Shallow levels in virgin hydrothermally grown n-type ZnO studied by thermal admittance spectroscopy |
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Authors: | R. Schifano W. Mtangi F.D. Auret |
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Affiliation: | a Department of Physics/Center for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo, Norway b Department of Physics, University of Pretoria, Pretoria 0002, South Africa |
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Abstract: | Three n-type single crystal hydrothermally grown ZnO samples with resistivities of 5.1±0.6, 15±2 and 220±20 Ω cm, respectively, have been electrically characterized using thermal admittance spectroscopy (TAS). The presence of three main donors: two shallow ones D1 and D2 and a deeper one D3 with activation energies of ∼30, ∼50 and ∼290 meV, respectively, are detected. In addition, the TAS spectra reveal the presence of a fourth level, DX, with a peak amplitude in the conductance spectra that decreases with the temperature occurrence. It is shown that this anomalous behavior is consistent with DX being a negative-U defect of donor-type. An activation energy of ∼80 meV for the ++/+ transition, a capture cross section equal to ∼3×10−17 cm2 and an energy barrier for atomic reconfiguration of ∼0.25 eV, respectively, deduced according to the assignment of DX to a negative-U defect. A tentative assignment of the DX defect with oxygen vacancies is discussed. |
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Keywords: | 61.72.J&minus 61.72.S&minus 61.72.uj 71.55.Gs |
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