Influence of uniaxial strain in Si and Ge p-type double-gate metal-oxide-semiconductor field effect transistors

Abstract

We theoretically investigate the impact of uniaxial strain in extremely thin Si and Ge p-type double-gate transistors. Quantum transport modeling is treated using a 6-band k.p Hamiltonian and the non-equilibrium Green's function formalism including phonon scattering. Based on this framework, we analyze the influence of strain on current characteristics considering different transport directions and gate lengths. Our results first confirm the superiority of Ge over Si in long devices (15 nm gate length) for which best electrical performances are obtained considering channels along 〈110〉 with a uni-axial compressive strain. For this configuration, Si devices suffer from inter-subband coupling which generates a strong hole-phonon scattering. Material dominance is reversed for shorter devices (7 nm gate length) where the small effective masses of Ge deteriorate the off-regime of the nano-transistor regardless of strain and crystallographic options. Due to weaker hole-phonon-scattering, 〈100〉-Si devices with a tensile strain are interestingly found to be more competitive than their 〈110〉-compressive counterparts. These results show that Si is still the most relevant material to reach the ultimate nanometer scale. More importantly, the same tensile strain can be considered to boost performances of both p- and n-type planar transistors which would lead to a significant simplification of the technological strain manufacturing.