T-emitter bipolar power transistor with negative-temperature-gradient current gain

A PNP epitaxial-base power transistor with double diffused emitter (T-emitter) which exhibits a negative temperature gradient for β is described. Qualitative analysis shows that a fall-off in β with increase in temperature is a consequence of both the T-emitter geometry and the boron double diffused emitter area. Measurements on realised transistors give a mean value of dβ/dt of −0.25 at temperatures ranging from 20°C to 110°C.