Formation mechanisms of electrical conductivity and optical properties of ZnO:N film produced by annealing treatment

The effects of annealing on the chemical states of N dopant, electrical, and optical properties of N-doped ZnO film grown by molecular beam epitaxy (MBE) are investigated. Both the as-grown ZnO:N film and the film annealed in N-2 are of n-type conductivity, whereas the conductivity converts into p-type conductivity for the film annealed in O-2. We suggest that the transformation of conductivity is ascribed to the change in ratio of the N molecular number on O site (N-2) O to the N atom number on O site (NO) in ZnO:N films under the various annealed atmosphere. For the ZnO:N film annealed in N2, the percentage content of (N-2) O is larger than that of NO, i.e. the ratio > 1, resulting in the n-type conductivity. However, in the case of the ZnO:N film annealed in O-2, the percentage content of (N-2) O is fewer than that of NO, i.e., the ratio < 1, giving rise to the p-type conductivity. There is an obvious difference between low-temperature (80 K) PL spectra of ZnO:N film annealed in N-2 and that of ZnO:N film annealed in O-2. An emission band located at 3.358 eV is observed in the spectra of the ZnO:N film after annealed in N-2, this emission band is due to donor-bound exciton ((DX)-X-0). After annealed in O-2, the PL of the donor-bound exciton disappeared, an emission band located at 3.348 eV is observed, this emission band is assigned to acceptor-bound exciton (A(0)X).