Aging characteristics of nickel contact on p-type silicon

Abstract

The effect of aging on the electrical properties of a Ni–p-Si contact was studied by measuring the electrical characteristics at different intervals of time. The current–voltage characteristics measured show a decrease in the current over time for the first few measurements at different aging times followed by an insignificant change for longer aging. The barrier height extracted from I−V characteristics was found to increase from an initial value to a final higher value after a prolonged period of aging. This is the opposite of those normally exhibited by an aging Al−SiO2−p-Si system [H. C. Card, IEEE Trans. Electron Devices ED-23, 538 (1976)]. Similar to the case of current, the device conductance and capacitance were also found to decrease with the aging time until they become saturated after longer periods of aging. The features of aging are explained by a theoretical model which considers the existence of an interfacial SiO2 layer and Si traps in the interfacial region. It is shown that the concentration of silicon traps decays exponentially over time. The interpretation of the aging characteristics of a Ni–p-Si contact on the basis of exponential decay in the silicon trap concentration is in contrast to an Al−SiO2−p-Si system where the aging behavior was accounted for in terms of the net growth in silicon concentration over time followed by saturation after longer aging. Analyses of the low and high frequency capacitance reveal two types of interface state that have different time constants and density. The time constants of these states were found to be dependent on the aging time via surface potential at the contact.