Impacts of Si-doping on vacancy complex formation and their influences on deep ultraviolet luminescence dynamics in Al_xGa_1−xN films and multiple quantum wells grown by metalorganic vapor phase epitaxy

To find a clue to increase the emission efficiencies of AlxGa1−xN-based deep ultraviolet light emitters, the origins and influences on carrier concentration and minority carrier lifetime (t_minority), which determines the internal quantum efficiency, of midgap recombination centers in c-plane Si-doped Al0.60Ga0.40N epilayers and Al0.68Ga0.32N quantum wells (QWs) grown by metalorganic vapor phase epitaxy were studied by temporally and spatially resolved luminescence measurements, making a correlation with the results of positron annihilation measurement. For the Al0.60Ga0.40N epilayers, t_minority decreased as the concentration of cation vacancies (VIII) increased, indicating that VIII, most probably decorated with nitrogen vacancies (VN), VIII(VN)n, are major nonradiative recombination centers (NRCs). For heavily Si-doped Al0.60Ga0.40N, a generation of electron-compensating complexes (VIII–SiIII) is suggested. For the lightly Si-doping regime, t_minority of the QW emission was increased by appropriate Si-doping in the wells, which simultaneously increased the terrace width. The importance of wetting conditions is suggested for decreasing the NRC concentration.