MULTI-EMITTER SI GEXSI1-X HETEROJUNCTION BIPOLAR-TRANSISTOR WITH NO BASE CONTACT AND ENHANCED LOGIC FUNCTIONALITY/

We demonstrate multi-emitter Si/GexSi1-x npn heterojunction bipolar tr ansistors (HBT's) which require no base contact for transistor operati on. The base current is supplied by the additional emitter contact und er reverse bias due to the heavy doping of the emitter-base junction. Large-area HBT test structures exhibit good transistor characteristics , with current gain beta approximate to 400 regardless of whether the base current is supplied by a test base electrode or one of the emitte r contacts. These devices have enhanced logic functionality because of emitter contact symmetry, Since device fabrication does not require b ase electrode formation, the number of processing steps can be reduced without significant penalty to HBT performance.