Vertical-tunneling field-effect transistor based on MoTe₂/MoS₂2D–2D heterojunction

Abstract

We demonstrate a vertical-tunneling field-effect transistor (FET) based on a MoTe2/MoS2 heterojunction. MoTe2 exhibits p-type characteristics, and it has a relatively small band gap and low electron affinity among 2D materials. On the contrary, MoS2 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 MoTe2 and MoS2, and it was confirmed that the stack of MoTe2 and MoS2 forms a staggered structure suitable for band-to-band tunneling. To improve the electrical characteristics of the device, MoS2 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 MoTe2 and MoS2, Pd was deposited on MoTe2 and Ti was deposited on MoS2 to lower contact resistance and suppress the ambipolar characteristics of MoTe2. Consequently, the MoTe2/MoS2 heterojunction vertical tunneling FET achieved a low subthreshold swing of 34 mV/dec and a high on/off ratio of 106 at room temperature. In addition, we confirmed band-to-band tunneling through temperature dependent transfer characteristics.