Modeling and design of an InP/InGaAs HBT for microwave transimpedance amplifiers in 20 Gb/s optical links

Abstract

This paper presents the design and simulation of an InP/InGaAs heterojunction bipolar transistor (HBT) fabricated on a 6H-SiC substrate for microwave applications. The device is modeled using the Silvaco TCAD simulation tool to analyze its electrical and physical characteristics. The heterojunction structure enables efficient carrier confinement and enhanced electron injection, leading to improved current gain and high-frequency performance. Key simulation results, including the energy band diagram, Gummel characteristics, output characteristics, recombination profile, and potential distribution, demonstrate the high quality of the device and its suitability for high-speed operation. The transistor exhibits a high current gain of β = 250, a transition frequency of f_T = 66 GHz, and a maximum oscillation frequency of f_max = 70 GHz confirming its potential for microwave circuit applications. The parameters extracted using Silvaco are subsequently imported into Keysight Advanced Design System (ADS) to implement a two-stage shunt-series feedback transimpedance amplifier (TIA) targeting 20 Gb/s optical links. The TIA achieves a transimpedance gain of 45 dBΩ, a −3 dB bandwidth of 14.5 GHz, and a supported data rate of approximately 20 Gb/s. The amplifier demonstrates unconditional stability across the entire 0–20 GHz frequency range, a noise figure in the range of 6.25–7.8 dB, and a group delay variation of 10 ps within the passband. Overall, the proposed InP/InGaAs HBT on a 6H-SiC substrate offers promising performance for high-frequency and microwave circuit integration, and the Silvaco-to-ADS design flow provides a rigorous and physically grounded methodology for device-to-circuit performance prediction.