Relation between Al vacancies and deep emission bands in AlN epitaxial films grown by NH_3-source molecular beam epitaxy

摘要

Intensity ratios of characteristic deep cathodoluminescence (CL) bands at 4.6, 3.8, and 3.1 eV to the near-band-edge emissions at 11 K of AlN epilayers grown by NH_3-source molecular beam epitaxy were correlated with the change in the S parameter of positron annihilation measurement, which represents the concentration or size of Al vacancies (V_(Al)). Since the relative intensities of 3.1 and 3.8 eV bands increased remarkably with lowering supply ratio of NH_3 to Al (Ⅴ/Ⅲ ratio) and growth temperature (T_g), they were assigned to originate from V_(Al)-O complexes. The V_(Al) concentration could be decreased by adjusting Ⅴ/Ⅲ ratio and T_g, 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 A exciton was determined to be 48 meV.