The effect of the collector field on common-emitter current gain in diffused-base transistors

The common-emitter current gain (ß0) of diffused-base transistors increases and eventually becomes negative as the temperature is raised. This effect is attributed to a field-dependent current of collector minority carriers flowing into the base. Two types of germanium transistor have been studied in detail. In the first transistor (gold-doped) the collector has low bulk lifetime and in the second (sand-blasted) a high surface recombination velocity at the collector contact. For both types satisfactory agreement between theory and experiment has been obtained. The results indicate that the principal source of the additional base current can be determined in any particular transistor by measuring the current and temperature dependence of ß0.