Optical characterization of bulk GaN substrates with c-, a-, and m-plane surfaces

Thick free-standing GaN grown by hydride vapour phase epitaxy and epi-ready substrates with c -, a -, m -plane surfaces are examined by variable-temperature photoluminescence (PL), polarized PL and spatially resolved micro-PL. Both as-grown samples and polished substrates exhibit linewidth of the donor-bound exciton emission below 0.7 meV at 2 K indicative of a high structural quality of the material. For as-grown samples the relative intensity of green (2.4 eV) and red (1.8 eV) deep-level-defect emissions are found to decrease with increasing sample thickness. Based on plentiful two-electron-transition spectra measured in the samples the electronic fine structure of the donors and their bound-exciton complexes was examined and discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)