III–V FETs are being developed for potential application in 0.3–3 THz systems and VLSI. To increase bandwidth, we must increase the drive current I d = qn s v inj W g per unit gate width W g , requiring both high sheet carrier concentrations n s and high injection velocities v inj . Present III–V NFETs restrict control region transport to the single isotropic Γ band minimum. As the gate dielectric is thinned, I d becomes limited by the effective mass m*, and is only increased by using materials with increased m* and hence increased transit times. ¹ The deep wavefunction also makes Γ -valley transport in low-m*materials unsuitable for < 22-nm gate length (L g ) FETs. Yet, the L-valleys in many III–V materials ² have very low transverse m t and very high longitudinal mass m 1 . L-valley bound state energies depend upon orientation, and the directions of confinement, growth, and transport can be chosen to selectively populate valleys having low mass in the transport direction ^3,4 . The high perpendicular mass permits placement of multiple quantum wells spaced by a few nm, or population of multiple states of a thicker well spaced by ∼10–100 meV. Using combinations of Γ and L valleys, n s can be increased, m* kept low, and vertical confinement improved, key requirements for <20-nm L g III–V FETs.

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