Enhancement of Optical Gain in Floating-Base InGaP–GaAs Heterojunction Phototransistors

Comparative studies on the performances of floating-base InGaP-GaAs heterojunction bipolar phototransistors (HPTs) with and without base contact metal were carried out. Both the fabricated HPTs with base contact metal (HPTs-WB) and without base contact metal (HPTs-WOB) exhibited collector dark current as low as 0.2 pA when they were operated in a floating-base configuration at V_CE = 1 V. The HPTs-WOB demonstrated much higher optical gain (120 at an optical power of 1.1 μW irradiated by a 635-nm laser) than the HPTs-WB. The optical gain showed dependency on the illuminating optical power, increasing as the illuminating optical power was increased.