Charge Transfer in Compensated GaN:Be Substrates Observed with Magnetic Resonance*

GaN:Be layers are used for electrical isolation, and the broad Be-related yellow luminescence (YL) may be used for white-light production. To understand this behavior, we investigate charge transfer using photo-induced electron paramagnetic resonance (EPR). GaN substrates grown from Ga solution under high N pressure (HNPS) and doped with 10$^{\mathrm{19}}$ O/cm$^{\mathrm{3}}$ and 10$^{\mathrm{17}}$ to 10$^{\mathrm{19}}$ Be/cm$^{\mathrm{3}}$ were studied using time-dependent photo-EPR at 3.5 K. Excitation with $E_{ph}$ \textgreater 2.6 eV increased EPR amplitude, while subsequent illumination with $E_{ph}$ \textgreater 1 eV quenched EPR. A charge transfer model fit to the data included electron-excitation, capture onto ionized donors and neutral acceptors, and recombination of neutral donors and acceptors. The spectral dependence of the optical absorption cross-section of the negative charge state (A$^{\mathrm{-}})$ of a Be-related acceptor revealed an acceptor level $E_{V} \quad +$ 0.7 eV and structural relaxation of 0.5 eV for the A$^{\mathrm{-}} \quad \to $ A$^{\mathrm{0}} \quad +$ e$^{\mathrm{-}}_{\mathrm{CB}}$ transition. Preliminary analysis of quenching suggests an acceptor level at $E_{V} \quad +$ 1 eV and a relaxation of 1 eV for A$^{\mathrm{0}} \quad +$ e$^{\mathrm{-}}_{\mathrm{VB}} \quad \to $ A$^{\mathrm{-}}$. The deep acceptor level provides an explanation for the efficacy of Be in producing resistive substrates and for the YL mechanism used for light conversion.