Hole mobility enhancement by double-gate mode in ultrathin-body silicon-on-insulator p -type metal-oxide-semiconductor field-effect transistors

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 (T_SOI) 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 (N_s). In particular, enhancement of mobility of the sub-10-nm-thick T_SOI devices is greater at higher N_s. As a result, it is demonstrated that μDG of the 8.1-nm-thick T_SOI device is 12.9% greater than the universal mobility when N_s 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 T_SOI devices is enhanced greatly at higher N_s, since the DG mode-induced increase in the hole population in LH bands is enhanced at higher N_s; the reduction in the hole population in LH bands due to the high- N_s -enhanced carrier confinement in the normal direction is larger in SG mode than in DG mode.