OPTICAL PROPERTIES AND ELECTRICAL CONDUCTION MECHANISMS OF ELECTRON BEAM EVAPORATED Cu-GeO2 THIN CERMET FILMS

Abstract

Abstract : Optical, on a number of electron beam evaporated Cu-GeO2 thin films with the aim of obtaining information about the DC conduction mechanism. Optical absorption studies showed that incorporation of Cu in the matrix of GeO2 introduces defect states energy gap. It was found that the optical energy increases decreases with increasing copper concentration. The DC conductivity results revealed that above a certain temperature Tc (i.e 355 K, 367 K and 375 K for 30, 20 and at.wt.$ Cu films, respectively) conductivity increased sharply with activation energy lying in the range 0.66 to 0.77 eV. Below Tc, conductivity is weakly activated with activation energy lying in the range 0.10 to 0.25 eV.Hall effect experiment was performed to investigate the Sharp transition points in the DC conductivity curves. Ain Hall mobility was observed for all the Furthermore, the Hall mobility showed a maximum critical temperature (Tc) identical to that of the DC conductivity. A detailed analysis of these results showed that the DC conductivity was dominated by a mixed conduction process and that the small polaron model best describes conductivity is identified with hopping of carriers through localized states. Above Tc, carrier concentration is believed to govern the conductivity. From the combined knowledge of optical absorption, DC conductivity and Hall effect results a room-temperature band diagram (for 30at.wt.% Cufilms) is proposed in which the mobility gap is calculated to be 3.78 eV. Above Tc, the mobility gap reduces to 2.62 eV. The AC minima around a cut-off frequency (=105 Hz) indicating