Electron transport in thin SOI, strained-SOI and GeOI MOSFET by Monte-Carlo simulation

Electron transport properties are investigated in slicon-on-insulator (SOI), strained-silicon-on-insulator (S-SOI) and germanium-on-insulator (GeOI) n-MOSFETs by Monte-Carlo simulation. The conduction band structure of germanium introduced in the Monte-Carlo simulator includes the four 〈1 1 1〉 minima at the edge of the Brillouin zone (name 'L valleys'), a single minimum at the center of the zone (name 'Γ valley'), and six 〈1 0 0〉 minima lying near the zone edge (name 'Δ valleys'). The electron-phonon scattering mechanisms within all the valleys are described. To validate this model, ohmic in-plane drift mobilities as well as saturation velocities are reported for undoped germanium for field oriented along [1 0 0] direction and for lattice temperature TL ∈ [77-300 K]. A good agreement is achieved with experimental data of Jacoboni et al. The in-plane drift mobility reaches 3930 cm2/Vs at 300 K and 39,550 cm2/Vs at 77 K which is about two times that in silicon. Having so determined the electron ohmic transport in germanium, we present a comparative simulation of inversion-layer mobility in long-channel SOI, S-SOI and GeOI n-MOSFETs of 15 nm-film thickness. It was found a mobility enhancement factor of ≈1.7 and ≈2 for an inversion charge Qinv=1 × 1012 cm−2 in S-SOI and GeOI n-MOSFET, respectively. Finally, non-equilibrium and ballistic transport in SOI, S-SOI and GeOI n-MOSFET with a 40 nm-channel length and 15 nm-film thickness are investigated.