Effect of band-tails on the subthreshold performance of 2D tunnel-FETs

2D layered materials have been recently demonstrated to be very promising for tunneling field-effect transistor (TFET) applications [1],[2]. However, a complete and detailed analysis of the band-edge properties of 2D semiconductors that determine the fundamental subthreshold performance limits of TFETs is still lacking. This work, for the first time, fills this gap and provides new insight into the unique advantages of 2D materials for designing TFETs. This is achieved by combining photoluminescence (PL) measurements as well as analytical modeling and first-principle calculations. It is unveiled that for near-intrinsic TFET channel materials at room temperature, 2D semiconductors outperform bulk materials primarily due to weak electron-phonon interaction arising from the low deformation potential and low phonon energy in these 2D materials. On the other hand, it is shown that 2D materials can be more adversely affected by doping impurities and defects, which degrades subthreshold characteristics. Furthermore, subthreshold characteristics of TFETs realized with various combinations of bulk and 2D materials are extracted and compared. It is shown that 2D-2D lateral heterostructure TFETs can provide superior subthreshold performance w.r.t other TFET structures due to stronger dielectric screening and tunable tunneling width. In particular, lateral BP-WSe
₂
and BP-WTe
₂
heterostructure TFETs exhibit the lowest achievable subthreshold swings.