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Sample records for cd sn te

  1. Cation Exchange Combined with Kirkendall Effect in the Preparation of SnTe/CdTe and CdTe/SnTe Core/Shell Nanocrystals.

    Science.gov (United States)

    Jang, Youngjin; Yanover, Diana; Čapek, Richard Karel; Shapiro, Arthur; Grumbach, Nathan; Kauffmann, Yaron; Sashchiuk, Aldona; Lifshitz, Efrat

    2016-07-01

    Controlling the synthesis of narrow band gap semiconductor nanocrystals (NCs) with a high-quality surface is of prime importance for scientific and technological interests. This Letter presents facile solution-phase syntheses of SnTe NCs and their corresponding core/shell heterostructures. Here, we synthesized monodisperse and highly crystalline SnTe NCs by employing an inexpensive, nontoxic precursor, SnCl2, the reactivity of which was enhanced by adding a reducing agent, 1,2-hexadecanediol. Moreover, we developed a synthesis procedure for the formation of SnTe-based core/shell NCs by combining the cation exchange and the Kirkendall effect. The cation exchange of Sn(2+) by Cd(2+) at the surface allowed primarily the formation of SnTe/CdTe core/shell NCs. Further continuation of the reaction promoted an intensive diffusion of the Cd(2+) ions, which via the Kirkendall effect led to the formation of the inverted CdTe/SnTe core/shell NCs. PMID:27331900

  2. The effect of high-resistance SnO2 on CdS/CdTe device performance

    Science.gov (United States)

    Li, X.; Ribelin, R.; Mahathongdy, Y.; Albin, D.; Dhere, R.; Rose, D.; Asher, S.; Moutinho, H.; Sheldon, P.

    1999-03-01

    In this paper, we have studied the effect of high-resistance SnO2 buffer layers, deposited by low-pressure chemical-vapor deposition, on CdS/CdTe device performance. Our results indicate that when CdS/CdTe devices have a very thin layer of CdS or no CdS at all, the i-SnO2 buffer layer helps to increase device efficiency. When the CdS layer is thicker than 600 Å, the device performance is dominated by CdS thickness, not the i-SnO2 layer. If a very thin CdS layer is to be used to enhance device performance, we conclude that a better SnO2 buffer layer is needed.

  3. Interdiffusion of CdS and Zn2SnO4 layers and its application in CdS/CdTe polycrystalline thin-film solar cells

    International Nuclear Information System (INIS)

    In this work, we found that the interdiffusion of the CdS and Zn2SnO4 (ZTO) layers can occur either at high temperature (550--650oC) in Ar or at lower temperature (400--420oC) in a CdCl2 atmosphere. By integrating a Zn2SnO4 film into a CdS/CdTe solar cell as a buffer layer, this interdiffusion feature can solve several critical issues and improve device performance and reproducibility of both SnO2-based and Cd2SnO4-based CdTe cells. Interdiffusion consumes the CdS film from both the ZTO and CdTe sides during the device fabrication process and improves quantum efficiency at short wavelengths. The ZTO film acts as a Zn source to alloy with the CdS film, which results in increases in the band gap of the window layer and in short-circuit current density Jsc. Interdiffusion can also significantly improve device adhesion after CdCl2 treatment, thus providing much greater process latitude when optimizing the CdCl2 process step. The optimum CdCl2-treated CdTe device has high quantum efficiency at long wavelength, because of its good junction properties and well-passivated CdTe film. We have fabricated a Cd2SnO4/Zn2SnO4/CdS/CdTe cell demonstrating an NREL-confirmed total-area efficiency of 15.8% (Voc=844.3mV, Jsc=25.00mA/cm2, and fill factor=74.82%). This high-performance cell is one of the best thin-film CdTe solar cells in the world

  4. Interdiffusion of CdS and Zn2SnO4 layers and its application in CdS/CdTe polycrystalline thin-film solar cells

    Science.gov (United States)

    Wu, X.; Asher, S.; Levi, D. H.; King, D. E.; Yan, Y.; Gessert, T. A.; Sheldon, P.

    2001-04-01

    In this work, we found that the interdiffusion of the CdS and Zn2SnO4 (ZTO) layers can occur either at high temperature (550-650 °C) in Ar or at lower temperature (400-420 °C) in a CdCl2 atmosphere. By integrating a Zn2SnO4 film into a CdS/CdTe solar cell as a buffer layer, this interdiffusion feature can solve several critical issues and improve device performance and reproducibility of both SnO2-based and Cd2SnO4-based CdTe cells. Interdiffusion consumes the CdS film from both the ZTO and CdTe sides during the device fabrication process and improves quantum efficiency at short wavelengths. The ZTO film acts as a Zn source to alloy with the CdS film, which results in increases in the band gap of the window layer and in short-circuit current density Jsc. Interdiffusion can also significantly improve device adhesion after CdCl2 treatment, thus providing much greater process latitude when optimizing the CdCl2 process step. The optimum CdCl2-treated CdTe device has high quantum efficiency at long wavelength, because of its good junction properties and well-passivated CdTe film. We have fabricated a Cd2SnO4/Zn2SnO4/CdS/CdTe cell demonstrating an NREL-confirmed total-area efficiency of 15.8% (Voc=844.3 mV, Jsc=25.00 mA/cm2, and fill factor=74.82%). This high-performance cell is one of the best thin-film CdTe solar cells in the world.

  5. A comparative study of (ZnO, In2O3: SnO2, SnO2)/CdS/CdTe/(Cu/)Ni heterojunctions

    International Nuclear Information System (INIS)

    The influence of the manufacturing technology on the structural properties of CdTe and CdS layers, components of the CdS/CdTe solar cells, has been investigated. CdTe based solar cells have been prepared using glass substrates coated with different transparent conductive oxides (TCOs: SnO2, In2O3: SnO2 (ITO), ZnO:Al, ZnO:Al/i-ZnO). The analysis of the technology combined with various investigation methods allowed to determine optimum deposition parameters for CdS and CdTe for each type of TCO used. X-ray diffraction (XRD) and grazing incidence XRD analysis have been carried out for TCO, CdS, and CdTe layers at different deposition stages before and after annealing in the presence of CdCl2 in air. The reflection spectra in the 100–600 cm−1 spectral region have been thoroughly studied by using Fourier transform infrared spectroscopy. It was found that (i) the best quality possess CdS and CdTe thin films sequentially deposited on ZnO:Al substrates and that (ii) the pre-treatment defects can be effectively cured and most of the secondary phases can be removed by annealing, while the basic structure of the investigated thin films does not essentially change. - Highlights: ► Deposition technology of CdS and CdTe thin films. ► Slightly improved CdS film quality obtained for deposition on ZnO:Al substrates. ► Improved quality of CdTe deposited on CdS layers grown at high substrate temperature. ► Defects and secondary phases removal as a result of thermal annealing

  6. Sn doped CdTe as candidate for intermediate-band solar cells: A first principles DFT+GW study

    Science.gov (United States)

    Flores, Mauricio A.; Menéndez-Proupin, Eduardo

    2016-05-01

    In this work, we investigate the electronic properties and defect formation energies of Sn doped CdTe combining first principles density-functional theory and many body GW calculations. Due to the Sn dopant, an isolated impurity band is formed in the middle of the forbidden band gap of CdTe allowing the absorption of sub-bandgap photons via an intermediate-band. Our results suggest CdTe:Sn as a promising candidate for the development of third-generation intermediate-band solar cells with theoretical efficiencies up to 63.2%.

  7. Ultrahigh sensitivity and gain white light photodetector based on GaTe/Sn : CdS nanoflake/nanowire heterostructures

    International Nuclear Information System (INIS)

    Optoelectronic diode based on PN heterostructure is one of the most fundamental device building blocks with extensive applications. Here we reported the fabrication and optoelectronic properties of GaTe/Sn : CdS nanoflake/nanowire PN heterojunction photodetectors. With high quality contacts between metal electrodes and Sn : CdS or GaTe, the electrical measurement of GaTe/Sn : CdS hybrid heterojunction under dark condition demonstrates an excellent diode characteristic with well-defined current rectification behavior. The photocurrent increases drastically under LED white light as well as red, green, UV illumination. The on-off ratio of current is about 100 for forward bias and 3000 for reverse bias, which clearly indicates the ultrahigh sensitivity of the heterostructure photodetector to white light. The responsivity and optical gain are determined to be 607 A W−1 and (1.06–2.16) × 105%, which is higher than previous reports of single GaTe or CdS nanostructures. Combination the Ids–Vds curves under different illumination power with energy band diagrams, we assign that both the light modulation effect under forward and reverse bias and the surface molecular oxygen adsorption/desorption mechanism are dominant to the electrical transport behavior of GaTe/Sn : CdS heterojunction. This heterostructure photodetector also shows good stability and fast response speed. Both the high photosensibility and fast response time described in the present study suggest strongly that the GaTe/Sn : CdS hybrid heterostructure is a promising candidate for photodetection, optical sensing and switching devices. (paper)

  8. Interdiffusion of CdS and Zn{sub 2}SnO{sub 4} layers and its application in CdS/CdTe polycrystalline thin-film solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Wu, X.; Asher, S.; Levi, D. H.; King, D. E.; Yan, Y.; Gessert, T. A.; Sheldon, P.

    2001-04-15

    In this work, we found that the interdiffusion of the CdS and Zn{sub 2}SnO{sub 4} (ZTO) layers can occur either at high temperature (550--650{sup o}C) in Ar or at lower temperature (400--420{sup o}C) in a CdCl{sub 2} atmosphere. By integrating a Zn{sub 2}SnO{sub 4} film into a CdS/CdTe solar cell as a buffer layer, this interdiffusion feature can solve several critical issues and improve device performance and reproducibility of both SnO{sub 2}-based and Cd{sub 2}SnO{sub 4}-based CdTe cells. Interdiffusion consumes the CdS film from both the ZTO and CdTe sides during the device fabrication process and improves quantum efficiency at short wavelengths. The ZTO film acts as a Zn source to alloy with the CdS film, which results in increases in the band gap of the window layer and in short-circuit current density J{sub sc}. Interdiffusion can also significantly improve device adhesion after CdCl{sub 2} treatment, thus providing much greater process latitude when optimizing the CdCl{sub 2} process step. The optimum CdCl{sub 2}-treated CdTe device has high quantum efficiency at long wavelength, because of its good junction properties and well-passivated CdTe film. We have fabricated a Cd{sub 2}SnO{sub 4}/Zn{sub 2}SnO{sub 4}/CdS/CdTe cell demonstrating an NREL-confirmed total-area efficiency of 15.8% (V{sub oc}=844.3mV, J{sub sc}=25.00mA/cm{sup 2}, and fill factor=74.82%). This high-performance cell is one of the best thin-film CdTe solar cells in the world.

  9. Interface Study of ITO/ZnO and ITO/SnO2 Complex Transparent Conductive Layers and Their Effect on CdTe Solar Cells

    Directory of Open Access Journals (Sweden)

    Tingliang Liu

    2013-01-01

    Full Text Available Transparent ITO/ZnO and ITO/SnO2 complex conductive layers were prepared by DC- and RF-magnetron sputtering. Their structure and optical and electronic performances were studied by XRD, UV/Vis Spectroscopy, and four-probe technology. The interface characteristic and band offset of the ITO/ZnO, ITO/SnO2, and ITO/CdS were investigated by Ultraviolet Photoelectron Spectroscopy (UPS and X-ray Photoelectron Spectroscopy (XPS, and the energy band diagrams have also been determined. The results show that ITO/ZnO and ITO/SnO2 films have good optical and electrical properties. The energy barrier those at the interface of ITO/ZnO and ITO/SnO2 layers are almost 0.4 and 0.44 eV, which are lower than in ITO/CdS heterojunctions (0.9 eV, which is beneficial for the transfer and collection of electrons in CdTe solar cells and reduces the minority carrier recombination at the interface, compared to CdS/ITO. The effects of their use in CdTe solar cells were studied by AMPS-1D software simulation using experiment values obtained from ZnO, ITO, and SnO2. From the simulation, we confirmed the increase of Eff, FF, Voc, and Isc by the introduction of ITO/ZnO and ITO/SnO2 layers in CdTe solar cells.

  10. Measurement of cross sections producing short-lived nuclei by 14MeV neutron. Cd, Sn, Te, Nd, Gd, Re

    Energy Technology Data Exchange (ETDEWEB)

    Sakane, H.; Yamamoto, H.; Kawade, K. [Nagoya Univ. (Japan); Iida, T.; Takahashi, A.

    1998-03-01

    Nine neutron activation cross sections producing the nuclei with half-lives between 25sec and 22min were measured at energy range between 13.4 and 14.9 MeV by activation method. The (n,p) and (n,{alpha}) reaction cross sections were measured for the isotopes of {sup 110}Cd, {sup 112}Sn, {sup 122}Te, {sup 130}Te and {sup 185}Re and those of {sup 130}Te, {sup 148}Nd and {sup 158}Gd, respectively. The present results were compared with our systematics proposed on the basis of 58 cross section data of (n,p) and 33 data of (n,{alpha}) reaction. Good agreements have been seen between them. (author)

  11. Calculations of low laying energy levels of even-even Cd, Sn and Te isotopes in the “Interacting Boson Model” framework

    OpenAIRE

    S. M. Mostajabodda’vati; Parvaresh, A.; E. Hassanzadeh

    2004-01-01

      The dynamical symmetries in even-even nuclei were investigated by Arima and Iachello in 1974, and led to a model called &quotInteracting Boson Model, (IBM)".   In this article we have outlined some basic ideas used in IBM-1 and carried out the calculations for low laying energy levels of even-even isotopes Cd, Sn and Te via PHINT code.   The calculations for energy and quadra pole moment transitions is done and compared to the available experimental data and IBM -.2 calculations...

  12. 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.

  13. 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)

  14. Investigation of polycrystalline CdZnTe, CdMnTe, and CdTe films for photovoltaic applications

    Energy Technology Data Exchange (ETDEWEB)

    Rohatgi, A.; Ringel, S.A.; Sudharsanan, R. (School of Electrical Engineering, Georgia Inst. of Tech., Atlanta, GA (USA)); Meyers, P.V.; Liu, C.H.; Ramanthan, V. (Ametek Applied Materials Lab., Harleysville, PA (USA))

    1989-10-15

    Polycrystalline thin films of CdZnTe and CdMnTe have been grown by molecular beam epitaxy and metal-organic chemical vapor deposition, respectively, on CdS/SnO{sub 2}/glass substrates, with bandgaps of 1.65-1.75 eV for the top of a two-cell tandem design. P-i-n cells were fabricated and tested using Ni/p{sup +}-ZnTe as a back contact to the ternary films. CdTe cells were also fabricated using both growth techniques, which resulted in 9-10% efficiency and provided a baseline for ternary cell development. It was found that standard CdTe processing (400deg C air annealing) reduces the ternary bandgaps from about 1.7 to about 1.55 eV, resulting in significantly reduced subgap transmission with cell efficiencies of 3-4%. Optimum air-annealing conditions were determined to retain the 1.7 eV bandgaps; however, the cell performance was still limited by both poor CdZnTe/CdS interface quality and high series resistance. The junction interface was found to improve by annealing in the presence of hydrogen, which resulted in V{sub oc} values from 0.500 V to as high as 0.65 V, but the cell performance became increasingly limited by series resistance. The effects of cell processing on the properties of the CdZnTe/CdS interface, the bulk CdZnTe film, and the back-contact region have been investigated to provide guidelines for achieving high efficiency in widegap ternary cells. (orig.).

  15. HgTe-CdTe SUPERLATTICES

    OpenAIRE

    Smith, D.; Mcgill, T.

    1984-01-01

    We report on a theoretical study of the electronic properties of HgTe-CdTe superlattices. The band gap as a function of layer thickness, effective masses normal to the layer plane and tunneling length are compared to the corresponding (Hg, Cd)Te alloys. We find that the superlattice possesses a number of properties that may make it superior to the corresponding alloy as an infrared material.

  16. Electrical and optical properties of magnetron sputtered Cd2SnO4 transparent conducting oxide thin films for use in CdTe solar devices

    International Nuclear Information System (INIS)

    In this study cadmium stannate Cd2SnO4 (CTO), was sputtered onto borosilicate glass under substrate temperatures of ∼ 25 °C (room temp), 200 °C, 300 °C and 400 °C. The CTO films were then annealed in contact with cadmium sulfide (CdS). This annealing process consisted of placing the CTO samples face up in a thermal furnace with a separate piece of CdS film on a borosilicate substrate face down on top of the CTO sample. This arrangement was then heated to a temperature of 600 °C and annealed for one hour. The goal was to fabricate a CTO film with the highest transparency without sacrificing good electrical conductivity. The quality of CTO films, i.e. transparency and electrical conductivity can be greatly affected by processing conditions. In this paper the optical and electrical properties of CTO are investigated before and after thermal annealing to determine the affect of varying process conditions on the quality of the film. Spectroscopic ellipsometry analysis was performed on both as-deposited and annealed CTO to determine the nature of the optical response of the films over the spectral range of 0.73 to 3.34 eV. The electrical properties of the films were examined using both Hall effect data and optical Drude modeling of free carrier absorption. Structural properties of the films were determined from X-ray diffraction data. The result of this investigation is a high quality CTO film with a sheet resistance of ∼ 8 Ω/□. - Highlights: • Cadmium stannate (CTO) is characterized to achieve optimization as a transparent conducting oxide (TCO). • Spectroscopic ellipsometry results were substantiated with other measurements. • Specialized CTO processing yields a TCO film with low sheet resistance

  17. Numerical Analysis of Novel Back Surface Field for High Efficiency Ultrathin CdTe Solar Cells

    OpenAIRE

    M. A. Matin; Tomal, M. U.; Robin, A. M.; Amin, N.

    2013-01-01

    This paper numerically explores the possibility of high efficiency, ultrathin, and stable CdTe cells with different back surface field (BSF) using well accepted simulator AMPS-1D (analysis of microelectronics and photonic structures). A modified structure of CdTe based PV cell SnO2/Zn2SnO4/CdS/CdTe/BSF/BC has been proposed over reference structure SnO2/Zn2SnO4/CdS/CdTe/Cu. Both higher bandgap materials like ZnTe and Cu2Te and low bandgap materials like As2Te3 and Sb2Te3 have been used as BSF ...

  18. Prospects of Back Surface Field Effect in Ultra-Thin High-Efficiency CdS/CdTe Solar Cells from Numerical Modeling

    Directory of Open Access Journals (Sweden)

    Nowshad Amin

    2010-01-01

    Full Text Available Polycrystalline CdTe shows greater promises for the development of cost-effective, efficient, and reliable thin film solar cells. Results of numerical analysis using AMPS-1D simulator in exploring the possibility of ultrathin, high efficiency, and stable CdS/CdTe cells are presented. The conventional baseline case structure of CdS/CdTe cell has been explored with reduced CdTe absorber and CdS window layer thickness, where 1 μm thin CdTe and 50 nm CdS layers showed reasonable efficiencies over 15%. The viability of 1 μm CdTe absorber layer together with possible back surface field (BSF layers to reduce minority carrier recombination loss at the back contact in ultra thin CdS/CdTe cells was investigated. Higher bandgap material like ZnTe and low bandgap materials like Sb2Te3 and As2Te3 as BSF were inserted to reduce the holes barrier height in the proposed ultra thin CdS/CdTe cells. The proposed structure of SnO2/Zn2SnO4/CdS/CdTe/As2Te3/Cu showed the highest conversion efficiency of 18.6% (Voc = 0.92 V, Jsc = 24.97 mA/cm2, and FF = 0.81. However, other proposed structures such as SnO2/Zn2SnO4/CdS/CdTe/Sb2Te3/Mo and SnO2/Zn2SnO4/CdS/CdTe/ZnTe/Al have also shown better stability at higher operating temperatures with acceptable efficiencies. Moreover, it was found that the cells normalized efficiency linearly decreased with the increased operating temperature with relatively lower gradient, which eventually indicates better stability of the proposed ultra thin CdS/CdTe cells.

  19. 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.

  20. Thin-film CdS/CdTe solar cells

    International Nuclear Information System (INIS)

    A thin-film solar cell with the configuration soda-lime glass ITO/CdS/CdTe/Au was reported earlier to have more than 10% conversion efficiency. To further improve the low-cost potential of the device, an SnO/sub 2/ layer was developed to replace ITO, and a new contact to CdTe using Ni or stainless steel to replace Au. The contact also improves the stability of the device. A low-cost method for monolithic integration of these cells to make a module is discussed. By this method, a module of 32 cm/sup 2/ area and 8.5% efficiency was fabricated. A simple and effective ''cross-cut'' method for minimizing the effects of shorting defects is also described

  1. Cd Te polycrystalline films grown by double process close-space vapor transport technique

    International Nuclear Information System (INIS)

    The characteristics of the Cd Te polycrystalline films grown by the new technique of double process-close-space vapor transport technique are presented. This process can be divided in two steps: at the first step, a graphite source boat packed with Cd Te powder act as the Cd Te source and other graphite block with or without Corning glass cover is used as auxiliary substrate. At the second step, the film deposited in the first step over graphite block or Corning glass is used as Cd Te source. Different substrates were used to obtain polycrystalline Cd Te films. we describe the oxygen and temperature influences on the structural and the morphological properties of different films: Cd Te/glass, Cd Te/SnO2/glass and Cd Te/CdS/SnO2/ glass. (Author)

  2. In situ oxygen incorporation and related issues in CdTe/CdS photovoltaic devices.

    OpenAIRE

    Emziane, M.; Durose, K; Halliday, D.P.; Bosio, A; Romeo, N.

    2006-01-01

    CdTe/CdS/SnO2/ITO:F solar cell devices were investigated using quantitative secondary ion mass spectrometry (SIMS) depth profiling. They were grown on sapphire substrates and potentially active impurity species were analyzed. The SIMS data were calibrated for both CdS window layer (grown by sputtering) and CdTe absorber layer (deposited by close-space sublimation). For comparison, some of the samples were grown with and without oxygen incorporation into the CdTe layer during its deposition, a...

  3. X-ray standing wave study of CdTe/MnTe/CdTe(001) heterointerfaces

    OpenAIRE

    Boulliard, Jean-Claude; Capelle, Bernard; Gualandris, Stéphane; Lifchitz, Alain; Cibert, Joel; Tatarenko, Serge

    1997-01-01

    The x-ray standing wave method is used to investigate some crystallographic features of the first stages of growth of ultrathin pseudomorphic MnTe(001) strained layers buried in CdTe on CdTe(001) substrates. Experiments with 004 and 113 reflecting planes show evidence of the presence of both MnTe clusters and diluted CdMnTe alloy.

  4. The system SnTe-InSe

    International Nuclear Information System (INIS)

    This paper discusses the nature of the interaction and physicochemical properties of the alloys of the system SnTe-InSe. The DTA was performed on an NTR-74 pyrometer, XPA on a Dron-2.0 diffractometer and MSA on an MIM-7 metallographic microscope. The microhardness of the samples was determined on a PMT-3 microhardness tester. The congruently melting compound SnInTeSe and solid solutions based on the starting components are formed in the system

  5. Facile method to prepare CdS nanostructure based on the CdTe films

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • CdS nanostructure is directly fabricated on CdTe film only by heating treatment under H2S/N2 mixed atmosphere at a relatively low temperature (450 °C) with gold layer as the intermediate. • Nanostructure of CdS layer, varying from nanowires to nanosheets, may be controlled by the thickness of gold film. • The change of morphology adjusts its luminescence properties. - Abstract: Nanostructured cadmium sulfide (CdS) plays critical roles in electronics and optoelectronics. In this paper, we report a method to fabricate CdS nanostructure directly on CdTe film, via a thermal annealing method in H2S/N2 mixed gas flow at a relatively low temperature (450 °C). The microstructure and optical properties of CdS nanostructure are investigated by X-ray diffraction, transmission electron microscopy, Raman, and photoluminescence. The morphology of CdS nanostructure, evolving from nanowires to nanosheets, can be controlled by the thickness of Au film deposited on the CdTe film. And CdS nanostructures are single crystalline with the hexagonal wurtzite structure. Raman spectroscopy under varying the excitation wavelengths confirm that synthesized CdS-CdTe films contain two layers, i.e., CdS nanostructure (top) and CdTe layer (bottom). The change of morphology modifies its luminescence properties. Obviously, through simply thermal annealing in H2S/N2 mixed gas, fabricating CdS nanostructure on CdTe film can open up the new possibility for obtaining high efficient CdTe solar cell

  6. HgCdTe/CdTe multiple quantum wells

    International Nuclear Information System (INIS)

    This paper reports on HgCdTe/CdTe multiple quantum wells by molecular beam epitaxy which show room temperature photoluminescence and sharp absorption steps at mid-infrared wavelengths. Quantitative chemical mapping, performed by transmission electron microscopy, indicates minimal interdiffusion during growth. Annealing experiments performed at higher temperatures show that the interdiffusion coefficient is a strong function of the depth of the interface below the surface. Absorption spectra have been accurately modeled with a square well/envelope function approach. The films have been used to passively mode lock color center lasers and produce pulses as short as 120 fsec near 2.7 μm

  7. PbSnTe injection lasers

    International Nuclear Information System (INIS)

    Carrier confined homostructure PbSnTe lasers were developed and investigated. In this laser structure good electrical and optical confinement can be achieved by a suitable carrier concentration profile. The advantage of these lasers over PbSnTe heterostructure lasers is the perfect lattice matching between the various layers of the structure. The desired carrier concentration profile was achieved by the growth of several epitaxial layers by the LPE method on a suitable substrate. The performance of these lasers was compared with that of previous homostructure and double heterostructure lasers. (H.K.)

  8. Thermodynamic investigations of CdTe-HgTe solid solutions

    Energy Technology Data Exchange (ETDEWEB)

    Nasar, A.; Shamsuddin, M. (Dept. of Metallurgical Engineering, Banaras Hindu Univ., Varanasi (India))

    1991-08-10

    The activity of CdTe in pseudobinary CdTe-HgTe solid solution (with CdTe added in 10 mol.% increments) has been determined in the temperature range 735-840 K by an electrochemical technique using LiCl-KCl+5 wt.% CdCl{sub 2} as the molten salt electrolyte. The activity of HgTe has been calculated by Gibbs-Duhem integration using the {alpha} function. From the e.m.f. values measured at different temperatures, various partial and excess thermodynamic quantities, namely {Delta}anti G{sup M}{sub CdTe}, {Delta}anti H{sup M}{sub CdTe}, {Delta}anti S{sup XS}{sub CdTe}, {Delta}anti G{sup XS}{sub CdTe} and {Delta}anti S{sup XS}{sub CdTe}, have been obtained. The corresponding thermodynamic parameters for HgTe have also been computed. The integral molar properties of the solid solutions have been estimated from the partial quantities of the two components, CdTe and HgTe. (orig.).

  9. Electrodeposited CdTe and HgCdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Basol, B.M.

    1988-01-15

    The processing steps necessary for producing high efficiency electrodeposited CdTe and HgCdTe solar cells are described. The key step in obtaining solar cell grade p-type CdTe and HgCdTe is the 'type conversion-junction formation' (TCJF) process. The TCJF process involves the heat treatment of the as-deposited n-type CdTe and HgCdTe layers at around 400 /sup 0/C. This procedure converts these n-type films into high resistivity p type and forms a rectifying junction between them and the underlying n-type window layers. Possible effects of oxygen on the TCJF process are discussed. The results of studies made on the structural, electrical and optical properties of the electrodeposited CdS, CdTe and HgCdTe films are presented. The resistivity of the electrodeposited HgCdTe can be made lower than that of CdTe. Consequently, solar cells made using the HgCdTe films have, on the average, better fill factors than those made using the CdTe layers, HgCdTe is also attractive for tandem-cell applications because of its variable band gap which can be easily tuned to the desired value. CdS/CdTe and CdS/HgCdTe heterojunction solar cells with 10.3% and 10.6% efficiency have been demonstrated using electrodeposition techniques and the TCJF process.

  10. 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)

  11. The interaction of laser generated methyl radicals with Cd, Te, and CdTe surfaces

    International Nuclear Information System (INIS)

    The mechanism of the interaction of methyl radicals with Cd, Te, and CdTe surfaces has been studied in ultrahigh vacuum by Auger electron spectroscopy and thermal desorption mass spectrometry. Methyl radicals generated by the laser photodissociation of acetone at 193 nm efficiently etch both Te and Te-rich CdTe surfaces. However, there is no evidence for reaction of methyl radicals with Cd or stoichiometric CdTe. A temperature dependence in the rate of methyl radical etching of Te-rich CdTe is related to a competition between acetone scavenging of radicals on the surface and reaction of radicals to form volatile metalorganics. Acetone itself has a small but finite reaction probability with Te and Te-rich CdTe surfaces

  12. Numerical Analysis of Novel Back Surface Field for High Efficiency Ultrathin CdTe Solar Cells

    Directory of Open Access Journals (Sweden)

    M. A. Matin

    2013-01-01

    Full Text Available This paper numerically explores the possibility of high efficiency, ultrathin, and stable CdTe cells with different back surface field (BSF using well accepted simulator AMPS-1D (analysis of microelectronics and photonic structures. A modified structure of CdTe based PV cell SnO2/Zn2SnO4/CdS/CdTe/BSF/BC has been proposed over reference structure SnO2/Zn2SnO4/CdS/CdTe/Cu. Both higher bandgap materials like ZnTe and Cu2Te and low bandgap materials like As2Te3 and Sb2Te3 have been used as BSF to reduce minority carrier recombination loss at the back contact in ultra-thin CdTe cells. In this analysis the highest conversion efficiency of CdTe based PV cell without BSF has been found to be around 17% using CdTe absorber thickness of 5 μm. However, the proposed structures with different BSF have shown acceptable efficiencies with an ultra-thin CdTe absorber of only 0.6 μm. The proposed structure with As2Te3 BSF showed the highest conversion efficiency of 20.8% ( V,  mA/cm2, and . Moreover, the proposed structures have shown improved stability in most extents, as it was found that the cells have relatively lower negative temperature coefficient. However, the cell with ZnTe BSF has shown better overall stability than other proposed cells with temperature coefficient (TC of −0.3%/°C.

  13. Time-Resolved Photoluminescence Spectroscopy Evaluation of CdTe and CdTe/CdS Quantum Dots

    OpenAIRE

    Yuan, Zhimin; Yang, Ping; Cao, Yongqiang

    2012-01-01

    CdTe and CdTe/CdS quantum dots (QDs) were prepared in aqueous solutions using thioglycolic acid as a stabilizing agent. The photoluminescence (PL) wavelength of the QDs depended strongly on the size of CdTe cores and the thickness of CdS shells. Being kept at room temperature for 130 days, the PL wavelength of CdTe and CdTe/CdS QDs was red-shifted. However the red-shifted degree of CdTe QDs is larger than that of CdTe/CdS QDs. The size of CdTe QDs and the thickness of CdS play important roles...

  14. Pathways toward higher performance CdS/CdTe devices: Te exposure of CdTe surface before ZnTe:Cu/Ti contacting

    International Nuclear Information System (INIS)

    Many studies of thin-film CdS/CdTe photovoltaic devices have suggested that performance may be improved by reducing recombination due to Te-vacancy (VTe), Te antisite (TeCd), or Te-interstitial (Tei) defects. Although formation of these intrinsic defects is likely influenced by CdTe deposition parameters, it may be also coupled to the formation of beneficial cadmium vacancy (VCd) defects. In this study, we expose the CdTe surface to Te vapor prior to ZnTe:Cu/Ti contact-interface formation with the goal of reducing VTe without significantly reducing VCd. Initial results show that when this modified contact is used on a CdCl2-treated CdS/CdTe device, poorer device performance results. This suggests two things: First, the amount of free-Te available during contact formation (either from chemical etching or CuxTe or ZnTe deposition) may be a more important parameter to device performance than previously appreciated. Second, if processes have been used to reduce the effect of VTe (e.g., oxygen and chlorine additions), adding even a small amount of Te may produce detrimental defects. - Highlights: ► Te exposure of CdS/CdTe back contact reduces device performance. ► Field strength and minority carrier lifetime reduced. ► Calculations suggest formation of Te on Cd antisite defect

  15. S and Te inter-diffusion in CdTe/CdS hetero junction

    Energy Technology Data Exchange (ETDEWEB)

    Enriquez, J. Pantoja [Cuerpo Academico-Energia y Sustentabilidad, Universidad Politecnica de Chiapas, Eduardo J. Selvas S/N, Col. Magisterial, Tuxtla Gutierrez 29010, Chiapas (Mexico); Gomez Barojas, E. [CIDS-ICUAP, Apdo. Postal 1651, 72000 Puebla (Mexico); Silva Gonzalez, R.; Pal, U. [Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, Puebla (Mexico)

    2007-09-22

    Effects of post formation thermal annealing of the CdTe-CdS device on the inter-diffusion of S and Te at the junction in a substrate configuration device have been studied by Auger electron spectroscopy. While the migration of S and Te atoms increases with annealing temperature, the extent of S diffusion is always higher than the diffusion of Te atoms. Inter-diffusion of S and Te causes the formation of CdTe{sub 1-x}S{sub x} ternary compound at the CdTe-CdS interface. (author)

  16. RAMAN SCATTERING AND EXCITATION SPECTROSCOPY IN CdTe/CdMnTe SUPERLATTICES

    OpenAIRE

    Viña, L.; Chang, L; J. Yoshino

    1987-01-01

    We have observed oscillatory structure in the excitation spectra of CdTe/CdxMN1-xTe superlattices. A comparison of these spectra with conventional Raman spectra shows that the structures correspond to first and higher order LO-phonons of the CdTe wells and the CdTe/CdxMn1-xTe barriers, as well as combination of them. A strong enhancement in Resonance Raman scattering of both the CdTe and the CdMnTe phonons, at the energy of the heavy-hole exciton of the superlattice, suggests a small valence-...

  17. Aluminum doping of CdTe polycrystalline films starting from the heterostructure CdTe/Al

    OpenAIRE

    Becerril, M.; O. Vigil-Galán; G. Contreras-Puente; O. Zelaya-Angel

    2011-01-01

    Aluminum doped CdTe polycrystalline films were obtained from the heterostructure CdTe/Al/Corning glass. The aluminum was deposited by thermal vacuum evaporation and the CdTe by sputtering of a CdTe target. The aluminum was introduced into the lattice of the CdTe from a thermal annealed to the CdTe/Al/Corning glas heterostructure. The electrical, structural, nd optical properties were analyzed as a function of the Al concentrations. It found that when Al is incorporated, the electrical resisti...

  18. Nonradiative recombination processes in (CdTe, CdCrTe)/CdMgTe quantum well structures

    International Nuclear Information System (INIS)

    Photoluminescence transitions in (CdTe,CdCrTe)/CdMgTe structure grown by molecular beam epitaxy are studied. Photoluminescence investigations show a very strong reduction of the photoluminescence intensity from chromium doped quantum wells. We explain this fact by a very efficient nonradiative recombination in the chromium-doped quantum wells. The present results indicate that the Auger-type energy transfer from excitons to chromium ions is responsible for the photoluminescence deactivation. The efficiency of this process is evaluated. (author)

  19. Study of CdTe and HgCdTe thin films obtained by electrochemical methods

    International Nuclear Information System (INIS)

    Cadmium telluride polycrystalline thin films were fabricated on SnO2-coated glass substrates by potentiostatic electrodeposition and characterized by X-ray diffraction, energy dispersive X-ray analyses (EDAX), optical and electrical measurements. The films dseposited at potentials more positive than -0.65 V vs.SCE were p-type but those deposited at more negative potentials were n-type. All CdTe thin films showed a band-gap energy about 1.45 eV and a large absorption coeffici-ent (a=105 cm-1) above de band edge. The addition of even small amounts of mercury to the CdTe produces higuer conductivity values and lower band-gap energies. We have prepared HgCdTe thin films where the band-gap energies ranged between 0.93 and 0.88 eV depending on the ratio of mercury to cadmium. Heat treatment at 3000C increases the crystalline diameter and alter the composition of the electrodeposited films, a decrease of the resistivity values was also observed. (Author)

  20. 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.).

  1. Recycling of CdTe photovoltaic waste

    Science.gov (United States)

    Goozner, Robert E.; Long, Mark O.; Drinkard, Jr., William F.

    1999-01-01

    A method for extracting and reclaiming metals from scrap CdTe photovoltaic cells and manufacturing waste by leaching the waste with a leaching solution comprising nitric acid and water, skimming any plastic material from the top of the leaching solution, separating the glass substrate from the liquid leachate and electrolyzing the leachate to separate Cd from Te, wherein the Te is deposits onto a cathode while the Cd remains in solution.

  2. Gamma spectrometric characterization of various CdTe and CdZnTe detectors

    CERN Document Server

    Arlt, R; Sumah, P

    1999-01-01

    CdZnTe and CdTe detectors are now used by the Department of Safeguards of the International Atomic Energy Agency in significant numbers. To prepare, plan and support various verification methods, their properties must be well characterized and understood. In this paper we present some of the results which were obtained with large volume hemispheric CdZnTe detectors and high-resolution CdTe detectors.

  3. 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)

  4. CdTe/CdS solar cells with transparent contacts

    Energy Technology Data Exchange (ETDEWEB)

    Birkmire, R.W.; McCandless, B.E.; Shafarman, W.N.

    1988-01-15

    Evaporated CdTe/CdS solar cells with a transparent Cu-indium tin oxide contact have been made with an efficiency greater than 8.5%. The deposition of single-phase CdTe films from a compound source required a cadmium-to-tellurium flux ratio of 1.7 incident on the substrate. To obtain the needed p-type conductivity of the CdTe films required a high temperature heat treatment in air which reduced the transmission through the CdTe film owing to the formation of a CdTeO/sub 3/ surface layer. The heating and cooling rates used for the heat treatment affected the open-circuit voltage and contact resistance of the cells. The total subband gap absorption of the entire cell is 40%-50%.

  5. New Architecture towards Ultrathin CdTe Solar Cells for High Conversion Efficiency

    Directory of Open Access Journals (Sweden)

    A. Teyou Ngoupo

    2015-01-01

    Full Text Available Solar Cell Capacitance Simulator in 1 Dimension (SCAPS-1D is used to investigate the possibility of realizing ultrathin CdTe based solar cells with high and stable conversion efficiency. In the first step, we modified the conventional cell structure by substituting the CdS window layer with a CdS:O film having a wide band gap ranging from 2.42 to 3.17 eV. Thereafter, we simulated the quantum efficiency, as well as the parameters of J-V characteristics, and showed how the thickness of CdS:O layer influences output parameters of Glass/SnO2/ZTO/CdS:O/CdTe1-xSx/CdTe/Ni reference cell. High conversion efficiency of 17.30% has been found using CdTe1-xSx (x=0.12 and CdTe layers of thickness 15 nm and 4 μm, respectively. Secondly, we introduced a BSR layer between the absorber layer and back metal contact, which led to Glass/SnO2/ZTO/CdS:O/CdTe1-xSx/CdTe/BSR/Ni configuration. We found that a few nanometers (about 5 nm of CdTe1-xSx layer is sufficient to obtain high conversion efficiency. For BSR layer, different materials with large band gap, such as ZnTe, Cu2Te, and p+-CdTe, have been used in order to reduce minority carrier recombination at the back contact. When ZnTe is used, high conversion efficiency of 21.65% and better stability are obtained, compared to other BSR.

  6. Tellurium antisites in CdZnTe

    Science.gov (United States)

    Chu, Muren; Terterian, Sevag; Ting, David; James, Ralph B.; Erickson, Jay C.; Yao, H. Walter; Lam, Terrance T.; Szawlowski, Marek; Szczebiot, Richard W.

    2001-12-01

    The n-type conduction of CdTe and Cd0.96Zn0.04Te crystals grown from melts with excess tellurium indicates that the origin of the donors with an energy level at 0.01 eV below the conduction band are most likely singly ionized tellurium antisites instead of cadmium interstitials. Based on this model, the deep level at 0.75 eV below the conduction band is therefore doubly ionized tellurium antisites. After increasing the zinc content over 7%, CdZnTe turns to p-type. The conduction type variation of CdZnTe crystals as a function of zinc contents is explained by the compensation between the donors of Te-antisites and the acceptors of Cd vacancies. High resitivity Cd0.9Zn0.1Te crystals are produced by compensating the p-type crystals with indium at a low doping level of 1- 5x1015 cm-3. At room temperature, the high yield CdZnTe radiation detectors can resolve the six low energy peaks from the Am241 source, a performance comparable to the best reported CdZnTe detectors.

  7. Dislocation reduction in HgCdTe grown on CdTe/Si

    Science.gov (United States)

    Wijewarnasuriya, Priyalal S.

    2016-05-01

    Bulk-grown CdZnTe (Zn = 3%) substrates are the natural choice for HgCdTe epitaxy since it is lattice matched to long wave LW-HgCdTe alloy. However, lack of large area CdZnTe substrates, high production costs, and more importantly, the difference in thermal expansion coefficients between CdZnTe and silicon Read out Integrated Circuits (ROIC) are some of the inherent drawbacks of CdZnTe substrates. Consequently, Hg1-xCdxTe detectors fabricated on silicon substrates are an attractive alternative. Recent developments in the molecular beam epitaxy (MBE) buffer layer growth technology on Si substrates has revolutionized the HgCdTe research and offered a new dimension to HgCdTe-based IR technology. Si substrates provide advantages in terms of relatively large area (3 to 6-inch diameter is easily obtained) compared to CZT substrate materials, durability during processing, and reliability to thermal cycling. Innovations in Si-based composite substrates made it possible to fabricate very large-format IR arrays that offer higher resolution, low-cost arrays and more dies per wafer. Between Si substrates and HgCdTe has large lattice mismatch of 19%. This leads to dislocation densities of low-107 cm-2 for optimal growth of HgCdTe on silicon-based substrates as compared to the mid-104 cm-2 dislocation density of HgCdTe grown on CdZnTe. This paper present dislocation reduction by two orders of magnitude using thermal cycle anneal under Hg environment on HgCdTe grown on Si substrates and as well as defect reduction in Cd(Se)Te buffer layers grown on Si Substrates.

  8. 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.

  9. Particulate contacts to Si and CdTe: Al, Ag, Hg-Cu-Te, and Sb-Te

    Science.gov (United States)

    Schulz, Douglas L.; Ribelin, Rosine; Curtis, Calvin J.; Ginley, David S.

    1999-03-01

    Our team has been investigating the use of particle-based contacts in both Si and CdTe solar cell technologies. First, in the area of contacts to Si, powders of Al and Ag prepared by an electroexplosion process have been characterized by transmission electron microscopy (TEM), TEM elemental determination X-ray spectroscopy (TEM-EDS), and TEM electron diffraction (TEM-ED). These Al and Ag particles were slurried and tested as contacts to p- and n-type silicon wafers, respectively. Linear current-voltage (I-V) was observed for Ag on n-type Si, indicative of an ohmic contact, whereas the Al on p-type Si sample was non-ideal. A wet-chemical surface treatment was performed on one Al sample and TEM-EDS indicated a substantial decrease in the O contaminant level. The treated Al on p-type Si films exhibited linear I-V after annealing. Second, in the area of contacts to CdTe, particles of Hg-Cu-Te and Sb-Te have been applied as contacts to CdTe/CdS/SnO2 heterostructures prepared by the standard NREL protocol. First, Hg-Cu-Te and Sb-Te were prepared by a metathesis reaction. After CdCl2 treatment and NP etch of the CdTe layer, particle contacts were applied. The Hg-Cu-Te contacted cells exhibited good electrical characteristics, with Voc>810 mV and efficiencies > 11.5% for most cells. Although Voc>800 mV were observed for the Sb-Te contacted cells, efficiencies in these devices were limited to 9.1% presumably by a large series resistance (>20 Ω) observed in all samples.

  10. 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.

  11. 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.

  12. 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.

  13. CdTe thin film solar cells with reduced CdS film thickness

    International Nuclear Information System (INIS)

    A study was performed to reduce the CdS film thickness in CdTe thin film solar cells to minimize losses in quantum efficiency. Using close space sublimation deposition for CdS and CdTe a maximum efficiency of ∼ 9.5% was obtained with the standard CdS film thickness of ∼ 160 nm. Reduction of the film CdS thickness to less than 100 nm leads to poor cell performance with ∼ 5% efficiency, mainly due to a lower open circuit voltage. An alternative approach has been tested to reduce the CdS film thickness (∼ 80 nm) by depositing a CdS double layer. The first CdS layer was deposited at high substrate temperature in the range of 520-540 deg. C and the second CdS layer was deposited at low substrate temperature of ∼ 250 deg. C. The cell prepared using a CdS double layer show better performance with cell efficiency over 10%. Quantum efficiency measurement confirmed that the improvement in the device performance is due to the reduction in CdS film thickness. The effect of double layer structure on cell performance is also observed with chemical bath deposited CdS using fluorine doped SnO2 as substrate.

  14. Electrical properties of CdS/CdTe heterojunctions

    Science.gov (United States)

    Chu, T. L.; Chu, Shirley S.; Ang, S. T.

    1988-08-01

    The electrical properties of n-CdS/p-CdTe heterojunctions depend strongly on the cleanliness of the interface region. In this work, CdTe films were deposited on CdS/glass substrates by close-spaced sublimation (CSS) under various conditions. The dark current-voltage characteristics of the resulting heterojunctions were measured over a wide temperature range, and the capacitance-voltage characteristics were measured in the dark and under illumination. When the CdS surface is in situ cleaned prior to the deposition of the CdTe film, the current transport across the junction is controlled by a thermally activated process. Tunneling makes an important contribution to the interface recombination at temperatures below room temperature when the in situ cleaning of CdS is not used. The dark capacitance of CdS/CdTe heterojunctions prepared with in situ etching is essentially independent of the reverse bias due to intrinsic interface states. Under white light illumination, the 1/C 2 vs V relation is nearly linear. The CdS/CdTe heterojunctions without in situ cleaning showed different 1/C 2 vs V relations due to higher density of interface states. The in situ cleaning also has pronounced effects on the frequency dependence of dark and illuminated capacitances. Using the in situ cleaning technique, solar cells of about 1 cm2 area have achieved an AM 1.5 (global) efficiency of about 10.5%.

  15. Electrical properties of CdS/CdTe heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Chu, T.L.; Chu, S.S.; Ang, S.T.

    1988-08-01

    The electrical properties of n-CdS/p-CdTe heterojunctions depend strongly on the cleanliness of the interface region. In this work, CdTe films were deposited on CdS/glass substrates by close-spaced sublimation (CSS) under various conditions. The dark current-voltage characteristics of the resulting heterojunctions were measured over a wide temperature range, and the capacitance-voltage characteristics were measured in the dark and under illumination. When the CdS surface is in situ cleaned prior to the deposition of the CdTe film, the current transport across the junction is controlled by a thermally activated process. Tunneling makes an important contribution to the interface recombination at temperatures below room temperature when the in situ cleaning of CdS is not used. The dark capacitance of CdS/CdTe heterojunctions prepared with in situ etching is essentially independent of the reverse bias due to intrinsic interface states. Under white light illumination, the 1/C /sup 2/ vs V relation is nearly linear. The CdS/CdTe heterojunctions without in situ cleaning showed different 1/C /sup 2/ vs V relations due to higher density of interface states. The in situ cleaning also has pronounced effects on the frequency dependence of dark and illuminated capacitances. Using the in situ cleaning technique, solar cells of about 1 cm/sup 2/ area have achieved an AM 1.5 (global) efficiency of about 10.5%.

  16. (112)面CdTe/Cd1-yZnyTe,Hg1-xCdxTe/CdTe和CdTe/GaAs异质结的方向倾斜%Oriental Shift at CdTe/Cd1-yZnyTe, Hg1-xCdxTe/CdTe and CdTe/GaAs Heterojunctions Grown on (112) plane

    Institute of Scientific and Technical Information of China (English)

    刘义族; 于福聚

    2001-01-01

    用X射线双晶衍射(XDCD)法测得分子束外延(MBE)法生长的CdTe/Cd0.959Zn0.041Te(112)B异质结的倾斜角为0.2185°,而且朝[1-1-1]晶体学方向倾斜.为了获得较精确的倾斜角值,绘制了外延层和衬底衍射角的差值Δθ与绕样品表面法线旋转的角度φ之间的准正弦函数.为高分辨率透射电子显微镜(HRTEM)分析制备了MBE法生长的Hg0.535Cd0.465Te/CdTe/GaAs(1-12)B多层异质结的横截面薄膜. CdTe/GaAs异质结的HRTEM明场象表明CdTe(1-12)缓冲层相对于GaAs(1-12)衬底朝[1-1 1-]方向倾斜约3°,并且在Hg0.535Cd0.465Te/CdTe异质结,Hg0.535Cd0.465Te(1-12)外延膜相对于CdTe(1-12)缓冲层在[1 1-1]方向,即[1-1 1-]的反方向倾斜约1°.也分析了Hg0.535Cd0.465Te/CdTe/GaAs多层膜之间的倾斜角关系.

  17. Cyclotron resonance excitation spectroscopy of CdTe and of CdTe/CdZnTe quantum wells

    Science.gov (United States)

    Lavigne, B.; Cox, R. T.

    1990-04-01

    Photoconductivity spectra for II-VI semiconductor samples were obtained without any need for electrical contacts by measuring the wavelength dependence of free-carrier cyclotron resonance at 35 GHz. For bulk CdTe, the surprisingly efficient creation of free electrons for h v below the bandgap energy is attributed to exciton-impurity interactions. Auger recombination and inelastic polariton-donor scattering are considered. Preliminary results for CdTe.CdZnTe quantum wells show sharp peaks corresponding to quantized states of free excitons in the well.

  18. n-(CdMgTe/CdTe)/(p-(CdTe/ZnCdTe/ZnTe)/p-GaAs heterostructure diode for photosensor applications

    Science.gov (United States)

    Yahia, I. S.; AlFaify, S.; Abutalib, M. M.; Chusnutdinow, S.; Wojtowicz, T.; Karczewski, G.; Yakuphanoglu, F.; Al-Bassam, A.; El-Naggar, A. M.; El-Bashir, S. M.

    2016-05-01

    High quality n-(CdMgTe:I/n-CdTe:I)/(p-CdTe:N/p-ZnCdTe:N/p-ZnTe:N)/p-GaAs heterojunction diodes have been fabricated by molecular beam epitaxial growth. The illumination effect on the complex impedance and conductivity of heterostructure diode was investigated. The illumination intensities were taken up to the 200 mW/cm2 with frequency range of 42 Hz to 1 MHz. The observed real and imaginary parts of the complex impedance were strongly dependent on the illumination frequency. The inverse relation was observed between the illumination intensity and the complex impedance. The relaxation mechanism of the diode was analyzed by the Cole-Cole plots. The radius of the Cole-Cole curve decreases with increasing illumination intensity. This suggests a mechanism of illumination dependent on the relaxation process. It is also found that the conductivity increases linearly with increasing the illumination intensity. We can conclude that the new design heterostructure diode in our work is a good candidate in photodetector and optoelectronic applications.

  19. Wide bandgap thin film solar cells from CdTe alloys

    International Nuclear Information System (INIS)

    Ternary films of CdZnTe and CdMnTe were grown by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD), respectively, on glass/SnO2/CdS substrates with target bandgap of 1.7 to 1.8 eV for solar cell applications. The authors describe x-ray diffraction, surface photovoltage spectroscopy, and Auger electron spectroscopy measurements performed to estimate bandgap, compositional uniformity, and interface quality of the films. Front-wall CdTe cell (glass/SnO2/CdS/CdTe/ZnTe/Metal) efficiencies were --9%, while CdZnTe and CdMnTe efficiencies were --3.6% and 6%, respectively. n-i-p cell efficiencies were consistently higher than n-p cells. Optimum cell processing temperature for CdZnTe films was found to be less than 4000C. Higher processing temperatures caused a shift in bandgap coupled with film quality degradation

  20. Electronic structures of HgTe and CdTe surfaces and HgTe/CdTe interfaces

    Science.gov (United States)

    Schick, J. T.; Bose, S. M.; Chen, A.-B.

    1989-01-01

    A Green's-function method has been used to study the surface and interface electronic structures of the II-VI compounds HgTe and CdTe. Localized surface and resonance states near the cation-terminated (100) surface of CdTe and the anion-terminated surface of HgTe have been found for the ideal surfaces. The energies and strengths of these surface states are altered by surface perturbations. The bulk states near the surface are drastically modified by the creation of the surface, but the band gaps remain unchanged. Numerical evaluation of the local densities of states at the Gamma and J points shows that, at the (100) interface of HgTe/CdTe, the previously observed surface states are no longer present. However, in the interface region, bulk states of one material penetrate some distance into the other material.

  1. Study of HgCdTe/CdTe interface structure grown by metal-organic chemical vapor deposition

    Science.gov (United States)

    Ma, Ke J.; Yu, Zhen Z.; Yanh, Jian R.; Shen, Shou Z.; He, Jin; Chen, Wei M.; Song, Xiangyun

    1991-11-01

    The interface of HgCdTe/CdTe thin film growth by MOCVD were investigated by high resolution electron microscope (HREM). It is shown that there is no monolayer abrupt interface between HgCdTe and CdTe films. The interface of HgCdTe/CdTe contains a lot of small and random distributed disorder regions. The disorder areas can be transformed into order one under long time electron beam irradiation.

  2. Studies on CdTe solar cell front contact properties using X-ray photoelectron spectroscopy

    International Nuclear Information System (INIS)

    The chemical changes between transparent conducting oxide (TCO) and cadmium sulphide (CdS) layers were analyzed using X-ray photoelectron spectroscopy (XPS). Commercially available indium tin oxide (ITO) and ITO/SnO2 were used as substrates. The CdS layers were deposited in vacuum (∼ 10−2 Pa) at two different (low and high) substrate temperatures by close spaced sublimation technique. During the growth of CdS layer, the substrate temperature was increased from 25 to 250 °C for low temperature layer and from 490 to 550 °C for high temperature CdS layer due to the high crucible temperature. Similar to CdTe solar cell device process steps, the samples (TCO/CdS) were annealed in vacuum (10−2 Pa) at 520 °C and in air at 375 °C with and without CdCl2. The XPS depth profile analysis shows that annealing ITO/CdS sample in vacuum induces diffusion of indium into the CdS layer from ITO. The most of the diffused indium atoms are found on top of the CdS layer. No indium diffusion into the CdS layer was observed for the TCO with SnO2 buffer layer between ITO and CdS. However, at SnO2/CdS interface Cd atoms diffuse into the SnO2 buffer layer after CdCl2 activation. The change in chemical and electronic properties of the ITO/CdS and ITO/SnO2/CdS interfaces is discussed in detail. - Highlights: • The chemical change between different layers of CdTe solar cell is analyzed. • The annealing treatment induces diffusion of chemical elements. • SnO2 buffer layer acts as barrier for indium diffusion. • The CdCl2 annealing induces cadmium diffusion into tin oxide layer

  3. 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)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1991-05-01

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

  5. 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...

  6. ELECTRON TRANSFER IN Hg1-xCdxTe-CdTe HETEROSTRUCTURES

    OpenAIRE

    Boebinger, G.; Vieren, J.; Guldner, Y.; Voos, M.; Faurie, J.

    1987-01-01

    Far infrared magneto-absorption experiments performed at 1.6K in HgCdTe-CdTe heterojunctions show that a two-dimensional electron gas is formed in the HgCdTe layer at the HgCdTe-CdTe interface. The electron effective masses of the two populated subbands is obtained and compared to previous theoretical calculations. The electron transfer across the interface involves deep traps in the CdTe layers.

  7. Study of point defects in CdTe and CdTe:V by cathodoluminescence

    OpenAIRE

    Pal, U.; Piqueras de Noriega, Javier; Fernández Sánchez, Paloma; M.D. Serrano; Diéguez, E.

    1994-01-01

    Cathodoluminescence in the scanning electron microscope has been used to investigate the relationship of point defects in CdTe and CdTe:V with luminescence bands at 1.40 and 1.13 eV. V has been found to inhibit the 1.40 eV luminescence. Annealing experiments indicate that Cd and Te vacancies are involved in the mentioned emission bands.

  8. Point defects with lattice distortion in CdTe and HgCdTe

    Energy Technology Data Exchange (ETDEWEB)

    Schick, J.T.; Morgan-Pond, C.G. (Department of Physics Astronomy, Wayne State University, Detroit, Michigan 48202 (US))

    1990-03-01

    Results of self-consistent, tight-binding supercell calculations of electronic defect levels and relaxation about defects for As, Sb, and Te interstitials in CdTe and for the Hg vacancy in HgTe are presented. Trends in the localized defect levels and the relaxation of the lattice seen for these defects and for Cd, Hg, and In interstitials, from previous calculations, are discussed. Te interstitials are found to have the largest lattice relaxation of these interstitials in their preferred tetrahedral positions. This may help explain the tendency for excess Te to condense into second-phase inclusions. It is also suggested that a strain-mediated interaction between Te interstitials and cation vacancies may promote the creation of Te antisites in Te-rich HgCdTe.

  9. 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.

  10. 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...

  11. IBIC analysis of CdTe/CdS solar cells

    CERN Document Server

    Colombo, E; Calusi, S; Giuntini, L; Giudice, A Lo; Manfredotti, C; Massi, M; Olivero, P; Romeo, A; Romeo, N; Vittone, E

    2016-01-01

    This paper reports on the investigation of the electronic properties of a thin film CdS/CdTe solar cell with the Ion Beam Induced Charge (IBIC) technique. The device under test is a thin film (total thickness around 10 um) multilayer heterojunction solar cell, displaying an efficiency of 14% under AM1.5 illumination conditions. The IBIC measurements were carried out using focused 3.150 MeV He ions raster scanned onto the surface of the back electrode. The charge collection efficiency (CCE) maps show inhomogeneous response of the cell to be attributed to the polycrystalline nature of the CdTe bulk material. Finally, the evolution of the IBIC signal vs. the ion fluence was studied in order to evaluate the radiation hardness of the CdS/CdTe solar cells in view of their use in solar modules for space applications.

  12. Development of optimal SnO{sub 2} contacts for CdTe photovoltaic applications. [Final technical report of Phase II

    Energy Technology Data Exchange (ETDEWEB)

    Xi, Jianping

    1999-09-16

    During this SBIR Phase II project, we have successfully established high quality SnO{sub 2}(F) based transparent conductive oxide coatings by atmospheric pressure chemical vapor deposition technique and built a large area prototype APCVD deposition system which incorporates innovative design features. This work enhances US photovoltaic research capability and other thin film oxide related research capability.

  13. High resistivity in undoped CdTe: carrier compensation of Te antisites and Cd vacancies

    International Nuclear Information System (INIS)

    In this paper, we focus on the high resistivity of intentionally undoped CdTe, where the most prevalent defects are Cd vacancies and Te antisites. Our calculated formation energies lead to the conclusion that the Fermi energy of undoped CdTe is at midgap due to carrier compensation of Te antisites and Cd vacancies, which explains the experimentally observed high resistivity. We use density functional theory with the hybrid functional of Heyd, Scuseria and Ernzerhof (HSE06) and show that the proper description of the native defects in general fails using the local density approximation (LDA) instead of HSE06. We conclude that LDA is insufficient to understand the high resistivity of undoped CdTe. We calculate the neutral and double acceptor state of the Te antisite to be intrinsic DX-centers. (paper)

  14. INVESTIGATION OF CdTe/CdS HETEROJUNCTION CHARACTERISTICS%CdTe/CdS异质结特性

    Institute of Scientific and Technical Information of China (English)

    郭江; 王万录; 刘高斌; 冯良桓

    2003-01-01

    从理论上对CdTe/CdS太阳电池CdS/CdTe异质结的特性进行了研究和讨论,结果表明可以简单利用改变CdTe、CdS两种半导体材料的掺杂浓度来改变CdS/CdTe异质结的能带结构.针对不同的能带结构采用了不同的物理模型,得到的CdS/CdTe异质结伏安特性曲线有一折点,且折点位置随异质结能带结构的变化而变化.

  15. Indoor stability tests on CdS/CdTe/ZnTe n-i-p submodules

    Energy Technology Data Exchange (ETDEWEB)

    Ramanathan, V.; Russell, L.A.; Liu, C.H.; Meyers, P.V. (Ametek Applied Materials Lab., Harleysville, PA (USA))

    1990-02-01

    Progress in the development of solar modules of the n-i-p CdS/CdTe/ZnTe structure is reported. By a combination of laser and mechanical scribing steps, several submodules were produced on 3 in x 6 in substrates. Results of the indoor stability tests show that the submodules are stable after 1500 h of exposure. (orig.).

  16. 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

  17. Reduced leakage currents of CdZnTe radiation detectors with HgTe/HgCdTe superlattice contacts

    Science.gov (United States)

    Chang, Y.; Grein, C. H.; Becker, C. R.; Huang, J.; Ghosh, S.; Aqariden, F.; Sivananthan, S.

    2012-10-01

    Room-temperature-operating CdZnTe radiation detectors have high energy resolution, linear energy response and are capable of operating in normal counting and spectroscopic modes, hence are highly desirable for medical diagnosis, nondestructive industrial evaluations, homeland security, counterterrorism inspections and nuclear proliferation detection to ensure national and international nuclear safety. HgTe/HgCdTe superlattices can be designed to selectively transport one carrier species while hindering transport of the other. Specifically, one designs a large carrier effective mass for undesired carriers in the electric field direction, which results in low carrier velocities, and yet a density of states for undesired carrier that is lower than that of a comparable bulk semiconductor, which results in low carrier concentrations, hence a low current density under an electric field. The opposite carrier species can be designed to have a large velocity and high density of states, hence producing a large current density. By employing HgTe/HgCdTe superlattices as contact layers intermediate between CdZnTe absorbers and metal contacts, leakage currents under high electric fields are reduced and improved x-ray and γ-ray detector performance is anticipated. Pixilated CdZnTe radiation detectors arrays were fabricated and characterized to evaluate the effectiveness of HgTe/HgCdTe superlattices in reducing leakage currents. Current-voltage characteristics show that HgTe/HgCdTe superlattice contact layers consistently result in significantly reduced leakage currents relative to detectors with only metal contacts.

  18. ZnTe/CdTe thin-film heterojunctions

    Directory of Open Access Journals (Sweden)

    M.M. Kolesnyk

    2009-01-01

    Full Text Available In this work we have studied the structural and electrophysical properties of the ZnTe/CdTe heterojunctions, obtained by the method of thermal evaporation in quasi-closed volume. Investigations allowed to define the films structural parameters, such as texture, lattice constant, sizes of grains and coherent-scattering domains, micro-deformation level, and their dependence on the conditions of films production as well. Electrophysical investigations allowed to define the charge-transport mechanism in heterojunction.

  19. HgCdTe barrier infrared detectors

    Science.gov (United States)

    Kopytko, M.; Rogalski, A.

    2016-05-01

    In the last decade, new strategies to achieve high-operating temperature (HOT) detectors have been proposed, including barrier structures such as nBn devices, unipolar barrier photodiodes, and multistage (cascade) infrared detectors. The ability to tune the positions of the conduction and valence band edges independently in a broken-gap type-II superlattices is especially helpful in the design of unipolar barriers. This idea has been also implemented in HgCdTe ternary material system. However, the implementation of this detector structure in HgCdTe material system is not straightforward due to the existence of a valence band discontinuity (barrier) at the absorber-barrier interface. In this paper we present status of HgCdTe barrier detectors with emphasis on technological progress in fabrication of MOCVD-grown HgCdTe barrier detectors achieved recently at the Institute of Applied Physics, Military University of Technology. Their performance is comparable with state-of-the-art of HgCdTe photodiodes. From the perspective of device fabrication their important technological advantage results from less stringent surface passivation requirements and tolerance to threading dislocations.

  20. Growth and properties of CdS/CdTe heterojunctions on soda lime glass substrates

    International Nuclear Information System (INIS)

    Polycrystalline thin films of CdTe grown on glass/SnO2/CdS substrates are studied using X-ray diffraction, atomic force microscopy, and time resolved photoluminescence decay techniques. CdS films were deposited by chemical solution. CdTe films were grown by close-spaced sublimation at substrate temperatures between 475--625 degree C. CdTe thin films deposited at temperatures higher than 525 degree C show preferential orientation in the left-angle 111 right-angle direction. The Grain size of the films increases with substrate temperature and the films are faceted for all the temperatures. The PL decay constant increases with substrate temperature up to 575 degree C for as-deposited films on soda-lime substrates. Films on borosilicate substrates show an increase up to the highest temperature used (625 degree C). There is systematic increase in the PL decay constant after CdCl2 heat treatment, and the range of values is 1--1.5 nsec for soda-lime samples and 1--2 nsec for borosilicate samples

  1. Optical characterization of CdZnTe/CdTe strained quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Reno, J.L.; Jones, E.D.

    1990-01-01

    Strained layer structures have received a great deal of attention due both to their possible application in electronic devices and their intrinsic interest. The study of strained layer quantum wells grown using lattice mismatched materials has been widely developed for III-V semiconductors. Strained layer quantum wells grown using II-VI materials have not been studied nearly so much as those from III-V, but they are a rapidly growing field of semiconductor research. The wide gap II-VI materials are of interest because they are generally direct gap materials. This makes them attractive for optoelectronic devices. The majority of the work on strained layer structures in the wide gap tellurium based materials has focused in two areas. The first is the inclusion of Mn to produce dilute magnetic semiconductors (DMS) strained layers and superlattices. The other area is CdTe/ZnTe quantum wells and superlattices. Some related work has been done with CdZnTe/ZnTe structures. For the CdZnTe/CdTe very little work has been done and the majority of that used very small amounts of Zn. In this paper we will present the growth and optical characterization of Cd{sub 1-x}Zn{sub x}Te/CdTe strained single quantum wells (SSQW) where the Zn concentration ranges from about 10 to 50%. 10 refs., 3 figs.

  2. 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

  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. 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

  5. Investigation of metalorganic chemical vapor deposition grown CdTe/CdS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Sudharsanan, R.; Rohatgi, A. (Georgia Inst. of Tech., Atlanta (USA). School of Electrical Engineering)

    1991-03-01

    Polycrystalline CdTe films were grown on CdS/SnO{sub 2}/glass substrates by metalorganic chemical vapor deposition (MOCVD) for solar cell applications. Cells fabricated on these films showed efficiency of 9.7% which is the highest efficiency reported so far for MOCVD grown CdTe solar cells. The bias-dependent spectral response of the 9.7% efficient cell showed an external quantum efficiency greater than 0.85 at zero bias but a significant wavelength-independent reduction in spectral response at higher voltages. The interface recombination model was used to calculate the interface collection function term to quantify the open-circuit voltage (V{sub oc}) and fill factor losses in the high efficiency cell. It was found that the interface recombination reduces the V{sub oc} and fill factor by 60 mV and 0.1 respectively. It was estimated that efficiency as high as 13.5% can be achieved by improving CdTe/CdS interface quality. (orig.).

  6. Recent Progress in CdTe and CdZnTe Detectors

    OpenAIRE

    Takahashi, Tadayui; Watanabe, Shin

    2001-01-01

    Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been regarded as promising semiconductor materials for hard X-ray and Gamma-ray detection. The high atomic number of the materials (Z_{Cd} =48, Z_{Te} =52) gives a high quantum efficiency in comparison with Si. The large band-gap energy (Eg ~ 1.5 eV) allows us to operate the detector at room temperature. However, a considerable amount of charge loss in these detectors produces a reduced energy resolution. This problem arises du...

  7. Photoluminescence Spectroscopy of CdZnTe/CdTe Single Strained Quantum Wells

    Science.gov (United States)

    Reno, J. L.; Jones, E. D.

    1991-12-01

    We have grown strained Cd1-xZnxTe/CdTe single strained quantum wells by molecular beam epitaxy. The Zn concentration was varied from 10 to 60% and the well widths were systematically increased until the critical thickness was exceeded. Low-temperature (liquid helium) photoluminescence spectroscopy was used to characterize the films. The energy of the quantum well luminescence is consistent with a simple square well model when strain is included. The critical layer thickness for the CdTe quantum wells was found to be in agreement with the model of Matthews and Blakeslee.

  8. CdTe and ZnTe metal interface formation and Fermi-level pinning

    Science.gov (United States)

    Wahi, A. K.; Carey, G. P.; Chiang, T. T.; Lindau, I.; Spicer, W. E.

    1989-01-01

    Interfacial morphology and Fermi-level pinning behavior at the interfaces of Al, Ag, and Pt with UHV-cleaved CdTe and ZnTe are studied using X-ray photoelectron and ultraviolet photoemission spectroscopies. Results are compared to metal/HgCdTe interface formation. For Al/CdTe, a case is found where significantly greater intermixing occurs in CdTe than seen on HgCdTe. The Al/ZnTe interface is also more abrupt than Al/CdTe. Band bending results for interfaces of all three metals with p-CdTe and p-ZnTe are presented and implications for metal/HgZnTe interface formation are considered.

  9. Effect of nanoscale tin-dioxide layers on the efficiency of CdS/CdTe-based film solar elements

    International Nuclear Information System (INIS)

    Comparative investigations of the output parameters and optical diode characteristics of ITO/CdS/CdTe/Cu/Au and SnO2: F/CdS/CdTe/Cu/Au film solar cells are carried out with the aim of optimizing the design of the front electrodes. It is established that the high voltage and large filling factor of the solar elements with SnO2: F films are caused by a lower diode saturation current density and series resistance due to the stability of the crystal structure and electrical properties of these films against chloride treatment of the base layer during device fabrication. At the same time, solar elements with an ITO front electrode exhibit a higher short-circuit current density due to the larger average light transmittance of the ITO layers. The use of nanoscale SnO2 layers in the ITO front contacts allows the efficiency of the CdS/CdTe-based solar elements to be enhanced to 11.4% on account of stabilization of the crystal structure and electrical properties of the ITO films and a possible reduction in the cadmium-sulphide-layer thickness without shunting the device structure

  10. Surface characterization of GSH-CdTe quantum dots

    International Nuclear Information System (INIS)

    The surface characterization of CdTe QDs synthesized by a novel procedure using glutathione (GSH), low temperatures (60–90 °C) and K2TeO3 as the –Te precursor is reported. Fluorescence of the produced QDs is stable in the pH range 6–13 and QDs inside eukaryotic cells are highly fluorescent. The surface composition of GSH-CdTe QDs with different spectroscopic properties and particle size distributions was determined by XPS. The XPS analysis indicated that the QDs are essentially CdTe, although all nanoparticles contain 12–24% of CdO (and in one case also TeO2). GSH decomposes with reaction time releasing small amounts of S−2 ions that react with Cd(Te) to yield Cd(Te)S in a smaller amount than that of CdTe. Finally, the use of QDs in fluorescence mediated immunodetection of bacterial pathogens has been evaluated. - Highlights: • Stable CdTe QDs of different sizes were synthesized by reacting thiol GSH and K2TeO3 at 90 °C. • XPS analysis shows that the QDs contain CdTe, Cd(Te)S and CdO at the surface. • Small amounts of TeO2 were also observed. • Sulphur allows the binding of the QDs at biomolecules

  11. MBE HgCdTe heterostructure detectors

    Science.gov (United States)

    Schulman, Joel N.; Wu, Owen K.

    1990-01-01

    HgCdTe has been the mainstay for medium (3 to 5 micron) and long (10 to 14 micron) wavelength infrared detectors in recent years. Conventional growth and processing techniques are continuing to improve the material. However, the additional ability to tailor composition and placement of doped layers on the tens of angstroms scale using molecular beam epitaxy (MBE) provides the opportunity for new device physics and concepts to be utilized. MBE-based device structures to be discussed here can be grouped into two categories: tailored conventional structures and quantum structures. The tailored conventional structures are improvements on familiar devices, but make use of the ability to create layers of varying composition, and thus band gap, at will. The heterostructure junction can be positioned independently of doping p-n junctions. This allows the small band gap region in which the absorption occurs to be separated from a larger band gap region in which the electric field is large and where unwanted tunneling can occur. Data from hybrid MBE/liquid phase epitaxy (LPE)/bulk structures are given. Quantum structures include the HgTe-CdTe superlattice, in which the band gap and transport can be controlled by alternating thin layers (tens of angstroms thick) of HgTe and CdTe. The superlattice has been shown to exhibit behavior which is non-alloy like, including very high hole mobilities, two-dimensional structure in the absorption coefficient, resonant tunneling, and anisotropic transport.

  12. 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.

  13. HgCdTe monolithic infrared detector

    Energy Technology Data Exchange (ETDEWEB)

    Yakushev, Maxim V.; Dvoretsky, Sergei A.; Kozlov, Alexander I.; Sabinina, Irina V.; Sidorov, Yu.G.; Sorochkin, Alexander V.; Fomin, Boris I.; Aseev, Alexander L. [A.V. Rzhanov Institute of Semiconductor Physics, Siberian Branch RAS, Novosibirsk (Russian Federation)

    2010-06-15

    We report the processes of fabricating monolithic 32 x 32 infrared detector based on (310) HgCdTe/CdTe/ZnTe/ Si photosensitive heterostructure which was grown by a molecular-beam epitaxy technique in the free surface of ROIC cells. Optimum parameters of the technological processes were determined. The minimum temperature of preepitaxial thermal annealing in vacuum of ROIC was determined as 450 C. The dark and photo current-voltage characteristics were measured and analyzed. A good sensitivity of diodes was observed. The product R{sub 0} x A {proportional_to} 10{sup 5} Ohm x cm{sup 2}. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. High performance p-i-n CdTe and CdZnTe detectors

    CERN Document Server

    Khusainov, A K; Ilves, A G; Morozov, V F; Pustovoit, A K; Arlt, R D

    1999-01-01

    A breakthrough in the performance of p-i-n CdTe and CdZnTe detectors is reported. The detector stability has been significantly improved, allowing their use in precise gamma and XRF applications. Detectors with energy resolution close to Si and Ge were produced operating with only -30--35 deg. C cooling (by a Peltier cooler of 15x15x10 mm size and a consumed power less than 5 W). Presently detectors with volume of up to 300 mm sup 3 are available. In terms of photoelectric effect efficiency it corresponds to HPGe detectors with volumes of about 1.5 cm sup 3. The possibilities of further improvement of CdTe and CdZnTe detector characteristics are discussed in this paper.

  15. High performance p-i-n CdTe and CdZnTe detectors

    Science.gov (United States)

    Khusainov, A. Kh; Dudin, A. L.; Ilves, A. G.; Morozov, V. F.; Pustovoit, A. K.; Arlt, R. D.

    1999-06-01

    A breakthrough in the performance of p-i-n CdTe and CdZnTe detectors is reported. The detector stability has been significantly improved, allowing their use in precise gamma and XRF applications. Detectors with energy resolution close to Si and Ge were produced operating with only -30--35°C cooling (by a Peltier cooler of 15×15×10 mm size and a consumed power less than 5 W). Presently detectors with volume of up to 300 mm 3 are available. In terms of photoelectric effect efficiency it corresponds to HPGe detectors with volumes of about 1.5 cm 3. The possibilities of further improvement of CdTe and CdZnTe detector characteristics are discussed in this paper.

  16. Preparation and Properties of Evaporated CdTe and All Thin Film CdTe/CdS Solar Cells

    Science.gov (United States)

    Shahzad, Naseem

    1991-05-01

    Cadmium telluride thin films were prepared by vacuum evaporation of CdTe powder in an attempt to fabricate all thin film solar cells of the type CdTe/CdS. Characterization of CdTe has shown it to have a band gap of 1.522 eV and a resistivity of 22Ω-cm. As prepared, solar cells exhibited low values of output parameters. Given quantity of copper was then deposited on top of the CdTe/CdS solar cells and the whole system was annealed at 350° C. This copper doping changed the output parameters favorably with a maximum efficiency of 1.9%.

  17. Si, CdTe and CdZnTe radiation detectors for imaging applications

    OpenAIRE

    Schulman, Tom

    2006-01-01

    The structure and operation of CdTe, CdZnTe and Si pixel detectors based on crystalline semiconductors, bump bonding and CMOS technology and developed mainly at Oy Simage Ltd. And Oy Ajat Ltd., Finland for X- and gamma ray imaging are presented. This detector technology evolved from the development of Si strip detectors at the Finnish Research Institute for High Energy Physics (SEFT) which later merged with other physics research units to form the Helsinki Institute of Physics (HIP). General ...

  18. Scaling and qualifying CdTe/CdS module production

    Science.gov (United States)

    Powell, R. C.; Jayamaha, U.; Dorer, G. L.; McMaster, H.

    1999-03-01

    This paper summarizes our development of high-throughput manufacturing and the long-term testing of CdS/CdTe photovoltaic (PV) modules. We report the development of a vapor transport deposition (VTD) process for II-VI thin-films capable of satisfying the requirements of very large-scale production. CdTe film deposition rates of ⩾1 μm/s have been translated into production line speeds up to 2.5 m/min and areal generation rates up to 1.5 m2/min. The best small-area devices fabricated using VTD material are more than 11% efficient. Long-term outdoor module testing continues to indicate a stable product while accelerated life testing has revealed the superiority of alternative processing methodologies.

  19. 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.

  20. 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

  1. SXPS studies of single crystalline CdTe/CdS interfaces

    International Nuclear Information System (INIS)

    Highlights: •Investigation of single crystalline surfaces of CdS and CdTe by SXPS. •Investigation of growth of CdS and CdTe on crystalline surfaces by SXPS and LEED. •Determination of band alignment between CdS and CdTe. -- Abstract: The interface formation between CdS and CdTe is investigated by synchrotron induced photoemission measurements at the BESSY II storage ring. CdS and CdTe layers were deposited by thermal evaporation on CdTe and CdS single crystal substrates with two different orientations for each substrate. Surface core level shifts show a passivation of dangling bonds for CdS substrates overgrown by CdTe. Te-Te bonds are found even on a 200 nm thick layer of CdS on CdTe. A valence band offset of 1.02 ± 0.05 eV, corresponding to a conduction band offset of −0.09 ± 0.05 eV is determined, independent of the substrate type and orientation and in agreement with measurements of polycrystalline interfaces. This alignment of every bands with a very small barrier for electron transfer and a maximized barrier for hole transport to the electron accepting front contact promises ideal properties for devices like CdS/CdTe hetero junction thin film solar cells

  2. Electronic structure and band alignments of ZnTe/CrTe(0 0 1), CdSe/CrTe(0 0 1) and CdTe/CrTe(0 0 1) interfaces

    Indian Academy of Sciences (India)

    F Ahmadian; R Zare

    2011-08-01

    All-electron full potential calculations based on spin density functional theory were performed to study cubic zincblende (ZB) and hexagonal NiAs structures of bulk CrTe and ZnTe/CrTe(0 0 1), CdTe/CrTe(0 0 1) and CdSe/CrTe(0 0 1) interfaces. The lattice mismatch effect in ZB CrTe and magnetic properties of CrTe in the ideal ZB CrTe structure were investigated. The band alignment properties of the ZnTe/CrTe(0 0 1), CdTe/CrTe(0 0 1) and CdSe/CrTe(0 0 1) interfaces were computed and a rather large minority valence band offset of about 1.09 eV was observed in ZnTe/CrTe(0 0 1) heterojunction. Also in the CdTe/CrTe(0 0 1) and CdSe/CrTe(0 0 1) interfaces, the conduction band minimum of minority spin in CrTe was above the conduction band minimum of CdTe and CdSe and so the majority spin electrons could be directly injected to both semiconductors, indicating the possibility of highly efficient spin injection into the CdSe and CdTe semiconductors.

  3. Ethanol gas sensing by Zn-doped CdS/CdTe nanoparticles

    Science.gov (United States)

    Prabhu, M.; Manikandan, V. S.; Soundararajan, N.; Ramachandran, K.

    2016-05-01

    Zn-doped CdS/CdTe nanoparticles (NPs) were synthesized and studied here for gas sensing. The crystallographic properties of the samples were studied by X-ray diffraction (XRD), which shows cubic structure for CdS and CdTe NPs. The three longitudinal optical phonon modes at 298, 595 and 895 cm-1 were obtained from Raman spectrum and this also reveals the cubic structure of CdS NPs. The band gap for Zn-doped CdS/CdTe NPs increased slightly when compared with pure sample. The ethanol gas sensing in CdS/CdTe NPs shows an enhancement on Zn substitution.

  4. 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)

  5. Isothermal close-spaced vapour growth of CdTe for CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Vaccaro, P.O.; Saura, J. (Comision Nacional de Energia Atomica, San Carlos de Bariloche (Argentina). Centro Atomico Bariloche)

    1991-01-01

    CdS(n)/CdTe(p) thin-film solar cells with an efficiency of >10% have been prepared by several fabrication methods. These methods include close-spaced vapour transport and sintering. Sintering, usually preceded by screen printing, has been especially attractive owing to the simplicity of the equipment and the small amount of waste material. This method implies coating the substrate with a slurry prepared with the semiconductor powder, an adequate binder and a sintering aid. In this letter we report preliminary results that indicate that growth of CdTe film on the CdS substrate could occur through a vapour-phase mechanism during the sintering stage of CdS/CdTe cells. In order to prepare the cells, the CdTe layers were deposited on the CdS sintered layer using two methods: sintering and isothermal close-spaced vapour transport (ICSVT). CdCl{sub 2} was used as a sintering aid. The ICSVT method shows promise for the preparation of CDTe dense films on CdS substrates. The presence of CdCl{sub 2} in the slurries is important, but at the moment it is not clear how this affects the deposition process. (author).

  6. Stable Water-dispersed CdTe Nanocrystals Dependent on Stoichiometric Ratio of Cd to Te Precursor

    Institute of Scientific and Technical Information of China (English)

    张旭瑞; 王李欣; 郭佳; 杨武利

    2012-01-01

    The improved properties of CdTe nanocrystals (NCs) synthesized by hydrothermal method were introduced. The experimental results indicated that the NCs properties could be dramatically influenced by means of changing Cd-to-Te molar ratio (the molar ratio of CdC12 and NaHTe in the precursor) of the MPA-capped CdTe NCs. With the increase of the ratio from 2 : 1 to 10 : 1, the formation time of near-infrared-emitting CdTe NCs was shortened. In particular, high Cd-to-Te molar ratio brought about MPA-capped CdTe NCs of superior radical oxidation-resis- tance and photostability. As a result, the optimum ratio was found to be 8 : 1 or 10 : 1 in the study in order to efficiently attain stable, water-dispersed CdTe NCs.

  7. 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.

  8. Photoluminescence of Cu-doped CdTe and related stability issues in CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Grecu, D. [University of Toledo, Toledo, Ohio 43606-3390 (United States); Compaan, A. D. [University of Toledo, Toledo, Ohio 43606-3390 (United States); Young, D. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Jayamaha, U. [First Solar LLC., Perrysburg, Ohio 43551 (United States); Rose, D. H. [First Solar LLC., Perrysburg, Ohio 43551 (United States)

    2000-09-01

    We explore Cu electronic states in CdTe using photoluminescence as the main investigative method. Our results are consistent with some Cu atoms occupying substitutional positions on the Cd sublattice and with others forming Frenkel pairs of the type Cu{sub i}{sup +}-V{sub Cd}{sup -} involving an interstitial Cu and a Cd vacancy. In addition, we find that Cu-doped CdTe samples exhibit a significant ''aging'' behavior, attributable to the instability of Cu acceptor states as verified by our Hall measurements. The aging appears to be reversible by a 150-200 degree sign C anneal. Our results are used to explain efficiency degradation of some CdTe solar-cell devices which use Cu for the formation of a backcontact. (c) 2000 American Institute of Physics.

  9. Radiative and interfacial recombination in CdTe heterostructures

    International Nuclear Information System (INIS)

    Double heterostructures (DH) were produced consisting of a CdTe film between two wide band gap barriers of CdMgTe alloy. A combined method was developed to quantify radiative and non-radiative recombination rates by examining the dependence of photoluminescence (PL) on both excitation intensity and time. The measured PL characteristics, and the interface state density extracted by modeling, indicate that the radiative efficiency of CdMgTe/CdTe DHs is comparable to that of AlGaAs/GaAs DHs, with interface state densities in the low 1010 cm−2 and carrier lifetimes as long as 240 ns. The radiative recombination coefficient of CdTe is found to be near 10−10 cm3s−1. CdTe film growth on bulk CdTe substrates resulted in a homoepitaxial interface layer with a high non-radiative recombination rate

  10. CdTe,核-壳型CdTe/CdS及CdTe/ZnS量子点的合成及表征%CdTe, Core-shell CdTe/CdS and CdTe/ZnS Quantum Dots: Their Synthesis and Characterization*

    Institute of Scientific and Technical Information of China (English)

    张纪梅; 许世超; 宋秀云; 代昭; 孙波; 姚翠翠

    2009-01-01

    Semiconductor CdTe, core-shell CdTe/CdS and CdTe/ZnS nanocrystals(quantum dots; QDs) were prepared in aqueous phase. Investigations of the prepared nanocrystals were performed via scanning tunneling microscope(STM) and fluorescence spectrum(FS), and quantum yields(Qys) was calculated based on the resulting data from FS. Particle size of well dispersed CdTe was evaluated to be ca 3 nm via STM. Some reaction conditions were investigated and discussed to enhance Qys of CdTe/CdS core-shell QDs, such as dependence of Cd2+ concentration, and effect of Cd2+∶S2- etc. Among all of those methods, Qys of core-shell CdTe/CdS is generally degressive with refluxing time elapsing. The best Qys of ca 80.0% can be achieved when pH was set at 8.5, Cd2+∶S2-=10:1(mol ratio). Moreover, CdTe/ZnS core-shell QDs was prepared, and results indicated a red-shift from 551 nm to 635 nm comparing with CdTe core, which suggested the growth of QDs size, however, Qys of CdTe/ZnS decreased to 14.4%. QDs currently discussed in this research are easily synthesized, and they will be useful in applications of biolabeling, imaging, and biosensing based on fluorescence resonance energy transfer(FRET).%在水相中制备了半导体CdTe纳米晶,核-壳型CdTe/CdS和CdTe/ZnS纳米晶(即量子点;QDs).利用扫描隧道显微镜(STM)和荧光光谱(FS)对合成的纳米晶量子点进行了研究,并且根据FS的数据进行了量子效率的计算.STM的结果表明合成的量子点直径约为3 nm并且分布良好.为了提高量子效率,对Cd2+浓度和Cd2+∶S2-比例等反应条件进行了研究,结果表明随着回流时间的增加,核-壳型量子点CdTe/CdS的量子效率总体上呈下降趋势.CdTe/CdS在pH8.5,Cd2+∶S2-=10∶1(摩尔比)时可获得80.0%的最大量子效率.同时制备了核-壳型量子点CdTe/ZnS,其最大发射波长由551 nm(CdTe)红移到635 nm(CdTe/ZnS)表明量子点的尺寸在增长,但是量子效率下降到14.4%. 当前研究的量子点可适用于生

  11. Study of in situ CdCl{sub 2} treatment on CSS deposited CdTe films and CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Paulson, P.D.; Dutta, V. [Indian Inst. of Tech., New Delhi (India). Centre for Energy Studies

    2000-07-17

    Effect of in situ CdCl{sub 2} treatment on the morphological, structural and electrical properties of CdTe films as well as on solar cell characteristics of CdS/CdTe junction has been investigated. XRD measurements show that the presence of CdCl{sub 2} vapours induces left angle 111 right angle oriented growth in the CdTe films. CdCl{sub 2} concentration required for this oriented growth is found to be directly proportional to the substrate temperature. SEM measurements show enhanced grain growth in the presence of CdCl{sub 2}. Spectral response of the CdCl{sub 2} treated CdS/CdTe solar cells shows an enhanced CdS diffusion in to the CdTe, which results in an improved spectral response in UV range and a consequent reduction in the interface states density. A drastic reduction in the deep levels due to the CdCl{sub 2} treatment, as seen in the photo-capacitance studies, has results in CdS/CdTe solar cells having efficiency >8%. (orig.)

  12. 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)

  13. 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.)

  14. Simulation of the Efficiency of CdS/CdTe Tandem Multi-Junction Solar Cells

    OpenAIRE

    Mirkamali, Ashrafalsadat S.; Muminov, Khikmat Kh.

    2016-01-01

    In this paper we study CdS/CdTe solar cells by means of AMPS-1D software. First we study the effect of thickness of semiconductor layers on the output parameters of the CdS/CdTe solar cell, such as density of short-circuit current, open circuit voltage, fill factor and efficiency. Numerical simulation shows that the highest efficiency of single-junction CdS/CdTe solar cell equal to 18.3% is achieved when the CdTe layer thickness is 1000 nm and a CdS layer is 60 nm. Then, in order to obtain th...

  15. Correlation of the Cd-to-Te ratio on CdTe surfaces with the surface structure

    Science.gov (United States)

    Wu, Y. S.; Becker, C. R.; Waag, A.; Kraus, M. M.; Bicknell-Tassius, R. N.; Landwehr, G.

    1991-10-01

    We report here that reconstruction on (100), (111)A, and (111)B CdTe surfaces is either c(2×2), (2×2), and (1×1) or (2×1), (1×1), and (1×1) when they are Cd or Te stabilized, respectively. There is a mixed region between Cd and Te stabilization in which the reflected high-energy electron-diffraction (RHEED) patterns contain characteristics of both Cd- and Te-stabilized surfaces. We have also found that the Cd-to-Te ratio of the x-ray photoelectron intensities of their 3d3/2 core levels is about 20% larger for a Cd-stabilized (111)A, (111)B, or (100) CdTe surface than for a Te-stabilized one. According to a simple model calculation, which was normalized by means of the photoelectron intensity ratio of a Cd-stabilized (111)A and a Te-stabilized (111)B CdTe surface, the experimental data for CdTe surfaces can be explained by a linear dependence of the photoelectron-intensity ratio on the fraction of Cd in the uppermost monatomic layer. This surface composition can be correlated with the surface structure, i.e., the corresponding RHEED patterns. This correlation can in turn be employed to determine Te and Cd evaporation rates. The Te reevaporation rate is increasingly slower for the Te-stabilized (111)A, (111)B, and (100) surfaces, while the opposite is true for Cd from Cd-stabilized (111)A and (111)B surfaces. In addition, Te is much more easily evaporated from all the investigated surfaces than is Cd, if the substrate is kept at normal molecular-beam-epitaxy growth temperatures ranging from 200 °C to 300 °C.

  16. Synthesis and Surface Modification of CdTe Nanocrystals

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    CdTe nanocrystals were prepared in aqueous solution via the reaction between Cd2+ and NaHTe in the presence of mercaptoacetic acid. Interactions between CdTe nanocrystals and phenylalanine were formed via electrostatic/coordinate self-assembly. The photoluminescence intensity of CdTe nanocrystals was improved obviously. The interaction mechanism was discussed and was considered to be surface passivation.

  17. Recent Progress in CdTe and CdZnTe Detectors

    CERN Document Server

    Takahashi, T; Takahashi, Tadayui; Watanabe, Shin

    2001-01-01

    Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been regarded as promising semiconductor materials for hard X-ray and Gamma-ray detection. The high atomic number of the materials (Z_{Cd} =48, Z_{Te} =52) gives a high quantum efficiency in comparison with Si. The large band-gap energy (Eg ~ 1.5 eV) allows us to operate the detector at room temperature. However, a considerable amount of charge loss in these detectors produces a reduced energy resolution. This problem arises due to the low mobility and short lifetime of holes. Recently, significant improvements have been achieved to improve the spectral properties based on the advances in the production of crystals and in the design of electrodes. In this overview talk, we summarize (1) advantages and disadvantages of CdTe and CdZnTe semiconductor detectors and (2) technique for improving energy resolution and photopeak efficiencies. Applications of these imaging detectors in future hard X-ray and Gamma-ray astronomy missions are briefly discus...

  18. The properties of CdTe solar cells with ZnTe/ZnTe: Cu buffer layers

    Institute of Scientific and Technical Information of China (English)

    Song Huijin; Zheng Jiagui; Feng Lianghuan; Yan Qiang; Lei Zhi; Wu Lili; Zhang Jingquan; Li Wei; Li Bing

    2008-01-01

    CdS/CdTe solar cells with ZnTe/ZnTe:Cu buffer layers were fabricated and studied. The energy band structure of it was analyzed. The C-V, I-V characteristics and the spectral response show that the ZnTe/ZnTe:Cu buffer layers improve the back contact characteristic properties, the diode characteristics of the forward junction and the short-wave spectral response of the CdTe solar cells. The ZnTe/ZnTe:Cu buffer layers affect the solar cell conversion efficiency and its fill factor.

  19. Correction of diagnostic x-ray spectra measured with CdTe and CdZnTe detectors

    Energy Technology Data Exchange (ETDEWEB)

    Matsumoto, M. [Osaka Univ., Suita (Japan). Medical School; Kanamori, H.; Toragaito, T.; Taniguchi, A.

    1996-07-01

    We modified the formula of stripping procedure presented by E. Di. Castor et al. We added the Compton scattering and separated K{sub {alpha}} radiation of Cd and Te (23 and 27keV, respectively). Using the new stripping procedure diagnostic x-ray spectra (object 4mm-Al) of tube voltage 50kV to 100kV for CdTe and CdZnTe detectors are corrected with comparison of those spectra for the Ge detector. The corrected spectra for CdTe and CdZnTe detectors coincide with those for Ge detector at lower tube voltage than 70kV. But the corrected spectra at higher tube voltage than 70kV do not coincide with those for Ge detector. The reason is incomplete correction for full energy peak efficiencies of real CdTe and CdZnTe detectors. (J.P.N.)

  20. 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 ...

  1. A model for the CdTe/CdS junction

    Energy Technology Data Exchange (ETDEWEB)

    Linam, David L; Singh, Vijay P; McClure, Jonh C; Lush, Gregory; Mathew, X [Centro de Investigacion en Energia, UNAM, Temixco, Morelos (Mexico)

    2000-07-01

    The saturation current and junction quality factor of a series of commercial CdTe/CdS solar cells have been measured. A high saturation current (compared to, for example, Si cells) is the primary cause of lower than theoretical efficiency. Furthermore, this current and the junction quality factor are functions of both light intensity and voltage bias level. It was found that tunneling is the predominant junction transport mechanism at high light levels and at low voltages while diffusion and regeneration/combination dominate at high voltage and low light levels. A model is presented to account for these observations. [Spanish] Se midieron las corrientes de saturacion y el factor de calidad de la union de una serie de celdas solares CdTe/CdS. Una corriente de saturacion alta (comparada por ejemplo a celdas de Si) es la causa primordial de eficiencia inferior a la teorica. Mas aun esta corriente y el factor de la calidad de la junta son funciones tanto de la intensidad de la luz y del nivel del voltaje de polarizacion. Se encontro que el paso a traves de una barrera de potencial (Tunneling) es el mecanismo de transporte predominate en la junta a altos niveles de luz y bajos voltajes mientras que la difusion y la regeneracion-combinacion predominaba a alto voltaje y bajos niveles de luz. Se presenta un modelo para tomar en cuenta estas observaciones.

  2. Photoluminescence of Cu-doped CdTe and related stability issues in CdS/CdTe solar cells

    Science.gov (United States)

    Grecu, D.; Compaan, A. D.; Young, D.; Jayamaha, U.; Rose, D. H.

    2000-09-01

    We explore Cu electronic states in CdTe using photoluminescence as the main investigative method. Our results are consistent with some Cu atoms occupying substitutional positions on the Cd sublattice and with others forming Frenkel pairs of the type Cui+-VCd- involving an interstitial Cu and a Cd vacancy. In addition, we find that Cu-doped CdTe samples exhibit a significant "aging" behavior, attributable to the instability of Cu acceptor states as verified by our Hall measurements. The aging appears to be reversible by a 150-200 °C anneal. Our results are used to explain efficiency degradation of some CdTe solar-cell devices which use Cu for the formation of a backcontact.

  3. Summary Abstract: HgTe–CdTe superlattices

    OpenAIRE

    McGill, T. C.; Smith, D L

    1983-01-01

    In their seminal paper on superlattices, Esaki and Tsu indicated that superlattices involving II-VI compounds and their alloys, could be of interest along with superlattices involving Group IV and III-V semiconductors. Independently, Schulman and McGill identified the Hg-Te-CdTe superlattice as an interesting case to study. HgTe and CdTe have the same crystal structure and lattice constrant to 0.3%. CdTe is a conventional zinc blende semiconductor with a band gap of about 1.6 eV; HgTe is a ze...

  4. Influence of capping on manganese diffusion in {CdTe}/{CdMnTe} quantum well structures

    Science.gov (United States)

    Maćkowski, S.; Nguyen The Khoi; Golnik, A.; Kossacki, P.; Gaj, J. A.; Kamińska, E.; Piotrowska, A.; Karczewski, G.; Wojtowicz, T.; Kossut, J.

    1998-06-01

    The influence of In- or SiO 2-capping on thermally induced interdiffusion in {CdTe}/{CdMnTe} quantum well structures was investigated by spin tracing method based on exciton Zeeman splitting measurements. The results show that the diffusion of manganese occurring at interfaces during an annealing process is strongly enhanced in the case of In-capped samples. SiO 2 protective layers, on the other hand, efficiently inhibit the diffusion of Mn across the interfaces, even in the case of In capping. The degree of the interdiffusion was found to be correlated with Cd and Te evaporation from the samples, measured by Rutherford Backscattering, indicating an important role of cation vacancies in the interdiffusion process.

  5. ZnSe-ZnMnSe and CdTe-CdMnTe superlattices

    Science.gov (United States)

    Gunshor, R. L.; Kolodziejski, L. A.; Otsuka, N.; Datta, S.

    1986-08-01

    We report the growth and characterization of superiattices of a new wide-gap, zincblende material system, Zn 1 - xMn xSe. ZnSe exhibiting dominant free excitonic emission in photoluminescence (PL) is the well material, while wider-band-gap Zn 1 - xMn xSe (0.23 efficiency compared to films of the ZnSe well material, while transmission electron microscopy shows extremely abrupt interfaces by the presence of seventh-order satellite spots. Previously reported superiattices in the CdTe-CdMnTe material system were grown with the (111) orientation, and exhibit unique excitonic properties believed related to the (111) interfaces. Using various techniques to select (111) or (100) heteroepitaxy of CdTe on (100) GaAs, we report the first (100) superlattices of this material, and compare the optical properties to the previous (111) structures.

  6. 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.

  7. Fundamental engineering analysis of CdTe/CdS photovoltaic processing

    Science.gov (United States)

    Baron, B. N.; Jackson, S. C.; Russell, T. W. F.

    1986-06-01

    An engineering analysis of the deposition of CdTe and CdS thin-films by vacuum evaporation for fabricating photovoltaic solar cells has been carried out. Mathematical models describing the mass flows, molecular beam distributions, and film growth kinetics of CdTe and HgCdTe deposition have been developed and verified in laboratoy-scale experiments. Small-area CdTe/CdS photovoltaic devices having efficiencies of 6% were fabricated. Verified mathematical models were used to design large-scale evaporation sources. Commercially available architectural glass coating equipment can be adapted for large-area deposition of CdTe/CdS thin films in an in-line process for economically fabricatig thin-film CdTe/CdS photovoltaic modules.

  8. TeV emission from SN 1006

    OpenAIRE

    Mastichiadis, A.; de Jager, O. C.

    1996-01-01

    Supernova 1006 is the first shell type supernova remnant to show evidence of particle acceleration to TeV energies. In the present paper we examine this possibility by modeling the observed X-ray non-thermal emission in terms of synchrotron radiation from Fermi accelerated electrons. The predicted synchrotron spectrum fits the radio and non-thermal component of the observed soft X-ray to hard X-ray emission quite well. These particles can produce TeV gamma rays by inverse Compton scattering o...

  9. Application of CdTe (CdZnTe) detectors for radioactive waste characterization

    CERN Document Server

    Dovbnya, N A; Kutny, V E

    2002-01-01

    The radiation detectors based on wide-zone semiconductor CdTe (CdZnTe) monocrystals have promising advantages for their application in investigation (characterization) of radioactive waste. Among these advantages there are the wide range of photons flux and energy, high registration efficiency and satisfactory energy resolution without deep cooling of the detector. This report discusses the obtained data concerning radiation stability of detectors, influence of different conditions (filters, collimators, registration channel fill etc.) on their energy resolution in spectrometric regime, as well as a dependence of radionuclide identification accuracy on detector size.

  10. Growth of CdTe-CdMnTe heterostructures by molecular beam epitaxy

    Science.gov (United States)

    Bicknell-Tassius, Robert N.

    1991-08-01

    The successful MBE growth of CdMnTe-CdTe heterostructures and superlattices has demonstrated the feasibility of growing layered structures incorporating dilute magnetic semiconductor materials (DMS). These materials exhibit new and interesting properties. These properties allow the band-gap engineering to continue after the structure has been grown through the application of an external magnetic field. During the growth process the engineering can be accomplished through traditional means, i.e., through the choice of layer thickness and/or the choice of the strain state of the structure.

  11. 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.

  12. Highest-order optical phonon-mediated relaxation in CdTe/ZnTe quantum dots

    International Nuclear Information System (INIS)

    The highest 19th-order longitudinal optical (LO) phonon-mediated relaxation was observed in photoluminescence excitation spectra of CdTe self-assembled quantum dots grown in ZnTe. Hot excitons photoexcited highly in the ZnTe barrier layer are relaxed into the wetting-layer state by emitting multiple LO phonons of the barrier layer successively. Below the wetting-layer state, the LO phonons involved in the relaxation are transformed to those of interfacial ZnxCd1-xTe surrounding CdTe quantum dots. The ZnTe-like and CdTe-like LO phonons of ZnxCd1-xTe and lastly acoustic phonons are emitted in the relaxation into the CdTe dots. The observed main relaxation is the fast relaxation directly into CdTe quantum dots and is not the relaxation through either the wetting-layer quantum well or the band bottom of the ZnTe barrier layer. This observation shows very efficient optical phonon-mediated relaxation of hot excitons excited highly in the ZnTe conduction band through not only the ZnTe extended state but also localized state in the CdTe quantum dots reflecting strong exciton-LO phonon interaction of telluride compounds

  13. 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...

  14. Room Temperature Ferroelectricity in Ultrathin SnTe Films

    Science.gov (United States)

    Chang, Kai; Liu, Junwei; Lin, Haicheng; Zhao, Kun; Zhong, Yong; Ji, Shuai-Hua; He, Ke; Wang, Lili; Ma, Xucun; Fu, Liang; Chen, Xi; Xue, Qi-Kun

    2015-03-01

    The ultrathin SnTe films with several unit cell thickness grown on graphitized SiC(0001) surface have been studied by the scanning tunneling microscopy and spectroscopy (STM/S). The domain structures, local lattice distortion and the electronic band bending at film edges induced by the in-plane spontaneous polarization along have been revealed at atomic scale. The experiments at variant temperature show that the Curie temperature Tc of the one unit cell thick (two atomic layers) SnTe film is as high as 280K, much higher than that of the bulk counterpart (~100K) and the 2-4 unit cell thick films even indicate robust ferroelectricity at room temperature. This Tc enhancement is attributed to the stress-free interface, larger electronic band gap and greatly reduced Sn vacancy concentration in the ultrathin films. The lateral domain size varies from several tens to several hundreds of nanometers, and the spontaneous polarization direction could be modified by STM tip. Those properties of ultrathin SnTe films show the potential application on ferroelectric devices. The work was financially supported by Ministry of Science and Technology of China, National Science Foundation and Ministry of Education of China.

  15. 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].

  16. Stabilizing CdTe/CdS solar cells with Cu-containing contacts to p-CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Dobson, K.D.; Visoly-Fisher, I.; Hodes, G.; Cahen, D. [Weizmann Inst. of Science, Rehovoth (Israel)

    2001-10-02

    High efficiency CdTe/CdS thin-film solar cells require low resistance contacts to p-CdTe, which is frequently achieved by addition of Cu. Decreases in cell efficiency over time, however, have been associated with Cu from the contact. The question that is considered here is if Cu is really detrimental to cell performance? By performing a series of thermal stress tests the authors reach a far more optimistic conclusion than what has hitherto been assumed.f (orig.)

  17. Preliminary study of CdTe and CdTe:Cu thin films nanostructures deposited by using DC magnetron sputtering

    International Nuclear Information System (INIS)

    Growth and properties of CdTe and CdTe:Cu thin films nanostrucures deposited by using dc magnetron sputtering are reported. Scanning electron microscope (SEM) was used to observe the surface morphologies of the thin films. At growth conditions of 250 °C and 14 W, CdTe films did not yet evenly deposited. However, at growth temperature and plasma power of 325 °C and 43 W, both CdTe and CdTe:Cu(2%) have deposited on the substrates. In this condition, the morphology of the films indicate that the films have a grain-like nanostructures. Grain size diameter of about 200 nm begin to appear on top of the films. Energy Dispersive X-rays spectroscopy (EDX) was used to investigate chemical elements of the Cu doped CdTe film deposited. It was found that the film deposited consist of Cd, Te and Cu elements. XRD was used to investigate the full width at half maximum (FWHM) values of the thin films deposited. The results show that CdTe:Cu(2%) thin film has better crystallographic properties than CdTe thin film. The UV-Vis spectrometer was used to investigate the optical properties of thin films deposited. The transmittance spectra showed that transmittance of CdTe:Cu(2%) film is lower than CdTe film. It was found that the bandgap energy of CdTe and CdTe:Cu(2%) thin films of about 1.48 eV

  18. Physical properties of electron beam evaporated CdTe and CdTe:Cu thin films

    International Nuclear Information System (INIS)

    In this paper, we report on physical properties of pure and Cu doped cadmium telluride (CdTe) films deposited onto corning 7059 microscopic glass substrates by electron beam evaporation technique. X-ray diffraction study showed that all the deposited films belong to amorphous nature. The average transmittance of the films is varied between 77% and 90%. The optical energy band gap of pure CdTe film is 1.57 eV and it decreased to 1.47 eV upon 4 wt. % of Cu addition, which may be due to the extension of localized states in the band structure. The refractive index of the films was calculated using Swanepoel method. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion energy (Ed) parameters, dielectric constants, plasma frequency, and oscillator energy (Eo) of CdTe and CdTe:Cu films were calculated and discussed in detail with the light of possible mechanisms underlying the phenomena. The variation in intensity of photoluminescence band edge emission peak observed at 820 nm with Cu dopant is due to the change in surface state density. The observed trigonal lattice of Te peaks in the micro-Raman spectra confirms the p-type conductive nature of films, which was further corroborated by the Hall effect measurement. The lowest resistivity of 6.61 × 104 Ω cm was obtained for the CdTe:Cu (3 wt. %) film

  19. The synthesis and modification of CdTe/CdS core shell quantum dots.

    Science.gov (United States)

    Chen, Jianqiu; Xiao, An; Zhang, Zhengwei; Yu, Yan; Yan, Zhengyu

    2015-12-01

    A simple and economical synthesis method of CdTe quantum dots (QDs) has been developed using glutathione as a modifier in an aqueous system. The fluorescent properties of as-prepared CdTe QDs at different reaction times were studied to optimize the synthesis conditions. CdTe/CdS QDs with core-shell structure was obtained by modifying as-synthesized CdTe QDs with refluxing and microwave method, respectively. The properties of the CdTe/CdS QDs were thoroughly investigated by photoluminescence (PL) and inverted fluorescence microscope, and exhibited high fluorescence intensity and good optical property. The study also shows that the microwave synthesis of CdTe/CdS QDs had more dispersed particle size and higher fluorescence intensity. PMID:26162337

  20. RAPID COMMUNICATION: The effect of the transparent conductive oxide on the performance of thin film CdS/CdTe solar cells

    Science.gov (United States)

    Alamri, S. N.; Brinkman, A. W.

    2000-01-01

    Thin film CdS/CdTe solar cells fabricated on SnOx -coated glass have been found to give higher efficiencies than similar cells produced on indium-tin oxide (ITO) coated glass substrates. Further investigation implicated the CdS/ITO interface as the cause of the problem; current-voltage measurements revealed that on heating in air the CdS/ITO junction became rectifying. This is consistent with recently reported findings which show that the work function of ITO is raised above that of CdS by oxidative treatments (such as heating in air) which would make the ITO/CdS junction rectifying rather than ohmic.

  1. Characterization of thin film ZnCdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Mahammad Hussain, O.; Sreedhara Reddy, P.; Srinivasalu Naidu, B.; Uthanna, S.; Jayarama Reddy, P. (Sri Venkateswara Univ., Tirupati (India). Dept. of Physics)

    1991-07-01

    n-ZnCdS/p-CdTe polycrystalline thin film solar cells were fabricated by laser evaporating CdTe onto sprayed ZnCdS films. The cells were characterized by studying current-voltage, capacitance-voltage and spectral response measurements. A maximum efficiency of 7.6% was observed for a cell area of 1 cm{sup 2}. (author).

  2. Ohmic contacts on n-type Hg0.4Cd0.6Te

    International Nuclear Information System (INIS)

    In this paper the electrical characteristics of In, Sn, Au and Pt contacts on n-type Hg0.4Cd0.6Te formed in the presence and absence of prior In2+ implantation are examined. Measurements of specific contact resistance made using a Transmission Line Model have shown that the unimplanted In/Hg0.4Cd0.6Te and Sn/Hg0.4Te junctions gave values of ρc = 3.0 x 10-3 ohm.cm2. Auger sputter profiles of the as-deposited In/Hg0.4Cd0.6Te and Sn/Hg0.4Cd0.6Te interfaces have shown a significant in-diffusion of the metal overlayer. The influence of shallow In2+ implantation prior to metallization was an increase in ρc which occurred above a dose of 1013 ions/cm2. In contrast, Pt and Au formed Schottky barrier diodes on n-type Hg0.4Cd0.6Te with φb = 0.69 eV for Pt and φb = 0.79 eV for Au. With prior In2+ implantation both Pt and Au contacts exhibited an ohmic behavior with ρc = 2 x 10-1 ohm.cm2. These results have significance in the fabrication of devices for 1.0 - 2.5μm optical communications

  3. Rietveld analysis of CdS/CdTe thin film junctions submitted to a CdCl2 heat treatment

    International Nuclear Information System (INIS)

    In this work we investigate the effects of a CdCl2 heat treatment on the interface of CdTe/CdS heterojunction solar cells using Rietveld analysis of X-ray diffraction patterns. Although the Rietveld method is an important tool for the study of materials by X-ray diffraction, there have been few reports of its use in thin film analysis. The results showed the occurrence of interdiffusion in the CdS–CdTe boundary, with substitution of tellurium by sulfur in the CdTe lattice that resulted in a CdSxTe1−x alloy. The sulfur content of the alloy was greater than in previous studies. This is attributed to the low oxygen concentration during processing and the strong (111) texture of the CdTe films. - Highlights: • CdS/CdTe solar cells were treated in the presence of CdCl2 vapor. • Interdiffusion in CdS/CdTe junction was investigated by Rietveld analysis. • Sulfur replaces tellurium in the CdTe layer. • Sulfur amount increases with the temperature of the CdCl2 heat treatment. • Introduction of sulfur led to a nanocrystalline component in CdTe layer

  4. 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

  5. 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...

  6. 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)

  7. 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.

  8. 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

  9. HgCdTe e-avalanche photodiode detector arrays

    OpenAIRE

    Anand Singh; Shukla, A. K.; Ravinder Pal

    2015-01-01

    Initial results on the MWIR e-APD detector arrays with 30 μm pitch fabricated on LPE grown compositionally graded p-HgCdTe epilayers are presented. High dynamic resistance times active area (R0A) product 2 × 106 Ω-cm2, low dark current density 4 nA/cm2 and high gain 5500 at -8 V were achieved in the n+-υ-p+ HgCdTe e-APD at 80 K. LPE based HgCdTe e-APD development makes this technology amenable for adoption in the foundries established for the conventional HgCdTe photovoltaic detector arrays w...

  10. A Comparative Study on the Optical Properties of Multilayer CdSe / CdTe Thin Film with Single Layer CdTe and CdSe Films

    OpenAIRE

    M. Melvin David Kumar; Suganthi Devadason

    2013-01-01

    CdTe and CdSe single layer thin films and CdSe / CdTe multilayer (ML) thin film were prepared by using physical vapour deposition method. Optical properties of CdSe / CdTe multilayer thin film shows different behavior due to type II band structure alignment. Energy band gap value of CdSe / CdTe ML thin film is shifted to higher value than that of single layer CdTe film. This is due to decrease in crystallite size to dimension smaller than the Bohr exciton radius of CdTe (14 nm). Crystallite ...

  11. Efficiency of Thin-Film CdS/CdTe Solar Cells

    OpenAIRE

    Kosyachenko, Leonid

    2010-01-01

    The findings of this paper give further insight into the problems and ascertain some requirements imposed on the CdTe absorber layer parameters in a CdTe/CdS solar cell, which in our opinion could be taken into account in the technology of fabrication of solar cells. The model taking into account the drift and diffusion photocurrent components with regard to recombination losses in the space-charge region, at the CdS-CdTe interface and the back surface of the CdTe layer allows us to obtain a ...

  12. 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.

  13. Electronic structure of SnSb2Te4 and PbSb2Te4 topological insulators

    International Nuclear Information System (INIS)

    The bulk and surface electronic structure of SnSb2Te4 and PbSb2Te4 ternary compounds consisting of three septuple layer blocks separated by van der Waals gaps has been theoretically studied. It has been shown these systems are three dimensional topological insulators. The calculations of the MSb2Te4 (M = Pb, Sn) surface electronic structure show that these compound are well promising for practical application compared to parent Sb2Te3 compound.

  14. Additional evidence concerning the valence-band offset in HgTe/CdTe

    Science.gov (United States)

    Young, P. M.; Ehrenreich, H.

    1991-05-01

    The consistency of large values of the valence-band offset, Λ, in HgTe/CdTe superlattices with magneto-optical experiments is examined in light of data on a 90-Å HgTe/40-Å CdTe superlattice. The data are shown to be consistent with values Λ=400+/-40 meV rather than the much smaller cited values. This analysis, when considered with photoemission experiments, leaves intact the conclusion that HgTe/CdTe superlattices are best explained by a large offset.

  15. 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.

  16. Aqueous Phase Synthesis of Red CdX (X=Te,Te/CdS,Te/ZnS) Quantum Dots and Their Toxic Effects%水相合成CdX(X=Te,Te/CdS,Te/ZnS)红色量子点及毒性效应

    Institute of Scientific and Technical Information of China (English)

    王显祥; 黄娟; 靳茹文; 杨中科; 单志; 杨婉身

    2009-01-01

    分别以巯基乙酸(Mercaptoacetic Acid,MA)、还原犁谷胱甘肽(Glutathione,GSH)为稳定剂在水相中直接合成了巯基乙酸CdTe(CdTe-MA)、红色巯基乙酸CdTe/CdS(CdTe/CdS-MA)、巯基乙酸CdTe/ZnS(CdTe/ZnS-MA)及谷胱甘肽CdTe(CdTe-GSH)量子点.其中,CdTe-GSH量子点的量子产率可达47.3%.体外溶血实验证实CdTe/ZnS-MA和CdTe-GSH量子点的溶血率较CdTe-MA和CdTe/CdS-MA低,浓度为0.05 mmol/L的量子点溶血率<5%,达到了生物医用材料的要求.活体实验证实:通过尾静脉方式把量子点注入小鼠体内后,荧光显微镜观察发现高剂量的量子点(0.4mmol/10 g)在体内主要在心、肝、脾、肾组织中分布较多,且引起不同程度的组织病变.

  17. Microalloying with Cd of Antifriction Sn-Sb-Cu Alloys

    OpenAIRE

    Cinca Ionel Lupinca; Constantin Marta; Attila Szabo

    2012-01-01

    In the case of bimetallic sliding linings with superior technological characteristics, the use of an antifriction ally is imposed an alloy of the type Sn-Sb-Cu, which possesses a high adherence to the steel stand and a high durability in exploitation. For this reason we use the microalloying of the antifriction alloy with cadmium. The microalloying with Cd of antifriction alloys Sn-Sb-Cu determines an increase of the adhesion property of the antifriction alloy on the steel ...

  18. Calorimetric study of tellurium rich Se-Te-Sn glasses

    Science.gov (United States)

    Heera, Pawan; Kumar, Anup; Jharwal, Manish; Sharma, Raman

    2016-05-01

    We report the calorimetric study of amorphous Se30Te70-x Snx alloys for x= 0, 1.5, 2.5, 4.5 in terms of kinetic parameters. The DSC curves recorded at four different heating rates are analyzed to determine the transition temperatures, activation energy, thermal stability, glass forming ability. The crystallization process has been investigated using Kissinger, Matusita, Augis and Bennett, and Gao and Wang models. Various kinetic parameters have been calculated for a better understanding of the growth mechanism. The glass transition temperatures Tg, onset crystallization Tc, peak crystallization Tp, and melting temperature Tm are found to increase with the increase in Sn content. The system under investigation is found to be thermally stable for at lower at% of Sn. The values of parameters HR, Hw, and S indicate that Glass forming ability (GFA) decays with an increase in Sn content.

  19. 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.

  20. Electrical characterization of CdTe grain-boundary properties from as processed CdTe/CdS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Woods, L.M.; Robinson, G.Y. [Colorado State Univ., Fort Collins, CO (United States); Levi, D.H.; Ahrenkiel, R.K. [National Renewable Energy Lab., Golden, CO (United States); Kaydanov, V. [Colorado School of Mines, Golden, CO (United States)

    1998-09-01

    An ability to liftoff or separate the thin-film polycrystalline CdTe from the CdS, without the use of chemical etches, has enabled direct electrical characterization of the as-processed CdTe near the CdTe/CdS heterointerface. The authors use this ability to understand how a back-contact, nitric-phosphoric (NP) etch affects the grain boundaries throughout the film. Quantitative determination of the grain-boundary barrier potentials and estimates of doping density near the grain perimeter are determined from theoretical fits to measurements of the current vs. temperature. Estimates of the bulk doping are determined from high-frequency resistivity measurements. The light and dark barrier potentials change after the NP etch, and the origin of this change is postulated. Also, a variable doping density within the grains of non-etched material has been determined. These results allow a semi-quantitative grain-boundary band diagram to be drawn that should aid in determining more accurate two-dimensional models for polycrystalline CdTe solar cells.

  1. 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.

  2. 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)

  3. Challenges and Prospects for Developing CdS/CdTe Substrate Solar Cells on Mo foils

    OpenAIRE

    Williams, Ben; Major, Jonathan; Bowen, Leon; Phillips, Laurie; Zoppi, Guillaume; Forbes, Ian; Durose, Ken

    2014-01-01

    ITO/ZnO/CdS/CdTe/Mo solar cells have been grown in the substrate configuration by a combination of close-space sublimation and RF sputtering. A peak efficiency of 8.01% was achieved. A two stage CdCl2 annealing process was developed, with the first stage contributing to CdTe doping and the second being linked to CdTe/CdS interdiffusion by secondary ion mass spectrometry analysis. The inclusion of a ZnO layer between CdS and ITO layers improved performance significantly (from η=6% to η=8%) by ...

  4. An ultrasensitive hydrogen peroxide biosensor based on electrocatalytic synergy of graphene-gold nanocomposite, CdTe-CdS core-shell quantum dots and gold nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Gu Zhiguo; Yang Shuping [School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122 (China); Li Zaijun, E-mail: zaijunli@263.net [School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122 (China); Sun Xiulan [School of Food Science and Technology, Jiangnan University, Wuxi 214122 (China); Wang Guangli [School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122 (China); Fang Yinjun [Zhejiang Zanyu Technology Co., Ltd., Hangzhou 310009 (China); Liu Junkang [School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122 (China)

    2011-09-02

    Graphical abstract: We first reported an ultrasensitive hydrogen peroxide biosensor in this work, which was fabricated by coating graphene-gold nanocomposite, CdTe-CdS core-shell quantum dots, gold nanoparticles and horseradish peroxidase in sequence on the surface of gold electrode. Since a promising their electrocatalytic synergy towards hydrogen peroxide was achieved, the biosensor displayed very high sensitivity, low detection limit (S/N = 3) (3.2 x 10{sup -11} M) and good long-term stability (20 weeks). Highlights: {center_dot} We for the first time integrated novel hydrogen peroxide biosensor based on G-AuNP, CdTe-CdS and AuNPs. {center_dot} Three nanomaterials show remarkable synergistic electrocatalysis towards hydrogen peroxide. {center_dot} The biosensor provides the best sensitivity in all biosensors based on graphene for detection of glucose up to now. - Abstract: We first reported an ultrasensitive hydrogen peroxide biosensor in this work. The biosensor was fabricated by coating graphene-gold nanocomposite (G-AuNP), CdTe-CdS core-shell quantum dots (CdTe-CdS), gold nanoparticles (AuNPs) and horseradish peroxidase (HRP) in sequence on the surface of gold electrode (GE). Cyclic voltammetry and differential pulse voltammetry were used to investigate electrochemical performances of the biosensor. Since promising electrocatalytic synergy of G-AuNP, CdTe-CdS and AuNPs towards hydrogen peroxide was achieved, the biosensor displayed a high sensitivity, low detection limit (S/N = 3) (3.2 x 10{sup -11} M), wide calibration range (from 1 x 10{sup -10} M to 1.2 x 10{sup -8} M) and good long-term stability (20 weeks). Moreover, the effects of omitting G-AuNP, CdTe-CdS and AuNP were also examined. It was found that sensitivity of the biosensor is more 11-fold better if G-AuNP, CdTe-CdS and AuNPs are used. This could be ascribed to improvement of the conductivity between graphene nanosheets in the G-AuNP due to introduction of the AuNPs, ultrafast charge transfer

  5. An ultrasensitive hydrogen peroxide biosensor based on electrocatalytic synergy of graphene-gold nanocomposite, CdTe-CdS core-shell quantum dots and gold nanoparticles

    International Nuclear Information System (INIS)

    Graphical abstract: We first reported an ultrasensitive hydrogen peroxide biosensor in this work, which was fabricated by coating graphene-gold nanocomposite, CdTe-CdS core-shell quantum dots, gold nanoparticles and horseradish peroxidase in sequence on the surface of gold electrode. Since a promising their electrocatalytic synergy towards hydrogen peroxide was achieved, the biosensor displayed very high sensitivity, low detection limit (S/N = 3) (3.2 x 10-11 M) and good long-term stability (20 weeks). Highlights: · We for the first time integrated novel hydrogen peroxide biosensor based on G-AuNP, CdTe-CdS and AuNPs. · Three nanomaterials show remarkable synergistic electrocatalysis towards hydrogen peroxide. · The biosensor provides the best sensitivity in all biosensors based on graphene for detection of glucose up to now. - Abstract: We first reported an ultrasensitive hydrogen peroxide biosensor in this work. The biosensor was fabricated by coating graphene-gold nanocomposite (G-AuNP), CdTe-CdS core-shell quantum dots (CdTe-CdS), gold nanoparticles (AuNPs) and horseradish peroxidase (HRP) in sequence on the surface of gold electrode (GE). Cyclic voltammetry and differential pulse voltammetry were used to investigate electrochemical performances of the biosensor. Since promising electrocatalytic synergy of G-AuNP, CdTe-CdS and AuNPs towards hydrogen peroxide was achieved, the biosensor displayed a high sensitivity, low detection limit (S/N = 3) (3.2 x 10-11 M), wide calibration range (from 1 x 10-10 M to 1.2 x 10-8 M) and good long-term stability (20 weeks). Moreover, the effects of omitting G-AuNP, CdTe-CdS and AuNP were also examined. It was found that sensitivity of the biosensor is more 11-fold better if G-AuNP, CdTe-CdS and AuNPs are used. This could be ascribed to improvement of the conductivity between graphene nanosheets in the G-AuNP due to introduction of the AuNPs, ultrafast charge transfer from CdTe-CdS to the graphene sheets and AuNP due to

  6. Development of electrodeposited ZnTe layers as window materials in ZnTe/CdTe/CdHgTe multi-layer solar cells

    International Nuclear Information System (INIS)

    Zinc telluride (ZnTe) thin films have been deposited on glass/conducting glass substrates using a low-cost electrodeposition method. The resulting films have been characterized using various techniques in order to optimize growth parameters. X-ray diffraction (XRD) has been used to identify the phases present in the films. Photoelectrochemical (PEC) cell and optical absorption measurements have been performed to determine the electrical conductivity type, and the bandgap of the layers, respectively. It has been confirmed by XRD measurement that the deposited layers mainly consist of ZnTe phases. The PEC measurements indicate that the ZnTe layers are p-type in electrical conduction and optical absorption measurements show that their bandgap is in the range 2.10-2.20 eV. p-Type ZnTe window materials have been used in CdTe based solar cell structures, following new designs of graded bandgap multi-layer solar cells. The structures of FTO/ZnTe/CdTe/metal and FTO/ZnTe/CdTe/CdHgTe/metal have been investigated. The results are presented in this paper using observed experimental data

  7. Anomalous Hall Effect in SnMnEuTe and SnMnErTe mixed crystals

    OpenAIRE

    Racka, K.; Kuryliszyn, I.; Arciszewska, M.; Dobrowolski, W.; Broto, J. -M.; Goiran, M.; Portugall, O.; Rakoto, H.; Raquet, B.; Dugaev, V.; Slynko, E. I.; Slynko, V. E.

    2002-01-01

    The Anomalous Hall Effect was investigated in IV-VI ferromagnetic semimagnetic semiconductors of Sn1-xMnxTe codoped with either Eu or Er. The analysis of experimental data: Hall resisitivity and magnetization showed that AHE coefficient RS depends on temperature, its value decreases with the temperature increase. We observe that above ferromagnet-paramagnet transition temperature RS changes sign. We discuss the possible physical mechanisms responsible for observed temperature dependence of RS...

  8. Comparative study of SnS recrystallization in molten CdI2, SnCl2and KI

    International Nuclear Information System (INIS)

    In the present study, the recrystallization of polycrystalline SnS in different molten salts CdI2, SnCl2 and KI as flux materials are presented. The recrystallization and growth of polycrystalline material in molten salts produces unique SnS monograin powders usable in monograin layer solar cells. XRD and Raman analysis revealed that single phase SnS powder can be obtained in KI at 740 C and in SnCl2 at 500 C. Long time heating of SnS in molten CdI2 was accompanied by chemical interaction between SnS and CdI2 that resulted in a mixture of CdS and Sn2S3 crystals. SEM images showed that morphology of crystals can be controlled by the nature of the flux materials: needle-like Sn2S3 together with round edged crystals of CdS in CdI2, flat crystals of SnS with smooth surfaces in SnCl2 and well-formed SnS crystals with rounded edges in KI had been formed. The temperatures of phase transitions and/or the interactions of SnS and flux materials were determined by differential thermal analysis. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. C-V Calculations in CdS/CdTe Thin Films Solar Cells with a CdSxTe1-x Interlayer

    Directory of Open Access Journals (Sweden)

    A. Gonzalez-Cisneros

    2013-01-01

    Full Text Available In CdS/CdTe solar cells, chemical interdiffusion at the interface gives rise to the formation of an interlayer of the ternary compound CdSxCdTe1-x. In this work, we evaluate the effects of this interlayer in CdS/CdTe photovoltaic cells in order to improve theoretical results describing experimental C-V (capacitance versus voltage characteristics. We extended our previous theoretical methodology developed on the basis of three cardinal equations (Castillo-Alvarado et al., 2010. The present results provide a better fit to experimental data obtained from CdS/CdTe solar cells grown in our laboratory by the chemical bath deposition (for CdS film and the close-spaced vapor transport (for CdTe film techniques.

  10. Photovoltaic properties of sintered CdS/CdTe solar cells doped with Cu

    International Nuclear Information System (INIS)

    In this paper, all polycrystalline CdS/CdTe solar cells doped with Cu are prepared by a screen printing and sintering method. Cell parameters of the sintered CdS/CdTe solar cells have been investigated in an attempt to find out the optimum doping conditions and concentrations of Cu by adding various amounts of CuCl2 either into CdTe layer or into back contact carbon layer. Cell parameters of the sintered CdS/CdTe solar cells which contained various amounts of CuCl2 in the CdTe layers before sintering stay at about the same values as the amount of CuCl2 increases up to 25 ppm, and then decreases sharply as the amount of CuCl2 further increases. The Cu added in the CdTe layer diffuses into the CdS layer during the sintering of the CdS-CdTe composite at 625 degrees C to densify the CdTe layer and causes the decrease in the optical transmission of CdS resulting in the degradation of the cell performance. In case the Cu dopant was dispersed in the back carbon paint and was followed by annealing, all cell parameters are improved significantly compared with those fabricated by adding CuCl2 in the CdTe layer before sintering. A sintered CdS/CdTe solar cell which contained 25 ppm CuCl2 in the carbon paste and was annealed at 350 degrees C for 10 min shows the highest efficiency. The efficiency of this cell is 12.4% under solar irradiation with an intensity of 80.4 mW/cm2

  11. Synthesis of near-infrared-emitting CdTe/CdSe/ZnSe/ZnS heterostructure.

    Science.gov (United States)

    Yang, Ping

    2014-04-01

    Near-infrared-emitting quantum dots (QDs) were fabricated via organic synthesis strategies through constructing CdTe/CdSe/ZnSe/ZnS multishell heterostructure. An effective shell-coating route was developed for multishell growth on CdTe cores. Core/shell growth was monitored by absorption and photoluminescence (PL) spectroscopy and transmission electron microscopy observation. Yellow emitting CdTe cores were coated with a CdSe shell to generate type II structure. This yields core/shell QDs with red photoluminescence. The passivation by the ZnSe shell having a substantially wide bandgap confines the excitons within the CdTe/CdSe interface and isolates them from the solution environment and consequently improves the stability of the heterostructure. An additional ZnS shell was deposited around the outer layer of CdTe/CdSe/ZnSe QDs to form a heterostructure through the reaction between zinc oleate and trioctylphosphine sulfur in the crude CdTe/CdSe/ZnSe solution. By varying CdTe core size and each shell thickness, the PL wavelength of the obtained heterostructure can span from 580 to 770 nm. The PL efficiency is quenched in CdTe QDs in diluted solution but increases substantially up to 24% for CdTe/CdSe core/shell QDs. The PL efficiency of CdTe/CdSe/ZnSe/ZnS QDs with average diameter of 5.4 nm and a PL peak wavelength of 770 nm is 20%. PMID:24734747

  12. Response of Cds/CdTe Devices to Te Exposure of Back Contact: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Gessert, T. A.; Burst, J. M.; Ma, J.; Wei, S. H.; Kuciauskas, D.; Barnes, T. M.; Duenow, J. N.; Young, M. R.; Rance, W. L.; Li, J. V.; Dippo, P.

    2012-06-01

    Theoretical predictions of thin-film CdS/CdTe photovoltaic (PV) devices have suggested performance may be improved by reducing recombination due to Te-vacancy (VTe) or Te-interstitial (Tei) defects. Although formation of these intrinsic defects is likely influenced by CdTe deposition parameters, it also may be coupled to formation of beneficial cadmium vacancy (VCd) defects. If this is true, reducing potential effects of VTe or Tei may be difficult without also reducing the density of VCd. In contrast, post-deposition processes can sometimes afford a greater degree of defect control. Here we explore a post-deposition process that appears to influence the Te-related defects in polycrystalline CdTe. Specifically, we have exposed the CdTe surface to Te prior to ZnTe:Cu/Ti contact-interface formation with the goal of reducing VTe but without significantly reducing VCd. Initial results show that when this modified contact is used on a CdCl2-treated CdS/CdTe device, significantly poorer device performance results. This suggests two things: First, the amount of free-Te available during contact formation (either from chemical etching or CuTe or ZnTe deposition) may be a more important parameter to device performance than previously appreciated. Second, if processes have been used to reduce the effect of VTe (e.g., oxygen and chlorine additions to the CdTe), adding even a small amount of Te may produce detrimental defects.

  13. 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.

  14. Raman scattering determination of strain in CdTe/ZnTe superlattices

    OpenAIRE

    Jackson, M K; Miles, R. H.; McGill, T. C.; Faurie, J. P.

    1989-01-01

    The strain configuration in CdTe/ZnTe strained-layer superlattices has been measured by Raman scattering near resonance. The ZnTe-like longitudinal optical phonon energy in the superlattice is significantly shifted from the bulk value to lower energies and the shift increases with increasing superlattice CdTe fraction. The observed shifts agree with calculations of strain shifts based on a free-standing strain distribution.

  15. Voltammetry as a Tool for Characterization of CdTe Quantum Dots

    OpenAIRE

    Vojtech Adam; Pavlina Sobrova; Marketa Ryvolova; Jaromir Hubalek; Rene Kizek

    2013-01-01

    Electrochemical detection of quantum dots (QDs) has already been used in numerous applications. However, QDs have not been well characterized using voltammetry, with respect to their characterization and quantification. Therefore, the main aim was to characterize CdTe QDs using cyclic and differential pulse voltammetry. The obtained peaks were identified and the detection limit (3 S/N) was estimated down to 100 fg/mL. Based on the convincing results, a new method for how to study stability an...

  16. A Simple Sb2Te3 Back-Contact Process for CdTe Solar Cells

    Science.gov (United States)

    Siepchen, B.; Späth, B.; Drost, C.; Krishnakumar, V.; Kraft, C.; Winkler, M.; König, J.; Bartholomé, K.; Peng, S.

    2015-10-01

    CdTe solar technology has proved to be a cost-efficient solution for energy production. Formation of the back contact is an important and critical step in preparing high-efficiency, stable CdTe solar cells. In this paper we report a simple CdTe solar cell (Sb2Te3) back contact-formation process. The CdS and CdTe layers were deposited by close-space sublimation. After CdCl2 annealing treatment, the CdTe surface was etched by use of a mixture of nitric and phosphoric acids to obtain a Te-rich surface. Elemental Sb was sputtered on the etched surface and successive post-annealing treatment induced Sb2Te3 alloy formation. Structural characterization by x-ray diffraction analysis confirmed formation of the Sb2Te3 phase. The performance of solar cells with nanoalloyed Sb2Te3 back contacts was comparable with that of reference solar cells prepared with sputtered Sb2Te3 back contact from a compound sputter target.

  17. Identification of cadmium vacancy complexes in CdTe(In), CdTe(Cl) and CdTe(I) by positron annihilation with core electrons

    International Nuclear Information System (INIS)

    Doppler-broadening of the 511 keV positron annihilation line was used for defect identification in CdTe materials. In electrically compensated lightly n-type CdTe(In) and lightly p-type or semi-insulating CdTe(Cl) crystals positron lifetime measurements show vacancy defects with characteristic positron lifetimes of 323 ps and 370 ps, respectively. The shapes of the high-momentum parts of the measured electron-momentum distributions indicate that both defects contain a cadmium vacancy VCd. The defects are assigned to vacancy-donor complexes VCd-In and VCd-Cl, respectively. A vacancy in MBE-grown CdTe(I) layers observed with a low-energy positron beam is also identified as a cadmium vacancy VCd which is most likely complexed with I-donors. (author)

  18. Depth profiling sulphur in bulk CdTe and {CdTe}/{CdS} thin film heterojunctions

    Science.gov (United States)

    Lane, D. W.; Conibeer, G. J.; Romani, S.; Healy, M. J. F.; Rogers, K. D.

    1998-03-01

    Polycrystalline CdTeCdS heterojunction solar cells are a possible candidate for the low cost, high efficiency conversion of solar energy. The formation of an intermediate CdS xTe 1- x layer during a high temperature annealing stage is believed to increase optical absorption and decrease cell efficiency. S diffusion in single crystal CdTe has been investigated by NRA using the 32S (d,p o) 33S nuclear reaction, at a deuteron energy of 2 MeV. Details of the NRA depth profiling procedure are given, which was found to be relatively straightforward and suitable for use on a small Van de Graaff accelerator. The resulting diffusion parameters are compared to those obtained by SIMS using a Cs + primary ion beam, examining negative secondary ions. The diffusion coefficients were found to be 1.1 × 10 -15cm 2 s -1 at 450°C and ˜8 × 10 -15cm -1 s at 550°C. S diffusion in thin films was also investigated by 2 MeV 4He + RBS on annealed polycrystalline CdSCdTe multilayers.

  19. Performance optimization of CdTe and CdZnTe detectors for γ-spectrometry

    International Nuclear Information System (INIS)

    This study deals with room-temperature gamma spectrometry with CdTe and CdZnTe semiconductor detectors. The aim was the improvement of energy resolution and detection efficiency. Some different phenomena have been investigated. Electronic noise knowledge has enabled us to optimize the design of filtering. Charge transport induces signal shape uncertainty and the processing circuit has been adapted in order to account for these variations. Study and simulation of electrical current induction process has permitted the development of a new Frisch-grid based detection structure. We have reached 3% energy resolutions at 122 keV without detection efficiency loss. Finally, the remaining limits of detector performances have been estimated by focusing on gamma interaction phenomena and material non-uniformity problems. (author)

  20. Proton irradiation of MWIR HgCdTe/CdZnTe

    Science.gov (United States)

    Fahey, Stephen; Velicu, Silviu; Bommena, Ramana; Zhao, Jun; Cowan, Vincent; Morath, Christian; Sivananthan, Sivalingam

    2015-09-01

    High performance infrared sensors are vulnerable to slight changes in defect densities and locations. For example in a space application where such sensors are exposed to proton irradiation capable of generating point defects the sensors are known to suffer performance degradation. The degradation can generally be observed in terms of dark current density and responsivity degradations. Here we report results of MWIR HgCdTe/CdZnTe single element diodes dark current densities before and after exposure to 63MeV protons at room temperature to a total ionizing dose of 100 kRad(Si). We find the irradiated diodes as a group show some signs of proton-induced damage in dark current.

  1. Achievements and Challenges of CdS/CdTe Solar Cells

    OpenAIRE

    Zhou Fang; Xiao Chen Wang; Hong Cai Wu; Ce Zhou Zhao

    2011-01-01

    Thin film CdS/CdTe has long been regarded as one promising choice for the development of cost-effective and reliable solar cells. Efficiency as high as 16.5% has been achieved in CdS/CdTe heterojunction structure in laboratory in 2001, and current techniques for CdS/CdTe solar cells gradually step toward commercialization. This paper reviews some novel techniques mainly within two years to solve this problem from aspects of promotion of fabrication technology, structural modification, and cho...

  2. Efficient CdTe/CdS solar cells and modules by spray processing

    Science.gov (United States)

    Albright, Scot P.; Ackerman, Bruce; Jordan, John F.

    1990-02-01

    Efforts have been directed toward production of efficient, large-area, low-cost photovoltaic modules based on the CdS/CdTe heterojunction, with the objective being to develop an improved materials technology and fabrication process for limited volume production of 1-sq ft and 4-sq ft CdS/CdTe photovoltaic modules. The present structure of the CdS/CdTe polycrystalline thin-film photovoltaic devices being produced is presented, along with its potential for efficiency improvement. Junction characterization studies are summarized. Module design is described, particularly with regard to encapsulation issues. Future developmental directions are discussed.

  3. Performance of thin-film CdS/CdTe solar cells

    Science.gov (United States)

    Hussain, O. M.; Reddy, P. J.

    1991-07-01

    A polycrystalline thin-film CdS/CdTe solar cell has been fabricated by means of a laser evaporation of CdTe onto thermally-evaporated CdS films. The cell has demonstrated a maximum efficiency of about 8.25 percent, in conjunction with a quantum efficiency of about 80 percent. The In-doped CdS 0.5-micron thick films were deposited onto conducting glass substrates at 473 K and annealed at 673 K in a hydrogen atmosphere; the Sb-doped CdTe 5-micron thickness films were deposited and then heat-treated in air at 673 K.

  4. Achievements and Challenges of CdS/CdTe Solar Cells

    Directory of Open Access Journals (Sweden)

    Zhou Fang

    2011-01-01

    Full Text Available Thin film CdS/CdTe has long been regarded as one promising choice for the development of cost-effective and reliable solar cells. Efficiency as high as 16.5% has been achieved in CdS/CdTe heterojunction structure in laboratory in 2001, and current techniques for CdS/CdTe solar cells gradually step toward commercialization. This paper reviews some novel techniques mainly within two years to solve this problem from aspects of promotion of fabrication technology, structural modification, and choice of back contact materials.

  5. Electrophysical properties of nCdS/pCdTe heterosystem

    International Nuclear Information System (INIS)

    Full text: In this work results of research of electrophysical properties n CdS/pCdTe heterostructure are given. It is shown that at density of current 10-8-10-5 A.cm-2 vol tamper characteristics in hetero system CdTe/CdS is described by thermo ionic law, and in the range 10-4-10-2A .cm-2 the current in heterostructure is limited by recombination in electronic neutral part of high-resistance of solid structure CdTe1-xSx. Certain life time τp and length of diffusion Lp of non basic current carriers in solid structure CdTe1-xSx, as well as superficial recombination rate vR on border of section between CdS and solid structures were considered at influence of irradiation and γ-quanta on the mechanism of current in n CdS/pCdTe heterostructure. From the analysis of dependence doze of sites the direct volt-ampere characteristics were obtained. It is shown that monotonous increase of doze of irradiation and γ-quanta leads to nonmonotonous change of micro parameters of nCdS/pCdTe heterostructure, superficial recombination rate - vR, values of both τp and lengths of diffusion Lp of non basic carriers of potential barrier - qφB. On border of CdTe1-xSx there is CdS-solid structure. (author)

  6. Eects of Post Deposition Treatments on Vacuum Evaporated CdTe Thin Films and CdS=CdTe Heterojunction Devices

    OpenAIRE

    BAYHAN, Habibe; ERÇELEBİ, Çiğdem

    1998-01-01

    CdTe, CdS thin films and n-CdS/p-CdTe heterostructures have been prepared by conventional vacuum evaporation technique. Some post deposition treatments to optimize the device efficiency have been analyzed and the effects of the individual process steps on the material and device properties were investigated. Annealing in air with and without CdCl2-treatment decreased the CdTe resistivity. The CdCl2-dip followed by annealing in air at 300\\circC for 5 min improved the grain size and polycrystal...

  7. Investigation of inter-diffusion in bilayer GeTe/SnSe phase change memory films

    International Nuclear Information System (INIS)

    A metal-chalcogenide layer, SnSe, is inserted between the memory layer GeTe and the top electrode to form a phase change memory cell. The GeTe layer exhibits ovonic threshold switching at a threshold field of ∼ 110 V/μm. For subsequent implementation into applications and reliability, material inter-diffusion and sublimation are examined in bilayer phase change films of GeTe/SnSe. Transmission electron microscopy and parallel electron energy loss spectroscopy analyses reveal Sn migration to the GeTe layer, which is responsible for lowering the rhombohedral to cubic structural transformation temperature in GeTe. Incongruent sublimation of SnSe and GeTe is observed at temperatures higher than 500 °C. Severe volatilization of Se results in the separation of a metallic Sn phase. The use of Al2O3 as a capping layer has been found to mitigate these effects. - Highlights: ► In the as-deposited state, GeTe is amorphous and SnSe is orthorhombic in structure. ► After 300 °C, Sn migration results in the formation of a GexSn1−xTe solid solution. ► Film decomposition and incongruent sublimation are observed at high temperatures. ► A consequence of incongruent sublimation is the separation of metallic Sn phase. ► Al2O3 capping mitigates volatilization and Sn phase separation at high temperatures.

  8. 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

  9. Properties of Al/p-CdTe Schottky barriers

    International Nuclear Information System (INIS)

    Al/p-CdTe Schottky barriers diodes were prepared from the Te (111) face of lightly doped p-type CdTe single crystals. The characteristics of the diodes have been found to depend strongly on the surface preparation of CdTe. The current-voltage characteristics of diodes prepared from Br2-CH3OH etched surfaces are dominated by the tunneling mechanism with high saturation current densities. The use of Br2-CH3OH etch followed by heating in hydrogen has pronounced effects on the diode quality factor and saturation current densities due to the restoration of the surface stoichiometry. The C-V measurements at 1 and 10 MHz indicate that Schottky diodes prepared from Br2-CH3OH etched and 4500C hydrogen-annealed CdTe have a barrier height of 0.76 V and that diodes prepared from Br2-CH3OH etched or lower-temperature hydrogen-annealed CdTe show larger barrier heights. In latter cases, the barrier height appears to be controlled by the metal-semiconductor interface states. In Al/p-CdTe Schottky barriers with low interface state density, the temperature dependence of the saturation current density suggests that diffusion is the dominant mechanism of current transport, due presumably to the low carrier density in CdTe

  10. BaCdSnS4 and Ba3CdSn2S8: syntheses, structures, and non-linear optical and photoluminescence properties.

    Science.gov (United States)

    Zhen, Ni; Wu, Kui; Wang, Ying; Li, Qiang; Gao, Wenhui; Hou, Dianwei; Yang, Zhihua; Jiang, Huaidong; Dong, Yongjun; Pan, Shilie

    2016-06-28

    Two non-centrosymmetric metal chalcogenides, BaCdSnS4 and Ba3CdSn2S8, were synthesized using a high temperature solid-state reaction in an evacuated silica tube. Although the two compounds have the same building units in their structures, namely CdS4, SnS4 and BaS8 units, both of them have different structures. BaCdSnS4 crystallizes in the orthorhombic space group Fdd2 and its structure can be characterized by the two-dimensional ∞[Cd-Sn-S] layers composed of corner- and edge-sharing CdS4 and SnS4 tetrahedra with Ba atoms located between the two adjacent ∞[Cd-Sn-S] layers. Ba3CdSn2S8 crystallizes in the space group I4[combining macron]3d of the orthorhombic system and the CdS4 and SnS4 groups are connected with each other via corner-sharing to form a three-dimensional framework, which is different from the 2D ∞[Cd-Sn-S] layer structure in BaCdSnS4. The UV-vis-NIR diffuse-reflectance spectra show that the experimental band gaps are about 2.30 eV for BaCdSnS4 and 2.75 eV for Ba3CdSn2S8, respectively. IR and Raman measurement results indicate that their transparent ranges are up to 25 μm. Second-order NLO measurements show that BaCdSnS4 exhibits strong powder second-harmonic generation (SHG) intensities at 2.09 μm laser pumping that are ∼5 and 0.7 times that of AgGaS2 in the particle size 38-55 and 150-200 μm, respectively, whereas Ba3CdSn2S8 only exhibits SHG intensities of about 0.8 and 0.1 times that of AgGaS2 at the same particle sizes. The origin of the NLO response in BaCdSnS4 may originate from the macroscopic arrangement of the SnS4 and CdS4 tetrahedra. Furthermore, the photoluminescence properties of the two compounds have also been investigated and show obvious blue and green light emission. PMID:27272926

  11. 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.

  12. Influence of deposition duration on CdS/CdTe solar cell performance

    International Nuclear Information System (INIS)

    The photo-electrical properties of thin film CdS/CdTe HJ were studied at their illumination with the integral light through the wide band gap component CdS (Eg = 2.42 eV). The CdTe layer thickness influence (according the time of deposition of CdTe layers) was studied on the photoelectrical parameters as well. Influence of the time deposition of the CdTe layer on the quantum efficiency was also studied. Quantum efficiency decreases with CdTe thickness increase. The photosensitivity covers the wavelength range from 0.50 mm to 0.86 mm for all cells. The most efficient carrier generation and collection is for the structure with CdTe layer time of deposition of 3.5 min. With increase of CdTe layer thickness a change in the form of quantum efficiency spectra can be observed. In the long wavelength region a maximum which indicates the high contribution CdTe in photocurrent appears. The time of CdTe layer deposition influences as well the value of the diffusion length of electrons Ln determined from QE measurements. In the case when the time of deposition is 3.5-4 min the spectral response includes a plateau expanding between band gap of CdTe and CdS. The diffusion length of the electrons in CdTe is Ln = 1.44 mm. The long wavelength cutoff implies an effective gap energy of about 1.48 eV. In the case when time of deposition is 5 min the Ln = 0.21 mm. Investigation of micro-nonuniformities in cell photocurrent response shows a big region where there is significantly smaller photo-current. The investigations suggest that the diffusion of CdS into CdTe reduces the lattice mismatch between CdS and CdTe by forming CdTe1-xSx buffer layer. (authors)

  13. Te inclusion-induced electrical field perturbation in CdZnTe single crystals revealed by Kelvin probe force microscopy.

    Science.gov (United States)

    Gu, Yaxu; Jie, Wanqi; Li, Linglong; Xu, Yadong; Yang, Yaodong; Ren, Jie; Zha, Gangqiang; Wang, Tao; Xu, Lingyan; He, Yihui; Xi, Shouzhi

    2016-09-01

    To understand the effects of tellurium (Te) inclusions on the device performance of CdZnTe radiation detectors, the perturbation of the electrical field in and around Te inclusions was studied in CdZnTe single crystals via Kelvin probe force microscopy (KPFM). Te inclusions were proved to act as lower potential centers with respect to surrounding CdZnTe matrix. Based on the KPFM results, the energy band diagram at the Te/CdZnTe interface was established, and the bias-dependent effects of Te inclusion on carrier transportation is discussed. PMID:27376976

  14. Formation and Properties of Polycrystalline p-Type High-Conductivity CdTe Films by Coevaporation of CdTe and Te

    Science.gov (United States)

    Hayashi, Toshiya; Hayashi, Hiroaki; Fukaya, Mitsuru; Ema, Yoshinori

    1991-10-01

    Polycrystalline p-type high-dark-conductivity CdTe films have been prepared by coevaporation of CdTe and Te. The structural and electrical properties were investigated. The dark conductivity of the films at 300 K ranged from 6.32× 10-8 to 3.41 S cm-1. The film structure was of the zincblende type with a preferential orientation of the (111) planes parallel to the substrate. The crystallinity was rather good. From the measurements of the carrier concentration versus ambient temperature characteristics, it was found that the high-conductivity p-type conduction of the films was due to the formation of Cd vacancies, acceptors resulting from the coevaporation of CdTe and Te. It is shown that the high-conductivity films obtained are suitable for p-CdTe/n-CdS solar cells.

  15. Flexible CdTe/CdS solar cells on thin glass substrates.

    Science.gov (United States)

    Seo, Won-Oh; Kim, Donghwan; Kim, Jihyun

    2015-04-01

    We demonstrate flexible CdTe/CdS thin-film solar cells in a superstrate configuration with a cell conversion efficiency as high as 10.9%. We deposit a CdS window layer and a CdTe absorber layer on a flexible glass substrate using the chemical bath deposition method and close-spaced sublimation method, respectively. The thin and flexible glass substrates were able to tolerate a high growth temperature and post-growth processes. We repeatedly apply a strain of 0.15% to the fabricated CdTe/CdS solar cells, and this was shown to have a negligible effect on their performances. Our proposed thin films-on-compliant substrate structure, which was prepared by replacing a rigid glass with a bendable one, demonstrated flexible CdTe/CdS p-n junction thin-film solar cells without compromising the cell performance. PMID:25968797

  16. The morphology, microstructure, and luminescent properties of CdS/CdTe films

    Energy Technology Data Exchange (ETDEWEB)

    Al-Jassim, M.M.; Dhere, R.G.; Jones, K.M.; Hasoon, F.S.; Sheldon, P. [National Renewable Energy Lab., Golden, CO (United States)

    1998-09-01

    This paper is concerned with the characterization of CdS/CdTe polycrystalline thin films for solar cells. The morphology, microstructure, and luminescent properties are studied by a powerful array of characterization techniques. The presence of pinholes in 100-nm thick CdS is observed. The microstructure of CdS and CdTe films is shown to be heavily faulted polycrystalline. The effect of deposition temperature on the grain size and the microstructure is investigated. The interdiffusion of sulfur and tellurium at the CdS/CdTe interface is studied for the first time by a nanoprobe technique. Considerable amount of sulfur is detected in CdTe in the vicinity of the interface of samples deposited at 625 C. The recombination behavior of grain boundaries and intragrain defects is investigated in as-deposited and heat-treated samples.

  17. Radiative and interfacial recombination in CdTe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Swartz, C. H., E-mail: craig.swartz@txstate.edu; Edirisooriya, M.; LeBlanc, E. G.; Noriega, O. C.; Jayathilaka, P. A. R. D.; Ogedengbe, O. S.; Hancock, B. L.; Holtz, M.; Myers, T. H. [Materials Science, Engineering, and Commercialization Program, Texas State University, 601 University Dr., San Marcos, Texas 78666 (United States); Zaunbrecher, K. N. [National Renewable Energy Laboratory, 15013 Denver West Parkway, Mississippi RSF200, Golden, Colorado 80401 (United States)

    2014-12-01

    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 10{sup 10 }cm{sup −2} and carrier lifetimes as long as 240 ns. The radiative recombination coefficient of CdTe is found to be near 10{sup −10} cm{sup 3}s{sup −1}. CdTe film growth on bulk CdTe substrates resulted in a homoepitaxial interface layer with a high non-radiative recombination rate.

  18. Optical modeling of graphene contacted CdTe solar cells

    Science.gov (United States)

    Aldosari, Marouf; Sohrabpoor, Hamed; Gorji, Nima E.

    2016-04-01

    For the first time, an optical model is applied on CdS/CdTe thin film solar cells with graphene front or back contact. Graphene is highly conductive and is as thin as a single atom which reduces the light reflection and absorption, and thus enhances the light transmission to CdTe layer for a wide range of wavelengths including IR. Graphene as front electrode of CdTe devices led to loss in short circuit current density of 10% ΔJsc ≤ 15% compared to the conventional electrodes of TCO and ITO at CdS thickness of dCdS = 100 nm. In addition, all the multilayer graphene electrodes with 2, 4, and 7 graphene layers led to Jsc ≤ 20 mA/cm2. Therefore, we conclude that a single monolayer graphene with hexagonal carbon network reduces optical losses and enhances the carrier collection measured as Jsc. In another structure design, we applied the optical model to graphene back contacted CdS/CdTe device. This scheme allows double side irradiation of the cell which is expected to enhance the Jsc. We obtained 1 ∼ 6 , 23, and 38 mA/cm2 for back, front and bifacial illumination of graphene contacted CdTe cell with CdS = 100 nm. The bifacial irradiated cell, to be efficient, requires an ultrathin CdTe film with dCdTe ≤ 1 μm. In this case, the junction electric field extends to the back region and collects out the generated carriers efficiently. This was modelled by absorptivity rather than transmission rate and optical losses. Since the literature suggest that ZnO can increase the graphene conductivity and enhance the Jsc, we performed our simulations for a graphene/ZnO electrode (ZnO = 100 nm) instead of a single graphene layer.

  19. Further development of electroplated CdTe-based photovoltaic cells

    Energy Technology Data Exchange (ETDEWEB)

    1990-02-01

    Over the last two years A.D. Plating has gained substantial experience in making CdTe based polycrystalline solar cells. A pilot station for the electrodeposition of CdTe was built. At this pilot station, with industrial grade chemicals, a 5.5% efficiency CdS/CdTe device and a 2% efficiency metal-insulator-semiconductor (MIS) device were produced. A detailed description of the processes, by which a good CdTe based solar cell can be obtained, is provided. The process is difficult; subtle changes in preparation have dramatic effects on performance. Further work is necessary to improve yield, to increase efficiency, and to produce submodules. 21 figs., 4 tabs.

  20. C-V Calculations in CdS/CdTe Thin Films Solar Cells with a CdSxTe1-x Interlayer

    OpenAIRE

    Gonzalez-Cisneros, A.; F. de L. Castillo-Alvarado; J. Ortiz-Lopez; G. Contreras-Puente

    2013-01-01

    In CdS/CdTe solar cells, chemical interdiffusion at the interface gives rise to the formation of an interlayer of the ternary compound CdSxCdTe1-x. In this work, we evaluate the effects of this interlayer in CdS/CdTe photovoltaic cells in order to improve theoretical results describing experimental C-V (capacitance versus voltage) characteristics. We extended our previous theoretical methodology developed on the basis of three cardinal equations (Castillo-Alvarado et al., 2010). The present r...

  1. Current transport mechanisms in epitaxial CdS/CdTe heterojunctions

    Science.gov (United States)

    Ercelebi, C.; Brinkman, A. W.; Furlong, T. S.; Woods, J.

    1990-04-01

    Epitaxial n-CdS/p-CdTe heterojunctions have been fabricated by the vacuum evaporation of CdS onto phosphorus doped {⦶111} B CdTe substrates. Analysis of the current-voltage and capacitance-voltage characteristics suggests that electrical transport across the junction is dominated by a multi-step tunneling process. Although open circuit voltage and short circuit current values were high, the overall photovoltaic conversion efficiency of the devices was restricted to ≈ 6%, because of the relatively high resistivity of the CdTe substrates.

  2. 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

  3. 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

  4. Effect of intermixing at CdS/CdTe interface on defect properties

    Science.gov (United States)

    Park, Ji-Sang; Yang, Ji-Hui; Barnes, Teresa; Wei, Su-Huai

    2016-07-01

    We investigated the stability and electronic properties of defects in CdTe1-xSx that can be formed at the CdS/CdTe interface. As the anions mix at the interface, the defect properties are significantly affected, especially those defects centered at cation sites like Cd vacancy, VCd, and Te on Cd antisite, TeCd, because the environment surrounding the defect sites can have different configurations. We show that at a given composition, the transition energy levels of VCd and TeCd become close to the valence band maximum when the defect has more S atoms in their local environment, thus improving the device performance. Such beneficial role is also found at the grain boundaries when the Te atom is replaced by S in the Te-Te wrong bonds, reducing the energy of the grain boundary level. On the other hand, the transition levels with respect to the valence band edge of CdTe1-xSx increases with the S concentration as the valence band edge decreases with the S concentration, resulting in the reduced p-type doping efficiency.

  5. Effect of Intermixing at CdS/CdTe Interface on Defect Properties

    Energy Technology Data Exchange (ETDEWEB)

    Park, Ji-Sang; Yang, Ji-Hui; Barnes, Teresa; Wei, Su-Huai

    2016-07-25

    We investigated the stability and electronic properties of defects in CdTe 1- xSx that can be formed at the CdS/CdTe interface. As the anions mix at the interface, the defect properties are significantly affected, especially those defects centered at cation sites like Cd vacancy, VCd, and Te on Cd antisite, TeCd, because the environment surrounding the defect sites can have different configurations. We show that at a given composition, the transition energy levels of VCd and TeCd become close to the valence band maximum when the defect has more S atoms in their local environment, thus improving the device performance. Such beneficial role is also found at the grain boundaries when the Te atom is replaced by S in the Te-Te wrong bonds, reducing the energy of the grain boundary level. On the other hand, the transition levels with respect to the valence band edge of CdTe 1- xSx increases with the S concentration as the valence band edge decreases with the S concentration, resulting in the reduced p-type doping efficiency.

  6. Phase transitions in CdTe/ZnTe strained-layer superlattices

    Science.gov (United States)

    Dunstan, D. J.; Prins, A. D.; Gil, B.; Faurie, J. P.

    1991-08-01

    In CdTe/ZnTe strained-layer superlattices under hydrostatic pressure, the CdTe phase transition does not occur until around 60 kbar, compared with the bulk CdTe value of 35 kbar. This dramatic superpressing cannot be explained by the model proposed to explain superpressing in unstrained (Al,Ga)As superlattices [Weinstein et al., Phys. Rev. Lett. 58, 781 (1987)] but can be accounted for by consideration of a probable microscopic mechanism of the phase transition, by shear on (111) planes. The results show that most semiconductors may be superpressed.

  7. Positron annihilation spectroscopy of vacancy-related defects in CdTe:Cl and CdZnTe:Ge at different stoichiometry deviations

    OpenAIRE

    L. Šedivý; J. Čížek; Belas, E.; Grill, R.; Melikhova, O.

    2016-01-01

    Positron annihilation spectroscopy (PAS) was used to examine the effect of defined Cd-rich and Te-rich annealing on point defects in Cl-doped CdTe and Ge-doped CdZnTe semi-insulating single crystals. The as-grown crystals contain open-volume defects connected with Cd vacancies . It was found that the Cd vacancies agglomerate into clusters coupled with Cl in CdTe:Cl, and in CdZnTe:Ge they are coupled with Ge donors. While annealing in Cd pressure reduces of the density, subsequent annealing in...

  8. 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.

  9. Counting efficiency of a CdTe detector

    International Nuclear Information System (INIS)

    The purpose of this work is to obtain some data about the energy dependence of the sensitivity of a CdTe detector in order to use it for a miniature dose rate meter. The intrinsic efficiencies of the CdTe detector were measured for several photon energies between 22 and 835 keV. The results showed the great dependence of the efficiency of the CdTe detector on photon energy, for example, the intrinsic efficiencies for the photons of 122 keV and 835 keV were 71% and 8.7% respectively. Some further problems were also presented and discussed. (author)

  10. Results of a Si/CdTe Compton Telescope

    OpenAIRE

    Oonuki, Kousuke; Tanaka, Takaaki; Watanabe, Shin; Takeda, Shin'ichiro; Nakazawa, Kazuhiro; Mitani, Takefumi; Takahashi, Tadayuki; Tajima, Hiroyasu; Fukazawa, Yasushi; Nomachi, Masaharu

    2005-01-01

    We have been developing a semiconductor Compton telescope to explore the universe in the energy band from several tens of keV to a few MeV. We use a Si strip and CdTe pixel detector for the Compton telescope to cover an energy range from 60 keV. For energies above several hundred keV, the higher efficiency of CdTe semiconductor in comparison with Si is expected to play an important role as an absorber and a scatterer. In order to demonstrate the spectral and imaging capability of a CdTe-based...

  11. Electrical properties of single CdTe nanowires

    Directory of Open Access Journals (Sweden)

    Elena Matei

    2015-02-01

    Full Text Available Ion track, nanoporous membranes were employed as templates for the preparation of CdTe nanowires. For this purpose, electrochemical deposition from a bath containing Cd and Te ions was employed. This process leads to high aspect ratio CdTe nanowires, which were harvested and placed on a substrate with lithographically patterned, interdigitated electrodes. Focused ion beam-induced metallization was used to produce individual nanowires with electrical contacts and electrical measurements were performed on these individual nanowires. The influence of a bottom gate was investigated and it was found that surface passivation leads to improved transport properties.

  12. Coal mining applications of CdTe gamma ray sensors

    Energy Technology Data Exchange (ETDEWEB)

    Entine, G.; Tiernan, T.; Waer, P.; Hazlett, T. (Radiation Monitoring Devices, Inc., Watertown, MA (USA))

    1990-01-01

    Cadmium telluride (CdTe) solid-state radiation detectors have been used in the development of instrumentation that improves the efficiency of coal-mining operations by helping to locate coal seams and preventing the mining of high-sulfur coal near the edges of the seam. CdTe detectors were selected for these applications because while they are small and durable, they offer good stopping power, deliver adequate spectral response and operate at low voltage. These CdTe-based instruments have passed the mine-safety standards and are now in operation in the mine. (author).

  13. Coal mining applications of CdTe gamma ray sensors

    International Nuclear Information System (INIS)

    Cadmium telluride (CdTe) solid-state radiation detectors have been used in the development of instrumentation that improves the efficiency of coal-mining operations by helping to locate coal seams and preventing the mining of high-sulfur coal near the edges of the seam. CdTe detectors were selected for these applications because while they are small and durable, they offer good stopping power, deliver adequate spectral response and operate at low voltage. These CdTe-based instruments have passed the mine-safety standards and are now in operation in the mine. (author)

  14. 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.

  15. 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.

  16. 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

  17. COBRA - Double beta decay searches using CdTe detectors

    OpenAIRE

    Zuber, K.

    2001-01-01

    A new approach (called COBRA) for investigating double beta decay using CdTe (CdZnTe) semiconductor detectors is proposed. It follows the idea that source and detector are identical. This will allow simultaneous measurements of 5 $\\beta^-\\beta^-$ - and 4 $\\beta^+\\beta^+$ - emitters at once. Half-life limits for neutrinoless double beta decay of Cd-116 and Te-130 can be improved by more than one order of magnitude with respect to current limits and sensitivities on the effective Majorana neutr...

  18. Simulation of the Efficiency of CdS/CdTe Tandem Multi-Junction Solar Cells

    CERN Document Server

    Mirkamali, Ashrafalsadat S

    2016-01-01

    In this paper we study CdS/CdTe solar cells by means of AMPS-1D software. First we study the effect of thickness of semiconductor layers on the output parameters of the CdS/CdTe solar cell, such as density of short-circuit current, open circuit voltage, fill factor and efficiency. Numerical simulation shows that the highest efficiency of single-junction CdS/CdTe solar cell equal to 18.3% is achieved when the CdTe layer thickness is 1000 nm and a CdS layer is 60 nm. Then, in order to obtain the maximal value of the efficiency, new tandem multi-junction structure consisting of layers of two solar cells connected with each other back to back are designed and engineered taking into account the results obtained for the single-junction solar cells. Numerical simulations show that its highest efficiency in 31.8% can be obtained when the thickness of CdS p-layer is equal to 50 nm, and the thickness of the CdS n-layer is equal to 200 nm, while thicknesses of the CdTe n-layer and CdTe p-layer are kept fixed and equal t...

  19. Facile method to prepare CdS nanostructure based on the CdTe films

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Ligang; Chen, Yuehui; Wei, Zelu; Cai, Hongling; Zhang, Fengming; Wu, Xiaoshan, E-mail: xswu@nju.edu.cn

    2015-09-15

    Graphical abstract: - Highlights: • CdS nanostructure is directly fabricated on CdTe film only by heating treatment under H{sub 2}S/N{sub 2} mixed atmosphere at a relatively low temperature (450 °C) with gold layer as the intermediate. • Nanostructure of CdS layer, varying from nanowires to nanosheets, may be controlled by the thickness of gold film. • The change of morphology adjusts its luminescence properties. - Abstract: Nanostructured cadmium sulfide (CdS) plays critical roles in electronics and optoelectronics. In this paper, we report a method to fabricate CdS nanostructure directly on CdTe film, via a thermal annealing method in H{sub 2}S/N{sub 2} mixed gas flow at a relatively low temperature (450 °C). The microstructure and optical properties of CdS nanostructure are investigated by X-ray diffraction, transmission electron microscopy, Raman, and photoluminescence. The morphology of CdS nanostructure, evolving from nanowires to nanosheets, can be controlled by the thickness of Au film deposited on the CdTe film. And CdS nanostructures are single crystalline with the hexagonal wurtzite structure. Raman spectroscopy under varying the excitation wavelengths confirm that synthesized CdS-CdTe films contain two layers, i.e., CdS nanostructure (top) and CdTe layer (bottom). The change of morphology modifies its luminescence properties. Obviously, through simply thermal annealing in H{sub 2}S/N{sub 2} mixed gas, fabricating CdS nanostructure on CdTe film can open up the new possibility for obtaining high efficient CdTe solar cell.

  20. HgTe/CdTe heterojunctions: A lattice-matched Schottky barrier structure

    OpenAIRE

    Kuech, T. F.; McCaldin, J. O.

    1982-01-01

    HgTe-CdTe lattice-matched heterojunctions were formed by the epitaxial growth of HgTe on CdTe substrates using a low-temperature metal organic chemical vapor deposition technique. These heterojunctions combine features of the Schottky barrier structure, due to the high carrier concentrations found in the semimetallic HgTe, with the structural perfection present in a lattice-matched heterojunction. The measured Schottky barrier height varied from 0.65 to 0.92 eV depending on the details of the...

  1. 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)

  2. Analysis of post deposition processing for CdTe/CdS thin film solar cells

    Energy Technology Data Exchange (ETDEWEB)

    McCandless, B.E.; Birkmire, R.W. (Inst. of Energy Conversion, Univ. of Delaware, Newark, DE (United States))

    1991-12-01

    A post-deposition process for optimizing the efficiency of thin film CdTe/CdS solar cells deposited by physical vapor deposition has been developed and the effects of the individual process steps on the materials and device properties have been analyzed. A 400degC heat treatment with CdCl{sub 2} restructures the CdTe resulting in enhanced grain size and crystallographic reorientation. Structural and optical measurements indicate interdiffusion of sulfur and tellurium during the heat treatment resulting in formation of a CdS{sub x}Te{sub 1-x} layer with a narrower band gap than CdTe. Bifacial current-voltage and quantum efficiency analysis of the CdTe devices at various stages of the optimization process shows the evolution of the device from a p-i-n structure to a heterojunction. A chemical treatment improves the open circuit voltage (V{sub oc}) and Cu/Au contact to the CdTe. The optimization process can be applied to cells using CdTe and CdS deposited by different methods. (orig.).

  3. The interfacial free energy of solid Sn on the boundary interface with liquid Cd-Sn eutectic solution

    International Nuclear Information System (INIS)

    Equilibrated grain boundary groove shapes for solid Sn in equilibrium with Cd-Sn liquid were directly observed after annealing a sample at the eutectic temperature for about 8 days. The thermal conductivities of the solid phase, KS, and the liquid phase, KL, for the groove shapes were measured. From the observed groove shapes, the Gibbs-Thomson coefficients were obtained with a numerical method, using the measured G, KS and KL values. The solid-liquid interfacial energy of solid Sn in equilibrium with Cd-Sn liquid was determined from the Gibbs-Thomson equation. The grain boundary energy for solid Sn was also calculated from the observed groove shapes

  4. 13.4% efficient thin-film CdS/CdTe solar cells

    Science.gov (United States)

    Chu, T. L.; Chu, S. S.; Ferekides, C.; Wu, C. Q.; Britt, J.; Wang, C.

    1991-12-01

    Cadmium telluride is a promising thin-film photovoltaic material as shown by the more than 10% efficient CdS/CdTe heterojunction solar cells. In this work, thin-film CdS/CdTe solar cells have been prepared using CdS films grown from an aqueous solution and p-CdTe films deposited by close-spaced sublimation (CSS). The properties of CdS films deposited from an ammonical solution of a Cd-salt, an ammonium salt, and thiourea have been controlled by optimizing the temperature and composition of the solution. The solution-grown CdS films have a high photoconductivity ratio, and its optical transmission is superior to that of vacuum evaporated CdS films. The properties of p-CdTe films deposited by CSS have been optimized by controlling the temperature and composition of the source material, and the substrate temperature. The properties of CdS/CdTe heterojunctions have been studied; junction photovoltage spectroscopy is used for the qualitative comparison of junction characteristics. Solar cells of 1-cm2 area with an AM 1.5 efficiency of 13.4% are reported.

  5. 13. 4% efficient thin-film CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Chu, T.L.; Chu, S.S.; Ferekides, C.; Wu, C.Q.; Britt, J.; Wang, C. (Department of Electrical Engineering, University of South Florida, Tampa, Florida (USA))

    1991-12-15

    Cadmium telluride is a promising thin-film photovoltaic material as shown by the more than 10% efficient CdS/CdTe heterojunction solar cells. In this work, thin-film CdS/CdTe solar cells have been prepared using CdS films grown from an aqueous solution and {ital p}-CdTe films deposited by close-spaced sublimation (CSS). The properties of CdS films deposited from an ammonical solution of a Cd-salt, an ammonium salt, and thiourea have been controlled by optimizing the temperature and composition of the solution. The solution-grown CdS films have a high photoconductivity ratio, and its optical transmission is superior to that of vacuum evaporated CdS films. The properties of {ital p}-CdTe films deposited by CSS have been optimized by controlling the temperature and composition of the source material, and the substrate temperature. The properties of CdS/CdTe heterojunctions have been studied; junction photovoltage spectroscopy is used for the qualitative comparison of junction characteristics. Solar cells of 1-cm{sup 2} area with an AM 1.5 efficiency of 13.4% are reported.

  6. Kinetic barriers for Cd and Te adatoms on Cd and Te terminated CdTe (111) surface using ab initio simulations

    Science.gov (United States)

    Naderi, Ebadollah; Nanavati, Sachin P.; Majumder, Chiranjib; Ghaisas, S. V.

    2014-03-01

    In the present work we have calculated using density functional theory (DFT), diffusion barrier potentials on both the CdTe (111) surfaces, Cd terminated (A-type) & Te terminated (B-type). We employ nudge elastic band method (NEB) for obtaining the barrier potentials. The barrier is computed for Cd and for Te adatoms on both A-type and B-type surfaces. We report two energetically favourable positions along the normal to the surface, one above and other below the surface. The one above the surface has binding energy slightly more the one below. According to the results of this work, binding energy (in all cases) for adatoms are reasonable and close to experimental data. The barrier potential for hopping adatoms (Cd and Te) on both the surfaces is less than 0.35 eV. Apart from these most probable sites, there are other at least two sites on both the types of surfaces which are meta stable. We have also computed barriers for hopping to and from these meta stable positions. The present results can shade light on the defect formation mechanism in CdTe thin films during growth. The authors would like to thank C-DAC for the computing time on its PARAM series of supercomputers and DST Govt. of India, for partial funding.

  7. Optimized conditions for the improvement of thin film CdS/CdTe solar cells

    International Nuclear Information System (INIS)

    Efficient thin film CdS/CdTe solar cell performance requires optimum parameters of each layer of this cell and of the barrier structure. Moreover, the effect of optical losses, recombination losses at front and back surface of CdTe and recombination losses in the space-charge region (SCR) must be considered in order to really analyze the role of these parameters on the performance of these cells. This work is focused on studying theoretically the effect of the thickness of the front contact (ITO), thickness of the window layer (CdS), thickness of the absorber layer (CdTe), width of the space-charge region and electron lifetime on the efficiency of CdS/CdTe solar cells. The reflection losses from interfaces and absorption losses in ITO and CdS, front and rear surface recombination losses of CdTe as well as recombination losses in SCR have been studied. It has been observed that the short-circuit current strongly depends on the thickness of ITO, thickness of CdS, thickness CdTe and electron lifetime. The concentration of uncompensated impurities (Na − Nd) in CdTe, which determines the width of SCR, plays a key role in the generation of photocurrent. The recombination losses in the SCR decrease rapidly with increasing the carrier lifetime in this region and can be ignored at lifetime of 10−7 s. The reflectivity from the back contact introduces a small influence in increasing the short-current density particularly at thick absorber layer (5–8 μm). Under the conditions of Na − Nd ~ 1016 cm−3, τn = 10−6 s, dCdTe = 8 μm, dITO = 100 nm, and dCdS = 100 nm, the recombination and optical losses record their minimum ratio of 27%. Most of these losses (24%) are due to the optical losses. The efficiency of CdS/CdTe under these parameters is about 18.2% which is exactly matching with the recent experimental studies. Moreover, an ultrathin CdTe (= 1 μm) is sufficient to introduce high efficiency of 16.4%. - Highlights: • This work represents a theoretical study

  8. High-efficiency large-area CdTe panels

    Science.gov (United States)

    Albright, Scot P.; Chamberlin, Rhodes R.; Jordan, John F.

    1990-11-01

    The objective of this three year effort has been to develop an improved materials technology and fabrication process for limited volume production of 1 and 4 sq ft CdS/CdTe photovoltaic modules. The module stability objective by the end of this three year subcontract was to develop techniques to provide ten year life exploration with no greater than 10 percent degradation. In order to achieve these efficiency and stability objectives, the research program has been separated into tasks including: (1) analysis and characterization of CdS/CdTe devices; (2) performance optimization on small cells; (3) encapsulation and stability testing; and (4) module efficiency optimization.

  9. Stimulated emission from a CdTe/HgCdTe separate confinement heterostructure grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Mahavadi, K.K.; Bleuse, J.; Sivananthan, S.; Faurie, J.P. (Microphysics Laboratory, Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60680 (USA))

    1990-05-21

    We present the results of low-temperature photoluminescence and stimulated emission experiments performed on a CdTe/Hg{sub 0.45}Cd{sub 0.55}Te/Hg{sub 0.67}Cd{sub 0.33}Te multiquantum well separate confinement heterostructure grown by molecular beam epitaxy. The photoluminescence results suggest that because of the growth conditions, there is a strong interdiffusion in the multiquantum well region. Pulsed stimulated emission was observed from this structure up to 77 K.

  10. The magnetic field influence on optical absorption in the CdTe/Cd1-xMnxTe magnetic superlattices

    International Nuclear Information System (INIS)

    In the present communication a new mechanism of the absorption edge shifting effect is proposed that is due to the exchange interaction between charge carriers in CdTe layers and localized spin momenta in the Cd1-xMnxTe layers. Such a coupling in the presence of an external magnetic field of direct current will lead to the Zeeman splitting of spin subbands also in non-magnetic CdTe layers giving rise to the described shifts of the absorption spectrum to lower energies. (N.H.A). 10 refs, 4 figs

  11. Au/Cu2Te/CdTe/CdS/TCO/Glass Solar Cells with CdIn2O4 Obtained by Sol-Gel as TCO

    OpenAIRE

    Márquez Marín, J.; Torres Delgado, G.; M. A. Aguilar Frutis; Castanedo Pérez, R.; Zelaya Ángel, O.

    2014-01-01

    An Au/Cu2Te/CdTe/CdS/TCO/glass heterostructure based superstrate solar cells with 2.5 mm2 of area, where the CdTe layer was prepared by means of closed spaced sublimation (CSS) and the CdS by chemical bath, reached an efficiency η value of 12.1%. As transparent conductive oxide (TCO), a thin film of cadmium-indium oxide (CdIn2O4:CIO), obtained by sol-gel technique, was used. A systematic optimization of the thermal activation of the CdTe/CdS/CIO central part of the device with a CdCl2 vapor a...

  12. Study of Back Contacts for CdTe Solar Cells

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    ZnTe/ZnTe∶Cu layer is used as a complex back contact. The parameters of CdTe solar cells with and without the complex back contacts are compared. The effects of un-doped layer thickness, doped concentration and post-deposition annealing temperature of the complex layer on solar cells performance are investigated.The results show that ZnTe/ZnTe∶Cu layer can improve back contacts and largely increase the conversion efficiency of CdTe solar cells. Un-doped layer and post-deposition annealing of high temperature can increase open voltage. Using the complex back contact, a small CdTe cell with fill factor of 73.14% and conversion efficiency of 12.93% is obtained.

  13. Study of a new architecture of gamma cameras with Cd/ZnTe/CdTe semiconductors

    International Nuclear Information System (INIS)

    This thesis studies new semi conductors for gammas cameras in order to improve the quality of image in nuclear medicine. The chapter 1 reminds the general principle of the imaging gamma, by describing the radiotracers, the channel of detection and the types of Anger gamma cameras acquisition. The physiological, physical and technological limits of the camera are then highlighted, to better identify the needs of future gamma cameras. The chapter 2 is dedicated to a bibliographical study. At first, semi-conductors used in imaging gamma are presented, and more particularly semi-conductors CDTE and CdZnTe, by distinguishing planar detectors and monolithic pixelated detectors. Secondly, the classic collimators of the gamma cameras, used in clinical routine for the most part of between them, are described. Their geometry is presented, as well as their characteristics, their advantages and their inconveniences. The chapter 3 is dedicated to a state of art of the simulation codes dedicated to the medical imaging and the methods of reconstruction in imaging gamma. These states of art allow to introduce the software of simulation and the methods of reconstruction used within the framework of this thesis. The chapter 4 presents the new architecture of gamma camera proposed during this work of thesis. It is structured in three parts. The first part justifies the use of semiconducting detectors CdZnTe, in particular the monolithic pixelated detectors, by bringing to light their advantages with regard to the detection modules based on scintillator. The second part presents gamma cameras to base of detectors CdZnTe (prototypes or commercial products) and their associated collimators, as well as the interest of an association of detectors CdZnTe in the classic collimators. Finally, the third part presents in detail the HiSens architecture. The chapter 5 describes both software of simulation used within the framework of this thesis to estimate the performances of the Hi

  14. 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.

  15. 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

  16. 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.

  17. CdTe-nuclear detector with rectifying contact

    International Nuclear Information System (INIS)

    MIS tunnel minority type structures are applied as a contact to the CdTe monocrystals for radiation devices sensitive to room temperature low energy gamma ray sensors. Thin insulating layer is grown on the CdTe monocrystal surface using electrochemical etching and photoanodization. Depth profiles, thickness and layer composition are studied with Auger electron spectroscopy. Current-voltage characteristics of Al- and Au-diodes are obtained and discussed. The charge collection efficiency of these diodes is compared with the efficiency of the Pt-CdTe-Pt ones on the basis of their pulse height spectra obtained using 57Co source. The results show strong rectification for the CdTe diodes with Al- or Au-contacts which is not consistent with Schottky or Dolega heterojunction theory. Significant improvement in the radiation charge collection efficiency with this type of contacts is established. 6 figs., 9 refs

  18. 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.

  19. 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.

  20. Analysis of Etched CdZnTe Substrates

    Science.gov (United States)

    Benson, J. D.; Bubulac, L. O.; Jaime-Vasquez, M.; Lennon, C. M.; Arias, J. M.; Smith, P. J.; Jacobs, R. N.; Markunas, J. K.; Almeida, L. A.; Stoltz, A.; Wijewarnasuriya, P. S.; Peterson, J.; Reddy, M.; Jones, K.; Johnson, S. M.; Lofgreen, D. D.

    2016-06-01

    State-of-the-art as-received (112)B CdZnTe substrates have been examined for surface impurity contamination and polishing residue. Two 4 cm × 4 cm and one 6 cm × 6 cm (112)B state-of-the-art as-received CdZnTe wafers were analyzed. A maximum surface impurity concentration of Al = 1.7 × 1015 atoms cm-2, Si = 3.7 × 1013 atoms cm-2, Cl = 3.12 × 1015 atoms cm-2, S = 1.7 × 1014 atoms cm-2, P = 1.1 × 1014 atoms cm-2, Fe = 1.0 × 1013 atoms cm-2, Br = 1.2 × 1014 atoms cm-2, and Cu = 4 × 1012 atoms cm-2 was observed on the as-received CdZnTe wafers. CdZnTe particulates and residual SiO2 polishing grit were observed on the surface of the as-received (112)B CdZnTe substrates. The polishing grit/CdZnTe particulate density on CdZnTe wafers was observed to vary across a 6 cm × 6 cm wafer from ˜4 × 107 cm-2 to 2.5 × 108 cm-2. The surface impurity and damage layer of the (112)B CdZnTe wafers dictate that a molecular beam epitaxy (MBE) preparation etch is required. The contamination for one 4 cm × 4 cm and one 6 cm × 6 cm CdZnTe wafer after a standard MBE Br:methanol preparation etch procedure was also analyzed. A maximum surface impurity concentration of Al = 2.4 × 1015 atoms cm-2, Si = 4.0 × 1013 atoms cm-2, Cl = 7.5 × 1013 atoms cm-2, S = 4.4 × 1013 atoms cm-2, P = 9.8 × 1013 atoms cm-2, Fe = 1.0 × 1013 atoms cm-2, Br = 2.9 × 1014 atoms cm-2, and Cu = 5.2 × 1012 atoms cm-2 was observed on the MBE preparation-etched CdZnTe wafers. The MBE preparation-etched surface contamination consists of Cd(Zn)Te particles/flakes. No residual SiO2 polishing grit was observed on the (112)B surface.

  1. Correlation of Interfacial Transportation Properties of CdS/CdTe Heterojunction and Performance of CdTe Polycrystalline Thin-Film Solar Cells

    OpenAIRE

    Guanggen Zeng; Jingquan Zhang; Wenwu Wang; Lianghuan Feng

    2015-01-01

    The light and dark output performances of CdS/CdTe solar cells made by close-spaced sublimation (CSS) were investigated to elucidate the transportation properties of carriers at CdS/CdTe heterojunction interface. It has been found that the interfacial transportation properties were relatively sensitive to variations of the characteristics of heterojunction due to the series resistance and shunting effects. For the high quality cell with 12.1% efficiency, narrow depletion region of ~1.1 micron...

  2. Optical properties of CuCdTeO thin films sputtered from CdTe-CuO composite targets

    International Nuclear Information System (INIS)

    The effective complex dielectric function (ε) of Cu and O containing CdTe thin films is reported in the spectral range of 0.05 to 6 eV. The films were fabricated by rf sputtering from targets comprised by a mixture of CdTe and CuO powders with nominal Cu and O concentrations in the range of 2–10 at.%. Low concentration levels improved the crystalline quality of the films. Spectroscopic ellipsometry and transmittance measurements were used to determine ε. The critical point energies E1, E1 + Δ1, and E2 of CdTe are red-shifted with the incorporation of Cu and O. Also, an absorption band is developed in the infrared range which is associated with a mixture of CdTe and low resistivity phases Cu2−xTe according to an effective medium analysis. The elemental distribution of the films was mapped by energy dispersive X-ray spectroscopy using scanning transmission electron microscopy. - Highlights: • Incorporation of 2 to 10 at.% of Cu and O atoms in CdTe films • Improved crystalline quality with 2 and 3 at.% of Cu and O • Complex dielectric function of Cu and O containing CdTe thin films • Effective medium modeling of below band-gap absorption

  3. Enhanced Thermoelectric Properties in the Counter-Doped SnTe System with Strained Endotaxial SrTe.

    Science.gov (United States)

    Zhao, Li-Dong; Zhang, Xiao; Wu, Haijun; Tan, Gangjian; Pei, Yanling; Xiao, Yu; Chang, Cheng; Wu, Di; Chi, Hang; Zheng, Lei; Gong, Shengkai; Uher, Ctirad; He, Jiaqing; Kanatzidis, Mercouri G

    2016-02-24

    We report enhanced thermoelectric performance in SnTe, where significantly improved electrical transport properties and reduced thermal conductivity were achieved simultaneously. The former was obtained from a larger hole Seebeck coefficient through Fermi level tuning by optimizing the carrier concentration with Ga, In, Bi, and Sb dopants, resulting in a power factor of 21 μW cm(-1) K(-2) and ZT of 0.9 at 823 K in Sn(0.97)Bi(0.03)Te. To reduce the lattice thermal conductivity without deteriorating the hole carrier mobility in Sn(0.97)Bi(0.03)Te, SrTe was chosen as the second phase to create strained endotaxial nanostructures as phonon scattering centers. As a result, the lattice thermal conductivity decreases strongly from ∼2.0 Wm(-1) K(-1) for Sn(0.97)Bi(0.03)Te to ∼1.2 Wm(-1) K(-1) as the SrTe content is increased from 0 to 5.0% at room temperature and from ∼1.1 to ∼0.70 Wm(-1) K(-1) at 823 K. For the Sn(0.97)Bi(0.03)Te-3% SrTe sample, this leads to a ZT of 1.2 at 823 K and a high average ZT (for SnTe) of 0.7 in the temperature range of 300-823 K, suggesting that SnTe is a robust candidate for medium-temperature thermoelectric applications. PMID:26871965

  4. Effects of CdS film thickness on the photovoltaic properties of sintered CdS/CdTe solar cells

    Science.gov (United States)

    Lee, J. S.; Jun, Y. K.; Im, H. B.

    1987-01-01

    All polycrystalline CdS/CdTe heterojunction solar cells with various thicknesses of CdS film were prepared by the coating and sintering method in an attempt to optimize the thickness of the sintered CdSfilm whose role is to be the window as well as the front contact for the CdS/CdS/CdTe solar cell. The thickness of the CdS films was varied from 14 to 55 microns by changing the screen mesh size of a screen printer and the solid-liquid ratio of the slurry which consisted of CdS powder, 9 weight percent CdCl2 and propylene glycol. Average grain size of the sintered CdS films increases and porosity decreases with an increase in film thickness. Electrical resistivity of the sintered CdS films shows a minimum value in 35-micron thick film. Highest optical transmission is observed in 20-micron thick CdS film. The CdCl2 remaining in the CdS film after the sintering causes an increase in the thickness of the CdS(1-x)Te(x) solid solution layer, acting as a sintering aid, at the interface between the CdS and the CdTe films. The combination of the optical transmission, the solid solution layer, and the sheet resistance effects resulted in the highest solar efficiency in a CdS/CdTe heterojunction solar cell with 20-micron thick CdS layer.

  5. 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.

  6. CdTe solar cells on thin molybdenum substrates

    Science.gov (United States)

    Matulionis, Ilvydas

    2000-10-01

    We report on the development of Mo/(ZnTe:N)/CdTe/CdS/ITO (inverted structure) solar cells grown by radio frequency sputtering. The 0.1 mm thick molybdenum substrate is lightweight and flexible which is advantageous for both terrestrial and space applications. Conversion efficiencies close to 8 percent have been achieved for 5 square millimeter area devices. The photovoltaic activity has also been observed on similar cells deposited on Mo coated kapton and stainless steel substrates.

  7. PERFORMANCE-LIMITING DEFECTS IN CdZnTe DETECTORS

    International Nuclear Information System (INIS)

    We studied the effects of small, <20 (micro)m, Te inclusions on the energy resolution of CdZnTe gamma-ray detectors using a highly collimated X-ray beam and gamma-rays, and modeled them via a simplified geometrical approach. Previous reports demonstrated that Te inclusions of about a few microns in diameter degraded the charge-transport properties and uniformity of CdZnTe detectors. The goal of this work was to understand the extent to which randomly distributed Te-rich inclusions affect the energy resolution of CZT detectors, and to define new steps to overcome their deleterious effects. We used a phenomenological model, which depends on several adjustable parameters, to reproduce the experimentally measured effects of inclusions on energy resolution. We also were able to hound the materials-related problem and predict the enhancement in performance expected by reducing the size and number of Te inclusions within the crystals

  8. Elaboration of the deposition technology and the investigation of the electrical and photoelectrical properties of CdS/CdTe heterojunctions

    International Nuclear Information System (INIS)

    This thesis is related to the elaboration of manufacturing technology of CdS/CdTe thin film heterojunctions and their properties study. Thin film CdS/CdTe heterojunctions were fabricated by using the close spaced sublimation method, onto SnO2 covered glass plates (2x2 cm2). The investigations of the source and substrates temperatures influence on the morphology and electrophysical properties of CdS and CdTe thin films, has been studied. The optimum source and substrate temperatures have been determined as follows: for CdS T source=640 degrees Celsius, T substrate=445 degrees Celsius, for CdTe T source=550 degrees Celsius, T substrate=445 degrees Celsius distribution in CdS and CdTe thin films are presented. It has been established, that Sn and Si atoms are presented in CdS thin films along with basic elements (Cd and S) due to diffusion processes. For to enhance CdS/CdTe heterojunctions photosensitivity, it has been annealed (390-420 degrees Celsius) in presence of CdCl2 for 15-60 min. As it came from the analysis of current-voltage dependencies in the 78-370 K temperature range, the current flow mechanism in CdS/CdTe heterojunction is determined by the tunneling processes through dislocations, which penetrate the space charge region. The concentration of dislocations has been estimated as 2-105 cm2. The multistep tunnelling processes through local centres in the space charge region predominate at reverse biases. The investigations of the photoluminescence spectra, optical absorption and reflection have revealed the presence of a layer consisting of CdSxTex solid solutions (x=0,03-0,05), which is formed at the heterojunction interface, after its annealing in the presence of CdCl2. The appearance of the excitonic maxima in the annealed heterojunctions indicates to an enhancement of the crystalline structure and the decrease of the defects concentration at the heterojunction interface. The study of the kinetics of CdTe thin films photoconductivity revealed a 20 me

  9. Spectroscopic laser parameters of Ag/CdTe nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Giba, A.E., E-mail: alaadin85@niles.edu.eg [Department of Laser Science and Interaction, National Institute of Laser Enhanced Science, Cairo University, 12613 Giza (Egypt); Gadallah, A.-S. [Department of Laser Science and Interaction, National Institute of Laser Enhanced Science, Cairo University, 12613 Giza (Egypt); Mohamed, M.B. [Department of Laser Applications in Metrology, Photochemistry & Agriculture, National Institute of Laser Enhanced Science, Cairo University, 12613 Giza (Egypt); Azzouz, I.M. [Department of Laser Science and Interaction, National Institute of Laser Enhanced Science, Cairo University, 12613 Giza (Egypt)

    2015-11-15

    We report spectroscopic laser parameters analysis for CdTe quantum dots (QDs) in the presence of Ag nanoparticles (NPs). Absorption and emission cross-sections of about 2 nm-particle size of aqueous CdTe QDs were estimated, when different contents of about 40 nm Ag nanoparticles were added. The fluorescence, radiative lifetimes and the energy transfer between Ag NPs and CdTe QDs have been investigated. Lasing parameters that evaluate the possibility of getting laser action for these nanomaterials were calculated. The energy transfer mechanism between Ag NPs and CdTe QDs was occurred by Forster resonance energy transfer (FRET) as the average distance between them is about 50 nm. - Highlights: • Absorption and emission cross sections of Ag/CdTe have been calculated. • Lasing parameters of these nanomaterials have been also estimated. • The energy transfer mechanism between Ag NPs and CdTe QDs was determined. • Our findings are promising candidate for photonic devices.

  10. Spectroscopic laser parameters of Ag/CdTe nanostructure

    International Nuclear Information System (INIS)

    We report spectroscopic laser parameters analysis for CdTe quantum dots (QDs) in the presence of Ag nanoparticles (NPs). Absorption and emission cross-sections of about 2 nm-particle size of aqueous CdTe QDs were estimated, when different contents of about 40 nm Ag nanoparticles were added. The fluorescence, radiative lifetimes and the energy transfer between Ag NPs and CdTe QDs have been investigated. Lasing parameters that evaluate the possibility of getting laser action for these nanomaterials were calculated. The energy transfer mechanism between Ag NPs and CdTe QDs was occurred by Forster resonance energy transfer (FRET) as the average distance between them is about 50 nm. - Highlights: • Absorption and emission cross sections of Ag/CdTe have been calculated. • Lasing parameters of these nanomaterials have been also estimated. • The energy transfer mechanism between Ag NPs and CdTe QDs was determined. • Our findings are promising candidate for photonic devices

  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. 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.

  13. Nonlinear terahertz response of HgTe/CdTe quantum wells

    International Nuclear Information System (INIS)

    Without breaking the topological order, HgTe/CdTe quantum wells can have two types of bulk band structure: direct gap type (type I) and indirect gap type (type II). We report that the strong nonlinear optical responses exist in both types of bulk states under a moderate electric field in the terahertz regime. Interestingly, for the type II band structure, the third order conductivity changes sign when chemical potentials lies below 10 meV due to the significant response of the hole excitation close to the bottom of conduction band. Negative nonlinear conductivities suggest that HgTe/CdTe quantum wells can find application in the gain medium of a laser for terahertz radiation. The thermal influences on nonlinear optical responses of HgTe/CdTe quantum wells are also studied

  14. 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.

  15. Interfacial chemistry of metals on CdTe and ZnTe (110)

    Energy Technology Data Exchange (ETDEWEB)

    Wahi, A.K.; Carey, G.P.; Miyano, K.; Chiang, T.T.; Lindau, I.; Spicer, W.E. (Stanford Electronics Laboratories, Stanford University, Stanford, California 94305 (US))

    1990-03-01

    We consider interfacial chemistry and band bending behavior for Al, In, Ag, and Pt overlayers on vacuum-cleaved {ital p}-CdTe and {ital p}-ZnTe (110) in a comparative study using ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy. A range of metal--substrate reactivities have been considered: Al reacts strongly with Te, Ag moderately, and In minimally, with no evidence seen for In reaction on ZnTe. Pt exhibits strong alloying behavior with both Cd and Zn. These results for the binaries are compared to metal/HgCdTe interface formation. We find that Hg loss can significantly influence the extent of reaction and/or intermixing for these overlayers, with resulting disruption either inhibiting or facilitating chemical interaction. Reaction and intermixing for Al, Ag, and Pt overlayers on CdTe and ZnTe indicate these interfaces are not ideal. The possible role of defects at these four metal/CdTe and metal/ZnTe interfaces is considered, and provides a consistent explanation for the final Fermi level positions observed.

  16. Do grain boundaries assist S diffusion in polycrystalline CdS/CdTe heterojunctions?

    International Nuclear Information System (INIS)

    We report on a transmission electron microscopy and energy-dispersive x-ray spectroscopy study of S diffusion in polycrystalline CdS/CdTe heterojunctions. We find that grain boundaries significantly assist S diffusion in the CdTe layer when the CdTe is grown without the presence of oxygen, i.e., the S diffuses more easily along the grain boundaries than in the grains. However, grain boundaries do not enhance the S diffusion in CdTe when it is grown in the presence of oxygen. The reason is likely to be the formation of Cd--O bonds at the grain boundaries, which are resistance to the S diffusion

  17. Impact of CdS annealing atmosphere on the performance of CdS–CdTe solar cell

    International Nuclear Information System (INIS)

    Highlights: • Annealed CdS films are used for CdTe based solar cells. • CdS–CdTe solar cell with air annealed CdS shows better performance. • The air annealed CdS brings the O2 and chloride at the place of junction formation. • H2 removes the oxygen containing compounds from CdS grain boundaries. - Abstract: CdS thin films obtained by chemical bath deposition and annealed in hydrogen and air ambients were combined with CdTe absorbers obtained by close spaced sublimation. CdS–CdTe solar cells in superstrate configuration were characterized by current–voltage and quantum efficiency measurements while the analysis of annealed CdS films was made by scanning electron microscopy, X-ray diffraction and UV–vis spectroscopy. It was found that in superstrate configuration, due to the big grains on CdS surface and gas emission from CdS film at high temperature deposition of the absorber, the delamination of layers take place. Annealing in H2 removes the oxygen compounds from CdS grain boundaries and opens them for formation of shortcutting through the CdS layer. The processing in air is most advantageous due to simultaneous presence of chloride and oxygen, contributing to the recrystallization and sintering of the highly textured columnar CdS. The direct influence of the CdS annealing on the solar cell parameters is shown for CdS–CdTe solar cell

  18. Impact of CdS annealing atmosphere on the performance of CdS–CdTe solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Maticiuc, N., E-mail: nataliamaticiuc@yahoo.com; Spalatu, N.; Mikli, V.; Hiie, J.

    2015-09-30

    Highlights: • Annealed CdS films are used for CdTe based solar cells. • CdS–CdTe solar cell with air annealed CdS shows better performance. • The air annealed CdS brings the O{sub 2} and chloride at the place of junction formation. • H{sub 2} removes the oxygen containing compounds from CdS grain boundaries. - Abstract: CdS thin films obtained by chemical bath deposition and annealed in hydrogen and air ambients were combined with CdTe absorbers obtained by close spaced sublimation. CdS–CdTe solar cells in superstrate configuration were characterized by current–voltage and quantum efficiency measurements while the analysis of annealed CdS films was made by scanning electron microscopy, X-ray diffraction and UV–vis spectroscopy. It was found that in superstrate configuration, due to the big grains on CdS surface and gas emission from CdS film at high temperature deposition of the absorber, the delamination of layers take place. Annealing in H{sub 2} removes the oxygen compounds from CdS grain boundaries and opens them for formation of shortcutting through the CdS layer. The processing in air is most advantageous due to simultaneous presence of chloride and oxygen, contributing to the recrystallization and sintering of the highly textured columnar CdS. The direct influence of the CdS annealing on the solar cell parameters is shown for CdS–CdTe solar cell.

  19. The large-area CdTe thin film for CdS/CdTe solar cell prepared by physical vapor deposition in medium pressure

    Science.gov (United States)

    Luo, Run; Liu, Bo; Yang, Xiaoyan; Bao, Zheng; Li, Bing; Zhang, Jingquan; Li, Wei; Wu, Lili; Feng, Lianghuan

    2016-01-01

    The Cadmium telluride (CdTe) thin film has been prepared by physical vapor deposition (PVD), the Ar + O2 pressure is about 0.9 kPa. This method is a newer technique to deposit CdTe thin film in large area, and the size of the film is 30 × 40 cm2. This method is much different from the close-spaced sublimation (CSS), as the relevance between the source temperature and the substrate temperature is weak, and the gas phase of CdTe is transferred to the substrate by Ar + O2 flow. Through this method, the compact and uniform CdTe film (30 × 40 cm2) has been achieved, and the performances of the CdTe thin film have been determined by transmission spectrum, SEM and XRD. The film is observed to be compact with a good crystallinity, the CdTe is polycrystalline with a cubic structure and a strongly preferred (1 1 1) orientation. Using the CdTe thin film (3 × 5 cm2) which is taken from the deposited large-area film, the 14.6% efficiency CdS/CdTe thin film solar cell has been prepared successfully. The structure of the cell is glass/FTO/CdS/CdTe/graphite slurry/Au, short circuit current density (Jsc) of the cell is 26.9 mA/cm2, open circuit voltage (Voc) is 823 mV, and filling factor (FF) is 66.05%. This technique can be a quite promising method to apply in the industrial production, as it has great prospects in the fabricating of large-area CdTe film.

  20. Influence of thermal treatment temperatures on CdTe nanocrystal films and photoelectric properties of ITO/CdTe/Al

    Institute of Scientific and Technical Information of China (English)

    Xu Wenqing; Qu Shengchun; Wang Kefan; Bi Yu; Liu Kong; Wang Zhanguo

    2012-01-01

    The influence of sintering temperatures on solution-processed cadmium telluride (CdTe) nanocrystal films is studied in order to maximize the performance of CdTe/Al Schottky nanocrystal solar cells,The best overall performance of 2.67% efficiency at air mass 1.5 was achieved from devices with CdTe films sintered at 350 ℃ X-ray diffraction,scanning electron microscopy and UV-vis absorption measurements show that the CdTe nanocrystal grains began to grow remarkably well when sintering temperatures increased to 350 ℃.By analyzing the current-voltage characteristics,we find that the short-circuit current densities of devices increase with sintering temperatures ranging from 200 to 400 ℃,but,the over-sintered (450 ℃) treatment induces the shunting of devices.

  1. Turnover of exciton spin states in CdTe/Cd0.88Mn0.12Te quantum wells

    International Nuclear Information System (INIS)

    Photoinduced exciton spin states in diluted magnetic semiconductor CdTe/Cd0.88Mn0.12Te quantum wells (QWs) were investigated by the time-resolved Kerr rotation (TRKR) technique at various temperatures and applied magnetic fields. Two oscillation components were observed in the TRKR signals. One component is ascribed to the spin precession of a localized electron, which was not affected by the Mn ions in the CdMnTe barrier layers. Its frequency increased linearly with the applied magnetic field. The other component was strongly dependent on the temperature, and its frequency showed a minimum at around 20 K in the 8.4 nm QW. This result was well explained by the turnover of exciton spin states in the CdTe QW, which is determined by the competition between the exciton Zeeman effect and an exciton–Mn exchange interaction. The temperature dependence of the exciton spin relaxation is also discussed. (author)

  2. Molecular beam epitaxial growth of ultrathin CdTe-CdMnTe quantum wells and their characterization

    Science.gov (United States)

    Waag, A.; Schmeusser, S.; Bicknell-Tassius, R. N.; Yakovlev, D. R.; Ossau, W.; Landwehr, G.; Uraltsev, I. N.

    1991-12-01

    We report the growth and optical characterization of CdTe/CdMnTe single quantum wells with well thicknesses ranging from 60 down to 6 Å. The single quantum wells were grown by standard molecular beam epitaxy without growth interruption and investigated by reflection, photoluminescence (PL), and excitation PL. All structures including the 6-Å-thick quantum well exhibit extraordinarily narrow photoluminescence lines. From an analysis of linewidth and Stokes shift of the photoluminescence lines informations on the structure of the CdTe/CdMnTe interfaces are derived. The good quality of those structures made it possible to identify for the first time recombination of two-dimensional free exciton magnetic polarons.

  3. Ion beam induced charge imaging of charge transport in CdTe and CdZnTe

    International Nuclear Information System (INIS)

    Ion beam induced charge (IBIC) imaging is a powerful technique for quantitative mapping of the charge transport performance of wide bandgap semiconductor materials. In this paper we present results from a study of electron and hole mobility-lifetime product and drift mobility in CdTe:Cl and CdZnTe, which are semiconductor materials used for radiation detector applications. IBIC imaging has been used to produce mobility-lifetime product maps in CdTe:Cl and CdZnTe, revealing the influence of extended defects and tellurium inclusions and assessing the large area response uniformity of the materials. The recent extension of this method in the form of digital time-resolved IBIC is also discussed and time of flight maps are presented which give quantitative images of electron and hole drift mobility

  4. The heat capacity of zinc and cadmium chalcogenides (ZnTe, CdSe, and CdTe)

    International Nuclear Information System (INIS)

    Heat capacity of zinc telluride, cadmium selenide and telluride are measured by the calorimetry method at 370-640 K (ZnTe) and 500-760 K (CdSe, CdTe). Analysis of literature data on heat capacity of the above-mentioned solid solutions at temperatures in excess of 298 K is carried out. On the basis of the results obtained and most dependable literature data on heat capacity of the compounds for temperature ranges of 220-1500 K (ZnTe, CdSe) and 220-1300 K (CdTe) new equations of heat capacity temperature dependence are suggested and thermodynamic functions of the compounds are calculated

  5. 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

  6. 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...

  7. RF Sputtered ZnTe:N as CdS/CdTe Solar Cell Back-Contact Material

    Science.gov (United States)

    Ma, X.

    1999-04-01

    The most frequently used electrical contact to CdTe thin-film polycrystalline solar cells on glass involves the use of copper. However, Cu is known to be a fast diffuser in many semiconductors and is suspected of leading to some deterioration of performance of CdTe solar cells under extreme conditions. In this work we report on the development of a reactively sputtered ZnTe:N back contact on solar cells. Promising low-resistive nitrogen-doped ZnTe films were obtained. Efficiencies up to 10.8 percent were obtained for solar cells fabricated with a ZnTe:N/Au back contact scheme. Comparison of cell performances using ZnTe:N and Cu/Au back-contacts is presented.

  8. Fabrication of CdTe/NiTe films on Ni foils by radio-frequency magnetron sputtering method

    International Nuclear Information System (INIS)

    Highlights: • The effects of Ts on CdTe deposited on Ni by magnetron sputtering is investigated. • An effective method is studied of making CdTe/NiTe without post-treatment. • As-prepared CdTe/NiTe raised optical absorption and PEC properties. • Pre-deposited Te can react with Ni to generate NiTe at Ts = 350 °C. - Abstract: Cadmium Telluride (CdTe) semiconductor thin films are fabricated on flexible Ni foil substrates using radio-frequency (RF) magnetron sputtering under different substrate temperatures. The crystal structure and properties of the prepared functional thin films were characterized with series analysis technologies. The characterization results revealed that Nickel Telluride (NiTe) phase formatted at the interface of CdTe and Ni substrate when substrate temperature (Ts) is 450 °C. Specially, XRD results demonstrated that CdTe/NiTe films could also be obtained by pre-depositing Te film on Ni and reducing Ts to 350 °C. The investigation on optical and photoelectrochemical (PEC) properties of the products illustrated that compact CdTe/NiTe films had improved the absorption in the visible region. Furthermore, PEC measurements indicated that CdTe/NiTe/Ni photoelectrode can have a promising application in photovoltaic devices

  9. Colloidal CdTe/HgTe quantum dots with high photoluminescence quantum efficiency at room temperature

    Science.gov (United States)

    Kershaw, Stephen V.; Burt, Mike; Harrison, Mike; Rogach, Andrey; Weller, Horst; Eychmüller, Alex

    1999-09-01

    We have used an aqueous colloidal growth technique to form hybrid CdTe/HgTe quantum dots with a broad, strong fluorescence in the infrared (800-1200 nm). The quantum efficiency is high, around 44%, when pumped in the visible (488 nm), and the excited state lifetime is around 130 ns, making the material interesting as an optical amplifier medium. Using a pump-probe experiment, we have demonstrated weak optical amplification in a dilute aqueous suspension of CdTe/HgTe dots in the short wavelength wing of the emission spectrum at 808 nm.

  10. Electronic properties of exciton and biexciton in a CdTe/ZnTe nano-heterostructure

    International Nuclear Information System (INIS)

    Energy eigen values and the binding energies of exciton and biexciton in a CdTe/ZnTe quantum dot are studied with the geometrical confinement effect. The single exciton binding energy and the biexciton binding energy are calculated as a function of dot radius. Overlap integral of the exciton and the biexciton is found in the CdTe/ZnTe quantum dot. The electron and hole potentials are calculated from the Poisson equations. Self-consistent method is to compute the energy eigenvalues of the exciton and the biexciton. The Hartree potential is employed to obtain the Coulomb interaction energy

  11. Band diagrams and performance of CdTe solar cells with a Sb2Te3 back contact buffer layer

    OpenAIRE

    Songbai Hu; Zhe Zhu; Wei Li; Lianghuan Feng; Lili Wu; Jingquan Zhang; Jingjing Gao

    2011-01-01

    Sb2Te3 thin films were prepared by vacuum co-evaporation and the crystallinity of the films was greatly improved after annealing at 573 K in N2 ambient. Then they were deposited on the CdTe thick films. Band diagrams of the as-deposited and annealed CdTe/Sb2Te3 interfaces were constructed. Consequently, Sb2Te3 was used as a back contact layer for CdTe thin film solar cells and the cell performance was investigated. It was found that the Sb impurities accumulated in the CdTe grain boundaries d...

  12. Eects of Post Deposition Treatments on Vacuum Evaporated CdTe Thin Films and CdS=CdTe Heterojunction Devices

    Science.gov (United States)

    Bayhan, Habibe; Erçelebý, Çiðdem

    1998-05-01

    CdTe, CdS thin films and n-CdS/p-CdTe heterostructures have been prepared by conventional vacuum evaporation technique. Some post deposition treatments to optimize the device efficiency have been analyzed and the effects of the individual process steps on the material and device properties were investigated. Annealing in air with and without CdCl2-treatment decreased the CdTe resistivity. The CdCl2-dip followed by annealing in air at 300°C for 5 min improved the grain size and polycrystalline nature of CdTe thin films. Solar efficiency improvements were achieved when heterojunctions were prepared on successively treated (i.e. etched, air annealed, CdCl2-processed) CdTe surfaces. Etching of the CdTe surface with potassium dichromate solution prior to metal contact deposition lead to the formation of low-resistance Au contacts and increase in open circuit voltage and fill factor values.

  13. Implantation effects on resonant Raman scattering in CdTe and Cd 0.23Hg 0.77Te

    Science.gov (United States)

    Ramsteiner, M.; Lusson, A.; Wagner, J.; Koidl, P.; Bruder, M.

    1990-04-01

    We have studied In + implanted CdTe and Cd 0.23Hg 0.77Te by resonant Raman scattering. The laser excitation was in resonance with the EO + Δ O band gap in CdTe or the E1 gap in Cd 0.23Hg 0.77Te. Under these conditions dipole forbidden but defect ind scattering by one longitudinal optical (LO) phonon as well as Fröhlich-induced two-LO phonon scattering is observed. In both cases scattering is found to be strongly affected by ion implantation. In + was implanted at an ion energy of 350 keV with doses ranging from 10 11 to 5×10 14 ions/cm 2. The intensity ratio of the one-LO phonon lines is found to be a quantitative measure of the implantation damage in CdTe and Cd 0.23Hg 0.77Te even for doses as low as 10 11 ions/cm 2. It is shown that the observed effects of implantation damage on resonant Raman scattering by LO phonons are due to a broadening and an energy shift of the corresponding resonances in the Raman scattering efficiency.

  14. Fabrication of screen printed optoelectronic CdS/CdTe device

    Science.gov (United States)

    Imran, Ali; Jiang, Jianliang; Naseem, S.; Sadaqat, Afifa; Khan, M. Khalid

    2015-08-01

    II-VI semiconductors have great importance in the fabrication and application of optoelectronic devices. CdTe is one of the most promising materials among photovoltaic materials. In this research work CdS/CdTe solar cell has been prepared using screen printing and sintering technique. Various factors affecting the surface morphology of CdS window layer were also investigated. Optical Microscopy, Scanning Electron Microscopy and Electrical characterization proved that best results can be achieved by increasing the sintering duration, the Mesh number and by CdCl2 doping. CdS/CdTe solar cell with an area of 8.8 cm2 was prepared. The Fill Factor was calculated to be 0.51, with Voc = 0.56 V and Isc = 31.5 mA. The efficiency was also measured and found to be 1.02%.

  15. Investigation of electroluminescence properties of CdTe@CdS core-shell nanocrystals (NCs)

    Indian Academy of Sciences (India)

    M Molaei; S Pourjafari

    2014-02-01

    In this work, CdTe@CdS NCs were synthesized using a thermochemical approach and synthesized NCs were used as an emissive layer, a light emitting device, with ITO/MoO3/PVK/CdTe@CdS(core-shell)/Mg:Ag structure. Structural and optical properties of synthesized NCs were investigated by means of XRD, UV–Vis and photoluminescence (PL) analyses. Fabricated device was characterized by electroluminescence spectra. XRD analysis demonstrated cubic phase NCs. Photoluminescence spectra showed a narrow band emission with a peak centred at about 600 nm. Fabricated device showed an emission at 600 nm, which is related to CdTe@CdS NCs. Turn on voltage of fabricated device is about 8 V and brightness is 53.7 Cd/m2 at a working voltage of about 14.57 V.

  16. Effect of CdCl2 annealing treatment on CdS thin films and CdTe/CdS thin film solar cells

    International Nuclear Information System (INIS)

    In order to study the effect of CdCl2 annealing treatment on thin CdS films and CdTe/CdS thin film solar cells, a comparative study was carried out on three types of CdTe/CdS solar cells, which had different kinds of CdS window layer: as-deposited CdS, air-annealed CdS without CdCl2 pre-coating, and CdCl2-annealed CdS. When annealed in air the CdS film was partially oxidated to CdO and CdSO4. These oxides increased the series resistance of the CdTe solar cell and led to the lowest fill factor. The presence of CdCl2 on the surface of a CdS thin film during heat treatment in air protected it from oxidation and promoted the recrystallization of the CdS film, resulting in large and closely packed grains with a grain size of ∝ 50 -150 nm. CdTe/CdS solar cell with such a kind of CdS window layer showed the largest short circuit current and highest conversion efficiency of 12.4%. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Nanoscale morphology of multilayer PbTe/CdTe heterostructures and its effect on photoluminescence properties

    International Nuclear Information System (INIS)

    We study nanoscale morphology of PbTe/CdTe multilayer heterostuctures grown by molecular beam epitaxy on hybrid GaAs/CdTe (100) substrates. Nominally, the structures consist of 25 repetitions of subsequently deposited CdTe and PbTe layers with comparable thicknesses of 21 and 8 nm, respectively. However, the morphology of the resulting structures crucially depends on the growth temperature. The two-dimensional layered, superlattice-like character of the structures remains preserved only when grown at low substrate temperatures, such as 230 °C. The samples grown at the slightly elevated temperature of 270 °C undergo a morphological transformation to structures consisting of CdTe and PbTe pillars and columns oriented perpendicular to the substrate. Although the pillar-like objects are of various shapes and dimensions these structures exhibit exceptionally strong photoluminescence in the near infrared spectral region. At the higher growth temperature of 310 °C, PbTe and CdTe separate completely forming thick layers oriented longitudinally to the substrate plane. The observed topological transformations are driven by thermally activated atomic diffusion in the solid state phase. The solid state phase remains fucrystlly coherent during the processes. The observed topological transitions leading to the material separation in PbTe/CdTe system could be regarded as an analog of spinodal decomposition of an immiscible solid state solution and thus they can be qualitatively described by the Cahn–Hillard model as proposed by Groiss et al (2014 APL Mater. 2 012105). (paper)

  18. Band diagrams and performance of CdTe solar cells with a Sb2Te3 back contact buffer layer

    Directory of Open Access Journals (Sweden)

    Songbai Hu

    2011-12-01

    Full Text Available Sb2Te3 thin films were prepared by vacuum co-evaporation and the crystallinity of the films was greatly improved after annealing at 573 K in N2 ambient. Then they were deposited on the CdTe thick films. Band diagrams of the as-deposited and annealed CdTe/Sb2Te3 interfaces were constructed. Consequently, Sb2Te3 was used as a back contact layer for CdTe thin film solar cells and the cell performance was investigated. It was found that the Sb impurities accumulated in the CdTe grain boundaries diffuse deeply in the CdTe layer, and more photogenerated electrons and holes are separated by the segregated SbCd+ donors into the GBs. What is more, the doping concentration in the vicinity of the CdTe/CdS heterojunction increases for the formation of substitutional SbTe- acceptors under the Cd-rich conditions. For the introduction of the p-type Sb2Te3 layers as the back contact to the CdTe thin film solar cells, the performance of CdTe thin film solar cells has been greatly improved and an efficiency of 13.1% (FF=62.3%, Jsc=25.8 mA/cm2, Voc= 815.8 mV obtained.

  19. Transport properties of the SnBi2Te4–PbBi2Te4 solid solution

    International Nuclear Information System (INIS)

    We report on the electrical and thermal transport properties of the Sn1−xPbxBi2Te4 series and we discuss the potential of these materials for thermoelectric conversion applications. From the evolution of the XRD patterns, we can confidently conclude that a complete solid solution exists between SnBi2Te4 and PbBi2Te4, with no miscibility gap. A crossover from p-type conduction in Sn-rich samples to n-type conduction in Pb-rich ones has been observed, with a transition between x=0.3 and 0.4. A concomitant increase of the electrical resistivity and of the Seebeck coefficient has been observed in the solid solution, which leads to almost constant values of the thermoelectric power factor. Moreover, the thermal conductivity is slightly reduced in the solid solution. The best figure of merit ZT values at room temperature have been observed for p-type Sn0.8Pb0.2Bi2Te4 with ZT=0.25 and for n-type Sn0.3Pb0.7Bi2Te4 with ZT=0.15. - Graphical abstract: Seebeck coefficient in (Pb/Sn)Bi2Te4 solid solution. - Highlights: • A complete solid solution exists between PbBi2Te4 and SnBi2Te4. • A crossover between p-type and n-type is observed for 0.3

  20. CdTe photovoltaics: Life cycle environmental profile and comparisons

    International Nuclear Information System (INIS)

    We discuss the emissions of cadmium throughout all the life stages of CdTe PV modules, from extracting, refining, and purifying the raw materials to producing, using, and disposing or recycling of the modules. Then, we compare these emissions with those in the life cycle of three different types of crystalline Si PV modules. The energy requirement and energy pay back times (EPBT) of CdTe PV modules are considerably shorter than that of crystalline Si modules, although the latter exhibit higher efficiencies. This difference is primarily due to the energy used to process silicon, a fraction of which is derived from fossil fuels, inevitably producing Cd and many other heavy-metal emissions. The lower energy requirement of CdTe PV results in lower emissions of all pollutants, including cadmium

  1. Recent developments in evaporated CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Khrypunov, G. [Kharkov State Polytechnic University, UA-310002 Kharkov (Ukraine); Romeo, A. [Faculty of Science, University of Verona, Ca' Vignal 2, Strada Delle Grazie, 37134 Verona (Italy); Kurdesau, F. [National Academy of Sciences Belarus, Logoysky Tract 22, Minsk 220090 (Belarus); Baetzner, D.L. [The Australian National University, ACTON, ACT 0200 (Australia); Zogg, H.; Tiwari, A.N. [Thin Film Physics Group, Laboratory for Solid State Physics, ETH (Swiss Federal Institute of Technology) Zuerich, Technoparkstrasse 1, 8005 Zurich (Switzerland)

    2006-04-14

    Recent developments in the technology of high vacuum evaporated CdTe solar cells are reviewed. High-efficiency solar cells of efficiencies up to 12.5% have been developed on soda-lime glass substrates with a low-temperature (<450{sup o}C) process. This simple process is suitable for in-line production of large-area solar modules on glass as well as on flexible polymer films with a roll-to-roll deposition process. Flexible and lightweight CdTe solar cells with a record efficiency of 11.4% have been developed in a superstrate configuration, and 3.5% efficiency mini-modules have been realised in a preliminary development. Deposition of high-temperature stable ITO front contact layer on polyimide is important for high-efficiency cells, as the layer should withstand processing steps maintaining its high electrical conductivity and optical transparency. Another development is an application of a transparent conducting oxide (TCO) ITO as a back electrical contact on CdTe leading to first bifacial CdTe solar cells, which can be illuminated from either or both sides. Accelerated long-term stability tests show that light soaking improves the efficiency of CdTe solar cells with ITO back contacts and performance does not degrade. Stability of CdTe solar cells has been measured after irradiation with high-energy protons and electrons of different fluences. These solar cells exhibit superior radiation tolerance compared to conventional Si and GaAs solar cells for space applications. Because of extreme stability, and high specific power (kW/kg) of flexible solar cells, CdTe has a promising potential for space applications. (author)

  2. Colloidal synthesis and optical properties of type-II CdSe-CdTe and inverted CdTe-CdSe core-wing heteronanoplatelets

    Science.gov (United States)

    Antanovich, A. V.; Prudnikau, A. V.; Melnikau, D.; Rakovich, Y. P.; Chuvilin, A.; Woggon, U.; Achtstein, A. W.; Artemyev, M. V.

    2015-04-01

    We developed colloidal synthesis to investigate the structural and electronic properties of CdSe-CdTe and inverted CdTe-CdSe heteronanoplatelets and experimentally demonstrate that the overgrowth of cadmium selenide or cadmium telluride core nanoplatelets with counterpartner chalcogenide wings leads to type-II heteronanoplatelets with emission energies defined by the bandgaps of the CdSe and CdTe platelets and the characteristic band offsets. The observed conduction and valence band offsets of 0.36 eV and 0.56 eV are in line with theoretical predictions. The presented type-II heteronanoplatelets exhibit efficient spatially indirect radiative exciton recombination with a quantum yield as high as 23%. While the exciton lifetime is strongly prolonged in the investigated type-II 2D systems with respect to 2D type-I systems, the occurring 2D giant oscillator strength (GOST) effect still leads to a fast and efficient exciton recombination. This makes type-II heteronanoplatelets interesting candidates for low threshold lasing applications and photovoltaics.We developed colloidal synthesis to investigate the structural and electronic properties of CdSe-CdTe and inverted CdTe-CdSe heteronanoplatelets and experimentally demonstrate that the overgrowth of cadmium selenide or cadmium telluride core nanoplatelets with counterpartner chalcogenide wings leads to type-II heteronanoplatelets with emission energies defined by the bandgaps of the CdSe and CdTe platelets and the characteristic band offsets. The observed conduction and valence band offsets of 0.36 eV and 0.56 eV are in line with theoretical predictions. The presented type-II heteronanoplatelets exhibit efficient spatially indirect radiative exciton recombination with a quantum yield as high as 23%. While the exciton lifetime is strongly prolonged in the investigated type-II 2D systems with respect to 2D type-I systems, the occurring 2D giant oscillator strength (GOST) effect still leads to a fast and efficient exciton

  3. Diffusion of Cd and Te adatoms on CdTe(111 surfaces: A computational study using density functional theory

    Directory of Open Access Journals (Sweden)

    Ebadollah Naderi

    2015-01-01

    Full Text Available CdTe is one of the most promising semiconductor for thin-film based solar cells. Here we report a computational study of Cd and Te adatom diffusion on the CdTe (111 A-type (Cd terminated and B-type (Te terminated surfaces and their migration paths. The atomic and electronic structure calculations are performed under the DFT formalism and climbing Nudge Elastic Band (cNEB method has been applied to evaluate the potential barrier of the Te and Cd diffusion. In general the minimum energy site on the surface is labeled as Aa site. In case of Te and Cd on B-type surface, the sub-surface site (a site just below the top surface is very close in energy to the A site. This is responsible for the subsurface accumulation of adatoms and therefore, expected to influence the defect formation during growth. The diffusion process of adatoms is considered from Aa (occupied to Aa (empty site at the nearest distance. We have explored three possible migration paths for the adatom diffusion. The adatom surface interaction is highly dependent on the type of the surface. Typically, Te interaction with both type (5.2 eV for A-type and 3.8 eV for B-type is stronger than Cd interactions(2.4 eV for B-type and 0.39 eV for A-type. Cd interaction with the A-type surface is very weak. The distinct behavior of the A-type and B-type surfaces perceived in our study explain the need of maintaining the A-type surface during growth for smooth and stoichiometric growth.

  4. Diffusion of Cd and Te adatoms on CdTe(111) surfaces: A computational study using density functional theory

    Science.gov (United States)

    Naderi, Ebadollah; Nanavati, Sachin; Majumder, Chiranjib; Ghaisas, S. V.

    2015-01-01

    CdTe is one of the most promising semiconductor for thin-film based solar cells. Here we report a computational study of Cd and Te adatom diffusion on the CdTe (111) A-type (Cd terminated) and B-type (Te terminated) surfaces and their migration paths. The atomic and electronic structure calculations are performed under the DFT formalism and climbing Nudge Elastic Band (cNEB) method has been applied to evaluate the potential barrier of the Te and Cd diffusion. In general the minimum energy site on the surface is labeled as Aa site. In case of Te and Cd on B-type surface, the sub-surface site (a site just below the top surface) is very close in energy to the A site. This is responsible for the subsurface accumulation of adatoms and therefore, expected to influence the defect formation during growth. The diffusion process of adatoms is considered from Aa (occupied) to Aa (empty) site at the nearest distance. We have explored three possible migration paths for the adatom diffusion. The adatom surface interaction is highly dependent on the type of the surface. Typically, Te interaction with both type (5.2 eV for A-type and 3.8 eV for B-type) is stronger than Cd interactions(2.4 eV for B-type and 0.39 eV for A-type). Cd interaction with the A-type surface is very weak. The distinct behavior of the A-type and B-type surfaces perceived in our study explain the need of maintaining the A-type surface during growth for smooth and stoichiometric growth.

  5. Diffusion of Cd and Te adatoms on CdTe(111) surfaces: A computational study using density functional theory

    International Nuclear Information System (INIS)

    CdTe is one of the most promising semiconductor for thin-film based solar cells. Here we report a computational study of Cd and Te adatom diffusion on the CdTe (111) A-type (Cd terminated) and B-type (Te terminated) surfaces and their migration paths. The atomic and electronic structure calculations are performed under the DFT formalism and climbing Nudge Elastic Band (cNEB) method has been applied to evaluate the potential barrier of the Te and Cd diffusion. In general the minimum energy site on the surface is labeled as Aa site. In case of Te and Cd on B-type surface, the sub-surface site (a site just below the top surface) is very close in energy to the A site. This is responsible for the subsurface accumulation of adatoms and therefore, expected to influence the defect formation during growth. The diffusion process of adatoms is considered from Aa (occupied) to Aa (empty) site at the nearest distance. We have explored three possible migration paths for the adatom diffusion. The adatom surface interaction is highly dependent on the type of the surface. Typically, Te interaction with both type (5.2 eV for A-type and 3.8 eV for B-type) is stronger than Cd interactions(2.4 eV for B-type and 0.39 eV for A-type). Cd interaction with the A-type surface is very weak. The distinct behavior of the A-type and B-type surfaces perceived in our study explain the need of maintaining the A-type surface during growth for smooth and stoichiometric growth

  6. Diffusion of Cd and Te adatoms on CdTe(111) surfaces: A computational study using density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Naderi, Ebadollah, E-mail: enaderi42@gmail.com [Department of Physics, Savitribai Phule Pune University (SPPU), Pune-411007 (India); Nanavati, Sachin [Center for Development of Advanced Computing (C-DAC), SPPU campus, Pune 411007 (India); Majumder, Chiranjib [Chemistry Division, Bhabha Atomic Research Center, Mumbai, 400085 (India); Ghaisas, S. V. [Department of Electronic Science, Savitribai Phule Pune University (SPPU), Pune-411007 (India); Department of Physics, Savitribai Phule Pune University (SPPU), Pune-411007 (India)

    2015-01-15

    CdTe is one of the most promising semiconductor for thin-film based solar cells. Here we report a computational study of Cd and Te adatom diffusion on the CdTe (111) A-type (Cd terminated) and B-type (Te terminated) surfaces and their migration paths. The atomic and electronic structure calculations are performed under the DFT formalism and climbing Nudge Elastic Band (cNEB) method has been applied to evaluate the potential barrier of the Te and Cd diffusion. In general the minimum energy site on the surface is labeled as A{sub a} site. In case of Te and Cd on B-type surface, the sub-surface site (a site just below the top surface) is very close in energy to the A site. This is responsible for the subsurface accumulation of adatoms and therefore, expected to influence the defect formation during growth. The diffusion process of adatoms is considered from A{sub a} (occupied) to A{sub a} (empty) site at the nearest distance. We have explored three possible migration paths for the adatom diffusion. The adatom surface interaction is highly dependent on the type of the surface. Typically, Te interaction with both type (5.2 eV for A-type and 3.8 eV for B-type) is stronger than Cd interactions(2.4 eV for B-type and 0.39 eV for A-type). Cd interaction with the A-type surface is very weak. The distinct behavior of the A-type and B-type surfaces perceived in our study explain the need of maintaining the A-type surface during growth for smooth and stoichiometric growth.

  7. Topics on thin film CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Tyan Yuansheng

    1988-01-15

    Efficient thin film CdS/CdTe solar cells can be prepared by the close-spaced sublimation technique onto soda-lime glass coated with either indium tin oxide or tin oxide. Oxygen is needed to enchance the p characteristics of CdTe; a high substrate temperature is needed to reduce the interfacial defects at the CdS/CdTe junction. Cells with gold electrodes are not stable owing to Au-CdTe interaction. Alternative electrodes to CdTe can be prepared by using a HNO/sub 3/-H/sub 3/PO/sub 4/ surface treatment. The cells showed 30-40% efficiency degradation when aged over 2 years at 100/sup 0/C under continuous air mass 1 illumination. The degradation appears to result from a decrease in the carrier concentration with aging. The aging process is not sensitive to ambience but is sensitive to the presence of light or voltage bias. It is believed to be related to the dependence of the effective carrier concentration on the cooling rate subsequent to the CdTe deposition. Defect interaction may be a possible cause of the aging behavior but photoluminescence and deep-level studies have not established the mechanism involved. The evidence suggests that trace impurities can have significant effects on the behavior of the cells and could be responsible for the aging behavior.

  8. Solvothermal preparation and thermoelectric properties of quasi-binary Sn(Pb)Te-Bi2Te3 compounds

    Institute of Scientific and Technical Information of China (English)

    ZHOU; Xisong; (周西松); DENG; Yuan; (邓; 元); WEI; Guodan; (韦国丹); LIU; Jing; (刘; 静); NAN; Cewen; (南策文)

    2003-01-01

    Bulk samples of quasi-binary compounds in the Sn(Pb)Te-Bi2Te3 system were prepared by solvothermal method followed by a sintering procedure of compacted pellets. The formation mechanism of the precursor powders, microstructure and thermoelectric properties of the final bulk samples were studied.

  9. 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.

  10. Electron transport and cyclotron resonance in (211)-oriented HgTe--CdTe superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Hoffman, C.A.; Meyer, J.R.; Wagner, R.J.; Bartoli, F.J. (Naval Research Laboratory, Washington, D. C. 20375 (USA)); Chu, X.; Faurie, J.P. (University of Illinois at Chicago, Chicago, Illinois 60680 (USA)); Ram-Mohan, L.R.; Xie, H. (Worcester Polytechnic Institute, Worcester, Massachusetts 01609 (USA))

    1990-03-01

    We discuss a magnetotransport and magneto-optical investigation of (211)-oriented HgTe--CdTe superlattices. Measurements were performed on seven {ital n}-type samples with well widths in the range 41--125 A and energy gaps between 0 and 128 meV. Both magnetotransport and magneto-optical results give evidence for an additional electron species besides the superlattice electrons and holes usually observed. We show that although these have quasi-two-dimensional character, their mobilities are quite sensitive to the superlattice well thickness. These findings are interpreted in terms of band bending and charge transfer from the CdTe substrate into the superlattice. We also discuss the first theoretical calculations of the band structure for (211)-oriented HgTe--CdTe heterostructures.

  11. A Comparative Study on the Optical Properties of Multilayer CdSe / CdTe Thin Film with Single Layer CdTe and CdSe Films

    Directory of Open Access Journals (Sweden)

    M. Melvin David Kumar

    2013-07-01

    Full Text Available CdTe and CdSe single layer thin films and CdSe / CdTe multilayer (ML thin film were prepared by using physical vapour deposition method. Optical properties of CdSe / CdTe multilayer thin film shows different behavior due to type II band structure alignment. Energy band gap value of CdSe / CdTe ML thin film is shifted to higher value than that of single layer CdTe film. This is due to decrease in crystallite size to dimension smaller than the Bohr exciton radius of CdTe (14 nm. Crystallite size of the multilayer sample was calculated with the predictions of the effective mass approximation model (i.e., Brus model. It is observed that the photoluminescence peak of CdSe / CdTe ML thin film is red shifted compared to the peaks corresponding to individual CdSe and CdTe thin films. This may be due to the presence of type II quantum dot formation in the CdSe / CdTe heterostructure multilayer thin film.

  12. Crystallization study of Sn additive Se–Te chalcogenide alloys

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Rahim, M.A.; Gaber, A.; Abu-Sehly, A.A.; Abdelazim, N.M., E-mail: nana841@hotmail.co.uk

    2013-08-20

    Highlights: • The aim of the work deals with studying the crystallization kinetics by using different method. • Values of various kinetic parameters were calculated. • The results indicate that the rate of crystallization is related to the thermal stability and glass forming ability. - Abstract: Results of differential thermal analysis (DTA) under non-isothermal conditions of glasses Se{sub 90−x}Te{sub 10}Sn{sub x} (x = 0, 2.5, 5 and 7 at.%) are reported and discussed. The glass transition temperature (T{sub g}), the onset crystallization temperature (T{sub c}) and the peak temperature of crystallization (T{sub p}) were found to be dependent on the compositions and the heating rate. Values of various kinetic parameters such as activation energy of glass transition (E{sub g}), activation energy of crystallization (E{sub c}), rate constant (K{sub p}), Hurby number (H{sub r}) and the order parameter (n) were determined. For the present systems, the results indicate that the rate of crystallization is related to thermal stability and glass forming ability (GFA). According to the Avrami exponent (n), the results show a one dimensional growth for the composition Se{sub 90}Te{sub 10} and a three dimensional growth for the three other compositions. The crystalline phases resulting from DTA and (SEM) have been identified using X-ray diffraction.

  13. Au/Cu2Te/CdTe/CdS/TCO/Glass Solar Cells with CdIn2O4 Obtained by Sol-Gel as TCO

    Directory of Open Access Journals (Sweden)

    J. Márquez Marín

    2014-01-01

    Full Text Available An Au/Cu2Te/CdTe/CdS/TCO/glass heterostructure based superstrate solar cells with 2.5 mm2 of area, where the CdTe layer was prepared by means of closed spaced sublimation (CSS and the CdS by chemical bath, reached an efficiency η value of 12.1%. As transparent conductive oxide (TCO, a thin film of cadmium-indium oxide (CdIn2O4:CIO, obtained by sol-gel technique, was used. A systematic optimization of the thermal activation of the CdTe/CdS/CIO central part of the device with a CdCl2 vapor ambient made the conversion efficiency of the Au/Cu2Te/CdTe/CdS/CIO/glass heterostructure reaches 9.94% for the CdTe layer with thickness of 1.8 μm. This efficiency was reached only through an open circuit voltage VOC optimization. A maximum η of 12.1% was reached with the established procedure of optimization and when the CdTe layer thickness was increased to 3.1 ± 0.05 μm. The substitution of CIO by commercial ITO provoked in the cell a decrease of η from 12.1% to 7.2%, both devices prepared under the same conditions. Starting from these results, we can say that CIO was a better TCO than commercial ITO in our solar cell, with the advantage that CIO was obtained by sol-gel, which is a simple and economical technique.

  14. Microalloying with Cd of Antifriction Sn-Sb-Cu Alloys

    Directory of Open Access Journals (Sweden)

    Cinca Ionel Lupinca

    2012-09-01

    Full Text Available In the case of bimetallic sliding linings with superior technological characteristics, the use of an antifriction ally is imposed an alloy of the type Sn-Sb-Cu, which possesses a high adherence to the steel stand and a high durability in exploitation. For this reason we use the microalloying of the antifriction alloy with cadmium. The microalloying with Cd of antifriction alloys Sn-Sb-Cu determines an increase of the adhesion property of the antifriction alloy on the steel stand. The steel stand is previously subjected to a process of degreasing with ZnCl2 and washing so that is can later be subjected to a thermal-chemical treatment of tinning.

  15. Characterization of thin film ZnCdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Hussain, O.M.; Reddy, P.S.; Naidu, B.S.; Uthanna, S.; Reddy, P.J. (Sri Venkateswara Univ., Tirupati (IN). Dept. of Physics)

    1991-11-01

    Thin films of II-VI compound semiconductors have attracted considerable interest in recent years due to their wide range of applications in the fabrication of cost effective solar cells. Among these, cadmium telluride is one of the most attractive candidates with a direct band gap of 1.5 eV which is optimum for solar energy conversion. Generally, n-CdS is used as window layer to p-CdTe to fabricate heterojunction solar cells because of its reasonable optical transparency and the ease of depositing low-resistivity films. n-ZnCdS/p-CdTe polycrystalline thin film solar cells were fabricated by laser evaporating CdTe onto sprayed ZnCdS films. The cells were characterized by studying current-voltage, capacitance-voltage and spectral response measurements. A maximum efficiency of 7.6% was observed for a cell area of 1 cm{sup 2}. (author).

  16. Dislocation Reduction in HgCdTe Mesa Structures Formed on CdTe/Si

    Science.gov (United States)

    Simingalam, Sina; Pattison, James; Chen, Yuanping; Wijewarnasuriya, Priyalal; Rao, Mulpuri V.

    2016-04-01

    Mercury cadmium telluride (MCT) epilayers have been grown on CdTe/Si using molecular beam epitaxy and 8-μm-deep mesa structures formed using plasma etching. Following previous work done on etching mesas and subjecting material to thermal cycle annealing, we set out to determine the limits and underlying physics of dislocation reduction in mesa-etched and annealed MCT. This paper describes the dependence of dislocation reduction on anneal time, cycle annealing, temperature, and etch depth. We show dislocation density reduction below 3 × 105 cm-2 in 10-μm-wide, long-bar mesas along the [0bar{1}1] orientation with only a 5-min anneal at 400°C.

  17. Optimization of thermoelectric efficiency in SnTe: the case for the light band.

    Science.gov (United States)

    Zhou, Min; Gibbs, Zachary M; Wang, Heng; Han, Yemao; Xin, Caini; Li, Laifeng; Snyder, G Jeffrey

    2014-10-14

    p-Type PbTe is an outstanding high temperature thermoelectric material with zT of 2 at high temperatures due to its complex band structure which leads to high valley degeneracy. Lead-free SnTe has a similar electronic band structure, which suggests that it may also be a good thermoelectric material. However, stoichiometric SnTe is a strongly p-type semiconductor with a carrier concentration of about 1 × 10(20) cm(-3), which corresponds to a minimum Seebeck coefficient and zT. While in the case of p-PbTe (and n-type La3Te4) one would normally achieve higher zT by using high carrier density in order to populate the secondary band with higher valley degeneracy, SnTe behaves differently. It has a very light, upper valence band which is shown in this work to provide higher zT than doping towards the heavier second band. Therefore, decreasing the hole concentration to maximize the performance of the light band results in higher zT than doping into the high degeneracy heavy band. Here we tune the electrical transport properties of SnTe by decreasing the carrier concentration with iodine doping, and increasing the carrier concentration with Gd doping or by making the samples Te deficient. A peak zT value of 0.6 at 700 K was obtained for SnTe0.985I0.015 which optimizes the light, upper valence band, which is about 50% higher than the other peak zT value of 0.4 for GdzSn1-zTe and SnTe1+y which utilize the high valley degeneracy secondary valence band. PMID:25162449

  18. Optical characterization of CdTe/ZnTe semiconductor wires and dots

    OpenAIRE

    Gourgon, C; Eriksson, B.; Dang, L.; Mariette, H.; Vieu, C.

    1993-01-01

    Arrays of wires and dots have been fabricated by electron beam lithography and Ar+ ion beam etching from CdTe/ZnTe quantum wells. Low temperature photoluminescence coming out from these structures is still observed for the smallest wires (40 nm) whereas for the dots, the detection limit occurs for lateral dimensions of 100 nm.

  19. 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.

  20. Effect of Substrate Temperature on the Photovoltaic Properties of a CdS/CdTe Solar Cell

    Science.gov (United States)

    Uda, Hiroshi; Ikegami, Seiji; Sonomura, Hajimu

    1990-10-01

    Structural and electrical properties of CdTe thin films prepared by the conventional vacuum evaporation method were studied. Photovoltaic properties of thin-film CdS (chemical-solution-deposited)/CdTe (vacuum-evaporated) solar cells were also investigated. The crystal structure of CdTe films deposited on the CdS films at the substrate temperature of 300˜ 520°C was of the zincblende type with a preferential orientation of the (111) plane parallel to the substrate. The dark resistivity of the CdTe films deposited on the glass substrates was about 107 Ωcm. Illumination caused the resistivity decrease of the films by about two orders of magnitude. The conversion efficiency of the CdS/CdTe solar cells increased with increasing substrate temperature. The present thin-film CdS/CdTe solar cell showed a conversion efficiency of greater than 5%.

  1. Probing the sensitive and selective luminescent detection of peroxynitrite using thiol-capped CdTe and CdTe-ZnS quantum dots

    International Nuclear Information System (INIS)

    CdTe and CdTe-ZnS quantum dots (QDs) capped with 3-mercaptopropionic acid (MPA), thioglycolic acid (TGA), or glutathione (GSH) have been employed for the first time as luminescent probes for the sensitive and selective detection of peroxynitrite (ONOO−) in aqueous solution. The sensitivity of the proposed probe followed the order: MPA–TGA–CdTe-ZnS>GSH–TGA–CdTe-ZnS>MPA–CdTe QDs. The varying degree of quenching is elucidated based on the QD–thiolate bond of CdTe-ZnS being more sensitive to oxidation from ONOO− than CdTe. The selectivity of the probe in the presence of co-existing species followed the order: GSH–TGA–CdTe-ZnS>MPA–TGA–CdTe-ZnS>MPA–CdTe QDs. QDs capped with MPA showed less selectivity for ONOO− than GSH. The best limit of detection (LOD) of 12.6 nM was obtained for MPA–TGA–CdTe-ZnS QDs. Time-resolved fluorescence measurements indicated that the interaction between ONOO− and the QDs is static in nature. - Graphical abstract: CdTe and CdTe-ZnS quantum dots capped with 3-mercaptopropionic acid or glutathione are employed for the detection of peroxynitrite in aqueous solution, with glutathione capped quantum dots showing the best selectivity and core–shell quantum dots showing better sensitivity than core quantum dots. Highlights: ► CdTe and CdTe-ZnS quantum dots were employed for the detection of peroxynitrite. ► The best limit of detection of 12.6 nM was obtained. ► Quantum dots capped with mercaptopropionic acid were less selective for ONOO− than glutathione. ► Interaction between peroxynitrite and the quantum dots is static in nature.

  2. Effect of in situ UHV CdCl2-activation on the electronic properties of CdTe thin film solar cells

    International Nuclear Information System (INIS)

    To reach reasonable conversion efficiencies of approximately 10% and above with CdTe thin film solar cells an activation step involving chlorine at elevated temperatures seems to be necessary before back contact formation. This activation process has been simulated in an ultrahigh-vacuum (UHV) system. Solar cells with a maximum efficiency of 9.1% have been prepared using this process. In addition the effect of the CdCl2 activation process on the electronic properties of each solar cell layer, SnO2, CdS and CdTe has been investigated in situ using photoelectron spectroscopy. The effects of the activation on the Fermi level position of all investigated layers is presented and discussed

  3. Effect of interdiffusion and impurities on thin film CdTe/CdS photovoltaic junctions.

    OpenAIRE

    Potter, M.D.G.; Cousins, M.; Durose, K; Halliday, D.P.

    2000-01-01

    We have used low temperature photoluminescence (PL) to study thin film CdTe/CdS solar cell structures. The devices were produced by close space sublimation (CSS) and have undergone a post-growth treatment, a vital step in increasing device efficiency. The treatment consisted of evaporating a thin layer of CdCl2 onto the back CdTe surface and heat treating in air at 400 °C for between 10 and 120 min. This produced a range of device efficiencies from 2% to 9%. The efficiency improvements are th...

  4. Fabrication of CdS/CdTe-Based Thin Film Solar Cells Using an Electrochemical Technique

    Directory of Open Access Journals (Sweden)

    I. M. Dharmadasa

    2014-06-01

    Full Text Available Thin film solar cells based on cadmium telluride (CdTe are complex devices which have great potential for achieving high conversion efficiencies. Lack of understanding in materials issues and device physics slows down the rapid progress of these devices. This paper combines relevant results from the literature with new results from a research programme based on electro-plated CdS and CdTe. A wide range of analytical techniques was used to investigate the materials and device structures. It has been experimentally found that n-, i- and p-type CdTe can be grown easily by electroplating. These material layers consist of nano- and micro-rod type or columnar type grains, growing normal to the substrate. Stoichiometric materials exhibit the highest crystallinity and resistivity, and layers grown closer to these conditions show n → p or p → n conversion upon heat treatment. The general trend of CdCl2 treatment is to gradually change the CdTe material’s n-type electrical property towards i-type or p-type conduction. This work also identifies a rapid structural transition of CdTe layer at 385 ± 5 °C and a slow structural transition at higher temperatures when annealed or grown at high temperature. The second transition occurs after 430 °C and requires more work to understand this gradual transition. This work also identifies the existence of two different solar cell configurations for CdS/CdTe which creates a complex situation. Finally, the paper presents the way forward with next generation CdTe-based solar cells utilising low-cost materials in their columnar nature in graded bandgap structures. These devices could absorb UV, visible and IR radiation from the solar spectrum and combine impact ionisation and impurity photovoltaic (PV effect as well as making use of IR photons from the surroundings when fully optimised.

  5. n-CdTe polycrystalline photoelectrode prepared by direct reaction of tellurium and Cd-substrate

    Energy Technology Data Exchange (ETDEWEB)

    Aushana, A.M.; Aliwi, S.M. (Mustansiriah Univ., Baghdad (IQ). College of Science)

    1990-01-01

    In the last 15 years, photoelectrochemical (PEC) solar cells, employing semiconductor polycrystalline electrode with liquid junction redox electrolyte have been extensively studied. Cadmium chalcogens have received considerable attention as photoactive electrodes in PEC solar cells. In comparison with Cd-sulphide and selenide, cadmium telluride has received little attention as photoactive semiconductor electrode. It has been reported that CdTe electrode could be prepared by several methods. In the present work we have produced polycrystalline n-CdTe film on Cd element as substrate by direct surface reaction between elemental Te and Cd surfaces, at elevated temperatures ranging between 180 and 275{sup 0}C under argon atmosphere. The film is characterized by X-ray diffraction and reflectance spectroscopy. The i-V characteristics and photoelectrochemical behaviour of CdTe in polysulphide electrolyte are investigated. The effect of light intensity on both short circuit current (i{sub sc}) and open circuit voltage (V{sub oc}) of the cell: Cd/CdTe/polysulphide/Pt is also recorded. (author).

  6. 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

  7. Comparison of solar cells sensitised by CdTe/CdSe and CdSe/CdTe core/shell colloidal quantum dots with and without a CdS outer layer

    International Nuclear Information System (INIS)

    CdTe/CdSe and CdSe/CdTe core/shell colloidal quantum dots, both with and without a second CdS shell, have been synthesised and characterised by absorption and photoluminescence spectroscopies, scanning transmission electron microscopy and X-ray diffraction. Each type of quantum dot had a zinc blende crystal structure and had an absorption edge in the near-infrared, potentially enabling the more efficient exploitation of the solar spectrum. Each was used to sensitise a photovoltaic cell of a ‘Grätzel-type’ design consisting of the dots coated onto mesoporous TiO2, a sulphur-based electrolyte and a platinum top electrode. The photovoltaic efficiency of the cells was found to be greater for Type-II dots as compared to the quasi-Type-II dots. However, the efficiency was reduced on the addition of an outer CdS shell indicating that it acts as a barrier to charge extraction. - Highlights: • CdTe/CdSe and CdSe/CdTe type-II quantum dots were synthesised and characterised. • A passivating CdS final shell was added to both orientations to improve stability. • Grätzel-type photovoltaic cells were made and performance tested for all examples. • CdTe-cored samples outperformed their CdSe-cored analogues. • The addition of a CdS passivating layer was detrimental to performance

  8. Thermoelectric Properties of Cu2HgSnSe4-Cu2HgSnTe4 Solid Solution

    Czech Academy of Sciences Publication Activity Database

    Navrátil, Jiří; Kucek, V.; Plecháček, T.; Černošková, E.; Laufek, František; Drašar, Č.; Knotek, P.

    2014-01-01

    Roč. 43, č. 10 (2014), s. 3719-3725. ISSN 0361-5235 R&D Projects: GA ČR GA13-33056S Institutional support: RVO:61389013 ; RVO:68378271 Keywords : quaternary diamond-like compounds * Cu2HgSnSe4 * Cu2HgSnTe4 Subject RIV: CA - Inorganic Chemistry Impact factor: 1.798, year: 2014

  9. Preparation and multicolored fluorescent properties of CdTe quantum dots/polymethylmethacrylate composite films

    International Nuclear Information System (INIS)

    A new simple route was presented for the preparation of stable fluorescent CdTe/polymethylmethacrylate (CdTe/PMMA) composite films by using hydrophilic thioglycolic acid capped CdTe quantum dots (TGA-CdTe QDs) and polymethylmethacrylate (PMMA) as raw materials. The TGA-CdTe QDs were firstly exchanged with n-dodecanethiol (DDT) to become hydrophobic DDT-CdTe QDs via a ligand exchange strategy, and then incorporated into PMMA matrix to obtain fluorescent CdTe/PMMA composite films. The structure and optical properties of DDT-CdTe QDs and CdTe/PMMA composite films were investigated by XRD, IR, UV and PL techniques. The results indicated that the obtained DDT-CdTe QDs well preserved the intrinsic structure and the maximum emission wavelength of the initial water-soluble QDs and the resulting 6.10 wt% CdTe/PMMA composite film exhibited significantly enhanced PL intensity. Furthermore, the multicolored composite films with green, yellow-green, yellow and orange light emissions were well tuned by incorporating the CdTe QDs of various maximum emission wavelengths. The TEM image demonstrated that the CdTe QDs were well-dispersed in the PMMA matrix without aggregation. Superior photostability of QDs in the composite film was confirmed by fluorescence lifetime measurement. Thermo-gravimetric analysis of CdTe/PMMA composite films showed no obvious enhancement of thermal stability compared with pure PMMA. - Highlights: • Ligand-exchange strategy was used to render CdTe QDs oil-soluble. • CdTe QDs were incorporated into PMMA matrix to fabricate fluorescent films. • The resulting 6.10 wt% CdTe/PMMA film exhibited significantly enhanced PL intensity. • Fluorescent colors of films were tuned by varying the λem of incorporated CdTe QDs

  10. Preparation and multicolored fluorescent properties of CdTe quantum dots/polymethylmethacrylate composite films

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Yanni; Liu, Jianjun, E-mail: jjliu717@aliyun.com; Yu, Yingchun; Zuo, Shengli

    2015-10-25

    A new simple route was presented for the preparation of stable fluorescent CdTe/polymethylmethacrylate (CdTe/PMMA) composite films by using hydrophilic thioglycolic acid capped CdTe quantum dots (TGA-CdTe QDs) and polymethylmethacrylate (PMMA) as raw materials. The TGA-CdTe QDs were firstly exchanged with n-dodecanethiol (DDT) to become hydrophobic DDT-CdTe QDs via a ligand exchange strategy, and then incorporated into PMMA matrix to obtain fluorescent CdTe/PMMA composite films. The structure and optical properties of DDT-CdTe QDs and CdTe/PMMA composite films were investigated by XRD, IR, UV and PL techniques. The results indicated that the obtained DDT-CdTe QDs well preserved the intrinsic structure and the maximum emission wavelength of the initial water-soluble QDs and the resulting 6.10 wt% CdTe/PMMA composite film exhibited significantly enhanced PL intensity. Furthermore, the multicolored composite films with green, yellow-green, yellow and orange light emissions were well tuned by incorporating the CdTe QDs of various maximum emission wavelengths. The TEM image demonstrated that the CdTe QDs were well-dispersed in the PMMA matrix without aggregation. Superior photostability of QDs in the composite film was confirmed by fluorescence lifetime measurement. Thermo-gravimetric analysis of CdTe/PMMA composite films showed no obvious enhancement of thermal stability compared with pure PMMA. - Highlights: • Ligand-exchange strategy was used to render CdTe QDs oil-soluble. • CdTe QDs were incorporated into PMMA matrix to fabricate fluorescent films. • The resulting 6.10 wt% CdTe/PMMA film exhibited significantly enhanced PL intensity. • Fluorescent colors of films were tuned by varying the λ{sub em} of incorporated CdTe QDs.

  11. Strong coupling and polariton lasing in Te based microcavities embedding (Cd,Zn)Te quantum wells

    International Nuclear Information System (INIS)

    We report on properties of an optical microcavity based on (Cd,Zn,Mg)Te layers and embedding (Cd,Zn)Te quantum wells. The key point of the structure design is the lattice matching of the whole structure to MgTe, which eliminates the internal strain and allows one to embed an arbitrary number of unstrained quantum wells in the microcavity. We evidence the strong light-matter coupling regime already for the structure containing a single quantum well. Embedding four unstrained quantum wells results in further enhancement of the exciton-photon coupling and the polariton lasing in the strong coupling regime

  12. 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.

  13. First principles modeling of grain boundaries in CdTe

    Science.gov (United States)

    Chan, Maria K. Y.; Sen, Fatih; Buurma, Christopher; Paulauskas, Tadas; Sun, Ce; Kim, Moon; Klie, Robert

    The role of extended defects is of significant interest for semiconductors, especially photovoltaics since energy conversion efficiencies are often affected by such defects. In particular, grain boundaries in CdTe photovoltaics are enigmatic since the achievable efficiencies of CdTe photovoltaics are higher in polycrystalline devices as compared to single crystalline devices. Yet, despite recent advances, the efficiency of poly-CdTe devices are still substantially below the theoretical maximum. We carry out an atomistic-level study using Scanning Transmission Electron Microscopy (STEM), together with first principles density functional theory (DFT) modeling, in order to understand the properties of specific bicrystals, i.e. artificial grain boundaries, constructed using wafer bonding. We discuss examples of bicrystals, including some involving large scale DFT calculations, and trends in defect and electronic properties. This work was funded by DOE SunShot BRIDGE program.

  14. Design of a thin film CdTe solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Meyers, P.V.

    1988-01-15

    Cadmium telluride was originally considered for thin film solar cells because of its optimum band gap, high optical absorption coefficient and ability to be doped. Furthermore, it is a stable compound which can be produced by a wide variety of methods from stable raw materials. As thin film photovoltaics mature, however, it is clear that several more subtle attributes have a significant impact on the viability of commercialization. We discuss the observations which have provided insight and direction to Ametek's CdTe solar cell program. Rather than try to modify the inherent material properties of CdTe, advances have been made by designing a solar cell that exploits existing properties. Specifically, the tendency to self-compensate, which makes low resistance contacting difficult, is turned into an advantage in the n-i-p configuration; the CdTe provides an intrinsic layer with good carrier collection efficiency.

  15. Resetting the Defect Chemistry in CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Metzger, Wyatt K.; Burst, James; Albin, David; Colegrove, Eric; Moseley, John; Duenow, Joel; Farrell, Stuart; Moutinho, Helio; Reese, Matt; Johnston, Steve; Barnes, Teresa; Perkins, Craig; Guthrey, Harvey; Al-Jassim, Mowafak

    2015-06-14

    CdTe cell efficiencies have increased from 17% to 21% in the past three years and now rival polycrystalline Si [1]. Research is now targeting 25% to displace Si, attain costs less than 40 cents/W, and reach grid parity. Recent efficiency gains have come largely from greater photocurrent. There is still headroom to lower costs and improve performance by increasing open-circuit voltage (Voc) and fill factor. Record-efficiency CdTe cells have been limited to Voc <; 880 mV, whereas GaAs can attain Voc of 1.10 V with a slightly smaller bandgap [2,3]. To overcome this barrier, we seek to understand and increase lifetime and carrier concentration in CdTe. In polycrystalline structures, lifetime can be limited by interface and grain-boundary recombination, and attaining high carrier concentration is complicated by morphology.

  16. 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...

  17. A Novel Method to Obtain Higher Deposition Rates of CdTe Using Low Temperature LPCVD for Surface Passivation of HgCdTe

    Science.gov (United States)

    Banerjee, Sneha; Dahal, Rajendra; Bhat, Ishwara B.

    2015-09-01

    The deposition rate of CdTe passivation films has been increased greatly by the implementation of a novel design of a graphite cracker cell. This cracker cell, consisting of an integrated diffuser, facilitates the efficient cracking of precursors. CdTe deposition rate has been increased from ~50 nm/h (without any cracker cell) to ~420 nm/h using this novel experimental set-up. H2 flow through the main gas flow line has been increased to obtain a progressive increase in deposition rates. CdTe deposited on high aspect ratio HgCdTe samples showed adequate conformal coverage on the side walls and also on the bottom of the trenches. Microwave photoconductive decay measurements were done on planar and patterned HgCdTe substrates at 77 K to extract the minority carrier lifetimes. There was a significant improvement in the lifetime of planar HgCdTe samples after CdTe passivation, though patterned HgCdTe samples showed a minor improvement. An additional annealing step was conducted at 250°C for 20 min in the presence of H2 after the deposition of CdTe passivation films. Minority carrier lifetimes improved further post-annealing, probably due to the formation of a graded interface between CdTe and HgCdTe.

  18. Shape-Controlled Narrow-Gap SnTe Nanostructures: From Nanocubes to Nanorods and Nanowires.

    Science.gov (United States)

    Guo, Shaojun; Fidler, Andrew F; He, Kai; Su, Dong; Chen, Gen; Lin, Qianglu; Pietryga, Jeffrey M; Klimov, Victor I

    2015-12-01

    The rational design and synthesis of narrow-gap colloidal semiconductor nanocrystals (NCs) is an important step toward the next generation of solution-processable photovoltaics, photodetectors, and thermoelectric devices. SnTe NCs are particularly attractive as a Pb-free alternative to NCs of narrow-gap lead chalcogenides. Previous synthetic efforts on SnTe NCs have focused on spherical nanoparticles. Here we report new strategies for synthesis of SnTe NCs with shapes tunable from highly monodisperse nanocubes, to nanorods (NRs) with variable aspect ratios, and finally to long, straight nanowires (NWs). Reaction at high temperature quickly forms thermodynamically favored nanocubes, but low temperatures lead to elongated particles. Transmission electron microscopy studies of reaction products at various stages of the synthesis reveal that the growth and shape-focusing of monodisperse SnTe nanocubes likely involves interparticle ripening, while directional growth of NRs and NWs may be initiated by particle dimerization via oriented attachment. PMID:26545157

  19. Thermoelectric properties of Eu-and Na-substituted SnTe

    Institute of Scientific and Technical Information of China (English)

    王新科; 郭凯; Igor Veremchuk4; Ulrich Burkhardt4; 冯贤娟; 赵景泰

    2015-01-01

    Thermoelectric properties of spark-plasma-sintering prepared bulk materials EuxNayzSn1–x–y–zTe above room temperature were investigated. The implementation of Eu and Na into the SnTe lattice was monitored by refinement of lattice parameters as well as energy dispersive X-ray spectroscopy (EDXS). The binary SnTe achieved the highest ZT value of 0.63 at 786 K, and showed a hole concentration of 4.6×1019 cm–3 at 300 K. In comparison with pristine SnTe, the samples containing Eu had lower carrier mobility but higher Hall carrier concentration. For Eu-and Na-substituted samples, the increased hole concentration was unfavorable for the improvement of thermoelectric properties.

  20. Microstructure of absorber layers in CdTe/CdS solar cells

    CERN Document Server

    Cousins, M A

    2001-01-01

    expected from extrapolating the linear trend in the bulk. These observations are explained in terms of the pinning of the CdTe grain size to the underlying CdS, and the small grain size this causes. A simple model was proposed for a link between the grain-growth to the efficiency improvement. The study also examines the behaviour of defects within grains upon CdCl sub 2 treatment provided the first direct evidence of recovery on CdCl sub 2 treatment in this system. Finally, a computer model is presented to describe the evolution of microstructure during growth. This is shown to be capable of reproducing the observed variation in grain size, but its strict physical accuracy is questioned. This work concerns the microstructure of CSS-grown CdTe layers used for CdTe/CdS solar cells. Particular attention is given to how the development of microstructure on annealing with CdCl sub 2 may correlate with increases in efficiency. By annealing pressed pellets of bulk CdTe powder, it is shown that microstructural change...

  1. High-performance ultraviolet photodetectors based on CdS/CdS:SnS2 superlattice nanowires

    Science.gov (United States)

    Gou, Guangyang; Dai, Guozhang; Qian, Chuan; Liu, Yufeng; Fu, Yan; Tian, Zhenyang; He, Yinke; Kong, Lingan; Yang, Junliang; Sun, Jia; Gao, Yongli

    2016-07-01

    CdS heterostructure nanomaterials are attractive for their potential applications in integrated optoelectronic devices. Herein, the high-quality CdS/CdS:SnS2 superlattice nanowires were synthesized through a micro-environmental controlled co-evaporation technique, which shows periodic emission properties and that their structures are periodic and alternating. For the first time, we demonstrate the fabrication of high-performance ultraviolet photodetectors using unique CdS/CdS:SnS2 superlattice nanowires. The optoelectronic properties of the photodetectors were studied and compared to those devices based on pure CdS nanowires. The as-fabricated photodetectors (under 365 nm) based on CdS/CdS:SnS2 superlattice nanowires showed a high photocurrent to dark current ratio of 105, a large photoresponsivity of 2.5 × 103 A W-1, a fast response time of 10 ms and an excellent external quantum efficiency of 8.6 × 105 at room temperature, which shows better performance than pure CdS nanowires photodetectors. The results indicate that CdS/CdS:SnS2 superlattice nanowires are very promising potential candidates in nanoscale electronic and optoelectronic devices.CdS heterostructure nanomaterials are attractive for their potential applications in integrated optoelectronic devices. Herein, the high-quality CdS/CdS:SnS2 superlattice nanowires were synthesized through a micro-environmental controlled co-evaporation technique, which shows periodic emission properties and that their structures are periodic and alternating. For the first time, we demonstrate the fabrication of high-performance ultraviolet photodetectors using unique CdS/CdS:SnS2 superlattice nanowires. The optoelectronic properties of the photodetectors were studied and compared to those devices based on pure CdS nanowires. The as-fabricated photodetectors (under 365 nm) based on CdS/CdS:SnS2 superlattice nanowires showed a high photocurrent to dark current ratio of 105, a large photoresponsivity of 2.5 × 103 A W-1, a

  2. Photovoltaic performance of a Cd1−xMgxTe/CdS top-cell structure

    International Nuclear Information System (INIS)

    In this paper we report the progress in developing a wide band gap alloy material based on CdTe to use as the top-cell absorber in tandem solar cells. High photovoltaic performance for a Cd1−xMgxTe/CdS top-cell was achieved by tuning the composition of the Cd1−xMgxTe film, and optimizing the device processing. We have carried out studies on the effect of vapor chloride treatment of the Cd1−xMgxTe/CdS device and the thermal annealing of the Cu/Au contacts on the opto-electronic properties of the device. With improved contact processing and post deposition treatments, we were able to achieve 9.3% efficiency for a 1.6 eV band gap top-cell; Cd1−xMgxTe/CdS on conductive glass substrate. - Highlights: • Cd1−xMgxTe films obtained by co-evaporation of CdTe and Mg • Band gap of Cd1−xMgxTe can be easily tuned by verifying x. • Band gap of Cd1−xMgxTe is stable only for short annealing durations. • Obtained efficiency of a Cd1−xMgxTe based device with a band gap of 1.6 eV is 9.3%

  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. Calorimetric investigation on the Cd-Te binary alloys

    International Nuclear Information System (INIS)

    The enthalpy of formation of the Cd-Te solid and liquid alloys was measured by direct reaction calorimetry (DRC) (drop method) at 737 and 1259 K with the help of a Tian-Calvet high temperature calorimeter. The DRC procedure used was very simple at 737 K but more sophisticated at 1259 K due to the high vapor pressures of both components. This allowed us to determine the enthalpy of formation of the CdTe solid compound in agreement with the data of the literature and the enthalpy of formation of the melts in the whole range of concentration. (orig.)

  7. Advances in CdTe n-i-p photovoltaics

    Energy Technology Data Exchange (ETDEWEB)

    Meyers, P.V. (Ametek Applied Materials Lab., Harleysville, PA (USA))

    1989-10-15

    Development of the CdTe n-i-p solar cell has enabled researchers to produce 11% efficient solar cells while eliminating stability problems associated with a low-resistance back contact. Furthermore, loss analysis indicates that significant increases in efficiency can still be realized through reduction of absorption and reflection and by passivation of recombination centers at the interfaces. Simplifications in the interconnection procedures make the CdTe n-i-p solar module more ''manufacturable''. A submodule with four interconnected cells has been produced. It has an aperture area efficiency over 8% with an area ratio of 0.91. (orig.).

  8. RELAXATION LONGUE DUREE DE LA PHOTOCONDUCTIVITE DANS CdTe

    OpenAIRE

    Zozime, A.; Schröter, W.

    1983-01-01

    Différents aspects des mesures de photoconductivité faites sur des monocristaux de CdTe sont présentés. Les signaux montrent l'existence d'un processus de relaxation de longue durée. Les spectres suivent une loi de variation du type loi d'Urbach. Enfin, le seuil d'énergie correspondant à la limite de détection des signaux mesurés dans CdTe de type n correspond à un niveau profond dans la bande interdite, associé aux dislocations.

  9. Electron-hole dynamics in CdTe tetrapods.

    Science.gov (United States)

    Malkmus, Stephan; Kudera, Stefan; Manna, Liberato; Parak, Wolfgang J; Braun, Markus

    2006-09-01

    We present transient absorption studies with femtosecond time resolution on the electron-hole dynamics in CdTe tetrapod nanostructures. Electron-hole pairs are generated by optical excitation in the visible spectral range, and an immediate bleach and induced absorption signal are observed. The relaxation dynamics to the lowest excitonic state is completed in about 6 ps. Experiments with polarized excitation pulses give information about the localization of the excited-state wave functions. The influence of the nanocrystal shape on the optical properties of CdTe nanoparticles is discussed. PMID:16942067

  10. Spray-deposited ITO-CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Adeeb, N.; Kretsu, I.V.; Sherban, D.A.; Simashkevich, A.V.; Sushkevich, K.D.

    1987-01-01

    The properties of an indium-tin-oxide (ITO)/CdTe solar cell fabricated by spraying an alcolholic solution of indium chloride and tin chloride on n-type single crystal CdTe, have been investigated by measuring the electrical and photoelectrical properties of the device. The maximum sensitivity of the cells in the visible range attains 0.42 A/W. The efficiency of the solar cells without antireflection coating at AM1 condition is 6.2%. Detailed numerical calculations have been made for the effect of interface state density and localized charges in the interfacial layer on the performance of the cell. 21 refs.

  11. Emitter/absorber interface of CdTe solar cells

    Science.gov (United States)

    Song, Tao; Kanevce, Ana; Sites, James R.

    2016-06-01

    The performance of CdTe solar cells can be very sensitive to the emitter/absorber interface, especially for high-efficiency cells with high bulk lifetime. Performance losses from acceptor-type interface defects can be significant when interface defect states are located near mid-gap energies. Numerical simulations show that the emitter/absorber band alignment, the emitter doping and thickness, and the defect properties of the interface (i.e., defect density, defect type, and defect energy) can all play significant roles in the interface recombination. In particular, a type I heterojunction with small conduction-band offset (0.1 eV ≤ ΔEC ≤ 0.3 eV) can help maintain good cell efficiency in spite of high interface defect density, much like with Cu(In,Ga)Se2 (CIGS) cells. The basic principle is that positive ΔEC, often referred to as a "spike," creates an absorber inversion and hence a large hole barrier adjacent to the interface. As a result, the electron-hole recombination is suppressed due to an insufficient hole supply at the interface. A large spike (ΔEC ≥ 0.4 eV), however, can impede electron transport and lead to a reduction of photocurrent and fill-factor. In contrast to the spike, a "cliff" (ΔEC CdTe solar cells, but the CdS/CdTe interface is in the cliff category and is not favorable from the band-offset perspective. The ΔEC of other n-type emitter choices, such as (Mg,Zn)O, Cd(S,O), or (Cd,Mg)Te, can be tuned by varying the elemental ratio for an optimal positive value of ΔEC. These materials are predicted to yield higher voltages and would therefore be better candidates for the CdTe-cell emitter.

  12. Synthesis and characterization of Sn-doped CdZnS nanoparticles

    Indian Academy of Sciences (India)

    R Shrivastava; S C Shrivastava

    2015-09-01

    Tin (Sn)-doped cadmium zinc sulphide nanoparticles (CdZnS : Sn) were synthesized by the chemical bath deposition method with two different concentrations of Sn (2 and 4 mol%). X-ray diffraction (XRD) pattern reveals the formation of CdZnS nanoparticles with cubic and hexagonal structure. It was observed that the presence of Sn does not alter the structure of CdZnS. Average crystallite size was measured from XRD data by using Scherrer’s formula. From the study of absorption spectra, band-to-band absorption was obtained at 460 and 490 nm, respectively, for the Sn-doped (2 and 4 mol%) CdZnS nanoparticles. Energy bandgap for undoped and Sn-doped CdZnS varies from 3.5 to 2.9 eV with error ± 0.05 eV. The presence of Sn was confirmed by energy-dispersive X-ray analysis. The effect of dopant concentration on the photoluminescence (PL) intensity has also been studied. The PL emission peak has been observed at 540, 550 and 560 nm for the Sn-doped (CdZnS, CdZnS 2 mol% and CdZnS 4 mol%), respectively, nanoparticles. XRD and PL analyses demonstrate that the Sn2+ ions uniformly substitute Cd2+ sites or interstitial sites in CdZnS lattice, which influence the optical properties. Increase in the concentration of Sn shifts the UV–vis absorption spectra and PL emission spectra towards higher wavelength side. Particle size and the crystallinity of CdZnS : Sn nanoparticles were confirmed through atomic force microscopy.

  13. The crystal structure of CdS-CdTe thin film heterojunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, K.D.; Painter, J.D.; Healy, M.J.; Lane, D.W. [Cranfield Univ. (United Kingdom). Dept. of Mater. and Medical Sci.; Ozsan, M.E. [B.P. Solar Ltd., Middlesex (United Kingdom)

    1999-02-08

    A detailed structural analysis of electrodeposited CdS-CdTe thin film heterojunction solar cells was undertaken. X-ray diffraction and Rutherford backscattering spectrometry were used to provide stoichiometric and microcrystalline data at increasing depths through the CdTe and CdS films. A model of the nature and extent of interdiffusion caused by a post deposition anneal is developed. A region in both pre-annealed and post-annealed samples which possesses a significantly different microstructure to that of the bulk CdTe, was identified. Within this region a stoichiometric gradient occurs and the grain size and preferred orientation decrease with increasing depth. Maximum CdTe film stress (post anneal) is estimated to be 140 MPa close to the interface and a shift in optical band gap of 6 x 10{sup -3} eV was also determined from structural measurements. We provide evidence that sulphur diffusion into CdTe is structurally rather than thermodynamically limited within these systems. (orig.) 15 refs.

  14. MBE (Molecular Beam Epitaxial) growth characterization and electronic device processing of HgCdTe, HgZnTe related heterojunctions and HgCdTe-CdTe superlattices

    Science.gov (United States)

    Faurie, Jean-Pierre

    1987-06-01

    As the MBE growth technique has continued to improve for Hg(1-x)Cd(x)Te films, the prospects for films of larger area have begun to be explored. These larger area films are important for imaging arrays and will be especially vital in the future for the efficient production of Hg(1-x)Cd(x)Te material. The growth of MBE of uniform Hg(1-x)Cd(x)Te epilayer on a large substrate is very difficult to achieve because of the non-uniform distribution of the fluxes and on the non-uniform temperature of the substrate.

  15. Characterization of CdS Thin-Film in High Efficient CdS/CdTe Solar Cells

    Science.gov (United States)

    Tsuji, Miwa; Aramoto, Tetsuya; Ohyama, Hideaki; Hibino, Takeshi; Omura, Kuniyoshi

    2000-07-01

    Cadmium sulfide (CdS) thin films are the most commonly used window materials for high efficient cadmium telluride (CdTe) and chalcopyrite polycrystalline thin-film photovoltaic devices. High efficient CdS/CdTe solar cells with thin CdS films have been developed using ultrathin CdS films with a thickness of less than 0.1 μm. CdS films were deposited on transparent conductive oxide (TCO)/glass substrates by the metal organic chemical vapor deposition (MOCVD) technique. CdTe films were subsequently deposited by the close-spaced sublimation (CSS) technique. The screen printing and sintering method fabricated carbon and silver electrodes. Cell performance depends primarily on the electrical and optical properties of CdS films. Therefore we started to develop higher-quality CdS films and found clear differences between high- and low-quality CdS films from the analyses of scanning electron microscope (SEM), atomic force microscope (AFM), secondary ion mass spectroscopy (SIMS), thermal desorption spectrometry (TDS) and Fourier transforms-infrared spectrometry (FT-IR) measurements. As a result of controlling the quality of CdS films, a photovoltaic conversion efficiency of 10.5% has been achieved for size of 1376 cm2 of the solar cells under the Air Mass (AM) 1.5 conditions of the Japan Quality Assurance Organization.

  16. High-efficiency large-area CdTe panels

    Energy Technology Data Exchange (ETDEWEB)

    Albright, S.P.; Chamberlin, R.R.; Jordan, J.F. (Photon Energy, Inc., El Paso, TX (USA))

    1990-11-01

    The objective of this three year effort has been to develop an improved materials technology and fabrication process for limited volume production of 1 ft{sup 2} and 4 ft{sup 2} CdS/CdTe photovoltaic modules. The module stability objective by the end of this three year subcontract was to develop techniques to provide ten year life exploration with no greater than 10% degradation. In order to achieve these efficiency and stability objectives, the research program has been separated into tasks including: (1) analysis and characterization of CdS/CdTe Devices; (2) performance optimization on small cells; (3) encapsulation and stability testing; and (4) module efficiency optimization. 27 refs., 18 figs., 3 tabs.

  17. 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

  18. Optimized conditions for the improvement of thin film CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Mohamed, H.A., E-mail: hussein_abdelhafez2000@yahoo.com

    2015-08-31

    Efficient thin film CdS/CdTe solar cell performance requires optimum parameters of each layer of this cell and of the barrier structure. Moreover, the effect of optical losses, recombination losses at front and back surface of CdTe and recombination losses in the space-charge region (SCR) must be considered in order to really analyze the role of these parameters on the performance of these cells. This work is focused on studying theoretically the effect of the thickness of the front contact (ITO), thickness of the window layer (CdS), thickness of the absorber layer (CdTe), width of the space-charge region and electron lifetime on the efficiency of CdS/CdTe solar cells. The reflection losses from interfaces and absorption losses in ITO and CdS, front and rear surface recombination losses of CdTe as well as recombination losses in SCR have been studied. It has been observed that the short-circuit current strongly depends on the thickness of ITO, thickness of CdS, thickness CdTe and electron lifetime. The concentration of uncompensated impurities (N{sub a} − N{sub d}) in CdTe, which determines the width of SCR, plays a key role in the generation of photocurrent. The recombination losses in the SCR decrease rapidly with increasing the carrier lifetime in this region and can be ignored at lifetime of 10{sup −7} s. The reflectivity from the back contact introduces a small influence in increasing the short-current density particularly at thick absorber layer (5–8 μm). Under the conditions of N{sub a} − N{sub d} ~ 10{sup 16} cm{sup −3}, τ{sub n} = 10{sup −6} s, d{sub CdTe} = 8 μm, d{sub ITO} = 100 nm, and d{sub CdS} = 100 nm, the recombination and optical losses record their minimum ratio of 27%. Most of these losses (24%) are due to the optical losses. The efficiency of CdS/CdTe under these parameters is about 18.2% which is exactly matching with the recent experimental studies. Moreover, an ultrathin CdTe (= 1 μm) is sufficient to introduce high

  19. Studies of CdS/CdTe interface: Comparison of CdS films deposited by close space sublimation and chemical bath deposition techniques

    International Nuclear Information System (INIS)

    The CdS layers were deposited by two different methods, close space sublimation (CSS) and chemical bath deposition (CBD) technique. The CdS/CdTe interface properties were investigated by transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM images showed a large CSS-CdS grain size in the range of 70-80 nm. The interface between CSS-CdS and CdTe were clear and sharp, indicating an abrupt hetero-junction. On the other hand, CBD-CdS layer had much smaller grain size in the 5-10 nm range. The interface between CBD-CdS and CdTe was not as clear as CSS-CdS. With the stepwise coverage of CdTe layer, the XPS core levels of Cd 3d and S 2p in CSS-CdS had a sudden shift to lower binding energies, while those core levels shifted gradually in CBD-CdS. In addition, XPS depth profile analyses indicated a strong diffusion in the interface between CBD-CdS and CdTe. The solar cells prepared using CSS-CdS yielded better device performance than the CBD-CdS layer. The relationships between the solar cell performances and properties of CdS/CdTe interfaces were discussed. - Highlights: • Studies of CdS deposited by close space sublimation and chemical bath deposition • An observation of CdS/CdTe interface by transmission electron microscope • A careful investigation of CdS/CdTe interface by X ray photoelectron spectra • An easier diffusion at the chemical bath deposition CdS and CdTe interface

  20. Studies of CdS/CdTe interface: Comparison of CdS films deposited by close space sublimation and chemical bath deposition techniques

    Energy Technology Data Exchange (ETDEWEB)

    Han, Jun-feng, E-mail: pkuhjf@bit.edu.cn [Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, UMR CNRS 6502, 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3 (France); Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); School of Physics, Beijing Institute of Technology, Beijing 100081 (China); Fu, Gan-hua; Krishnakumar, V.; Schimper, Hermann-Josef [Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); Liao, Cheng [Department of Physics, Peking University, Beijing 100871 (China); Jaegermann, Wolfram [Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); Besland, M.P. [Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, UMR CNRS 6502, 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3 (France)

    2015-05-01

    The CdS layers were deposited by two different methods, close space sublimation (CSS) and chemical bath deposition (CBD) technique. The CdS/CdTe interface properties were investigated by transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM images showed a large CSS-CdS grain size in the range of 70-80 nm. The interface between CSS-CdS and CdTe were clear and sharp, indicating an abrupt hetero-junction. On the other hand, CBD-CdS layer had much smaller grain size in the 5-10 nm range. The interface between CBD-CdS and CdTe was not as clear as CSS-CdS. With the stepwise coverage of CdTe layer, the XPS core levels of Cd 3d and S 2p in CSS-CdS had a sudden shift to lower binding energies, while those core levels shifted gradually in CBD-CdS. In addition, XPS depth profile analyses indicated a strong diffusion in the interface between CBD-CdS and CdTe. The solar cells prepared using CSS-CdS yielded better device performance than the CBD-CdS layer. The relationships between the solar cell performances and properties of CdS/CdTe interfaces were discussed. - Highlights: • Studies of CdS deposited by close space sublimation and chemical bath deposition • An observation of CdS/CdTe interface by transmission electron microscope • A careful investigation of CdS/CdTe interface by X ray photoelectron spectra • An easier diffusion at the chemical bath deposition CdS and CdTe interface.

  1. The role of oxygen in CdS/CdTe solar cells deposited by close-spaced sublimation

    Energy Technology Data Exchange (ETDEWEB)

    Rose, D.H.; Levi, D.H.; Matson, R.J. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1996-05-01

    The presence of oxygen during close-spaced sublimation (CSS) of CdTe has been previously reported to be essential for high-efficiency CdS/CdTe solar cells because it increases the acceptor density in the absorber. The authors find that the presence of oxygen during CSS increases the nucleation site density of CdTe, thus decreasing pinhole density and grain size. Photoluminescence showed that oxygen decreases material quality in the bulk of the CdTe film, but positively impacts the critical CdS/CdTe interface. Through device characterization the authors were unable to verify an increase in acceptor density with increased oxygen. These results, along with the achievement of high-efficiency cells (13% AM1.5) without the use of oxygen, led the authors to conclude that the use of oxygen during CSS deposition of CdTe can be useful but is not essential.

  2. Low temperature interdiffusion in the HgCdTe/CdTe system, studied at near-atomic resolution

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Y.; Ourmazd, A.; Feldman, R.D. (AT T Bell Laboratories, Holmdel, New Jersey 07733 (US))

    1990-03-01

    By combining chemical lattice imaging and vector pattern recognition we determine, as a function of annealing temperature, the composition of individual atomic planes across each HgCdTe/CdTe interface of a multiquantum well stack. The resultant composition profiles, which directly reveal the chemical change across each interface at near atomic resolution, are analyzed in terms of linear and nonlinear diffusion theory, to deduce the interdiffusion coefficient and its activation energy. We find the interdiffusion coefficient to be nonlinear, and a sensitive function of the interface depth beneath the surface.

  3. Detector Performance of Ammonium-Sulfide-Passivated CdZnTe and CdMnTe Materials

    Energy Technology Data Exchange (ETDEWEB)

    Kim, K.H.; Bolotnikov, A.E.; Camarda, G.S.; Marchini, L.; Yang, G.; Hossain, A.; Cui, Y.; Xu, L.; and James, R.B.

    2010-08-01

    Dark currents, including those in the surface and bulk, are the leading source of electronic noise in X-ray and gamma detectors, and are responsible for degrading a detector's energy resolution. The detector material itself determines the bulk leakage current; however, the surface leakage current is controllable by depositing appropriate passivation layers. In previous research, we demonstrated the effectiveness of surface passivation in CZT (CdZnTe) and CMT (CdMnTe) materials using ammonium sulfide and ammonium fluoride. In this research, we measured the effect of such passivation on the surface states of these materials, and on the performances of detectors made from them.

  4. CdZnTe and CdTe detector arrays for hard X-ray and gamma-ray astronomy

    International Nuclear Information System (INIS)

    A variety of CdZnTe and CdTe detector arrays were fabricated at NASA/GSFC for use in hard X-ray and gamma-ray astronomy. Mosaic, pixel, and 3-D position-sensitive detector arrays were built to demonstrate the capabilities for high-resolution imaging and spectroscopy for 10 to 2 MeV. This paper will summarize the different arrays and their applications for instruments being developed at NASA/GSFC. Specific topics to be addressed include materials characterization, fabrication of detectors, ASIC readout electronics, and imaging and spectroscopy tests

  5. CdZnTe and CdTe detector arrays for hard X-ray and gamma-ray astronomy

    Energy Technology Data Exchange (ETDEWEB)

    Stahle, C.M. E-mail: carl.stahle@gsfc.nasa.gov; Parker, B.H.; Parsons, A.M.; Barbier, L.M.; Barthelmy, S.D.; Gehrels, N.A.; Palmer, D.M.; Snodgrass, S.J.; Tueller, J

    1999-10-21

    A variety of CdZnTe and CdTe detector arrays were fabricated at NASA/GSFC for use in hard X-ray and gamma-ray astronomy. Mosaic, pixel, and 3-D position-sensitive detector arrays were built to demonstrate the capabilities for high-resolution imaging and spectroscopy for 10 to 2 MeV. This paper will summarize the different arrays and their applications for instruments being developed at NASA/GSFC. Specific topics to be addressed include materials characterization, fabrication of detectors, ASIC readout electronics, and imaging and spectroscopy tests.

  6. Characterization of CdS thin film in high efficient CdS/CdTe solar cells

    Science.gov (United States)

    Tsuji, Miwa; Aramoto, Tetsuya; Ohyama, Hideaki; Hibino, Takeshi; Omura, Kuniyoshi

    2000-06-01

    Cadmium sulfide (CdS) thin film is the most commonly used window material for high-efficient cadmium telluride (CdTe) thin-film photovoltaic devices. High-efficient CdS/CdTe solar cells have been developed using ultra-thin CdS films having a thickness of below 0.1 μm. CdS film is deposited on transparent conductive oxide (TCO) film coated glass substrates by the metal organic chemical vapor deposition (MOCVD) technique, CdTe film is subsequently deposited by the close-spaced sublimation (CSS) technique. Finally, carbon and Ag-In electrodes are fabricated by the screen printing and sintering method. Cell performance depends primarily on the electrical and optical properties of CdS film, and hence we started to develop higher quality CdS film and found out clear differences between high- and low-quality CdS films from various analyses: SEM, AFM, SIMS, TDS and FT-IR. As a result of controlling qualities of CdS films, photovoltaic conversion efficiency of 10.5% has been achieved for a size of 1376 cm 2 of the solar module under air mass (AM) 1.5 conditions by the Japan Quality Assurance Organization (JQA).

  7. Stability testing of ZnTe:N as a Cu-free back contact to CdTe/CdS solar cells

    Science.gov (United States)

    Simmons, D. A.

    2000-03-01

    Most CdTe/CdS solar cell devices use Cu as a back contact, but recent studies have suggested Cu may cause instabilities in the device under some extreme conditions. We have used rf-sputter deposited ZnTe:N as an alternative back contact to CdTe/CdS solar cells. Identical CdTe/CdS solar cells were back-contacted with ZnTe:N or a standard Cu/Au contact. Sets of both types of cells were subjected to either 3000 hours of baking at 100 C in the dark, or 3000 hours of light-soaking at 1 sun. While initial efficiencies of the Cu cells were slightly higher than the ZnTe:N cells, the ZnTe:N cells performed much better after baking and equally as well after light-soaking as the Cu cells.

  8. Compositional Change of the Au-Cu2Te Contact for Thin-Film CdS/CdTe Solar Cells

    Science.gov (United States)

    Uda, Hiroshi; Ikegami, Seiji; Sonomura, Hajimu

    1990-03-01

    The stability of thin-film CdS/CdTe solar cells with evaporated Au-Cu2Te contacts to the CdTe film has been investigated. A decrease in conversion efficiency due to an increase in series resistance was observed in the solar cells stored in air at room temperature for 120 days. The increase in series resistance is caused by an increase in contact resistance resulting from the compositional change in the Au-Cu2Te contact to the CdTe film.

  9. Electrical Characterization of Cu Composition Effects in CdS/CdTe Thin-Film Solar Cells with a ZnTe:Cu Back Contact: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Li, J. V.; Duenow, J. N.; Kuciauskas, D.; Kanevce, A.; Dhere, R. G.; Young, M. R.; Levi, D. H.

    2012-07-01

    We study the effects of Cu composition on the CdTe/ZnTe:Cu back contact and the bulk CdTe. For the back contact, its potential barrier decreases with Cu concentration while its saturation current density increases. For the bulk CdTe, the hole density increases with Cu concentration. We identify a Cu-related deep level at {approx}0.55 eV whose concentration is significant when the Cu concentration is high. The device performance, which initially increases with Cu concentration then decreases, reflects the interplay between the positive influences and negative influences (increasing deep levels in CdTe) of Cu.

  10. Growth and Characterization of CdTe Thin Films on CdS/TCO/glass superstrate

    Science.gov (United States)

    Oladeji, Isaiah O.; Chow, Lee; Zhou, Dan; Stevie, Fred

    1998-11-01

    The performance of CdTe/CdS/TCO/glass structure which is generally used as a solar cell depends on the impurities incorporated in the system before and after electrodeposition of CdTe thin films. In this report we present a detailed investigation of this structure using secondary ion mass spectrometry(SIMS), x-ray microanalysis, x-ray diffraction(XRD), and scanning electron microscopy(SEM) to identify those impurities. We also discuss possible ways of minimizing or eliminating some of these impurities in order to improve the cell efficiency.

  11. Light and voltage dependence of the junction transport properties of CdTe/CdS photovoltaics

    Energy Technology Data Exchange (ETDEWEB)

    Linam, D.L.; McClure, J.C.; Lush, G.B. [Electrical and Computer Engineering Department, University of Texas El Paso-UTEP, 79968-0520 El Paso, TX (United States); Singh, V.P. [Electrical Engineering Department, University of Kentucky, 40506 Lexington, KY (United States); Mathew, X.; Sebastian, P.J. [Centro de Investigacion en Energia, UNAM, Temixco, Morelos (Mexico)

    2001-12-31

    The J-V curve of CdTe/CdS photovoltaics does not consist of a simple superposition of a loss current and a light generated current with a considerable loss in conversion efficiency. This paper uses capacitance/voltage measurements and J-V measurements at a variety of temperatures and light levels to develop a model for this non-superposition. It was found that a light dependent tunneling mechanism dominates at low voltages. Moreover, the tunneling takes place from a trap level within the CdTe.

  12. Synthesis of CdTe Quantum Dots with Tunable Photoluminescence Using Tellurium Dioxide as Tellurium Source

    Institute of Scientific and Technical Information of China (English)

    刘声燕; 王益林; 杨昆; 周立亚

    2012-01-01

    A simple and convenient method has been developed for synthesis of water-soluble CdTe quantum dots (QDs) under ambient atmospheric conditions. In contrast to the traditional aqueous synthesis, green to red emitting CdTe QDs were prepared by using TeO2 to replace Te or AIzTe3 as tellurium source in this method. The influences of ex- perimental variables, including pH value, 3-mercaptopropionic acid (MPA)/Cd and Te/Cd molar ratios, on the emis- sion peak and photoluminescence (PL) quantum yield (QY) of the obtained CdTe QDs have been systematically investigated. Experimental results indicate that green to red emitting CdTe QDs with a maximum photolumines- cence quantum yield of 35.4% can be prepared at pH 11.3 and rt(Cd) : n(Te) : n(MPA)= 1 : 0.1 : 1.7.

  13. ELECTRICAL AND PHOTOELECTRICAL PROPERTIES OF CdS/Cd1-xMnxTe HETEROJUNCTIONS

    Directory of Open Access Journals (Sweden)

    Petru GAŞIN

    2015-12-01

    Full Text Available Electrical and photoelectrical properties of CdS/Cd1-xMnxTe heterojunction at different temperatures from 293 K to 393 K were studied. The potential barrier at 293 K makes 0,78 V and is linearly decreasing with temperature increase with a temperature coefficient of 5,5·10-3 V·K-1. From lnIinv= f(1/T dependence at U=1V the activation energy of 0,61 eV was determined. CdS/Cd0,6Mn0,4Te heterojunction spectral sensitivity at 300 K covers the wavelength region.PROPRIERĂŢILE ELECTRICE ŞI FOTOELECTRICE ALE HETEROJONCŢIUNILOR CdS/Cd1-xMnxTeÎn intervalul de temperaturi de la 293K până la 393K au fost cercetate proprietăţile electrice şi fotoelectrice ale hetero-joncţiunilor CdS/Cd1-xMnxTe. La 293K potenţialul de difuzie constituie 0,78 V şi cu creşterea temperaturii mărimea lui se micşorează linear cu coeficientul termic egal cu 5,5·10-3 V·K-1. Din dependenţa lnIinv= f(1/T la tensiunea de 1V a fost determinată energia de activare care este egală cu 0,61 eV. Spectrele fotoconductibilităţii denotă că la 300 K hetero-joncţiunile CdS/Cd0,6Mn0,4Te sunt fotosensibile în regiunea de lungimi de undă 0,52÷0,83µm.

  14. Microstructure of absorber layers in CdTe/CdS solar cells

    International Nuclear Information System (INIS)

    This work concerns the microstructure of CSS-grown CdTe layers used for CdTe/CdS solar cells. Particular attention is given to how the development of microstructure on annealing with CdCl2 may correlate with increases in efficiency. By annealing pressed pellets of bulk CdTe powder, it is shown that microstructural change does occur on heating the material, enhanced by the inclusion of CdCl2 flux. However, the temperature required to cause significant effects is demonstrated to be higher than that at which heavy oxidation takes place. The dynamics of this oxidation are also examined. To investigate microstructural evolution in thin-films of CdTe, bi-layers of CdTe and CdS are examined by bevelling, thus revealing the microstructure to within ∼1 μm of the interface. This allows optical microscopy and subsequent image analysis of grain structure. The work shows that the grain-size, which is well described by the Rayleigh distribution, varies linearly throughout the layer, but is invariant under CdCl2 treatment. Electrical measurements on these bi-layers, however, showed increased efficiency, as is widely reported. This demonstrates that the efficiency of these devices is not dictated by the bulk microstructure. Further, the region within 1 μm of the interface, of similar bi-layers to above, is examined by plan-view TEM. This reveals five-fold grain-growth on CdCl2 treatment. Moreover, these grains show a considerably smaller grain size than expected from extrapolating the linear trend in the bulk. These observations are explained in terms of the pinning of the CdTe grain size to the underlying CdS, and the small grain size this causes. A simple model was proposed for a link between the grain-growth to the efficiency improvement. The study also examines the behaviour of defects within grains upon CdCl2 treatment provided the first direct evidence of recovery on CdCl2 treatment in this system. Finally, a computer model is presented to describe the evolution of

  15. Microstructure of absorber layers in CdTe/CdS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Cousins, M.A

    2001-04-01

    This work concerns the microstructure of CSS-grown CdTe layers used for CdTe/CdS solar cells. Particular attention is given to how the development of microstructure on annealing with CdCl{sub 2} may correlate with increases in efficiency. By annealing pressed pellets of bulk CdTe powder, it is shown that microstructural change does occur on heating the material, enhanced by the inclusion of CdCl{sub 2} flux. However, the temperature required to cause significant effects is demonstrated to be higher than that at which heavy oxidation takes place. The dynamics of this oxidation are also examined. To investigate microstructural evolution in thin-films of CdTe, bi-layers of CdTe and CdS are examined by bevelling, thus revealing the microstructure to within {approx}1 {mu}m of the interface. This allows optical microscopy and subsequent image analysis of grain structure. The work shows that the grain-size, which is well described by the Rayleigh distribution, varies linearly throughout the layer, but is invariant under CdCl{sub 2} treatment. Electrical measurements on these bi-layers, however, showed increased efficiency, as is widely reported. This demonstrates that the efficiency of these devices is not dictated by the bulk microstructure. Further, the region within 1 {mu}m of the interface, of similar bi-layers to above, is examined by plan-view TEM. This reveals five-fold grain-growth on CdCl{sub 2} treatment. Moreover, these grains show a considerably smaller grain size than expected from extrapolating the linear trend in the bulk. These observations are explained in terms of the pinning of the CdTe grain size to the underlying CdS, and the small grain size this causes. A simple model was proposed for a link between the grain-growth to the efficiency improvement. The study also examines the behaviour of defects within grains upon CdCl{sub 2} treatment provided the first direct evidence of recovery on CdCl{sub 2} treatment in this system. Finally, a computer model is

  16. Theoretical investigation of Sn-doped Ge2Sb2Te5 alloy in crystalline phase

    International Nuclear Information System (INIS)

    Ge2Sb2Te5 (GST) is technologically important for phase-change random access memory applications. It has been shown that the 2.2 atomic % doping of Sn weakens the Ge–Te bond strength while maintaining the symmetry of stable phase of GST. The influence of Sn doping upon the phase change characteristics of the crystalline GST alloy has been investigated by ab initio calculations. The lattice parameter, average interface distances between two adjacent (111) layers, equilibrium volume, metallic character and electrical resistance has been calculated for the stable phase of GST and Sn-doped GST

  17. Theoretical investigation of Sn-doped Ge2Sb2Te5 alloy in crystalline phase

    Science.gov (United States)

    Singh, Janpreet; Singh, Gurinder; Kaura, Aman; Tripathi, S. K.

    2015-06-01

    Ge2Sb2Te5 (GST) is technologically important for phase-change random access memory applications. It has been shown that the 2.2 atomic % doping of Sn weakens the Ge-Te bond strength while maintaining the symmetry of stable phase of GST. The influence of Sn doping upon the phase change characteristics of the crystalline GST alloy has been investigated by ab initio calculations. The lattice parameter, average interface distances between two adjacent (111) layers, equilibrium volume, metallic character and electrical resistance has been calculated for the stable phase of GST and Sn-doped GST.

  18. 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.

  19. 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.).

  20. 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.

  1. Fabrication of CdTe/Si heterojunction solar cell

    Science.gov (United States)

    Bera, Swades Ranjan; Saha, Satyajit

    2016-01-01

    A simple cost effective method is preferred to grow nanoparticles of CdTe. Nanoparticles of CdTe are grown by simple chemical reduction route using EDA as capping agent and Sodium Borohydride as reducing agent. The grown nanoparticles are characterized using transmission electron microscopy (TEM), X-ray diffraction, optical absorption, and photoluminescence study. From optical absorption study, the band-gap was found to be 2.46 eV. From TEM study, the average particle size was found to be within 8-12 nm which confirms the formation of CdTe nanoparticles. Pl spectra indicate the luminescence from surface states at 2.01 eV, which is less compared to the increased band-gap of 2.46 eV. The grown nanoparticles are used to fabricate a heterojunction of CdTe on P-Si by a spin coating technique for solar cell fabrication in a cost effective way. I-V characteristics of the grown heterojunction in dark as well as under light are measured. Efficiency and fill-factor of the device are estimated.

  2. Results of a Si/CdTe Compton Telescope

    CERN Document Server

    Oonuki, K; Watanabe, S; Takeda, S; Nakazawa, K; Mitani, T; Takahashi, T; Tajima, H; Fukazawa, Y; Nomachi, M; Oonuki, Kousuke; Tanaka, Takaaki; Watanabe, Shin; Takeda, Shin'ichiro; Nakazawa, Kazuhiro; Mitani, Takefumi; Takahashi, Tadayuki; Tajima, Hiroyasu; Fukazawa, Yasushi; Nomachi, Masaharu

    2005-01-01

    We have been developing a semiconductor Compton telescope to explore the universe in the energy band from several tens of keV to a few MeV. We use a Si strip and CdTe pixel detector for the Compton telescope to cover an energy range from 60 keV. For energies above several hundred keV, the higher efficiency of CdTe semiconductor in comparison with Si is expected to play an important role as an absorber and a scatterer. In order to demonstrate the spectral and imaging capability of a CdTe-based Compton Telescope, we have developed a Compton telescope consisting of a stack of CdTe pixel detectors as a small scale prototype. With this prototype, we succeeded in reconstructing images and spectra by solving the Compton equation from 122 keV to 662 keV. The energy resolution (FWHM) of reconstructed spectra is 7.3 keV at 511 keV and 3.1 keV at 122 keV, respectively. The angular resolution obtained at 511 keV is measured to be 12.2degree (FWHM).

  3. Electron transient transport in CdTe polycrystalline films

    Science.gov (United States)

    Ramírez-Bon, R.; Sánchez-Sinencio, F.; González de la Cruz, G.; Zelaya, O.

    1991-11-01

    Electron transient currents between coplanar electrodes have been measured in intrinsic polycrystalline films of CdTe, by means of the time of flight technique. The experimental results: electron transient current vs time, transit time vs voltage and the temperature dependence of the electron drift mobility, show features characteristics of dispersive electrical transport similar to that observed in disordered solids.

  4. 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.

  5. Radiation induced polarization in CdTe detectors

    Science.gov (United States)

    Vartsky, D.; Goldberg, M.; Eisen, Y.; Shamai, Y.; Dukhan, R.; Siffert, P.; Koebel, J. M.; Regal, R.; Gerber, J.

    1988-01-01

    Polarization induced by irradiation with intense gamma ray sources has been studied in chlorine-compensated CdTe detectors. The influence of several parameters, such as applied field strength, temperature and incident photon flux, on the polarization effect have been investigated. A relationship was found between the degree of polarization, detector efficiency and detector leakage current.

  6. Radiation induced polarization in CdTe detectors

    Energy Technology Data Exchange (ETDEWEB)

    Vartsky, D.; Goldberg, M.; Eisen, Y.; Shamai, Y.; Dukhan, R.; Siffert, P.; Koebel, J.M.; Regal, R.; Gerber, J.

    1988-01-15

    Polarization induced by irradiation with intense gamma ray sources has been studied in chlorine-compensated CdTe detectors. The influence of several parameters, such as applied field strength, temperature and incident photon flux, on the polarization effect have been investigated. A relationship was found between the degree of polarization, detector efficiency and detector leakage current.

  7. Simulation of charge transport in pixelated CdTe

    International Nuclear Information System (INIS)

    The Voxel Imaging PET (VIP) Pathfinder project intends to show the advantages of using pixelated semiconductor technology for nuclear medicine applications to achieve an improved image reconstruction without efficiency loss. It proposes designs for Positron Emission Tomography (PET), Positron Emission Mammography (PEM) and Compton gamma camera detectors with a large number of signal channels (of the order of 106). The design is based on the use of a pixelated CdTe Schottky detector to have optimal energy and spatial resolution. An individual read-out channel is dedicated for each detector voxel of size 1 × 1 × 2 mm3 using an application-specific integrated circuit (ASIC) which the VIP project has designed, developed and is currently evaluating experimentally. The behaviour of the signal charge carriers in CdTe should be well understood because it has an impact on the performance of the readout channels. For this purpose the Finite Element Method (FEM) Multiphysics COMSOL software package has been used to simulate the behaviour of signal charge carriers in CdTe and extract values for the expected charge sharing depending on the impact point and bias voltage. The results on charge sharing obtained with COMSOL are combined with GAMOS, a Geant based particle tracking Monte Carlo software package, to get a full evaluation of the amount of charge sharing in pixelated CdTe for different gamma impact points

  8. Applications of CdTe to nuclear medicine. Final report

    International Nuclear Information System (INIS)

    Uses of cadmium telluride (CdTe) nuclear detectors in medicine are briefly described. They include surgical probes and a system for measuring cerebral blood flow in the intensive care unit. Other uses include nuclear dentistry, x-ray exposure control, cardiology, diabetes, and the testing of new pharmaceuticals

  9. Band structure of CdTe under high pressure

    International Nuclear Information System (INIS)

    The band structures and density of states of cadmium telluride (CdTe) under various pressures ranging from normal to 4.5 Mbar are obtained. The electronic band structure at normal pressure of CdTe (ZnS structure) is analyzed and the direct band gap value is found to be 1.654 eV. CdTe becomes metal and superconductor under high pressure but before that it undergoes structural phase transition from ZnS phase to NaCl phase. The equilibrium lattice constant, bulk modulus and the phase transition pressure at which the compounds undergo structural phase transition from ZnS to NaCl are predicted from the total energy calculations. The density of states at the Fermi level (N(EF)) gets enhanced after metallization, which leads to the superconductivity in CdTe. In our calculation, the metallization pressure (PM = 1.935 Mbar) and the corresponding reduced volume ((V/V0)M = 0.458) are estimated. Metallization occurs via direct closing of band gap at Γ point. (author)

  10. Hydrothermal synthesis for high-quality CdTe nanocrystals

    International Nuclear Information System (INIS)

    Synthesis of water-soluble CdTe nanocrystals with high photoluminescence quantum yield and narrow fluorescence emission spectra is developed under the conditions of low precursor concentration and moderate temperature of hydrothermal growth. The relatively high temperature accelerates the particle growth rate and enhances the photoluminescence quantum yield. (Abstract Copyright [2003], Wiley Periodicals, Inc.)

  11. Intracavity CdTe modulators for CO2 lasers.

    Science.gov (United States)

    Kiefer, J. E.; Nussmeier, T. A.; Goodwin, F. E.

    1972-01-01

    The use of cadmium telluride as an electrooptic material for intracavity modulation of CO2 lasers is described. Included are the predicted and measured effects of CdTe intracavity modulators on laser performance. Coupling and frequency modulation are discussed and experimental results compared with theoretically predicted performance for both techniques. Limitations on the frequency response of the two types of modulation are determined.

  12. Electronic, lattice vibration and mechanical properties of CdTe, ZnTe, MnTe, MgTe, HgTe and their ternary alloys

    International Nuclear Information System (INIS)

    The main representative telluride family, CdTe, ZnTe, MnTe, MgTe and HgTe, and their mixed ternary alloys have been extensively studied, but some points bearing on phonon frequencies properties have never been previously reported or are still not clear. In this paper, we report results on the electronic, lattice dynamical and mechanical properties for this family in the zinc–blende (ZB) structure. Numerical calculations based on the empirical pseudo-potential method under the virtual crystal approximation combined with the Harrison bond orbital model are used to investigate these properties. Our results are found to be generally in good agreement with the available experimental data. Other case, our results are predictions and may serve as a reference. The information derived from the present study demonstrates the potential of the materials of interest for optoelectronic and photovoltaic device applications from the ultraviolet to infrared and mid-infrared

  13. Structure of CdZnTe films on glass

    International Nuclear Information System (INIS)

    Polycrystalline Cd1-xZnxTe films were grown on glass substrates over the full range of compositions (0 1-xZnxTe on the composition followed Vegard's law. The thick Cd1-xZnxTe films were shown to be of a single phase and structurally stable. The average grain size in the thick films was in the range 3-5 μm. The dominant imperfections in the films were twins (mostly Σ = 3) and dislocations. The x-ray diffraction (XRD) FWHM parameter reached a maximum at x = 0.5. Transmission electron microscopy (TEM) in situ heating in the range 200-400 deg. C caused plastic deformation in the grains without causing ordering effects. Optical absorption and low-temperature photoluminescence measurements confirmed the XRD and TEM results

  14. Nanowire CdS-CdTe Solar Cells with Molybdenum Oxide as Contact

    Science.gov (United States)

    Dang, Hongmei; Singh, Vijay P.

    2015-10-01

    Using a 10 nm thick molybdenum oxide (MoO3-x) layer as a transparent and low barrier contact to p-CdTe, we demonstrate nanowire CdS-CdTe solar cells with a power conversion efficiency of 11% under front side illumination. Annealing the as-deposited MoO3 film in N2 resulted in a reduction of the cell’s series resistance, from 9.97 Ω/cm2 to 7.69 Ω/cm2, and increase in efficiency from 9.9% to 11%. Under illumination from the back, the MoO3-x/Au side, the nanowire solar cells yielded Jsc of 21 mA/cm2 and efficiency of 8.67%. Our results demonstrate use of a thin layer transition metal oxide as a potential way for a transparent back contact to nanowire CdS-CdTe solar cells. This work has implications toward enabling a novel superstrate structure nanowire CdS-CdTe solar cell on Al foil substrate by a low cost roll-to roll fabrication process.

  15. Characterization of thin film CdS-CdTe solar cells. [CDS-CDTE

    Energy Technology Data Exchange (ETDEWEB)

    Singh, V.P.; Brafman, H.; Makwana, J. (Texas Univ., El Paso (USA). Dept. of Electrical Engineering); McClure, J.C. (Texas Univ., El Paso, TX (USA). Metallurgical and Materials Engineering Dept.)

    1991-02-01

    Current-voltage, junction capacitance and optical characteristics of thin film CdS-CdTe cells on sprayed CdS films were measured. These characteristics have some interesting features such as reversal of the polarity of the a.c. short-circuit current and the a.c. open-circuit voltage when a large forward bias is applied across the cell. The reverse saturation current density j{sub 0} increases from 5.9x10{sup -9} A cm{sup -2} in the dark to 18.1x10{sup -6} A cm{sup -2} under '1 sun' illumination. Diode ideality factors are higher than 2.0 and the slope {alpha} of log I vs. V curve is almost temperature independent. The zero-bias depletion layer width is 1.9 {mu}m. The experimental results are interpreted by a model which proposes a highly compensated layer in CdTe and a high space charge layer in CdTe next to the CdS-CdTe interface. The origin of the high space charge layer is thought to be the ionization of a deep trap level at energy E{sub T} below the conduction band edge. For our calculations, we have used E{sub T}=0.45 eV. (orig.).

  16. Cumulative effects of Te precipitates in CdZnTe radiation detectors

    International Nuclear Information System (INIS)

    High-quality radiation detector-grade CdZnTe material is free from large-scale defects, such as grain boundaries, twins, and large Te or Cd inclusions (>50 μm), although it usually contains high concentrations of uniformly distributed Te inclusions and precipitates, typically of ∼20-μm-diameter size or smaller. We address the effects of the small-size Te precipitates on charge collection in CZT detectors, the significance of which is not yet well characterized. The strong correlation that we earlier found between the high-resolution X-ray maps and IR images proved that even small Te precipitates can trap substantial fractions of charge from the electron cloud. In this work, we modeled the transport of an electron cloud across idealized CZT devices containing Te precipitates to demonstrate that their cumulative effect can explain the degradation of energy resolution and the detection efficiency losses observed in actual CZT devices. Due to lack of experimental data on how the Te precipitates interact with an electron cloud, we developed a simplified (phenomenological) model based on the geometrical aspects of the problem. Despite its simplicity, the model correctly reproduced many experimental facts and gave quantitative predictions on the extent to which the presence of Te precipitates and inclusions can be tolerated. The broadening of the electron cloud due to repulsion and diffusion is at the core of the problem, making even low concentrations of small precipitates important in the device's performance

  17. Folic acid-CdTe quantum dot conjugates and their applications for cancer cell targeting

    OpenAIRE

    Suriamoorthy, Preethi; Zhang, Xing; Hao, Guiyang; Joly, Alan G.; Singh, Surya; Hossu, Marius; Sun, Xiankai; Chen, Wei(Department of Physics, State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing, 100871, China)

    2010-01-01

    In this study, we report the preparation, luminescence, and targeting properties of folic acid-CdTe quantum dot conjugates. Water-soluble CdTe quantum dots were synthesized and conjugated with folic acid using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-N-hydroxysuccinimide chemistry. The influence of folic acid on the luminescence properties of CdTe quantum dots was investigated, and no energy transfer between them was observed. To investigate the efficiency of folic acid-CdTe nanoconjuga...

  18. Electrical properties of phase change materials along the pseudo binary line between GeTe and SnTe analysed with temperature dependent Hall effect measurements

    Energy Technology Data Exchange (ETDEWEB)

    Lange, Felix; Volker, Hanno; Schlockermann, Carl; Karvonen, Jenni; Wuttig, Matthias [RWTH Aachen University, I. Physikalisches Institut (IA), Aachen (Germany)

    2010-07-01

    Phase change materials are a class of materials that can be reversibly switched between an amorphous and a crystalline state. These two states exhibit characteristic differences in their physical properties such as the reflectivity and the electrical resistivity. By assigning these two states to the binary values 1 and 0 one can store information as already realized in optical data storage media like CD{+-}RW and DVD{+-}RW. The electrical induced switching within nanoseconds makes PC- materials also interesting for non-volatile RAM applications. It is obvious that a comprehensive understanding of the electrical transport properties is crucial in order to match the low power requirements of the device. Therefore we have investigated electrical properties along the pseudo binary line between GeTe and SnTe by temperature dependent Hall effect measurements.

  19. Photoluminescence Spectroscopy of CdTe/ZnTe Self-Assembled Quantum Dots

    Directory of Open Access Journals (Sweden)

    Nebojša Romčević

    2009-01-01

    Full Text Available We present photoluminescence (PL measurements of two different, 3 monolayers and 12 monolayers (ml, CdTe self-assembled quantum dot (SAQD samples. The spectra were recorded in the temperature range 20 K–300 K, with photoexcitation over the ZnTe barrier layer. PL spectra displayed two main emission bands. High-energy PL emission (E1 is ZnTe LO like phonon- (ωLO = 204.2 cm−1 (3 ml, ωLO = 207.3 cm−1 (12 ml assisted deexcitation. Dominant low-energy band (E2 presents the direct deexcitation to ground state of the CdTe quantum dots.

  20. Crystal and electronic structure of PbTe/CdTe nanostructures

    Directory of Open Access Journals (Sweden)

    Sankowski Piotr

    2011-01-01

    Full Text Available Abstract In this article, the authors reported a theoretical study of structural and electronic properties of PbTe inclusions in CdTe matrix as well as CdTe nano-clusters in PbTe matrix. The structural properties are studied by ab initio methods. A tight-binding model is constructed to calculate the electron density of states (DOS of the systems. In contrast to the ab initio methods, the latter allows studying nanostructures with diameters comparable to the real ones. The calculations show that both kinds of inclusions lead to changes of the DOS of the carriers near the Fermi level, which may affect optical, electrical and thermoelectric properties of the material. These changes depend on the size, shape, and concentration of inclusions.

  1. 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.

  2. Atomic layer epitaxy of (CdTe) sub m (ZnTe) sub n -ZnTe multiquantum wells on (001)GaAs substrate

    Energy Technology Data Exchange (ETDEWEB)

    Li Jie; He Li; Shan Wei; Cheng Xingyu; Yuan Shixin (Shanghai Inst. of Technical Physics, Academia Sinica (China))

    1991-05-01

    (CdTe){sub m}(ZnTe){sub n}-ZnTe multiquantum well structure has been proposed and grown on (001)GaAs substrate by atomic layer epitaxy. Growth has been investigated using reflection high energy electron diffraction. Material characterizations have been performed by X-ray diffraction and photoluminescence. With this structure, great improvements have been made in crystalline quality compared with CdTe-ZnTe multiquantum wells, due to the reduction of misfit dislocations. (orig.).

  3. Interface roughness limited electron mobility in HgTe-CdTe superlattices

    Science.gov (United States)

    Meyer, J. R.; Arnold, D. J.; Hoffman, C. A.; Bartoli, F. J.

    1991-06-01

    It is demonstrated that interface roughness is the dominant low-temperature scattering mechanism for electrons in HgTe-CdTe superlattices with thin wells. Not only do the experimental mobilities follow the expected d6(W) dependence, but the observed temperature dependence is accurately reproduced by theory when the treatment of interface roughness scattering is generalized for narrow-gap superlattices. The fits to data yield roughness correlation lengths in the range 60-200 A.

  4. Magnetic activation of bipolar plasmas in HgTe-CdTe superlattices

    Science.gov (United States)

    Meyer, J. R.; Hoffman, C. A.; Bartoli, F. J.; Wojtowicz, T.; Dobrowolska, M.; Furdyna, J. K.; Chu, X.; Faurie, J. P.; Ram-Mohan, L. R.

    1991-08-01

    It is shown theoretically that in semimetallic HgTe-CdTe superlattices, there is a critical magnetic field above which minority carriers with density proportional to B-Bcrit are expected to coexist with majority carriers in the zero-temperature limit. Experimental confirmation of the magnetically activated bipolar plasma is provided by low-temperature magneto-optical data showing the emergence of minority holes in an n-type superlattice whenever B>Bcrit.

  5. Self-induced persistent photoconductivity in ZnTe-Cd1-xMnxTe1-ySey heterojunctions

    International Nuclear Information System (INIS)

    At temperatures lower than 200 K the photomemory effect has been observed in ZnTe-Cd1-xMnxTe1-ySey heterojunctions. The persistent photoconductivity can be achieved either by the illumination from an external light source or by a self-absorption of the electroluminescence radiation when a voltage of about 10 V for a few seconds is applied to the diode. Current-voltage characteristics are of the form I ∼ Vm. The capacitance and electroluminescence measurements show that the photomemory effect in ZnTe-Cd1-xMnxTe1-ySey heterojunctions can be caused by the bistable nature of the In dopant in the Cd1-xMnxTe1-ySey substrate. In the high resistivity interface layer and the substrate material indium forms centers similar to DX-like centers in ZnxCd1-xTe and Cd1-xMnxTe. (author)

  6. CdS/CdTe solar cells with improved CdS films fabricated by the writing method

    Energy Technology Data Exchange (ETDEWEB)

    Arita, T.; Hanafusa, A.; Ueno, N.; Nishiyama, Y.; Kitamura, S.; Murozono, M. (Matsushita Battery Industrial Co., Ltd., Osaka (Japan))

    1991-12-01

    A new deposition technique called 'the writing method' is examined for fabrication of CdS window layer in CdS/CdTe solar cells by the screen-printing and sintering method. Obtained CdS film is very smooth with very few pinholes. This technique also processes high patterning precision and realizes the active/total area ratio of 0.8 by reducing the separation of CdS stripes. As a result of the optimization of patterning dimensions, the conversion efficiency of 7.8% in 1200 cm{sup 2} large area cell (9.8% in active area) is obtained. (orig.).

  7. Solution-Processed, Ultrathin Solar Cells from CdCl3(-)-Capped CdTe Nanocrystals: The Multiple Roles of CdCl3(-) Ligands.

    Science.gov (United States)

    Zhang, Hao; Kurley, J Matthew; Russell, Jake C; Jang, Jaeyoung; Talapin, Dmitri V

    2016-06-22

    Solution-processed CdTe solar cells using CdTe nanocrystal (NC) ink may offer an economically viable route for large-scale manufacturing. Here we design a new CdCl3(-)-capped CdTe NC ink by taking advantage of novel surface chemistry. In this ink, CdCl3(-) ligands act as surface ligands, sintering promoters, and dopants. Our solution chemistry allows obtaining very thin continuous layers of high-quality CdTe which is challenging for traditional vapor transport methods. Using benign solvents, in air, and without additional CdCl2 treatment, we obtain a well-sintered CdTe absorber layer from the new ink and demonstrate thin-film solar cells with power conversion efficiency over 10%, a record efficiency for sub-400 nm thick CdTe absorber layer. PMID:27269672

  8. CdZnTe and CdTe materials for X-ray and gamma ray radiation detector applications

    International Nuclear Information System (INIS)

    Good detection efficiency and high energy-resolution make Cadmium Zinc Telluride (CdZnTe) and Cadmium Telluride (CdTe) detectors attractive in many room temperature X-ray and gamma-ray detection applications such as medical and industrial imaging, industrial gauging and non-destructive testing, security and monitoring, nuclear safeguards and non-proliferation, and astrophysics. Advancement of the crystal growth and device fabrication technologies and the reduction of bulk, interface and surface defects in the devices are crucial for the widespread practical deployment of Cd1-xZnxTe-based detector technology. Here we review the effects of bulk, interface and surface defects on charge transport, charge transport uniformity and device performance and the progress in the crystal growth and device fabrication technologies aiming at reducing the concentration of harmful defects and improving Cd1-xZnxTe detector performance. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. CdTe and CdZnTe detectors behavior in X-ray computed tomography conditions

    CERN Document Server

    Ricq, S; Garcin, M

    2000-01-01

    The application of CdTe and CdZnTe 2D array detectors for medical X-ray Computed Tomography (XCT) is investigated. Different metallic electrodes have been deposited on High-Pressure Bridgman Method CdZnTe and on Traveling Heater Method CdTe:Cl. These detectors are exposed to X-rays in the CT irradiation conditions and are characterized experimentally in current mode. Detectors performances such as sensitivity and response speed are studied. They are correlated with charge trapping and de-trapping. The trapped carrier space charges may influence the injection from the electrodes. This enables one to get information on the nature of the predominant levels involved. The performances achieved are encouraging: dynamic ranges higher than 4 decades and current decreases of 3 decades in 4 ms after X-ray beam cut-off are obtained. Nevertheless, these detectors are still limited by high trap densities responsible for the memory effect that makes them unsuitable for XCT.

  10. Deposition and doping of CdS/CdTe thin film solar cells

    International Nuclear Information System (INIS)

    1% oxygen is incorporated into both CdS and CdTe layers through RF sputtering of CdS/CdTe thin film solar cells. The optical and electrical parameters of the oxygenated and O2-free devices are compared after CdCl2 treatment and annealing in ambient Ar and/or air. The effects of ambient annealing on the electrical and optical properties of the films are investigated using current—voltage characterization, field emission scanning electron microscopy, X-ray diffraction, and optical transmission spectroscopy. The 1% oxygen content can slightly increase the grain size while the crystallinity does not change. Annealing in ambient Ar can increase the transmission rate of the oxygenated devices. (paper)

  11. Effect of shells on photoluminescence of aqueous CdTe quantum dots

    International Nuclear Information System (INIS)

    Graphical abstract: Size-tunable CdTe coated with several shells using an aqueous solution synthesis. CdTe/CdS/ZnS quantum dots exhibited high PL efficiency up to 80% which implies the promising applications for biomedical labeling. - Highlights: • CdTe quantum dots were fabricated using an aqueous synthesis. • CdS, ZnS, and CdS/ZnS shells were subsequently deposited on CdTe cores. • Outer ZnS shells provide an efficient confinement of electron and hole inside the QDs. • Inside CdS shells can reduce the strain on the QDs. • Aqueous CdTe/CdS/ZnS QDs exhibited high stability and photoluminescence efficiency of 80%. - Abstract: CdTe cores with various sizes were fabricated in aqueous solutions. Inorganic shells including CdS, ZnS, and CdS/ZnS were subsequently deposited on the cores through a similar aqueous procedure to investigate the effect of shells on the photoluminescence properties of the cores. In the case of CdTe/CdS/ZnS quantum dots, the outer ZnS shell provides an efficient confinement of electron and hole wavefunctions inside the quantum dots, while the middle CdS shell sandwiched between the CdTe core and ZnS shell can be introduced to obviously reduce the strain on the quantum dots because the lattice parameters of CdS is situated at the intermediate-level between those of CdTe and ZnS. In comparison with CdTe/ZnS core–shell quantum dots, the as-prepared water-soluble CdTe/CdS/ZnS quantum dots in our case can exhibit high photochemical stability and photoluminescence efficiency up to 80% in an aqueous solution, which implies the promising applications in the field of biomedical labeling

  12. The influence of grain boundary diffusion on the electro-optical properties of CdTe/CdS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Levi, D.H.; Albin, D.S.; Gessert, T.A.; Reedy, R.C.; Ahrenkiel, R.K. [National Renewable Energy Lab., Golden, CO (United States); Woods, L.M. [Colorado State Univ., Fort Collins, CO (United States)

    1998-09-01

    The authors report on a study of the effects of diffusion of metals through polycrystalline CdTe thin films. The metals Ni, Pd, Cu, Cr, and Te are deposited onto the back surface of 10-{micro}m thick CdTe/CdS device structures using room-temperature evaporation. The authors found that four out of the five metals produce significant changes in the photoluminescence (PL) of the near-junction CdTe material. These changes are explained in terms of spatial variations of the photoexcited carrier distribution and spatial variations in the sulfur composition of the CdTeS alloy material near the CdTeS interface. The changes in carrier distribution appear to be associated with band bending and electric fields induced by diffusion of the metals to the CdTe/CdS interface. In addition to PL measurements, the authors have also utilized a technique for detaching the CdTe film from the CdS/TCO/glass superstrate to directly access the front surface of the CdTe absorber layer. The authors have used secondary ion mass spectroscopy to measure the metal diffusion profiles from this interface.

  13. Technological aspects of development of pixel and strip detectors based on CdTe and CdZnTe

    Energy Technology Data Exchange (ETDEWEB)

    Gostilo, V.; Ivanov, V.; Kostenko, S.; Lisjutin, I.; Loupilov, A.; Nenonen, S.; Sipila, H.; Valpas, K

    2001-03-11

    Current and spectrometrical characteristics, stability in time and reliability of pixel and strip detectors depend on initial material properties, crystal processing quality and contacts manufacture technology. The work presents analysis of current-voltage and spectrometrical characteristics for initial CdTe and CdZnTe crystals applied for pixel and strip detectors manufacture. The crystal surface preparation before contacts manufacture comprises a modified technology. The contacts were made by photolithography with the surface protected by photoresist with further windows lift-off and crystal surface metallization in lifted-off windows. Metal pads were made by gold deposition from chloroauric acid. Thermocompression, ultrasonic and pulse wirebonding, as well as traditional contacts glueing method for CdTe and CdZnTe detectors have been tested for contacts wiring. The pulse wirebonding has revealed the best results. Wiring is made of gold wire with a diameter of 30 {mu}m and is good enough for pixel and strip wirebonding, providing rather low labour-intensiveness for their assembly by standard equipment. The possibility of fabrication of pressing contacts to strip and pixel detectors by Zebra elastomeric connectors has been investigated. The pressing contacts have provided qualitative and reliable electrical contact and signal layout from pixels and strips to readout electronics. Developed technologies were applied in the manufacture of the following CdTe and CdZnTe detectors: 4x4 pixels detector with rectangular pixels 0.65x0.65 mm and pitch 0.75 mm; 4x4 pixels ring miltiple-electrode detector with anode diameter 0.32 mm and pitch 0.75 mm; strip detector with 100 {mu}m width strip and 125 {mu}m pitch. The 4x4 pixels CdZnTe detector has provided at optimal temperature energy resolutions of 808 eV and 1.19 keV at energies of 5.9 and 59.6 keV, respectively. Interstrip resistance between two strips with a distance of 25 {mu}m on detector was 2-8 G{omega}.

  14. Technological aspects of development of pixel and strip detectors based on CdTe and CdZnTe

    International Nuclear Information System (INIS)

    Current and spectrometrical characteristics, stability in time and reliability of pixel and strip detectors depend on initial material properties, crystal processing quality and contacts manufacture technology. The work presents analysis of current-voltage and spectrometrical characteristics for initial CdTe and CdZnTe crystals applied for pixel and strip detectors manufacture. The crystal surface preparation before contacts manufacture comprises a modified technology. The contacts were made by photolithography with the surface protected by photoresist with further windows lift-off and crystal surface metallization in lifted-off windows. Metal pads were made by gold deposition from chloroauric acid. Thermocompression, ultrasonic and pulse wirebonding, as well as traditional contacts glueing method for CdTe and CdZnTe detectors have been tested for contacts wiring. The pulse wirebonding has revealed the best results. Wiring is made of gold wire with a diameter of 30 μm and is good enough for pixel and strip wirebonding, providing rather low labour-intensiveness for their assembly by standard equipment. The possibility of fabrication of pressing contacts to strip and pixel detectors by Zebra elastomeric connectors has been investigated. The pressing contacts have provided qualitative and reliable electrical contact and signal layout from pixels and strips to readout electronics. Developed technologies were applied in the manufacture of the following CdTe and CdZnTe detectors: 4x4 pixels detector with rectangular pixels 0.65x0.65 mm and pitch 0.75 mm; 4x4 pixels ring miltiple-electrode detector with anode diameter 0.32 mm and pitch 0.75 mm; strip detector with 100 μm width strip and 125 μm pitch. The 4x4 pixels CdZnTe detector has provided at optimal temperature energy resolutions of 808 eV and 1.19 keV at energies of 5.9 and 59.6 keV, respectively. Interstrip resistance between two strips with a distance of 25 μm on detector was 2-8 GΩ

  15. Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications

    Directory of Open Access Journals (Sweden)

    Anna Maria Mancini

    2009-05-01

    Full Text Available Over the last decade, cadmium telluride (CdTe and cadmium zinc telluride (CdZnTe wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si and germanium (Ge, CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector performance and some major applications. Astrophysical and medical applications are discussed, pointing out the ongoing Italian research activities on the development of these detectors.

  16. Synthesis of CdTe/SiO2 Composites and Their Fluorescence Properties

    Institute of Scientific and Technical Information of China (English)

    WANG Mei-ping; LIN Jin-hui; SHAN Chuan-sheng

    2011-01-01

    Thioglycolic acid(TGA)-stabilized CdTe nanocrystals(NCs) were prepared with sodium tellurite as tellurium source,which avoids the cumbersome processes associated with H2Te or NaHTe sources.Fluorescent CdTe/SiO2 composites were synthesized by a sol-gel method without the exchange of surface ligands.The phase structure of CdTe NCs was investigated by X-ray diffractometry.For comparison,some characterizations were done for both the CdTe NCs and the composites.CdTe NCs and CdTe/SiO2 composites were characterized with TEM,digital camera and fluorescence spectrophotometer.The stability of CdTe NCs and the composites were investigated in phosphate-buffered saline(PBS) buffer and the fluorescent properties of the composites were discussed in detail.

  17. Post-growth process for flexible CdS/CdTe thin film solar cells with high specific power.

    Science.gov (United States)

    Cho, Eunwoo; Kang, Yoonmook; Kim, Donghwan; Kim, Jihyun

    2016-05-16

    We demonstrated a flexible CdS/CdTe thin film solar cell with high specific power of approximately 254 W/kg. A flexible and ultra-light weight CdS/CdTe cell treated with pre-NP etch process exhibited high conversion efficiency of 13.56% in superstrate configuration. Morphological, structural and optical changes of CdS/CdTe thin films were characterized when pre-NP etch step was incorporated to the conventional post-deposition process. Improvement of photovoltaic parameters can be attributed to the removal of the oxide and the formation of Te-rich layer, which benefit the activation process. Pre-NP etched cell maintained their flexibility and performance under the repeated tensile strain of 0.13%. Our method can pave a way for manufacturing flexible CdS/CdTe thin film solar cells with high specific power for mobile and aerospace applications. PMID:27409952

  18. In-situ CdS/CdTe Heterojuntions Deposited by Pulsed Laser Deposition

    KAUST Repository

    Avila-Avendano, Jesus

    2016-04-09

    In this paper pulsed laser deposition (PLD) methods are used to study p-n CdTe/CdS heterojunctions fabricated in-situ. In-situ film deposition allows higher quality p-n interfaces by minimizing spurious contamination from the atmosphere. Morphologic and structural analyses were carried for CdTe films deposited on various substrates and different deposition conditions. The electrical characteristics and performance of the resulting p-n heterojunctions were studied as function of substrate and post-deposition anneal temperature. In-situ growth results on diodes with a rectification factor of ~ 105, an ideality factor < 2, and a reverse saturation current ~ 10-8 A. The carrier concentration in the CdTe film was in the range of ~ 1015 cm-3, as measured by C-V methods. The possible impact of sulfur diffusion from the CdS into the CdTe film is also investigated using High Resolution Rutherford Back-Scattering.

  19. Long Carrier Lifetimes in Large-Grain Polycrystalline CdTe Without CdCl2

    Energy Technology Data Exchange (ETDEWEB)

    Jensen, Soren A.; Burst, James M.; Duenow, Joel N.; Guthrey, Harvey L.; Moseley, John; Moutinho, Helio R.; Johnston, Steve W.; Kanevce, Ana; Al-Jassim, Mowafak M.; Metzger, Wyatt K.

    2016-06-27

    For decades, polycrystalline CdTe thin films for solar applications have been restricted to grain sizes of microns or less whereas other semiconductors such as silicon and perovskites have produced devices with grains ranging from less than a micron to more than 1 mm. Because the lifetimes in as-deposited polycrystalline CdTe films are typically limited to less than a few hundred picoseconds, a CdCl2 treatment is generally used to improve the lifetime; but this treatment may limit the achievable hole density by compensation. Here, we establish methods to produce CdTe films with grain sizes ranging from hundreds of nanometers to several hundred microns by close-spaced sublimation at industrial manufacturing growth rates. Two-photon excitation photoluminescence spectroscopy shows a positive correlation of lifetime with grain size. Large-grain, as-deposited CdTe exhibits lifetimes exceeding 10 ns without Cl, S, O, or Cu. This uncompensated material allows dopants such as P to achieve a hole density of 1016 cm-3, which is an order of magnitude higher than standard CdCl2-treated devices, without compromising the lifetime.

  20. Long carrier lifetimes in large-grain polycrystalline CdTe without CdCl2

    Science.gov (United States)

    Jensen, S. A.; Burst, J. M.; Duenow, J. N.; Guthrey, H. L.; Moseley, J.; Moutinho, H. R.; Johnston, S. W.; Kanevce, A.; Al-Jassim, M. M.; Metzger, W. K.

    2016-06-01

    For decades, polycrystalline CdTe thin films for solar applications have been restricted to grain sizes of microns or less whereas other semiconductors such as silicon and perovskites have produced devices with grains ranging from less than a micron to more than 1 mm. Because the lifetimes in as-deposited polycrystalline CdTe films are typically limited to less than a few hundred picoseconds, a CdCl2 treatment is generally used to improve the lifetime; but this treatment may limit the achievable hole density by compensation. Here, we establish methods to produce CdTe films with grain sizes ranging from hundreds of nanometers to several hundred microns by close-spaced sublimation at industrial manufacturing growth rates. Two-photon excitation photoluminescence spectroscopy shows a positive correlation of lifetime with grain size. Large-grain, as-deposited CdTe exhibits lifetimes exceeding 10 ns without Cl, S, O, or Cu. This uncompensated material allows dopants such as P to achieve a hole density of 1016 cm-3, which is an order of magnitude higher than standard CdCl2-treated devices, without compromising the lifetime.

  1. CdTe and CdZnTe gamma ray detectors for medical and industrial imaging systems

    International Nuclear Information System (INIS)

    CdTe and CdZnTe X-ray and gamma ray detectors in the form of single elements or as segmented monolithic detectors have been shown to be useful in medical and industrial imaging systems. These detectors possess inherently better energy resolution than scintillators coupled to either photodiodes or photomultipliers, and together with application specific integrated circuits they lead to compact imaging systems of enhanced spatial resolution and better contrast resolution. Photopeak efficiencies of these detectors is greatly affected by a relatively low hole mobility-lifetime product. Utilizing these detectors as highly efficient good spectrometers, demands use of techniques to improve their charge collection properties, i.e., correct for variations in charge losses at different depths of interaction in the detector. The corrections for the large hole trapping are made either by applying electronic techniques or by fabricating detector or electrical contacts configurations which differ from the commonly used planar detectors. The following review paper is divided into three parts: The first part discusses detector contact configurations for enhancing photopeak efficiencies and the single carrier collection approach which leads to improved energy resolutions and photopeak efficiencies at high gamma ray energies. The second part demonstrates excellent spectroscopic results using thick CdZnTe segmented monolithic pad and strip detectors showing energy resolutions less than 2% FWHM at 356 keV gamma rays. The third part discusses advantages and disadvantages of CdTe and CdZnTe detectors in imaging systems and describes new developments for medical diagnostics imaging systems

  2. CdTe and CdZnTe gamma ray detectors for medical and industrial imaging systems

    Science.gov (United States)

    Eisen, Y.; Shor, A.; Mardor, I.

    1999-06-01

    CdTe and CdZnTe X-ray and gamma ray detectors in the form of single elements or as segmented monolithic detectors have been shown to be useful in medical and industrial imaging systems. These detectors possess inherently better energy resolution than scintillators coupled to either photodiodes or photomultipliers, and together with application specific integrated circuits they lead to compact imaging systems of enhanced spatial resolution and better contrast resolution. Photopeak efficiencies of these detectors is greatly affected by a relatively low hole mobility-lifetime product. Utilizing these detectors as highly efficient good spectrometers, demands use of techniques to improve their charge collection properties, i.e., correct for variations in charge losses at different depths of interaction in the detector. The corrections for the large hole trapping are made either by applying electronic techniques or by fabricating detector or electrical contacts configurations which differ from the commonly used planar detectors. The following review paper is divided into three parts: The first part discusses detector contact configurations for enhancing photopeak efficiencies and the single carrier collection approach which leads to improved energy resolutions and photopeak efficiencies at high gamma ray energies. The second part demonstrates excellent spectroscopic results using thick CdZnTe segmented monolithic pad and strip detectors showing energy resolutions less than 2% FWHM at 356 keV gamma rays. The third part discusses advantages and disadvantages of CdTe and CdZnTe detectors in imaging systems and describes new developments for medical diagnostics imaging systems.

  3. 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)

  4. Emitter/absorber interface of CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Song, Tao [Physics Department, Colorado State University, Fort Collins, Colorado 80523, USA; Kanevce, Ana [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Sites, James R. [Physics Department, Colorado State University, Fort Collins, Colorado 80523, USA

    2016-06-17

    The performance of CdTe solar cells can be very sensitive to their emitter/absorber interfaces, especially for high-efficiency cells with improved bulk properties. When interface defect states are located at efficient recombination energies, performance losses from acceptor-type interface defects can be significant. Numerical simulations show that the emitter/absorber band alignment, the emitter doping and thickness, and the defect properties of the interface (i.e. defect density, defect type, and defect energy) can all play significant roles in the interface recombination. In particular, a type I heterojunction with small conduction-band offset (0.1 eV /= 0.4 eV), however, can impede electron transport and lead to a reduction of photocurrent and fill-factor. In contrast to the spike, a 'cliff' (.delta..EC < 0 eV) is likely to allow many holes in the vicinity of the interface, which will assist interface recombination and result in a reduced open-circuit voltage. In addition, a thin and highly-doped emitter can invert the absorber, form a large hole barrier, and decrease device performance losses due to high interface defect density. CdS is the most common emitter material used in CdTe solar cells, but the CdS/CdTe interface is in the cliff category and is not favorable from the band-offset perspective. Other n-type emitter choices, such as (Mg,Zn)O, Cd(S,O), or (Cd,Mg)Te, can be tuned by varying the elemental ratio for an optimal positive value of ..delta..EC. These materials are predicted

  5. 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

  6. Surface treatment of the window layer in CdS/CdTe solar cells

    International Nuclear Information System (INIS)

    CdS films are used as window layers in CdS/CdTe solar cells, and an annealing process is required to promote grain growth and recrystallization in them. However, when annealing is performed in an air atmosphere, oxides such as CdO and CdSO4 form on parts of the layer's surface, which reduces the shunt resistance and the fill factor and results in poor device performance. In this study, we annealed the CdS film in a CdCl2 atmosphere instead of air. Then, CdCl2 annealing and air annealing were compared by investigating the structural and the electrical properties of the CdS window layers. Our results reveal that the CdCl2 annealing protects the CdS film from oxidation and provides good recrystallization conditions. We also found that this CdCl2 annealing enhance the device's performance. In particular, considerably higher shunt resistance and conversion efficiency were obtained for the CdCl2-annealed device compared with the air-annealed device.

  7. 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.

  8. Comparative study of SnS recrystallization in molten CdI{sub 2}, SnCl{sub 2}and KI

    Energy Technology Data Exchange (ETDEWEB)

    Timmo, Kristi; Kauk-Kuusik, Marit; Pilvet, Maris; Mikli, Valdek; Kaerber, Erki; Raadik, Taavi; Leinemann, Inga; Altosaar, Mare; Raudoja, Jaan [Department of Materials Science, Tallinn University of Technology, Tallinn (Estonia)

    2016-01-15

    In the present study, the recrystallization of polycrystalline SnS in different molten salts CdI{sub 2}, SnCl{sub 2} and KI as flux materials are presented. The recrystallization and growth of polycrystalline material in molten salts produces unique SnS monograin powders usable in monograin layer solar cells. XRD and Raman analysis revealed that single phase SnS powder can be obtained in KI at 740 C and in SnCl{sub 2} at 500 C. Long time heating of SnS in molten CdI{sub 2} was accompanied by chemical interaction between SnS and CdI{sub 2} that resulted in a mixture of CdS and Sn{sub 2}S{sub 3} crystals. SEM images showed that morphology of crystals can be controlled by the nature of the flux materials: needle-like Sn{sub 2}S{sub 3} together with round edged crystals of CdS in CdI{sub 2}, flat crystals of SnS with smooth surfaces in SnCl{sub 2} and well-formed SnS crystals with rounded edges in KI had been formed. The temperatures of phase transitions and/or the interactions of SnS and flux materials were determined by differential thermal analysis. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. Improved photovoltaic performance of heterostructured tetrapod-shaped CdSe/CdTe nanocrystals using C60 interlayer

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yanqin; Mastria, Rosanna; Fiore, Angela; Nobile, Concetta; Yin, Lunxiang; Cheng, Gang; Cingolani, Roberto; Manna, Liberato; Gigli, Giuseppe [National Nanotechnology Lab of CNR-INFM (NNL), University of Salento, Lecce (Italy); Biasiucci, Mariano [National Nanotechnology Lab of CNR-INFM (NNL), University of Salento, Lecce (Italy); Physical Department, University of Salerno, Baronissi (Italy); Cucolo, Anna Maria [Physical Department, University of Salerno, Baronissi (Italy)

    2009-11-26

    Photovoltaic (PV) devices based on CdSe/CdTe-C60 active layers, in which the nanocrystal and fullerene (C60) layers work as electron-donor and electron-acceptor/transport layers, respectively, were fabricated. Efficiencies up to 0.62% were reached in the hybrid cells. The PV performance was greatly improved with respect to that of CdSe/CdTe-P3HT- and CdSe/CdTe-based devices, fabricated as reference. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  10. 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.

  11. Effects of the Annealing Temperature and CdCl2 Treatment on the Photovoltaic Properties of the CdS/CdTe Solar Cell

    Science.gov (United States)

    Lee, Jae-Hyung; textscLee, Ho-Yeol; Park, Yong-Kwan; Shin, Sung-Ho; Park, Kwang-Ja

    1998-06-01

    Effects of the annealing temperature and CdCl2 treatment of CdTe films prepared by vacuum evaporation on structural properties of the CdTe films and photovoltaic properties of thin film CdS/CdTe solar cells were investigated. The crystal structure of as-deposited CdTe films was zincblende type with preferential orientation of the (111) plane parallel to the substrate. The preferential orientation of the (111) plane in CdTe films decreased, and the grain size of CdTe films increased with the increase of the annealing temperature and the CdCl2 treatment. As increasing annealing temperature, the conversion efficiency of the CdS/CdTe solar cells without and with CdCl2 was increased due to increasing grain size and improving crystalline of CdTe films. However, the efficiency of cells annealed at the temperature of higher than 500°C for cells without CdCl2 treatment and 450°C for cells with CdCl2 treatment was reduced because of increasing reverse saturation current density and series resistance.

  12. Influence of CdCl2 activation treatment on ultra-thin Cd1−xZnxS/CdTe solar cells

    International Nuclear Information System (INIS)

    Ultra-thin CdTe photovoltaic solar cells with an absorber thickness of 0.5 μm were produced by metal organic chemical vapour deposition onto indium tin oxide coated boroaluminosilicate glass. A wide band gap Cd1−xZnxS alloy window layer was employed to improve spectral response in the blue region of the solar spectrum. X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy were used to monitor changes in the chemical composition and microstructure of the Cd1−xZnxS/CdTe solar cell after varying the post-deposition CdCl2 activation treatment time and annealing temperature. The CdCl2 treatment leached Zn from the Cd1−xZnxS layer causing a redshift in the spectral response onset of window absorption. S diffusion occurred across the Cd1−xZnxS/CdTe interface, which was more pronounced as the CdCl2 treatment was increased. A CdTe1−ySy alloy was formed at the interface, which thickened with CdCl2 treatment time. Small concentrations of S (up to 2 at.%) were observed throughout the CdTe layer as the degree of CdCl2 treatment was increased. Greater S diffusion across the Cd1−xZnxS/CdTe interface caused the device open-circuit voltage (Voc) to increase. The higher Voc is attributed to enhanced strain relaxation and associated reduction of defects in the interface region as well as the increase in CdTe grain size. - Highlights: • Increased CdCl2 activation treatment resulted in loss of Zn from Cd1−xZnxS. • Sulphur diffusion into CdTe was enhanced with greater CdCl2 activation treatment. • Improvement to Voc correlated with increased sulphur diffusion into CdTe

  13. Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications

    OpenAIRE

    Anna Maria Mancini; Andrea Zappettini; Ezio Caroli; Leonardo Abbene; Stefano Del Sordo; Pietro Ubertini

    2009-01-01

    Over the last decade, cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status...

  14. 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.

  15. 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...

  16. High Flux Energy-Resolved Photon-Counting X-Ray Imaging Arrays with CdTe and CdZnTe for Clinical CT

    International Nuclear Information System (INIS)

    We have fabricated fast room-temperature energy dispersive photon counting x-ray imaging arrays using pixellated cadmium zinc (CdTe) and cadmium zinc telluride (CdZnTe) semiconductors. We have also fabricated fast application specific integrated circuits (ASICs) with a two dimensional (2D) array of inputs for readout from the CdZnTe sensors. The new CdTe and CdZnTe sensors have a 2D array of pixels with a 0.5 mm pitch and can be tiled in 2D. The new 2D ASICs have four energy discriminators per pixel with a linear energy response across the entire dynamic range for clinical CT. The ASICs can also be tiled in 2D and are designed to fit within the active area of the 2D sensors. We have measured several important performance parameters including; an output count rate (OCR) in excess of 20 million counts per second per square mm, an energy resolution of 7 keV full width at half maximum (FWHM) across the entire dynamic range, and a noise floor less than 20 keV. This is achieved by directly interconnecting the ASIC inputs to the pixels of the CdTE and CdZnTe sensors incurring very little additional capacitance. We present a comparison of the performance of the CdTe and CdZnTe sensors including the OCR, FWHM energy resolution, and noise floor. (authors)

  17. A longitudinally electron-beam-pumped CdHgTe laser

    Science.gov (United States)

    Borisov, B. G.; Lavrushin, B. M.; Nasibov, A. S.; Sypchenko, M. N.; Sherman, B. L.

    1989-10-01

    Lasers have been fabricated utilizing CdHgTe/CdTe heterostructures which were grown by the liquid-phase epitaxy method. The epitaxial CdHgTe layer was the active region of the cavity and the CdTe substrate was passive. Laser action in Cd(0.65)Hg(0.35)Te was achieved at a wavelength of 1.48 micron, a temperature of 77 K, and an electron energy of 50 keV. A maximum external differential efficiency of 3.4 percent was achieved.

  18. BRIEF COMMUNICATIONS: Longitudinal electron-beam-pumped CdHgTe laser

    Science.gov (United States)

    Borisov, B. G.; Lavrushin, B. M.; Nasibov, A. S.; Sypchenko, M. N.; Sherman, B. L.

    1989-10-01

    A CdHgTe/CdTe heterostructure grown by liquid phase epitaxy was used to develop a laser. The CdHgTe epitaxial laser formed the active region whilst the CdTe substrate formed the passive part of the resonator. At an electron energy of 50 keV and a temperature of 77 K, lasing was obtained at 1.48 μm in Cd0.65Hg0.35Te. The maximum external differential efficiency was 3.4%.

  19. Dynamics of photoexcited carrier relaxation and recombination in CdTe/CdS thin films

    Energy Technology Data Exchange (ETDEWEB)

    Levi, D.H.; Fluegel, B.D.; Ahrenkiel, R.K. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1996-05-01

    Efficiency-limiting defects in photovoltaic devices are readily probed by time-resolved spectroscopy. This paper presents the first direct optical measurements of the relaxation and recombination pathways of photoexcited carriers in the CdS window layer of CdTe/CdS polycrystalline thin films. Femtosecond time-resolved pump/probe measurements indicate the possible existence of a two-phase CdS/CdSTe layer, rather than a continuously graded alloy layer at the CdTe/CdS interface. Complementary time-resolved photoluminescence (PL) measurements show that the photoexcited carriers are rapidly captured by deep-level defects. The temporal and density-dependent properties of the photoluminescence prove that the large Stokes shift of the PL relative to the band edge is due to strong phonon coupling to deep-level defects in CdS. The authors suggest that modifications in the CdS processing may enhance carrier collection efficiency in the blue spectral region.

  20. Positron annihilation spectroscopy of vacancy-related defects in CdTe:Cl and CdZnTe:Ge at different stoichiometry deviations

    Science.gov (United States)

    Šedivý, L.; Čížek, J.; Belas, E.; Grill, R.; Melikhova, O.

    2016-02-01

    Positron annihilation spectroscopy (PAS) was used to examine the effect of defined Cd-rich and Te-rich annealing on point defects in Cl-doped CdTe and Ge-doped CdZnTe semi-insulating single crystals. The as-grown crystals contain open-volume defects connected with Cd vacancies . It was found that the Cd vacancies agglomerate into clusters coupled with Cl in CdTe:Cl, and in CdZnTe:Ge they are coupled with Ge donors. While annealing in Cd pressure reduces of the density, subsequent annealing in Te pressure restores . The CdTe:Cl contains negatively-charged shallow traps interpreted as Rydberg states of A-centres and representing the major positron trapping sites at low temperature. Positrons confined in the shallow traps exhibit lifetime, which is shorter than the CdTe bulk lifetime. Interpretation of the PAS data was successfully combined with electrical resistivity, Hall effect measurements and chemical analysis, and allowed us to determine the principal point defect densities.

  1. Nanosized Thin SnO2 Layers Doped with Te and TeO2 as Room Temperature Humidity Sensors

    Directory of Open Access Journals (Sweden)

    Biliana Georgieva

    2014-05-01

    Full Text Available In this paper the humidity sensing properties of layers prepared by a new method for obtaining doped tin oxide are studied. Different techniques—SEM, EDS in SEM, TEM, SAED, AES and electrical measurements—are used for detailed characterization of the thin layers. The as-deposited layers are amorphous with great specific area and low density. They are built up of a fine grained matrix, consisting of Sn- and Te-oxides, and a nanosized dispersed phase of Te, Sn and/or SnTe. The chemical composition of both the matrix and the nanosized particles depends on the ratio RSn/Te and the evaporation conditions. It is shown that as-deposited layers with RSn/Te ranging from 0.4 to 0.9 exhibit excellent characteristics as humidity sensors operating at room temperature—very high sensitivity, good selectivity, fast response and short recovery period. Ageing tests have shown that the layers possess good long-term stability. Results obtained regarding the type of the water adsorption on the layers’ surface help better understand the relation between preparation conditions, structure, composition and humidity sensing properties.

  2. Rapid synthesis of aqueous CdTe/CdSe core-shell quantum dots with highly photostability using microwave irradiation%微波辅助快速合成水溶性CdTe/CdSe核壳量子点

    Institute of Scientific and Technical Information of China (English)

    徐昕; 贺蓉; 崔大祥

    2011-01-01

    以巯基乙酸(TGA)作为稳定剂,用微波辅助法快速合成了水溶性CdTe/CdSe核壳量子点.比较了传统水热法和微波辅助法制备的量子点性能,研究了加热温度、反应物配比及CdTe量子点浓度对CdTe/CdSe核壳量子点的性能影响.研究结果表明,核壳结构的CdTe/CdSe量子点比单一的CdTe量子点具有更优异的光致发光强度和光稳定性.%In this paper, present a new procedure for the rapid synthesis of luminescent CdTe/CdSe core-shell quantum dots (QDs) in water phase by microwave irradiation method. The influences of microwave irradiation and a series of experimental variables, including heating temperature, molar ratios and concentration of precursors on the synthesis of QDs were investigated systematically. The results of high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) showed that the as-prepared nanocrystals had high crystallinity. In comparison with the plain CdTe QDs, both the photoluminescence quantum yield (PLQY) and photostability against UV irradiation of the CdTe/CdSe core-shell QDs have been greatly improved.

  3. Open-circuit voltage, fill factor, and efficiency of a CdS/CdTe solar cell

    International Nuclear Information System (INIS)

    The dependences of the open-circuit voltage, fill factor, and efficiency of the thin-film CdS/CdTe solar cell on the resistivity ρ and carrier lifetime τ in the absorbing CdTe layer were studied. In the common case in which the uncompensated acceptor concentration and the electron lifetime in the CdTe layer are within 1015-1016 cm-3 and 10-10-10-9 s, the calculation results correspond to the achieved efficiency of the best thin-film CdS/CdTe solar cells. It was shown that, by decreasing ρ and increasing τ in the absorbing CdTe layer, the open-circuit voltage, fill factor, and efficiency can be substantially increased, with their values approaching the theoretical limit for such devices.

  4. Resistivity and activation energy of CdTe electrodeposited at various Cd(II) concentrations

    Energy Technology Data Exchange (ETDEWEB)

    von Windheim, J.A.; Cocivera, M. (Guelph-Waterloo Centre for Graduate Work in Chemistry, Univ. of Guelph, Guelph, Ontario N1G 2WI (CA))

    1991-01-01

    This paper reports on two methods investigated for incorporating excess cadmium into CdTe electrodeposited from tri-n-butyl-phosphine telluride. These were: (i) variation of the Cd(II):Te concentration ratio in situ from 0.009 to 0.30 and (ii) the diffusion of metallic cadmium at high temperature. Resistivity and light response of various samples were studied after they had been removed from their substrates. Scanning electron microscopy was used to examine the morphology of some of the samples. For the series of films in which the Cd(II):Te concentration ratio was varied in situ the resistivity was found to increase moderately with increasing Cd(II) concentration. However, the activation energy was found to increase significantly only at the highest Cd(II):Te ratio, otherwise it remained more or less constant. The light response was similarly unaffected. When cadmium was diffused into the film, the light response was increased markedly and the resistivity generally decreased while the activation energy remained more or less the same.

  5. Resistivity and activation energy of CdTe electrodeposited at various Cd(II) concentrations

    International Nuclear Information System (INIS)

    This paper reports on two methods investigated for incorporating excess cadmium into CdTe electrodeposited from tri-n-butyl-phosphine telluride. These were: (i) variation of the Cd(II):Te concentration ratio in situ from 0.009 to 0.30 and (ii) the diffusion of metallic cadmium at high temperature. Resistivity and light response of various samples were studied after they had been removed from their substrates. Scanning electron microscopy was used to examine the morphology of some of the samples. For the series of films in which the Cd(II):Te concentration ratio was varied in situ the resistivity was found to increase moderately with increasing Cd(II) concentration. However, the activation energy was found to increase significantly only at the highest Cd(II):Te ratio, otherwise it remained more or less constant. The light response was similarly unaffected. When cadmium was diffused into the film, the light response was increased markedly and the resistivity generally decreased while the activation energy remained more or less the same

  6. First-principles study of roles of Cu and Cl in polycrystalline CdTe

    International Nuclear Information System (INIS)

    Cu and Cl treatments are important processes to achieve high efficiency polycrystalline cadmium telluride (CdTe) solar cells, thus it will be beneficial to understand the roles they play in both bulk CdTe and CdTe grain boundaries (GBs). Using first-principles calculations, we systematically study Cu and Cl-related defects in bulk CdTe. We find that Cl has only a limited effect on improving p-type doping and too much Cl can induce deep traps in bulk CdTe, whereas Cu can enhance p-type doping of bulk CdTe. In the presence of GBs, we find that, in general, Cl and Cu will prefer to stay at GBs, especially for those with Te-Te wrong bonds, in agreement with experimental observations

  7. First-principles study of roles of Cu and Cl in polycrystalline CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ji-Hui; Park, Ji-Sang; Metzger, Wyatt [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Yin, Wan-Jian [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); College of Physics, Optoelectronics and Energy and Collaborative, Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006 (China); Wei, Su-Huai, E-mail: suhuaiwei@csrc.ac.cn [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Beijing Computational Science Research Center, Beijing 100094 (China)

    2016-01-28

    Cu and Cl treatments are important processes to achieve high efficiency polycrystalline cadmium telluride (CdTe) solar cells, thus it will be beneficial to understand the roles they play in both bulk CdTe and CdTe grain boundaries (GBs). Using first-principles calculations, we systematically study Cu and Cl-related defects in bulk CdTe. We find that Cl has only a limited effect on improving p-type doping and too much Cl can induce deep traps in bulk CdTe, whereas Cu can enhance p-type doping of bulk CdTe. In the presence of GBs, we find that, in general, Cl and Cu will prefer to stay at GBs, especially for those with Te-Te wrong bonds, in agreement with experimental observations.

  8. First-principles study of roles of Cu and Cl in polycrystalline CdTe

    Science.gov (United States)

    Yang, Ji-Hui; Yin, Wan-Jian; Park, Ji-Sang; Metzger, Wyatt; Wei, Su-Huai

    2016-01-01

    Cu and Cl treatments are important processes to achieve high efficiency polycrystalline cadmium telluride (CdTe) solar cells, thus it will be beneficial to understand the roles they play in both bulk CdTe and CdTe grain boundaries (GBs). Using first-principles calculations, we systematically study Cu and Cl-related defects in bulk CdTe. We find that Cl has only a limited effect on improving p-type doping and too much Cl can induce deep traps in bulk CdTe, whereas Cu can enhance p-type doping of bulk CdTe. In the presence of GBs, we find that, in general, Cl and Cu will prefer to stay at GBs, especially for those with Te-Te wrong bonds, in agreement with experimental observations.

  9. Photoluminescence waveguiding in CdSe and CdTe QDs-PMMA nanocomposite films

    Energy Technology Data Exchange (ETDEWEB)

    Suarez, I; Gordillo, H; Abargues, R; Albert, S; Martinez-Pastor, J, E-mail: isaac.suarez@uv.es [UMDO - Unidad Asociada al CSIC-IMM, Instituto de Ciencia de los Materiales, Universidad de Valencia, PO Box 22085, 46071 Valencia (Spain)

    2011-10-28

    In this paper, active planar waveguides based on the incorporation of CdSe and CdTe nanocrystal quantum dots in a polymer matrix are demonstrated. In the case of doping the polymer with both types of quantum dots, the nanocomposite film guides both emitted colors, green (550 nm, CdTe) and orange (600 nm, CdSe). The optical pumping laser can be coupled not only with a standard end-fire coupling system, but also directing the beam to the surface of the sample, indicating a good absorption cross-section and waveguide properties. To achieve these results, a study of the nanocomposite optical properties as a function of the nanocrystal concentration is presented and the optimum conditions are found for waveguiding.

  10. Photoluminescence studies of type-II CdSe/CdTe superlattices

    International Nuclear Information System (INIS)

    CdSe/CdTe type-II superlattices grown on GaSb substrates by molecular beam epitaxy are studied using time-resolved and steady-state photoluminescence (PL) spectroscopy at 10 K. The relatively long carrier lifetime of 188 ns observed in time-resolved PL measurements shows good material quality. The steady-state PL peak position exhibits a blue shift with increasing excess carrier concentration. Self-consistent solutions of the Schrödinger and Poisson equations show that this effect can be explained by band bending as a result of the spatial separation of electrons and holes, which is critical confirmation of a strong type-II band edge alignment between CdSe and CdTe.

  11. 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.).

  12. INCORPORATION DU PHOSPHORE DANS CdTe PAR RECUIT LASER

    OpenAIRE

    Uzan, C.; Legros, R.; Marfaing, Y.

    1983-01-01

    La méthode du recuit laser a été utilisée pour incorporer du phosphore dans CdTe à partir d'une couche de Cd3P2 déposée en surface. La caractérisation par photoluminescence et mesure de profil à l'analyseur ionique montre le caractère actif du phosphore introduit et permet d'évaluer à 1018cm-3 la concentration atteinte à 1 µm de profondeur.

  13. Digital pulse-shape processing for CdTe detectors

    International Nuclear Information System (INIS)

    CdTe detectors suffer from low photo-peak efficiency and poor energy resolution. These problems are due to the drift properties of charge carriers in CdTe where particularly the holes have small mobility and trapping time. This is reflected in the amplitude and the shape of the detector output. To improve this situation a digital method is introduced where a sampling ADC is used to make a detailed measurement of the time evolution of the pulse. The measured pulse shape is fitted with a model. For the detector under study a model taking hole trapping into account significantly improves the photo-peak efficiency. The description of the hole component is, however, not fully satisfactory since for pulses with a large hole contribution a broadening of the full-energy peak occurs. Allowing for inhomogeneities in the detector material within the model partially remedies this deficiency

  14. Digital pulse-shape processing for CdTe detectors

    CERN Document Server

    Bargholtz, C; Maartensson, L; Wachtmeister, S

    2001-01-01

    CdTe detectors suffer from low photo-peak efficiency and poor energy resolution. These problems are due to the drift properties of charge carriers in CdTe where particularly the holes have small mobility and trapping time. This is reflected in the amplitude and the shape of the detector output. To improve this situation a digital method is introduced where a sampling ADC is used to make a detailed measurement of the time evolution of the pulse. The measured pulse shape is fitted with a model. For the detector under study a model taking hole trapping into account significantly improves the photo-peak efficiency. The description of the hole component is, however, not fully satisfactory since for pulses with a large hole contribution a broadening of the full-energy peak occurs. Allowing for inhomogeneities in the detector material within the model partially remedies this deficiency.

  15. Charge transport properties of CdMnTe radiation detectors

    Directory of Open Access Journals (Sweden)

    Prokopovich D. A.

    2012-10-01

    Full Text Available Growth, fabrication and characterization of indium-doped cadmium manganese telluride (CdMnTe radiation detectors have been described. Alpha-particle spectroscopy measurements and time resolved current transient measurements have yielded an average charge collection efficiency approaching 100 %. Spatially resolved charge collection efficiency maps have been produced for a range of detector bias voltages. Inhomogeneities in the charge transport of the CdMnTe crystals have been associated with chains of tellurium inclusions within the detector bulk. Further, it has been shown that the role of tellurium inclusions in degrading charge collection is reduced with increasing values of bias voltage. The electron drift velocity was calculated from the rise time distribution of the preamplifier output pulses at each measured bias. From the dependence of drift velocity on applied electric field the electron mobility was found to be μn = (718 ± 55 cm2/Vs at room temperature.

  16. Digital pulse-shape processing for CdTe detectors

    Science.gov (United States)

    Bargholtz, Chr.; Fumero, E.; Mårtensson, L.; Wachtmeister, S.

    2001-09-01

    CdTe detectors suffer from low photo-peak efficiency and poor energy resolution. These problems are due to the drift properties of charge carriers in CdTe where particularly the holes have small mobility and trapping time. This is reflected in the amplitude and the shape of the detector output. To improve this situation a digital method is introduced where a sampling ADC is used to make a detailed measurement of the time evolution of the pulse. The measured pulse shape is fitted with a model. For the detector under study a model taking hole trapping into account significantly improves the photo-peak efficiency. The description of the hole component is, however, not fully satisfactory since for pulses with a large hole contribution a broadening of the full-energy peak occurs. Allowing for inhomogeneities in the detector material within the model partially remedies this deficiency.

  17. Digital pulse-shape processing for CdTe detectors

    Energy Technology Data Exchange (ETDEWEB)

    Bargholtz, Chr.; Fumero, E.; Maartensson, L. E-mail: martensson@physto.se; Wachtmeister, S

    2001-09-21

    CdTe detectors suffer from low photo-peak efficiency and poor energy resolution. These problems are due to the drift properties of charge carriers in CdTe where particularly the holes have small mobility and trapping time. This is reflected in the amplitude and the shape of the detector output. To improve this situation a digital method is introduced where a sampling ADC is used to make a detailed measurement of the time evolution of the pulse. The measured pulse shape is fitted with a model. For the detector under study a model taking hole trapping into account significantly improves the photo-peak efficiency. The description of the hole component is, however, not fully satisfactory since for pulses with a large hole contribution a broadening of the full-energy peak occurs. Allowing for inhomogeneities in the detector material within the model partially remedies this deficiency.

  18. 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.).

  19. Dependence of CdTe response of bias history

    Energy Technology Data Exchange (ETDEWEB)

    Sites, J.R.; Sasala, R.A.; Eisgruber, I.L. [Colorado State Univ., Boulder, CO (United States)

    1995-11-01

    Several time-dependent effect have been observed in CdTe cells and modules in recent years. Some appear to be related to degradation at the back contact, some to changes in temperature at the thin-film junction, and some to the bias history of the cell or module. Back-contact difficulties only occur in some cases, and the other two effects are reversible. Nevertheless, confusion in data interpretation can arise when these effects are not characterized. This confusion can be particularly acute when more than one time-dependent effect occurs during the same measurement cycle. The purpose of this presentation is to help categorize time-dependent effects in CdTe and other thin-film cells to elucidate those related to bias history, and to note differences between cell and module analysis.

  20. Point Defect Characterization in CdZnTe

    Energy Technology Data Exchange (ETDEWEB)

    Gul,R.; Li, Z.; Bolotnikov, A.; Keeter, K.; Rodriguez, R.; James, R.

    2009-03-24

    Measurements of the defect levels and performance testing of CdZnTe detectors were performed by means of Current Deep Level Transient Spectroscopy (I-DLTS), Transient Charge Technique (TCT), Current versus Voltage measurements (I-V), and gamma-ray spectroscopy. CdZnTe crystals were acquired from different commercial vendors and characterized for their point defects. I-DLTS studies included measurements of defect parameters such as energy levels in the band gap, carrier capture cross sections, and defect densities. The induced current due to laser-generated carriers was measured using TCT. The data were used to determine the transport properties of the detectors under study. A good correlation was found between the point defects in the detectors and their performance.

  1. Charge transport properties of CdMnTe radiation detectors

    Energy Technology Data Exchange (ETDEWEB)

    Kim K.; Rafiel, R.; Boardman, M.; Reinhard, I.; Sarbutt, A.; Watt, G.; Watt, C.; Uxa, S.; Prokopovich, D.A.; Belas, E.; Bolotnikov, A.E.; James, R.B.

    2012-04-11

    Growth, fabrication and characterization of indium-doped cadmium manganese telluride (CdMnTe)radiation detectors have been described. Alpha-particle spectroscopy measurements and time resolved current transient measurements have yielded an average charge collection efficiency approaching 100 %. Spatially resolved charge collection efficiency maps have been produced for a range of detector bias voltages. Inhomogeneities in the charge transport of the CdMnTe crystals have been associated with chains of tellurium inclusions within the detector bulk. Further, it has been shown that the role of tellurium inclusions in degrading chargecollection is reduced with increasing values of bias voltage. The electron transit time was determined from time of flight measurements. From the dependence of drift velocity on applied electric field the electron mobility was found to be n = (718 55) cm2/Vs at room temperature.

  2. Poly CdTe thin films solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Marfaing, Y.

    1982-01-01

    CdTe is potentially one of the most interesting materials for the photovoltaic conversion of solar energy. The width of its forbidden band of 1.5 eV puts it to the maximum of the theoretical yield curve (24%). Its high coefficient of optical absorption in the main band allows the use of thin films (2 to 3 microns). It is appropriate for production of thin polycristalline films with good optical and photoelectrical properties, which is probably due to its ionic character. The goal of the research performed as part of this contract is to determine the optimum conditions for the use of CdTe as photovoltaic converter. The authors think that the virtual efficiency of this material calls for confirmation and evidence provided by a systematic and profound investigation.

  3. Interaction of CdTe/CdS quantum dots with antibodies

    Institute of Scientific and Technical Information of China (English)

    Chen Shi; Xiang Yi Huang; Chao Qing Dong; Hong Jin Chen; Ji Cun Ren

    2009-01-01

    In the study,we observed the strong adsorption of CdTe/CdS QDs to antibodies and the formation of QDs-antibodies conjugates.Capillary electrophoresis with laser-induced fluorescence detection(CE-LIF),fluorescence spectrometry and fluorescence correlation spectroscopy(FCS)were used to characterize the QDs conjugates with antibody.We found that the QDs-antibody conjugates possessed high fluorescence,small hydrodynamic radii and good stability in aqueous solution.

  4. Mass spectrometric study of the phase boundaries of the CdS-CdTe system

    Energy Technology Data Exchange (ETDEWEB)

    Nunoue, S.Y.; Hemmi, T.; Kato, E. (Dept. of Materials Science and Engineering, Waseda Univ., Shinjuku-ku Tokyo 160 (JP))

    1990-04-01

    An isothermal evaporation method by means of a Knudsen cell-mass spectrometer combination has been applied to the determination of the phase boundaries in the CdS-CdTe system in the temperature range of 650{degrees}--720{degrees}C. The phase boundaries obtained were compared with published phase boundaries. The advantages of the present method over the x-ray diffraction technique are discussed.

  5. Heterojunction properties of electrodeposited CdTe/CdS solar cells

    Science.gov (United States)

    Rakhshani, A. E.

    2001-10-01

    Solar cells of p-CdTe/n-CdS structure with a conversion efficiency of 10%±1% (AM1 spectrum, 127 mW/cm2 irradiance) were prepared by electrodeposition of CdTe on CdS-coated conducting glass. CdS was coated by chemical bath deposition. The tin-oxide conducting glass was prepared by the spray pyrolysis technique. The current-voltage, capacitance-voltage, photocurrent-voltage, photocurrent spectroscopy, and photoinduced current transient spectroscopy measurements proved to be powerful tools for the characterization of junction. The concentration of donors and acceptors in both sides of the junction are comparable, in the range of 1016cm-3. The cell built-in potential is 1.20 V from which 0.65 V drops across the depletion width of CdTe. From the analysis of experimental data to construct the energy band diagram, it becomes evident that an electric dipole layer must exist at the CdTe/CdS interface. The presence of this layer is associated with a discontinuity of electrostatic potential at the interface by 0.28 V and a conduction-band spike of 64 meV. The conduction-band spike and an interfacial recombination center are accountable for the collection losses of photogenerated carriers. The recombination center that is likely related to the interstitial cadmium defect is energetically located 0.63 eV below the conduction-band edge and has a capture cross section of 8.8×10-12 cm2. 2001 American Institute of Physics.

  6. CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms

    OpenAIRE

    Denise Feder; Menna-Barreto, Rubem F. S.; Cesar, Carlos L.; Santos-Mallet, Jacenir R.; Suzete A.O. Gomes; Cecilia Stahl Vieira; Almeida, Diogo B.

    2011-01-01

    Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellul...

  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. One-Pot Aqueous Phase Synthesis of CdTe and CdTe/ZnS Core/Shell Quantum Dots.

    Science.gov (United States)

    Zhou, Beiying; Yang, Fengjiu; Zhang, Xin; Cheng, Wenyan; Luo, Wei; Wang, Lianjun; Jiang, Wan

    2016-06-01

    A facile and economical one-pot strategy has been developed for the synthesis of water-solute CdTe and CdTe/ZnS core/shell quantum dots (QDs) using tellurium dioxide (TeO2) as a tellurium precursor and thioglycolic acid (TGA) as stabilizer without any pre-treatment and inert atmosphere protection. As-synthesized QDs were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction spectroscopy (EDS), X-ray powder diffraction (XRD), UV-vis and photoluminescence (PL). The spherical particles were uniformly distributed with the average diameters of 3.2 nm (CdTe QDs) and -5 nm (CdTe/ZnS QDs). By altering the reaction conditions, the emission wavelengths of the CdTe core QDs and CdTe/ZnS core/shell QDs could be tuned from 508 to 574 nm and 526 to 600 nm with narrow full widths at half maximum (FWHM) of 33 to 58 nm, respectively. Meanwhile, on the optimum condition, the luminescence efficiency of CdTe/ZnS QDs can achieve to 74%, which was higher than that of CdTe core QDs (24%). PMID:27427627

  9. Effect of ZnTe/ZnTe:Cu complex back-contact on device characteristics of CdTe solar cells

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    ZnTe/ZnTe:Cu complex layers deposited by vacuum co-evaporation have been in- troduced to CdS/CdTe solar cells. The C-V and I-V curves have been investigated and the effects of un-doped ZnTe layer thickness as well as annealing temperatures on I-V characteristics of CdTe solar cells have been studied. The results show that the “roll over” and “cross over” phenomena of dark and light I-V curves can be eliminated by use of ZnTe/ZnTe:Cu layer and the fill factor for a typical sample has increased to 73%, where there is no high resistance transparent layer. The reasons have been discussed combined with the energy band diagram of CdTe solar cells.

  10. Simulation of charge transport in pixelated CdTe

    OpenAIRE

    Kolstein, M.; Ariño, G.; Chmeissani, M.; De Lorenzo, G.

    2014-01-01

    The Voxel Imaging PET (VIP) Pathfinder project intends to show the advantages of using pixelated semiconductor technology for nuclear medicine applications to achieve an improved image reconstruction without efficiency loss. It proposes designs for Positron Emission Tomography (PET), Positron Emission Mammography (PEM) and Compton gamma camera detectors with a large number of signal channels (of the order of 106). The design is based on the use of a pixelated CdTe Schottky detector to have op...

  11. Highly luminescent water-soluble CdTe quantum dots

    OpenAIRE

    Wuister, SF; Swart, A.N.; van Driel, F; Hickey, SG; Donega, CD; Swart, Ingmar

    2003-01-01

    Colloidal CdTe quantum dots prepared in TOP/DDA (trioctylphosphine/dodecylamine) are transferred into water by the use of aminoethanethiol.HCl (AET) or mercaptopropionic acid (MPA). This results in an increase in the photoluminescence quantum efficiency and a longer exciton lifetime. For the first time, water-soluble semiconductor nanocrystals presenting simultaneously high band-edge photoluminescence quantum efficiencies (as high as 60% at room temperature), monoexponential exciton decays, a...

  12. Determining energy production of CdTe photovoltaic system

    OpenAIRE

    Virtič, Peter; Šlamberger, Jan

    2015-01-01

    This paper presents a method for determining energy production of Cadmium-Telluride photovoltaic system, which has a different working performance than the most used Silicon photovoltaic systems. The main difference is sensitivity to the temperature and the solar irradiance. The CdTe cells are less sensitive to the temperature and in contrast to the Si Cells they have a higher efficiency at lower irradiance.

  13. CdTe Nanowires studied by Transient Absorption Microscopy

    Directory of Open Access Journals (Sweden)

    Kuno M.

    2013-03-01

    Full Text Available Transient absorption measurements were performed on single CdTe nanowires. The traces show fast decays that were assigned to charge carrier trapping at surface states. The observed power dependence suggests the existence of a trap-filling mechanism. Acoustic phonon modes were also observed, which were assigned to breathing modes of the nanowires. Both the fundamental breathing mode and the first overtone were observed, and the dephasing times provide information about how the nanowires interact with their environment.

  14. Two-electron DX state in CdTe:In

    International Nuclear Information System (INIS)

    In this paper we investigate electron emission (capture form) to DX state of indium in CdTe by means of high pressure freeze out cycle and steady state photo-conductivity experiments. The results indicate that the DX state is occupied by two electrons. A comparison with deep level transient spectroscopy data shows that two-electron emission occurs at low temperatures, while one-electron emission takes place at high temperatures. (author)

  15. Two-electron DX state in CdTe:In

    Energy Technology Data Exchange (ETDEWEB)

    Skierbiszewski, C.; Wisniewski, P.; Litwin-Staszewska, E.; Suski, T. [High Pressure Research Center, Polish Academy of Science, Warsaw (Poland); Wilamowski, Z.; Zakrzewski, A.K.; Karczewski, G. [Institute of Physics, Polish Academy of Sciences, Warsaw (Poland); Jantsch, W. [Institut fuer Experimentalphysik, J. Kepler Universitaet, Linz (Austria)

    1996-12-31

    In this paper we investigate electron emission (capture form) to DX state of indium in CdTe by means of high pressure freeze out cycle and steady state photo-conductivity experiments. The results indicate that the DX state is occupied by two electrons. A comparison with deep level transient spectroscopy data shows that two-electron emission occurs at low temperatures, while one-electron emission takes place at high temperatures. (author) 6 refs, 1 fig

  16. Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

    Energy Technology Data Exchange (ETDEWEB)

    Si, Weidong, E-mail: wds@bnl.gov, E-mail: qiangli@bnl.gov; Zhang, Cheng; Wu, Lijun; Ozaki, Toshinori; Gu, Genda; Li, Qiang, E-mail: wds@bnl.gov, E-mail: qiangli@bnl.gov [Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973 (United States)

    2015-08-31

    Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF{sub 2} crystalline substrates, respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk. With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.

  17. Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

    International Nuclear Information System (INIS)

    Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF2 crystalline substrates, respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk. With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors

  18. Time-resolved and temperature-dependent photoluminescence studies on CdTe/ZnTe quantum dots with different ZnTe capping layer thicknesses

    International Nuclear Information System (INIS)

    We investigate the effects of the capping layer thickness on the optical properties of CdTe/ZnTe quantum dots (QDs). The time-resolved photoluminescence (PL) measurements used to study the carrier dynamics show a shorter decay time for CdTe/ZnTe QDs with decreasing thickness of the ZnTe cap layer due to an increase in the nonradiative surface recombination rate. The activation energy of the electrons confined in the CdTe/ZnTe QDs, as obtained from the temperature-dependent PL spectra, decreases with the thickness of the ZnTe cap layer. These results indicate that the carrier dynamics and activation energy of CdTe/ZnTe QDs are affected by the thickness of the ZnTe cap layer. - Highlights: ► Optical properties of CdTe/ZnTe quantum dots (QDs) are investigated. ► Different ZnTe capping layer thicknesses are used for the QDs. ► QD photoluminescence peak shifts to a higher energy with cap layer thickness increase. ► Decay time of QDs decreases with cap layer thickness decrease. ► Activation energy of QDs increases with cap layer thickness increase

  19. CdTe/Si复合衬底Ex-situ退火研究%Research of CdTe/Si composite substrate by annealing

    Institute of Scientific and Technical Information of China (English)

    刘铭; 周立庆; 巩锋; 常米; 王经纬; 王丛

    2012-01-01

    One of the main methods to reduce the HgCdTe/Si dislocation density is to reduce CdTe/Si composite substrate's dislocation density. How to improve the CdTe/Si composite substrate's crystal quality is very critical for HgCdTe/Si FPAs. The general methods to reduce CdTe/Si composite substrate dislocation density are: growth of su-perlattice buffer layer,Si substrate misorientention and annealing etc. This paper presents the result of the influence on the quality of CdTe/Si composite substrate by Ex-situ annealing. The research indicates that after Ex-situ annealing, the EPD of composite substrate can reduce to 4. 2 × 105 cm-2 ,and the FWHM can reduce to 60 arcsec.%复合衬底CdTe/ZnTe/Si的晶体质量是导致随后外延的HgCdTe外延膜高位错密度的主要原因之一,因此如何提高复合衬底CdTe/Si晶体质量是确保硅基碲镉汞走上工程化的关键所在.降低复合衬底CdTe/Si位错密度方法一般有:生长超晶格缓冲层、衬底偏向、In-situ退火和Ex-situ退火等,本文主要研究Ex-situ退火对复合衬底CdTe/Si晶体质量的影响.研究表明复合衬底经过Ex-situ退火后位错密度最好值达4.2×105 cm-2,双晶半峰宽最好值达60arcsec .

  20. Assessment of Hot-Carrier Effects on Charge Separation in Type-II CdS/CdTe Heterostructured Nanorods.

    Science.gov (United States)

    Okano, Makoto; Sakamoto, Masanori; Teranishi, Toshiharu; Kanemitsu, Yoshihiko

    2014-09-01

    Charge separation in semiconducting materials is an essential process that determines the efficiency of photovoltaic devices and photocatalysts. Herein, we report the charge-separation dynamics in type-II CdS/CdTe heterostructured nanorods revealed by femtosecond transient-absorption (TA) measurements with a broad-band white-light probe. Under selective excitation of the CdTe segment, bleaching signals at the band gap energy of CdS were clearly observed with a rise component on a subpicosecond time scale, which indicates efficient electron transfer from CdTe to CdS. The pump-energy dependence of the TA dynamics shows that hot electrons rapidly relax to the bottom of the conduction band of CdTe, and then the electrons transfer to the CdS segment. PMID:26278242

  1. CdSe/CdTe type-II superlattices grown on GaSb (001) substrates by molecular beam epitaxy

    International Nuclear Information System (INIS)

    CdSe/CdTe superlattices are grown on GaSb substrates using molecular beam epitaxy. X-ray diffraction measurements and cross-sectional transmission electron microscopy images indicate high crystalline quality. Photoluminescence (PL) measurements show the effective bandgap varies with the superlattice layer thicknesses and confirm the CdSe/CdTe heterostructure has a type-II band edge alignment. The valence band offset between unstrained CdTe and CdSe is determined as 0.63 ± 0.06 eV by fitting the measured PL peak positions using the envelope function approximation and the Kronig-Penney model. These results suggest that CdSe/CdTe superlattices are promising candidates for multi-junction solar cells and other optoelectronic devices based on GaSb substrates.

  2. Novel synthesis of β-cyclodextrin functionalized CdTe quantum dots as luminescent probes

    International Nuclear Information System (INIS)

    Graphical abstract: A novel, inexpensive procedure for the preparation of highly fluorescent and water-soluble CdTe quantum dots (QDs) using β-cyclodextrin (β-CD) as surface-coating agents was fabricated through the substitution reaction at the C-6 position of mono-6-deoxy-6-(p-tolylsulfonyl)-cyclodextrin (6-TsO-β-CD) by the -NH2 of (3-aminopropyl)triethoxysilane-coated CdTe QDs (APTES/CdTe QDs) under mild conditions. The results revealed that β-CD/APTES/CdTe QDs simultaneously possessed unique optical properties of QDs and excellent molecules recognition ability of β-CD through combining their individual distinct advantages. Highlights: ► A novel preparation of β-cyclodextrin (β-CD) functionalized CdTe quantum dots has been constructed. ► The chemicals and reagents used are inexpensive and straightforward. ► This nanomaterial shows highly fluorescence and the molecular recognition properties. - Abstract: A novel, inexpensive procedure for the preparation of highly fluorescent and water-soluble CdTe quantum dots (QDs) using β-cyclodextrin (β-CD) as surface-coating agents was fabricated through the substitution reaction at the C-6 position of mono-6-deoxy-6-(p-tolylsulfonyl)-cyclodextrin (6-TsO-β-CD) by the -NH2 of (3-aminopropyl)triethoxysilane-coated CdTe QDs (APTES/CdTe QDs) under mild conditions. X-ray powder diffraction (XRD), Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), ultraviolet and visible (UV–vis) spectrophotometer, and fluorescence (FL) spectrophotometer were used to characterize the obtained nanoparticles, which proved that the CdTe QDs have been effectively modified by β-CD. The quantum yields (QYs) of CdTe QDs, APTES/CdTe QDs and β-CD/APTES/CdTe QDs in water comparative to Rhodamine 6G were about 17%, 12%, and 9%, respectively. A pair of isomer o,p′-DDT and p,p′-DDT was chosen as the template molecules to evaluate the molecular recognition properties of β-CD/APTES/CdTe

  3. Novel synthesis of {beta}-cyclodextrin functionalized CdTe quantum dots as luminescent probes

    Energy Technology Data Exchange (ETDEWEB)

    Chen Xiaofeng; Zhou Min; Chang Yanping [State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000 (China); Department of Chemistry, Lanzhou University, Lanzhou 730000 (China); Ren Cuiling [State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000 (China); Department of Chemistry, Lanzhou University, Lanzhou 730000 (China); Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, Lanzhou 730000 (China); Chen Hongli, E-mail: hlchen@lzu.edu.cn [State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000 (China); Department of Chemistry, Lanzhou University, Lanzhou 730000 (China); Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, Lanzhou 730000 (China); Chen Xingguo [State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000 (China); Department of Chemistry, Lanzhou University, Lanzhou 730000 (China); Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, Lanzhou 730000 (China)

    2012-12-15

    Graphical abstract: A novel, inexpensive procedure for the preparation of highly fluorescent and water-soluble CdTe quantum dots (QDs) using {beta}-cyclodextrin ({beta}-CD) as surface-coating agents was fabricated through the substitution reaction at the C-6 position of mono-6-deoxy-6-(p-tolylsulfonyl)-cyclodextrin (6-TsO-{beta}-CD) by the -NH{sub 2} of (3-aminopropyl)triethoxysilane-coated CdTe QDs (APTES/CdTe QDs) under mild conditions. The results revealed that {beta}-CD/APTES/CdTe QDs simultaneously possessed unique optical properties of QDs and excellent molecules recognition ability of {beta}-CD through combining their individual distinct advantages. Highlights: Black-Right-Pointing-Pointer A novel preparation of {beta}-cyclodextrin ({beta}-CD) functionalized CdTe quantum dots has been constructed. Black-Right-Pointing-Pointer The chemicals and reagents used are inexpensive and straightforward. Black-Right-Pointing-Pointer This nanomaterial shows highly fluorescence and the molecular recognition properties. - Abstract: A novel, inexpensive procedure for the preparation of highly fluorescent and water-soluble CdTe quantum dots (QDs) using {beta}-cyclodextrin ({beta}-CD) as surface-coating agents was fabricated through the substitution reaction at the C-6 position of mono-6-deoxy-6-(p-tolylsulfonyl)-cyclodextrin (6-TsO-{beta}-CD) by the -NH{sub 2} of (3-aminopropyl)triethoxysilane-coated CdTe QDs (APTES/CdTe QDs) under mild conditions. X-ray powder diffraction (XRD), Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), ultraviolet and visible (UV-vis) spectrophotometer, and fluorescence (FL) spectrophotometer were used to characterize the obtained nanoparticles, which proved that the CdTe QDs have been effectively modified by {beta}-CD. The quantum yields (QYs) of CdTe QDs, APTES/CdTe QDs and {beta}-CD/APTES/CdTe QDs in water comparative to Rhodamine 6G were about 17%, 12%, and 9%, respectively. A pair

  4. Infrared Illuminated CdZnTe detectors with improved performance

    International Nuclear Information System (INIS)

    It was found that IR illumination of a properly chosen wavelength and intensity can significantly improve spectrometric characteristics of CdZnTe quasi-hemispherical detectors [1]. Improving of the spectrometric characteristics is due to improvement of uniformity of charge collection by the detector volume. For operation at room temperature the optimal wavelength of IR illumination is about 940 nm, but for operation at lower temperature of -20 deg. C the optimal wavelengths of IR illumination is about 1050 nm. Infrared illumination can be performed using conventional low-power IR LEDs. Application of SMD LEDs allows produce miniature detection probes with IR illuminated CdZnTe detectors. We have fabricated and tested a variety of detection probes with CdZnTe quasi-hemispherical detectors from the smallest with volumes of 1-5 mm3 to larger with volumes of 1.5 cm3 and 4.0 cm3. The use of IR illumination significantly improves spectrometric characteristics of the probes operating at room temperature, especially probes with detectors of large volumes. The probe with the detector of 4 cm3 without IR illumination had energy resolution of 24.2 keV at 662 keV and of 12.5 keV with IR illumination. (authors)

  5. HgCdTe APDs for free space optical communications

    Science.gov (United States)

    Rothman, J.; Lasfargues, G.; Abergel, J.

    2015-10-01

    HgCdTe avalanche photodiode single element detectors have been developed for a large scope of photon starved applications. The present communication is dedicated to use of these detectors for free space optical communications. In this perspective we present and discuss the sensitivity and bandwidth that has been measured directly on HgCdTe APDs and on detector modules. In particular, we report on the performance of TEC cooled large area detectors with sensitive diameters ranging from 30- 200 μm, characterised by detector gains of 2- 20 V/μW and noise equivalent input power of 0.1-1 nW for bandwidths ranging from 20 to 400 MHz. One of these detectors has been used during the lunar laser communication demonstration (LLCD) and the results The perspectives for high data rate transmission is estimated from the results of impulse response measurements on HgCdTe APDs. These results indicate that bandwidths close to 10 GHz can be achieved in these devices. The associated sensitivity at an APD gain of 100 is estimated to be below 4 photons rms (NEP<10 nW) for APDs operated at 300 K.

  6. Alpha particle response characterization of CdZnTe

    Energy Technology Data Exchange (ETDEWEB)

    Amman, Mark; Lee, Julie S.; Luke, Paul N.

    2001-06-28

    The coplanar-grid as well as other electron-only detection techniques are effective in overcoming some of the material problems of CdZnTe and, consequently, have led to efficient gamma-ray detectors with good energy resolution while operating at room temperature. The performance of these detectors is limited by the degree of uniformity in both electron generation and transport. Despite recent progress in the growth of CdZnTe material, small variations in these properties remain a barrier to the widespread success of such detectors. Alpha-particle response characterization of CdZnTe crystals fabricated into simple planar detectors is an effective tool to accurately study electron generation and transport. We have used a finely collimated alpha source to produce two-dimensional maps of detector response. A clear correlation has been observed between the distribution of precipitates near the entrance contact on some crystals and their alpha-response maps. Further studies are ongoing to determine the mechanism for the observed response variations and the reason for the correlation. This paper presents the results of these studies and their relationship to coplanar-grid gamma-ray detector performance.

  7. Alpha particle response characterization of CdZnTe

    International Nuclear Information System (INIS)

    The coplanar-grid as well as other electron-only detection techniques are effective in overcoming some of the material problems of CdZnTe and, consequently, have led to efficient gamma-ray detectors with good energy resolution while operating at room temperature. The performance of these detectors is limited by the degree of uniformity in both electron generation and transport. Despite recent progress in the growth of CdZnTe material, small variations in these properties remain a barrier to the widespread success of such detectors. Alpha-particle response characterization of CdZnTe crystals fabricated into simple planar detectors is an effective tool to accurately study electron generation and transport. We have used a finely collimated alpha source to produce two-dimensional maps of detector response. A clear correlation has been observed between the distribution of precipitates near the entrance contact on some crystals and their alpha-response maps. Further studies are ongoing to determine the mechanism for the observed response variations and the reason for the correlation. This paper presents the results of these studies and their relationship to coplanar-grid gamma-ray detector performance

  8. Studium vlastností CdTe senzorů

    OpenAIRE

    Vašíček, Martin

    2011-01-01

    Tato bakalářská práce se zabývá studiem vlastností CdTe detektorů. Popisuje analýzu transportních a šumových charakteristik vzorků CdTe při různých teplotách. Vyhodnocení získaných výsledků dokazuje, že se rozhraní CdTe chová jako dvojice antisériově zapojených diod. Průběhy VA charakteristik se vyznačují lineárním nebo lehce exponenciálním růstem. Při vzrůstající teplotě roste i vodivost vzorků. Měření prokázala rozdíl vodivosti testovaných vzorků při stejné teplotě. Dále je zřejmé, že v roz...

  9. Leakage current measurements on pixelated CdZnTe detectors

    International Nuclear Information System (INIS)

    In the field of the R and D of a new generation hard X-ray cameras for space applications we focus on the use of pixelated CdTe or CdZnTe semiconductor detectors. They are covered with 64 (0.9x0.9 mm2) or 256 (0.5x0.5 mm2) pixels, surrounded by a guard ring and operate in the energy ranging from several keV to 1 MeV, at temperatures between -20 and +20 oC. A critical parameter in the characterisation of these detectors is the leakage current per pixel under polarisation (∼50-500 V/mm). In operation mode each pixel will be read-out by an integrated spectroscopy channel of the multi-channel IDeF-X ASIC currently developed in our lab. The design and functionality of the ASIC depends directly on the direction and value of the current. A dedicated and highly insulating electronics circuit is designed to automatically measure the current in each individual pixel, which is in the order of tens of pico-amperes. Leakage current maps of different CdZnTe detectors of 2 and 6 mm thick and at various temperatures are presented and discussed. Defect density diagnostics have been performed by calculation of the activation energy of the material

  10. Prospects of Back Surface Field Effect in Ultra-Thin High-Efficiency CdS/CdTe Solar Cells from Numerical Modeling

    OpenAIRE

    Nowshad Amin; M. A. Matin; Aliyu, M. M.; Alghoul, M. A.; M. R. Karim; K. Sopian

    2010-01-01

    Polycrystalline CdTe shows greater promises for the development of cost-effective, efficient, and reliable thin film solar cells. Results of numerical analysis using AMPS-1D simulator in exploring the possibility of ultrathin, high efficiency, and stable CdS/CdTe cells are presented. The conventional baseline case structure of CdS/CdTe cell has been explored with reduced CdTe absorber and CdS window layer thickness, where 1 μm thin CdTe and 50 nm CdS layers showed reasonable efficiencies over...

  11. Characterization and Modeling of CdS/CdTe Heterojunction Thin-Film Solar Cell for High Efficiency Performance

    OpenAIRE

    Fatima Buny; Hamid Fardi

    2013-01-01

    Device simulation is used to investigate the current-voltage efficiency performance in CdTe/CdS photovoltaic solar cell. The role of several limiting factors such as back contact Schottky barrier and its relationship to the doping density and layer thickness is examined. The role of surface recombination velocity at back contact interface and extended CdTe layer is included. The base CdS/CdTe experimental device used in this study shows an efficiency of 16-17%. Simulation analysis is used to ...

  12. Band bending at Al, In, Ag, and Pt interfaces with CdTe and ZnTe (110)

    Energy Technology Data Exchange (ETDEWEB)

    Wahi, A.K.; Miyano, K.; Carey, G.P.; Chiang, T.T.; Lindau, I.; Spicer, W.E. (Stanford Electronics Laboratories, Stanford University, Stanford, CA (USA))

    1990-05-01

    Band bending behavior and interfacial chemistry for Al, In, Ag, and Pt overlayers on vacuum-cleaved {ital p}-CdTe and {ital p}-ZnTe (110) have been studied using ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS). These metals provide a range of metal--substrate reactivities: Al reacts strongly with Te, Ag moderately, and In minimally, with no evidence seen for In reaction on ZnTe. Pt exhibits strong alloying behavior with both Cd and Zn. All four metals are found to yield Schottky barriers on CdTe and ZnTe, with a narrow range of final Fermi level positions, {ital E}{sub {ital fi}}={ital E}{sub {ital f}}{minus}{ital E}{sub VBM}, observed on CdTe, from 0.9 to 1.05{plus minus}0.1 eV, and on ZnTe from 0.65 to 1.0{plus minus}0.1 eV. The prediction of the MIGS model that a difference in barrier height exists for two semiconductors dependent upon their band lineup (valence band offset) is examined and found to agree with experiment for Ag, Pt, and Al, but not for In. For the highly reactive Al, no evidence for the overlayer metallicity required for metal-induced gap states (MIGS) to operate is seen on CdTe or ZnTe until after band bending has stabilized. Reaction and intermixing for Al, Ag, and Pt overlayers on CdTe and ZnTe indicate these interfaces are not ideal. The possible role of defects at these four metal/CdTe and metal/ZnTe interfaces is considered, and provides a consistent explanation for the final Fermi level positions observed.

  13. Search for ICC anomalies in nuclear transitions of 115In, 117Sn and 125Te

    International Nuclear Information System (INIS)

    One measured αC internal conversion factors in K-shell of 35 keV energy M1-transition in 115In nucleus, of M4-transitions of γ156.0 keV in 117Sn nucleus and of γ109 keV in 125Te nucleus. One derived αC=8.74+-0.09 for M1-transition in 115In, αC=30.8+-0.6 for 117Sn and αC=181.3+-3.6 for 125Te

  14. Terahertz magneto-spectroscopy of a point contact based on CdTe/CdMgTe quantum well

    Science.gov (United States)

    Grigelionis, Ignas; Białek, Marcin; Grynberg, Marian; Czapkiewicz, Magdalena; Kolkovskiy, Valery; Wiater, Maciej; Wojciechowski, Tomasz; Wróbel, Jerzy; Wojtowicz, Tomasz; Diakonova, Nina; Knap, Wojciech; Łusakowski, Jerzy

    2015-01-01

    To understand a terahertz (THz) response of a point contact device, a number of samples based on CdTe/CdMgTe quantum wells grown by a molecular beam epitaxy were investigated at low temperatures and high magnetic fields. The experiments involved magneto-transport, photocurrent, and transmission measurements carried out with monochromatic THz sources or a Fourier spectrometer. Samples of different geometry with and without gate metallization were used. We observed excitations of a two-dimensional electron plasma in the form of optically induced Shubnikov-de Haas oscillations, cyclotron resonance transitions, and magneto-plasmon resonances. A polaron effect was observed at magnetic fields higher than 10 T. A point contact device processed with an electron beam lithography was investigated as a detector of THz radiation. It was shown that the main mechanism responsible for a THz performance of the point contact was excitation of magneto-plasmons with a wavevector defined by geometrical constrictions of the device mesa.

  15. CdTe and CdZnTe gamma ray detectors for medical and industrial imaging systems

    CERN Document Server

    Eisen, Y; Mardor, I

    1999-01-01

    CdTe and CdZnTe X-ray and gamma ray detectors in the form of single elements or as segmented monolithic detectors have been shown to be useful in medical and industrial imaging systems. These detectors possess inherently better energy resolution than scintillators coupled to either photodiodes or photomultipliers, and together with application specific integrated circuits they lead to compact imaging systems of enhanced spatial resolution and better contrast resolution. Photopeak efficiencies of these detectors is greatly affected by a relatively low hole mobility-lifetime product. Utilizing these detectors as highly efficient good spectrometers, demands use of techniques to improve their charge collection properties, i.e., correct for variations in charge losses at different depths of interaction in the detector. The corrections for the large hole trapping are made either by applying electronic techniques or by fabricating detector or electrical contacts configurations which differ from the commonly used pla...

  16. Donor bound or negatively charged excitons in thin CdTe/Cd1-xMnxTe quantum wells

    Science.gov (United States)

    Paganotto, N.; Siviniant, J.; Coquillat, D.; Scalbert, D.; Lascaray, J.-P.; Kavokin, A. V.

    1998-08-01

    Magnetophotoluminescence spectroscopy of unintentionally doped thin CdTe/(Cd,Mn)Te single and double quantum wells (QW's) revealed a pronounced excitonic transition that can be associated with either an exciton bound to a neutral donor (D0X) or a negatively charged exciton (X-). Comparative experimental study and theoretical analysis of this transition in quantum wells of different thicknesses allowed us to attribute it to the D0X complex in a single QW and to the X- state in the double QW. A record X- binding energy of 3.7 meV has been detected. The double QW structure was shown to be favorable for the formation of X- in the wide well due to the efficient interwell electron tunneling.

  17. Study of the spectrometric performances of monolithic CdZnTe / CdTe gamma ray detectors

    International Nuclear Information System (INIS)

    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 correlations between anodes pitch, material physic properties (resistivity and electron transport properties), and detectors spectrometric performances. We have compared several methods of measuring the photon interaction depth, and have obtained an energy resolution ranging from 1.7% to 7% at 122 keV, according to material, for 5 mm thick detectors. Charge sharing between adjacent anodes has been studied and a measured data processing is proposed. (author)

  18. Correlation of Interfacial Transportation Properties of CdS/CdTe Heterojunction and Performance of CdTe Polycrystalline Thin-Film Solar Cells

    Directory of Open Access Journals (Sweden)

    Guanggen Zeng

    2015-01-01

    Full Text Available The light and dark output performances of CdS/CdTe solar cells made by close-spaced sublimation (CSS were investigated to elucidate the transportation properties of carriers at CdS/CdTe heterojunction interface. It has been found that the interfacial transportation properties were relatively sensitive to variations of the characteristics of heterojunction due to the series resistance and shunting effects. For the high quality cell with 12.1% efficiency, narrow depletion region of ~1.1 microns and large electric field intensity of ~1.3 V/μm allow the sufficient energy-band bending close to CdS layer at CdS/CdTe heterojunction, which changes the carrier transportation mechanism from emission to diffusion and leads to the optimal rectifying characteristics with small dark saturation current density ~6.4 × 10−10 A/cm2. As a result, the schematic diagram of heterojunction band structure corresponding to various performances of solar cells has also been presented.

  19. Deposition of Cl-doped CdTe polycrystalline films by close-spaced sublimation

    International Nuclear Information System (INIS)

    The effects of Cl-doping on the CdTe layers by the close-spaced sublimation (CSS) deposition were investigated. Cl-doped CdTe polycrystalline films were deposited on graphite substrates by CSS method using a mixture of CdTe and CdCl2 powder as a source. In X-ray diffraction (XRD) patterns of the obtained films with various deposition times, many diffraction peaks other than CdTe peaks were observed in the deposition times lower than 10 min. These diffraction peaks were probably due to the formation of chlorides of Cd, Te and C, such as CdCl2, TeCl4, Te3Cl2 and C10Cl8. X-ray fluorescence (XRF) and secondary ion mass spectrometry (SIMS) analyses revealed that a large amount of chlorine was contained in the films with the deposition times lower than 10 min, and that Cl concentration decreased with increasing the deposition time above 3 min. These results indicate that the films containing the chlorides of Cd, Te and C in addition to CdTe are formed in the initial stage of the CSS deposition using a mixture of CdTe and CdCl2 powder as a source. Cross-sectional images revealed that the grain size was decreased by the effect of Cl-doping. Furthermore, current-voltage (I -V) characteristics of the CdTe/graphite structures were measured, and it was found that the resistivity of the Cl-doped CdTe layer was much higher than that of the undoped CdTe layer. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  20. CdS/Cd Te solar cells. Part I. Solar cells processed by the gradient recrystallization and growth technique (GREG); Celdas solares de heterounion de CdS/CdTe. Parte I. Celdas solares procesadas por la tecnica GREG

    Energy Technology Data Exchange (ETDEWEB)

    Tufino V, M.; Contreras P, G.; Albor A, M.L.; Gonzalez T, M.A. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional , 07738 Mexico D.F. (Mexico); Compaan, A.D. [Department of Physics and Astronomy and Center for Materials Science and Engineering, The University of Toledo, Toledo OH 43606 (United States)

    1998-12-31

    In this paper we present the processing and characterization of thin film CdS/Cd Te solar cells obtained by the gradient recrystallization and growth technique, GREG. The cells were deposited on soda-lime LOF{sup TM} conducting glass substrates and Cu-Au contacts were evaporated on top of the Cd Te film. The films deposition conditions were: for CdS the source temperature T{sub f} varied between 750 and 800 Centigrade and the substrate temperature T{sub s} varied between 480 and 550 Centigrade, while for Cd Te T{sub f} varied between 570 and 650 Centigrade and T{sub s} from 460 to 480 Centigrade; both films were deposited under a constant Ar gas pressure. The films were characterized by X-ray diffraction, atomic force microscopy, optical absorption and photoluminescence . Both CdS and Cd Te films were polycrystalline with preferential orientation in the (002) direction for CdS and in the (111) direction for Cd Te; the grain size ranges for the films were 0.2-1 {mu} m for CdS and 0.5-5 {mu} m for Cd Te. The solar cell photoconductive parameters were determined yielding the best cell performance values of V{sub OC} = 0.7 V, J{sub SC} = 31 m A/cm{sup 2} , f f = 50% , SQE{sub max} = 0.6 elect./photon at 550 nm and 8 % solar energy conversion efficiency. (Author)

  1. Effect of magnetic field on the donor impurity in CdTe/Cd1-xMnxTe quantum well wire

    Science.gov (United States)

    Kalpana, P.; Reuben, A. Merwyn Jasper D.; Nithiananthi, P.; Jayakumar, K.

    2016-05-01

    The donor impurity binding energy in CdTe / Cd1-xMnxTe QWW with square well confinement along x - direction and parabolic confinement along y - direction under the influence of externally applied magnetic field has been computed using variational principle in the effective mass approximation. The spin polaronic shift has also been computed. The results are presented and discussed.

  2. 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)

  3. 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,...

  4. Growth of CdZnTe Crystals the Bridgman Technique with Controlled Overpressures of Cd

    Science.gov (United States)

    Su, Ching-Hu; Lehoczky, S. L.

    2008-01-01

    Cd(1-x)Zn(x)Te crystals with x = 0.15 and 0.20, were grown in this study by closed-ampoule directional solidification (Bridgman) technique with a controlled Cd overpressure. The growth ampoule was made of quartz with inner diameter from 20 to 40 mm and a tapered length of 2.5 cm at the growth tip. Both unseeded and seeded growths were performed with total material charges up to 400 g. After the loading of starting CdZnTe material, a typical amount of 2 g of Cd was also loaded inside a Cd reservoir basket, which was attached beneath the seal-off cup. The ampoule was sealed off under a vacuum below lxl0(exp -5) Torr. The sealed ampoule was placed inside a 4-zone Bridgman furnace - a Cd reservoir zone with a heat-pipe furnace liner on the top, followed by a hot zone, a booster heating zone and a cold zone at the bottom. The Cd zone was typically 300 to 400 C below the hot zone setting. High resistivity material has been obtained without any intentional dopants but has been reproducibly obtained with In doping. The crystalline and the electrical properties of the crystals will be reported.

  5. Coexistence of optically active radial and axial CdTe insertions in single ZnTe nanowire.

    Science.gov (United States)

    Wojnar, P; Płachta, J; Zaleszczyk, W; Kret, S; Sanchez, Ana M; Rudniewski, R; Raczkowska, K; Szymura, M; Karczewski, G; Baczewski, L T; Pietruczik, A; Wojtowicz, T; Kossut, J

    2016-03-14

    We report on the growth, cathodoluminescence and micro-photoluminescence of individual radial and axial CdTe insertions in ZnTe nanowires. In particular, the cathodoluminescence technique is used to determine the position of each emitting object inside the nanowire. It is demonstrated that depending on the CdTe deposition temperature, one can obtain an emission either from axial CdTe insertions only, or from both, radial and axial heterostructures, simultaneously. At 350 °C CdTe grows only axially, whereas at 310 °C and 290 °C, there is also significant deposition on the nanowire sidewalls resulting in radial core/shell heterostructures. The presence of Cd atoms on the sidewalls is confirmed by energy dispersive X-ray spectroscopy. Micro-photoluminescence study reveals a strong linear polarization of the emission from both types of heterostructures in the direction along the nanowire axis. PMID:26903109

  6. Electron mobilities and quantum Hall effect in modulation-doped HgTe-CdTe superlattices

    Science.gov (United States)

    Hoffman, C. A.; Meyer, J. R.; Bartoli, F. J.; Lansari, Y.; Cook, J. W., Jr.; Schetzina, J. F.

    1991-10-01

    Photoassisted molecular-beam epitaxy and controlled modulation doping have been used to grow HgTe-CdTe superlattices with n-type carrier concentrations of up to 3×1017 cm-3. It is found that in contrast to Hg1-xCdxTe alloys where the electron mobility decreases strongly with donor concentration, μn in the modulation-doped superlattices is nearly independent of ND at large ND. We also discuss an observation of the quantum Hall effect associated with carriers distributed throughout the interior of a HgTe-CdTe superlattice. Whereas previous reports of quantized steps in the Hall conductivity have involved a small number of conduction channels (hence a small fraction of the superlattice periods), we observe plateaus at multiples of ~=200e2/h in a number of 200-period superlattices with high doping levels. This indicates participation by nearly all wells in the superlattice, and implies that the controlled doping is extremely uniform.

  7. 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.

  8. Analysis of fill factor losses in thin film CdS/CdTe photovoltaic devices

    International Nuclear Information System (INIS)

    In this paper, CdS/CdTe solar cells with conversion efficiency values of η = 5.1, 3.6, 3.5, and 2.9% are analyzed and the effects of the device parameters, such as the diode ideality factor (n), the saturation current-density (Jo), and the series resistance (Rs,) on the fill factor, both in the dark and under illumination are investigated. The solar cells with efficiency η = 5.1, 3.6, and 2.9% were grown from 3N source material. A solar cell with 3.5% efficiency was made of a 6N CdTe source. The temperature current density-voltage (J-U-T) and capacitance-voltage characteristics (C-U-T) of CdS/CdTe solar cells were measured in a temperature range of 303-383 K. For all studied cells, the diode ideality factor in the dark is much higher than 2 and the saturation current density increases under illumination, while both the series and shunt resistances decrease under illumination and temperature. (authors)

  9. Cancer Cell Targeting Using Folic Acid/Anti-HER2 Antibody Conjugated Fluorescent CdSe/CdS/ZnS-MPA and CdTe-MSA Quantum Dots.

    Science.gov (United States)

    Singh, Gurpal; Kumar, Manoj; Soni, Udit; Arora, Vikas; Bansal, Vivek; Gupta, Dikshi; Bhat, Madhusudan; Dinda, Amit K; Sapra, Sameer; Singh, Harpal

    2015-12-01

    CdSe/CdS/ZnS and CdTe quantum dots (QDs) were synthesized by successive ion layer adsorption and reaction (SILAR) technique and direct aqueous synthesis respectively using thiol stabilizers. Synthesized CdSe/CdS/ZnS and CdTe QDs stabilized with 3-mercaptopropionic acid (MPA) and mercaptosuccinic acid (MSA) were used as fluorescent labels after conjugation with folic acid (FA) and anti-HER2 antibodies. Photoluminescence quantum yield of folated CdSe/CdS/ZnS-MPA and CdTe-MSA QDs was 59% and 77% than that of non-folated hydrophilic QDs. The folate receptor-mediated delivery of folic acid-conjugated CdTe-MSA and CdSe/CdS/ZnS-MPA QDs showed higher cellular internalization as observed by confocal laser scanning microscopic studies. Folated and non-folated CdTe-MSA QDs were highly toxic and exhibited only 10% cell viability as compared to > 80% cell viability with CdSe/CdS/ZnS-MPA QDs over the concentration ranging from 3.38 to 50 pmoles. Immunohistochemistry (IHC) results of human breast cancer tissue samples showed positive results with anti-HER2 antibody conjugated CdSe/CdS/ZnS-MPA QDs with better sensitivity and specificity as compared to conventional IHC analysis using diaminobenzedene staining. PMID:26682358

  10. A study of vapor CdCl{sub 2} treatment by CSS in CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Rios-Flores, A.; Pena, J.L.; Castro-Pena, V.; Ares, O.; Castro-Rodriguez, R. [Applied Physics Department, CINVESTAV-IPN Merida, C.P. 97310 Merida, Yucatan (Mexico); Bosio, A. [University of Parma, Department of Physics, v.le G.P. Usberti 7/A, 43100 Parma (Italy)

    2010-06-15

    We report the effect of CdCl{sub 2} vapor treatment on the photovoltaic parameters of CdS/CdTe solar cells. Vapor treatment allows combining CdCl{sub 2} exposure time and annealing in one step. In this alternative treatment, the CdS/CdTe substrates were treated with CdCl{sub 2} vapor in a close spaced sublimation (CSS) configuration. The substrate temperature and CdCl{sub 2} powder source temperature were 400 C. The treatment was done by varying the treatment time (t) from 15 to 90 min. Such solar cells are examined by measuring their current density versus voltage (J-V) characteristics. The open-circuit voltage (V{sub oc}), short circuit current density (J{sub sc}) and fill factor (FF) of our best cell, fabricated and normalized to the area of 1 cm{sup 2}, were V{sub oc} = 663 mV, J{sub sc} = 18.5 mA/cm{sup 2} and FF = 40%, respectively, corresponding to a total area conversion efficiency of {eta} = 5%. In cells of minor area (0.1 cm{sup 2}) efficiencies of 8% have been obtained. (author)

  11. Nanowire CdS-CdTe Solar Cells with Molybdenum Oxide as Contact

    OpenAIRE

    Hongmei Dang; Singh, Vijay P

    2015-01-01

    Using a 10 nm thick molybdenum oxide (MoO3−x) layer as a transparent and low barrier contact to p-CdTe, we demonstrate nanowire CdS-CdTe solar cells with a power conversion efficiency of 11% under front side illumination. Annealing the as-deposited MoO3 film in N2 resulted in a reduction of the cell’s series resistance, from 9.97 Ω/cm2 to 7.69 Ω/cm2, and increase in efficiency from 9.9% to 11%. Under illumination from the back, the MoO3−x/Au side, the nanowire solar cells yielded Jsc of 21 mA...

  12. Electroluminescence of different colors from polycation/CdTe nanocrystal self-assembled films

    Science.gov (United States)

    Gao, Mingyuan; Lesser, Constanze; Kirstein, Stefan; Möhwald, Helmuth; Rogach, Andrey L.; Weller, Horst

    2000-03-01

    Water soluble thiol capped CdTe nanocrystals are assembled into ultrathin films in combination with poly(diallyldimethylammonium chloride) (PDDA) by the self-assembly method of layer-by-layer adsorption of oppositely charged polyelectrolytes. Electroluminescent devices, which produce different color emissions, are fabricated by sandwiching CdTe/PDDA films between indium-tin-oxide (ITO) and aluminum electrodes using CdTe nanocrystals of different sizes. It is shown that the electroluminescence (EL) spectra of the CdTe/polymer films are nearly identical to the photoluminescence spectra of the corresponding CdTe nanocrystals in aqueous solutions. The devices produce room-light visible light output with an external quantum efficiency up to 0.1%. Light emission is observed at current densities of 10 mA/cm2 and at low onset voltages of 2.5-3.5 V, which depends on the thickness of the film indicating field-dependent current injection. A variation of the EL efficiency with the size of the CdTe particles is observed and explained by the size dependent shift of the CdTe energy levels with respect to the work function of the electron injecting Al electrode. This is confirmed by the behavior of two-layer devices prepared from two differently sized CdTe particles being spatially separated, i.e., one size CdTe near ITO and the other size CdTe near Al by using the self-assembly method.

  13. 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

  14. Electrical properties of modulation-doped HgTe-CdTe superlattices

    Science.gov (United States)

    Hwang, S.; Lansari, Y.; Yang, Z.; Cook, J. W.; Schetzina, J. F.

    1991-10-01

    Growth of modulation-doped HgTe-CdTe superlattices (SLs) at very low temperatures (140 °C) by photoassisted molecular beam epitaxy is reported. SL layer thicknesses were intentionally chosen such that most of the SLs studied are inverted-band semimetals or inverted-band semiconductors. Both p- and n-type samples were successsfully prepared and studied. The doped superlattices exhibit excellent electrical properties. Lack of carrier freeze-out at low temperatures provides convincing evidence that modulation-doping has been achieved.

  15. Finite size effects of helical edge states in HgTe/CdTe quantum wells

    OpenAIRE

    Zhou, Bin; Lu, Hai-Zhou; Chu, Rui-Lin; Shen, Shun-Qing; Niu, Qian

    2008-01-01

    The solutions for the helical edge states for an effective continuum model for the quantum spin Hall effect in HgTe/CdTe quantum wells are presented. For a sample of a large size, the solution gives the linear dispersion for the edge states. However, in a finite strip geometry, the edge states at two sides will couple with each other, which leads to a finite energy gap in the spectra. The gap decays in an exponential law of the width of sample. The magnetic field dependence of the edge states...

  16. Cu-doped CdS and its application in CdTe thin film solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Yi [School of Automation, Wuhan University of Technology, Wuhan, Hubei 430070 (China); College of Electronic and Information Engineering, Hankou University, Wuhan, Hubei 430212 (China); Yang, Jun; Yang, Ruilong; Shen, Kai; Wang, Dezhao [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Wang, Deliang, E-mail: eedewang@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Key Laboratory of Materials for Energy Conversion, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2016-01-15

    Cu is widely used in the back contact formation of CdTe thin film solar cells. However, Cu is easily to diffuse from the back contact into the CdTe absorber layer and even to the cell junction interface CdS/CdTe. This phenomenon is generally believed to be the main factor affecting the CdTe solar cell stability. In this study Cu was intentionally doped in CdS thin film to study its effect on the microstructural, optical and electrical properties of the CdS material. Upon Cu doping, the V{sub Cd{sup −}} and the surface-state-related photoluminescence emissions were dramatically decreased/quenched. The presence of Cu atom hindered the recrystallization/coalescence of the nano-sized grains in the as-deposited CdS film during the air and the CdCl{sub 2} annealing. CdTe thin film solar cell fabricated with Cu-doped CdS window layers demonstrated much decreased fill factor, which was induced by the increased space-charge recombination near the p-n junction and the worsened junction crystalline quality. Temperature dependent current-voltage curve measurement indicated that the doped Cu in the CdS window layer was not stable at both room and higher temperatures.

  17. Structural and optical properties of Cd 0.7Hg 0.3Te-CdTe heterostructures grown by molecular beam epitaxy

    Science.gov (United States)

    Lentz, G.; Magnea, N.; Mariette, H.; Tuffigo, H.; Feuillet, G.; Fontenille, J.; Ligeon, E.; Saminadayar, K.

    1990-04-01

    Layers and single quantum wells of Cd xHg 1- xTe with x ⋍ 0.7 have been grown by molecular beam epitaxy. Structural analysis shows that growth free of defects (twins, dislocations) can be achieved on (111)Te Cd 0.96Zn 0.04Te substrates. The Photoluminescence analysis of the layers and the wells reveal that they are efficient light emittors in the 1.3-1.5 μm range.

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

    International Nuclear Information System (INIS)

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

  19. 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.

  20. CdTe polycrystalline films on Ni foil substrates by screen printing and their photoelectric performance

    International Nuclear Information System (INIS)

    Highlights: • The sintered CdTe polycrystalline films by a simple screen printing. • The flexible Ni foil was chose as substrates to reduce the weight of the electrode. • The compact CdTe film was obtained at 550 °C sintering temperature. • The photoelectric activity of the CdTe polycrystalline films was excellent. - Abstract: CdTe polycrystalline films were prepared on flexible Ni foil substrates by sequential screen printing and sintering in a nitrogen atmosphere for the first time. The effect of temperature on the quality of the screen-printed film was investigated in our work. The high-quality CdTe films were obtained after sintering at 550 °C for 2 h. The properties of the sintered CdTe films were characterized by scanning electron microscopy, X-ray diffraction pattern and UV–visible spectroscopy. The high-quality CdTe films have the photocurrent was 2.04 mA/cm2, which is higher than that of samples prepared at other temperatures. Furthermore, CdCl2 treatment reduced the band gap of the CdTe film due to the larger grain size. The photocurrent of photoelectrode based on high crystalline CdTe polycrystalline films after CdCl2 treatment improved to 2.97 mA/cm2, indicating a potential application in photovoltaic devices