The effect of N+ and O+ implantation upon the Knoop hardness of epitaxially grown material was studied. It was found that implantation increased the surface hardness, and this was attributed to the formation of N interstitials which pinned the dislocations and prevented plastic deformation.

Ion Implantation Effects upon the Microhardness and Microstructure of GaN. P.Kavouras, M.Katsikini, N.Vouroutzis, C.B.Lioutas, E.C.Paloura, J.Antonopoulos, T.Karakostas: Journal of Crystal Growth, 2001, 230[3-4], 454-8