THE EFFECT OF HYDROGEN DILUTION ON GLOW-DISCHARGE A-SIGE-H ALLOYS

Amorphous SiGe:H alloy is the key material for highly efficient and stable a-Si-based tandem solar cells. We have studied the effect of H2 dilution (0% < H2 < 95%) of the source gas mixture (SiH4 + GeH4) on the glow discharge a-Si1-xGe(x):H alloys with x varying from 0 to 0.55. The dependence of composition, deposition rate, IR absorption spectra and optical properties on hydrogen dilution are reported and analyzed. The CPM method was used to obtain sub-band-gap absorption spectra. The a-SiGe:H alloys show high photosensitivity, a low Urbach energy (< 60 meV) and a low density of states in the gap (< 3 x 10(16) cm3) for as low as 1.3 eV band gap material. Hydrogen dilution was found to improve the photoelectrical properties; it minimizes the silicon dihydride bonding and lowers the incorporation of Ge into the film.