Zinc vacancy related emission in homoepitaxial N-doped ZnO microrods

Vertically aligned N-doped ZnO microrods have been homoepitaxially grown on a high-quality ZnO template via chemical vapor transport method without employing any catalysts. In spite of the incorporation of nitrogen, the as-grown microrods exhibited excellent crystalline and optical quality, and the behavior of intrinsic point defects and impurity-related defects have been investigated in detail by the temperature-dependent photoluminescence spectra. The emissions at 3.377, 3.368, and 3.363 eV are ascribed to free excitons, surface bound excitons and excitons bound to neutral shallow donors: zinc interstitials, respectively. The emissions at 3.359, 3.311, and 3.240 eV correspond to the radiative recombination of excitons bound to neutral acceptors, free electrons to acceptors and donor acceptor pairs, all of which are originated from the same shallow acceptor of zinc vacancy clusters with its energy level of about 126 meV above the valence band maximum. The isolated zinc vacancy is a deep acceptor, which results in the emission at 3.318 eV and the green band emissions. This study suggests that the intrinsic point defects play an extremely important role in optical properties of ZnO besides the external dopants and the understanding of intrinsic defects is crucial to get stable p-type conductivity and finally realize a ZnO homojunction for optoelectronic applications.