Relation between distribution of states and the space-charge-region capacitance in semiconductors

In contrast with recent suggestions we show that frequency dependent capacitance-voltage (C-V) characteristics can yield information on the state distribution in the forbidden gap of semiconductors which have a continuous state distribution there. For this purpose we have applied an analysis which is based on the solution of the Poisson equation in various sections of the space-charge region. Then, by using a new recursion approach we found new general expressions for the frequency and temperature dependence of the C-V characteristics. The present work yields analytic results and a transparent physical picture so that clear correlation is obtained between features of the above characteristics and features of the state distribution. In particular, it is shown that under deep depletion the well-known linear 1/C² vs V relation is maintained regardless of the state distribution. This enables the use of the frequency, or temperature, dependence of the corresponding slope for the evaluation of the state distribution from experimental data.