Optical and structural properties of m -plane GaN substrates grown by ammonothermal method and GaN epilayers grown on these substrates



m -plane oriented GaN substrates of size 6 x 8 mm have been obtained by ammonothermal method and used to growing GaN epilayers by metalorganic chemical vapor deposition. The structural and optical properties have been determined for both m -plane GaN substrates and GaN epilayers deposited on these substrates. Excellent structural quality of m -plane GaN substrates has been confirmed by very narrow XRD peaks (the full-width-half-maximum for the symmetrical (10.0) and asymmetrical (20.1) peaks are 16 and 19 arcsec, respectively) and the low concentration of threading dislocation density (∼ 104 cm-2). In addition, these substrates exhibit quite good optical quality: the energy gap-related transition is clearly observed at room temperature in photoluminescence and contactless electroreflectance spectra. The optical quality becomes excellent for GaN epilayers deposited on these substrates. In low temperature reflectance spectra very narrow intrinsic exciton lines which are very sensitive to the optical selection rules typical for the hexagonal symmetry were observed. In low temperature photoluminescence spectra a strong bound exciton line, relatively strong FXA and FXB lines and no emission band around 3.42 eV, which could be associated with the stacking faults, were observed. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)