A Model to Explain the Effective Passivation of the GaAs Surface by (NH4)2Sx Treatment

Abstract
A model is presented to explain why and how the GaAs surface is passivated and stabilized by (NH4)2S x treatment. Natural oxide, together with a thin layer of GaAs, is removed and the fresh GaAs surface is covered with a monoatomic layer of sulfur which has no dangling bonds. On this surface, foreign atoms are prohibited from chemical adsorption. Thus, the As and Ga vacancies which are, according to Spicer's “unified defect model”, the cause of the interface trap level are not introduced. The present model of the passivation successfully interprets different experimental data on the surfaces treated with solutions of sodium sulfide and ammonium sulfide with and without excess sulfur.