Deep impurity transitions involving cation vacancies and complexes in AlGaN alloys

Deep ultraviolet (UV) photoluminescence (PL) spectroscopy has been employed to study deep impurity transitions in AlxGa1-xN (0 <= x <= 1) epilayers. Two groups of deep impurity transitions were observed, which are assigned to the recombination between shallow donors and two different deep level acceptors involving cation vacancies (V-cation) and V-cation complexes in AlxGa1-xN alloys. These acceptor levels are pinned to two different energy levels common to AlxGa1-xN alloys (0 <= x <= 1). The deep impurity transitions related with V-cation complexes were observed in AlxGa1-xN alloys between x=0 and 1, while those related with V-cation were only observed in AlxGa1-xN alloys between x=0.58 and 1. This points out to the fact that the formation of V-cation is more favorable in Al-rich AlGaN alloys, while V-cation complexes can be formed in the whole range of x between 0 and 1. The implications of our findings to the UV optoelectronic devices using AlGaN alloys are also discussed. (c) 2005 American Institute of Physics.