Simulation analysis of the DC current gain in an n-p-n a-Si:H/SiGe/Si heterojunction bipolar transistor

✍ Scribed by Francesco G.Della Corte; Fortunato Pezzimenti

• Publisher: Elsevier Science
• Year: 2004
• Tongue: English
• Weight: 134 KB
• Volume: 35
• Category: Article
• ISSN: 0026-2692
• DOI: 10.1016/j.mejo.2004.01.006

✦ Synopsis

This paper presents the results of a simulation study focused on the evaluation of the DC characteristics of an n-p-n SiGe-based heterojunction bipolar transistor (HBT) performing an extremely thin n þ hydrogenated amorphous silicon (a-Si:H) emitter. The a-Si:H(n)/SiGe(p) structure exhibits an energy gap difference of approximately 0.8 eV mostly located at the valence band side and this results in an optimal configuration for the emitter/base junction to improve the emitter injection efficiency and thus the device performance.

Considering a 20% Ge uniform concentration profile in the base region, simulations indicate that the DC characteristics of an a-Si:H/SiGe HBT are strictly dependent on two essential geometrical parameters, namely the emitter width and the base width. In particular, the emitter thickness degrades device characteristics in terms of current handling capabilities whereas higher current gains are obtained for progressively thinner base regions. A DC current gain exceeding 9000 can be predicted for an optimized device with a thin emitter and a 10 nm-thick, 7 £ 10 18 cm 23 -doped base.