Bound excitons in GaN

The electronic structure of bound excitons in GaN is discussed, with reference to available optical data. Emphasis is given to the neutral-donor and neutral-acceptor spectra, which are the most prominent ones in the experimental photoluminescence data. Two dominant donor bound excitons are observed with photoluminescence lines just above 3.47 eV at 2 K in unstrained samples, tentatively associated with Si and O shallow donors. Several acceptor bound excitons are present; the most prominent one with a photoluminescence line at about 3.466 eV is tentatively assigned to the Mg acceptor. We attempt an explanation of the available data from magneto-optical experiments on this line in terms of a spin-like acceptor hole, as observed in independent magnetic resonance data. Characteristic deep emissions related to P and As doping are reported; they may be interpreted in terms of isoelectronic bound excitons. Excitons bound to structural defects in GaN are also briefly discussed.