On the Lifetime and Diffusion Constant of the Injected Carriers and the Emitter Efficiency of a Junction Transistor†

Abstract

Values of the effective lifetime and of the apparent diffusion constant of the minority carriers in the base region of p-n-p alloy junction transistors of three different types have been determined. It is found that for a given temperature the effective lifetime passes through a maximum as the bias current is increased from a, low value. This is explained on the basis of the relative contributions to the lifetime of volume and surface recombination, The analysis also yields separately the values of the volume and the surface recombination lifetimes. Both the lifetimes are found to decrease with decreasing temperature. Further, the volume recombination lifetime is found to be appreciably smaller than those observed in n-typo germanium in bulk. The true values of the diffusion constants, as determined from the measured apparent values, arc found to obey an empirical relation that closely agrees with the relation for bulk germanium semi-conductor of the same type. A method of estimating the emitter efficiency based on a critical analysis of the observed apparent values of the diffusion constant in the light of the theoretical relation given by Webster is also suggested. It is found that for the transistors under investigation the estimated values of the emitter efficiency remain closely equal to unity under the usual operating conditions.