HIGH-SPEED INP-INGAAS HETEROJUNCTION PHOTOTRANSISTORS EMPLOYING A NONALLOYED ELECTRODE METAL AS A REFLECTOR

High-speed InP-InGaAs heterojunction phototransistors (HPT's) with a base terminal (three-terminal HPT's) have been fabricated. These HPT's have nonalloyed electrodes functioning as reflectors and a configuration in which light is incident through the substrate, These features lead to an increase in quantum efficiency in spite of the thin base and collector light-absorbing layers, Optical gain dependence on collector current is weak because of the low recombination current at the emitter-base interface. Maximum optical-gain cutoff frequencies of 22 and 14 GHz are obtained for a 3 x 3-mu m(2) emitter HPT illuminated by 1.3- and 1.55-mu m light, respectively, This HPT has the capability of operating as a high-speed heterojunction bipolar transistor (HBT) as well. A current-gain cutoff frequency (fr) of 128 GHz is obtained for a 3 x 9-mu m(2) emitter HBT fabricated on the same wafer, Equivalent circuit analysis, in which all the components are determined by measuring both the electrical and optical characteristics of a three-terminal HPT, shows good agreement with experimental results,