Interface characteristics of (Zn,Mn)O/ZnO grown on ZnO substrate

Abstract

ZnO single layer and (Zn,Mn)O/ZnO hetero-structure were fabricated on an O-face ZnO substrate. Both surfaces were very smooth, consisting of steps and terraces, and were very similar. These results suggest that the interface between the ZnO and (Zn,Mn)O layers is very smooth. The temperature dependence of the electron mobility indicates the existence of accumulated electrons beside the interface. However, the electron mobility was lower than that of the two-dimensional electron gas (2DEG) beside the (Zn,Mn)O/ZnO hetero-interface reported in our previous paper. In addition, the electron mobility at room temperature suggests that the electrons are confined in the (Zn,Mn)O layer, although the 2DEG observed in the previous study was confined in the ZnO layer. Therefore, the band alignments of the hetero-structures of the present study are expected to be very different from those reported in the previous study. In order to confirm the band alignment with confined electrons in the (Zn,Mn)O layer, an electron-supplying layer was fabricated in the ZnO layer. The resulting change in the electron mobility supports the band alignment. Enlargement of the energy band gap of (Zn,Mn)O was carried out by Mg doping. The results for the electron transport properties also support the band alignment. All of the present results support the band alignment having confined electrons in the (Zn,Mn)O side of the hetero-interface, although, in our previous study, the 2DEG was confirmed to be in the ZnO layer. The discrepancy in band alignment was assumed to be caused by the unintentional change in Mn concentration related to the parameters defining the band alignment, such as the energy band gap, electron affinity and Fermi level of the (Zn,Mn)O layer.