On the Theory of the A-C. Impedance of a Contact Rectifier

THE a-c. impedance of the rectifying contact between a metal and a semiconductor is measured by superimposing a small a-c. current on a d-c. bias current. It is generally recognized1that an equivalent circuit consists of a parallel resistance and capacitance in series with a resistance as shown in Fig. 1. The parallel components represent the impedance of the barrier layer itself and depend on the d-c. bias current flowing. The series resistance is that of the body of the semiconductor. It has been shown theoretically by Spenke2that under quite general conditions the parallel capacitance and resistance are independent of frequency. Unfortunately Spenke's proof is highly mathematical and is also not readily available. The derivation of the impedance relations which is presented here is in some ways more general and gives more physical insight into the problem.