Correlation of surface morphology with chemical structures of sulfur-passivated GaAs(100) investigated by scanning tunneling microscopy and x-ray photoelectron spectroscopy

Abstract

The surface morphology and chemical structures of GaAs(100) after etching with sulfuric acid and sulfur passivation with ammonium sulfide [(NH4)2Sx] solution were investigated using a scanning tunneling microscope and x-ray photoelectron spectroscopy (XPS). Depending on the chemical treatments which are routinely used in semiconductor processes, the surface morphology was observed to be quite different. The effects of water rinse, HCl treatment, and sulfur treatment time on the surface morphology were studied. Comparison of the surface morphology with chemical structures obtained by XPS was used to explain the evolution of surface morphology during the chemical treatments. In particular, a very flat surface with a surface undulation of ±6 Å was obtained by sulfur passivation with (NH4)2Sx solution after chemical etching of a n-GaAs(100) wafer. These studies enable a better understanding of a correlation of the chemical structures with the surface morphology of the GaAs(100) surface on a nanometer scale.