Real-time studies of gallium arsenide anodic oxidation

Advantages of native oxides as insulating layers on semiconductors include simplicity of processing, dependable film adhesion, and system purity. Anodic oxidation has been used to produce native oxide layers on gallium arsenide of sufficient quality for use in some electronic applications; however, a clear structural-chemical understanding of the anodic oxide has yet to be fully obtained. In this study, surface IR spectroscopy has been applied both for the characterization of pre-oxidized GaAs and for investigation of the oxide as it is being formed. The technique is applied in an in situ, multiple internal reflection geometry to measure directly the composition and growth rate of anodic oxides at the GaAs-electrolyte interface. The IR spectra show that the anodic oxide is not a simple mixture of Ga₂O₃ and As₂O₃, but instead appears to be composed of AsO₃ and GaO₄ units linked through bridging oxygen atoms at the molecular level. An oxide grown chemically by immersion in H₂O₂ showed a higher incorporation of hydroxyl groups and interstitial water as well as a higher proportion of termal oxygen atoms (lower degree of crystallinity) than the anodic oxide. The effects of process parameters on kinetics and on composition are under study to determine optimum growth conditions.