High power transistor with highly doped buried base layer

Abstract

A novel diffusion type transistor which is useful for relatively high-power and high-current applications and a method for manufacturing the transistor are disclosed. In constructing the transistor, the base under emitter has three zones, one of which is a buried layer such as used in the fabrication of bipolar integrated circuits. Two of the zones, including the buried layer base zone, are highly doped to provide a low resistivity base current path. The last zone is a low impurity concentration epitaxially grown base zone and which accepts and transports the injected minority carriers from the emitter to the collector. Hence, the emitter periphery is determined by the sum of the total PN junction boundary between the buried layer base zone, the epitaxially grown base zone and a diffused emitter. The phenomenon of current crowding at the emitter periphery is reduced by an increase in emitter periphery for the same chip size and by a reduction in the potential gradient caused by the lateral base current due to the lowered resistivity of the highly doped base zones.