Extrinsic base surface-passivated dual-emitter heterojunction phototransistors

N-p-n InGaP/GaAs Dual-Emitter HPTs (DEHPTs) with and without extrinsic base surface passivation were fabricated to investigate the influence of the surface leakage on the device's optical performance. There are four operating regions appearing in the output characteristics of DEHPTs under illumination: negative-saturation, negative-tuning, positive-tuning and positive-saturation regions. The InGaP-passivated DEHPT (P-DEHPT), i.e. DEHPT with the extrinsic base surface passivated by InGaP, exhibits the maximum optical gains of 46.57, 46.86 and 47.39 while the non-passivated one (NP-DEHPT) shows ones of 32.02, 33.55 and 33.57 for optical powers of 8.62, 13.2 and 17.5 μW, respectively. However, the NP-DEHPT exhibits the larger peak gain-tuning efficiencies of 37.35, 41.03 and 44.10 compared to 12.76, 13.72 and 16.01 V −1 for the P-DEHPT for optical powers of 8.62, 13.2 and 17.5 μW, respectively. The better tuning efficiency makes the NP-DEHPT a possible low optical power optoelectronic application.