EXCITONIC TRANSITIONS IN MBE GROWN H-GAN WITH CUBIC INCLUSIONS

Undoped and magnesium doped MBE grown GaN epilayers on sapphire substr ates show a particular variety of near-bandgap luminescent transitions . Despite the large lattice mismatch to the substrate, pronounced free - and bound-exciton transitions allow for an estimation of the exciton ic binding energies. For the given thickness range (about I mu m), we find an almost strain-relaxed situation with the main exciton transiti on energies well corresponding to the bulk values. On their low-energy side, we identify lines having been tentatively assigned to stacking fault excitons, and interface-related exciton transitions correlated t o extended defects and/or dislocations in this spatial region. Evidenc e of cubic inclusions of a size up to 500 nm is doubtless given by obs erving sharp c-GaN related donor-bound exciton emission and respective structures in transmission electron microscope investigations. (C) 19 98 Elsevier Science B.V. All rights reserved.