Study of ion beam induced defects in ZnO by using slow positron beam

Chen, Z. Q.; Maekawa, Masaki; Yamamoto, Shunya; Sekiguchi, Takashi*; Kawasuso, Atsuo

Undoped ZnO crystals were implanted with Al, N and Al/N respectively. The implantation induced defects and their recovery were studied using a variable energy slow positron beam. Vacancy clusters are introduced in all the implanted samples. The annealing of the defects in Al-implanted sample shows two stages, which might be due to the agglomeration of vacancy clusters and their recovery, respectively. Large voids are also observed when the Al dose is higher than 10 cm, which suggest amorphization of ZnO. However, for both the N-implanted and the Al/N co-implanted sample, the annealing behavior of the defects shows four stages. The last two stages might be related with the formation and recovery of nitrogen related defect complexes. Hall measurements show a strong n-type conductive layer after Al implantation and annealing, suggesting that all the Al ions are activated. However, for the N-implanted and Al/N co-implanted ZnO, the implanted layer still shows n-type conductivity. The possible reason is discussed.