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Pseudo-HBT with polysilicon emitter contact and an ultrashallow highly doped bases by photoepitaxy

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6 Author(s)
Suzuki, K. ; Fujitsu Lab. Ltd., Kanagawa, Japan ; Fukano, T. ; Yamazaki, T. ; Hijiya, S.
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It is noted that reducing the base width to below 50 nm and increasing the base concentration to above 10/sup 19/ cm/sup -3/ are the key to high-speed pseudo-HBT (heterojunction bipolar transistor) operation at 77 K. To overcome the limitation on the base concentration due to tunneling, an emitter was fabricated with a reduced impurity concentration (4.4*10/sup 18/ cm/sup -3/) and a 55-nm ultrathin heavily doped base using a photoepitaxial growth technique. The device was free from tunneling current despite a base concentration of 1.2*10/sup 19/ cm/sup -3/. Current gain degradation at low temperatures was less than that of conventional devices. Heavily doped polysilicon between the medium-doped emitter layer and metal electrode improves the pseudo-HBT's current gain by about three times at 300 K and by 1.5 times at 77 K. The transit time due to this polysilicon layer, although large at 300 K, is negligible at 77 K.<>

Published in:

Electron Devices Meeting, 1989. IEDM '89. Technical Digest., International

Date of Conference:

3-6 Dec. 1989