Determination of physical parameters and geometry of a junction transistor

An investigation is made of the problem of determining the physical parameters and geometrical dimensions of a junction transistor from measurements of its equivalent circuit parameters. It is shown that simple manipulations of certain known relations in the theory of low-level transistor operation provide a method of determining to a reasonable degree of accuracy the values of lifetime, diffusion constant and mobility of injected carriers in the base region, the carrier concentrations in the emitter, base and collector regions, the base width and the effective junction areas. Methods involving consideration of certain aspects of high-level operation are also discussed for estimating the probable values of lifetime and mobility of minority carriers in the emitter and collector regions and also the volume and surface recombination lifetimes of such carriers in the base region. Representative experimental results obtained by the method under low-level operating conditions are described, and the accuracies of a few of these are checked by comparison with known values. The reliability and the general usefulness of the method of measurement are briefly discussed.