Low-temperature luminescence of exciton and defect states in heteroepitaxial GaN grown by hydride vapor phase epitaxy

Low-temperature (1.7–20 K) photoluminescence and reflectance are used to investigate the free and bound exciton and shallow impurity states in GaN. A 300-μm-thick GaN layer grown by hydride vapor phase epitaxy on sapphire(0001), with an exceptionally low dislocation density (3×106 cm−2) is used to obtain very high quality spectra. Both free and bound n=2 excitons are identified, leading to a confirmation of the A free exciton binding energy as about 26.4 meV, independent of strain. Principal neutral donor-bound exciton (D0,X) peaks involving two to three different donors are resolved, as are two-electron satellites involving up to five different residual donors with binding energies ranging from 22 to 34.5 meV.