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Improved Mobility Silicon Field-Effect Transistor

IP.com Disclosure Number: IPCOM000042280D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Keyes, RW: AUTHOR

Abstract

The mobility and transconductance of a field-effect transistor (FET) is improved when the transistor is fabricated in a thin film of silicon grown epitaxially on a semiconductor substrate with a lattice parameter slightly greater than that of silicon. The mismatch is accommodated by strain; the lattice of the film is distended in the plane of the interface and compressed along the perpendicular to the film. If the interface is a 100 Ùsurface, then this distortion lowers the energy of the 100 Ùvalleys of silicon. These valleys will then be preferentially occupied by electrons. The [100] valleys have higher mobility and lower effective mass in the plane of the film, which is the direction of current flow in an FET fabricated on the surface of the silicon. An alloy of GaP and GaAs serves as a substrate.

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Improved Mobility Silicon Field-Effect Transistor

The mobility and transconductance of a field-effect transistor (FET) is improved when the transistor is fabricated in a thin film of silicon grown epitaxially on a semiconductor substrate with a lattice parameter slightly greater than that of silicon. The mismatch is accommodated by strain; the lattice of the film is distended in the plane of the interface and compressed along the perpendicular to the film. If the interface is a 100 Ùsurface, then this distortion lowers the energy of the 100 Ùvalleys of silicon. These valleys will then be preferentially occupied by electrons. The [100] valleys have higher mobility and lower effective mass in the plane of the film, which is the direction of current flow in an FET fabricated on the surface of the silicon. An alloy of GaP and GaAs serves as a substrate. Varying the alloy composition allows the lattice mismatch to be varied from 0.5% to 4%. Such substrates can also be doped in a way similar to silicon. AlP (mismatch 1%) and Ge (mismatch 4%) are other possibilities. The difference in energy between the favorably and unfavorably oriented valleys is 15 eV times the mismatch. Thus, 2% mismatch causes a 0.3 eV difference, larger than the thermal energy at 300OEK, yielding a large effect.

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