Single crystal epitaxial gallium nitride films on GaN buffer layers were grown on (0001) sapphire using magnetron sputter epitaxy. The films were characterized using x-ray diffraction, photoluminescence, scanning electron microscopy and transmission electron microscopy. In the layers investigated thus far, the optimum buffer layer had a thickness of 500 Å at a growth temperature of 550 °C, while the optimum growth temperature range for the active GaN epilayer was found to be 900 °C–950 °C. The growth rates for the buffer layer and GaN epilayer were 0.2 and 0.35 μm/h, respectively. In general, photoluminescence studies showed emission from a broad defect band centered around 2.4 eV and a strong exciton peak at 3.48 eV. The exciton/defect intensity ratio was strongly dependent on crystal quality at constant excitation intensity. The transmission electron microscopy studies revealed highly epitaxial GaN films, showing a kind of columnar growth structure. GaN films grown at 950 °C appeared to have the best structural quality.

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