A detailed study was made of the thermal evolution of H ion-induced vacancy related complexes and voids in bulk GaN implanted under ion-cut conditions. By using transmission electron microscopy, it was found that the damage band in as-implanted GaN was decorated with a high density of nanobubbles of ∼1–2nm in diameter. Variable energy Doppler broadening spectroscopy showed that this band contained vacancy clusters and voids. In addition to vacancy clusters, the presence of VGa, VGa-H2, and VGaVN complexes was evidenced by pulsed low-energy positron lifetime spectroscopy. Subtle changes upon annealing in these vacancy complexes were also investigated. As a general trend, a growth in open-volume defects was detected in parallel to an increase in both size and density of nanobubbles. The observed vacancy complexes appeared to be stable during annealing. However, for temperatures above 450 C, unusually large lifetimes were measured. These lifetimes were attributed to the formation of positronium in GaN. Since the formation of positronium was not possible in a dense semiconductor, the present finding demonstrated the presence of sufficiently large open-volume defects in this temperature range. Based upon the Tao-Eldrup model, the average lattice opening during thermal annealing was quantified. It was found that a void diameter of 0.4nm was induced

Experimental Elucidation of Vacancy Complexes Associated with Hydrogen Ion-Induced Splitting of Bulk GaN. O.Moutanabbir, R.Scholz, U.Gösele, A.Guittoum, M.Jungmann, M.Butterling, R.Krause-Rehberg, W.Anwand, W.Egger, P.Sperr: Physical Review B, 2010, 81[11], 115205