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On the profile design and optimization of epitaxial Si- and SiGe-base bipolar technology for 77 K applications. I. Transistor DC design considerations

1993; Institute of Electrical and Electronics Engineers; Volume: 40; Issue: 3 Linguagem: Inglês

10.1109/16.199358

1557-9646

John D. Cressler, J.H. Comfort, E.F. Crabbé, G.L. Patton, J.M.C. Stork, J.Y.-C. Sun, B.S. Meyerson,

Silicon Carbide Semiconductor Technologies

The DC design considerations associated with optimizing epitaxial Si- and SiGe-base bipolar transistors for the 77-K environment are examined in detail. Transistors and circuits were fabricated using four different vertical profiles, three with a graded-bandgap SiGe base, and one with a Si base for comparison. All four epitaxial-base profiles yield transistors with DC properties suitable for high-speed logic applications in the 77-K environment. The differences between the low-temperature DC characteristics of Si and SiGe transistors are highlighted both theoretically and experimentally. A performance tradeoff associated with the use of an intrinsic spacer layer to reduce parasitic leakage at low temperatures and the consequent base resistance degradation due to enhanced carrier freeze-out is identified. Evidence that a collector-base heterojunction barrier effect severely degrades the current drive and transconductance of SiGe-base transistors operating at low temperatures is provided. >