Deposition of photosensitive hydrogenated amorphous silicon–germanium films with a tantalum hot wire

We study the optical, electrical and structural properties of a-SiGe:H thin films deposited by hot-wire chemical vapor deposition (HWCVD). The best films are deposited with a Ta filament heated to 1750 °C and the substrate temperature held at 200 °C. For the same precursor gas ratio of GeH4 to SiH4, a lower filament temperature produces films with higher Ge incorporation than with a higher filament temperature. For Tauc band gaps between 1.22 and 1.30 eV, the photoconductivity and photosensitivity are significantly higher than for plasma-enhanced CVD a-SiGe:H films exhibiting the same band gap. The filament lifetime is much longer for a Ta filament than for a W filament at these operating temperatures.