Demonstration of Direction Dependent Conduction through MoS₂Films Prepared by Tunable Mass Transport Fabrication

Abstract

This work focuses on the synthesis of MoS 2 films grown by sulfurization of pre-deposited ultra-thin Mo films in the presence of a sulfur-containing gaseous precursor. The growth of high-quality TMDs requires careful control of specific thermodynamic and kinetic parameters. A deep understanding of mass transport mechanisms is achieved through a systematic investigation of the structural properties of MoS 2 films grown using different sulfurization conditions. Mass transport smoothing is used to reduce surface roughness and fabricate MoS 2 films in conformal contact with the underlying substrate. Oriented MoS 2 films are obtained by combining kinetically controlled sulfurization conditions and the use of single crystal templates. Good uniformity and excellent conformity of layers over large area has enabled the synthesis of patterned MoS 2 films which show anisotropic conduction properties. Two dimensional (2D) TMD materials, due to their unique physical properties, represent an interesting alternative to conventional semiconductors. They consist of molecular layers stacked together via weak van der Waals (vdW) forces.1 The big interest toward 2D TMD for transistor applications arises from their ultra-thin body nature and low dielectric constants.2 As a consequence, this class of materials potentially provides a superior scalability option compared to conventional materials. Another important quality of vdW materials is that ideally their surfaces are chemically saturated and have no dangling bonds. This additional feature makes 2D TMD ideal building blocks for the realization of artificial heterojunctions with designed band alignment. 3To enable the transition from the laboratory level, where most work is done on exfoliated flakes, to the industrial full-wafer scale, a large area deposition technique becomes indispensable. However, synthesis of large area, high quality TMD films using industry-compatible processes remains a major challenge and requires the development of highly controllable growth processes. Large area TMD layers can be grown using various techniques including chemical vapor deposition (CVD), 4-6 atomic layer deposition (ALD) 7 and molecular beam epitaxy (MBE) processes. 8 An interesting low cost approach that is capable of providing large-area sheets of TMDs with controllable thicknesses is chalcogenidation of ultrathin transition metal films. 9,10This method is simple, fast, easily upscalable, and can be used to synthesize a large variety of TMDs, including TMD hetorostructures. 11,12 However, the huge potential of this versatile technique is limited by the fact that chalcogenidation processes normally result in the formation of nano-crystalline highly defective films. To significantly improve material quality it is necessary to gain a deeper understanding of mass transport effects taking place during the chemical conversion process. In this work we propose a mass transport study based on roughness analysis of MoS 2 films grown by sulfurization of pre-deposited ultrathin Mo films. The followin...

Facile Fabrication of a Two-Dimensional TMD/Si Heterojunction Photodiode by Atmospheric-Pressure Plasma-Enhanced Chemical Vapor Deposition

“…Furthermore, chemical conversion from MoO 3 into MoS 2 always involves the volume change of the lattice. Fast sulfurization rate under the high pressure plasma condition in our system can prevent the relaxation of mechanical stress induced by the lattice volume change . Thus, the as-synthesized 2D materials have an imperfect lattice structure, inevitably generating corrugations of the as-synthesized 2D film.…”

“…Fast sulfurization rate under the high pressure plasma condition in our system can prevent the relaxation of mechanical stress induced by the lattice volume change. 35 Thus, the as-synthesized 2D materials have an imperfect lattice structure, inevitably generating corrugations of the as-synthesized 2D film. However, the very low temperature growth (<200 °C) possible in our technique allows us to directly synthesize the TMD layers even onto flexible polymer substrates with low glass-transition temperatures.…”

Impact of MoS2 layer transfer on electrostatics of MoS2/SiO2 interface

“…Thanks to the possibility of direct synthesis on top of SiO 2 and the good chemical stability of MoS 2 prepared by metallic Mo sulfurization, the latter represents an optimal 'test vehicle' to examine electrical impact of the layer transfer. The technologies of synthesis and transfer of few-ML thin MoS 2 films used in this work have been described in previous publications [29][30][31][32][33][34]. In short, the synthesis starts from thermal evaporation of few-Å thin Mo films on 8″-diam.…”

Nucleation and Growth of Monolayer MoS2 at Multisteps of MoO2 Crystals by Sulfurization

“…Promising properties of 2D semiconductor materials have previously been reported. − Most studies on 2D materials still use 2D material flakes obtained by mechanical exfoliation. Various synthetic methods have been developed to improve the yield and scale of 2D materials including pulsed layer deposition (PLD), − atomic layer deposition (ALD), − chemical vapor deposition (CVD), − metal–organic chemical vapor deposition (MOCVD), , and sulfurization of Mo film − or molybdenum oxide − to synthesize MoS 2 . However, several challenges are faced regarding the understanding of kinetics of the growth process and control of the quality and growth at the desired location.…”

“…Among these methods, sulfurization has attracted attention for producing large-scale MoS 2 through the substitution of large-area films and homogeneous films. However, MoS 2 formed by sulfurization of various Mo-source-based materials (such as Mo metal film − and MoO 3 − ) has been crystallized in a polycrystalline form with numerous randomly oriented domains and domain boundaries. Therefore, the quality of the film thereby formed shows relatively poor properties compared with single-crystal two-dimensional materials synthesized differently.…”