Optical and electronic properties of an amorphous silicon-germanium alloy with a 1.28 eV optical gap

We report the deposition and comprehensive evaluation of a hydrogenated, fluorinated amorphous silicon-germanium alloy with an optical gap of 1.28 eV. This low-gap alloy of the a-Si, Ge system possesses a small midgap defect density (6.5×1016 cm−3), and useful electron (σph/σd=23) and hole (LD=0.13 μm) transport properties. The alloy was grown by radio-frequency plasma-enhanced decomposition of SiF4, GeF4, and H2 in a reactor built to ultrahigh-vacuum specifications.