Direct Measurement of Impurity Distribution in Semiconducting Materials

Differential capacitance‐voltage measurements are commonly used to determine the impurity distribution in a semiconducting material whereby a Schottky or a diffused junction is reverse biased by a dc voltage. If the biased junction is driven by an ac current, the voltage generated by the diode contains first and second harmonics of the frequency of the driving current. The first harmonic is proportional to the depletion width and the second harmonic to the inverse of the impurity density, thus providing an absolute representation of the impurity distribution without any computations. The ratio of the amplitude of the second harmonic to the amplitude of the first harmonic, is, however, very small and separation of the second harmonic from the first harmonic requires a carefully designed circuit. The method and the electrical circuit is described in detail. Limitations of the technique and the methods for eliminating these limitations are also discussed.