Vapor-Phase Synthesis of Two-Dimensional Molybdenum Ditelluride Polymorphs and Their Epitaxial Integration

Abstract

Crystal polymorphism in atomically thin transition-metal dichalcogenides often stabilizes the concurrent electronic phases as metals or semiconductors, offering the exciting potential to be integrated into two-dimensional (2D) electronic circuitry. Developing controlled growth of such 2D polymorphs in vapor-phases is a critical step yet to be realized. In this work, we have chosen MoTe2 as model 2D polymorphs for our synthetic integration by direct growth, because of the relatively small difference in the ground state energy between polymorphic phases. We reported the selective growth of few-layered 1T’ (metallic) and 2H (semiconducting) MoTe2 polymorphs by chemical vapor deposition. It was found that modulation of the growth temperature (TG) under the relatively high Te vapor pressure was the key parameter to stabilize specific crystal phases over thermodynamic instabilities. Then, we demonstrated lateral integration of atomically-thin 1T’- and 2H-MoTe2 single crystals within the same atomic planes by a simple TG-varying two-step reaction. Furthermore, we achieved epitaxial heterojunction, where continuous films of metal MoTe2 are seamlessly stitched to the entire facet of a single-crystalline semiconductor MoTe2 enabling to control the geometry by lithography. The polymorphic 1T’-2H MoTe2 interfaces within the few-layer 2D planes are atomically sharp, and show electrically low edge-contact resistance. This coplanar metal-semiconductor heterojunctions may establish a new design rule of the true 2D semiconductor circuitry.