A study of minority carrier response in a metal-insulator-semiconductor structure

Abstract

The minority carrier effect on capacitance-voltage characteristics of MIS structures with examples for Si02-Si and Ai 2o3-Ge is studied. C-V curves for intrinsic Ge are presented. The small-signal state equations for the semiconductor neglecting recombination are obtained and put into a set of first-order linear differential equations, y=Ay, which comprise a boundary value problem. This set of equations is solved numerically. First, the static equation in the semiconductor is solved to obtain the matrix, A. Then the general method of complementary functions using the orthonormalization process is employed. The semiconductor impedance is found and the capacitance-voltage characteristics of the MIS structure are obtained. The effect of the semiconductor ohmic contact is also considered by proper changes to the boundary conditions. The charge analysis approach is also used and its results are compared to the numerical solution of state equations in different cases. The results of this study show considerable amount of minority carrier response for Germanium-based devices even above 1 MHz. It is also found that this response depends strongly both on frequency and level of impurity.