Formation of deep acceptor centers in AlGaN alloys

AlGaN alloy thin film materials are of high interest for light emitting diodes (LED of the ultraviolet (UV) spectral region. Origin of the deep intrinsic and impurity Si states in the AlxGa1-xN (0 < x < 0.35) epilayer structures grown by metalorganic chemical vapor deposition (MOCVD) technique have been considered. Effects of the lattice mismatch and Si-doping in the heterostructures of epilayers with different alloy composition are investigated using time resolved photoluminescence (PL) of donor - deep acceptor (DA) pairs. It is shown that the undoped AlGaN alloys, grown on a GaN buffer layer, due to the lattice mismatch contain the increased concentration of cation vacancy (Vcation) defects acting as a deep acceptor centers and responsible for PL. Si-doping results in both the additional increase of Vcation concentration and the formation in cation sub lattice of new (VcationSication) deep acceptor complexes. It is shown that by increase of the Al content in the AlGaN alloy the composition disorder of both deep acceptor centers Vcation and (VcationSication) complex appears. The corresponding broad PL bands are resolved in number of subbands. It is stated that deposition of Si-doped AlGaN alloy on undoped GaN results in formation of Si-doped GaN interlayer.