Competition between continuous etching and surface passivation for Cl2 chemisorption onto GaAs(100) c(8×2), GaAs(100) c(2×8), and GaAs(110) (1×1) surfaces

Abstract

The effects of surface temperature (Ts) and surface structure upon the passivation and etching of GaAs(100) and GaAs(110) surfaces by Cl2 have been studied. The Ga-rich GaAs(100) Ga-c(8×2) and the stoichiometric GaAs(110) (1×1) surfaces form stable ordered monochloride overlayers when exposed to Cl2 at 300 K. The ordered overlayers formed are AsCl on the GaAs(110) (1×1) surface and GaCl on the GaAs(100) Ga-c(8×2) surface. In contrast, the As-rich GaAs(100) As-c(2×8) surface undergoes continuous uptake of Cl2 under equivalent conditions. All three surfaces exhibit continuous uptake of Cl2 at surface temperatures above 600 K, where continuous etching is known to occur. In this paper, the continuous uptake of Cl2 is shown to result from etching of the surface. In addition it is shown that the Ga-rich GaAs(100) Ga-c(8×2) and the stoichiometric GaAs(110) (1×1) surfaces can be induced to undergo continuous etching at surface temperatures of 300 K, if they are first exposed to Cl2 with surface temperatures above 600 K. This slight pre-etch disrupts the surface order and exposes multiple dangling bonds. The disrupted surface does not allow for a monochloride passivation layer to form; instead, volatile trichloride products form, leading to continuous etching. Therefore, the dissociative adsorption of molecular chlorine on GaAs(100) and GaAs(110) surfaces involves a competition between etching and passivation in which monochloride passivation is favored only on the well-ordered surfaces.