Strained-Si/strained-Ge type-II staggered heterojunction gate-normal-tunneling field-effect transistor

A SiGe-based n-channel tunnel field-effect transistor design employing a strained-Si/strained-Ge staggered-gap heterojunction with a small effective band-gap (122 meV) at the interface is investigated via numerical simulations using a semi-classical quantum correction obtained from the density-gradient model. A gate-normal tunneling geometry is used to increase tunneling area and reduce subthreshold swing. The strain leads to degeneracy breaking among the silicon conduction band valleys, reducing the density of states and associated quantum capacitance with better gate-to-tunnel barrier coupling. Performance evaluation using a figure-of-merit “I₆₀,” where the drain current corresponds to a subthreshold slope of 60 mV/decade, suggests that the device has the potential to be competitive with modern metal-oxide-semiconductor field-effect transistors.