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

The photoluminescence spectra of a thick layer of heteroepitaxial GaN, which has an exceptionally low dislocation density of 3×10⁶ is presented. Analysis of this structure gives data on the excitonic and impurity states. The undoped sample was grown by hydride vapor phase epitaxy (HVPE) on sapphire(0001) using HCl, metallic Ga, and NH₃ as precursors. The spectra permits identification of n = 2 and three two-electron satellites involving up to five donor species with ionization energies from 22 to 34.5 meV. The free exciton binding energy confirmed as 26.4 meV, independent of strain.