Effects of increased acoustic phonon deformation potential and surface roughness scattering on quasi-ballistic transport in ultrascaled Si-MOSFETs

Abstract

It is a common view that ballistic transport is enhanced by channel length scaling because of a decreased scattering number. On the other hand, the acoustic phonon (AP) scattering rate is higher in silicon-on-insulator (SOI) MOSFETs than in bulk Si-MOSFETs; moreover, surface roughness (SR) scattering caused by spatial fluctuation of quantized subbands emerges in extremely scaled SOI channels. Therefore, the influences of these scattering mechanisms on ballistic transport in ultrathin-body Si-MOSFETs are examined in this paper using a Monte Carlo simulation technique. First of all, the effect of increased AP scattering rate on the drain current and ballistic efficiency is found to be negligible. Furthermore, contrary to the common view, ballistic transport in double-gate MOSFETs is shown to be degraded when the channel length decreases to less than 10 nm, mainly owing to SR scattering intensified by the spatial fluctuation of quantized subbands. The gate and drain bias voltage dependencies of ballistic efficiency are also discussed.

Role of remote Coulomb scattering on the hole mobility at cryogenic temperatures in SOI p-MOSFETs*

“…Here, the acoustic deformation potential D ac is set to a higher value of D ac = 9.65 eV [45] than the value adopted in the bulk silicon devices, in agreement with Ref. [34], which is the reasonable way [48] for the need to reproduce the experimental data for SOI devices. ∆ = 0.4 nm and Λ = 1.6 nm are used for the SR scattering parameters, which are significantly different from those in Fig.…”

Theoretical investigation of the phonon-limited carrier mobility in (001) Si films

“…The peak near t Si % 3 nm and the small dip above have been observed in FDSOI devices. 7 This behavior results from the effects of quantum confinement on the band structure of (001) Si films, 7,25 as illustrated in Fig. 4.…”

“…To solve this issue, other authors have introduced a spatially dependent N e ac , which sharply increases close to the interfaces with the oxide. 11,25,78 The reality of this enhancement could be questioned since the mobility in bulk MOSFETs and FDSOI devices results from a complex interplay between carrier-phonon interactions, interface roughness, 17,79,80 and Coulomb scattering. 20,32,35 However, experiments show that the lowtemperature (25 K) mobility in FDSOI devices is the same for t Si ¼ 60 nm and t Si ¼ 7.2 nm, whereas at room temperature the mobility is much smaller for t Si ¼ 7.2 nm than for t Si ¼ 60 nm.…”

“…[3][4][5][6][7][8][9][10][11][12] In FDSOI devices, the thickness of the channel is well below 10 nm, so that structural confinement effects can be significant. Quantum modeling has, therefore, become an important tool for their design and understanding, 6,[13][14][15][16][17][18][19][20][21][22][23][24][25][26] as was already the case for bulk MOSFETs in the strong inversion regime. [27][28][29][30][31][32][33][34][35][36] But quantum simulations are still based on severe approximations and free parameters that must be assessed using detailed comparisons with experiments 23 or more advanced modeling schemes.…”