Determination of the density of Si-metal interface states and excess capacitance caused by them

Abstract

Schottky diodes were fabricated by evaporation of Al on a strongly etched n-type Si surface for 3 min after mechanical cleaning. The measurements of one of the better working of the Al-nSi diodes has been carried out at room temperature. Two expressions were found for the ideality factor n by supposing that all the interface states at first are in equilibrium with the metal and then with the semiconductor. The diode showed non-ideal I–V behaviour with an ideality factor of 1.46. The density distribution of interface states was obtained from the forward bias I–V characteristics. Non-linearity or curvature in the reverse bias C -2− V plots was a quantity called the “excess capacitance” C 0 caused by the presence of the interface states. The excess capacitance was observed to decrease with increasing frequency: this behaviour was ascribed to the fact that the apparent density of the interface states decreases with increasing frequency. In addition, the parameters obtained from C− V characteristics were corrected by means of a simple graphical method for excess capacitance suggested by Vasudev et al. and of a theoretical model of an MIS structure introduced by Fonash.