ANALYTICAL AND EXPERIMENTAL CHARACTERISTICS OF SIGE HETEROJUNCTION BIPOLAR-TRANSISTORS WITH THIN ALPHA-SI-H EMITTERS

SiGe heterojunction bipolar transistors (HBTs) with thin n(+) hydrogen ated amorphous Si (alpha-Si:H) emitters are discussed. A first order a nalytical model is used to illustrate the leverage of the structures i n terms of current gain, resulting from the barrier height created by the thin alpha-Si:H emitters, and high Early voltage resulting from op timizing the Ge profile and doping concentration in the base. Two-dime nsional simulations were carried out to investigate device performance parameters. Devices with 50 Angstrom alpha-Si:H emitters and various base doping concentrations and Ge distribution profiles were fabricate d. A current of 100, current gain-Early voltage product larger than 11 040 and unity gain cutoff frequency f(r) of 14.5 GHz were obtained for devices having base doping concentrations of 1 x 10(19) cm(-3), a bas e Ge grading of 0-20% and an emitter size of 2 x 4 mu m(2).