Electron Injection into Anodic Valve Metal Oxides: II Further Experimental Results for , and

Abstract

Electron injecting contacts can be formed at valve metal oxide/semiconducting metal oxide interfaces with applied fields of the order of some 106 V/cm. Electronic current injection as a function of time and applied field (activation) has been measured for , , and electrodes in contact with as the semiconducting transition metal oxide. The activation process is explained on the basis of interacting ionic and electronic processes with the ionic charge transport following the empirical field law for anodic oxide growth . The explicit dependence of the electronic process on parameters of the ionic conduction process has been confirmed by determining the ionic conduction parameters from the field and temperature dependence of the activation process. Quantitative agreement with values reported from measurements of the kinetics of anodic oxide growth has been obtained. The electronic current resulting from activation of and electrodes in contact with electrolytes showed a field dependence typical for thermionic emission. Linear log i vs. characteristics could be obtained extending over 4–5 decades with slopes in agreement with thermionic emission following a Poole‐Frenkel mechanism. It appears that valve metal/valve metal oxide/semiconducting oxide electrodes with two oxides in intimate but initially blocking contact provide model systems for the generation of coulombic centers from which thermally activated electron emission with Poole‐Frenkel characteristic can take place. The barrier height for the thermionic emission process and its change with progressing activation has been determined from measurements of the temperature dependence of the electronic current with applied field and state of activation as parameters. The barrier heights were found to be of the order of 1 eV.