Effect of the crystallinity of MOCVD-grown ZnO:N on the diffusion of impurities

The solubility of nitrogen in ZnO films grown at various temperatures by metalorganic chemical vapor deposition, using NO as both oxygen and nitrogen sources, was investigated. ZnO films were grown at 270, 310 and 370 °C, and subsequently annealed in oxygen at either 700 or 850 °C. In addition to nitrogen, hydrogen and carbon were also present in the samples. The presence of these impurities is partially explained by the formation of complexes such as (CN)O and CHx (x=1,2,3). Post-growth annealing performed on the samples suggests that the out-diffusion of such complexes is strongly influenced by the crystallinity of the films. The high porosity of films grown at temperatures ≤310 °C is favorable for the diffusion of the complexes, which results in a more efficient thermal activation of nitrogen acceptors in ZnO:N.