Abstract

We report the electrical and photoresponse characteristics of InP/InGaAs HBT phototransistor (HPT) according to the base contact configuration. It is shown that improved base contact design can provide optical gain Gopt, and unit optical gain cut-off frequency fc very near to the current gain H21 and unit current gain cut-off frequency ft, of the phototransistor H21 and ft being the upper limit performances of the HPT. fc = 42 GHz for ft = 55 GHz, (i.e. a fc/ft ratio = 0.76) were obtained for the type-B phototransistor. Equivalent circuit analysis shows good agreement with experimental results.