Mosaicity and stress effects on luminescence properties of GaN



High-resolution X-ray diffraction (HRXRD) of several GaN layers grown on Si/N treated c -plane sapphire substrate by metal-organic chemical vapour phase deposition (MOCVD) were investigated. Photoluminescence (PL) measurements were carried out at 13 K. GaN mosaicity was studied at different growth stage with a thickness varying from 0.1 to 4.5 µm. Rocking curves of symmetric and asymmetric plane reflections were investigated to determine respectively the tilt and twist mosaic. Using PL spectra and HRXRD scattering a correlation were found between the intensity and the full width at half maximum (FWHM) of the bound exciton neutral donor (I2) with the GaN mosaicity. The I2 intensity increased significantly with increasing the interaction parameter (m) between tilt and twist mosaic, whereas the FWHM of I2 decreased with increasing m. The evolution of the compressive stress with thickness is extracted from HRXRD and correlated with PL measurements. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)