It was noted that the exposure of p-type Ca-doped material, prepared by Ca+ implantation or Ca+ plus P+ co-implantation, to a H plasma at 250C led to an order of magnitude reduction in the sheet carrier density and an associated increase in hole mobility. The passivation process could be reversed by post-hydrogenation annealing (400 to 500C, N2). This reactivation of the acceptors was characteristic of the formation of neutral (Ca-H) complexes. The thermal stability of the passivation was similar to that of Mg-H complexes in material which had also been prepared by implantation, and had similar initial dopant levels. It was pointed out that the H passivation of acceptor dopants in this nitride appeared to be an ubiquitous phenomenon.

J.W.Lee, S.J.Pearton, J.C.Zolper, R.A.Stall: Applied Physics Letters, 1996, 68[15], 2102-4