Charge-Induced Two-Step Structural Phase Transition in the MoTe2–WSeTe Hetero-Bilayer

Abstract

Structural phase transition, which enables dynamic control of the conductivity, occurs in several transition-metal dichalcogenides (TMDs). This property has potential application for next-generation field-effect transistors and storage devices. Mo- and W-based TMDs are the most appropriate materials for this purpose because of the existence of an exceptional semimetallic phase (T′) that has a small energy difference with the semiconducting phase (H), which leads to the switching of conductivity with a relatively small energy. By employing ab initio simulations, this work reports a two-step phase transition in a type of MoTe2–WSeTe hetero-bilayers driven by electrostatic gating with energy differences of EH–T’ – EH–H = 4.4 meV and ET′–T′ – EH–T′ = 30.2 meV/fu, which leads to phase transition voltages of −0.79 and −6.57 V in the studied device. Nudge elastic band (NEB) calculations depicted that the kinetic barriers for H–H to H–T′ are 0.779 and 0.775 eV in forward and backward phase transitions, respectively, while H–T′ to T′–T′ kinetic barriers for forward and backward phase transitions are 0.729 and 0.691 eV, respectively. This indicates a higher transition rate in this material compared to MoTe2 as a standard phase change material. The presented results pave the way for realizing phase transition materials based on hetero-bilayers of two-dimensional materials.