| AVS 55th International Symposium & Exhibition | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM-TuM |
| Session: | ZnO Materials and Devices |
| Presenter: | C.F. McConville, University of Warwick, UK |
| Authors: | C.F. McConville, University of Warwick, UK T.D. Veal, University of Warwick, UK P.D.C. King, University of Warwick, UK S.A. Hatfield, University of Warwick, UK B. Martel, CNRS, France J. Chai, Univ. of Canterbury, New Zealand M.W. Allen, Univ. of Canterbury, New Zealand S.M. Durbin, Univ. of Canterbury, New Zealand J. Zuniga-Perez, CNRS, France V. Munoz-Sanjose, Valencia University, Spain |
| Correspondent: | Click to Email |
The surface and interface electronic properties of ZnO have been investigated using high-resolution x-ray photoemission spectroscopy (XPS). Understanding the surface and interface electronic properties of ZnO is vital for the realisation of its potential in applications as diverse as gas, chemical and biological sensors, Schottky diodes, light emitters and transparent electrodes. A wide range of ZnO bulk and epi-samples grown by different techniques and with different surface orientations and bulk carrier densities have been studied. These include m-plane and Zn- and O-polarity c-plane hydrothermally-grown bulk ZnO, a-plane and c-plane ZnO grown by metal organic vapour phase epitaxy and c-plane ZnO grown by plasma-assisted molecular-beam epitaxy (MBE). Valence-band XPS indicates that the surface Fermi level is significantly above the conduction band minimum for all of the samples studied, with small variations observed as a function of surface orientation. These results are explained in terms of the band structure of ZnO with its low Gamma-point conduction band minimum, significantly below the charge neutrality level. The results are further discussed in the context of a wide range of previous results on ZnO surface electronic properties, particularly surface conductivity data. Additionally, the first steps towards the development of hybrid oxide/nitride heterostructures have been taken with the MBE growth of ZnO on AlN. XPS has been used to determine the valence band offset of the ZnO/AlN heterojunction. Using the transitivity rule, and our measurements of the III-nitride band offsets, this has enabled all the ZnO/III-N band offsets to be determined. The band offset measurements enable an experimental estimation of the location of the charge neutrality level in ZnO to be made which is found to be consistent with both the observed surface electronic properties and the predictions of band structure calculations.