Hole mobility enhancement in double-gate (DG) ultrathin-body (UTB) silicon-on-insulator (SOI) p -type metal-oxide-semiconductor field-effect transistors (MOSFETs) is investigated systematically in comparison with single-gate (SG) UTB MOSFETs for various SOI thicknesses (TSOI) ranging from 2 to 30 nm. It is found that mobility in DG mode (μ DG) is higher than that in SG mode (μ SG) in all the measured ranges of T SOI and the surface carrier concentrations (Ns). In particular, enhancement of mobility of the sub-10-nm-thick TSOI devices is greater at higher Ns. As a result, it is demonstrated that μDG of the 8.1-nm-thick TSOI device is 12.9% greater than the universal mobility when Ns is 6× 1012 cm -2 Higher μDG is attributed to the average effective mass reduction in DG mode because of the increased population in the light hole (LH) bands. Careful investigation also clarifies that mobility in the sub-10-nm-thick TSOI devices is enhanced greatly at higher Ns, since the DG mode-induced increase in the hole population in LH bands is enhanced at higher Ns; the reduction in the hole population in LH bands due to the high- Ns -enhanced carrier confinement in the normal direction is larger in SG mode than in DG mode.
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