Interface behavior and crystallographic relationships of aluminum on GaAs(100) surfaces

Abstract

The degree of covalent bond formation of Al to GaAs at the interface determines both its stability against an exchange reaction with Ga, and the crystallographic relationships between substrate and overgrowths. At elevated temperatures the observed exchange reaction and subsequent interdiffusion of the constituent atoms results in a nonabrupt interface, which facilitates the accommodation of the resulting Al(110) overgrowth. These properties are observed irrespective of the As coverage of the starting GaAs(100) surface. At room temperature, the presence of As on the surface of the GaAs(100)-c(2×8) structure stabilizes the interface against a replacement reaction and constrains the Al to a (110) growth rotate 90° with respect to the high temperature phase. On the predominantly Ga terminated GaAs(100)-(4×6) structure the metallic interfacial bonds permit a lattice matched Al(100)-45° overgrowth to dominate. For this surface a partial replacement reaction is observed beyond a critical overgrowth thickness of ∠1.5 Å and appears in conjunction with the Al nucleation process which invariably occurs for all surfaces and growth conditions. At room temperature, the net energy release during the nucleation process is the determining quantity necessary to overcome the barrier for the exchange reaction. The heat of adsorption of Al on GaAs is not sufficient to trigger the replacement reaction on the GaAs(100) surface, and its high value on the As-stabilized surface inhibits the reaction from occurring.