Abstract

New stack-shared layer scheme has been developed to integrate monolithically InP-based heterojunction bipolar transistor (HBT)and p-i-n photodiode.In this layer scheme,a p + -and intrinsic InGaAs layers for a photodiode were stacked on n + -InP emitter layer, which is shared as both emitter contact layer for an HBT and n-type contact layer for a photodiode.The fabricated HBTs demonstrated excellent high-speed characteristics of f T =108 GHz and f max =300 GHz.The photodiode,formed with an undoped 4300 Å-thick InGaAs as an absorption layer,exhibited a dark current of 6 nA under 5 V reverse bias,with a responsivity of 0.3 A/W at 1.55 Pm optical radiation.A 3-dB bandwidth of the photodiodes with diameters smaller than 25 Pm was over 20 GHz.High- frequency performances of both devices were observed dueto the advantages of the stack-shared layer scheme,characterized by independent optimization of the devicelayer structure and moderate nonplanarity.