Interpretation of capacitance versus voltage measurements in the presence of a high density of deep levels

We present a detailed discussion of the physical significance of measurements of capacitance as a function of applied bias voltage to a Schottky barrier when the semiconductor involved contains not only shallow levels but also deep levels. Whether deep levels are affecting the capacitance can be determined by measuring the capacitance versus voltage as a function of frequency or of temperature, and observing the frequency or temperature dependence of the slope of a plot of inverse capacitance as a function of voltage compared to the frequency or temperature dependence of the slope of a plot of inverse squared capacitance as a function of voltage. The slope of the inverse capacitance as a function of voltage should not be a function of frequency or temperature regardless of whether deep levels are significant or not, whereas the slope of the inverse squared capacitance as a function of voltage should depend on frequency and/or temperature if deep levels are significant. Examples of this behavior are given from measurements on CdTe single crystals and thin films.