Effect of prepared GaAs surface on the sulfidation with (NH₄)₂S_x solution

Surface properties of wet-cleaned or successively passivated GaAs with (NH₄)₂S_x solution were analyzed using x-ray photoelectron spectroscopy. All the treatments were carried out in a glove box under nitrogen controlled atmosphere. Every cleaning process with HCl or H₃PO₄ solution produced elemental As and the amount depends on the etching capability of acid to GaAs. Successive sulfidation treatment resulted in the formation of an As-S bond, and the observed quantity of the arsenic sulfide was closely related to the amount of elemental As. In particular, the As-S was hardly observed in the sulfidation treated GaAs surface after NH₄OH treatment because elemental As had not been produced by the NH₄OH treatment. The in situ annealed GaAs surface at 600°C contained a large amount of elemental Ga and showed an effective formation of Ga-S after the sulfidation treatment. Therefore, it could be assured that the elemental forms of As and Ga bind with S through the sulfidation treatment using a (NH₄)₂S_x solution.