Structural properties of GaN layers grown on Al2O3 (0001) and GaN/Al2O3 template by reactive radio-frequency magnetron sputter epitaxy

GaN single-crystalline layers were grown by reactive radio-frequency magnetron sputter epitaxy using N2/Ar ambient gas and Ga target. The GaN layers were grown directly on Al2O3 (0001) substrates and GaN/Al2O3 templates. The crystalline quality and the surface morphology of GaN layer depending on substrate temperature and N2 composition ratio, were measured. The crystalline quality of GaN layer was improved by increasing substrate temperature and also decreasing N2 composition ratio. The full-width at half-maximum (FWHM) value of X-ray rocking curve (XRC) of GaN layer grown on Al2O3 at 900 °C and 6% N2, was 27 and 338 arcsec for highly c-axis oriented columnar domains and disordered structure inside the GaN layer, respectively, for (0002) plane. The FWHM values of XRCs of the GaN layers on GaN/Al2O3 for both (0002) and (1012) planes, decreased with the increase of substrate temperature, and at above 890 °C they were similar to those of the metal-organic vapor phase epitaxy-grown GaN template, which were approximately 300 and 310 arcsec, respectively. The threading dislocation densities were also estimated using the FWHM values of XRCs, and those of GaN layers on GaN/Al2O3 were considerably decreased as compared with those on Al2O3 at substrate temperatures more than 890 °C.