Enhancement of band-to-band tunneling in mono-layer transition metal dichalcogenides two-dimensional materials by vacancy defects

Abstract

The band-to-band tunneling of monolayer transition metal dichalcogenides nano-junction is investigated using atomistic ab initio quantum transport simulations. From the simulation, it is found that the transition metal vacancy defect in the two-dimensional MX2 (M = Mo,W; X = S,Se) band-to-band tunneling diode can dramatically boost the on-state current up to 10 times while maintaining the device sub-threshold swing. The performance enhancement mechanism is discussed in detail by examining partial density of states of the system. It is found that the transition metal vacancy induces band-gap states, which reduce the effective length of the tunneling transition region.

Ab initio quantum transport calculations using plane waves

“…and the valence band of the right electrode are just about to overlap. As can be seen from the comparison, by introducing the transition-metal vacancy, the ON-state BTBT current is increased by a factor of 10 (similar results are found for other TMDCs [55]). Also note that, if the chalcogenide vacancy is introduced, there is almost no effect on the BTBT current.…”

“…15). However, since the band edge states of TMDCs are mainly located on the central transition-metal layer [55], one expects major effects from the transition-metal vacancy, not the chalcogenide vacancy, which is confirmed by our direct calculations.…”

“…The degraded SS in sub-10 nm physical gate length cases is a result of the source-to-drain direct tunneling due to the thin tunneling barrier, rather than the interband tunneling leakage at the channel-drain interface in small band gap semiconductor (such as InAs) based TFETs, where drain underlap must be used for leakage suppression. To further enhance the TFET performance (by increasing the turn-on tunneling current), we have investigated the atomic design of the mono-layer TMDC tunneling diode by introducing transition-metal and S vacancies [55]. The band structure as well as the potential profile of the mono-layer MoS 2 tunneling diode are shown in Fig.…”

“…16. Note that the bias voltage V b ¼ 0 is defined as when the conduction band of the left electrode [55]. and the valence band of the right electrode are just about to overlap.…”

Atomic-Monolayer MoS2Band-to-Band Tunneling Field-Effect Transistor

“…By the use of an atomically thin layer, 2D materials may give much higher tunneling current densities. In fact, some theoretical works predict that layered transition metal dichalcogenide (TMD) materials support direct BTBT in their monolayer sheet forms in addition to providing high on‐state currents due to the atomically thin tunneling barrier and low SS . However, there currently only exist a few experimental reports on TFETs made from few‐layered TMD materials .…”