A model for Be-related photo-absorption in compensated GaN:Be substrates

A photo-induced electron paramagnetic resonance (EPR) attributed to beryllium-related acceptors was identified in GaN:Be substrates grown by the high nitrogen pressure solution technique. The acceptors, initially compensated by shallow O-related donors, were observed after illumination with photon energy greater than 2.7 eV. To adequately fit the time-dependent photo-EPR data over time periods up to 90 min, a two-defect model was developed based on three charge transfer processes: (1) photo-excitation of electrons from compensated acceptors, (2) electron capture by the positively charged donors and neutral acceptors directly from the conduction band, and (3) electron transfer from the donors to acceptors. The analysis of the spectral dependence of the optical cross section leads to the Be-related acceptor level lying 0.7 eV above the valence band maximum, consistent with the role of the acceptor as a compensating center as well as the 2.2 eV luminescence that others observed from these and other GaN:Be samples.