Donor–acceptor pair recombination in non-stoichiometric ZnO thin films

The stoichiometry of pulsed-laser deposited, nominally undoped ZnO thin films can be controlled via oxygen partial pressure during growth. Samples grown under zinc-rich conditions at pressures below 0.02 mbar show the formation of a donor–acceptor pair recombination at 3.104 eV. Temperature- and excitation-dependent photoluminescence studies revealed structural defects, namely zinc interstitials and zinc vacancies, with donor and acceptor binding energies of ED=40meV and EA=320meV, respectively, to be accountable for this recombination. The findings were confirmed via calculations within the quantum defect model.