Capacitance of p-n Junctions: Space-Charge Capacitance

Abstract

Exact calculations of the total space-charge density in a p-n junction reveal it to be unrelated to the charge density assumed in the Schottky theory. The difference can be as large as orders of magnitude. Consequently, the space-charge capacitance is also found, by detailed analysis, to be unrelated to the Schottky result. A simplified closed-form solution is then obtained for the space-charge capacitance using the Shockley injection relation. In symmetrical junctions, there is some agreement between the exact space-charge capacitance and the Schottky result. In asymmetrical junctions, the space-charge capacitance is nearly constant for negative biases. These results indicate the need for further detailed analysis of the capacitance of p-n junctions.