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 in vestigate the free and bound exciton and shallow impurity states in GaN. A 300-mu m- thick GaN layer grown by hydride vapor phase epitaxy on sapphire( 0001), with an exceptionally low dislocation density (3 x 10(6) cm(-2)) is used to obtain very high quality spectra. Both free and bound n = 2 exciton s are identified, leading to a confirmation of the A free exciton binding e nergy as about 26.4 meV, independent of strain. Principal neutral donor-bou nd exciton (D-0, X) peaks involving two to three different donors are resol ved, as are two-electron satellites involving up to five different residual donors with binding energies ranging from 22 to 34.5 meV. (C) 1999 America n Institute of Physics. [S0003-6951(99)04116-9].