Comparison of surface properties of sodium sulfide and ammonium sulfide passivation of GaAs

Sodium sulfide has been demonstrated to significantly improve the electrical properties of the ambient-exposed (100) GaAs surface. It has also shown usefulness in several practical device structures. Ammonium sulfide has been proposed to have similar properties and has already been demonstrated to improve InP and GaAs devices. We compare the photoluminescence behavior and band bending of GaAs samples treated with these two different sulfide species. We also compare the chemical nature of the surfaces treated using these two processes by Auger electron spectroscopy. The surface recombination velocity was found to be similarly affected by the two treatments and the band bending found to be essentially identical. Sodium sulfide produces a film and interfacial region rich in oxygen due to hydration. However, the ammonium sulfide was found to leave very little oxygen on the surface, even compared to conventional GaAs cleaning and etching procedures.