Identity of the shallowest acceptor in GaN

The Be-related ultraviolet luminescence band with a maximum at about $3.38\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ in GaN:Be is caused by the shallowest acceptor in GaN with the \ensuremath{-}/0 transition level at $0.113\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ above the valence band. The luminescent properties of this acceptor were studied in detail. First-principles calculations identify this acceptor as the ${\mathrm{Be}}_{\mathrm{Ga}}{\mathrm{O}}_{\mathrm{N}}{\mathrm{Be}}_{\mathrm{Ga}}$ complex. These calculations also predict a deep level, at $0.34\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ above the valence band. However, we were not able to find evidence for this level in photoluminescence experiments.