Optical Properties of Nitrogen-Doped Epitaxial ZnO Layers

Epitaxial nitrogen-doped ZnO (ZnO:N) films are obtained by the method of radical beam gettering epitaxy. Their optical properties are examinated by means of transmission and photoluminescence (PL) spectroscopy. The as-grown ZnO:N films show high transmittance (about 90%) in the visible range. A peak at 3.31 eV is seen in the low-temperature PL spectrum of the N-doped ZnO films, which is probably due to a neutral acceptor-bound exciton NO. Post-thermal annealing is performed on ZnO:N films in the atomic oxygen conditions. The PL of the annealed samples shows a strong response improvement, when compare with the non-annealed samples. The nature of the donor-acceptor band located at 3.23 eV and the ‘green’ band at 2.56 eV is discussed.