Study of quantum confinement effects on hole mobility in silicon and germanium double gate metal-oxide-semiconductor field-effect transistors

Abstract

Quantum confinement effects on hole mobility in silicon and germanium double gate p-channel metal-oxide-semiconductor field-effect transistors ͑MOSFETs͒ are studied by using a Monte Carlo method. Uniaxial stress and channel/substrate orientation effects are considered. Our result shows that the hole mobility in a ͑100͒/͓110͔ silicon well decreases with a decreasing well thickness, which is in agreement with the experimental result. The hole mobility in a germanium channel MOSFET, however, exhibits a peak in a sub-20 nm well because of the interplay between intrasubband and intersubband scatterings.Double-gate ͑DG͒ metal-oxide-semiconductor fieldeffect transistors ͑MOSFETs͒ and fin field-effect transistor have been considered as promising alternatives to bulk MOSFETs in 22 nm technology node and beyond 1-3 due to their immunity to short channel effects. Recently, advanced channel materials with higher carrier mobility than bulk Si, such as Ge ͑Ref. 4͒ and III-V materials, 5 have attracted much attention. Experimental works have shown the possibility that the inversion carrier mobility can be further improved in quantum structure MOSFETs by a subband modulation. 6,7 However, there has been little work on Ge-channel DGpMOSFETs addressing valence subband and substrate/ channel orientation effects on hole mobility.In this paper, we analyze quantum confinement effects on hole mobility as a function of a body thickness in Si-and Ge-channel DG-pMOSFETs. The low-field hole mobility is calculated by a Monte Carlo method. 8 The impact of substrate orientation on hole mobility is also evaluated. Furthermore, the effect of uniaxial compressive stress is discussed.Instead of the effective-mass approximation, the valence subband structures for two-dimensional holes in Si-and Gechannel DG-pMOSFETs are calculated self-consistently from the coupled Poisson and Schrödinger equations with a six-band Luttinger-Kohn Hamiltonian including spin-orbit coupling. 9 The Bir-Pikus deformation potentials 10 are also included to take into account the stress effect. In addition, an appropriate rotation matrix is employed when dealing with substrate orientations other than the ͑100͒ direction. 11,12 Material parameters, including Luttinger parameters, deformation potentials, and elastic constants used in the simulation, are given in Refs. 13-15. Relevant scattering mechanisms, including acoustic phonon scattering, optical phonon scattering, and surface roughness scattering, are considered in the Monte Carlo simulation. [16][17][18][19] The scattering parameters of Si and Ge are calibrated from a conventional Si MOSFET and from a SiGe-on-insulator device, respectively. 18 Figure 1 compares the hole mobility as a function of a body thickness in ͑100͒/͓110͔ Si-and Ge-channel DGpMOSFETs, where ͑͒ and ͓͔ are the notations of substrate orientation and channel direction, respectively. The choice of the ͓110͔ channel in Si is because it has a larger stress effect. The inversion hole density, p inv , is set to be 4 ϫ 10 12 cm −2 . The simulated hole mobi...

Si‐core/SiGe‐shell channel nanowire FET for sub‐10‐nm logic technology in the THz regime

“…Firstly, the wavefunction's peak in the inversion layer is approximately 20 Å from the gate oxide‐semiconductor interface . In addition, the wavefunction with a thinner channel has a wider distribution in the momentum space due to the uncertainty principle . Figure shows I on and S , where I on is evaluated at V DD = V GS = V DS = –0.7 V. The I on shows a turn‐around characteristic, which has a maximum at t of 3 nm.…”

Performance analysis of long Ge channel double gate (DG) p MOSFETs with high-k gate dielectrics based on carrier concentration formulation

“…Such threshold charge density for Ge channel DG MOSFETs can be determined with simulations and/ or measurements. In the present work we utilize Q th = 6.4 Â 10 À7 C/cm 2 using the quoted value of inversion hole density p inv = 4 Â 10 12 cm À2 for germanium channel DG MOSFETs as found in [25]. The inversion charge density at the interface in terms of p 0 can be expressed as…”

“…This formulation is based on the solution of Poisson Boltzmann equations, utilizes physical parameters like carrier concentration and also takes into account the effect of volume inversion. Using Monte Carlo technique the study of quantum confinement effects on hole mobility in germanium DG MOSFETs for various channel orientations was found in [25] where the enhanced value of hole mobility was predicted for (1 1 0)/[À1 1 0] channel orientation with Ge body thickness in the range 12-18 nm. Some good work on the sub-threshold drain current model of Ge channel DG MOSFETs was reported without considering the impact of interface trap charge density on device parameters such as threshold voltage roll-off, sub-threshold slope and drain induced barrier lowering for various geometric dimensions of the device [26].…”