The role of vacancy clustering and acceptor activation on resistivity evolution in N ion-implanted n-type hydrothermally grown bulk ZnO was investigated by positron annihilation spectroscopy, resistivity measurements, and chemical profiling. Room temperature 220keV N implantation using doses in the low 1015/cm2 range induced small and large vacancy clusters containing at least 2 and 3 to 4 Zn vacancies, respectively. The small clusters were present already in as-implanted samples and remain stable up to 1000C with no significant effect on the resistivity evolution. In contrast, formation of the big clusters at 600C was associated with a significant increase in the free electron concentration attributed to gettering of amphoteric Li impurities by these clusters. Further annealing at 800C resulted in a dramatic decrease in the free electron concentration correlated with activation of 1016–1017/cm3 acceptors likely to be N and/or Li related. The samples remain n type, however, and further annealing at 1000C results in passivation of the acceptor states while the big clusters dissociate.

Vacancy Clustering and Acceptor Activation in Nitrogen-Implanted ZnO. Børseth, T.M., Tuomisto, F., Christensen, J.S., Monakhov, E.V., Svensson, B.G., Kuznetsov, A.Y.: Physical Review B, 2008, 77[4], 045204