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.