The oxidation of gallium nitride epilayers in dry oxygen
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The oxidation of GaN epilayers in dry oxygen has been investigated. The GaN epilayers, about 1 μm thick, were grown on (0001) sapphire substrates by rapid thermal process/low pressure metalorganic chemical vapor deposition. Bulk θ-2θ X-ray diffraction (XRD) data showed that the slight oxidation of GaN began to occur at 800 °C for 6 h. The oxide was identified as the monoclinic β-Ga2O3. The GaN epilayers were completely oxidized at 1050 °C for 4 h or at 1100 °C for 1 h. For all samples, the strongest oxide’s peak is (11-3), and (30-6) followed. There is a rapid oxidation process in the initial stage of oxidation, and a relatively slow process followed when the temperature was over 1000 °C. The oxidation of two stages was limited by the rate of an interfacial reaction mechanism and by the diffusion mechanism, respectively. When the temperature reaches 1100 °C, the oxidation rate is very fast, which is considered as the results of the GaN decomposition at high temperature under atmosphere. The oxide layers were also observed by a scanning electron microscope, which shows a rough oxide surface and an expansion of the volume of 40%. The photoluminescence (PL) seriously influenced by the oxidation is also discussed.
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