In situ study of the electronic structure of polar-to-polar SrTiO3/(0001‾)ZnO heterointerface

• SrTiO 3 film on ZnO substrate exhibited two types of polar interface structures. • Ultraviolet photoelectron spectroscopy showed downward bending band. • Transformation of Ti valence states from 4+ to 3+ appeared at polar interface. The SrTiO 3 (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 (1 1 1) STO and (0 1 1) STO orientations for the STO film deposited on the ZnO-(000 1 - ) substrate via pulsed laser deposition. High-resolution transmission electron microscopic results revealed two types of polar interfaces: [11 2 - ][10 1 - ](1 1 1) STO //[1 2 - 10][10 1 - 0](000 1 - ) ZnO and [1 1 1][2 1 - 1 - ](0 1 1) STO //[10 2 - 1 ][10 1 - 0](000 1 - )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 t 2g 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/(000 1 - )ZnO heterointerface.