Analysis of the Space Charge Capacitance of Bipolar Semiconductor Passive Films

Measurement of the space charge capacitance (Mott-Schottky (M-S) plot) is an important method to study semiconductor properties of passive films. The slope of the linear part of the M-S plot of a bipolar semiconductor passive film should change in the depletion region. A uniform expression for the space charge capacitance in the accumulation, depletion and reversion regions was established. The space charge capacitance of a bipolar semiconductor passive film is regarded as capacitance at the passive film/solution interface and the np-junction capacitance at the outer layer film/inner layer film interface in series. The change of slope for the linear part of the M-S plot to the bipolar passive film is well explained by the calculated results. An error would be obtained for the bipolar passive film if the flat potential and carrier density are determined directly from the linear zone in the M-S plot.