The critical Mg doping on the blue light emission in p-type GaN thin films grown by metal-organic chemical vapor deposition

The photoluminescence and the photo-current from p-type GaN films were investigated on both room- and low-temperatures for various Mg doping concentrations. At a low Mg doping level, there exists a photoluminescence center of the donor and the acceptor pair transition of the 3.28-eV band. This center is correlated with the defects for a shallow donor of the VGa and for an acceptor of MgGa. The acceptor level shows the binding energy of 0.2-0.25 eV, which was observed by the photon energy of the photo-current signal of 3.02-3.31 eV. At a high Mg doping level, there is a photoluminescence center of a deep donor and an acceptor pair transition of the 2.76-eV blue band. This center is attributed to the defect structures of MgGa-VN for the deep donor and MgGa for the acceptor. For low. doped samples, thermal annealing provides an additional photo-current signal for an unoccupied deep acceptor levels of 0.87-1.35 eV above valence band, indicating the p-type activation.