Simulation of Nanowire Tunneling Transistors: From the Wentzel-Kramers-Brillouin Approximation to Full-Band Phonon-Assisted Tunneling

Nanowire band-to-band tunneling field-effect transistors ͑TFETs͒ are simulated using the Wentzel– Kramers–Brillouin ͑WKB͒ approximation and an atomistic, full-band quantum transport solver including direct and phonon-assisted tunneling ͑PAT͒. It is found that the WKB approximation properly works if one single imaginary path connecting the valence band ͑VB͒ and the conduction band ͑CB͒ dominates the tunneling process as in direct band gap semiconductors. However, PAT is essential in Si and Ge nanowire TFETs where multiple, tightly-coupled, imaginary paths exist between the VB and the CB.