Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

We present a detailed study of the thermal evolution of H ion-induced vacancy related complexes and voids in bulk GaN implanted under ion-cut condition. By using transmission electron microscopy, we found that the damaged band in as-implanted GaN is decorated with a high density of nanobubbles of ~1-2 nm in diameter. Variable energy Doppler broadening spectroscopy showed that this band contains 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 is detected in parallel to an increase in both size and density of nanobubbles. The observed vacancy complexes appear to be stable during annealing. However, for temperatures above 450ºC, unusually large lifetimes were measured. These lifetimes are attributed to the formation of positronium in GaN. Our finding contradicts the prevalent belief that the formation of postronium is not possible in a semiconductor. Based on the Tao-Eldrup model, the lattice opening during thermal annealing was quantified. We found that a wall spacing of 0.4 nm is induced by annealing at 600ºC. The role of these complexes in the sub-surface microcraking is discussed.