ORIENTATION EFFECT ON ALGAAS GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS/

Orientation effects on N-p-n A1GaAs/GaAs heterojunction bipolar transi stors (HBT's) have been demonstrated for the first time. We have obser ved that the current gains of HBT's fabricated on the same wafer are s trongly dependent on the emitter direction. The HBT's with emitter dir ection of [010] show the highest current gain and the smallest emitter -size effect. This orientation effect could be attributed to the piezo electric effect, which superposes the piezoelectric charges to the ori ginal emitter doping and generates the weak lateral electric field tha t drifts the injected carriers at the emitter periphery. The differenc e of the saturation voltage between collector-emitter of those HBT's c orresponds to the superposed piezoelectric charges.