Effect of phonon-assisted tunneling on the subthreshold swing of tunnel field-effect transistor

The tunnel field-effect transistor (TFET) is considered to be one of the best hopes for achieving a subthermal switch with a subthreshold swing (SS) smaller than the Boltzmann limit, (kBT/q) x ln(10), which is 60 mV/dec at room temperature. However, many experimental studies show that the realistic SSs of TFETs are far inferior to the idealized simulation results. To explain the discrepancy between experiments and simulations, we developed a first-principles model of multiphonon-assisted tunneling and calculated the parasitic leakage current induced by phonon-assisted tunneling. The purpose of this work is to show the importance of phonon-assisted transport in the so-called cold-source device designs. The results show that this is an unavoidable intrinsic mechanism and that phonon-assistance effects impose a fundamental limit on the TFET performance.