A theoretical study was made of the diffusion behavior of H in N-doped ZnO, and it was found that N could trap the diffusing H nearby, by overcoming activation energies of no more than 0.5eV. Then the trapped H moved around the doped N by overcoming low-energy (<0.4eV) barriers. Breaking the N–H bond to release the H atom requires an energy of at least 1.25eV, which was significantly higher than that for H diffusion in perfect ZnO (~0.5eV). Therefore, the acceptor N in ZnO was favourably passivated by donor H, being partly responsible for the experimental phenomenon that high hole concentrations in N doped p-type ZnO was difficult to be obtained. Calculations of electronic structures revealed that the location of H around the doped N atom sensitively affected the gap states.

Hydrogen Diffusion Behavior in N Doped ZnO - First-Principles Study. Hu, J., He, H.Y., Pan, B.C.: Journal of Applied Physics, 2008, 103[11], 113706