Importance of the substrate’s surface evolution during the MOVPE growth of 2D-transition metal dichalcogenides

Abstract

In this paper, we explore the impact of changing the growth conditions on the substrate surface during the metal-organic vapor phase epitaxy of 2D-transition metal dichalcogenides. We particularly study the growth of molybdenum disulfide (MoS 2 ) on sapphire substrates at different temperatures. We show that a high temperature leads to a perfect epitaxial alignment of the MoS 2 layer with respect to the sapphire substrate underneath, whereas a low temperature growth induces a 30°epitaxial alignment. This behavior is found to be related to the different sapphire top surface re-arrangement under H 2 S environment at different growth temperatures. Structural analyses conducted on the different samples confirm an improved layer quality at high temperatures. MoS 2 channel-based metal-oxide-semiconductor field-effect transistors are fabricated showing improved device performance with channel layers grown at high temperature.

Covalent functionalization of molybdenum disulfide by chemically activated diazonium salts

“…The secondary domains are formed as a result of uncontrolled defect sites in the first MoS2 layer which acts as nucleation sites. 32 From the AFM images an overall increase in the surface coverage of features with an increase in the concentration of 4-NBD is also observed for CVD-MoS2. We also compared AFM images of 4-NP functionalized bulk and CVD-MoS2, and similar features were observed on both bulk and CVD-MoS2 as shown in figure SI 4.…”

Engineering Wafer-Scale Epitaxial Two-Dimensional Materials through Sapphire Template Screening for Advanced High-Performance Nanoelectronics

“…Two-dimensional (2D) transition metal dichalcogenides (MX 2 , with M being a transition metal and X a chalcogen) attract lots of attention for next-generation electronics, optoelectronics, and photonics. − Their advanced properties predominantly excel in monolayer and few-layer form which fuels research on the large-area deposition of atomically thin MX 2 material. A variety of thin film deposition techniques have been explored, − ranging from powder vapor transport (PVT, often termed chemical vapor transport, CVT), ,,− molecular beam epitaxy, , and chalcogenidation of predeposited films, to atomic layer deposition and chemical vapor deposition (CVD). − The PVT method has been widely adopted to grow MX 2 layers with millimeter or even centimeter grain size on both amorphous and crystalline substrates . Yet, it remains challenging to deliver a constant precursor supply uniformly across the reactor zone, which eventually hampers control over MX 2 layer thickness and layer properties across large-area substrates and renders PVT not compatible with high-volume manufacturing. , On the other hand, in CVD, gas-phase precursors are delivered to the reaction chamber through dedicated precursor delivery systems.…”

Role of Stronger Interlayer van der Waals Coupling in Twin‐Free Molecular Beam Epitaxy of 2D Chalcogenides

“…This is a similar epitaxial relationship as previously reported for the growths of WSe 2 /MoS 2 on various reconstructed sapphire surfaces. [ 21,23,37 ] The identical and (01) diffraction streaks observed from the diffraction patterns uncover an important limitation of the quasi‐vdW epitaxy experiment. In Figure 2b, the RHEED pattern in the WSe 2 direction is presented where several intensity line profiles are extracted from various “ k z ” positions that give information about the out‐of‐plane ordering of the grown 2D crystal planes.…”

“…[ 15 ] Therefore, the quasi‐vdW and vdW epitaxy (2D‐on‐3D and 2D‐on‐2D, respectively) of layered chalcogenides is extensively being researched in the literature. [ 15–20 ] One of the major concerns in (quasi‐)vdW epitaxy of these materials is the systematic formation of stacking faults like 60° twins, as observed in either molecular beam epitaxy (MBE) (quasi‐vdW [ 21–29 ] and vdW [ 21,30–36 ] ), metalorganic vapor phase epitaxy (quasi‐vdW [ 21,37–42 ] and vdW [ 21,43,44 ] ), and chemical vapor epitaxy (quasi‐vdW [ 45–47 ] and vdW [ 48–53 ] ). To mitigate the formation of these defects, several approaches are being reported that rely on optimized growth conditions, [ 54–56 ] buffer layer growth, [ 57 ] growth on h‐BN templates, [ 54,58 ] or the introduction of a 3D aspect in the growth surface like surface roughness [ 59 ] or surface step edges.…”