Band to band tunneling in semiconductors fundamentally depends of the complex bandstructure of the semiconductor
within its bandgap. In this work, the orientation dependent complex bandstructure of InSb, InAs, GaSb, InP and GaAs, and
the orientation dependent probability of band to band tunneling in these materials have been computed using an <i>sp<sup>3</sup>d<sup>5</sup>s<sup>∗</sup></i>
tight binding model. These direct bandgap III-V materials are attractive candidates for Tunnel FETs. Comparison of our
results with Kane’s two-band model commonly used in TCAD simulation, demonstrates the inaccuracies of the latter. Our
results will be useful in the design of better performing Tunnel FETs in these materials.