Three-Terminal Dual-Emitter Phototransistor with Both Voltage- and Power-Tunable Optical Gains

Abstract

InGaP/GaAs dual-emitter heterojunction phototransistors (DEPTs) with an emitter biased using a voltage is reported for comparison to heterojunction phototransistors (HPTs) with a floating base operated in the p–i–n and transistor modes and to the HPTs with a base biased using a voltage. Although the power- and voltage-tunable optical gains are expected when the base of the HPT is floated and biased using a voltage, respectively, a conventional HPT's configuration does not simultaneously exhibit both. On the contrary, the optical gains of the DEPT can be tuned by both the voltage applied to the emitter and the incident optical power. Experimental results show that (1) the power-tunable optical gains are in the range of 11–29 as determined by the incident optical power upon the HPT with a floating base, (2) the small optical gains tuned by a voltage are 0.83–1.6 with a gain-tuning efficiency of 4.4 V-1 for the HPT with a base electrode, and (3) the DEPT with an emitter biased using a voltage exhibits an enhanced optical gain, with a gain-tuning efficiency of 43.4 V-1, when compared with the HPT with a floating base. Finally, a new concept of current-sharing effects in the base region is introduced to explain power- and/or voltage-tunable characteristics with good agreement found.