Optical and magnetic resonance studies of Mg-doped GaN homoepitaxial layers grown by molecular beam epitaxy

Low-temperature photoluminescence (PL) and optically detected magnetic resonance (ODMR) at 24 GHz have been performed on a series of MBE-grown Mg-doped (1017–1020 cm−3) GaN homoepitaxial layers. High-resolution PL at 5 K revealed intense bandedge emission with narrow linewidths (0.2–0.4 meV) attributed to annihilation of excitons bound to shallow Mg acceptors. In contrast to many previous reports for GaN heteroepitaxial layers doped with [Mg]>3×1018 cm−3, the only visible PL observed was strong shallow donor–shallow acceptor recombination with zero phonon line at 3.27 eV. Most notably, ODMR on this emission from a sample doped with [Mg] of 1×1017 cm−3 revealed the first evidence for the highly anisotropic g-tensor (g∥∼2.19, g⊥∼0) expected for Mg shallow acceptors in wurtzite GaN. This result is attributed to the much reduced dislocation densities (⩽5×106 cm−3) and Mg impurity concentrations compared to those characteristic of the more conventional investigated Mg-doped GaN heteroepitaxial layers.