Vertical-tunneling field-effect transistor based on MoTe 2 /MoS 2 2D–2D heterojunction

We demonstrate a vertical-tunneling field-effect transistor (FET) based on a MoTe 2 /MoS 2 heterojunction. MoTe 2 exhibits p-type characteristics, and it has a relatively small band gap and low electron affinity among 2D materials. On the contrary, MoS 2 exhibits high electron affinity and n-type characteristics. Therefore, it is possible to improve the tunneling property by stacking two materials. X-ray photoelectron spectroscopy analysis was carried out to confirm the band alignment between MoTe 2 and MoS 2 , and it was confirmed that the stack of MoTe 2 and MoS 2 forms a staggered structure suitable for band-to-band tunneling. To improve the electrical characteristics of the device, MoS 2 with high conductivity was placed on the upper part of the heterojunction, on which the top gate was formed, and gate controllability was improved. In addition, when a source/drain was formed by considering the work function of MoTe 2 and MoS 2 , Pd was deposited on MoTe 2 and Ti was deposited on MoS 2 to lower contact resistance and suppress the ambipolar characteristics of MoTe 2 . Consequently, the MoTe 2 /MoS 2 heterojunction vertical tunneling FET achieved a low subthreshold swing of 34 mV/dec and a high on/off ratio of 10 6 at room temperature. In addition, we confirmed band-to-band tunneling through temperature dependent transfer characteristics.