Tensile strained Ge tunnel field-effect transistors: k • p material modeling and numerical device simulation

摘要

Group Ⅳ based tunnel field-effect transistors generally show lower on-current than Ⅲ-Ⅴ based devices because of the weaker phonon-assisted tunneling transitions in the group Ⅳ indirect bandgap materials. Direct tunneling in Ge, however, can be enhanced by strain engineering. In this work, we use a 30-band k • p method to calculate the band structure of biaxial tensile strained Ge and then extract the bandgaps and effective masses at Γ and L symmetry points in k-space, from which the parameters for the direct and indirect band-to-band tunneling (BTBT) models are determined. While transitions from the heavy and light hole valence bands to the conduction band edge at the L point are always bridged by phonon scattering, we highlight a new finding that only the light-hole-like valence band is strongly coupling to the conduction band at the Γ point even in the presence of strain based on the 30-band k • p analysis. By utilizing a Technology Computer Aided Design simulator equipped with the calculated band-to-band tunneling BTBT models, the electrical characteristics of tensile strained Ge point and line tunneling devices are self-consistently computed considering multiple dynamic nonlocal tunnel paths. The influence of field-induced quantum confinement on the tunneling onset is included. Our simulation predicts that an on-current up to 160 (260) μA/μm can be achieved along with on/off ratio ＞ 10~6 for V_(DD) = 0.5 V by the n-type (p-type) line tunneling device made of 2.5% biaxial tensile strained Ge.