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United States Patent | 5,329,144 |
Luryi | July 12, 1994 |
The disclosed novel heterojunction bipolar transistor, to be referred to as the enhanced diffusion transistor (EDT), comprises a base of composition selected such that the base bandgap narrows from emitter towards collector in substantially step-wise fashion, resulting in N (N.gtoreq.2) substantially flat levels in the base bandgap. The height .DELTA..sub.j of the steps in the bandgap is greater than kT (typically at least about 30 meV), and also greater than the threshold energy of an appropriate rapid inelastic minority carrier scattering mechanism (e.g., optical phonon scattering, plasmon scattering) in the base material. The presence of the "steps" in the base bandgap of the EDT can, in consequence of the resulting strongly accelerated diffusive minority carrier transport in the base, lead to, e.g., improved high frequency characteristics, as compared to otherwise identical prior art (N=1) transistors.
Inventors: | Luryi; Serge (Bridgewater, NJ) |
Assignee: | AT&T Bell Laboratories (Murray Hill, NJ) |
Appl. No.: | 052352 |
Filed: | April 23, 1993 |
Current U.S. Class: | 257/197; 257/198; 257/592 |
Intern'l Class: | H01L 031/072; H01L 031/109; H01L 027/082 |
Field of Search: | 257/197,198,592,591,593 |
Foreign Patent Documents | |||
3-138949 | Jun., 1991 | JP | 257/198. |
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