HOT-CARRIER-INDUCED PHOTOVOLTAGE IN SILICON BIPOLAR JUNCTION TRANSISTORS

As bipolar junction transistors (BJTs) are scaled down, the current density increases and base pushout may happen. To prevent base widening, the collector doping concentration is increased; therefore, this increases the electric field in the base-collector junction. In the active operation of BJTs, impact ionization happens and impact-ionization-induced photon emission is created in the base-collector (BC) junction and photon absorption happens in the base-emitter (BE) junction. This makes the carrier injection from the BE junction to the BC junction with avalanche different from that without avalanche. Similarly, the avalanche-induced light emission in the BE junction will induce photocarriers in the BC junction diode. In this paper, we report observation of the photovoltage in the BC junction resulting from hot-carrier electroluminescence in the BE junction on a conventional low-power n-p-n bipolar transistor. We found a photovoltage of 0.36 V and a collector current reversal in the inverse active operation.