Metal-dichalcogenide hetero-TFETs: Are they a viable option for low power electronics?

Introduction and Motivation: Band-to-band tunneling field-effect transistors (TFETs) have attracted a great deal of attention lately as potential active components of low power electronic circuits [1,2]. To meet this objective, two critical issues must be addressed: a reduction of the inverse sub-threshold slope (iSS) below 60 mV/dec over several orders of magnitudes and an increase of the ON-current above 100 μA/μm at low supply voltages V_DD. While iSS in TFETs can be decreased through improved manufacturing processes (low EOT, clean semiconductor/dielectric interfaces, high source doping concentrations, and so on) [3], delivering a high ON-current remains very challenging. Recent results indicate that heterostructures are the most likely candidates to provide the desired ON-current levels, especially Si-InAs [4], GaAsSb-InGaAs [5,6], or Ge-(Si)GeSn [7]. However, to fully leverage the potential of these materials, excellent electrostatic properties are needed. This is where single-layer metal-dichalcogenide semiconductors come into play. Due to their 2-D nature, their electrostatics can be very well-controlled and several theoretical studies point to the fact that band alignments very favorable to tunneling can be achieved in metal-dichalcogenide heterostructures [8,9]. Here, we propose to verify this hypothesis and use a full-band and atomistic quantum transport simulator to determine the characteristics of a strained WTe₂-MoS₂ hetero-TFET, as shown in Fig. 1(a). The key findings are that (i) a broken gap heterojunction can be realized, (ii) the average iSS is lower than 60 mV/dec over more than 7 orders of magnitude, and (iii) the ON-current reaches a promising value of 80 μA/μm at V _DD=0.4 V.