Photo-EPR study of compensated defects in Be-doped GaN substrates

Abstract

Time-dependent photo-induced electron paramagnetic resonance measurements were performed on GaN crystals grown by the high nitrogen pressure solution method. A resonance was induced in Be-doped samples by illuminating with photon energies greater than 2.7 eV. The EPR was thermally stable at T=4K and was quenched with photon energies between 0.5 and 2.7 eV. Optical cross sections for EPR excitation and quenching processes were extracted from time-dependent measurements using a model for defect charge state populations. A fit to the cross sections was performed using a lineshape for photon absorption by deep centers in GaN. The threshold for photo-excitation of a compensated acceptor (A−+hν→A0+eCB−) was 2.5 eV followed by a lattice relaxation of 0.3 eV. The threshold for the complimentary process (A0+hν→A−+hVB+) was 0.75 eV with a relaxation energy of 0.3 eV. These values are consistent with CN being the EPR-active acceptor. Thermal quenching is attributed to delocalization of carriers from a beryllium-related electron trap, which are then captured by neutral CN.