Sulfidation mechanism of pre-cleaned GaAs surface using (NH₄)₂S_x solution

Wet cleaning and successive sulfidation of GaAs with (NH₄)₂S_x solution were carried out in air or in an atmosphere controlled glove box with nitrogen, respectively. The wet cleaned GaAs was revealed to contain oxide and/or elemental forms of As and/or Ga. Successive sulfidation with (NH₄)₂S_x brought about a large decrease of surface oxides and elemental forms, and the occurrence of As-S and/or Ga-S bonds. The formation of passivation layer with sulfur was shown to be mainly dependent on the surface state of wet cleaned GaAs before the sulfidation, and especially on the presence of elemental As and Ga. The amount of sulfur bonds with As and Ga was determined by the quantity of elemental form of As and Ga generated during the surface preparation for the sulfidation. X-ray photoelectron spectroscopy was employed to investigate a chemical bonding state of wet etched and sulfidation treated GaAs surface.