Performance enhancement of GaInP/GaAs heterojunction bipolar phototransistors using dc base bias

GaInP-GaAs heterojunction bipolar phototransistors grown by metal organic vapor phase epitaxy (MOVPE) and operated with frontside optical injection through the emitter are reported with high optical gain (<88) and record high frequency performance (28 GHz). Heteropassivation of the extrinsic base surface is employed using a depleted GaInP emitter layer between the nonself-aligned base contact and the emitter mesa. The phototransistor's performance is shown to improve with increasing dc base bias in agreement with predictions of a recently reported Gummel-Poon model. Experimental results are reported for devices with optical active areas of 10/spl times/10 /spl mu/m/sup 2/, 20/spl times/20 /spl mu/m/sup 2/, and 30/spl times/30 /spl mu/m/sup 2/, with peak measured cutoff frequencies of 28.5, 23.1, and 18.5 GHz, respectively, obtained at collector current densities between 2/spl times/10/sup 3/ and 6/spl times/10/sup 3/ A/cm/sup 2/.