Influence of carriers on the capacitance of p-n junctions with deep donors

Abstract

Applying the definition of p-n junction capacitance [1], which takes into account the effect of carriers in the space-charge region, a sufficiently accurate approximate expression is derived for the low-frequency capacitance of an abrupt p-n junction containing both deep and shallow donor impurities within the n-region. The capacitance expression can be written in conventional Schottky form, putting the intercept voltage if Vin instead of the diffusion potential. It is shown that Vin differs considerably from the generally known Vi0 expression obtained on the basis of the depletion layer approximation. This difference increases with the degree of p-n junction asymmetry, or the decrease of deep donor impurity ionisation energy, and is dependent also on the concentration ratio of deep and shallow donors. The most important difference between Vin and Vi0 lies in the fact that Vi0 in contrast to Vin, is independent of the applied voltage, and is therefore applicable only with very high reverse voltages, where equivalence between Vin and Vi0 is valid.