Full-3D real-space treatment of surface roughness in double gate MOSFETs

We analyze the effects of surface roughness on double gate (DG) MOSFETs by means of a full-3D real-space self-consistent Poisson-Schrodinger algorithm within the non equilibrium Green´s function (NEGF) formalism. We include periodic (Cauchy) boundary conditions along one of the transverse directions, whereas Dirichlet conditions are imposed along the vertical one. Surface roughness (SR) is included via a random generation of spatial fluctuations obeying an exponential autocorrelation law, and transfer characteristics are computed for different values of the root mean square (RMS) of such fluctuations. Simulation results show an impact of SR on the drain current and a shift of the threshold voltage proportional to the RMS. Quasi-ballistic transport is analyzed by means of backscattering coefficient. This is found to be limited by subband fluctuations at low inversion charge density and by mode-mixing at large one.