Establishment of 2D Crystal Heterostructures by Sulfurization of Sequential Transition Metal Depositions: Preparation, Characterization, and Selective Growth.

A nine-layer WS/MoS heterostructure is established on a sapphire substrate after sequential growth of large-area and uniform five- and four-layer MoS and WS films by using sulfurization of predeposited 1.0 nm molybdenum (Mo) and tungsten (W), respectively. By using the results obtained from the ultraviolet photoelectron spectroscopy and the absorption spectrum measurements of the standalone MoS and WS samples, a type-II band alignment is predicated for the WS/MoS heterostructure. Increasing drain currents and enhanced field-effect mobility value of the transistor fabricated on the heterostructure suggested that a channel with higher electron concentration compared with the standalone MoS transistor channel is obtained with electron injection from WS to MoS under thermal equilibrium. Selective 2D crystal growth with (I) blank sapphire substrate, (II) standalone MoS, (III) WS/MoS heterostructure, and (IV) standalone WS was demonstrated on a single sapphire substrate. The results have revealed the potential of this growth technique for practical applications.