Si1-xGex(x=0.25) substrates were treated with aqueous ammonium sulfide with the goal of passivating the surface both electrically and chemically. X-ray photoelectron spectroscopy (XPS) showed that no sulfur was deposited. Instead the surface was oxidized in solution, and the higher the ammonium sulfide concentration, the more oxide that formed. Spectroscopic ellipsometry showed that samples treated with dilute ammonium sulfide oxidized much more rapidly when exposed to air than those treated with a higher concentration. Addition of halogen acids to the sulfur solution deposited sulfides, but oxides were also present. The density of interface defects (Dit) was extracted from capacitance-voltage measurements of metal-insulator-semiconductor capacitors for the clean acid last surface and after either ammonium sulfide alone or ammonium sulfide plus acid. Samples treated in ammonium sulfide plus acid showed the smallest increase in interface defects compared to the other two surfaces.