| Optical and electron paramagnetic resonance (EPR) studies of point defects in GaN and AlN are presented in this dissertation. The EPR is detected optically (ODEPR), either in the luminescence or the absorption of the material.; New luminescence (PL) and associated magnetic resonance (PL-ODEPR) spectra are reported for HVPE-grown GaN. The relationship between the PL wavelength and the relative level position ordering of the characteristic deep PL-ODEPR centers (estimated from the relative magnitude of their g-values) suggests that, in each case, the spin-dependent recombination is a precursor to the luminescence, rather than being directly responsible for it. A highly anisotropic PL-ODEPR signal is identified as arising from copper, unintentionally introduced in trace amounts during growth. Crystal-field analysis establishes that it substitutes for gallium, and that its anisotropy arises from spin-orbit and trigonal field interactions of comparable strength. The analysis developed for copper is then successfully applied to understanding a different, unrelated system (interstitial tellurium in ZnTe).; Intrinsic defects (vacancies and interstitials on both GaN sublattices), preferentially introduced by room temperature 2.5MeV electron-irradiation, are investigated in several samples. Two PL-ODEPR spectra, each displaying hyperfine interaction with a single gallium atom, are identified as trapped gallium interstitials. Another PL-ODEPR spectrum, displaying partially resolved hyperfine interaction with three, or possibly four equivalent Ga atoms, is tentatively identified with the nitrogen vacancy, either isolated, or part of a defect complex. An S = 1 center is also observed after irradiation, but its chemical identity could not be positively established.; In AIN, a new ODEPR spectrum is observed via magnetic circular dichroism in absorption (MCDA). Its unusual relaxation properties establish that both the magnetic resonance and the spin-lattice relaxation take place in the excited state of the defect, which in turn affects the ground state population being observed in the experiment, by spin memory in the optical pumping cycle. |
