Observations of nitrogen-related photoluminescence bands from nitrogen-doped ZnO films

We report the synthesis and photoluminescence (PL) properties of nitrogen-doped ZnO films. These films were synthesized by filtered cathodic vacuum arc technique; nitrogen gas was used as a dopant source. X-ray diffraction results indicated that the ZnO films were highly c-axis oriented. The appearance of the nitrogen-related local vibrational Raman scattering peaks showed that nitrogen was incorporated into the films. In the PL spectrum of the undoped films, a near band edge exciton emission peak at 384nm and a weak visible band related to oxygen interstitial at 660nm were observed. For nitrogen-doped films, besides the two emission bands observed in the undoped samples, two additional PL bands at around 450 and 890nm were detected. According to the first-principle total energy calculation, nitrogen-induced acceptor energy level is located at 0.4eV above the valence band maximum. Therefore the emission band at around 450nm may originate from the recombination of photo-generated electrons with neutral nitrogen acceptors, and the 890nm band is attributed to electron transition from oxygen interstitial to this neutral nitrogen acceptors.