ODMR of bound excitons in Mg-doped GaN

Abstract

GaN bulk crystals compensated with Mg exhibit a strong yellow photoluminescence (PL) band. However, optically detected magnetic resonance (ODMR) experiments show that the microscopic origin of this luminescence is completely different from the one observed in n-type GaN. The ODMR spectra of GaN:Mg bulk crystals are dominated by a fine-structure-split pair of lines. At magnetic field orientations between 45 and 60° from the c-axis, additional substructure on these peaks is resolved, characterized by a splitting of 14mT, and tentatively assigned to a superhyperfine interaction. Additionally a half-field resonance split by 50 up to 70mT is detected. The spectra are described by an electron–hole pair located at a close donor–acceptor pair. Axial donor and acceptor g-values of ge||=ge⊥=1.83, gh||=2.18, and gh⊥=2.22 are found. The exchange interaction can be described by an axial fine-structure tensor with D||=0.18cm−1 and D⊥=0.09cm−1.