DC ELECTRICAL-CONDUCTION IN ELECTRON-BEAM EVAPORATED CU-GEO2 THIN CERMET FILMS

Dc conductivity, Hall effect, and optical absorption measurements were performed on Cu-GeO2 thin films to elucidate the de conduction mechan ism. The de activation energy is temperature dependent, increasing sig nificantly above a transition temperature T-t. Hall mobility exhibited a sign reversal around T-t, above which it increased to a maximum val ue at a critical temperature T-c. The almost identical transition temp eratures in conductivity and Hall mobility suggest that the conductivi ty results from a combination of two processes. Above T-t, the conduct ivity is best described by small polaron phonon-assisted hopping model ; hopping appears to be non-adiabatic in nature. Below T-t, the conduc tivity is weakly activated, magnetoresistance is negative, and the Hal l mobility shows a significant rise with decreasing temperature. These are features which suggest non-polaronic thermally activated hopping through a spectrum of localized states. Various parameters associated with polaron formation are calculated.