ZnTeO and Oxygen Doped II-VI Ternary Alloys for Intermediate Band Solar Cells.

Solar Cell;II-VI materials;Molecular Beam Epitaxy;Electrical Engineering;Engineering;Applied Physics

Chen, ChihyuClarke, Roy ;

University of Michigan

关键词: Solar Cell;    II-VI materials;    Molecular Beam Epitaxy;    Electrical Engineering;    Engineering;    Applied Physics;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/111427/chenchih_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

ZnTeO is a promising material for next generation photovoltaics and X-ray scintillators. ZnTeO is a highly mismatched alloy (HMA) where O is much more electronegative than the host Te. O and HMA effects between O and the CB of ZnTe have been predicted to form a sub-bandgap band[1]. When the oxygen concentration is high, the oxygen related states have been said to merge into a band, and called an intermediate band (IB), and may potentially be an Intermediate Band Solar Cell (IBSC) absorber. In the case of X-ray scintillators, ZnTeO as an X-ray phosphor material has the some of the fastest decay time of ~1 µs, largest gain efficiency of, and lowest afterglow with respect to common material systems, which are important for fast time resolution, brightness, and signal to noise, respectively, for the final X-ray detection system. The thesis presents detailed work on ZnTeO material. Structural, chemical, optical, and lifetime data shows that oxygen induces an intermediate band (IB) approximately 0.4 eV below the conduction band (CB) edge, when the oxygen concentration is approximately 1020 cm-3. It is shown that the electronic structure of the oxygen induced energy levels are influenced by oxygen location in the crystal lattice, which can be influenced by oxygen plasma back ground pressure used during material synthesis. Photoluminescence, X-ray diffraction and Nuclear Reaction Analysis channeling data reveals that the oxygen likely resides in both Te substitutional positions and interstitial positions. A novel two pump time resolved photoluminescence was used to observe the time resolved electron transfer from the VB to IB, and then from IB to CB with two sub-bandgap pulses. A novel way to prepare GaSb(100) substrate for ZnTe epitaxy was developed to enable near lattice matched growth of ZnTeO on GaSb(100). The reduction of the FWHM of the XRD peak from approximately 300 arc-seconds for ZnTe/GaAs(100) to 40 arc-seconds for ZnTe/GaSb(100) was achieved. Ternary II-VI alloys of ZnSeTe, CdMgTe, and CdZnTe with bandgaps of approximately 2 eV, near the ideal bandgap for IBSCs were synthesized. Oxygen was then introduced during synthesis to form sub-bandgap electronic states for use as IB.