| AVS 57th International Symposium & Exhibition | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM-TuA |
| Session: | Defects in Semiconductors and Oxides |
| Presenter: | T.C. Lovejoy, University of Washington |
| Authors: | T.C. Lovejoy, University of Washington R. Chen, University of Washington S.X. Zheng, University of Washington E.G. Villora, NIMS, Japan K. Shimamura, NIMS, Japan H. Yoshikawa, NIMS, Japan Y. Yamashita, NIMS, Japan S. Ueda, SPring-8, Japan K. Kobayashi, SPring-8, Japan S. Dunham, University of Washington F.S. Ohuchi, University of Washington M.A. Olmstead, University of Washington |
| Correspondent: | Click to Email |
Wide-band-gap oxides like Ga2O3, In2O3, SnO2, and ZnO, are of key importance as transparent conductors and gas sensing materials. The conductivity in these materials is almost-always observed to be n-type, although the mechanism is under debate. An inverse correlation between oxygen partial pressure, p(O2), during growth and measured conductivity has been reported, leading to a commonly held model that oxygen vacancy defects in the crystals are responsible for the conductivity. This model is supported by some density functional theory (DFT) calculations, in SnO2 for example, but excluded by others. beta-Ga2O3 has the largest band gap of the oxides listed above, ~(4.8 eV), making it unique among them for near-UV applications. We report on a combined experimental and theoretical study of beta-Ga2O3 single crystals. Using density functional theory we compute the formation energies of various intrinsic defects as function of the Fermi level position relative to the valence band maximum (E_F-E_VBM). We show by a combination of hard x-ray photoemission (HXPS) and Hall measurements that the near-surface value of E_F-E_VBM is very different from that in the bulk due to band bending. By comparing the experimental results with the calculations we conclude that oxygen vacancies have too high an activation energy in the bulk to contribute substantially to the conductivity, but band bending enables them to play a role near the surface.