New experimental results for electron transport in weak accumulation layers of ZnO crystals |
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Authors: | W Thoren G Heiland D Kohl H Von Löhneysen W Platen HJ Schink |
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Institution: | 2. Physikalisches Institut der Rheinisch-Westfälischen Technischen Hochschule Aachen, D-5100 Aachen, Fed. Rep. of Germany |
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Abstract: | Previous Hall measurements on (0001) and (0001̄) faces of ZnO have shown a Hall mobility oscillating as a function of Hall surface electron density in the range between NSH=106 and 1011 cm?2. Here we report on new results obtained by a field effect arrangement for free surfaces in UHV. With donors from H exposure or by illumination weak accumulation layers (nsh <1011 cm?2) are established. The field effect shows oscillations in surface conductivity as a function of gate voltage. Also the combination of a field effect with a Hall effect measurement reveals discrete values of Hall surface electron density nsh. Various pretreatments do not change the periodicity of these oscillations. Necessary preconditions are a temperature below 130 K, a Hall surface electron density below 3 × 1012 cm?2 and a source-drain field of a few V/cm. A model regarding impurity levels in the space charge layer relates the results of the field effect measurements to the results of the Hall effect measurements. |
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