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Effect of emitter contact on current gain of silicon bipolar devices

1980; Institute of Electrical and Electronics Engineers; Volume: 27; Issue: 11 Linguagem: Inglês

10.1109/t-ed.1980.20148

1557-9646

T.H. Ning, R. Isaac,

Advancements in Semiconductor Devices and Circuit Design

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 2 Si + Al, or iii) n + polysilicon + Al are compared. For the same base doping profile, β(Al) is typically about 25 percent larger than β(Pd 2 Si), while β(poly) is typically several times larger than β(Pd 2 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 + polysilicon layer. A simple two-region (n + silicon region and n + polysilicon region) model is presented which satisfactorily explains the experimental results in terms of lower hole mobility in the n + polysilicon than in the monocrystalline n + silicon.