cm²-Scale Synthesis of MoTe₂ Thin Films with Large Grains and Layer Control.

Abstract

Owing to the small energy differences between its polymorphs, MoTe₂ can access a full spectrum of electronic states from the 2H semiconducting state to the 1T' semimetallic state and from the T_d Weyl semimetallic state to the superconducting state in the 1T' and T_d phase at low temperature. Thus, it is a model system for phase transformation studies as well as quantum phenomena such as the quantum spin Hall effect and topological superconductivity. Careful studies of MoTe₂ and its potential applications require large-area MoTe₂ thin films with high crystallinity and thickness control. Here, we present cm²-scale synthesis of 2H-MoTe₂ thin films with layer control and large grains that span several microns. Layer control is achieved by controlling the initial thickness of the precursor MoO_<i>x</i> thin films, which are deposited on sapphire substrates by atomic layer deposition and subsequently tellurized. Despite the van der Waals epitaxy, the precursor-substrate interface is found to critically determine the uniformity in thickness and grain size of the resulting MoTe₂ films: MoTe₂ grown on sapphire show uniform films while MoTe₂ grown on amorphous SiO₂ substrates form islands. This synthesis strategy decouples the layer control from the variabilities of growth conditions for robust growth results and is applicable to growing other transition-metal dichalcogenides with layer control.