Evolution of the native oxide composition on Al$_{0.3}$Ga$_{0.7}$As(100)

Morphology and composition of the oxide layers formed on Al$_{0.3}$Ga$_{0.7}$As(100) surfaces under air exposure for several months, as well as their evolution under treatment with concentrated aqueous sodium sulfide solution are investigated by atomic-force microscopy and x-ray photoelectron spectroscopy. It is shown that the native oxide layer formed at the Al$_{0.3}$Ga$_{0.7}$As(100) surface is non-uniform. In particular, its upper part contains III-group metal oxides and arsenic oxides, whereas the semiconductor/oxide interface is enriched with elemental arsenic. Treatment with concentrated aqueous sodium sulfide solution causes almost complete oxides removal. After treatment the elemental arsenic coat of about 1 nm thick remains, which roughness increases with the time of surface treatment.