Improving narrow bandgap a-SiGe:H alloys grown by hot-wire chemical vapor deposition |
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Authors: | Yueqin Xu B P Nelson L M Gedvilas R C Reedy |
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Affiliation: | National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401, USA |
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Abstract: | We have improved the electronic properties of narrow-bandgap (Tauc gap below 1.5 eV) amorphous-silicon germanium alloys (a-SiGe:H) grown by hot-wire chemical vapor deposition (HWCVD) by lowering the substrate temperature and deposition rate. Prior to this work, we were unable to grow a-SiGe:H alloys with bandgaps below 1.5 eV that had photo-to-dark conductivity ratios comparable with our plasma-enhanced CVD (PECVD) grown materials B.P. Nelson et al., Mater. Res. Soc. Symp. 507 (1998) 447]. Decreasing the filament diameter from our standard configuration of 0.5 mm to 0.38 or 0.25 mm provides first big improvements in the photoresponse of these alloys. Lowering the substrate temperature from our previous optimal temperatures (Tsub starting at 435 °C) to at 250 °C provides additional photo-to-dark conductivity ratio increasing by two orders of magnitude for growth conditions containing 20–30% GeH4 in the gas phase (relative to the total GeH4+SiH4 flow). |
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Keywords: | Amorphous-silicon germanium alloy Optical bandgap Tauc gap Photo-to-dark conductivity ratio Photoresponse Substrate Filament |
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