Positron annihilation spectroscopy was used to elucidate the nature and thermal behavior of defects introduced by Cu in free-standing GaN crystals. The Cu atoms were intentionally introduced into the GaN lattice via thermally activated diffusion from an ultra-thin Cu capping layer. During isochronal annealing of the obtained Cu-doped GaN at 450 to 850K, vacancy clusters were found to form, grew and finally vanish. Doppler broadening measurements demonstrated the presence of vacancy-like defects across the 600nm-thick layer below the surface corresponding to the Cu-diffused layer as evidenced by secondary ion mass spectrometry. A more qualitative characterization of these defects was accomplished by positron lifetime measurements. It was found that annealing at 450K triggered the formation of divacancies, whereas a further increase in the annealing temperature up to 550K led to the formation of large clusters of about 60 vacancies. The observations suggested that the formation of these vacancy-like defects in bulk GaN was related to the out-diffusion of Cu.

Cu Diffusion-Induced Vacancy-Like Defects in Freestanding GaN. M.Elsayed, R.Krause-Rehberg, O.Moutanabbir, W.Anwand, S.Richter, C.Hagendorf: New Journal of Physics, 2011, 13[1], 013029