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

© 2018 IEEE. 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 I ON [1]. The I ON 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 In 0.53 Ga 0.47 As 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].status: publishe

Signature of Ballistic Band-Tail Tunneling Current in Tunnel FET

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Calibration of the high-doping induced ballistic band-tails tunneling current in In0.53Ga0.47As Esaki diodes

© 2017 IEEE. I. Introduction The growing demand for power efficient devices has accelerated the research into the use of the tunnel field-effect transistor (TFET) in future ultra-low power applications because of its promising potential for sub-60 mV/dec subthreshold swing achieved through quantum mechanical band-To-band tunneling (BTBT) [1]-[3]. Unfortunately, a significant gap between theoretical predictions and experiments remains to be bridged [2]. Considerable efforts are being made to develop models for some of the main causes of suboptimal TFET performance such as trap-Assisted tunneling (TAT) [4], [5], phonon-Assisted tunneling (PAT) [6], and Auger generated leakage currents [7]. However, aside from qualitative analyses [8] and purely predictive work on the device impact of tunneling transitions involving high-doping induced band-Tails states in InSb nanowire TFETs [9] and 2D-TFETs [10], no attempts have been made to calibrate these contributions. This work aims to fill this gap by developing and calibrating an approximate ballistic semi-classical (SC) model for high-doping induced band-Tails using the experimental I-V data of In0.53Ga0.47As p-i-n Esaki diodes [11]. The hypothesis is posited that the mismatch between measurement and simulation in the negative differential resistance regime (see Fig. 1), which cannot be explained by SC TAT models, is caused by ballistic band-Tails tunneling. The calibration thus gives an upper limit to the band-Tails current. Lastly, the impact of band-Tails on the performance of a p-n-i-n TFET is investigated.status: publishe