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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. Characterization of high-resistivity CdTe and Cd0.9Zn0.1Te crystals grown by Bridgman method for radiation detector applications

    Science.gov (United States)

    Mandal, Krishna C.; Krishna, Ramesh M.; Pak, Rahmi O.; Mannan, Mohammad A.

    2014-09-01

    CdTe and Cd0.9Zn0.1Te (CZT) crystals have been studied extensively for various applications including x- and γ-ray imaging and high energy radiation detectors. The crystals were grown from zone refined ultra-pure precursor materials using a vertical Bridgman furnace. The growth process has been monitored, controlled, and optimized by a computer simulation and modeling program developed in our laboratory. The grown crystals were thoroughly characterized after cutting wafers from the ingots and processed by chemo-mechanical polishing (CMP). The infrared (IR) transmission images of the post-treated CdTe and CZT crystals showed average Te inclusion size of ~10 μm for CdTe and ~8 μm for CZT crystal. The etch pit density was ≤ 5×104 cm-2 for CdTe and ≤ 3×104 cm-2 for CZT. Various planar and Frisch collar detectors were fabricated and evaluated. From the current-voltage measurements, the electrical resistivity was estimated to be ~ 1.5×1010 Ω-cm for CdTe and 2-5×1011 Ω-cm for CZT. The Hecht analysis of electron and hole mobility-lifetime products (μτe and μτh) showed μτe = 2×10-3 cm2/V (μτh = 8×10-5 cm2/V) and 3-6×10-3 cm2/V (μτh = 4- 6×10-5 cm2/V) for CdTe and CZT, respectively. Detectors in single pixel, Frisch collar, and coplanar grid geometries were fabricated. Detectors in Frisch grid and guard-ring configuration were found to exhibit energy resolution of 1.4% and 2.6 %, respectively, for 662 keV gamma rays. Assessments of the detector performance have been carried out also using 241Am (60 keV) showing energy resolution of 4.2% FWHM.

  9. 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)

  10. The Effect of the Wall Contact and Post-Growth, Cool-Down on Defects in CdTe Crystals Grown By 'Contactless' PVT

    Science.gov (United States)

    Palosz, W.; Grasza, K.; Dudley, M.; Raghothamachar, B.; Cai, L.; Dunrose, K.; Halliday, D.; Boyall, N. M.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    To take a maximum advantage of materials processing in microgravity for understanding the effects of gravity, gravity-independent effects should be minimized. In crystal growth, the quality of the grown crystals may depend, among other factors, on their interaction with the walls of the processing container during and after growth, and on the rate of the crystal cool-down at the end of the process. To investigate the above phenomena, a series of CdTe crystal growth processes was carried out. The crystals were grown by physical vapor transport without contact with the side walls of the silica glass ampoules. To eliminate the effect of the seed quality, and to reduce the number of nuclei and related crystal grains, the Low Supersaturation Nucleation technique was applied. The source temperature was 930 C, the undercooling was a few degrees. The crystals, having the diameter of 25 mm, grew at the rate of a few mm per day. The post-growth cool-down to the room temperature was conducted at different rates, and lasted from a few minutes to four days. The crystals were characterized using chemical etching, low temperature luminescence, and Synchrotron White Beam X-ray Topography techniques. The dislocation (etch pit) density was measured and its distribution was analyzed by comparison with Poisson curves and with the Normalized Radial Distribution Correlation Function. In the regions where the crystal is in contact with silica, the materials show a considerable strain field which extends for a few mm or more from the silica-crystal interface. In the reference crystal grown with contact with the ampoule walls, and when the crystals are cooled at the highest rates, the etch pit/dislocation density is in the high 10(exp 5) per square centimeter region. Typical EPD values for lower cool-down rates are in the lower 10(exp 4) per square centimeter region. In some areas the actual dislocation density was about 10(exp 3) per square centimeter or even less. No apparent effect of

  11. The Effect of the Wall Contact and Post-Growth C001-Down on Defects in CdTe Crystals Grown by Contactless PVT

    Science.gov (United States)

    Palosz, W.; Grasza, K.; Dudley, M.; Raghothamachar, B.; Cai, L.; Durose, K.; Halliday, D.; Boyall, N. M.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    In crystal growth, the quality of the final material may depend, among other factors, on its interaction with the walls of the ampoule during and after the growth, and on the rate of the crystal cool-down at the end of ate the process. To investigate the above phenomena, a series of CdTe crystal growth processes was carried out, The crystals were grown by physical vapor transport without contact with the side walls of the silica glass ampoules, applying the Low Supersaturation Nucleation technique. The source temperature was 930 C, the undercooling was a few degrees. The crystals, having the diameter of 25 mm, grew at the rate of a few mm per day. The post-growth cool-down to the room temperature was conducted at different rates, and lasted from a few minutes to four days. The crystals were characterized using chemical etching low temperature luminescence, and Synchrotron White Beam X-ray Topography techniques. The dislocation (etch pit) density was measured and its distribution was analyzed by comparison with Poisson curves and with the Normalized Radial Distribution Correlation Function. It was found that the contact of the crystal with silica leads to a strain field and high (in the 105 sq cm range) dislocation (etch pit) density. Similar defect concentrations were found in crystals subjected to fast post-growth cool-down. Typical EPD values for lower cool-down rates and in regions not affected by wall interactions are in the lower 10(exp 4) sq cm range. In some areas the actual dislocation density was about 10(exp 3) sq cm or even less. No apparent effect of the cool-down rate on polygonization was observed. A fine structure could be discerned in low-temperature PL spectra of crystals with low dislocation density.

  12. 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.

  13. 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.

  14. Investigation of swift heavy ion irradiation effects in CdTe crystals

    International Nuclear Information System (INIS)

    CdTe crystals grown by the Bridgman technique were irradiated by swift heavy ions (SHIs), 100 MeV Ag7+ ions, with fluences varying from 1011 to 1014 ions cm-2 and the damage is investigated by atomic force microscopy, x-ray diffraction, hall effect measurements and photoluminence. It is found that the behaviour of CdTe crystals under a SHI irradiation induces structural disorder, generation of optically active defects, decrease in the electron mobility but an increase in the carrier concentration compared with as-grown samples. The observed effects are mainly due to the intense electronic excitation created by SHIs

  15. 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.

  16. 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.)

  17. 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.)

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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...

  3. 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...

  4. 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.

  5. 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.).

  6. 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.

  7. 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)

  8. 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.

  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. 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.

  12. Melt Grown ZnO Bulk Crystals

    OpenAIRE

    Schulz, Detlev; Ganschow, Steffen; Klimm, Detlef

    2009-01-01

    Bulk crystals of zinc oxide can be grown from the melt by a Bridgman technique under pressure. This new technology using an iridium crucible shows the potential to yield large single crystals of good crystalline perfection. Crystals with diameters up to 33 mm and a length of up to 50 mm have been demonstrated. The impurity content can be strongly reduced by using the crucibles repeatedly.

  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

    International Nuclear Information System (INIS)

    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. 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...

  17. 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.).

  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. 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.

  20. 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.

  1. 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.).

  2. 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

  3. Modeling of axial vibrational control technique for CdTe VGF crystal growth under controlled cadmium partial pressure

    Science.gov (United States)

    Avetissov, I.; Kostikov, V.; Meshkov, V.; Sukhanova, E.; Grishechkin, M.; Belov, S.; Sadovskiy, A.

    2014-01-01

    A VGF growth setup assisted by axial vibrations of baffle submerged into CdTe melt with controlled Cd partial pressure was designed. An influence of baffle shape on flow velocity map, temperature distribution in CdTe melt and interface shape of growing crystal was analyzed by numerical simulation and physical modeling. To produce the desirable shape of crystal melt interface we slant under different angles vertical generatrix in a cylindrical disk and made chasing on faceplates of a disk. It was ascertained that a disk with conical generatrix formed more intensive convective flows from a faceplate with larger diameter. It was shown that at CdTe VGF crystal growth rate about 10 mm/h application of AVC technique made it possible to produce convex interface for 2 in. crystal diameter.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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)

  10. 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.

  11. Characterization of sodium chloride crystals grown in microgravity

    Science.gov (United States)

    Fontana, Pietro; Schefer, Jürg; Pettit, Donald

    2011-06-01

    NaCl crystals grown by the evaporation of an aqueous salt solution in microgravity on the International Space Station (ISS) were characterized and compared to salt crystals grown on earth. NaCl crystallized as thin wafers in a supersaturated film of 200-700 μm thickness and 50 mm diameter, or as hopper cubes in 10 mm diameter supersaturated spheres. Neutron diffraction shows no change in crystal structure and in cell parameters compared to earth-grown crystals. However, the morphology can be different, frequently showing circular, disk-like shapes of single crystals with perpendicular to the disks, an unusual morphology for salt crystals. In contrast to the growth on earth the lateral faces of the microgravity tabular hopper crystals are symmetrical because they are free floating during the crystallization process. Hopper cubes were produced without the need to suspend the growing crystals by an ongoing stirring. "Fleur de Sel" is shown as an example of two-dimensional growth of salt on earth and compared to the space grown crystals. It is shown that in microgravity conditions brine fluid inclusions form within the salt crystals.

  12. 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.

  13. Effect of CdTe single crystal surface state on the processes of charge carrier annihilation

    International Nuclear Information System (INIS)

    In the case of CdTe single crystals doped by CI as a result of the etching in Br2-methanol solution the spectrum beyond fundamental absorption caused by LO-phonon scattering of the free and bound electron-hole states is investigated. Formation of the scattering phonons is connected with indirect electron transitions into conduction band Γ-minimum from impurity band associated with CI levels at the edge of Brillouin zone. Explanation of the above-band-gap photoluminescence (APL) nature is based on the theoretical elaborations for direct and indirect exciton absorption in the wide-band-gap AI'IBV'I compounds. APL structure dependence on conditions of sample preparation and surface state is discussed

  14. Influence of a background pollution level on electric heterogeneity in monocrystals CdTe and Cd1-xZnxTe grown from fusion

    International Nuclear Information System (INIS)

    In this paper are considered growth and it is pure crystalline reasons of non-uniform distribution background impurity at monocrystals grown from fusion. Features of high ohmic conditions monocrystals CdTe with formation of channel conductivity are analyzed. Are offered noncontact methods of diagnostics of a background pollution level and definition of conductivity type. Typical kinds of dot defects are analysed and shown ways of reduction of their concentration

  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. 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.

  17. 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

  18. Single Crystals Grown Under Unconstrained Conditions

    Science.gov (United States)

    Sunagawa, Ichiro

    Based on detailed investigations on morphology (evolution and variation in external forms), surface microtopography of crystal faces (spirals and etch figures), internal morphology (growth sectors, growth banding and associated impurity partitioning) and perfection (dislocations and other lattice defects) in single crystals, we can deduce how and by what mechanism the crystal grew and experienced fluctuation in growth parameters through its growth and post-growth history under unconstrained condition. The information is useful not only in finding appropriate way to growing highly perfect and homogeneous single crystals, but also in deciphering letters sent from the depth of the Earth and the Space. It is also useful in discriminating synthetic from natural gemstones. In this chapter, available methods to obtain molecular information are briefly summarized, and actual examples to demonstrate the importance of this type of investigations are selected from both natural minerals (diamond, quartz, hematite, corundum, beryl, phlogopite) and synthetic crystals (SiC, diamond, corundum, beryl).

  19. Hardening mechanism of twin boundaries during nanoindentation of soft-brittle CdTe crystals

    International Nuclear Information System (INIS)

    Deformations of cadmium telluride (CdTe) under nanoindentation were simulated by molecular dynamics. CdTe slides along the {1 1 1} planes under nanoindentation through edge dislocations. During loading, the sliding of CdTe was limited at twin boundaries, inducing the pile-up phenomenon. When dislocations transferred across the twin boundary, a sessile dislocation and steps formed. The coherence effect of both twin boundaries locked the dislocations at the twin boundary effectively, indicating a better hardening effect

  20. 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.

  1. 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.

  2. Dewetted growth of CdTe in microgravity (STS-95)

    International Nuclear Information System (INIS)

    Two CdTe crystals had been grown in microgravity during the STS-95 mission. The growth configuration was dedicated to obtain dewetting of the crystals and to achieve high quality material. Background for the performed experiments was based on the theory of the dewetting and previous experience. The after flight characterization of the crystals has demonstrated existence of the dewetting areas of the crystals and their improved quality regarding the earth grown reference sample. The samples had been characterized by EDAX, Synchrotron X-ray topography, Photoluminescence and Optical and IR microscopy. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Dewetted growth of CdTe in microgravity (STS-95)

    Energy Technology Data Exchange (ETDEWEB)

    Fiederle, M.; Babentsov, V.; Benz, K.W. [Freiburger Materialforschungszentrum, D-79104 Freiburg (Germany); Duffar, T. [EPM, ENSHMG BP95 F-38402 Saint Martin d' Heres (France); Dusserre, P. [DTEN, Commissariat a l' Energie Atomique, 17, rue des Martyrs, F-38054 Grenoble (France); Corregidor, V.; Dieguez, E. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, E-28034 Madrid (Spain); Delaye, P.; Roosen, G. [Laboratoire Charles Fabry, Institut d' Optique Theorique et Appliquee, 91403 Orsay Cedex (France); Chevrier, V.; Launay, J.C. [Institut de Chimie de la Matiere Condensee de Bordeaux, ICMCB-CNRS-UPR 9048, 87 avenue du Docteur A. Schweitzer, 33608 Pessac Cedex (France)

    2004-06-01

    Two CdTe crystals had been grown in microgravity during the STS-95 mission. The growth configuration was dedicated to obtain dewetting of the crystals and to achieve high quality material. Background for the performed experiments was based on the theory of the dewetting and previous experience. The after flight characterization of the crystals has demonstrated existence of the dewetting areas of the crystals and their improved quality regarding the earth grown reference sample. The samples had been characterized by EDAX, Synchrotron X-ray topography, Photoluminescence and Optical and IR microscopy. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. 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 ...

  5. 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)

  6. 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.

  7. 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.

  8. Spectral response of THM grown CdZnTe crystals

    DEFF Research Database (Denmark)

    Chen, H.; Awadalla, S.A.; Harris, F.; Lu, Pinghe; Redden, R.; Bindley, G.; Copete, A.; Hong, J.; Grindlay, J.; Amman, M.; Lee, J.S.; Luke, P.; Kuvvetli, Irfan; Budtz-Jørgensen, Carl

    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...

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. 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.).

  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. Spectral, thermal and hardness studies on unidirectional grown dichlorido diglycine zinc dihydrate single crystal

    International Nuclear Information System (INIS)

    Bulk semi-organic single crystal of dichlorido diglycine zinc dihydrate has been grown by unidirectional crystal growth method from aqueous solution. The phase of the grown crystal was identified using single crystal XRD analysis. The functional groups present in the crystal were confirmed using FTIR and 1H NMR analysis. Transmission study shows 70% of transmission in the entire visible region, which reveals the good optical quality of the grown crystal. A stable broad peak in the range of violet-green emission was observed in the emission spectrum, which is due to the existence of defects in the crystal. The thermal and mechanical properties of the grown crystal were studied using TG/DTA and the Vickers microhardness tester, respectively. -- Research highlights: → Dichlorido diglycine zinc dihydrate has been grown by unidirectional crystal growth method. → Optical good quality single crystal of 108 mm length and 12 mm diameter was grown. → Single crystal XRD, FTIR, NMR, transmission and emission studies are discussed. → NMR and photoluminescence studies are reported in this paper for the first time. → The thermal and mechanical properties of the grown crystal are discussed in detail.

  17. Modification of oxygen content in LiF crystals grown by skull method

    Science.gov (United States)

    Taranyuk, V.; Gektin, A.; Shiran, N.; Shlyakhturov, V.; Gridin, S.; Boiaryntseva, I.; Sofronov, D.

    2013-10-01

    The work is devoted to the controlled crystal growth procedure providing of optimal doping of dielectric halide materials (LiF crystals in particular). Two series of LiF crystals were studied. One series is represented by ultra- and nominal pure crystals, as well as crystals doped with polyvalent oxides (Nb2O5, WO3 and TiO2), which were grown by classical Kyropoulos method in vacuum, second series involves crystals grown using the skull method. It is shown that the skull technique is a quite efficient method of variously doped LiF crystal growth as compare with the classic Kyropoulos method.

  18. Defect studies in 4H- Silicon Carbide PVT grown bulk crystals, CVD grown epilayers and devices

    Science.gov (United States)

    Byrappa, Shayan M.

    Silicon Carbide [SiC] which exists as more than 200 different polytypes is known for superior high temperature and high power applications in comparison to conventional semiconductor materials like Silicon and Germanium. The material finds plethora of applications in a diverse fields due to its unique properties like large energy bandgap, high thermal conductivity and high electric breakdown field. Though inundated with superior properties the potential of this material has not been utilized fully due to impeding factors such as defects especially the crystalline ones which limit their performance greatly. Lots of research has been going on for decades to reduce these defects and there has been subsequent improvement in the quality as the diameter of SiC commercial wafers has reached 150mm from 25mm since its inception. The main focus of this thesis has been to study yield limiting defect structures in conjunction with several leading companies and national labs using advanced characterization tools especially the Synchrotron source. The in depth analysis of SiC has led to development of strategies to reduce or eliminate the density of defects by studying how the defects nucleate, replicate and interact in the material. The strategies discussed to reduce defects were proposed after careful deliberation and analysis of PVT grown bulk crystals and CVD grown epilayers. Following are some of the results of the study: [1] Macrostep overgrowth mechanism in SiC was used to study the deflection of threading defects onto the basal plane resulting in stacking faults. Four types of stacking faults associated with deflection of c/c+a threading defects have been observed to be present in 76mm, 100mm and 150mm diameter wafers. The PVT grown bulk crystals and CVD grown epilayers in study were subjected to contrast studies using synchrotron white beam X-ray topography [SWBXT]. The SWBXT image contrast studies of these stacking faults with comparison of calculated phase shifts for

  19. Characterization of charged defects in Cd_xHg_(1-x)Te and CdTe crystals by electron beam induced current and scanning tunneling spectroscopy

    OpenAIRE

    Panin, G. N.; Diaz-Guerra, C.; Piqueras de Noriega, Javier

    1998-01-01

    A correlative study of the electrically active defects of CdxHg1-xTe and CdTe crystals has been carried out using a scanning electron microscope/scanning tunneling microscope (SEM/STM) combined system. Charged structural and compositional defects were revealed by the remote electron beam induced current (REBIC) mode of the scanning electron microscope. The electronic inhomogeneities of the samples were analyzed with nm resolution by current imaging tunneling spectroscopy (CITS) measurements, ...

  20. Structure of KTiOPO4 single crystals grown by the top-seeded solution and spontaneous flux crystallization methods

    International Nuclear Information System (INIS)

    This paper reports on the results of precision X-ray structural investigations of KTiOPO4 single crystals grown by one method (crystallization from a solution in the melt) in two variants (the spontaneous formation of crystallization centers or top-seeded solution growth during slow cooling of saturated solution melts). It is shown that spontaneous flux crystallization leads to the formation of a larger number of defects. Potassium atoms are found to be disordered. The splitting of the K1 and K2 potassium positions is equal to 0.347(4) and 0.279(3) A, respectively, for the crystals grown by the top-seeded solution method and 0.308(5) and 0.321(4) A, respectively, for the crystals grown through the spontaneous flux crystallization.

  1. On the microstructure of as-grown TiN whisker-like crystals

    Energy Technology Data Exchange (ETDEWEB)

    Wokulski, Z. [Silesia Univ., Katowice (Poland). Inst. of Physics and Chemistry of Metals

    2001-02-16

    The microstructure of as-grown TiN whisker-like crystals was examined using Lang X-ray topography, transmission electron microscopy (TEM) and also the Eshelby measurement of the twist of the crystal lattice. It was found that the as-grown TiN whisker-like crystals exhibit a very high degree of structural perfection. In a few cases the observed dislocations were deformation-type dislocations and occurred only in areas of brittle fracture of whiskers. In none of the tested as-grown whisker-like crystals axial dislocations were detected. (orig.)

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

    International Nuclear Information System (INIS)

    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. (paper)

  3. 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.

  4. 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)

  5. 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,...

  6. 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

  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.

    2016-04-01

    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.

  8. 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.

  9. 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.

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

    International Nuclear Information System (INIS)

    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. 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.

  13. Perfection of NaNO3 single crystals grown by axial vibrational control technique in Czochralski configuration

    Science.gov (United States)

    Avetissov, I. Ch.; Sadovskiy, A. P.; Sukhanova, E. A.; Orlova, G. Yu.; Belogorokhov, I. A.; Zharikov, E. V.

    2012-12-01

    Perfection of NaNO3 single crystals grown by axial vibrational control technique in the Czochralski configuration (AVC-CZ) by submerging an oscillating baffle into the melt under the crystal was studied. The characteristics of AVC-CZ grown crystals were analyzed by micro-Raman technique, X-ray structural analysis and chemical dislocation etching. For the AVC-CZ grown NaNO3 single crystals the structure sensitive properties of high-quality were demonstrated.

  14. 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.

  15. Transport property measurements of Bi2Se3 crystal grown by Bridgman method

    OpenAIRE

    M.P. Deshpande; PANDYA, Nilesh N.; PARMAR, and M. N.

    2009-01-01

    This paper deals with the growth of Bi2Se3 crystal by newly designed experimental set-up of Bridgman technique in our laboratory. Grown crystal is characterized by EDAX (Energy Dispersive Analysis of X-rays), XRD (X-ray Diffraction), low temperature thermopower measurements (17-284 K), resistivity measurements (16-294 K) and Hall Effect at room temperature in order to study its various properties. The surface study of the grown crystal using AFM (Atomic Force Microscopy) shows a hexa...

  16. Fabrication of radiation detectors with HgI2 crystals grown from a solution

    International Nuclear Information System (INIS)

    Mercuric Iodide crystals grown from a solution of molecular complexes with dimethylsulfoxide have been evaluated as γ-ray and X-ray room temperature detectors. Compared with materials grown from the vapor phase these crystals are characterized by a larger size, a lower level of native defects, but a higher impurity level. Detector technology, X-ray and γ-ray (up to 662 keV) detection properties and characterization measurements (T.S.C., photoconductivity, photovoltaic effect) are described. The effect of light on crystal properties is briefly discussed

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. A naturally grown three-dimensional nonlinear photonic crystal

    International Nuclear Information System (INIS)

    Nonlinear frequency conversion via three-dimensional (3D) quasi-phase matching (QPM) process is experimentally realized based on a Ba0.77Ca0.23TiO3 (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

  2. 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.

  3. Defect formation in 4H-SiC single crystal grown on the prismatic seeds

    International Nuclear Information System (INIS)

    The defect structure of 4H silicon carbide single crystals grown by PVT method on three prismatic seeds (10-10), (11-20) and (8.3.-11.0) is considered. The only defects existing in the grown ingots are stacking faults and basal plane dislocations. The type of stacking fault is studied. The dependence of stacking fault morphology on the seed orientation is analyzed

  4. 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.

  5. Sources of optical distortion in rapidly grown crystals of KH2PO4

    International Nuclear Information System (INIS)

    We report results of x-ray topographic and optical measurements on KH2PO4 crystals grown at rates of 5 to 30mm/day. We show that optical distortion in these crystals is caused primarily by 3 sources: dislocations, differences in composition between adjacent growth sectors of the crystal, and differences in composition between adjacent sectors of vicinal growth hillocks within a single growth sector of the crystal. We find that the compositional heterogeneities cause spatial variations in the refractive index and induced distortion of the transmitted wave front while large groups of dislocations are responsible for strain induced birefringence which leads to beam depolarization

  6. Video microscopic studies of an electrochemically-grown molecular crystal

    Science.gov (United States)

    Kobayashi, Y.; Fortune, N. A.

    1996-03-01

    We have adapted a trinocular microscope, CCD video camera and computer-interfaced video frame grabber to monitor and control the growth of molecular crystals in conventional and specially designed electrochemical cells. By digitally subtracting old images from new images, we are able to distinguish new growth from old growth and actively adjust external parameters during crystal growth. Our new electrochemical cell design not only improves our ability to optically study growth processes in the cell but also allows solution flow into and out of each cell chamber, providing the possibility of controlling anion composition and concentration over time. We are presently investigating how external parameters such as temperature, voltage and current density physically affect growth mechanisms. Applications include maintaining a constant crystal current density to maximize crystal size and quality for a given time interval, subject to additional constraints on the voltage across the electrochemical cell. At this conference, we report our progress to date in studying the growth of the prototypical molecular superconductor κ-(BEDT-TTF)_2Cu(NCS)_2.

  7. Optical and mechanical studies on unidirectional grown tri-nitrophenol methyl p-hydroxybenzoate bulk single crystal

    Science.gov (United States)

    Uthrakumar, R.; Vesta, C.; Robert, R.; Mangalam, G.; Jerome Das, S.

    2010-10-01

    The bulk single crystal of tri-nitrophenol methyl p-hydroxybenzoate (TNMPHB) of length 90 mm and diameter 12 mm was obtained by employing unidirectional growth technique. Single crystal X-ray diffraction studies and powder XRD analysis have been carried out to confirm the identity of the crystal. The optical band gap of the grown crystal was calculated to be 4.91 eV from UV transmission spectrum. The mechanical strength of the grown crystal has been studied using Vicker's microhardness tester. Low dielectric loss shows that the grown crystal contains lesser defects authenticating the suitability of the crystal towards device applications. The surface morphology studies have been carried out on the grown crystal.

  8. Optical and mechanical studies on unidirectional grown tri-nitrophenol methyl p-hydroxybenzoate bulk single crystal

    International Nuclear Information System (INIS)

    The bulk single crystal of tri-nitrophenol methyl p-hydroxybenzoate (TNMPHB) of length 90 mm and diameter 12 mm was obtained by employing unidirectional growth technique. Single crystal X-ray diffraction studies and powder XRD analysis have been carried out to confirm the identity of the crystal. The optical band gap of the grown crystal was calculated to be 4.91 eV from UV transmission spectrum. The mechanical strength of the grown crystal has been studied using Vicker's microhardness tester. Low dielectric loss shows that the grown crystal contains lesser defects authenticating the suitability of the crystal towards device applications. The surface morphology studies have been carried out on the grown crystal.

  9. Optical and mechanical studies on unidirectional grown tri-nitrophenol methyl p-hydroxybenzoate bulk single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Uthrakumar, R. [Department of Physics, Loyola College, Chennai 600 034 (India); Vesta, C. [Department of Physics, SDNB Vaishnav College, Chennai 600 044 (India); Robert, R. [Department of Physics, Government Arts College (Men), Krishnagiri 635 001 (India); Mangalam, G. [Department of Physics, MGR University, Chennai 600 095 (India); Jerome Das, S., E-mail: jerome@loyolacollege.ed [Department of Physics, Loyola College, Chennai 600 034 (India)

    2010-10-15

    The bulk single crystal of tri-nitrophenol methyl p-hydroxybenzoate (TNMPHB) of length 90 mm and diameter 12 mm was obtained by employing unidirectional growth technique. Single crystal X-ray diffraction studies and powder XRD analysis have been carried out to confirm the identity of the crystal. The optical band gap of the grown crystal was calculated to be 4.91 eV from UV transmission spectrum. The mechanical strength of the grown crystal has been studied using Vicker's microhardness tester. Low dielectric loss shows that the grown crystal contains lesser defects authenticating the suitability of the crystal towards device applications. The surface morphology studies have been carried out on the grown crystal.

  10. 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.)

  11. Quantitative Schlieren analysis applied to holograms of crystals grown on Spacelab 3

    Science.gov (United States)

    Brooks, Howard L.

    1986-01-01

    In order to extract additional information about crystals grown in the microgravity environment of Spacelab, a quantitative schlieren analysis technique was developed for use in a Holography Ground System of the Fluid Experiment System. Utilizing the Unidex position controller, it was possible to measure deviation angles produced by refractive index gradients of 0.5 milliradians. Additionally, refractive index gradient maps for any recorded time during the crystal growth were drawn and used to create solute concentration maps for the environment around the crystal. The technique was applied to flight holograms of Cell 204 of the Fluid Experiment System that were recorded during the Spacelab 3 mission on STS 51B. A triglycine sulfate crystal was grown under isothermal conditions in the cell and the data gathered with the quantitative schlieren analysis technique is consistent with a diffusion limited growth process.

  12. Controlling crystal phases in GaAs nanowires grown by Au-assisted molecular beam epitaxy

    International Nuclear Information System (INIS)

    Control of the crystal phases of GaAs nanowires (NWs) is essential to eliminate the formation of stacking faults which deteriorate the optical and electronic properties of the NWs. In addition, the ability to control the crystal phase of NWs provides an opportunity to engineer the band gap without changing the crystal material. We show that the crystal phase of GaAs NWs grown on GaAs(111)B substrates by molecular beam epitaxy using the Au-assisted vapor–liquid–solid growth mechanism can be tuned between wurtzite (WZ) and zinc blende (ZB) by changing the V/III flux ratio. As an example we demonstrate the realization of WZ GaAs NWs with a ZB GaAs insert that has been grown without changing the substrate temperature. (paper)

  13. 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

  14. 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...

  15. Structure of Zn_(1-x)Mn_xIn_2Se_4 crystals grown by CVT

    OpenAIRE

    Mantilla, J.; Brito, G. E. S.; Ter Haar, E.; Sagredo, V.; Bindilatti, V.

    2003-01-01

    Single crystals of Zn_(1-x)Mn_xIn_2Se_4 were grown by the chemical vapour phase transport technique (CVT). The Mn concentration was varied from x=1 to x=0.01. Through X-rays powder diffraction patterns and Laue diagrams of single crystals we studied the transformation from the hexagonal structure of MnIn_2Se_4 to the tetragonal structure of ZnIn_2Se_4.

  16. 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.

  17. 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 ...

  18. Te-and Zn-Doped InSb Crystals Grown in Microgravity

    Science.gov (United States)

    Ostrogorsky, A. G.; Marin, C.; Volz, M.; Bonner, W. A.; Duffar, T.

    2004-01-01

    In 2002, within the SUBSA (Solidification Using a Baffle in Sealed Ampoules) investigation, seven doped InSb crystals were grown in microgravity at the International Space Station. The key goals of the SUBSA investigation are: (a) to clarify the origin of the melt convection in space laboratories; (b) to reduce melt convection to the level which allows reproducible diffusion-controlled segregation; (e) to explore the submerged baffle process and liquid encapsulation in microgravity. 30 crystal growth experiments were conducted in the ground unit, to optimize the design of flight ampoules and to test the transparent SUBSA furnace developed by TecMasters Inc. The specially designed furnace, allowed observation of the crystal growth process (melting, seeding, motion of the solid-liquid interface, etc.). In the summer of 2002, eight crystal growth experiments were conducted in the Microgravity Science Glovebox (MSG) facility at the ISS. Four Te-doped (k = 0.5) and three Zn-doped (k2.9) crystals were grown on undoped seeds. In one experiment, we were not able to seed and grow. The seven grown crystals were sectioned and analyzed using SIMS. The design of the SUBSA ampoules, the segregation data and the video images obtained during the SUBSA flight experiments will be presented and discussed.

  19. 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.

  20. 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.

  1. 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.

  2. Microstructural and vibrational properties of PVT grown Sb2Te3 crystals

    Science.gov (United States)

    Kokh, K. A.; Atuchin, V. V.; Gavrilova, T. A.; Kuratieva, N. V.; Pervukhina, N. V.; Surovtsev, N. V.

    2014-01-01

    High-quality Sb2Te3 microcrystals have been grown by the physical vapor transport (PVT) method without using a foreign transport agent. The microcrystals grown under optimal temperature gradient are well facetted and they have dimensions up to ~200 μm. The phase composition of the grown crystals has been identified by the X-ray single crystal structure analysis in space group R-3m, a=4.2706(1), b=30.4758(8) Ǻ, Z=3 (R=0.0286). Raman microspectrometry has been used to describe the vibration parameters of Sb2Te3 microcrystals. The FWHM parameters obtained for representative Raman lines at 69 and 111 cm-1 are as low as 5 and 8.6 cm-1, respectively.

  3. 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.

  4. 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.

  5. 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

  6. X-ray topographic study of growth defects of trans-stilbene crystals grown from solutions

    Science.gov (United States)

    Klapper, Helmut; Zaitseva, Natalia; Carman, Leslie

    2015-11-01

    Single crystals of trans-stilbene, C14H12, with properties suitable for high-energy neutron detection were grown from solution in anisole and toluene by the temperature reduction method with growth rates up to 6 mm/day. From these crystals, slices of appropriate orientation and thickness of 2-4 mm were cut and studied by X-ray diffraction topography applying the Lang method using CuKα radiation. The topographs exhibit growth defects such as liquid inclusions, dislocations, striations, and faulty growth-sector boundaries. These defects occur in the same typical arrangements and geometries as is observed in all kinds of crystals grown on habit faces from solution. Besides growth dislocations originating from inclusions and propagating with the growth front, many plastic glide dislocations in the shape of loops or half-loops emitted from inclusions by stress relaxation are observed. The glide system underlying this plasticity is discussed.

  7. 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.

  8. Structural features of Ge(Ga) single crystals grown by the floating zone method in microgravity

    Science.gov (United States)

    Prokhorov, I. A.; Zakharov, B. G.; Senchenkov, A. S.; Egorov, A. V.; Camel, D.; Tison, P.

    2008-11-01

    Structural features of the Ge(Ga) single crystal grown by the floating zone (FZ) method in microgravity environment aboard the FOTON-9 spacecraft are investigated by methods of X-ray topography, double-crystal diffractometry, selective chemical etching and spreading resistance measurements. It is established that the crystal structure is characterized by the presence of an incompletely melted region and defects caused by its formation. Growth striations revealed in regrown part of the crystal, testify to development of non-stationary capillary Marangoni convection in melt at the realized parameters of FZ remelting under space conditions. Periodicity of the growth striations is compared to frequency characteristics of heat flux pulsations through the crystallization front, found as a result of numerical simulation of melt hydrodynamics.

  9. 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.

  10. Structural and optical properties of LiKB4O7 single crystals grown by Czochralski technique

    International Nuclear Information System (INIS)

    One of the alkali metal borates, lithium potassium borate (LiKB4O7) 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 LiKB4O7 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 LiKB4O7 crystal from (a) top portion and (b) bottom portion. - Highlights: • LiKB4O7 crystal was grown under two different micro stepping movements by the crystal puller. • Crystalline nature, optical properties and micro morphology of LiKB4O7 were investigated. • The micro stepping pull movement reduces the dislocation density during the growth of LiKB4O7 crystals

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Characterization of large-sized Nd:YAG single crystals grown by horizontal directional solidification

    Energy Technology Data Exchange (ETDEWEB)

    Han, Jiecai; Guo, Huaixin; Zhang, Mingfu; Song, Ningning; Xu, Chenghai [Center for Composite Materials, Harbin Institute of Technology, Harbin, 150080 (China)

    2012-05-15

    Nd{sup 3+}-doped Y{sub 3}Al{sub 5}O{sub 12} single crystals have been grown by the horizontal directional solidification (HDS) method in different thermal zone. The Grashof (G{sub r}), Prandtl (P{sub r}), Marangoni (M{sub a}) and Rayleigh (R{sub a}) numbers of melt in HDS system have been discussed for our experimental system to understand the mechanism of melt flow patterns and concentration gradient of dopant. The concentration gradient of Nd{sup 3+} ions was explained with melt flow processes during crystal growth in different thermal zone, and results indicated that high growth temperature will be helpful for uniformity of dopant in HDS-grown single crystal. The main microscopic growth defects such as bubbles and irregular inclusions in HDS-grown Nd:YAG crystals were observed, and the causes were discussed as well. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Origin of green luminescence in hydrothermally grown ZnO single crystals

    International Nuclear Information System (INIS)

    Combining photoluminescence and positron annihilation studies of hydrothermally grown ZnO crystals with stoichiometry varied by controlled annealing enabled us to clarify the origin of green luminescence. It was found that green luminescence in ZnO has multiple origins and consists of a band at 2.3(1) eV due to recombination of electrons of the conduction band by zinc vacancy acceptors coupled with hydrogen and a band at 2.47(2) eV related to oxygen vacancies. The as-grown ZnO crystals contain zinc vacancies associated with hydrogen and exhibit a green luminescence at 2.3(1) eV. Annealing in Zn vapor removed zinc vacancies and introduced oxygen vacancies. This led to disappearance of the green luminescence band at 2.3(1) eV and appearance of a green emission at higher energy of 2.47(2) eV. Moreover, the color of the crystal was changed from colorless to dark red. In contrast, annealing of the as-grown crystal in Cd vapor did not remove zinc vacancies and did not cause any significant change of green luminescence nor change in coloration

  17. 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

  18. 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}.

  19. 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.

  20. Defect Density Comparison of Detached versus Attached Bridgman Grown Germanium Crystals

    Science.gov (United States)

    Schweizer, M.; Cobb, S. D.; Volz, M. P.; Szofran, F. R.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Semiconductor Bridgman growth without contact between the growing crystal and the growth ampoule has been observed on Earth in the last few years during several experiments. Previously, this so-called detached or dewetted growth phenomenon occurred preferentially under microgravity conditions due to the absence of the hydrostatic pressure. Many theoretical as well as experimental investigations helped to provide a better understanding of the mechanism and to identify the parameters leading to the detachment. Thus, recent attempts to get stable detached growth under terrestrial conditions by Duffar et al. growing III-V compounds and our own group with germanium and germanium-silicon alloys were frequently successful. At this conference we present the results of several germanium growth experiments performed in pyrolytic boron nitride containers. To exert an influence on the pressure ratio above and below the melt we used closed-bottom and open-bottom containers. This resulted in mainly detached-grown single crystals with the closed-bottom crucibles and attached single crystals with the open-bottom tubes. Evidence of detached growth is obtained from the crystal surface with a combination of axial profilometer scans and optical and electron microscopy. Detailed investigations of the defect structure, which is the main focus of this presentation, have shown an improvement of the crystal quality in the detached-grown samples, with a strong reduction of the etch pit density by about two orders of magnitude.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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...

  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. 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.

  8. 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.

  9. 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.

  10. 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.)

  11. 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.)

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Characterization of Cadmium-Zinc Telluride Crystals Grown by 'Contactless' PVT Using Synchrotron White Beam Topography

    Science.gov (United States)

    Palosz, W.; Gillies, D.; Grasza, K.; Chung, H.; Raghothamachar, B.; Dudley, M.

    1997-01-01

    Crystals of Cd(1-x)Zn(x)Te grown by Physical Vapor Transport (PVT) using self-seeding 'contactless' techniques were characterized using synchrotron radiation (reflection, transmission, and Laue back-reflection X-ray topography). Crystals of low (x = 0.04) and high (up to x approx. = 0.4) ZnTe content were investigated. Twins and defects such as dislocations, precipitates, and slip bands were identified. Extensive inhomogeneous strains present in some samples were found to be generated by interaction (sticking) with the pedestal and by composition gradients in the crystals. Large (up to about 5 mm) oval strain fields were observed around some Te precipitates. Low angle grain boundaries were found only in higher ZnTe content (x greater than or equal to 0.2) samples.

  17. Dramatic Improvement of Crystal Quality for Low-temperature-grown Rabbit Muscle Aldolase

    Energy Technology Data Exchange (ETDEWEB)

    Park, H.; Rangarajan, E; Sygusch, J; Izard, T

    2010-01-01

    Rabbit muscle aldolase (RMA) was crystallized in complex with the low-complexity domain (LC4) of sorting nexin 9. Monoclinic crystals were obtained at room temperature that displayed large mosaicity and poor X-ray diffraction. However, orthorhombic RMA-LC4 crystals grown at 277 K under similar conditions exhibited low mosaicity, allowing data collection to 2.2 {angstrom} Bragg spacing and structure determination. It was concluded that the improvement of crystal quality as indicated by the higher resolution of the new RMA-LC4 complex crystals was a consequence of the introduction of new lattice contacts at lower temperature. The lattice contacts corresponded to an increased number of interactions between high-entropy side chains that mitigate the lattice strain incurred upon cryocooling and accompanying mosaic spread increases. The thermodynamically unfavorable immobilization of high-entropy side chains used in lattice formation was compensated by an entropic increase in the bulk-solvent content owing to the greater solvent content of the crystal lattice.

  18. 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)

  19. 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)

  20. Development of CdTe radiation detectors and their applications

    International Nuclear Information System (INIS)

    We have been developing radiation detectors using cadmium telluride (CdTe), which has the high radiation absorption characteristic. The image pickup tube using polycrystalline CdTe thin film has been developed at the first stage. Furthermore, the X-ray imaging line sensor with high scanning speed and the radiation spectrometer with thermo-electric Peltier cooler were developed by using CdTe single crystal, which has high electric charge collection characteristics. At present, the energy discriminating photon counting radiation line sensors are developing. In this presentation, the feature of the detector using CdTe and their applications are described examples of development until now. (author)

  1. 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)

  2. 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....../precipitates of these crystals indicate that the THM is suitable for the mass production of CZT radiation detectors that can be used in a variety of applications. Our result also proves that with careful material selection using IR and high-quality fabrication processes, the theoretical energy resolution limit can be achieved....

  3. 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.

  4. Color centers in Yb:YAG crystals grown by temperature-gradient techniques

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Yongjun [Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Qinghe Road, 390, P.O. Box 800-211, Shanghai 201800 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China); Xu, Jun; Zhou, Guoqing; Zhao, Guangjun; Su, Liangbi; Xu, Xiaodong; Li, Hongjun; Si, JiLiang; Qian, Xiaobo; Li, Xiaoqing; Shen, Jun [Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Qinghe Road, 390, P.O. Box 800-211, Shanghai 201800 (China)

    2006-08-15

    Yb:YAG (Yb:Y{sub 3}Al{sub 5}O{sub 12}) crystals have been grown by temperature-gradient techniques (TGT) and their color centers and impurity defects were investigated by means of gamma irradiations and thermal treatment. Two color centers located at 255 and 290 nm were observed in the as-grown TGT-Yb:YAG. Analysis shows that the 255 nm band may be associated with Fe{sup 3+} ions. Absorption intensity changes of the 290 nm band after gamma irradiation and thermal treatment indicate that this band may be associated with oxygen-vacancy defects. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Color centers in Yb:YAG crystals grown by temperature-gradient techniques

    International Nuclear Information System (INIS)

    Yb:YAG (Yb:Y3Al5O12) crystals have been grown by temperature-gradient techniques (TGT) and their color centers and impurity defects were investigated by means of gamma irradiations and thermal treatment. Two color centers located at 255 and 290 nm were observed in the as-grown TGT-Yb:YAG. Analysis shows that the 255 nm band may be associated with Fe3+ ions. Absorption intensity changes of the 290 nm band after gamma irradiation and thermal treatment indicate that this band may be associated with oxygen-vacancy defects. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. 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%.

  7. 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

  8. 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)

  9. 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.

  10. 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...

  11. Studies on multiphased mixed crystals grown from NaBr and KCl

    Energy Technology Data Exchange (ETDEWEB)

    Padma, C.M. [Physics Research Centre, S.T. Hindu College, Nagercoil 629 002, Tamilnadu (India); Mahadevan, C.K. [Physics Research Centre, S.T. Hindu College, Nagercoil 629 002, Tamilnadu (India)], E-mail: mahadevan58@yahoo.co.in

    2008-05-01

    We have grown multiphased binary and ternary mixed crystals by the melt method using the miscible alkali halides, viz. NaBr and KCl and physically characterized. Thermal parameters like Debye-Waller factor, Debye temperature, Debye frequency and mean square amplitude of vibration were determined using the X-ray powder diffraction intensity data. DC and AC electrical measurements were carried out by using the parallel plate capacitor method at various temperatures. Activation energies (DC and AC), mean jump frequency, compressibility and mean sound velocity were also determined. The results obtained are reported here.

  12. 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.

  13. 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.

  14. Superstructure studies in hydrothermal-grown RbBe2BO3F2 crystals

    International Nuclear Information System (INIS)

    Highlights: • Three extra peaks were found in PXRD patterns of hydrothermal RBBF crystals. • A centrosymmetric structure of R3¯c was obtained in hydrothermal RBBF crystals. • A stacking fault model of hydrothermal RBBF crystals was proposed. • R32 and R3¯c structures co-exist with different weight fractions. - Abstract: Deep-UV nonlinear optical crystal RbBe2BO3F2 (RBBF) grown by the hydrothermal method was found to have a centrosymmetric structure of R3¯c by powder X-ray diffraction. The structure of R3¯c has cell parameters of a = 4.44223(11) Å and c = 39.6696(12) Å in the lattice where the (BO3)3− groups turn 60° along each (Be2BO3F2)∞ 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¯c structures using the DIFFaX program

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

    Science.gov (United States)

    Taboada, A. G.; MeduÅa, M.; Salvalaglio, M.; Isa, F.; Kreiliger, T.; Falub, C. V.; Barthazy Meier, E.; Müller, E.; Miglio, L.; Isella, G.; von Känel, H.

    2016-02-01

    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.

  16. 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.

  17. 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

  18. 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.

  19. 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

  20. 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 %.

  1. 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.

  2. Optical properties of Ni-doped MgGa2O4 single crystals grown by floating zone method

    International Nuclear Information System (INIS)

    The single crystal growth conditions and spectroscopic characterization of Ni-doped MgGa2O4 with inverse-spinel structure crystal family are described. Single crystals of this material have been grown by floating zone method. Ni-doped MgGa2O4 single crystals have broadband fluorescence in the 1100-1600 nm wavelength range, 1.6 ms room temperature lifetime, 56% quantum efficiency and 1.05x10-21cm2 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.

  3. Crystal Quality and Light Output Power of GaN-Based LEDs Grown on Concave Patterned Sapphire Substrate

    OpenAIRE

    YewChung Sermon Wu; A. Panimaya Selvi Isabel; Jian-Hsuan Zheng; Bo-Wen Lin; Jhen-Hong Li; Chia-Chen Lin

    2015-01-01

    The crystal quality and light output power of GaN-based light-emitting diodes (LEDs) grown on concave patterned sapphire substrate (CPSS) were investigated. It was found that the crystal quality of GaN-based LEDs grown on CPSS improved with the decrease of the pattern space (percentage of c-plane). However, when the pattern space decreased to 0.41 μm (S0.41-GaN), the GaN crystallinity dropped. On the other hand, the light output power of GaN-based LEDs was increased with the decrease of the p...

  4. 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.

  5. 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

  6. 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)

  7. 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)

  8. Excitonic photoluminescence spectra of C{sub 60} single crystals grown by different techniques

    Energy Technology Data Exchange (ETDEWEB)

    Capozzi, V.; Santoro, M.; Perna, G.; Celentano, G.; Minafra, A.; Casamassima, G. [Bari Univ. (Italy). Dipt. di Fisica; Ist. Nazionale di Fisica della Materia, Bari (Italy)

    2001-04-01

    We report photoluminescence spectra of C{sub 60} single crystals grown by vapor phase transport method using either the sealed ampoule technique or the open tube technique. The spectra for both types of samples show similar features, but different line resolution related to the two different growth techniques. An analysis of temperature and excitation intensity dependencies of the luminescence spectra is reported. The main structures of the spectra have been interpreted according to a model involving intramolecular polaron-exciton recombinations. In particular, emissions due to purely electronic transitions of singlet and triplet or the exciton and related vibronic recombinations have been resolved. At low temperature, emission bands due to X-traps have been observed on the high-energy side of the excitonic singlet purely electronic transition. (orig.)

  9. X-ray topography study of LiB3O5 crystals grown from molybdate flux

    International Nuclear Information System (INIS)

    The real defect structure of LiB3O5 crystal grown by a top seeded solution growth method has been observed using x-ray projection and reflective topography. Space mapping of such defects as growth sector boundaries, striation and dislocations have been produced by the topography analysis. The density of the dislocations is -2. It has been shown that the dominant part of the dislocations detected is generated in the under-seed zone of the crystal

  10. 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

  11. High pressure studies of as grown WX2-x single crystals

    International Nuclear Information System (INIS)

    The structural optical and transport properties of tungsten metal dichalogenides having layered structure have been extensively studied in the last two decades. These materials shows highly anisotropic behaviour and have been receiving considerable interest for a variety of applications. Several of these layered semiconductors have attracted attention as a new class of solar cell material. We present here the results of simultaneous resistivity and thermoelectric power (TEP) measurements upto 7 GPa on single crystals of WS2, WS1.9, WSe2 and WSe1.9 grown using Direct Vapour Transport (DVT) technique. The observations clearly shows WS2 and WS1.9 are more resistive compared to other two crystals. In all samples an exponential fall of resistivity on increases in pressure upto 2.1 GPa but after 2.2 GPa the resistivity decreases substantially with increases pressure. The TEP of WSe2 increases steadily and reaches maximum at 0.65 GPa, while for WSe1.9 TEP increases upto pressure 0.5 GPa. In both the cases after attaining the maximum TEP, then decreases monotonically with increase in pressure. TEP of WS2 and WS1.9 increase upto pressure 1.1 GPa, beyond 1.1 GPa pressure in both the cases TEP decreases steadily with further increase in pressure. In all the samples, the sign of TEP is positive indicating that all of them are p-type and remain p-type with increase in pressure. The variation of thermoelectric power factor with pressure has been thoroughly studied. An analysis of the data point out that perfectly stoichiometric crystals of WSe2 work as superior thermoelectric materials. The results have been presented and implications have been discussed. (author)

  12. 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.

  13. Observation of nanometer-sized crystalline grooves in as-grown β-Ga2O3 single crystals

    Science.gov (United States)

    Hanada, Kenji; Moribayashi, Tomoya; Uematsu, Takumi; Masuya, Satoshi; Koshi, Kimiyoshi; Sasaki, Kohei; Kuramata, Akito; Ueda, Osamu; Kasu, Makoto

    2016-03-01

    On the surface of as-grown β-Ga2O3 single crystals that are cut and polished, we found nanometer-sized grooves elongated in the [001] direction. We confirmed that these grooves terminate within the crystals in the [010] direction. This proves that the grooves are different from micropipes penetrating crystals. Their typical length and width are 50-1200 nm in the [001] direction and ˜40 nm in the [100] direction, respectively. The grooves tend to form an array in the [001] direction. The type of nanometer-sized grooves should be essentially different from etch pits.

  14. 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

  15. Concentration and structure inhomogeneities in GaSb(Si) single crystals grown at different heat and mass transfer conditions

    Science.gov (United States)

    Serebryakov, Yu. A.; Prokhorov, I. A.; Vlasov, V. N.; Korobeynikova, E. N.; Zakharov, B. G.; Shul'pina, I. L.; Marchenko, M. P.; Fryazinov, I. V.

    2007-06-01

    Results of ground-based experiments on crystallization of gallium antimonide on the POLIZON facility carried out within the framework of space experiment preparation aboard FOTON satellite are submitted. Technical and technological opportunities of suppression of disturbing factors for improvement of quality of grown crystals in space are substantiated. Features of formation of concentration and structure inhomogeneities in GaSb:Si crystals grown under non-stationary and stationary convection conditions are investigated. Experimental data about structure and dopant distribution inhomogeneities are discussed taking into account results of numerical researches of GaSb:Si crystallization. Also earlier received results of modeling of GaSb:Te crystallization under close temperature conditions are used. Correlation between computational and experimental data is shown. The data on intensity of flows close to crystallization front are received at which non-stationary or stationary conditions of crystallization are realized. The forecast for space conditions is made. The influence of a rotating magnetic field on convection in melt for application in space experiment projected is investigated.

  16. Study on Methods to Strenthen and Toughen Sapphire Crystal by Carbon Doped Grown by Temperature Gradient Technique (TGT

    Directory of Open Access Journals (Sweden)

    HU Ke-Yan, XU Jun, TANG Hui-Li, LI Hong-Jun, ZOU Yu-Qi, YANG Qiu-Hong

    2013-03-01

    Full Text Available Mechanical properties of carbon-doped sapphire crystals with different carbon concentrations were studied at room temperature. The present work showed that the fracture strength and fracture toughness of as grown crystals were significantly improved by carbon doping and the visible-infrared optical property did not adversely affect. When the concentration of doped carbon was 5×10-3, the fracture strength and fracture toughness were increased to 752 MPa and 2.81 MPa·m1/2 in average, respectively, and the transmition of visible-infrared was about 80%. Appropriate carbon dopant in the crystals played the roles of clearance ions and created blocking effect to the sapphires cracking, which improved fracture strength and fracture toughness of sapphires at room temperature. However the mechanical properties and optical properties declined when carbon dopant was excessive, due to carbon inclusions grown from composition segregation.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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

  2. Magnetic properties of Cu-flux-grown UCu2Si2 single crystals

    International Nuclear Information System (INIS)

    In order to solve a serious problem of understanding the magnetic properties of UCu2Si2, 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 UCu2Si2 no signs of the transition into antiferromagnetic behavior have been observed below T 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 μB. In the paramagnetic region the effective moments for the easy and hard directions are both about 3.0 μB. 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 TC has been detected. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. 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...

  4. 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.

  5. X-Ray Characterization of Structural Defects in Seeded and Self-Seeded ZnSe Crystal Grown by PVT in Horizontal and Vertical Configurations

    Science.gov (United States)

    Raghothamachar, B.; Dudley, M.; Su, C.-H.; Volz, H. M.; Matyi, R.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    As part of a pre-flight ground based investigation of crystal growth of II-VI compound semiconductors, a number of ZnSe boules have been grown by physical vapor transport (PVT) at Marshall Space Flight Center. Boules were grown in both horizontal and vertical configurations and seeded and self-seeded growth techniques were employed. As-grown and/or cleaved boules were examined by a combination of synchrotron white beam x-ray topography (SWBXT) and high resolution triple axis diffraction (HRTXD) to characterized the structural defects and correlate them with the growth conditions. Horizontal grown boules tend to grow away from the ampoule wall (contactless growth) and generally exhibit large (110) facets parallel to the gravity vector. Vertical grown boules grew to the full diameter of the ampoule and exhibited no faceting. X-ray topography combined with back reflection x-ray diffraction revealed the presence of lamellar twins (180 deg type about the [111] axis) in horizontal grown boules while vertically grown boules contain a few large grains, some of which are twinned. X-ray topographs and reciprocal space maps recorded from the boules show the better crystal quality of horizontal grown boules. The relationship between crystal quality and gravity vector is investigated. Further, an attempt is made to extend the Hurle theory of twin nucleation in Czochralski grown crystals to explain the twinning mechanisms in horizontal grown boules.

  6. The effect of radiation damage on optical and scintillation properties of BGO crystals grown by the LTG Cz technique

    CERN Document Server

    Gusev, V A; Kupriyanov, I N; Kuznecov, G N; Shlegel, V N; Antsygin, V D; Vasiliev, Y V

    2002-01-01

    BGO crystals grown by the low-thermal-gradient Czochralski technique (LTG Cz) exhibit two distinct types of behavior upon radiation damage and recovery. The crystals termed as of L-type remain colorless after gamma-radiation doses as high as 10 Mrad. As the irradiation dose increases the scintillation light output shows a weak monotonous degradation to 15-25%, saturating at around several hundreds krad doses. The crystals termed as of N-type attain yellow coloration after irradiation. The light output drops abruptly for 35-50% as early as after 1 krad and does not change further on. The present work is devoted to the study of radiation damage effects, self-recovery, optically stimulated recovery and thermo-stimulated current in the L- and N-type BGO crystals produced by LTG Cz.

  7. 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.

  8. 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

  9. 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)

  10. 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)

  11. 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.

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

    International Nuclear Information System (INIS)

    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

  13. Crystal Quality and Light Output Power of GaN-Based LEDs Grown on Concave Patterned Sapphire Substrate

    Directory of Open Access Journals (Sweden)

    YewChung Sermon Wu

    2015-04-01

    Full Text Available The crystal quality and light output power of GaN-based light-emitting diodes (LEDs grown on concave patterned sapphire substrate (CPSS were investigated. It was found that the crystal quality of GaN-based LEDs grown on CPSS improved with the decrease of the pattern space (percentage of c-plane. However, when the pattern space decreased to 0.41 μm (S0.41-GaN, the GaN crystallinity dropped. On the other hand, the light output power of GaN-based LEDs was increased with the decrease of the pattern space due to the change of the light extraction efficiency.

  14. 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.

  15. Irradiation effects on carrier transport and the trapping process in high-resistivity CdTe

    International Nuclear Information System (INIS)

    Radiation-induced defects and their annealing behaviour in solution-grown p- and n-type CdTe single crystals irradiated with 60Co gamma rays or 1.5 MeV electrons have been investigated by means of Hall-effect, photoluminescence spectrum and time-of-flight measurements. An electron-trap level lying at 0.058 eV below the conduction band is observed in n-type crystals irradiated with gamma rays. This electron trap anneals at about 600 K and is tentatively attributed to a complex involving Te vacancies. After gamma-ray irradiation, electron-drift mobility at room temperature is remarkably reduced, possibly due to the introduction of an electron-trap level at 0.54 eV below the conduction band. (author)

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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...

  1. 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.

  2. 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.

  3. 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.

  4. 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.

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

    International Nuclear Information System (INIS)

    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

  6. 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.

  7. 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.

  8. 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.

    2016-06-01

    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.

  9. 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

  10. 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.

  11. 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.

  12. 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

  13. Optical and scintillation properties of Dy3+:Y3Al5O12 and undoped Y3Al5O12 crystals grown in reduction atmosphere

    International Nuclear Information System (INIS)

    Optical and scintillation properties of a 1.0-mol% Dy-doped yttrium aluminium garnet (YAG) grown under N2 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 + H2 (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 Dy3+. 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, 241Am). The scintillation decay time constants for Dy-doped YAG crystal was around 400 ns and 40 ns. Undoped YAG crystals grown under Ar + H2(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.)

  14. Electrical and infrared optical properties of CdIn2S4 single crystals grown by chemical transport

    International Nuclear Information System (INIS)

    Single crystals of CdIn2S4 were grown by chemical transport with iodine as transporting agent using different transporter concentrations and temperature gradients. It is found that the electron concentration increases with increasing transporter concentration and decreases after annealing in a sulphur atmosphere. Infrared reflectivity and absorption spectra are measured at room temperature in the wavenumber range from 180 to 4000 cm-1 in order to determine to optical mode parameters of the compound and to evaluate the scattering mechanism of the electrons from the free carrier absorption. Lattice scattering is found to be prodominant at room temperature for electron concentrations below about 4 · 1017 cm-3. (author)

  15. 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.

  16. 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.

  17. Power scaling of directly dual-end-pumped Nd:GdVO4 laser using grown-together composite crystal.

    Science.gov (United States)

    Li, XuDong; Yu, Xin; Chen, Fei; Yan, RenPeng; Luo, Ming; Yu, JunHua; Chen, DeYing

    2010-03-29

    Power scaling of end-pumped Nd:GdVO(4) laser was realized by direct pumping, grown-together composite crystal and dual-end-pumping. A maximum CW output power of 46.0W with M(2)switch operation, peak power of 304.1kW, 58.6kW and 23.8kW, pulse width of 7.2ns, 11.3ns and 16.2ns were obtained at the repetition rates of 10kHz, 50kHz and 100kHz, respectively. PMID:20389763

  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. A crystal of a typical EF-hand protein grown under microgravity diffracts X-rays beyond 0.9 Å resolution

    OpenAIRE

    Declercq, Jean-Paul; Evrard, Christine; Carter, Daniel; Wright, Brenda; Etienne, Gérard; Parello, Joseph

    1999-01-01

    We report on our recent observation that crystals of a typical EF-hand protein (parvalbumin or Pa; Ca-loaded component from pike muscle with isoelectric point 4.10) grown under microgravity conditions diffract X-rays to a resolution better than 0.9 Å. The crystals were grown in the US space shuttle and characterized at 100 K, using an X-ray synchrotron beam. An effective atomic resolution has been achieved and substates in the conformation of the protein are observed. Large crystals up to 3 m...

  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. Flux-enhanced monochromator by ultrasound excitation of annealed Czochralski-grown silicon crystals

    CERN Document Server

    Koehler, S; Seitz, C; Magerl, A; Mashkina, E; Demin, A

    2003-01-01

    The neutron flux from monochromator crystals can be increased by ultrasound excitation or by strain fields. Rocking curves of both a perfect float-zone silicon crystal and an annealed Czochralski silicon crystal with oxygen precipitates were measured at various levels of ultrasound excitation on a cold-neutron backscattering spectrometer. We find that the effects of the dynamic strain field from the ultrasound and the static strain field from the defects are not additive. Rocking curves were also taken at different ultrasound frequencies near resonance of the crystal/ultrasound-transducer system with a time resolution of 1 min. Pronounced effects of crystal heating are observed, which render the conditions for maximum neutron reflectivity delicate. (orig.)

  2. Flux-enhanced monochromator by ultrasound excitation of annealed Czochralski-grown silicon crystals

    International Nuclear Information System (INIS)

    The neutron flux from monochromator crystals can be increased by ultrasound excitation or by strain fields. Rocking curves of both a perfect float-zone silicon crystal and an annealed Czochralski silicon crystal with oxygen precipitates were measured at various levels of ultrasound excitation on a cold-neutron backscattering spectrometer. We find that the effects of the dynamic strain field from the ultrasound and the static strain field from the defects are not additive. Rocking curves were also taken at different ultrasound frequencies near resonance of the crystal/ultrasound-transducer system with a time resolution of 1 min. Pronounced effects of crystal heating are observed, which render the conditions for maximum neutron reflectivity delicate. (orig.)

  3. Single crystals of DPPH grown from diethyl ether and carbon disulfide solutions - Crystal structures, IR, EPR and magnetization studies

    OpenAIRE

    Zilic, Dijana; Pajic, Damir; Juric, Marijana; Molcanov, Kresimir; Rakvin, Boris; Planinic, Pavica; Zadro, Kreso

    2012-01-01

    Single crystals of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) obtained from diethyl ether (ether) and carbon disulfide (CS2) were characterized by the X-ray diffraction, IR, EPR and SQUID magnetization techniques. The X-ray structural analysis and IR spectra showed that the DPPH form crystallized from ether (DPPH1) is solvent free, whereas that one obtained from CS2 (DPPH2) is a solvate of the composition 4DPPH.CS2. Principal values of the g-tensor were estimated by the X-band EPR ...

  4. 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.

  5. Single-Crystal like MgB2 thin films grown on c-cut sapphire substrates

    International Nuclear Information System (INIS)

    Single-crystal like MgB2 thin film was grown on (000l) Al2O3 substrate by using hybrid physical-chemical vapor deposition (HPCVD) system. Single crystal properties were studied by X-ray diffraction (XRD) and the full width at half maximum (FWHM) of the (0001) MgB2 peak is 0.15 degrees, which is very close to that has been reported for MgB2 single-crystal. It indicates that the crystalline quality of thin film is good. Temperature dependence on resistivity was investigated by physical property measurement system (PPMS) in various applied fields from 0 to 9 T. The upper critical field (Hc2) and irreversibility field (Hirr) were determined from PPMS data, and the estimated values are comparable with that of MgB2 single-crystals. The thin film shows a high critical temperature (Tc) of 40.4 K with a sharp superconducting transition width of 0.2 K, and a high residual resistivity ratio (RRR=21), it reflects that MgB2 thin film has a pure phase structure.

  6. 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.

  7. 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

  8. Single crystals of DPPH grown from diethyl ether and carbon disulfide solutions - Crystal structures, IR, EPR and magnetization studies

    Science.gov (United States)

    Žilić, Dijana; Pajić, Damir; Jurić, Marijana; Molčanov, Krešimir; Rakvin, Boris; Planinić, Pavica; Zadro, Krešo

    2010-11-01

    Single crystals of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) obtained from diethyl ether (ether) and carbon disulfide (CS2) were characterized by the X-ray diffraction, IR, EPR and SQUID magnetization techniques. The X-ray structural analysis and IR spectra showed that the DPPH form crystallized from ether (DPPH1) is solvent free, whereas that one obtained from CS2 (DPPH2) is a solvate of the composition 4DPPH·CS2. Principal values of the g-tensor were estimated by the X-band EPR spectroscopy at room and low (10 K) temperatures. Magnetization studies revealed the presence of antiferromagnetically coupled dimers in both types of crystals. However, the way of dimerization as well as the strength of exchange couplings are different in the two DPPH samples, which is in accord with their crystal structures. The obtained results improved parameters accuracy and enabled better understanding of properties of DPPH as a standard sample in the EPR spectrometry.

  9. 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

  10. Observation of edge-facets in InP crystals grown by LEC method

    Science.gov (United States)

    Shibata, Masatomo; Sasaki, Yukio; Inada, Tomoki; Kuma, Shoji

    1990-05-01

    The growth of edge-facets on InP crystals has been investigated using microscopy. The solid/liquid interface in the region of edge-facets was found to have a knife-edged shape, while that of a region without facets had a smooth shape. The irregular patterns of edge-facets point to instability in the growth at the periphery of a crystal, and this instability is found to be related to the generation of twins.

  11. High-quality LaCoO{sub 3} single crystal grown by optical floating zone method and its electromagnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Song, Gengxin [National Laboratory of Superhard Materials, Jilin University, Changchun (China); Northeast Dianli University, Jilin (China); Li, Liang; Xu, Dapeng [College of Physics, Jilin University, Changchun (China)

    2010-05-15

    A LaCoO{sub 3} single crystal with 4 mm in diameter and 30 mm in length has been grown by optical floating zone method. The as-grown crystal is highly crystalline with the rhombohedral perovskite structure (R3c) and grows parallel to the (121) direction. The room temperature resistivity of the as-grown crystal is 0.12 {omega}.cm and the insulator-metal transition occurs around 500 K. The coercivity and the remanence of the as-grown crystal are 5 Oe and 6.61 x 10{sup -5}{mu}{sub B}/f.u. at 5 K, respectively. In 1000 Oe under zero-field cooling, the magnetic susceptibility of the as-grown crystal shows an upturn in a Curie tail fashion below 35 K, and appears a wave crest over the interval 55 K{<=}T{<=}90 K. In addition, a slope change of 1/{chi}(T) at about 12 K is observed in 50000 Oe under zero-field cooling. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. 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.

  13. 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.

  14. 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...

  15. FT-IR, Thermal and Optical Studies of Gel Grown Cobalt Tartrate Crystals

    Directory of Open Access Journals (Sweden)

    S.J. Nandre

    2014-01-01

    Full Text Available The growth of cobalt tartrate crystals was achieved in silica gel by single diffusion method. Optimum conditions were established for the growth of good quality crystals. Fourier transform infrared (FT-IR spectroscopic study indicates the presence of water molecules and suggests that tartrate ions are doubly ionized. The thermal behavior of the material was studied using thermogravimetry (TG and differential thermal analysis (DTA. The results show that the material is thermally stable up to30 C, beyond which it decomposes through many stages till the formation of cobalt oxide at 995 C. The non linear optical behavior of these crystals is reported and explained.

  16. Anisotropy in Ba2Cu3O4Cl2 single crystals grown by the traveling solvent floating zone method

    International Nuclear Information System (INIS)

    Magnetic and electrical properties of layered copper oxychloride Ba2Cu3O4Cl2 single crystals are measured. Single crystal growth of Ba2Cu3O4Cl2 by the traveling solvent floating zone method is attempted using Ba3Cu2O4Cl2 as solvent. By optimization of the growth conditions, large single crystals of (φ5mmx30mm) of Ba2Cu3O4Cl2 are grown. The resistivity with the current parallel to the c-axis is 102-103 times larger than that with the current perpendicular to the a-axis. The temperature dependence of the dielectric spectrum for each direction is measured and analyzed by using the Debye model. The spectrum width, which is related to the effective number of electrons (n/m), does not show an appreciable dependence on temperature. The characteristic frequencies at which the dielectric constant changes, which are related to the dissipation (γ), increase with warming. The temperature dependence is almost the same as the resistivity curve. This indicates that the hopping process dominates both DC- and AC-type electrical transport. The spectrum width with the electric field parallel to the a-axis is 30 times larger than that with the electric field parallel to the c-axis. On the other hand, the characteristic frequencies do not show an appreciable dependence on electric field direction

  17. Opto-structural studies of well-dispersed silicon nano-crystals grown by atom beam sputtering.

    Science.gov (United States)

    Saxena, Nupur; Kumar, Pragati; Kabiraj, Debulal; Kanjilal, Dinakar

    2012-01-01

    Synthesis and characterization of nano-crystalline silicon grown by atom beam sputtering technique are reported. Rapid thermal annealing of the deposited films is carried out in Ar + 5% H2 atmosphere for 5 min at different temperatures for precipitation of silicon nano-crystals. The samples are characterized for their optical and structural properties using various techniques. Structural studies are carried out by micro-Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), high resolution transmission electron microscopy, and selected area electron diffraction. The optical properties are studied by photoluminescence and UV-vis absorption spectroscopy, and bandgaps are evaluated. The bandgaps are found to decrease after rapid thermal treatment. The micro-Raman studies show the formation of nano-crystalline silicon in as-deposited as well as annealed films. The shifting and broadening in Raman peak suggest formation of nano-phase in the samples. Results of micro-Raman, photoluminescence, and TEM studies suggest the presence of a bimodal crystallite size distribution for the films annealed at higher temperatures. The results show that atom beam sputtering is a suitable technique to synthesize nearly mono-dispersed silicon nano-crystals. The size of the nano-crystals may be controlled by varying annealing parameters. PMID:23031449

  18. Analysis of polytype stability in PVT grown silicon carbide single crystal using competitive lattice model Monte Carlo simulations

    Science.gov (United States)

    Guo, Hui-Jun; Huang, Wei; Liu, Xi; Gao, Pan; Zhuo, Shi-Yi; Xin, Jun; Yan, Cheng-Feng; Zheng, Yan-Qing; Yang, Jian-Hua; Shi, Er-Wei

    2014-09-01

    Polytype stability is very important for high quality SiC single crystal growth. However, the growth conditions for the 4H, 6H and 15R polytypes are similar, and the mechanism of polytype stability is not clear. The kinetics aspects, such as surface-step nucleation, are important. The kinetic Monte Carlo method is a common tool to study surface kinetics in crystal growth. However, the present lattice models for kinetic Monte Carlo simulations cannot solve the problem of the competitive growth of two or more lattice structures. In this study, a competitive lattice model was developed for kinetic Monte Carlo simulation of the competition growth of the 4H and 6H polytypes of SiC. The site positions are fixed at the perfect crystal lattice positions without any adjustment of the site positions. Surface steps on seeds and large ratios of diffusion/deposition have positive effects on the 4H polytype stability. The 3D polytype distribution in a physical vapor transport method grown SiC ingot showed that the facet preserved the 4H polytype even if the 6H polytype dominated the growth surface. The theoretical and experimental results of polytype growth in SiC suggest that retaining the step growth mode is an important factor to maintain a stable single 4H polytype during SiC growth.

  19. Analysis of polytype stability in PVT grown silicon carbide single crystal using competitive lattice model Monte Carlo simulations

    Directory of Open Access Journals (Sweden)

    Hui-Jun Guo

    2014-09-01

    Full Text Available Polytype stability is very important for high quality SiC single crystal growth. However, the growth conditions for the 4H, 6H and 15R polytypes are similar, and the mechanism of polytype stability is not clear. The kinetics aspects, such as surface-step nucleation, are important. The kinetic Monte Carlo method is a common tool to study surface kinetics in crystal growth. However, the present lattice models for kinetic Monte Carlo simulations cannot solve the problem of the competitive growth of two or more lattice structures. In this study, a competitive lattice model was developed for kinetic Monte Carlo simulation of the competition growth of the 4H and 6H polytypes of SiC. The site positions are fixed at the perfect crystal lattice positions without any adjustment of the site positions. Surface steps on seeds and large ratios of diffusion/deposition have positive effects on the 4H polytype stability. The 3D polytype distribution in a physical vapor transport method grown SiC ingot showed that the facet preserved the 4H polytype even if the 6H polytype dominated the growth surface. The theoretical and experimental results of polytype growth in SiC suggest that retaining the step growth mode is an important factor to maintain a stable single 4H polytype during SiC growth.

  20. 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.

  1. Structural, thermal and dielectric studies on the novel solution grown (4-dimethylaminopyridinium) chloroantimonate(III) and chlorobismuthate(III) crystals

    Energy Technology Data Exchange (ETDEWEB)

    Plowas, I.; Szklarz, P.; Jakubas, R.; Bator, G., E-mail: gb@wchuwr.pl

    2011-08-15

    Research Highlights: {yields} The one-dimensional (1D) and the zero-dimensional (0D) anionic structure. {yields} The 'crystal bending' discovered in RMX{sub 4}-type analogue. {yields} The low frequency relaxation processes attributed to the dynamics of the organic cations. -- Abstract: The single crystals of the following 4-dimethylaminopyridinium chloroantimonates(III) and chlorobismuthates(III) have been grown by the solvent evaporation method: (C{sub 7}H{sub 11}N{sub 2})SbCl{sub 4}, (C{sub 7}H{sub 11}N{sub 2})BiCl{sub 4} and (C{sub 7}H{sub 11}N{sub 2}){sub 4}Bi{sub 2}Cl{sub 10}. The one-dimensional (1D) structures for (C{sub 7}H{sub 11}N{sub 2})SbCl{sub 4} or (C{sub 7}H{sub 11}N{sub 2})BiCl{sub 4} and the zero-dimensional (0D) one for (C{sub 7}H{sub 11}N{sub 2}){sub 4}Bi{sub 2}Cl{sub 10} have been solved by the single-crystal X-ray diffraction method. (C{sub 7}H{sub 11}N{sub 2})SbCl{sub 4} and (C{sub 7}H{sub 11}N{sub 2})BiCl{sub 4} appeared to be isomorphous and crystallize in the monoclinic space group, C2/c, whereas (C{sub 7}H{sub 11}N{sub 2}){sub 4}Bi{sub 2}Cl{sub 10} in the orthorhombic one, Imma. The molecular arrangements in the subsequent crystal lattices have been studied. For all three compounds by using the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) no structural phase transition has been detected in temperature region between 100 and 400 K. Nevertheless, the dielectric relaxation processes in temperature region 100-450 K and frequency range between 100 Hz and 2 MHz have been found in all crystals studied. The experimental results of the real and imaginary parts of the dielectric permittivity allow us to estimate the parameters of the relaxation processes, i.e. macroscopic relaxation times, {tau}, and activation energies, E{sub A}. The dynamics of the dipolar organic cations is expected to contribute to the relaxations process in the crystals under investigation.

  2. Structural, thermal and dielectric studies on the novel solution grown (4-dimethylaminopyridinium) chloroantimonate(III) and chlorobismuthate(III) crystals

    International Nuclear Information System (INIS)

    Research Highlights: → The one-dimensional (1D) and the zero-dimensional (0D) anionic structure. → The 'crystal bending' discovered in RMX4-type analogue. → The low frequency relaxation processes attributed to the dynamics of the organic cations. -- Abstract: The single crystals of the following 4-dimethylaminopyridinium chloroantimonates(III) and chlorobismuthates(III) have been grown by the solvent evaporation method: (C7H11N2)SbCl4, (C7H11N2)BiCl4 and (C7H11N2)4Bi2Cl10. The one-dimensional (1D) structures for (C7H11N2)SbCl4 or (C7H11N2)BiCl4 and the zero-dimensional (0D) one for (C7H11N2)4Bi2Cl10 have been solved by the single-crystal X-ray diffraction method. (C7H11N2)SbCl4 and (C7H11N2)BiCl4 appeared to be isomorphous and crystallize in the monoclinic space group, C2/c, whereas (C7H11N2)4Bi2Cl10 in the orthorhombic one, Imma. The molecular arrangements in the subsequent crystal lattices have been studied. For all three compounds by using the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) no structural phase transition has been detected in temperature region between 100 and 400 K. Nevertheless, the dielectric relaxation processes in temperature region 100-450 K and frequency range between 100 Hz and 2 MHz have been found in all crystals studied. The experimental results of the real and imaginary parts of the dielectric permittivity allow us to estimate the parameters of the relaxation processes, i.e. macroscopic relaxation times, τ, and activation energies, EA. The dynamics of the dipolar organic cations is expected to contribute to the relaxations process in the crystals under investigation.

  3. CdTe nano-structures for photovoltaic devices

    Science.gov (United States)

    Corregidor, V.; Alves, L. C.; Franco, N.; Barreiros, M. A.; Sochinskii, N. V.; Alves, E.

    2013-07-01

    CdTe nano-structures with diameter of ∼100 nm and variable length (200-600 nm) were fabricated on glass substrates covered with conductive buffer layers such as NiCr, ZAO (ZnO:Al2O3 + Ta2O5) or TiPd alloys. The fabrication process consisted of the starting vapour deposition of metal catalyst dropped layer followed by the isothermal catalyst-prompted vapour growth of CdTe nano-structured layer of controllable shape and surface filling. The effect of buffer layers on the crystallographic orientation and thickness of CdTe nano-structured layers is investigated by means of IBA techniques, SEM and X-ray diffraction. It was shown that the formed CdTe nano-layers have a cubic structure, mainly oriented towards the [1 1 1] crystallographic direction, except for those grown on ZAO layer where the X-ray diffraction signal is very weak to be associated to any crystallographic form. The RBS spectra recorded on different areas of each sample type showed an almost constant thickness and SEM images revealed an homogeneous and dense distribution of the structures. It was also possible to study the first stage of the nano-structures grown on the Bi2Te3 seeds.

  4. CdTe nano-structures for photovoltaic devices

    International Nuclear Information System (INIS)

    CdTe nano-structures with diameter of ∼100 nm and variable length (200–600 nm) were fabricated on glass substrates covered with conductive buffer layers such as NiCr, ZAO (ZnO:Al2O3 + Ta2O5) or TiPd alloys. The fabrication process consisted of the starting vapour deposition of metal catalyst dropped layer followed by the isothermal catalyst-prompted vapour growth of CdTe nano-structured layer of controllable shape and surface filling. The effect of buffer layers on the crystallographic orientation and thickness of CdTe nano-structured layers is investigated by means of IBA techniques, SEM and X-ray diffraction. It was shown that the formed CdTe nano-layers have a cubic structure, mainly oriented towards the [1 1 1] crystallographic direction, except for those grown on ZAO layer where the X-ray diffraction signal is very weak to be associated to any crystallographic form. The RBS spectra recorded on different areas of each sample type showed an almost constant thickness and SEM images revealed an homogeneous and dense distribution of the structures. It was also possible to study the first stage of the nano-structures grown on the Bi2Te3 seeds

  5. CdTe nano-structures for photovoltaic devices

    Energy Technology Data Exchange (ETDEWEB)

    Corregidor, V., E-mail: vicky.corregidor@itn.pt [Instituto Tecnológico e Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, E.N. 10, 2686-953 Sacavém (Portugal); CFNUL, Av. Prof. Gama Pinto 2, 1649-003 Lisboa (Portugal); Alves, L.C. [Instituto Tecnológico e Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, E.N. 10, 2686-953 Sacavém (Portugal); CFNUL, Av. Prof. Gama Pinto 2, 1649-003 Lisboa (Portugal); Franco, N. [Instituto Tecnológico e Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, E.N. 10, 2686-953 Sacavém (Portugal); Barreiros, M.A. [LNEG, Estrada Estrada do Paço do Lumiar 22, 1649-038 Lisboa (Portugal); Sochinskii, N.V. [Consorzio CREO, SS 17 Località Boschetto, 67100 L’Aquila (Italy); Alves, E. [Instituto Tecnológico e Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, E.N. 10, 2686-953 Sacavém (Portugal); CFNUL, Av. Prof. Gama Pinto 2, 1649-003 Lisboa (Portugal)

    2013-07-01

    CdTe nano-structures with diameter of ∼100 nm and variable length (200–600 nm) were fabricated on glass substrates covered with conductive buffer layers such as NiCr, ZAO (ZnO:Al{sub 2}O{sub 3} + Ta{sub 2}O{sub 5}) or TiPd alloys. The fabrication process consisted of the starting vapour deposition of metal catalyst dropped layer followed by the isothermal catalyst-prompted vapour growth of CdTe nano-structured layer of controllable shape and surface filling. The effect of buffer layers on the crystallographic orientation and thickness of CdTe nano-structured layers is investigated by means of IBA techniques, SEM and X-ray diffraction. It was shown that the formed CdTe nano-layers have a cubic structure, mainly oriented towards the [1 1 1] crystallographic direction, except for those grown on ZAO layer where the X-ray diffraction signal is very weak to be associated to any crystallographic form. The RBS spectra recorded on different areas of each sample type showed an almost constant thickness and SEM images revealed an homogeneous and dense distribution of the structures. It was also possible to study the first stage of the nano-structures grown on the Bi{sub 2}Te{sub 3} seeds.

  6. Analysis of oxygen shell splitting in hydrothermally grown single crystal ThO2(200)

    International Nuclear Information System (INIS)

    Single crystals of ThO2 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 O2- transport in a ThO2 matrix and corroborating research indicating partial Th 5f occupancy that is similar to hyper-stoichiometric UO2+x compounds. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  7. 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.

  8. Free-standing thin film Ge single crystals grown by plasma-enhanced chemical vapor deposition

    Science.gov (United States)

    Outlaw, R. A.; Hopson, P., Jr.

    1984-01-01

    The films, which are approximately 10 microns in thickness, are grown epitaxially on polished (100) NaCl substrates at 450 C by plasma enhanced chemical vapor deposition. Upon cooling, the films are separated from the substrate by differential shear stress, leaving free-standing films of Ge which can be handled. Growths are attained by nucleating at minimum plasma power for very brief intervals and then raising the power to 65 W to increase the growth rate to approximately 10 microns/h. It is found that substrate exposure to the plasma at too high a power for too long a time sputters and erodes the surface, thereby substantially degrading the nucleation process and the ultimate growths. It is noted that the free-standing films are visually specular and exhibit a high degree of crystalline order when examined by X-ray diffraction. Auger electron spectroscopy and energy dispersive analysis of X-rays reveal no detectable bulk contamination.

  9. Study on third order nonlinear optical properties of a metal organic complex-Monothiourea-cadmium Sulphate Dihydrate single crystals grown in silica gel

    Science.gov (United States)

    Sivanandan, T.; Kalainathan, S.

    2015-04-01

    The third order nonlinear optical properties of Monothiourea-cadmium Sulphate Dihydrate crystal were measured using a He-Ne laser (λ=632.8 nm) by a Z-scan technique. The magnitude of nonlinear refractive index (n2) and nonlinear absorption coefficient was found to be 4.4769×10-11 m2/W and 1.233×10-2 m/W respectively. The third order non-linear optical susceptibility χ(3) was found to be in the order of 3.6533×10-2 esu. The negative sign of non-linear refractive index shows the self-defocusing nature of the gel grown crystal. The second-order molecular hyperpolarizability γ of the grown crystal is 1.2822×10-33 esu. Laser damage threshold was measured by using an Nd: YAG laser (1064 nm). Photoconductivity studies of the gel grown crystal revealed that the crystal possesses positive photoconducting nature. The results obtained from Z-scan, laser damage threshold and photoconducting studies reveal that the crystal can be a possible candidate material for photonics device, optical switches, and optical power limiting application.

  10. Improvement of crystal quality of AlN grown on sapphire substrate by MOCVD

    Energy Technology Data Exchange (ETDEWEB)

    Lai, Mu-Jen; Chang, Liann-Be; Lin, Ray-Ming [Department of Electronic Engineering and Green Technology Research Center, Chang Gung University, Taoyuan, Taiwan 333 (China); Yuan, Tzu-Tao [Department of Electrical and Electronic Engineering, Chung Cheng Institute of Technology, Taoyuan, Taiwan 335 (China)

    2010-07-15

    The crystalline quality of aluminum nitride (AlN) epilayers grown on sapphire substrates by MOCVD was improved by increasing hydrogen flow rate during the high temperature growth process. The AlN epilayer exhibited a root mean square (rms) of roughness was 1.944 nm from the 2 x 2 {mu}m{sup 2} size atomic force microscopy (AFM) images. Full widths at half maximum (FWHMs) of (002) and (102) rocking curves of triple-axis high resolution X-ray diffraction (HRXRD) measurements were as narrow as 28.8 arc sec and 868 arc sec, respectively. The optical transmittance spectra showed a sharp absorption edge at a wavelength of 200 nm and strong Fabry-Perot (FP) oscillations. It is proposed that the improvement in crystalline quality is due to the surface in the low-temperature aluminum nitride (LT-AlN) buffer layer is promoted to be stable Al-polarity by the conditions of increasing hydrogen flow rate and ramping up the growth temperature. Addtionally, the parasitic reactions are effectively suppressed by increasing the hydrogen flow rate during the growth process of high temperature. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. 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.

  12. 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.

  13. 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.

  14. Structural characteristics and physical properties of diortho(pyro)silicate crystals of lanthanides yttrium and scandium grown by the Czochralski technique

    International Nuclear Information System (INIS)

    Optically uniform monocrystals of diortho (pyro) silicates of lanthanides, yttrium, and scandium were grown by the Czochralski technique. Four structural types of Ln2[Si2O7] crystals were determined by the roentgenographic method. The presence of structural subgroups was also supported by the method of spectroscopic probes. Structural parameters were determined and data on certain physical properties (fusion temperature, density, refractive indices, transparency) of investigated crystals were presented. The generation of induced emission at lambda=1.057 μm was obtained in La2[Si2O7]-Nd3+ crystal

  15. 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

  16. 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.

  17. 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}

  18. Influence of EDTA2− on the hydrothermal synthesis of CdTe nanocrystallites

    International Nuclear Information System (INIS)

    Transformation from Te nanorods to CdTe nanoparticles was achieved with the assistance of EDTA as a ligand under hydrothermal conditions. Experimental results showed that at the beginning of reaction Te nucleated and grew into nanorods. With the proceeding of reaction, CdTe nucleus began to emerge on the surface, especially on the tips of Te nanorods. Finally, nearly monodispersed hexagonal CdTe nanoparticles with diameters of about 200 nm were obtained. The effects of EDTA on the morphology and formation of CdTe nanoparticles were discussed in consideration of the strong ligand-effect of EDTA, which greatly decreased the concentration of Cd2+. Furthermore, the possible formation process of CdTe nanoparticles from Te nanorods was further proposed. The crystal structure and morphology of the products were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). - Graphical Abstract: Firstly, Te nucleated and grew into nanorods in the presence of EDTA2−. Then CdTe nucleus began to emerge on Te nanorods and finally monodispersed CdTe nanoparticles were obtained. Highlights: ► EDTA serves as a strong ligand with Cd2+. ► The existence of EDTA constrains the nucleation of CdTe and promotes the formation of Te nanorods. ► With the proceeding of reaction, CdTe nucleus began to emerge on the surface, especially on the tips of Te nanorods. ► Nearly monodispersed hexagonal CdTe nanoparticles with diameters of about 200 nm were finally obtained.

  19. 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.

  20. 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.

  1. 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.

  2. Crystal growth and dielectric property of Na0.5K0.5NbO3 single crystal grown by flux method using B2O3 flux

    International Nuclear Information System (INIS)

    Potassium sodium niobate (K0.5Na0.5NbO3, KNN) single crystals have been grown by a high temperature flux solution method in which the additions of small amounts of boron oxide in the flux were used, because of its reduced the Growth temperature and we study the X-ray diffraction (XRD) pattern, SEM and EDAX, FTIR, UV-VIS, SPECTRUM, AFM and Dielectric properties of NKN single crystal. (author)

  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. 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.

  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. 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.

  7. 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.

  8. Optical investigation of non-equilibrium carrier dynamics in differently doped VGF-grown ZnTe single crystals

    International Nuclear Information System (INIS)

    We applied a time-resolved FWM technique to study the dynamics of photoexcited carriers in differently doped VGF-grown ZnTe crystals at room temperature. We observed a fast carrier trapping to deep levels in phosphorus doped and undoped samples. The measurements at below and above band-gap excitations revealed the much higher concentration of these levels near the surface than in the bulk in both samples. The concentration of deep traps has been estimated for phosphorus doped sample N T = (1 - 2) x 1015 cm-3 in the bulk and N = (3 - 5) x 1018 cm-3 near the surface. In the undoped sample these traps are present at much higher concentration. The electron and hole mobilities μ n = (500 ± 28) cm2/Vs and μ h = (16 ± 6) cm2/Vs were estimated from the measured diffusion coefficient values D = (12.5 ± 0.7) cm2/s in the p-type sample and D = (0.8 ± 0.3) cm2/s in the semi-insulating one. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. 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.

  10. 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.

  11. Preparation and characterization of thin films of electrodeposited CdTe semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Soliman, M.; Elgamal, M. [Alexandria University (Egypt). Institute of Graduate Studies and Research; Kashyout, A.B. [Mubarak City for Scientific Research and Technological Applications, Alexandria (Egypt); Shabana, M. [Alexandria University (Egypt). Faculty of Engineering

    2001-07-01

    Thin films of CdTe semiconductors were prepared by electrodeposition technique in aqueous solutions. The deposition mechanism was investigated by cyclic voltammetry. The potential regions for the formation of the n-CdTe and p-CdTe films were determined. The structure, composition and morphology characteristics of as-deposited thin films of CdTe grown on SnO{sub 2}/glass and CdS/SnO{sub 2}/glass were investigated by XRD, EDAX and SEM techniques. The optical properties were measured to determine the absorption coefficient and band gap values. The as-deposited CdTe films grown on SnO{sub 2}/glass contained free Te while those grown on CdS/SnO{sub 2}/glass did not contain this phase. The CdTe has the cubic structure with strong (111) orientation. The EDAX analysis showed a nearly stoichiometric Cd:Te ratio. The band gap has a value of 1.48 eV, which is in a good accordance with those reported in the literature. The effect of annealing at 350 and 400{sup o}C after, CdCI{sub 2} treatment on the structure and morphology was also examined. (author)

  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. 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.

  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. New CdTe photoconductor array detector for x-ray applications

    International Nuclear Information System (INIS)

    A CdTe photoconductor array x-ray detector was grown using molecular beam epitaxy (MBE) on a Si(100) substrate. The temporal response of the photoconductor arrays is as fast as 21 ps rise time and 38 ps full width half-maximum (FWHM). The spatial resolution of the photoconductor was good enough to provide 75 μm FWHM using a 50 μm synchrotron x-ray beam. A substantial number of x-ray photons are absorbed effectively within the MBE CdTe layer as observed from the linear response up to 15 keV. These results demonstrate that MBE grown CdTe is a suitable choice of the detector materials to meet the requirements for x-ray detectors

  17. Magnetic and electrical properties of flux grown single crystals of Ln6M4Al43 (Ln=Gd, Yb; M=Cr, Mo, W)

    International Nuclear Information System (INIS)

    Millimeter-sized single crystals of Ln6M4Al43 (Ln=Gd, Yb; M=Cr, Mo, W) were successfully grown with a molten aluminum flux. Synthetic conditions and physical properties for single crystals of all six analogs are discussed. The compounds exhibit metallic resistivity with room temperature values between 0.1 and 0.6 mΩ-cm. The Yb analogs are Pauli paramagnets with the Yb ion adopting the nonmagnetic divalent configuration (Yb2+). Gd6Cr4Al43, Gd6Mo4Al43, and Gd6W4Al43 appear to order antiferromagnetically at 19, 15, and 15 K, respectively. - Graphical abstract: The crystal structure of Yb6Cr4Al43. The light and dark green polyhedra show the chromium sublattice. Highlights: ► Single crystals up to 0.5 cm in length were grown with a molten aluminum flux. ► Physical property measurements were conducted on single crystals. ► Gadolinium analogs appear to order antiferromagnetically with positive θ. ► All analogs show metallic resistivity.

  18. Effects of CuO doping on properties (Na0.5K0.5)NbO3 piezoelectric 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 Cux) NbO3 (where x = .02, .04, .06) single crystal were grown using a high temperature flux method. The effects of cationic substitution of Cu 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)

  19. 95 K Sm1+xBa2-xCu3Oz single crystal with controlled stoichiometry grown under 1 atm oxygen pressure

    International Nuclear Information System (INIS)

    In this communication, for the first time, we report on a high-Tc 95 K Sm1+xBa2-xCu3Oz (SmBCO) single crystal with a small transition width of less than 0.5 K grown under 1 atm oxygen pressure. We found that the substitution of Ba by Sm could be effectively suppressed by using liquid composition control. Jc-B curves and scaling analysis of samples at 77 K with B-vector parallel c indicate that a delta Tc style defect is the predominant pinning in SmBCO crystals. (rapid communication)

  20. 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.

  1. 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.

  2. Applications of CdTe to nuclear medicine. Annual report, February 1, 1977--January 31, 1978

    Energy Technology Data Exchange (ETDEWEB)

    Entine, G.

    1978-01-01

    The development of CdTe has now progressed to the point where a wide variety of prototype medical applications are being explored. It appears that as the more dramatic applications such as the camera became widely known, expanded interest will be developed for the more mundane but medically still useful areas of medicine such as probes and small arrays. The basic limitation to the increased use of CdTe in medicine remains an economic one as all applications must bear a heavy cost of fundatmental CdTe crystal and device research. A second problem is the fact that the existence of CdTe detectors is not known to most medical researches. This latter problem is being successfully addressed by this contract.

  3. 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

  4. 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.

  5. 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.).

  6. 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.

  7. 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

  8. Observation of Flux-Grown α-Fe2O3 Single Crystal at the Morin Transition by 57Fe Synchrotron Radiation Mössbauer Diffraction

    Science.gov (United States)

    Mitsui, Takaya; Nakamura, Shin; Ikeda, Naoshi; Fujiwara, Kosuke; Masuda, Ryo; Kobayashi, Yasuhiro; Seto, Makoto

    2016-05-01

    The Morin transition of a high-quality flux-grown single crystal of α-Fe2O3 was studied by 57Fe synchrotron radiation Mössbauer diffraction. The measured rocking curves and Mössbauer spectra gave direct evidence that the coexistence of magnetic phases during the Morin transition occurred over a wide temperature range. The complex magnetic structure at the phase coexistence induced a large magnetostrictive distortion in the α-Fe2O3 crystal surface. In contrast, however, when the antiferromagnetic phase was dominant at low temperatures, the distortion disappeared, and the initial high crystal perfection was recovered. The spectral line shapes were discussed in terms of the interference between electronic and nuclear scatterings.

  9. 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.

  10. Effect of tantalum substitution for niobium on the crystal structure, dielectric properties of (K0.5Na0.5)NbO3 single crystal grown by flux method

    International Nuclear Information System (INIS)

    Potassium sodium niobate (K0.5Na0.5)NbO3 single crystal and co-doped (K0.5Na(1-x)0.5Tax)NbO3 (where x=.20,.30,40,.) single crystal were grown using a high temperature flux method. The effects of cationic substitution of Ta 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)

  11. 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)

  12. 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)

  13. 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

  14. 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.).

  15. Highly coercive L10-FePd thin films grown on MgO single crystal substrates

    International Nuclear Information System (INIS)

    L10-ordered systems are of great interest from both the technological and research point of view since their high magnetocrystalline anisotropy makes them suitable candidates for future high density recording media. FePd and FePt are isostructural alloys that in their ordered phase show very different magnetic behaviour. In this work ultra-thin films of FePd and FePt films have been grown showing very hard magnetic properties. The coercivity of FePd films grown at 7000C reaches values well above 10 kOe much greater than that obtained in FePt films grown in the same conditions.

  16. 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.

  17. 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.

  18. 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

  19. ZnO nanowires array grown on Ga-doped ZnO single crystal for dye-sensitized solar cells.

    Science.gov (United States)

    Hu, Qichang; Li, Yafeng; Huang, Feng; Zhang, Zhaojun; Ding, Kai; Wei, Mingdeng; Lin, Zhang

    2015-01-01

    High quality ZnO nanowires arrays were homoepitaxial grown on Ga-doped ZnO single crystal (GZOSC), which have the advantages of high conductivity, high carrier mobility and high thermal stability. When it was employed as a photoanode in the DSSCs, the cell exhibited a 1.44% power-conversion efficiency under the illumination of one sun (AM 1.5G). The performance is superior to our ZnO nanowires/FTO based DSSCs under the same condition. This enhanced performance is mainly attributed to the perfect interface between the ZnO nanowires and the GZOSC substrate that contributes to lower carrier scattering and recombination rates compared with that grown on traditional FTO substrate. PMID:26099568

  20. Investigation of deep level defects in CdTe thin films

    Energy Technology Data Exchange (ETDEWEB)

    Shankar, H.; Castaldini, A. [Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy); Dieguez, E.; Rubio, S. [Crystal Growth Lab, Department of Materials Physics, Faculty of Science, University Autonoma of Madrid, Ciudad Universitaria de Cantoblanco, 28049, Madrid (Spain); Dauksta, E.; Medvid, A. [Institute of Technical Physics, Riga Technical University, 14 Azenes Str, Riga, Latvia, Department of Materials (Latvia); Cavallini, A. [Department of Physics and Astronomy,University of Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy)

    2014-02-21

    In the past few years, a large body of work has been dedicated to CdTe thin film semiconductors, as the electronic and optical properties of CdTe nanostructures make them desirable for photovoltaic applications. The performance of semiconductor devices is greatly influenced by the deep levels. Knowledge of parameters of deep levels present in as-grown materials and the identification of their origin is the key factor in the development of photovoltaic device performance. Photo Induced Current Transient Spectroscopy technique (PICTS) has proven to be a very powerful method for the study of deep levels enabling us to identify the type of traps, their activation energy and apparent capture cross section. In the present work, we report the effect of growth parameters and LASER irradiation intensity on the photo-electric and transport properties of CdTe thin films prepared by Close-Space Sublimation method using SiC electrical heating element. CdTe thin films were grown at three different source temperatures (630, 650 and 700 °C). The grown films were irradiated with Nd:YAG LASER and characterized by Photo-Induced Current Transient Spectroscopy, Photocurrent measurementand Current Voltage measurements. The defect levels are found to be significantly influenced by the growth temperature.

  1. 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

  2. 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.

  3. 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.)

  4. 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.

  5. 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.

  6. Three-dimensional evaluation of gettering ability for oxygen atoms at small-angle tilt boundaries in Czochralski-grown silicon crystals

    International Nuclear Information System (INIS)

    Three-dimensional distribution of oxygen atoms at small-angle tilt boundaries (SATBs) in Czochralski-grown p-type silicon ingots was investigated by atom probe tomography combined with transmission electron microscopy. Oxygen gettering along edge dislocations composing SATBs, post crystal growth, was observed. The gettering ability of SATBs would depend both on the dislocation strain and on the dislocation density. Oxygen atoms would agglomerate in the atomic sites under the tensile hydrostatic stress larger than about 2.0 GPa induced by the dislocations. It was suggested that the density of the atomic sites, depending on the tilt angle of SATBs, determined the gettering ability of SATBs

  7. Intrinsic defect complexes in CdTe and ZnTe

    International Nuclear Information System (INIS)

    Radiation defects in CdTe and ZnTe are modeled from first principles. The most important intrinsic defects resulting from cation evaporation or displacement are cation vacancies and tellurium anti-sites, electrically active defects characterized by a low formation energy. The reactions between those two defects are investigated. Since cation vacancy clusters of less than four vacancies are not stable, it is argued that cation vacancy aggregation is not a dominant process in near-equilibrium conditions. In-grown or radiation-induced clusters of four cation vacancies may serve as a nucleation center for tellurium precipitation. The formation energy of these small voids is lower in ZnTe than in CdTe. Additionally, cation-anion divacancies are stable in ZnTe and in p-type CdTe.

  8. 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)

  9. 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.

  10. 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)

  11. 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...

  12. 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).

  13. 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)

  14. Annealing effects on the crystal structure of GaInNAs quantum wells with large In and N content grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    The impact of rapid thermal annealing on the optical emission of GaInNAs/GaAs quantum wells (QWs) grown by molecular beam epitaxy with high In and N content is shown to be highly dependent on the crystal structure of the QWs, as determined by transmission electron microscopy. Due to the presence of higher concentrations of nonradiative recombination centers, the annealing temperature required to obtain maximum photoluminescence emission is higher for the QW with strong structural modulation of the upper interface [at the onset of three-dimensional (3D) growth], intermediate for the two-dimensional (2D) grown QW with compositional fluctuations, and lower for the homogeneous 2D grown QW. Moreover, the transition from homogeneous 2D growth, to 2D growth with compositional fluctuations, and finally 3D growth, leads to progressively deeper carrier localization states below the conduction-band edge. Increasing annealing temperatures gradually shifts the localization states closer to the conduction-band edge, predominantly when compositional fluctuations are present. These results suggest a link between the formation of carrier localization centers and the presence of alloy fluctuations along the QW

  15. Detection of non stoichiometric vacancy defects in CdTe, HgTe and Hg1-xCdxTe by positron annihilation

    International Nuclear Information System (INIS)

    Native vacancies are evidenced from positron lifetime measurements in as-grown CdTe, HgTe and Hg0.8Cd0.2Te. The positron lifetime depends on the conducting type of the materials rather than on the growing conditions. The native vacancies have two levels of ionisation and are identified as Cd-vacancies (VCd) in CdTe. (author) 2 figs., 2 tabs., 9 refs

  16. 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...

  17. 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...

  18. 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.

  19. 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.

  20. Stacking faults and structural transformations in Zn xMn 1-xS single crystals grown from vapour

    Science.gov (United States)

    Sebastian, M. T.; Krishna, P.

    1984-05-01

    This paper reports an X-ray diffraction study of the stacking faults and solid state transformations observed in Zn xMn 1- xS (0.9 twinned 3C structure on annealing around 600°C. The rest of the crystals transformed first to a disordered 6H structure and then, on further annealing at higher temperatures, to the disordered twinned 3C structure. Most of the transformed 3C structures showed an intensity enhancement near the positions of the 6H reflections on X-ray diffraction photographs. All the 3C crystals transform back to a disordered 2H structure on annealing above 1050°C. To determine the nature of stacking faults involved in the 2H-6H transformation we have investigated the broadening of X-ray diffraction maxima along reciprocal lattice rows with H - K ≠ 3 n produced by crystals undergoing the transformation. The point intensity distribution along the 10. L reciprocal lattice row of several partially transformed crystals were recorded on a four circle single crystal diffractometer in steps of Δ L = 0.01. A study of the experimental profiles obtained by plotting the diffractometer record of intensity versus L in reciprocal space shows that the transformation occurs by the non-random insertion of deformation faults in the 2H structure. It is shown that the one-parameter model proposed by Pandey, Lele and Krishna [Proc. Roy. Soc. (London) A369 (1980) 451 is not applicable to 2H-6H solid state transformation in Zn xMn 1- xS crystals. A two-parameter model involving different fault probabilities for the nucleation (α) and the growth (β) of the 6H phase in the 2H structure is suggested.

  1. Structure and properties of quartz crystals grown from fluoride solutions: I. The morphology of basal pinacoid habit

    International Nuclear Information System (INIS)

    The mechanism of growth of quartz crystals from fluoride media has been investigated. It is shown by different independent methods (selective etching, X-ray diffraction analysis, optical microscopy) that the faceted forms of autonomous growth regions (trigonal pyramids formed on nonsingular crystal faces) are unstable and degenerate during growth. This degeneracy is accompanied by torsion deformation of autonomous growth regions and, as a result, formation of a series of hollow helical channels at boundaries of autonomous growth regions, whose axes make an angle of ∼16o with the OZ axis, and their projections on the XOY plane are directed along the +X axes.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. Research Update: Point defects in CdTexSe1−x crystals grown from a Te-rich solution for applications in detecting radiation

    Directory of Open Access Journals (Sweden)

    R. Gul

    2015-04-01

    Full Text Available We investigated cadmium telluride selenide (CdTeSe crystals, newly grown by the Traveling Heater Method (THM, for the presence and abundance of point defects. Current Deep Level Transient spectroscopy (I-DLTS was used to determine the energies of the traps, their capture cross sections, and densities. The bias across the detectors was varied from 1 to 30 V. Four types of point defects were identified, ranging from 10 meV to 0.35 eV. Two dominant traps at energies of 0.18 eV and 0.14 eV were studied in depth. Cd vacancies are found at lower concentrations than other point defects present in the material.

  10. 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.

  11. 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.

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

    International Nuclear Information System (INIS)

    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

  13. Synthesis and application of TiO2 single-crystal nanorod arrays grown by multicycle hydrothermal for dye-sensitized solar cells

    International Nuclear Information System (INIS)

    TiO2 is a wide band gap semiconductor with important applications in photovoltaic cells. Vertically aligned TiO2 nanorod arrays (NRs) are grown on the fluorine-doped tin oxide (FTO) substrates by a multicycle hydrothermal synthesis process. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED). It is found that dye-sensitized solar cells (DSSCs) assembled by the as-prepared TiO2 single-crystal NRs exhibit different trends under the condition of different nucleation and growth concentrations. Optimum cell performance is obtained with high nucleation concentration and low growth cycle concentration. The efficiency enhancement is mainly attributed to the improved specific surface area of the nanorod. (interdisciplinary physics and related areas of science and technology)

  14. Fluorescence spectra of Na5Lu9F32 single crystals co-doped with Ho3+/Tm3+ grown by Bridgman method

    Science.gov (United States)

    Feng, Zhigang; Xia, Haiping; Wang, Cheng; Zhang, Zhixiong; Jiang, Dongsheng; Zhang, Jian; He, Shinan; Tang, Qingyang; sheng, Qiguo; Gu, Xuemei; Zhang, Yuepin; Chen, Baojiu; Jiang, Haochuan

    2016-05-01

    This work presents the luminescent properties of Ho3+/Tm3+ co-doped Na5Lu9F32 single crystals that were grown by an improved Bridgman method for the first time. The J-O intense parameters of Ho3+ ions were calculated. An intense 2.0 μm emission was achieved with Tm3+ ions sensitizing Ho3+ ions by the processing of energy transfer from Tm3+ ions to Ho3+ ions under excitation of 800 nm LD. The maximum emission intensity at 2.0 μm is obtained, and the cross sections of Tm3+ ions and Ho3+ ions were calculated. The physical mechanism for energy transfer from Tm3+ to Ho3+ ions was analyzed by using Inokuti-Hirayama's model.

  15. 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.

  16. Single-crystal SrTiO3 fiber grown by laser heated pedestal growth method: influence of ceramic feed rod preparation in fiber quality

    Directory of Open Access Journals (Sweden)

    D. Reyes Ardila

    1998-10-01

    Full Text Available The rapidly spreading use of optical fiber as a transmission medium has created an interest in fiber-compatible optical devices and methods for growing them, such as the Laser Heated Pedestal Growth (LHPG. This paper reports on the influence of the ceramic feed rod treatment on fiber quality and optimization of ceramic pedestal processing that allows improvements to be made on the final quality in a simple manner. Using the LHPG technique, transparent crack-free colorless single crystal fibers of SrTiO3 (0.50 mm in diameter and 30-40 mm in length were grown directly from green-body feed rods, without using external oxygen atmosphere.

  17. 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.

  18. 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 ...

  19. Microstructure of InGaN quantum wells grown on GaN single crystals and sapphire

    International Nuclear Information System (INIS)

    In the last decade, the III-N compounds have attracted much interest because of their applications in blue, violet and ultraviolet optoelectronics. Most of the devices and research use sapphire as a substrate for epitaxy of nitrides. However, these epi-structures contain a very high dislocation density induced by the 16% lattice mismatch between GaN and sapphire. In our laboratory, we grow single crystals of GaN at a high hydrostatic pressure of 10 kbar of nitrogen. These crystals have an ultra-low dislocation density and are successfully used for construction of violet laser diodes. This work presents experimental data of high resolution x-ray diffractometry and photoluminescence. This work consist of three parts: (i) comparison between GaN substrates and GaN/sapphire templates; (ii) influence of AlGaN layers on bowing of samples; (iii) microstructure of InGaN/GaN multiple quantum wells

  20. 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).

  1. Surface and interface analysis of epitaxially grown Au film on InP(001) crystal by means of LEED/AES/RBS-channeling techniques

    International Nuclear Information System (INIS)

    Atomic arrangements at the surface and interface of the Au film epitaxially grown on the p(2 x 4) surface of the InP(001) crystal only by room temperature deposition have been studied in-situ by means of RBS-channeling technique. The epitaxially grown Au film of 20 A in thickness has shown a clear LEED pattern of p(1 x 1) spots which correspond to c(2 x 2) spots for the Au(001) face. The RBS-channeling measurement along the direction of the InP substrate has shown that the average minimum yield for the Au film is 32.5 % and that the yield of In surface peak is 3.0 atoms/row, which is a little enhanced in comparison with that, 2.7 atoms/row for the as-cleaned InP(001)-p(2 x 4) surface. The minimum yield of 32.5 % for the Au film is well explained in terms of lateral displacement by 0.18 A of a pair of Au atoms in a c(2 x 2) unit cell at the surface producing the reconstructed structure. The enhance In surface peak yield indicates that the atomic rows in the Au single crystal film do not shadow the In atomic rows as well as the P rows in the InP substrate. It is shown from the enhancement that the In atomic rows are situated within the radius of 0.72 A around the center of the channel of the Au lattice. (author)

  2. 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.

  3. 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.).

  4. Ion channeling studies of CdTe films on GaAs

    International Nuclear Information System (INIS)

    Thin films of [111] oriented CdTe have been MOCVD grown onto [111] GaAs substrates. When thickness exceed 1000 Angstrom the epitaxy is quite good (backscattering minimum yield of approximately 15%) in spite of a 14% lattice mismatch. A narrowing of the Cd angular scan suggests a displacement of some of the Cd atoms in the lattice. A model based on a Te vacancy is presented to describe the data

  5. Material properties of pulsed-laser crystallized Si thin films grown on yttria-stabilized zirconia crystallization-induction layers by two-step irradiation method

    Science.gov (United States)

    Thi Kieu Lien, Mai; Horita, Susumu

    2016-03-01

    Amorphous Si thin films on yttria-stabilized zirconia (YSZ) layers were crystallized widely in solid phase by the two-step method with a pulsed laser, moving the sample stage. The crystalline quality, impurity diffusion, and electrical properties of the crystallized Si films were investigated. It was found that the crystallinity of the Si thin films was improved and their surface was smooth without an incubation layer at the interface, indicating the uniform crystallinity of Si on YSZ. The diffusion of Zr and Y into the Si thin films was as small as or smaller than the order of 1017 atoms/cm3. We evaluated the electrical properties of carrier concentration and Hall mobility of the Si thin films with/without YSZ layers by using the resistivity and AC Hall effect measurements. The temperature and doping concentration dependences were measured for both undoped and P-doped films. It was found that both the undoped and P-doped Si/YSZ/glass films showed higher mobilities and carrier concentrations (and therefore higher conductivities), which indicate a smaller number of defects, than the Si/glass films. This suggested that the Si film crystallized on the YSZ layer is more suitable for application to electronic devices than the Si film on glass.

  6. 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.

  7. Localized Si enrichment in coherent self-assembled Ge islands grown by molecular beam epitaxy on (001)Si single crystal

    International Nuclear Information System (INIS)

    Transmission electron microscopy (TEM), atomic force microscopy, and Rutherford backscattering spectrometry (RBS) have been used to investigate the morphology, structure, and composition of self-assembled Ge islands grown on Si (001) substrates by molecular beam epitaxy (MBE) at different temperatures. Increasing the temperature from 550 °C to 700 °C causes progressive size and shape uniformity, accompanied by enhanced Si-Ge intermixing within the islands and their wetting layer. Elemental maps obtained by energy filtered-TEM (EF-TEM) clearly show pronounced Si concentration not only in correspondence of island base perimeters, but also along their curved surface boundaries. This phenomenon is strengthened by an increase of the growth temperature, being practically negligible at 550 °C, while very remarkable already at 650 °C. The resulting island shape is affected, since this localized Si enrichment not only provides strain relief near their highly stressed base perimeters but it also influences the cluster surface energy by effective alloying, so as to form Si-enriched SiGe interfaces. Further increase to 700 °C causes a shape transition where more homogenous Si-Ge concentration profiles are observed. The crucial role played by local “flattened” alloyed clusters, similar to truncated pyramids with larger bases and enhanced Si enrichment at coherently stressed interfaces, has been further clarified by EF-TEM analysis of a multi-layered Ge/Si structure containing stacked Ge islands grown at 650 °C. Sharp accumulation of Si has been here observed not only in proximity of the uncapped island surface in the topmost layer but also at the buried Ge/Si interfaces and even in the core of such capped Ge islands.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. 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.

  18. New trends in CdTe and CdZnTe detectors for X- and gamma-ray applications

    International Nuclear Information System (INIS)

    The CdTe gamma-ray camera IBIS/ISGRI, on board the INTEGRAL satellite launched in October 2002, is currently the largest spectro-imager of this type in the world. The development of this detector, for research in the field of astrophysics, has provided the opportunity to demonstrate the feasibility of massive integration of CdTe nuclear detectors, taking advantage of the CdTe good spectral performances and high modularity. Many other groups in the world work also to further develop detectors using this material in view of improving its spectral performances (crystal quality, electrode geometry and type, electronics and filtering, etc.), the spatial resolution (pixelization of monolithic crystals) and the detection efficiency at high energy (thickness). In this review, I will detail the main directions in which to strive in order to explore these fields in the upcoming years through examples of techniques or applications

  19. 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.

  20. Thin yttrium iron garnet films grown by pulsed laser deposition: Crystal structure, static, and dynamic magnetic properties

    Science.gov (United States)

    Sokolov, N. S.; Fedorov, V. V.; Korovin, A. M.; Suturin, S. M.; Baranov, D. A.; Gastev, S. V.; Krichevtsov, B. B.; Maksimova, K. Yu.; Grunin, A. I.; Bursian, V. E.; Lutsev, L. V.; Tabuchi, M.

    2016-01-01

    Pulsed laser deposition has been used to grow thin (10-84 nm) epitaxial layers of Yttrium Iron Garnet Y3Fe5O12 (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.

  1. Thin yttrium iron garnet films grown by pulsed laser deposition: Crystal structure, static, and dynamic magnetic properties

    International Nuclear Information System (INIS)

    Pulsed laser deposition has been used to grow thin (10–84 nm) epitaxial layers of Yttrium Iron Garnet Y3Fe5O12 (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

  2. 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.

  3. 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.).

  4. 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.

  5. Material and detector properties of cadmium manganese telluride (Cd{sub 1−x}Mn{sub x}Te) crystals grown by the modified floating-zone method

    Energy Technology Data Exchange (ETDEWEB)

    Hossain, A., E-mail: hossain@bnl.gov; 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 (Cd{sub 1−x}Mn{sub x}Te; 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 Cd{sub 1−x}Mn{sub x}Te 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.

  6. 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)

  7. 1.5-μm emission of naturally-oxidized InN crystals grown by MOVPE

    International Nuclear Information System (INIS)

    Photoluminescence (PL) spectrum of a naturally-oxidized InN sample has been investigated. The PL-peak wavelength locates at around 1.53 μm, which is by 250-300 nm shorter than that of an intrinsic InN. In addition to this PL peak shift of the InN crystals (corresponding bandgap variation) their quality seems to be improved from the analysis of PL spectra. The naturally-oxidized layer is found to have the original lattice structure of InN from X-ray diffraction measurements. The 8-20% of oxygen atoms has been evaluated to be incorporated in the InN layer by the energy dispersive X-ray spectroscopy. The PL spectra have been affected by temperature. While a PL-peak intensity increases with temperature decrease, a PL-peak shifts toward the longer wavelength. Such red-shift tendency is opposite to the case of other III-V compounds. This anomalous temperature effect has been proved from variation of PL spectra with time after excitation. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. 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].

  9. 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)

  10. 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.

  11. 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.

  12. Influence of air annealing temperature and time on the optical properties of Yb:YAG single crystal grown by HDS method

    Science.gov (United States)

    Nie, Ying; Liu, Yang; Zhao, Yequan; Zhang, Mingfu

    2015-08-01

    8 at.% Yb:YAG plate single crystal with the dimension of 170 mm × 150 mm × 30 mm was grown in vacuum by Horizontal Directional Solidification method. Aimed at blue-green color centers, annealing treatments of 15 mm × 15 mm × 1 mm samples from 900 °C to 1400 °C for 5 h and at 900 °C from 5 h to 40 h in air were conducted. The absorption spectra, emission spectra, fluorescence lifetime and X-ray photoelectron spectroscopy of samples under different annealing conditions were measured at room temperature, respectively. Annealing at above 1000 °C for 5 h or at 900 °C for 40 h made the blue-green color centers disappear and the samples turned to transparent. Absorption coefficients decreased in the 300 nm-800 nm wavelength range, emission intensities increased and emission bands broadened around 486 nm and 1029 nm with increasing temperature up to 1200 °C, then varied inversely. These values decreased or increased monotonically with increasing annealing time at 900 °C. The maximal increases of fluorescence lifetime were 62.3% and 64.7%, respectively. The calculated emission cross section of 1200 °C for 5 h was up to 4.4 × 10-20 cm2. In X-ray photoelectron spectroscopy, the concentrations of oxygen vacancies reduced from 1.28% down to absence by annealing. These experiments show that color centers are detrimental to the optical properties of HDS-Yb:YAG laser crystal and optimal annealing treatments should be conducted.

  13. Development of surgical gamma probes with TlBr semiconductors and CsI(Tl) scintillators crystals

    International Nuclear Information System (INIS)

    Radio guided surgery, using probes with radiation detectors, has been prominence in the medical area in the last decade. This technique consists in injecting a radioactive substance to concentrate in tumour and assist the localization during the surgical procedure. The radio guided surgeries allowing the identification of lymph node has revolutioned the behavior of tumour in initial stadium when are being spread by lymphatic way. The conditions imposed to the surgery due the proximity between some lymph nodes, demands of the probes, a small diameters and capacity of individual identification of these lymph nodes radiolabelled by a specific tracer. The international market supplies these probes with CdTe semiconductors and scintillators, but there is some time lack a promptly technical assistance in the Brazilian market. This work developed probes with national technology, using CsI(Tl) scintillators crystals and, in substitution to CdTe crystals semiconductors, the TlBr crystal, that is a new semiconductor detector in a world-wide development, with advantages in relation to the CdTe. Both crystals have been grown in IPEN. All the necessary electronics, specially, the preamplifier, that was also a restrictive factor for development of these types of probe in the country, have been developed with components found in the national market. Systematic measures of spatial resolution, spatial selectivity, maximum sensitivity and quality of the shielding have been carried the probes development. The results have shown that the probes, one with the CsI(Tl) crystal and another with TlBr semiconductor presented the requested performance in the international literature for radio guided probes. (author)

  14. 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)

  15. 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.).

  16. 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...

  17. 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.

  18. 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.

  19. Dislocation-induced electronic levels in semi-insulated CdTe

    International Nuclear Information System (INIS)

    We studied deformation-induced defects in semi-insulating CdTe and CdZnTe by infrared photoluminescence (PL) and compared our data with earlier results. We confirmed the direct correlation between Y-emission and dislocation density in both compounds. The Y-band intensified near an indenter deformation or near a scribing line, but was barely visible in low-dislocation areas (etch pit density 5 cm-2). Plastic deformation also increased the concentrations of grown-in defects, namely, those of an important midgap level EC-0.74 eV in CdTe and Cd1-xZnxTe (x<0.1), the materials of choice in today's detector technology. Our findings demonstrate that dislocation-induced defects can degrade charge collection in radiation detectors.

  20. High-Quality Large-Sized Single Crystals of Pb-Doped Bi2Sr2CuO6+δ High-Tc Superconductors Grown with Traveling Solvent Floating Zone Method

    International Nuclear Information System (INIS)

    High quality Pb-doped Bi2Sr2CuO6+δ (Pb-Bi2201) single crystals are grown by the traveling solvent floating zone technique, with dimensions as large as ∼ 50 mm× ∼ 5.0 mm× ∼ 2 mm. The Pb-Bi2201 single crystals with different doping levels are obtained by the annealing process which covers a wide doping range of the overdoped region. We describe in detail the growth and annealing procedures and the characterization and physical property measurements of the Pb-Bi2201 crystals. The availability of these crystals provides a good opportunity to experimentally investigate high-Tc cuprate superconductors, particularly in the overdoped region. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  1. 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.).

  2. 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.).

  3. 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...

  4. 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.

  5. 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

  6. 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.

  7. 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.).

  8. 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.

  9. Electrochemical quartz crystal impedance study on immobilization of glucose oxidase in a polymer grown from dopamine oxidation at an Au electrode for glucose sensing

    International Nuclear Information System (INIS)

    Glucose oxidase (GOD) was codeposited into a polymer grown from oxidation of dopamine (DA) at an Au electrode in a neutral phosphate aqueous solution for the first time. The electrochemical quartz crystal impedance analysis (EQCIA) method was used to monitor the GOD-immobilization process. Effects of concentrations of phosphate buffer, DA and GOD were investigated, and the optimal concentrations were found to be 20.0mM phosphate buffer (pH 7.0), 30.0mM DA and 5.00mgml-1 GOD. A glucose biosensor was thus constructed, and effects of various experimental parameters on the sensor performance, including applied potential, solution pH and electroactive interferents, were examined. At an optimal potential of 0.6V versus the KCl-saturated calomel electrode (SCE), the current response of the biosensor in the selected phosphate buffer (pH 7.0) was linear with the concentration of glucose from 0.05 to 9mM, with a lower detection limit of 3μM (S/N=3), short response time (within 15s) and good anti-interferent ability. The Michaelis constant (Kmapp) was estimated to be 9.6mM. The biosensor exhibited good storage stability, i.e. 96% of its initial response was retained after 7-day storage in the selected phosphate buffer at 4deg. C, and even after another 3 weeks the biosensor retained 86% of its initial response. In addition, the enzymatic specific activity and enzymatic relative activity of the GOD immobilized in the polymer from dopamine oxidation (PFDO) were estimated from the EQCIA method to be 1.43kUg-1 and 3.7%, respectively, which were larger than the relevant values obtained experimentally using poly(o-aminophenol) and poly(N-methylpyrrole) matrices, suggesting that the PFDO is a better matrix to immobilize GOD

  10. Post-growth annealing of Bridgman-grown CdZnTe and CdMnTe crystals for room-temperature nuclear radiation detectors

    International Nuclear Information System (INIS)

    Bridgman-grown cadmium zinc telluride (CdZnTe or CZT) and cadmium manganese telluride (CdMnTe or CMT) crystals often have Te inclusions that limit their performances as X-ray- and gamma-ray-detectors. We present here the results of post-growth thermal annealing aimed at reducing and eliminating Te inclusions in them. In a 2D analysis, we observed that the sizes of the Te inclusions declined to 92% during a 60-h annealing of CZT at 510 °C under Cd vapor. Further, tellurium inclusions were eliminated completely in CMT samples annealed at 570 °C in Cd vapor for 26 h, whilst their electrical resistivity fell by an order of 102. During the temperature-gradient annealing of CMT at 730 °C and an 18 °C/cm temperature gradient for 18 h in a vacuum of 10−5 mbar, we observed the diffusion of Te from the sample, so causing a reduction in size of the Te inclusions. For CZT samples annealed at 700 °C in a 10 °C/cm temperature gradient, we observed the migration of Te inclusions from a low-temperature region to a high one at 0.022 μm/s. During the temperature-gradient annealing of CZT in a vacuum of 10−5 mbar at 570 °C and 30 °C/cm for 18 h, some Te inclusions moved toward the high-temperature side of the wafer, while other inclusions of the same size, i.e., 10 µm in diameter, remained in the same position. These results show that the migration, diffusion, and reaction of Te with Cd in the matrix of CZT- and CMT-wafers are complex phenomena that depend on the conditions in local regions, such as composition and structure, as well as on the annealing conditions

  11. 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.

  12. CdTe X-ray detectors for medical computerized tomography

    International Nuclear Information System (INIS)

    The kinetic and lux-ampere characteristics (BAC) of pure CdTe crystals of p- and n-types used as X-ray detectors for medical tomography are studied. It is shown that proper reproducibility of the excitation pulse form, strict LAC linearity and low photocurrent memary of the detectors with a regquired maintained sensitivity maintained may be attained using semi-insulating cadmium telluride crystals with a low concentration of adhesion centers equal to the concentration of recombination levels. In that case, the detector should operate under the double injection regime

  13. 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.

  14. 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.

  15. 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.

  16. Thermoelectric power and Hall effect measurements in polycrystalline CdTe thin films

    Energy Technology Data Exchange (ETDEWEB)

    Paez, B.A. [Pontificia Univ. Javeriana, Santafe de Bogota (Colombia). Thin Films Group

    2000-07-01

    Polycrystalline CdTe thin films deposited by close space sublimation (CSS), were characterized through thermoelectric power, {alpha}, Hall coefficient, and resistivity, {rho}, measurements in the range of 90 to 400 K. This was in order to determine the scattering mechanisms which mainly affect the electrical transport properties in CdTe thin films. The results were analyzed based on theoretical calculations of {alpha} against temperature. This model includes scattering processes within the grains and at the grain boundaries. Some of the parameters used in this calculation were determined experimentally: grain size, crystal structure, activation energy and effective mass. It is important to state that the main approximations were justified according to experimental measurements. (orig.)

  17. 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

  18. 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

  19. Spatial uniformity of electron charge transport in high resistivity CdTe

    International Nuclear Information System (INIS)

    Electron charge transport in high resistivity CdTe was investigated in terms of drift mobility, charge collection efficiency, and mobility-lifetime product. CdTe devices were produced from material grown by the Travelling Heater Method. Infrared microscopy was used to assess the quality of CdTe wafers, which showed a concentration of bulk defects and tellurium precipitates around the edges of the wafers. Laser-induced time of flight was used to measure the electron drift velocity, which was linear with respect to electric field at field strengths up to 200 V/cm. The measured electron drift mobility was 1040±20 cm2/V s. Ion-beam induced charge (IBIC) imaging of the device cathode was carried out to produce high resolution maps of signal amplitude and electron drift time. Excellent spatial uniformity was observed in the sample, and a value of 6x10-3 cm2/V was measured for the electron mobility-lifetime product

  20. 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

  1. 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.).

  2. Infra-red photodiodes in Hg1-xCdxTe grown by OMVPE

    International Nuclear Information System (INIS)

    Hg1-xCdxTe layers, grown by the organometallic vapor phase epitaxy (OMVPE), are p-type with carrier concentrations around 4 x 1016/cm3 due to the Group II vacancies in them. Following a Hg saturated anneal at 220 degrees C, these layers became n-type with carrier concentrations around 4 x 1014/cm3. In order to fabricate p-n junction diodes, Hg1-xCdxTe layers were grown with a 0.5-0.8 μm thick CdTe cap. By opening windows in this CdTe cap, the underlying Hg1-xCdxTe layer was annealed in a selective manner, thus forming planar p-n junctions. The CdTe cap, which is used as the diffusion barrier for Hg during the selective anneal, also served as the junction passivant for the photodiodes. Details of device fabrication and characterization are presented in this paper

  3. 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

  4. 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

  5. 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.

  6. Electronic structure, structural and optical properties of thermally evaporated CdTe thin films

    International Nuclear Information System (INIS)

    Thin films of CdTe were deposited on glass substrates by thermal evaporation. From the XRD measurements it is found that the films are of zinc-blende-type structure. The lattice parameter was determined as a=6.529A, which is larger than 6.48A of the powder sample, because the recrystallized lattice of the grown films is subjected to a compressive stress aroused as a result of the lattice mismatch and/or differences in thermal expansion coefficient between the CdTe and the underlying substrate. Transmittance, absorption, extinction and refractive coefficients are measured. Electronic structure, band parameters and optical spectra of CdTe were calculated from ab initio studies within the LDA and LDA+U approximations. It is shown that LDA underestimates the band gap, energy levels of the Cd-4d states, s-d coupling and band dispersion. However, it calculates the spin-orbit coupling correctly. LDA+U did not increase much the band gap value, but it corrected the s-d coupling by shifting the Cd-4d levels towards the experimentally determined location and by splitting the LDA-derived single s peak into two peaks, which originates from admixture of s and d states. It is shown that the s-d coupling plays an important role in absorption and reflectivity constants. The calculated optical spectra fairly agree with experimental data. Independent of wave vector scissors operator is found to be a good first approximation to shift rigidly the band gap of CdTe underestimated by LDA

  7. 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.

  8. 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.

  9. 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.

  10. 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)

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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)

  17. 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.

  18. 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...

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. Effects of excitation intensity on photoluminescence of pure CdTe

    International Nuclear Information System (INIS)

    The photoluminescence of high purity n-type CdTe single crystals (n approximately 2.9 x 1014 cm-3) at liquid helium temperature is studied at different excitation intensities. Emissions due to the recombination of free excitons and excitons bound to neutral donors, ionized donors, and neutral acceptors are discussed as well as the transitions of free carriers to various impurities. Other impurity related spectral features are observed within the range of 120 meV from the band edge and their origin is described in analogy to the present knowledge of the spectra of III-V and other II-VI compounds. (author)

  4. Structural study of vapour phase deposited 3,4,9,10-perylene tetracarboxylicacid diimide: Comparison between single crystal and ultra thin films grown on Pt(100)

    International Nuclear Information System (INIS)

    Structural properties of a single crystal and of a thin film of 3,4,9,10-perylene-tetracarboxylic-acid-diimide are compared. The two samples are both obtained from the vapour phase, the latter being deposited at room temperature, in an ultrahigh vacuum environment, on a clean Pt(100) substrate. In the single crystal we have pointed out interactions between adjacent molecules by overlapping of the π systems in the stacks and by hydrogen bonds between neighbouring stacks. The various surface unit cells of the nanocrystals from the film, identified by means of scanning tunnelling microscopy, are not comparable to those expected from the X-ray diffraction study of the single crystal and to those already published for other substrates. This fact clearly highlights the role played by the type of substrate chosen and/or the substrate-molecule interaction that affects the stacking and crystallinity of the growing crystal on top

  5. 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.

  6. 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.

  7. Extended defects in MBE-grown CdTe-based solar cells

    International Nuclear Information System (INIS)

    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)

  8. 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)

  9. 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.

  10. Virtual Crystallizer

    Energy Technology Data Exchange (ETDEWEB)

    Land, T A; Dylla-Spears, R; Thorsness, C B

    2006-08-29

    Large dihydrogen phosphate (KDP) crystals are grown in large crystallizers to provide raw material for the manufacture of optical components for large laser systems. It is a challenge to grow crystal with sufficient mass and geometric properties to allow large optical plates to be cut from them. In addition, KDP has long been the canonical solution crystal for study of growth processes. To assist in the production of the crystals and the understanding of crystal growth phenomena, analysis of growth habits of large KDP crystals has been studied, small scale kinetic experiments have been performed, mass transfer rates in model systems have been measured, and computational-fluid-mechanics tools have been used to develop an engineering model of the crystal growth process. The model has been tested by looking at its ability to simulate the growth of nine KDP boules that all weighed more than 200 kg.

  11. 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.

  12. 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

  13. 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.).

  14. 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.

  15. 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.

  16. The structure and properties of quartz crystals grown from fluoride solutions: Part II. The burgers vector of the growth screw superdislocations

    International Nuclear Information System (INIS)

    The birefringence method is used to investigate the distribution of microstresses around screw superdislocations with a hollow core in quartz crystals and to determine the Burgers vector and core size. The core size was found to be 5 x 10-7 m; this value was confirmed independently by studying the light diffraction on hollow cores in different quartz cuts.

  17. Preparation and characterization of pure and Pr(III)-doped lead chloride single crystals grown by the modified micro-pulling-down method

    Czech Academy of Sciences Publication Activity Database

    Král, Robert; Nitsch, Karel; Jarý, Vítězslav; Yokota, Y.; Futami, F.; Yoshikawa, A.; Nikl, Martin

    2013-01-01

    Roč. 375, JUL (2013), s. 57-61. ISSN 0022-0248 R&D Projects: GA MŠk LH12150 Institutional support: RVO:68378271 Keywords : luminescence * single crystal growth * micro-pulling-down method Subject RIV: CA - Inorganic Chemistry Impact factor: 1.693, year: 2013 http://www.sciencedirect.com/science/article/pii/S0022024813002674

  18. 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.

  19. 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.)

  20. 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.

  1. 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.

  2. 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)

  3. 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...

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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 ...

  10. Research Update: Point defects in CdTe{sub x}Se{sub 1−x} crystals grown from a Te-rich solution for applications in detecting radiation

    Energy Technology Data Exchange (ETDEWEB)

    Gul, R.; Roy, U. N.; Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Hossain, A.; Yang, G.; James, R. B. [Brookhaven National Laboratory, Upton, New York 11973 (United States); Lee, W. [Korea University, Seoul 136-701 (Korea, Republic of); Cui, Y.; Burger, A. [Fisk University, Nashville, Tennessee 37208 (United States)

    2015-04-01

    We investigated cadmium telluride selenide (CdTeSe) crystals, newly grown by the Traveling Heater Method (THM), for the presence and abundance of point defects. Current Deep Level Transient spectroscopy (I-DLTS) was used to determine the energies of the traps, their capture cross sections, and densities. The bias across the detectors was varied from 1 to 30 V. Four types of point defects were identified, ranging from 10 meV to 0.35 eV. Two dominant traps at energies of 0.18 eV and 0.14 eV were studied in depth. Cd vacancies are found at lower concentrations than other point defects present in the material.

  11. 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.

  12. 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.

  13. 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

  14. Enhancement of exchange bias with crystal orientation in NiFe/CoO and CoO/NiFe bilayers grown on MgO(100) and MgO(111)

    International Nuclear Information System (INIS)

    We present the comparative study of the structural and magnetic properties of the NiFe/CoO and CoO/NiFe bilayers grown on both MgO(111) and MgO(100) substrates by using the ion beam sputtering technique. We observed that crystallographic orientation and crystal quality strongly affected the exchange bias properties of the bilayers. The NiFe layers showed fourfold magnetocrystalline anisotropy when we used MgO(100) substrate and uniaxial anisotropy when we used MgO(111) substrate. When the CoO layer is grown on MgO(111) and MgO(100) substrates as a first layer, instead of the NiFe, the increase of the crystalline quality and stoichiometric CoO phase has been achieved so that the exchange bias field increases by five and three times for NiFe/CoO/MgO(111) and NiFe/CoO/MgO(100) systems, respectively. The blocking temperature significantly increases for NiFe/CoO on MgO(111) and (100) substrates, indicating the increase of the stoichiometric stable Co1O1 phase in the exchange-biased system. The magnitude of the exchange bias field is 800 Oe at 10 K for NiFe/CoO/MgO(111) and more than two times as compared to that of NiFe/CoO/MgO(100). This high exchange bias value observed for NiFe/CoO/MgO(111) was explained with the uncompensated spins in CoO(111) surface. We also carried out training effect measurements to observe the durability of the exchange bias for technological applications. - Highlights: • This paper analyses magnetization dynamic of exchange biased of NiFe/CoO thin films. • Exchange bias is enhanced by crystal orientation and quallity. • High exchange bias value observed due to the uncompensated spins in CoO(111) surface

  15. 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.

  16. 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

  17. Temperature dependence of photoluminescence of CdTe

    International Nuclear Information System (INIS)

    Temperature dependences of photoluminescence (PL) spectra of CdTe quantum dots (QDs) in a polymer matrix have been studied. The CdTe QDs in a polymer matrix were prepared by transferring them from an aqueous colloid solution. A long storage of specimens was found to result in a bimodal distribution of CdTe QDs by their size in the polymer matrix. The activation energies of the temperature quenching of photoluminescence bands of CdTe QDs in the polymer matrix that correspond to PL bands produced by QDs with different sizes have been determined. The photoluminescence of investigated specimens was found to have the exciton mechanism, which is confirmed by the temperature dependence of the PL peak position and the dependence of the integral PL intensity on the optical excitation intensity.

  18. 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

  19. 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.

  20. Bifacial configurations for CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Romeo, A. [Scientific and Technological Department, University of Verona, Ca' Vignal 2, Strada Delle Grazie 15, 37134 Verona (Italy); Khrypunov, G. [National Technical University, 61002 Kharkov (Ukraine); Galassini, S. [Medicine and Public Health Department, University of Verona, Ca' Vignal 2, Strada Delle Grazie, 37134 Verona (Italy); Zogg, H. [Thin Film Physics Group, Laboratory for Solid State Physics, ETH, Swiss Federal Institute of Technology, Zuerich, Technoparkstrasse 1, 8005 Zurich (Switzerland); Tiwari, A.N. [Thin Film Physics Group, Laboratory for Solid State Physics, ETH, Swiss Federal Institute of Technology, Zuerich, Technoparkstrasse 1, 8005 Zurich (Switzerland); Department of Electronic and Electrical Engineering, Centre for Renewable Energy Systems and Technology (CREST), Loughborough University, Leicestershire LE11 3TU (United Kingdom)

    2007-09-22

    We present a different back contact for CdTe solar cell by the application of only a transparent conducting oxide (TCO), typically ITO, as a back electrical contact on all-PVD CdTe/CdS photovoltaic devices that acts as a free-Cu stable back contact and at the same time allows to realize bifacial CdTe solar cells, which can be illuminated from either or both sides. Also devices with thin CdTe layers (from {proportional_to}2 {mu}m down to 1 {mu}m) have been prepared to improve the conversion efficiency on the back side illumination, which is limited by the collection of carriers far away from the junction and to reduce the amount of material in the CdTe device. Reproducible solar cells exceeding 10% efficiency on the front side illumination and exceeding 3% on the back side illumination are reported. (author)

  1. 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.

  2. 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.

  3. [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

  4. 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

  5. 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

  6. On anomalous photo- and dark conductivity in semi-insulating CdTe

    International Nuclear Information System (INIS)

    An investigation of photoconductivity of semi-insulating single crystals of CdTe at 77 K has shown that a residual conductivity is noticed in the spectral interval of 0.8-2.0 Mkm. The amount of the residual conductivity depends upon quanta energy and is independent of intensity i.e. the observed residual conductivity has signs of anomalous photoconductivity. The measurement of dark conductivity in these crystals sometimes reveals an increase in conductivity by 4 orders when temperature is decreased from 250 to 77 K. The observed peculiarities are related to large potential fluctuations, the depth of the fluctuations being of the order of half-width of the forbidden zone

  7. 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

  8. 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

  9. Strategies for recycling CdTe photovoltaic modules

    Science.gov (United States)

    Eberspacher, Chris; Gay, Charles F.; Moskowitz, Paul D.

    1994-12-01

    Recycling end-of-life cadmium telluride (CdTe) photovoltaic (PV) modules may enhance the competitive advantage of CdTe PV in the marketplace, but the experiences of industries with comparable Environmental, Health and Safety (EH&S) challenges suggest that collection and recycling costs can impose significant economic burdens. Customer cooperation and pending changes to US Federal law may improve recycling economics.

  10. 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...

  11. 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.

  12. Sputtered CdTe thin film solar cells with Cu2Te/Au back contact

    International Nuclear Information System (INIS)

    In this work, Cu2Te/Au back contact for CdTe thin film solar cells were prepared by vacuum evaporation. Influence of annealing temperature on the structure and electrical properties of Cu2Te films were investigated by field emission scanning electron microscope, X-ray diffraction, and Hall effect measurement. Also, CdS/CdTe thin film solar cells were fabricated by magnetron sputtering process, which is favorable for large area deposition and mass production, and the photovoltaic characteristics were studied. As the annealing temperature was increased, the crystal structure transformed from Cu2Te for as-deposited film to Cu2−xTe hexagonal phase, and the grains in the film became bigger. The electrical resistivity was slightly higher by the annealing. The cell efficiency was significantly improved by the heat treatment, and showed a maximum value of 9.14% at 180 °C. From these results, Cu2Te/Au contact acts as the proper pseudo-ohmic contact onto CdTe film. However, further increase of annealing temperature caused the deterioration of cell performance. - Highlights: • Annealing effects of the vacuum evaporated Cu2Te films were investigated. • The transformation from Cu2Te to Cu2−xTe hexagonal phase occurred by annealing. • The performance of the solar cell was highly increased by annealing at 180 °C. • Cu2Te/Au contact acts as the proper pseudo-ohmic contact onto CdTe film

  13. 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.

  14. 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.

  15. Good electrical contacts for high resistivity (Cd,Mn)Te crystals

    Energy Technology Data Exchange (ETDEWEB)

    Witkowska-Baran,M.; Mycielski, A.; Kochanowska, D.; Szadkowski, A. J.; Jakiela, r.; Witkowska, B.; Kaliszek, W.; Domagala, J.; Lusakowska, E.; Domukhovski, V.; Dybko, K.; Cui, Y.; James, R. B.

    2008-10-19

    We consider that semi-insulating (Cd,Mn)Te crystals may well successfully replace the commonly used (Cd,Zn)Te crystals as a material for manufacturing large-area X- and gamma-ray detectors. The Bridgman growth method yields good quality and high-resistivity (10{sup 9}-10{sup 10} {Omega}-cm) crystals of (Cd,Mn)Te:V. Doping with vanadium ({approx} 10{sup 16} cm{sup -3}), which acts as a compensating agent, and annealing in cadmium vapors, which reduces the number of cadmium vacancies in the as-grown crystal, ensure this high resistivity. Detector applications of the crystals require satisfactory electrical contacts. Hence, we explored techniques of ensuring good electrical contacts to semi-insulating (Cd,Mn)Te crystals. Our findings are reported here. Before depositing the contact layers, we prepared an 'epi-ready' surface of the crystal platelet by a procedure described earlier for various tellurium-based II-VI compound crystals. A molecular beam epitaxy (MBE) apparatus was used to deposit various types of contact layers: Monocrystalline semiconductor layers, amorphous- and nanocrystalline semiconductor layers, and metal layers were studied. We employed ZnTe heavily doped ({approx} 10{sup 18} cm{sup -3}) with Sb, and CdTe heavily doped ({approx} 10{sup 17} cm{sup -3}) with In as the semiconductors to create contact layers that subsequently enable good contact (with a narrow, tunneling barrier) to the Au layer that usually is applied as the top contact layer. We describe and discuss the technology and some properties of the electrical contacts to semi-insulating (Cd,Mn)Te.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. 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.