Correlation between the violet luminescence intensity and defect density in AlN epilayers grown by ammonia-source molecular beam epitaxy

摘要

Intensity ratios of deep eathodoluminescence (CL) bands at 4.6, 3.8 and 3.1 eV to the near-band-edge emission of AlN epilayers grown by NH_3-source molecular beam epitaxy were correlated with the change in S parameter of positron annihilation measurement, which represents the concentration or size of A1 vacancies (V_(Al)). The origins of the deep emission bands were assigned to donor-acceptor pairs associated withrnV_(Al) and/or V_(Al)-defect complexes. The V_(Al) concentration was decreased by adjusting the flux ratio of NH_3 to Al and growth temperature, resulting in observation of fine excitonic features in the CL spectra. From the energy separation between the ground and first excited states, the binding energy of free A-ex.citon was estimated to be 48 meV.