| AVS 54th International Symposium | |
| Electronic Materials and Processing | Thursday Sessions |
| Session EM-ThM |
| Session: | Zinc Oxide |
| Presenter: | S.M. Durbin, University of Canterbury, New Zealand |
| Authors: | C.H. Swartz, University of Canterbury, New Zealand M.W. Allen, University of Canterbury, New Zealand S.M. Durbin, University of Canterbury, New Zealand T.H. Myers, West Virginia University |
| Correspondent: | Click to Email |
One of the major advantages of ZnO over other wide bandgap semiconductors is the availability of bulk, single crystal growth of high quality material using a variety of techniques. Of these, hydrothermally grown ZnO is somewhat unique in that it is highly resistive with carrier concentrations typically 2 - 3 orders of magnitude lower than other bulk ZnO, due to compensation from unintentionally introduced Li and Na acceptor impurities. This high resistivity makes the measurement of its electrical properties particularly susceptible to complications such as persistent photoconductivity, increased temperature sensitivity and surface conduction effects. The surface conductivity of ZnO is known to depend strongly on the ambient atmosphere and can increase significantly under vacuum conditions. After being placed in a vacuum, the expiration of atmospheric effects on the surface can take many hours and, even when equilibrium is reached, the surface conductivity remains a significant, and often dominant, contributing factor to electrical measurements. Variable magnetic field Hall effect measurements can be used to separate surface or interface conducting layers from the bulk conductivity of a given sample. In this paper, we report on the results of temperature dependent, variable magnetic field Hall effect measurements on hydrothermally grown ZnO single crystal wafers from Tokyo Denpa Co. Ltd. (Japan). Measurements were carried out over a temperature range of 80 - 300 K and magnetic field strengths up to 12 T. Multiple carrier fitting was used to remove surface conduction effects and produce temperature dependent mobility and carrier concentration data for the bulk carriers only, which was then theoretically fitted. A significantly higher bulk carrier mobility and an order of magnitude lower ionised impurity concentration was found than is apparent from standard single field Hall effect measurements. These results also indicate that the use of single field, temperature dependent Hall effect measurements to determine donor concentration and activation energies may be problematic unless surface conduction effects are first isolated.