A Monolithically Integrated InP-Based HBT and p-i-n Photodiode Using New Stack-Shared Layer Scheme

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 fT = 108 GHz and fmax = 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 due to the advantages of the stack-shared layer scheme, characterized by independent optimization of the device layer structure and moderate nonplanarity. I