Band alignment and band bending at a-Ga2O3/ZnO n-n isotype hetero-interface

Understanding the electronic structures at the interfaces of wide bandgap oxide heterostructures is crucial for the rational design of oxidebased optoelectronic devices with novel functionality and improved performance. In this work, the electronic band diagram at a ZnO/ a-Ga2O3 n-n isotype heterojunction is investigated by depth-profile x-ray photoemission spectroscopy (XPS). The directly measured valence-band offset is 0.61 6 0.1 eV and a type-I (straddling gap) band alignment is formed at the ZnO/a-Ga2O3 heterointerface. As probed by the depth profile of core-levels and VB-XPS, the formation of an interfacial layer is observed due to Ga and Zn interdiffusion, where charged interfacial states result in the downward and upward band-bending at the ZnO and a-Ga2O3 sides, respectively. The influence of band bending and band discontinuity at the interface is confirmed by the rectifying characteristics in the Au/a-Ga2O3/ZnO heterojunction with electron accumulation at its interface. Taking the thermionic-field emission and band-to-band tunneling mechanisms into account, the simulated transport properties agrees well with the reported I-V characteristics of Au/a-Ga2O3/ZnO avalanche photodiode, a further validation of the deduced band alignment of the heterostructure.This work was supported by the National Key R&D Program (No. 2018YFB0406502), the State Key R&D project of Jiangsu (No. BE2018115), the National Nature Science Foundation (Nos. 61774081 and 91850112), the Natural Science Foundation of Jiangsu Province (No. BK20161401), Shenzhen Fundamental Research Project (Nos. 201773239, 201888588, and 20180307163240991), State Key Laboratory of Wide-Bandgap Semiconductor Power Electric Devices (No. 2017KF001), and the Fundamental Research Funds for the Central Universities (Nos. 021014380135, 021014380112, and 021014380110)