Author: Andreas Goebel
Publisher:
ISBN:
Category : Cadmium compounds
Languages : en
Pages : 156

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Author: Kenneth R. Zanio
Publisher:
ISBN:
Category : Cadmium telluride
Languages : en
Pages : 136

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Author: Samuel Bigbee-Hansen
Publisher:
ISBN:
Category : Cadmium telluride
Languages : en
Pages : 0

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In the pursuit of creating efficient CdTe p-n homojunctions, we developed iodine (I) n-type doped CdTe using Cadmium Iodide (CdI2) as a dopant in varying concentrations (1018 cm-3, 1019 cm-3 and 1020 atoms℗ʺcm-3 target concentrations) in CdTe. Iodide doped crystals were grown using a Modified Vertical Bridgman furnace (MVB). Single crystals were characterized using XRD (X-Ray Diffraction), Hall effect, IR (Infrared) Microscopy, UV-VIS-NIR (Ultraviolet-Visible-Near infrared Spectroscopy) and FTIR (Fourier Transform Infrared Spectroscopy). Partners at the National Renewable Energy Laboratory (NREL) also provided data for Hall Effect and Two Photon Excitation Time Resolved Photoluminescence (2PE TRPL) of wafers and films. Photoluminescence mapping (PL mapping) was obtained from Klar scientific, and glow discharge mass spectrometry (GDMS) for purity and final doping concentration was obtained from the National Research Council Canada. Due to poor carrier properties in the crystals as-grown, two annealing treatments were explored, in either tellurium or cadmium vapor. Homojunctions were made at NREL by depositing n-type films from these crystals on p-type single crystals, CdTe:P grown and WSU. The n-type films were created using the close-space sublimation epitaxy (CSSE) process. Herein is reported the results of the grown CdTe:I crystals and, to a lesser extent, the properties of the CdTe:I thin films formed by CSSE.

Author:
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ISBN:
Category : Military research
Languages : en
Pages : 572

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Author:
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ISBN:
Category :
Languages : en
Pages : 6

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We grew single crystals of cadmium telluride, doped with bromine by the Bridgman method, annealed them under a cadmium overpressure (PCd = 102 - 105 Pa) at 800-1100 K, and investigated their electrical properties at high- and low-temperature. The influence of impurities on the crystals' electrical properties were analyzed using the defect subsystem model; the model includes the possibility of the formation of point intrinsic defects (V2−Cd, Cd2i, V2Te, Te2−i), and substitutional ones (Br0Te, Br+Te), as well as complexes of point defects, i.e., (Br+Te V2−Cd)− and (2Br+Te V2−Cd)0. We established the concentration dependence between free charge carriers and the parameters of the annealing process. Here, n(T) and n(PCd) are determined by two dominant defects - Br+Te and (2Br+Te V2−Cd)0. Their content varies with the annealing temperature and the vapor pressure of the component; the concentration of other defects is much smaller and almost does not affect the electron density.

Author: Olanrewaju Sunday Ogedengbe
Publisher:
ISBN:
Category : Molecular beam epitaxy
Languages : en
Pages : 368

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CdTe is one of the leading materials used in thin-film photovoltaic (PV) devices due to some of its basic properties such as its ability to permit both n- and p-type doping, its relatively high absorption coefficient for photons in the visible range, and its direct band gap of 1.514 eV at room temperature, which is near the optimal band gap for solar energy conversion. Despite the near optimal band gap, the highest power conversion efficiency in a CdTe solar cell to date, achieved using polycrystalline CdTe, stands at 21%. This is far less than the Shockley-Queisser limit, which is about 32% for a single-junction cell under AM 1.5 illumination condition. Research efforts have shown that short circuit current (Jsc) is near its theoretical limit, implying that strategies to improve cell efficiency will have to be contingent on improving open-circuit voltage (Voc) and fill factor. Heavy doping has the potential to improve Voc. There is also evidence that inclusion of a Cd1-xMgxTe barrier in a solar cell structure may improve open circuit voltage, and, ultimately, cell efficiency. Doped and undoped CdTe layers were grown by molecular beam epitaxy (MBE). Secondary ion mass spectrometry (SIMS) characterization was used to measure dopant concentration, while Hall measurement and the capacitance-voltage technique were used for determining carrier concentration. Photoluminescence intensity (PL-I) and time-resolved photoluminescence (TRPL) techniques were used for optical characterization. The incorporation and limits of iodine and arsenic dopants in CdTe were studied. Maximum n-type carrier concentrations of 7.4x1018 cm-3 for iodine-doped CdTe and 3x1017 cm-3 for iodine-doped Cd0.65Mg0.35Te were achieved. Studies suggest that electrically active doping with iodine is limited with dopant concentration much above these values. Dopant activation of about 80% was observed in most of the iodine-doped CdTe samples. The estimated activation energy is about 6 meV for CdTe and the value for Cd0.65Mg0.35Te is about 58 meV. Iodine-doped CdTe samples exhibit long lifetimes with no evidence of photoluminescence degradation with doping as high as 2x1018 cm-3 while indium shows substantial non-radiative recombination at carrier concentrations above 5x1016 cm-3. Also, maximum p-type carrier concentration of 2x1016 cm-3 for arsenic-doped CdTe was achieved. Dopant activation greater than 20% was observed in most of the arsenic-doped CdTe samples. The process compatibility of iodine and magnesium in CdTe was evaluated for the solar cell device. Iodine was shown to be thermally stable in CdTe at temperatures up to 600oC and magnesium showed a slow diffusion at 500oC. Doped CdTe structures were used to make solar cell device structures, where open circuit voltage up to 880 mV and fill factor up to ~60% were measured.

Author: Richard L. Lane
Publisher:
ISBN:
Category :
Languages : en
Pages : 72

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Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 704

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Author:
Publisher:
ISBN:
Category : Metallurgy
Languages : en
Pages : 1058

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Author:
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 2002

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