InN thin films have been grown epitaxially on GaN-buffered sapphire substrates by molecular-beam epitaxy at 500 °C. A high level of oxygen contamination in the growth chamber led to formation of In2 O3 precipitates in the films. These precipitates were characterized in detail by transmission electron microscopy (TEM). The concentration of In2 O3 was estimated to be less than 0.07 vol % in the present samples of oxygen content ∼0.5 at. %. Cross-sectional TEM investigations revealed that the precipitates adopt a preferred crystallographic orientation within the InN matrix, and show a characteristic diameter of ∼5 nm with average distance of ∼500 nm. These observations suggest the effective solubility of O in InN could be below 1 at. % at 500 °C.
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