ODMR of bound excitons in Mg-doped GaN

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 degrees from the c-axis, additional substructure on these peaks is resolved, characterized by a splitting of 14 mT, and tentatively assigned to a superhyperfine interaction. Additionally a half-field resonance split by 50 up to 70 mT 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 gc(parallel to) = g(c perpendicular to) = 1.83, g(h parallel to) = 2.18, and g(h perpendicular to) = 2.22 are found. The exchange interaction can be described by an axial fine-structure tensor with D(parallel to) = 0.18 cm(-1) and D(perpendicular to) = 0.09 cm(-1). (C) 1999 Elsevier Science B.V. All rights reserved.