Multi-emitter Si/GexSi/sub 1-x/ heterojunction bipolar transistor with no base contact and enhanced logic functionality

We demonstrate multi-emitter Si/Ge/sub x/Si/sub 1-x/ n-p-n heterojunction bipolar transistors (HBT's) which require no base contact for transistor operation. The base current is supplied by the additional emitter contact under reverse bias due to the heavy doping of the emitter-base junction. Large-area HBT test structures exhibit good transistor characteristics, with current gain /spl beta//spl ap/400 regardless of whether the base current is supplied by a test base electrode or one of the emitter contacts. These devices have enhanced logic functionality because of emitter contact symmetry. Since device fabrication does not require base electrode formation, the number of processing steps can be reduced without significant penalty to HBT performance.