Impact of calibrated band-tails on the subthreshold swing of pocketed TFETs

The tunnel field-effect transistor (TFET) is one of the prime steep-slope device candidates to be employed in future ultra-low power logic applications [1], [2], and can achieve sub-60 mV/dec subthreshold swings (SS) using quantum mechanical (QM) band-to-band tunneling (BTBT). One of the main challenges for TFETs is obtaining a sufficiently high drive-current ION [1]. The ION can be enhanced by introducing a highly-counter-doped pocket at the tunnel junction [3], [4]. However, it is well known that high doping concentrations introduce band-tails states in the bandgap [5]. First assessments on band-tails in TFETs, linked to diode measurements, have been made [6]-[8]. However, it is unknown whether the band-tails-induced tunneling contributions limit the performance of optimized pocketed TFETs. In this work, we investigate the impact of band-tails on the SS of p-n-i-n In0.53Ga0.47As and InAs TFETs for different pocket thicknesses and doping concentrations in the source and pocket, while using band-tails density-of-states (DOS) obtained from successful diode calibrations [8].