It is shown that for large imposed velocities, dendrites are obtained. After dendritic growth, aging or recrystallization processes set in rather quickly, c

  14. Technological aspects of development of pixel and strip detectors based on CdTe and CdZnTe

    Energy Technology Data Exchange (ETDEWEB)

    Gostilo, V.; Ivanov, V.; Kostenko, S.; Lisjutin, I.; Loupilov, A.; Nenonen, S.; Sipila, H.; Valpas, K

    2001-03-11

    Current and spectrometrical characteristics, stability in time and reliability of pixel and strip detectors depend on initial material properties, crystal processing quality and contacts manufacture technology. The work presents analysis of current-voltage and spectrometrical characteristics for initial CdTe and CdZnTe crystals applied for pixel and strip detectors manufacture. The crystal surface preparation before contacts manufacture comprises a modified technology. The contacts were made by photolithography with the surface protected by photoresist with further windows lift-off and crystal surface metallization in lifted-off windows. Metal pads were made by gold deposition from chloroauric acid. Thermocompression, ultrasonic and pulse wirebonding, as well as traditional contacts glueing method for CdTe and CdZnTe detectors have been tested for contacts wiring. The pulse wirebonding has revealed the best results. Wiring is made of gold wire with a diameter of 30 {mu}m and is good enough for pixel and strip wirebonding, providing rather low labour-intensiveness for their assembly by standard equipment. The possibility of fabrication of pressing contacts to strip and pixel detectors by Zebra elastomeric connectors has been investigated. The pressing contacts have provided qualitative and reliable electrical contact and signal layout from pixels and strips to readout electronics. Developed technologies were applied in the manufacture of the following CdTe and CdZnTe detectors: 4x4 pixels detector with rectangular pixels 0.65x0.65 mm and pitch 0.75 mm; 4x4 pixels ring miltiple-electrode detector with anode diameter 0.32 mm and pitch 0.75 mm; strip detector with 100 {mu}m width strip and 125 {mu}m pitch. The 4x4 pixels CdZnTe detector has provided at optimal temperature energy resolutions of 808 eV and 1.19 keV at energies of 5.9 and 59.6 keV, respectively. Interstrip resistance between two strips with a distance of 25 {mu}m on detector was 2-8 G{omega}.

  15. Technological aspects of development of pixel and strip detectors based on CdTe and CdZnTe

    International Nuclear Information System (INIS)

    Current and spectrometrical characteristics, stability in time and reliability of pixel and strip detectors depend on initial material properties, crystal processing quality and contacts manufacture technology. The work presents analysis of current-voltage and spectrometrical characteristics for initial CdTe and CdZnTe crystals applied for pixel and strip detectors manufacture. The crystal surface preparation before contacts manufacture comprises a modified technology. The contacts were made by photolithography with the surface protected by photoresist with further windows lift-off and crystal surface metallization in lifted-off windows. Metal pads were made by gold deposition from chloroauric acid. Thermocompression, ultrasonic and pulse wirebonding, as well as traditional contacts glueing method for CdTe and CdZnTe detectors have been tested for contacts wiring. The pulse wirebonding has revealed the best results. Wiring is made of gold wire with a diameter of 30 μm and is good enough for pixel and strip wirebonding, providing rather low labour-intensiveness for their assembly by standard equipment. The possibility of fabrication of pressing contacts to strip and pixel detectors by Zebra elastomeric connectors has been investigated. The pressing contacts have provided qualitative and reliable electrical contact and signal layout from pixels and strips to readout electronics. Developed technologies were applied in the manufacture of the following CdTe and CdZnTe detectors: 4x4 pixels detector with rectangular pixels 0.65x0.65 mm and pitch 0.75 mm; 4x4 pixels ring miltiple-electrode detector with anode diameter 0.32 mm and pitch 0.75 mm; strip detector with 100 μm width strip and 125 μm pitch. The 4x4 pixels CdZnTe detector has provided at optimal temperature energy resolutions of 808 eV and 1.19 keV at energies of 5.9 and 59.6 keV, respectively. Interstrip resistance between two strips with a distance of 25 μm on detector was 2-8 GΩ

  16. RHEED study of the (1 1 0) cleavage surface of CdTe:Cr single crystals

    Science.gov (United States)

    Sagan, P.; Kuzma, M.

    2007-03-01

    The structure of (1 1 0) plane of Cr-doped CdTe single crystals has been studied by reflection high energy electron diffraction and scanning electron microscopy. Diffraction patterns consist of diffraction spots and Kikuchi lines. However, for very small incident angle, the Debye rings are observed. The constant lattice attributed to these rings is 0.8% less then for pure CdTe. These anomalous properties of the near surface layer are likely to occur due to the concentration of Cr atoms creating compressive surface strains or the effect of crystal cleavage.

  17. CdTe polycrystalline films on Ni foil substrates by screen printing and their photoelectric performance

    International Nuclear Information System (INIS)

    Highlights: • The sintered CdTe polycrystalline films by a simple screen printing. • The flexible Ni foil was chose as substrates to reduce the weight of the electrode. • The compact CdTe film was obtained at 550 °C sintering temperature. • The photoelectric activity of the CdTe polycrystalline films was excellent. - Abstract: CdTe polycrystalline films were prepared on flexible Ni foil substrates by sequential screen printing and sintering in a nitrogen atmosphere for the first time. The effect of temperature on the quality of the screen-printed film was investigated in our work. The high-quality CdTe films were obtained after sintering at 550 °C for 2 h. The properties of the sintered CdTe films were characterized by scanning electron microscopy, X-ray diffraction pattern and UV–visible spectroscopy. The high-quality CdTe films have the photocurrent was 2.04 mA/cm2, which is higher than that of samples prepared at other temperatures. Furthermore, CdCl2 treatment reduced the band gap of the CdTe film due to the larger grain size. The photocurrent of photoelectrode based on high crystalline CdTe polycrystalline films after CdCl2 treatment improved to 2.97 mA/cm2, indicating a potential application in photovoltaic devices

  18. Aluminum doping of CdTe polycrystalline films starting from the heterostructure CdTe/Al

    OpenAIRE

    Becerril, M.; O. Vigil-Galán; G. Contreras-Puente; O. Zelaya-Angel

    2011-01-01

    Aluminum doped CdTe polycrystalline films were obtained from the heterostructure CdTe/Al/Corning glass. The aluminum was deposited by thermal vacuum evaporation and the CdTe by sputtering of a CdTe target. The aluminum was introduced into the lattice of the CdTe from a thermal annealed to the CdTe/Al/Corning glas heterostructure. The electrical, structural, nd optical properties were analyzed as a function of the Al concentrations. It found that when Al is incorporated, the electrical resisti...

  19. CdTe polycrystalline films on Ni foil substrates by screen printing and their photoelectric performance

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Huizhen [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China); Ma, Jinwen [College of New Energy, Bohai University, Jinzhou, Liaoning 121013 (China); Mu, Yannan [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China); Department of Physics and Chemistry, Heihe University, Heihe 164300 (China); Su, Shi; Lv, Pin; Zhang, Xiaoling; Zhou, Liying; Li, Xue; Liu, Li; Fu, Wuyou [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China); Yang, Haibin, E-mail: yanghb@jlu.edu.cn [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China)

    2015-06-15

    Highlights: • The sintered CdTe polycrystalline films by a simple screen printing. • The flexible Ni foil was chose as substrates to reduce the weight of the electrode. • The compact CdTe film was obtained at 550 °C sintering temperature. • The photoelectric activity of the CdTe polycrystalline films was excellent. - Abstract: CdTe polycrystalline films were prepared on flexible Ni foil substrates by sequential screen printing and sintering in a nitrogen atmosphere for the first time. The effect of temperature on the quality of the screen-printed film was investigated in our work. The high-quality CdTe films were obtained after sintering at 550 °C for 2 h. The properties of the sintered CdTe films were characterized by scanning electron microscopy, X-ray diffraction pattern and UV–visible spectroscopy. The high-quality CdTe films have the photocurrent was 2.04 mA/cm{sup 2}, which is higher than that of samples prepared at other temperatures. Furthermore, CdCl{sub 2} treatment reduced the band gap of the CdTe film due to the larger grain size. The photocurrent of photoelectrode based on high crystalline CdTe polycrystalline films after CdCl{sub 2} treatment improved to 2.97 mA/cm{sup 2}, indicating a potential application in photovoltaic devices.

  20. Photoluminescence and Electroluminescence Properties of CdTe Nanoparticles in Conjugated Polymer Hosts

    Institute of Scientific and Technical Information of China (English)

    GUO, Fengqi; XIE, Puhui

    2009-01-01

    The photoinduced energy transfer process from conjugated polymer (PPE4+) to CdTe nanocrystals was found both in solutions and in thin films by a fluorescence spectroscopic technique. Films of PPE4+ blended with CdTe-2 nanocrystals were formed by an electrostatic layer-by-layer assembly technique. Light emitting diodes were fabricated using CdTe-2 as an emitter in PPE4+ host. PPE4+ works as a molecular wire in the energy transfer process from the polymer to the CdTe-2 nanocrystals.