Analytical and experimental characteristics of SiGe heterojunction bipolar transistors with thin α-Si:H emitters

Abstract

SiGe heterojunction bipolar transistors (HBTs) with thin n + hydrogenated amorphous Si (α-Si:H) emitters are discussed. A first order analytical model is used to illustrate the leverage of the structures in terms of current gain, resulting from the barrier height created by the thin α-Si:H emitters, and high Early voltage resulting from optimizing the Ge profile and doping concentration in the base. Two-dimensional simulations were carried out to investigate device performance parameters. Devices with 50 Å α-Si:H emitters and various base doping concentrations and Ge distribution profiles were fabricated. A current of 100, current gain-Early voltage product larger than 11040 and unity gain cutoff frequency f T of 14.5 GHz were obtained for devices having base doping concentrations of 1 × 10 19 cm −3, a base Ge grading of 0–20% and an emitter size of 2 × 4 μm 2.