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Publication
IEEE T-ED
Paper
Effect of Emitter Contact on Current Gain of Silicon Bipolar Devices
Abstract
The common-emitter current gain β of silicon n-p-n bipolar transistors with shallow (200 nm) emitters contacted by either i) Al, ii) Pd<inf>2</inf>Si + Al, or iii) n<sup>+</sup> polysilicon + Al are compared. For the same base doping profile, β(Al) is typically about 25 percent larger than β(Pd<inf>2</inf>Si), while β(poly) is typically several times larger than β(Pd<inf>2</inf>Si). The dependence of the base current on temperature and on the thickness of the polysilicon layer indicates that the base current is not determined by the silicon-polysilicon interface properties, such as tunneling through an interfacial oxide layer, but by the transport of holes in the n<sup>+</sup> polysilicon layer. A simple two-region (n<sup>+</sup> silicon region and n<sup>+</sup> polysilicon region) model is presented which satisfactorily explains the experimental results in terms of lower hole mobility in the n<sup>+</sup> polysilicon than in the monocrystalline n<sup>+</sup> silicon. Copyright © 1980 by The Institute of Electrical and Electronics Engineers, Inc.