Oxide growth on cleaved (011̄) cross sections of GaAs/AlGaAs heterostructures exposed to air was investigated using atomic force microscopy. Measurements of the height profile at constant force provide information on the oxide growth rate as a function of time and Al-mole fraction. We observe an initial field-aided oxidation mode that follows the Cabrera–Mott model for metal oxidation. After a critical time, oxidation proceeds more slowly, probably assisted by a thermal diffusion process. We used the dependence of oxide thickness on alloy composition for imaging the Al content in GaAs/AlGaAs heterostructures deposited on nonplanar substrates, with a lateral resolution of ≊1 nm.
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Reinhardt et al. (1996) studied this question.