In situ study of the electronic structure of polar-to-polar SrTiO3/(000[formula omitted])ZnO heterointerface

Abstract

The SrTiO3(STO)/ZnO heterointerface, which is widely used in the fabrication of novel optoelectronic devices, is a classical system combining functional perovskite oxides and wurtzite-structure semiconductor materials. The electronic structure of the heterointerface often plays a significant role in controlling the functions of novel devices. In this study, the electronic structure was explored using in situ photoemission spectroscopy and X-ray absorption spectroscopy. X-ray diffraction results showed the coexistence of (111)STO and (011)STO orientations for the STO film deposited on the ZnO-(0001-) substrate via pulsed laser deposition. High-resolution transmission electron microscopic results revealed two types of polar interfaces: [112-][101-](111)STO//[12-10][101-0](0001-)ZnO and [111][21-1-](011)STO//[102-1][101-0](0001-)ZnO. In situ photoemission spectroscopic results revealed downward band bending and the transformation of the valence states of Ti from 4+ to 3+, with extra electrons transferring to the hybridization states between O 2p and Ti t2g orbitals at the polar-to-polar STO/ZnO interface. We propose that the polar discontinuity drives the electron transfer to the STO/ZnO interface during the growth process. This study provides insight into the electronic structure of the STO/(0001-)ZnO heterointerface.