Electrode effects in amorphous semiconductors

The electrical properties of certain binary and ternary amorphous semiconductors are presented. Frequency dependent conductance, noise, voltage-current relationships and switching in these materials were investigated. The electrode effects on frequency variation of conductance were determined by making admittance measurements while applying a dc bias to the device. A small signal ac model based on the formation of space charge regions at the two metal-semiconductor interfaces was proposed. The frequency behavior of the model is found to be a good approximation to the frequency behavior of Ge4Te15As aluminum sandwich and aluminum planar devices. Noise data for the Ge4Te15As aluminum sandwich, aluminum planar and molybdenum planar devices were taken under dc bias and zero bias conditions. The nonohmic voltage-current relationship observed for the aluminum sandwich and aluminum planar devices was explained in terms of Schottky barrier formations at the two metal-semiconductor interfaces. Filamentary structural changes were observed under pulsed conditions using the scanning electron microscope.