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Superlattice Tailoring to Obtain Devices With High Saturation Velocity

IP.com Disclosure Number: IPCOM000062555D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Van Zeghbroeck, BJ: AUTHOR

Abstract

For use in semiconductor devices, a superlattice is tailored to increase the saturation velocity by introducing forbidden bandgaps, thereby preventing carriers from assuming undesirable states. More particularly, in GaAs devices, electrons are prevented from scattering into the L-valleys, where electrons are slow, because of their high effective mass. Fig. 1 shows, for GaAs, a plot of energy versus crystal momentum or wave vector (k) illustrating the energy band structure within the Brillouin zone associated with the crystal having a lattice spacing a. Fig. 2 illustrates the electron velocity as a function of k. Under large field conditions, the electrons scatter to the so- called L-valleys.

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Superlattice Tailoring to Obtain Devices With High Saturation Velocity

For use in semiconductor devices, a superlattice is tailored to increase the saturation velocity by introducing forbidden bandgaps, thereby preventing carriers from assuming undesirable states. More particularly, in GaAs devices, electrons are prevented from scattering into the L-valleys, where electrons are slow, because of their high effective mass. Fig. 1 shows, for GaAs, a plot of energy versus crystal momentum or wave vector (k) illustrating the energy band structure within the Brillouin zone associated with the crystal having a lattice spacing a. Fig. 2 illustrates the electron velocity as a function of k. Under large field conditions, the electrons scatter to the so- called L-valleys. Because of the high density of states (compared to the energy minimum at k=0), the electrons will remain in the higher

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valley where they have a higher effective mass resulting in a lower saturation velocity. By introducing a superlattice consisting of alternating layers of different doping or composition, a bandgap between the two lowest bands of the superlattice can be provided that is sufficiently large to prevent the electrons from crossing since the gap is much larger than the thermal energy or the optical phonon energy. This is illustrated by the dotted curves in Fig. 1. The electrons stay in the lowest band, i.e., their effective mass is substantially lower, compared to the L-valley,...