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.