Analytical expression of diffusion capacitance of a uniformly doped high barrier Schottky barrier diode

In this paper, diffusion capacitance of a uniformly doped high barrier Schottky barrier diode and its behavior for different device parameters are studied. When barrier height is low, Schottky barrier diode acts as a majority carrier device. But, a high barrier Schottky diode injects minority carrier charge at forward bias. For this reason minority carrier charge is stored in the drift region. This stored charge gives rise to diffusion capacitance which affects the device speed remarkably. In the past, there has been some notable work in this regard. In this work, a new approach is taken to find out the analytical expression of diffusion capacitance. Solving a second order nonlinear differential equation, minority carrier charge profile is obtained for all level of injections in our previous work. Using this expression, analytical expressions of both total stored minority carrier charge and diffusion capacitance are obtained. Once the expression of diffusion capacitance is obtained, then its dependence on various device parameters such as device length, bias voltage and effective surface recombination velocity has been studied. In this work, both majority and minority carrier current and their drift and diffusion components are considered. Recombination of carriers in the epitaxial layer is also neglected.