Dissociation of H-related defect complexes in Mg-doped GaN

Abstract

Post-growth annealing and electron beam irradiation during cathodoluminescence were used to determine the chemical origin of the main optical emission lines in moderately and heavily Mg-doped GaN. The 3.27 eV donor-acceptor pair (DAP) emission line that dominates the emission spectrum in moderately Mg-doped (p-type) GaN was found to be strongly reduced by electron irradiation and of different chemical origin than the DAP at a similar energetic position in Si-doped (n-type) GaN. These results suggest that the acceptor responsible for the 3.27 eV DAP emission in Mg-doped GaN is Mg and that the donor (20--30 meV) is hydrogen-related, possibly a $({\mathrm{V}}_{\mathrm{N}}\ensuremath{-}\mathrm{H})$ complex. This complex is dissociated either by electron irradiation or thermal annealing in ${\mathrm{N}}_{2}$ or ${\mathrm{O}}_{2}$ atmosphere. We found that upon electron irradiation, a deeper emission line (centered at 3.14 eV) emerged, which was assigned to a DAP consisting of the same Mg acceptor level and a deeper donor (100--200 meV) with a similar capture cross section as the donor in the 3.27 eV emission. Moreover, two different deep donor levels at $350\ifmmode\pm\else\textpm\fi{}30$ and $440\ifmmode\pm\else\textpm\fi{}40\mathrm{meV}$ were identified as being responsible for the blue band (2.8--3.0 eV) in heavily Mg-doped GaN. The donor level at $350\ifmmode\pm\else\textpm\fi{}30\mathrm{meV}$ was strongly affected by electron irradiation and attributed to a H-related defect.