preparation-large-area-vertical-2d-crystal-hetero-structures-through

Preparation of Large-area Vertical 2D Crystal Hetero-structures Through the Sulfurization of Transition Metal Films for Device Fabrication

We have demonstrated that through the sulfurization of transition metal films such as molybdenum (Mo) and tungsten (W), large-area and uniform transition ...

National Taiwan University

Academia Sinica

Atomically-flat surfaces are obtained after thin GaAsSb buffer layer growth on GaAs substrates with regular-distributed nano-holes formed after oxide desorption of the local atomic-force-microscopy anode oxidation. Different from the samples with GaAsSb buffer layers, increasing surface root-mean-square roughness is observed for the GaAs-buffered samples with increasing GaAs buffer layer thickness. The phenomenon is attributed to the enhanced adatom migration resulting from the incorporation of Sb atoms. By using the substrates with nano-holes after buffer layer growth, site-controlled self-assembled InAs quantum dots (QDs) are observed with the deposition of a below-critical-thickness InAs coverage of 1.3 monolayer (ML).

Site-controlled self-assembled InAs quantum dots grown on GaAs substrates.

A nine-layer WS2/MoS2 heterostructure is established on a sapphire substrate after sequential growth of large-area and uniform five- and four-layer MoS2 and WS2 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 MoS2 and WS2 samples, a type-II band alignment is predicated for the WS2/MoS2 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 MoS2 transistor channel is obtained with electron injection from WS2 to MoS2 under thermal equilibrium. Selective 2D crystal growth with (I) blank sapphire substrate, (II) standalone MoS2, (III) WS2/MoS2 heterostructure, and (IV) standalone WS2 was demonstrated on a single sapphire substrate. The results have revealed the potential of this growth technique for practical applications.

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

A growth model is proposed for the large-area and uniform MoS2 film grown by using sulfurization of pre-deposited Mo films on sapphire substrates. During the sulfurization procedure, the competition between the two mechanisms of the Mo oxide segregation to form small clusters and the sulfurization reaction to form planar MoS2 film is determined by the amount of background sulfur. Small Mo oxide clusters are observed under the sulfur deficient condition, while large-area and complete MoS2 films are obtained under the sulfur sufficient condition. Precise layer number controllability is also achieved by controlling the pre-deposited Mo film thicknesses. The drain currents in positive dependence on the layer numbers of the MoS2 transistors with 1-, 3- and 5- layer MoS2 have demonstrated small variation in material characteristics between each MoS2 layer prepared by using this growth technique. By sequential transition metal deposition and sulfurization procedures, a WS2/MoS2/WS2 double hetero-structure is demonstrated. Large-area growth, layer number controllability and the possibility of hetero-structure establishment by using sequential metal deposition and following sulfurization procedures have revealed the potential of this growth technique for practical applications.

The Growth Mechanism of Transition Metal Dichalcogenides by using Sulfurization of Pre-deposited Transition Metals and the 2D Crystal Hetero-structure Establishment.

Article	Year
Site-controlled self-assembled InAs quantum dots grown on GaAs substrates. Nanotechnology\| PubMed ID: 20601753	2010
Establishment of 2D Crystal Heterostructures by Sulfurization of Sequential Transition Metal Depositions: Preparation, Characterization, and Selective Growth. Nano letters\| PubMed ID: 27763763	2016
The Growth Mechanism of Transition Metal Dichalcogenides by using Sulfurization of Pre-deposited Transition Metals and the 2D Crystal Hetero-structure Establishment. Scientific reports\| PubMed ID: 28176836	2017

Shih-Yen Lin

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