Modeling of Surface-Roughness Scattering in Ultrathin-Body SOI MOSFETs

A rigorous surface-roughness scattering model for ultrathin-body silicon-on-insulator (SOI) MOSFETs is derived, which reduces to Ando´s model in the limit of bulk MOSFETs. The matrix element of the scattering potential reflects the fluctuations of both the wavefunction and the potential energy. The matrix element reflecting the fluctuation of the wavefunction is expressed in an integral form which can be considered as a generalized Prange-Nee term-to which it is equivalent in the limit of an infinitely high insulator-semiconductor barrier-giving more accurate results in the case of a finite barrier height. The matrix element reflecting the fluctuation of the potential energy is due to the Coulomb interactions originating from the roughness-induced fluctuation of the electron charge density, the interface polarization charge, and the image-charge density. The roughness-limited low-field electron mobility in thin-body SOI MOSFETs is obtained using the matrix elements that we have derived. We study its dependence on the silicon body thickness, effective field, and dielectric constant of the insulator.