Preparation and properties of GaN:Al layers grown by radio-frequency magnetron sputter epitaxy

Ga-rich AlxGa1-xN (x « 0.01) (GaN:Al) single-crystalline layers were grown by radio-frequency magnetron sputter epitaxy using N2/Ar gas and a 6-N grade AlGa alloy target. When an Al0.6Ga0.4 alloy was used as the target, the Al molar fraction in the AlGaN layer increased with the increase of substrate temperature; at temperatures >1000 °C, it increased to more than 60% of the Al molar fraction of AlGa target. For an Al0.1Ga0.9 alloy target, the Al molar fraction in the AlGaN layer was less than 10% of the Al molar fraction of the target material. The GaN:Al layers, similar to GaN layers, could be grown at 900 °C and 3-12% N2 composition ratios in N2/Ar ambient gas using an Al0.1Ga0.9 target. The full-width at half-maximum (FWHM) value of the X-ray rocking curve (XRC) of the GaN:Al layer grown at 6% N2, was 28 and 368 arcsec for highly c-axis-oriented columnar domains and disordered structures inside the GaN:Al layer, respectively, for the (0002) plane. The FWHM (XRC) of the GaN:Al layer grown at 10% N2 was 600 and 1320 arcsec for the disordered structure and/or the partially relaxed portion. The threading dislocation densities depended on the N2 composition ratio.