Capacitance spectroscopy of localized states at metal-semiconductor interfaces. I. Theory

The influence of interface states on some electrical properties of Schottky diodes is studied. Assuming that Shockley-Read-Hall statistics and tunnelling-like mechanism controls the flows between interface states and the semiconductor and metal bands, the occupancy of interface states is derived for two limiting cases: The discrete level and the rectangular band. The role of demarcation levels is demonstrated. The particular range consisting of forward bias is explored because its ability to vary the interface states population owing to the carrier concentration changes at the interface. The small signal admittance due to interface state is then obtained, and the behavior of the parallel capacitance Cp is peculiarly analyzed versus the frequency f and the difference between the quasi-Fermi levels of the semiconductor and metal Fn−Fm. Eventually, a method for the determination of the interface states parameters is developed. It is shown that the experimental results are to be analyzed by studying the slopes d log Cp/d log f versus normalized quasi-Fermi level position x = Fn−Fm/kT and d log Cp/dx vs x.