Alloys of hydrogenated amorphous silicon and germanium are disclosed that exhibit unexpectedly low saturated defect densities, particularly relative to the initial defect densities of the alloys, so as to render them substantially resistant to Staebler-Wronski degradation. The alloys are producible using conventional equipment, but glow-discharge methods are preferred. The preferred amount of germanium in the alloy is about 15 at. % to about 50 at. %. The alloys are particularly useful for making photovoltaic cells. The alloys can be used as intrinsic semiconductors and doped for use as "n" or "p" materials. Methods for making the alloys are also disclosed.