Properties of RF sputtered hydrogenated amorphous germanium-silicon alloys

Abstract

Amorphous GeSi:H alloys have been prepared by rf sputtering in an argon-hydrogen atmosphere of varying hydrogen partial pressures. Electrical transport properties in the temperature range of 80 K to 373 K and optical and structural properties of these films have been measured. It is found that for a fixed GeSi composition, the hydrogen content strongly affects the electrical conductivity. The absorption edge has been seen to suffer an initial blue shift yielding to a small red shift at higher hydrogen concentrations and is consistent with the conductivity data. The optical pseudo-gap obtained approaches closer to twice the corresponding mobility gap at higher hydrogen concentrations. Structural studies by Raman scattering confirm the amorphous nature of the films. Raman spectra also reveals the presence of various hydrogenic and lattice modes attributable to siliconhydrogen, germaniumhydrogen, SiSi and GeGe interactions. The depolarization ratio ϱ, measured for both unannealed annealed samples, indicates stabilization, due to annealing at selected temperatures. In view of the development of possible material for photovoltaic conversion of solar energy, it is suggested that by an appropriate choice of a fixed GeSi composition and varying the hydrogen content it will be possible to optimize the electrical conductivity and optical band gap in sputtered hydrogenated a-GeSi alloys.