# Differential Resistance and Diffusion Capacitance of Junctions in p-n-n^{+} Structures at high Injection Levels

## Abstract

An analysis is made of the current and frequency dependences of the impedance of p-n and n-n^{+} junctions in a p-n-n^{+} structure (an expression for this impedance has been derived earlier by the present authors [1]). The analysis is carried out for high injection currents through the structure, when it is necessary to take into account the drift component of the current in the base and the injection leakage through the contacts. The impedance of the junctions is represented by an equivalent circuit in the form of a differential resistance and diffusion capacitance, connected in parallel. An investigation is made of the influence of the leakage on the frequency characteristics of the junctions in the case of low and high rates of leakage through the contacts, compared with the carrier combination velocity in the base. Expressions are deduced for the lowfrequency differential resistance and diffusion capacitance whose values can be used, in some cases, to determine the length of the base and the lifetime of nonequilibrium carriers in the structure. It is shown that strong deviations of the frequency dependence of the junction impedance from the suggested law are possible at high frequencies. Thus, for example, at low rates of leakage in short diodes at moderate frequencies, the junction capacitances are frequency-independent and the resistances are inversely proportional to the square of the frequency. It is also shown that the differential resistance of the junctions is inversely proportional to the current for any ratio of the leakage rate and the carrier recombination velocity in the base. The junction capacitance is proportional to the current only in some cases: for example, at high leakage rates, the junction capacitance is proportional to the square root of the current. The results obtained can be used in an analysis of the reactive and active (resistive) components of the impedance of the bulk of a diode.

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