Deposition of amorphous silicon alloys

Hydrogenated amorphous silicon alloys of carbon and germanium can be deposited by glow-discharge decomposition of gaseous hydrides or fluorides. Non-plasma methods such as photochemical vapour deposition are also used and offer guidelines for understanding and improving the standard glow-discharge method. These amorphous alloys usually have poorer structural and electronic properties than pure hydrogenated amorphous silicon but significant improvements can be obtained by different approaches such as hydrogen dilution of the gases, use of fluorides, selection of discharge conditions yielding predominantly XH3 O(=Si,Ge,C) radicals, or moderate energy ion bombardment. The correlations between the film stoichiometry, microstructure and opto-electronic properties and the plasma gas-phase physico-chemistry and surface reaction kinetics are emphasized.