Surface morphology of (NH₄₂s_x-treated gaas(100) investigated by scanning tunneling microscopy

The surface morphology of n-GaAs(100) after etching with sulfuric acid and sulfur passivation with ammonium sulfide ((NH₄)₂s_x) solution were systematically investigated using a scanning tunneling microscope (STM) under ambient conditions. Depending on the etching and passivation conditions, the surface roughness was observed to vary widely. The effects of water rinse, HC1 treatment, and passivation time on the surface morphology were studied through etching and passivation reactions. In particular, a very flat surface with a sub-nanometer surface undulation was obtained.after sulfur passivation for 20 min without postetch water rinse. These studies enabled a better understanding of the effects of the routinely used etching and passivation reactions on the surface morphology of GaAs(100) in nanometer scale and showed that GaAs can be used as a substrate for nanofabrication.