Forward-voltage capacitance of heterojunction space-charge regions

An analytical treatment is presented for modeling the capacitance of heterojunction space-charge regions under forward voltages. First, the conventional depletion model is reviewed and the inadequacy of the use of such a model at forward voltages is noted. The study then turns to the development of a more accurate model for the thickness and potential barrier of the space-charge region for all voltages. Based on this model and the approximation that the intrinsic level is piecewise linear with respect to position in the space-charge region, an analytical quasistatic capacitance model applicable for forward-biased conditions is derived. The model, however, encounters difficulties at very large forward voltages, and a qualitative treatment is employed there. The comparison of the present capacitance model with measured dependencies and with existing capacitance models is included.