Superior structural and electronic properties for amorphous silicon–germanium alloys deposited by a low temperature hot wire chemical vapor deposition process

Very good electronic properties of hot-wire CVD a-Si,Ge:H alloys have been established by junction capacitance methods. The samples were deposited using a tantalum filament maintained at about 1800 °C instead of the usual 2000 °C tungsten filament process. Urbach energies below 45 meV were found, as well as annealed defect densities below 1016 cm−3, for Ge fractions up to 30 at.%. However, samples with 1019 cm−3 levels of oxygen exhibited much broader Urbach energies and higher defect densities. Light induced degradation was examined in detail for one a-Si,Ge:H alloy sample and compared to the behavior of PECVD grown a-Si:H alloys of similar optical gap.