Strain Release Enabled Bandgap Scaling in Ge Nanowire and Tunnel FET Application

The cross-sectional scaling-induced electronic property variations of the Ge and Si nanowires are studied numerically. After removing extra atoms from bulk materials to build the nanowires, not only the lateral quantum confinement is enhanced, but also the cross-sectional size will expand due to the breaking of the intrinsic strain balance. Compared with Si, the strain release-induced size expansion is more obvious in the Ge nanowires, shrinking the bandgaps and thus providing another bandgap modulation direction relative to the quantum confinement. At specific sizes, the strain release effect dominates the modulation and reduces the bandgaps of Ge nanowires even below the bulk value, while the reductions in Si nanowires are negligible, enlarging the band offsets of their heterostructures. As an application, the Ge/Si heterostructure tunnel FET (TFET) is designed and the TCAD simulation reveals a subthreshold swing (SS) of 13.8 mV/dec and an ON-state current of
$93 ~\mu \text{A}/\mu \text{m}$
, three orders of magnitude larger than that using the bulk materials.