C and N co-implantation in Be-doped GaN

Carbon and nitrogen co-implantation characteristics in Be-doped GaN with different dopant concentration ratios have been systematically investigated. It was found that the conductive characteristics of Be-doped GaN convert to p-type by co-implantation of C or N atoms and subsequent annealing, which are essentially related to the dopant concentration ratio and annealing conditions. The conversion could be attributed to the reduction of self-compensation and the shift of the surface Fermi level towards the valance band edge. The outcome was reasonably in agreement with the surface stoichiometric switching as determined by x-ray photoelectron spectroscopy measurements. From photoluminescence data, the activation energy of the Be acceptor level was evaluated to be about 145-155 meV, which is shallower than that of Mg acceptors. These experimental results indicated that co-implanting C or N with Be atoms into the selective area of GaN is an effective method to enhance the electrical activation efficiency of Be acceptors and to reduce the surface barrier height, which can help to decrease the metal contact resistivity to p-type GaN.