The atomic structure of the characteristic defects (Mg-rich hexagonal pyramids) in p-doped bulk and metal-organic chemical vapour deposited GaN:Mg thin films grown with Ga polarity was determined at atomic resolution via direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects, as confirmed by positron annihilation. The inside walls of the cavities were covered with GaN of reverse polarity, compared with the matrix. Annealing of the metal-organic chemical vapour deposited layers led to a slight increase in the defect size and an increase in the room temperature photoluminescence intensity. Positron annihilation confirmed the presence of vacancy clusters of various sizes, triggered by the Mg doping of as-grown samples a decrease in their concentration upon annealing at 900 or 1000C.

Atomic Structure of Pyramidal Defects in GaN:Mg - Influence of Annealing. Z.Liliental-Weber, T.Tomaszewicz, D.Zakharov, M.O’Keefe, S.Hautakangas, K.Saarinen, J.A.Freitas, R.L.Henry: Physica Status Solidi A, 2006, 203[7], 1636-40