Formation of a native-oxide structure on the surface of n-GaAs under natural oxidation in air

Abstract

Using scanning tunneling microscopy, the native-oxide film on epitaxial n-GaAs(100) was found to be formed by tightly joining nanoclusters involving oxides of Ga and As as well as an excess As layer on the interface between Ga₂O₃ and n-GaAs. The fractal structure of surface of the clusters is formed by three levels of similar grainlike elements, whose sizes satisfy the ratio 9: 3: 1. In the three-dimensional case, approximately six finer grains can be arranged on a coarser grain. Two possible cases of forming the fractal structure of clusters were considered. If the As₂O₃ and As fluxes to the surface are identical (the first case), the formation of cluster structure is governed by the As diffusion over the cluster surface. If the As flux exceeds that of As₂O₃, the cluster-structure formation is governed by the Ga diffusion over the cluster surface (the second case). The cluster growth under normal conditions and, therefore, the increase in the oxide-film thickness cease when the clusters are tightly joined because it hampers reactants through the oxide film and the chemical reactions to proceed.