Intensity ratios of deep cathodoluminescence  bands at 4.6, 3.8 and 3.1eV to the near-band-edge emission of AlN epilayers grown by NH3-source molecular beam epitaxy were correlated with the change in S parameter of positron annihilation measurement, which represents the concentration or size of Al vacancies (VAl). The origins of the deep emission bands were attributed to donor-acceptor pairs associated with VAl and/or VAl-defect complexes. The VAl concentration was decreased by adjusting the flux ratio of NH3 to Al and growth temperature, resulting in observation of fine excitonic features in the cathodoluminescence spectra. From the energy separation between the ground and first excited states, the binding energy of free A-exciton was estimated to be 48meV.

Correlation between the Violet Luminescence Intensity and Defect Density in AlN Epilayers Grown by Ammonia-Source Molecular Beam Epitaxy. T.Hoshi, T.Koyama, M.Sugawara, A.Uedono, J.F.Kaeding, R.Sharma, S.Nakamura, S.F.Chichibu: Physica Status Solidi C, 2008, 5[6], 2129-32