Roles of Al-vacancy complexes on the luminescence spectra of low dislocation density Si-doped AlN grown by halide vapor phase epitaxy

Roles of Al-vacancy (V-AI) complexes on the cathodoluminescence (CL) spectra of Si-doped AlN grown by halide vapor phase epitaxy (HVPE) on a physical-vapor-transported (0001) AlN substrate are described, making a connection with the results of positron annihilation measurements. A combination of HVPE and AlN substrate enabled decreasing deleterious carbon concentration and dislocation density, respectively, thus accentuating the influences ofVAI -complexes on the luminescence processes. A low-temperature CL spectrum of unintentionally doped AlN exhibited predominant excitonic emissions at around 6 eV and a marginal deep-state emission band at around 3.7 eV that originates from residual carbon (<10(16) cm(-3)) on nitrogen sites (CN ). However, the sample was revealed to contain a considerable amount (similar to 10(17) cm(- 3)) of vacancy clusters, most likely comprising a V(AI )and nitrogen-vacancies (V-N), namely,V-AI(V-N)1 (- 2) , which act as nonradiative recombination centers that decrease overall CL intensity at elevated temperatures. With increasing Si-doping concentration ([Si]), major vacancy species progressively changed from VAI(V-N)(1 - 2) to V-AI(ON) (1 - 2) , where (ON) is oxygen on N sites, which exhibit other deep-state emission bands ranging from 3.2 to 3.5 eV. Further increase in [Si] gave rise to the formation of donor-compensating defects comprising V(AI )and Si on the second-nearest-neighbor Al sites ( Si Al ), abbreviated by V-AI- Si Al n , which exhibit emission shoulders at around 2.9-3.0 eV. When [Si] exceeded 5 x 10(18) cm(-3), an emission band at around 4.5 eV emerged, which had been ascribed to originate from the nearest-neighbor SiAlCN complexes. Because V-AI-complexes, including those containing impurities, are thermally stable, incorporation of vacancies should be blocked at the growth stage.