Monte Carlo Simulation of Double Gate Silicon on Insulator Inversion Layers: The Role of Volume Inversion

The electron mobility in a double-gate silicon on insulator (DGSOI) de-vice is studied as a function of the transverse electric field and silicon layer thickness. The contributions of the main scattering mechanisms (phonon scattering, surface roughness scattering due to both Si - SiO₂ interfaces, and Coulomb interaction with the interface traps of both interfaces) are taken into account and carefully analyzed. We demonstrate that the con-tribution of surface scattering mechanisms is by no means negligible; on the contrary, it plays a very important role which must be taken into account
when calculating the mobility in these structures. The electron mobility in DGSOI devices as T^w, decreases is compared with the mobility in Single-Gate Silicon On Insulator (SGSOI) structures, i) when only phonon scatter-ing is considered; ii) when the effect of surface roughness scattering is taken
into account, and iii), when the contribution of Coulomb interaction with charges trapped at both interfaces is taken into consideration (in addition to phonon and surface roughness scattering). From this comparison, we determined (in the three cases above) the existence of the following three
regions: i) A first region for thick silicon layers (T_w, > 20 - 30nm), where mobility for both structures tends to coincide, approaching the bulk value P-ii) As T_w decreases, we show that volume inversion modifies the electron transport properties by reducing the effect of all the scattering mechanisms.
Accordingly, the electron mobility in a DGSOI inversion increases by an im-portant factor which depends on the silicon thickness and the transverse effective field. iii)Finally, for very small thicknesses, the limitations to elec-tron transport are due to geometrical effects, and therefore the two mobilit,y curves, which again coincide, fall abruptly. We show the existence of a range of thicknesses of silicon layer (between 5nm and 20nm) in which electron mobility is improved by 25 % or more.