Positron annihilation spectroscopy was employed to elucidate the nature and thermal behavior of defects induced 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, grow 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 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