The interpretation of capacitance and conductance measurements on metal-amorphous silicon barriers

Abstract

In a recent paper we investigated the formation, profile and capacitance of the metal/a-Si barrier by means of model calculations based on the experimentally determined distribution of localized states. This approach has been developed in the present paper and is used in a detailed comparison with capacitance measurements on Au/a-Si barriers.

The a-Si specimens, either undoped or with donor concentrations of up to 2 × 10¹⁸ cm⁻³, were produced by the glow-discharge technique. It has been possible to give a satisfactory interpretation of the observed frequency, bias and temperature dependence of the barrier capacitance. For this two important aspects had to be included in the model calculations : first the electronic behaviour of the barrier, determined by the known space-charge distribution, and secondly the properties of the specimen in the measuring circuit, analysed by means of an equivalent circuit. In the final section of the paper we present current-voltage curves for different donor concentrations, showing that, in highly doped specimens, forward current densities of up to 30 A cm⁻² can be obtained. Typical high-field breakdown characteristics are observed in reverse bias which are briefly discussed in terms of the theory of Padovani and Stratton (1966).