ELECTRON-MOBILITY IN SINGLE-CRYSTALLINE AND POLYCRYSTALLINE GA2O3

Ga2O3 is a purely n-conducting metal oxide at high temperatures. Increasing interest is being shown in this material as the basic material for gas sensors since its electrical conductivity is gas dependent. To investigate its electrical conductivity mechanism in the temperature range between 800 and 1000-degrees-C, conductivity and Hall measurements were performed on single crystals and on polycrystalline ceramics. In the conductivity measurements, identical results were obtained with dc and low-frequency ac, thus confirming the notion of purely electron current transport. A thermally activated specific conductivity is observed in both cases, that of the single crystals lying around three and a half orders of magnitude above that of the ceramic. The carrier densities are determined from the Hall measurements, a thermally activated behavior always being observed. The carrier density of the ceramic is only 2 X 10(13) cm-3 at 1000-degrees-C, that of the single crystals lying somewhat more than three orders of magnitude above this. The Hall mobilities are determined by combining the conductivity and Hall measurements. Within the limits of measurement accuracy, the Hall mobilities in the ceramic and the single crystals are shown to be identical. The Hall mobility is about 10 cm2/V s at 1000-degrees-C with a thermal activation energy of about 0.6 eV. The results suggest that conduction in Ga2O3 at high temperatures is well described by the small polaron model.