  Thickness engineered tunneling field-effect transistors (TE-TFET) as a high
performance ultra-scaled steep transistor is proposed. This device exploits a
specific property of 2D materials: layer thickness dependent energy bandgap
(Eg). Unlike the conventional hetero-junction TFETs, TE-TFET uses spatially
varying layer thickness to form a hetero-junction. This offers advantages by
avoiding the interface states and lattice mismatch problems. Furthermore, it
boosts the ON-current to 1280$\mu A/\mu m$ for 15nm channel length. TE-TFET
shows a channel length scalability down to 9nm with constant field scaling $E =
V_{DD}/L_{ch}= 30V/nm$. Providing a higher ON current, phosphorene TE-TFET
outperforms the homojunction phosphorene TFET and the TMD TFET in terms of
extrinsic energy-delay product. In this work, the operation principles of
TE-TFET and its performance sensitivity to the design parameters are
investigated by the means of full-band atomistic quantum transport simulation.
