Orientation effect on AlGaAs/GaAs heterojunction bipolartransistors

Orientation effects on N-p-n AlGaAs/GaAs heterojunction bipolar transistors (HBT's) have been demonstrated for the first time. We have observed that the current gains of HBT's fabricated on the same wafer are strongly dependent on the emitter direction. The HBT's with emitter direction of [010] show the highest current gain and the smallest emitter-size effect. This orientation effect could be attributed to the piezoelectric effect, which superposes the piezoelectric charges to the original emitter doping and generates the weak lateral electric field that drifts the injected carriers at the emitter periphery. The difference of the saturation voltage between collector-emitter of those HBT's corresponds to the superposed piezoelectric charges