Bound excitons in GaN

The electronic structure of bound excitons in GaN is discussed, with refere nce to available optical data. Emphasis is given to the neutral-donor and n eutral-acceptor spectra, which are the most prominent ones in the experimen tal photoluminescence data. Two dominant donor bound excitons are observed with photoluminescence lines just above 3.47 eV at 2 K in unstrained sample s, tentatively associated with Si and O shallow donors. Several acceptor bo und excitons are present; the most prominent one with a photoluminescence l ine at about 3.466 eV is tentatively assigned to the Mg acceptor. We attemp t 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 bou nd excitons. Excitons bound to structural defects in GaN are also briefly d iscussed.