Characterization study of GaAs(001) surfaces using ion scattering spectroscopy and x-ray photoelectron spectroscopy

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Abstract
A surface characterization study using ion scattering spectroscopy (ISS) and x-ray photoelectron spectroscopy (XPS) has been performed on solvent cleaned, n-type GaAs(001) substrates before and after cleaning by ion sputtering and annealing. The native oxide layer on this surface contains large amounts of As2O5,As2O3, and Ga2O3 according to XPS with Ga2O3 being the predominant species. Before cleaning C is present as hydrocarbons, carbonates, and carbide with hydrocarbons as the predominant chemical state. Ion sputtering converts the hydrocarbons into carbide, which is difficult to remove by further sputtering/annealing cleaning cycles, but O is removed by these cycles. According to ISS data, the outermost atomic layer is enriched in Ga before cleaning, but after cleaning the ISS Ga-to-As atom ratio is about 1:2. The results obtained in this study are consistent with the presence of a layered oxide structure with Ga2O3 just above the interface. A sputter-cleaned surface initially exhibits an increase in the Ga-to-As surface atom ratio which returns to the initial state with time (∼2 h) as observed by ISS. The Ga-to-As surface atom ratio also increases by annealing at temperatures as low as 180 °C.

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