Simulation Study of Thin-Body Ballistic n-MOSFETs Involving Transport in Mixed $\Gamma$-L Valleys

Abstract

Transistor designs based on using mixed -L valleys for electron transport are proposed to overcome the density of states bottleneck while maintaining high injection velocities. Using a self-consistent top-of-the-barrier transport model, improved current density over Si is demonstrated in GaAs/AlAsSb, GaSb/AlAsSb, and Ge-on-insulator-based singlegate thin-body n-channel metal-oxide-semiconductor field-effect transistors. All the proposed designs successively begin to outperform strained-Si-on-insulator and InAs-on-insulator (InAs-OI) in terms of ON-state currents as the effective oxide thickness is reduced below 0.7 nm. InAs-OI still exhibits the lowest intrinsic delay (τ ) due to its single valley.

Review Article: Molecular beam epitaxy of lattice-matched InAlAs and InGaAs layers on InP (111)A, (111)B, and (110)

“…Bhat et al showed by MOCVD that specular surfaces nearly free of defects can be obtained for a 3 offcut toward (111)A or (111)B, and they suggest that further improvement is possible with a higher offcut. 102 Mitsuhara et al confirmed this result for chemical beam epitaxy growth, and found gradual improvement in the surface morphology with offcut angle up to 6 . 103 Smooth growth of GaAs (110) as well as InGaAs (110) and InAlAs(110) can be achieved using very …”

“…2 The L-valleys of III-V semiconductors offer both high DOS and high injection velocities. Through the appropriate application of quantum confinement, [3][4][5][6][7][8] strain, [4][5][6] and III-V materials with low L-C valley separation, 3 conduction in the L-valleys can occur in parallel with the C-valley, resulting in large drive currents. In particular, thin layers of GaAs (111) and GaSb (111) are predicted to have superior drive currents compared to Si.…”

“…In particular, thin layers of GaAs (111) and GaSb (111) are predicted to have superior drive currents compared to Si. 3,4,7,8 One proposed device structure relies on the growth of a tensile strained GaAs quantum well on InP(111), 4,6 a material system that has been successfully grown for novel (111) quantum dots 9,10 (described later in this section). Fabrication of a III-V MOSFET using these strategies has yet to be demonstrated, and its realization relies on the growth of high quality III-Vs on (111) surfaces.…”

Quasi-Ballistic $\Gamma $ - and L-Valleys Transport in Ultrathin Body Strained (111) GaAs nMOSFETs

“…At such small thicknesses surface roughness (SR) scattering poses severe limits to the mobility [35], and frustrates any hope to achieve an improved performance at the device level. Compressive biaxial strain reduces the Γ-L energy offset, and can increase the population of L-valley subbands even in relatively thick wells [22], [23]. The unfavorable trade-off between confinement and surface roughness limited mobility of unstrained GaAs can be alleviated, thus gaining some design margin.…”

“…Design guidelines to mitigate the detrimental effects of the DoS bottleneck include the selection of materials and orientations with a large quantization mass (to reduce the energy spacing between subbands and thus effectively increase the number of subbands available for transport), a high in-plane effective mass perpendicular to the transport direction (to [001] [100] [010] [211] increase the charge density per subband), and a low mass parallel to the transport direction (for high υ inj ). At this regard, it has been recently proposed that such a subband engineering can be achieved using the L-valleys in (111) ultrathin-body (UTB) III-V materials having low Γ-L energy separation, such as strained GaAs and GaSb [3], [12], [20], [21], [22], [23]. In fact in UTB MOSFETs with (111) surface orientation, the L[111] valley, located in the center of the 2D Brillouin zone in Fig.…”