ELECTRON-MOBILITY IN SINGLE-CRYSTALLINE AND POLYCRYSTALLINE GA2O3

Ga2O3 is a purely n-conducting metal oxide at high temperatures. Incre asing interest is being shown in this material as the basic material f or gas sensors since its electrical conductivity is gas dependent. To investigate its electrical conductivity mechanism in the temperature r ange between 800 and 1000-degrees-C, conductivity and Hall measurement s were performed on single crystals and on polycrystalline ceramics. I n 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 obs erved in both cases, that of the single crystals lying around three an d a half orders of magnitude above that of the ceramic. The carrier de nsities are determined from the Hall measurements, a thermally activat ed 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 Ha ll mobilities are determined by combining the conductivity and Hall me asurements. Within the limits of measurement accuracy, the Hall mobili ties 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 therma l activation energy of about 0.6 eV. The results suggest that conducti on in Ga2O3 at high temperatures is well described by the small polaro n model.