The Zn-vacancy related green luminescence and donor-acceptor pair emission in ZnO grown by pulsed laser deposition

A low temperature (10 K) photoluminescence study shows that green luminescence (GL) peaking at 2.47 eV and near band edge (NBE) emission at 3.23 eV are introduced in undoped ZnO grown by pulsed laser deposition (PLD) after 900 degrees C annealing. The NBE emission exhibiting blue shift with increasing temperature is assigned to the transitions of the donor-acceptor-pair (DAP)/free-electron-to-acceptor (FA). Positron annihilation spectroscopy (PAS) study shows that the introduction of the GL is correlated with the formation of the Zn vacancy-related defect (V-Zn). Comparing the transition energies of V-Zn obtained by the previous first principles calculation [Janotti and Van de Walle, Phys. Rev. B: Condens. Matter Mater. Phys., 2007, 76, 165202], the GL is associated with the transition from the conduction band to the epsilon(-/2-) state of V-Zn and the DAP/FA emission involves the acceptor level epsilon(0/-) of V-Zn.