Molecular Beam Epitaxy Scalable Growth of Wafer‐Scale Continuous Semiconducting Monolayer MoTe₂ on Inert Amorphous Dielectrics

Abstract

Transition metal dichalcogenides (TMDs) (MX 2 , M = Mo or W, X = S, Se, or Te) have attracted intense interest for developing ultrascaled electronics and optoelectronics by virtue of their attractive 2D layered structures and unique physical properties that are absent in their bulk counterparts. [1][2][3][4][5] Monolayer semiconducting TMDs show sizable direct bandgaps, quantum confinement effects, large exciton binding energies and effective valley polarizations, which unveils widespread applications in field-effect transistors (FETs), photodetectors, light-emitting diodes, pumped lasers, solar cells, and valleytronic devices. [6][7][8][9][10] More excitingly, their 2D structures offer superior electrostatic controllability and exemptible short-channel effects, rendering TMDs promising candidates for future sub-10 nm complimentary metal-oxide-semiconductor (CMOS) devices. [5,11,12] The applications of exfoliated TMD flakes in building high-performance prototypes of electronics, photonics, and optoelectronics have already been demonstrated. [13][14][15][16] The exfoliated flakes, however, suffer from Monolayer MoTe 2 , with the narrowest direct bandgap of ≈1.1 eV among Mo-and W-based transition metal dichalcogenides, has attracted increasing attention as a promising candidate for applications in novel near-infrared electronics and optoelectronics. Realizing 2D lateral growth is an essential prerequisite for uniform thickness and property control over the large scale, while it is not successful yet. Here, layer-by-layer growth of 2 in. wafer-scale continuous monolayer 2H-MoTe 2 films on inert SiO 2 dielectrics by molecular beam epitaxy is reported. A single-step Mo-flux controlled nucleation and growth process is developed to suppress island growth. Atomically flat 2H-MoTe 2 with 100% monolayer coverage is successfully grown on inert 2 in. SiO 2 /Si wafer, which exhibits highly uniform in-plane structural continuity and excellent phonon-limited carrier transport behavior. The dynamics-controlled growth recipe is also extended to fabricate continuous monolayer 2H-MoTe 2 on atomic-layer-deposited Al 2 O 3 dielectric. With the breakthrough in growth of wafer-scale continuous 2H-MoTe 2 monolayers on device compatible dielectrics, batch fabrication of high-mobility monolayer 2H-MoTe 2 field-effect transistors and the three-level integration of vertically stacked monolayer 2H-MoTe 2 transistor arrays for 3D circuitry are successfully demonstrated. This work provides novel insights into the scalable synthesis of monolayer 2H-MoTe 2 films on universal substrates and paves the way for the ultimate miniaturization of electronics.

Wafer‐scale vertical van der Waals heterostructures

“…191,192 Hence, modifying the metalsemiconductor contact interface is an effective strategy to improve device performance. Specifically, using metallic 2D materials (graphene, 193 some 1 T phase TMDs 47,187,[194][195][196][197] ) as electrodes for (opto)electronics through epitaxy growth 35 or phase transition 198,199 will alleviate the pining effect. In addition, transferring the prefabricated metal electrodes can also avoid creating defects and strains, resulting in an atomically sharp and near perfect metal/2D semiconductor interface.…”

“…2 Wafer-scale 2D materials prepared by various methods can be regarded as the atomically thin blocks for building large-scale vdWHs. Taking advantages of well controlling of preparation process on atomic scale, wafer-size 2D materials have been reported to be synthesized through diverse methods, including CVD, [37][38][39][40][41][42] pulsed laser deposition (PLD), 43,44 atomic layer deposition (ALD), 45,46 molecular beam epitaxy (MBE), 47,48 thermal evaporation, 49 controlled crack propagation, 50 Au-assisted mechanical exfoliation, 51 and solution processing. [52][53][54][55] In recent years, a mass of researches have been conducted to nondestructively transfer and integrate the fragile wafer-size 2D materials with as few contaminants as possible.…”

“…Deposition methods, including CVD, 87,88 physical vapor deposition (PVD), 89 metal-organic chemical vapor deposition (MOCVD), 90 PLD, 44 ALD, 45 MBE, 47 electron beam evaporation (EBE), 91 magnetron sputter (MS), 92 have demonstrated high efficiency and controllability of synthesis 2D materials with large area and superb quality. Based on that, wafer-scale vdWHs can be fabricated through successive deposition, that is, cycling the deposition step twice ( Figure 3A).…”

Toward Wafer‐Scale Production of 2D Transition Metal Chalcogenides

“…The mobilities determined from 100 devices fell in a narrow range of 19.2-27.0 cm 2 V -1 s -1 , comparable with exfoliated flakes, suggesting the relative high-quality uniformity. [134] Liu et al also reported to grow wafer-scale 8 nm 2D ferromagnetic Fe 3 GeTe 2 films on sapphire by MBE, with confirmation of a van der Waals gap of 0.82 nm by HR-TEM measurements and indication of high-crystalline quality by RHEED pattern. [171] This shows the versatility of the TMC material that MBE is able to grow.…”

Recent progress in devices and circuits based on wafer-scale transition metal dichalcogenides

“…Among various 2DLMs already explored, transition metal dichalcogenides (TMDs) exhibit interesting electronic properties, especially tunable bandstructures which depend on the conditions including material composition, thickness and crystal phases [8][9][10][11][12]. TMDs have a general formula of MX 2 , where M and X represents a transition metal (e.g., Mo, W, Pt) and chalcogen (e.g., S, Se, Te), respectively, indicating versatile electronic properties by the combination of various elements (more than 30 TMDs) [13][14][15][16]. Moreover, the 2D nature of TMDs allows thickness controlled quantum confinement and vdWs stacking without lattice mismatch, which gives additional degree of freedoms on material engineering for electronic application [1,17,18].…”