It was noted that Li was present in high concentrations in hydrothermally-grown ZnO and compensated both n- and p-type doping due to its amphoteric nature. The Li could be manipulated by annealing and ion-implantation. Fast (20ms) flash-annealing at 900 to 1400C resulted in vacancy-cluster formation and, simultaneously, in a low-resistivity layer in the implanted part of He- and Li-implanted ZnO. The vacancy clusters, which involved 3 to 4 Zn vacancies, trapped and deactivated Li; leaving other in-grown donors to govern the electrical properties. Such clusters were not present, in sufficient concentrations, after longer 1h-annealing because of the relatively low (about 2.6eV) dissociation barrier. Thus, ZnO remained compensated until the Li diffused out during annealing at 1250C.

Deactivation of Li by Vacancy Clusters in Ion-Implanted and Flash-Annealed ZnO. T.M.Børseth, F.Tuomisto, J.S.Christensen, W.Skorupa, E.V.Monakhov, B.G.Svensson, A.Y.Kuznetsov: Physical Review B, 2006, 74[16], 161202 (4pp)