Formation of ohmic contact to n-GaAs using (NH₄)₂S surface passivation

Ohmic contacts between Au and sulfur‐passivated n‐GaAs have been formed without annealing after deposition of the metal. The GaAs samples doped with either 2×10¹⁶ or 3×10¹⁸ cm⁻³ Si were passivated with (NH4)2S in an aqueous solution, then the passivating sulfur was thermally desorbed in a vacuum. Desorption was followed immediately by in situ thermal evaporation of Au with the substrate at room temperature. Ohmic I‐V behavior was measured ex situ. C‐V measurements on a sample with a native oxide surface barrier layer showed the surface carrier concentration on the higher doped sample increased from 3×10¹⁸ to 7×10¹⁸ cm⁻³ after S desorption. Secondary ion mass spectroscopy data showed that S had diffused into the GaAs surface region. Thus S passivation prevented interfacial oxide formation during the exposure to air after the sample was passivated and before the vacuum chamber was pumped to a low pressure. Sulfur apparently diffused into the surface region during flash desorption in vacuum and increased the surface n‐doping concentration which led to ohmic contacts without post‐annealing of the Au films.