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Abbreviated Journal Title

J. Appl. Phys.

Keywords

Physics; Applied

Abstract

Charge storage in the quasineutral regions of a bipolar transistor often limits the switching speed of the device, particularly when the transistor is operated in saturation mode (both emitter-base and base-collector junctions are forward biased), a bias condition which occurs frequently in logic circuits. This paper studies and compares the free-carrier charges stored in the quasineutral regions of the conventional Si homojunction bipolar transistor (Si BJT) and the increasingly important AlGaAs/GaAs and Si/SiGe heterojunction bipolar transistors (HBTs). The diffusion capacitances associated with this stored charge, which are used in the Gummel-Poon bipolar transistor model, are also calculated and discussed. It is shown that the AlGaAs/GaAs HBT has the least carrier accumulation in the quasineutral regions among the three devices due primarily to the relatively large energy band gap of GaAs-related materials. Also, the Si/SiGe HBT is expected to operate at a higher switching speed compared to the Si BJT, because the valence band discontinuity at the Si/SiGe base-collector heteroface impedes the minority-carrier injection from the base into the collector.

Journal Title

Journal of Applied Physics

Volume

71

Issue/Number

8

Publication Date

1-1-1992

Document Type

Article

Language

English

First Page

4059

Last Page

4065

WOS Identifier

WOS:A1992HP36600061

ISSN

0021-8979

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