Band Structure Effects in Extremely Scaled Silicon Nanowire MOSFETs With Different Cross Section Shapes

A multiscale simulation package based on ab initio calculation is used to study the band structure effects in extremely scaled gate-all-around silicon nanowire (SNW) MOSFETs with different cross-sectional shapes. All the interactions are computed directly from ab initio method without semiempirical parameters, and the effects of crystal atom relaxations and boundary atom dangling bond saturations are included intrinsically. The tight-binding Hamiltonian is obtained from ab initio results with maximally localized Wannier functions. The device performances are obtained with nonequilibrium Green's function method. With this simulation flow, the band structure and its impacts on the device performance of SNWs with different cross-sectional shapes are studied. Simulation results show that the crystal relaxation has notable effects on the band structure with different cross-sectional shapes and sizes. The SNWs with triangular cross-sectional shape are very competitive due to a smaller average conductivity effective mass ascribed to the valley splitting at extremely scaled size.