A theory and some characterisitcs of power transistors at high-level conditions

The concentration of injected carriers is large compared with the impurity doping concentration in the base region of a power transistor operating at high level. Carrier concentration and characteristics of a two-dimensional transistor model are calculated for this case. Emitter and base contacts are in the form of strips. Most of the injected emitter current reaches the collector while the remainder recombines in the slightly doped base region under the emitter, resulting in a current in the highly doped base contact. In addition, a recombination current generated in the base region under the base contact is added to this base current and results in a decrease of current gain. In order to analyze the base recombination current, a special transistor with divided collector contacts was prepared. In this way, the collector current due to the region under the emitter contact can be separated from the collector current due to the region under the base contact. The presented theory could be verified. Additional corrections are necessary, however, in the direction of the current in the slightly doped base region.