Limited growth of 2D materials and their heterostructures

Abstract

Two-dimensional (2D) materials and their heterostructures represent a promising pathway for next-generation electronics. Nevertheless, there are difficulties in (i) controlling the growth of single-layer (ML)-by-ML 2D materials, (ii) maintaining single-domain growth, and (iii) controlling the number of layers and crystallinity at the wafer scale. The deterministic confined growth technique disclosed herein simultaneously addresses these difficulties to produce wafer-scale single-domain 2D ML and their heterostructures on any substrate. The growth of a first nucleus (122) is confined by defining a selective or confined growth region by patterning a SiO2 mask (110) on a 2-inch substrate (100). Each growth region or trench (102) is only a few micrometers wide and is filled with single-domain ML (124) before a second set (132) of nuclei is introduced. The growth of a second set of nuclei (132) within the trench creates an array of single-domain bilayers (124, 134) on a 2-inch wafer scale. A device made of single-domain bilayers exhibits excellent performance across the entire wafer.

Description

Background Technology

[0001] Cross-reference of related application(s)

[0002] This application claims the benefit of priority under 35 USC 119(e) of U.S. Application No. 63 / 374,090 filed on August 31, 2022, the entirety of which is incorporated herein by reference for all purposes.

[0003] Background of the Invention

[0004] Two-dimensional (2D) transition metal dichalcogenides (TMDs) and their heterostructures are promising platforms for next-generation electronics, spintronics, valleytronics, and optoelectronics. However, to date, integrating semiconductor 2D heterostructures into industrial platforms has been challenging due to limited scalability. Conventional methods for constructing 2D heterostructures involve the mechanical exfoliation and stacking of 2D flakes, which is a trial-and-error-based process and consequently imposes severe size limitations on the structures that can be produced. Furthermore, fabricating 2D heterostructures using mechanical exfoliation and stacking is time-consuming.

[0005] Recently, significant progress has been made in improving scalability by using epitaxial growth methods to obtain single-crystal monolayer (ML) TMDs on single-crystal hexagonal substrates, such as sapphire. However, growing large-scale 2D heterostructures remains a major challenge due to the lack of strategies for the layer-by-layer growth of single-domain TMDs. Furthermore, some current growth methods involve the undesirable step of implanting 2D material into silicon devices when grown on hexagonal non-silicon substrates. Single-domain TMD arrays can also be grown via laser irradiation of nucleation spots. However, growth via laser irradiation presents difficulties because the second heterolayer is highly likely to nucleate at the margins of the first single-domain patch. To date, there is no viable solution for obtaining single-domain 2D heterostructures at the wafer scale.

[0006] Summary of the Invention

[0007] The present technology involves the layer-by-layer growth of 2D materials on any substrate. These technologies can be used to grow single-domain homojunction and heterojunction TMDs at the wafer scale. They also include non-epitaxy strategies for growing single-domain TMDs on amorphous materials, thereby enabling single-crystal 2D materials on Si wafers coated with any layer.

[0008] This technology solves the fundamental kinetic problem of TMD growth. A SiO2 mask on an amorphous Al2O3 or HfO2 layer on a Si substrate confines the growth of a first set of TMD nuclei to an array of selective growth regions called pockets or trenches (102), the lateral dimensions (width and length) of which are each less than a few micrometers. Density functional theory (DFT) calculations confirm higher TMD binding energies on these substrates (100) than on the SiO2 mask (110). As a result, the nucleation of TMDs is concentrated on the surface of the substrate (100) rather than on the walls (112) of the SiO2 mask. The reduced size of the pocket or trench in the SiO2 mask (110) significantly reduces the growth duration, thereby creating a first set of nuclei (122) that are completely filled (i.e., a single domain (124) completely fills one pocket) within the incubation period for a second set of nuclei (132) of the second layer (134) of the TMD. Thus, the ML-TMD layer within each trench across the wafer is a single-crystal domain. The limited geometry enables precise control of the number of layers so that the TMD ML can grow on top of each other to fill the trench.

[0009] This technology can be used to fabricate single-domain, double-layer (BL)-WSe2 on a 2-inch wafer scale by the subsequent confined growth of WSe2. FETs fabricated on an array of single-domain WSe2 on a full 2-inch wafer exhibit performance close to that of mechanically exfoliated WSe2 flakes, for example, up to 72.8 cm for ML-WSe2. 2 V -1 s -1 and for BL-WSe2, 103.5 cm 2 V -1 s -1 It represents the effective mobility of.

[0010] In addition, these techniques can be used for the layer-by-layer confined growth of MoS2 / WSe2 heterostructures at the wafer scale. Valley lifetime measurements for arrays of single-domain MoS2 / WSe2 heterostructures are similar to those obtained from single-domain flakes of TMDs. The confined growth techniques of the present invention enable the fabrication of single-domain ML-by-ML homo- or heterojunctions at the wafer scale.

[0011] The limited method of the present invention for growing a 2D material (e.g., TMD, e.g., MoS2, MoSe2, WS2, or WSe2) on a substrate (100) (e.g., HfO2 or amorphous Al2O3) having a first binding energy with the 2D material can be implemented as follows: A mask layer (110) (e.g., SiO2) having a second binding energy with the 2D material lower than the first binding energy is formed on the substrate (100). A trench (102) having sidewalls (112) surrounding an exposed portion of the substrate (100) is formed in the mask layer (110). A nucleus (122) of the 2D material is placed on the exposed portion of the substrate (100) and grown into a single-domain monolayer (124) of the 2D material. This single-domain monolayer (124) can fill the trench (102). A single-domain monolayer (124) can be used to form a semiconductor device, such as a valleyronics device, a fork sheet field-effect transistor (FET), or a complementary FET.

[0012] The maximum lateral dimension of the trench (102) may be approximately equal to the product of the incubation time of another nucleus of the 2D material on the single-domain monolayer and the growth rate of the 2D material. For example, the maximum lateral dimension of the trench (102) may be about 2 micrometers. The trench (102) may be one of many trenches in an array of trenches formed in the mask layer (110), and a single nucleus (122) of the 2D material is deposited in each trench of the array of trenches. If the critical trench size in each pocket is at a critical value, e.g., 2 micrometers or less, the formation of such a single nucleus (122) of the 2D material is obtained. These nuclei may grow into each single-domain monolayer (124) of the 2D material filling the trenches in the array of trenches.

[0013] In some cases, the nucleus (122) is the first nucleus (122), and the single-domain monolayer (124) is the first single-domain monolayer (124). In these cases, the second nucleus (132) of the 2D material is deposited on the first single-domain monolayer (124) and grows into the second single-domain monolayer (134) of the 2D material to form a double layer of the 2D material in the trench. Alternatively, in these cases, the 2D material is the first 2D material, and the nucleus (132) of the second 2D material, which is different from the first 2D material, is deposited and grown on the single-domain monolayer (124) to form a heterostructure of the first 2D material (124) and the second 2D material (134) in the trench (102). For example, the first and second 2D materials can each be selected from the group consisting of MoS2, MoSe2, WS2, and WSe2.

[0014] In one embodiment, the present invention comprises: (a) providing a substrate (100) of a first material; (b) depositing a mask material (110) on the substrate (100); and (c) forming a trench array on the mask material (110), wherein the trench array comprises a plurality of trenches (102), and each trench (102)l x w It has a trench geometry having lateral dimensions, where l and w The method comprises: (d) a step in which each trench (102) is selected to have a maximum dimension of 2 μm and each trench (102) has an exposed portion of the substrate (100) surrounded by a sidewall (112) formed of a mask material (110); (d) a step of depositing adatoms (120) of a second material on the exposed portion of the substrate (100), wherein the first binding energy between the first material and the second material is greater than the second binding energy between the mask material (110) and the second material; (e) a step in which the adatoms (120) can selectively nucleate into nuclei (122) within each trench (102) of the trench array; and (f) a step of growing nuclei (122) within each trench (102) of the trench array; Here, the lateral dimensions associated with the trench geometry provide a method of limiting the growth of the nucleus (122) to a single-domain monolayer (124) of the second material.

[0015] In one embodiment, the first material comprises one of hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HZO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO). In one embodiment, the second material comprises one of graphene, carbon nanotubes (CNT), hexagonal boron nitride (h-BN), metallic transition-metal dichalcogenides (e.g., vanadium disulfide (VS2), vanadium diselenide (VSe2), cobalt sulfide (CoS2), cobalt selenide (CoSe2), titanium disulfide (TiS2), or titanium diselenide (TiSe2)), semiconductor transition-metal dichalcogenides (e.g., molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), or tungsten diselenide (WSe2)), or a high-k material (e.g., Bi2SeO5 or Sb2O3). In one embodiment, the mask material is amorphous silicon dioxide (a-SiO2), amorphous silicon (a-Si), and amorphous silicon nitride (a-SiN). x It includes at least one of amorphous carbon (α-carbon), hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HfZrO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO).

[0016] In one extended embodiment in which the nucleus (122) is the first nucleus (122) and the single-domain monolayer (124) is the first single-domain monolayer (124), the method further comprises: (g) a step of waiting for an incubation period; (h) a step of depositing another adsorbed atom (130) of the third material on top of the first single-domain monolayer (124) in at least one trench of the trench array, wherein the third binding energy between the second material and the third material is greater than the second binding energy between the mask material (110) and the third material; (i) a step of enabling the other adsorbed atom (130) of the third material to selectively nucleate into a second nucleus (132) on top of the first single-domain monolayer (124) within at least one trench of the trench array; and (j) a step of growing the nucleus (132) within at least one trench of the trench array; Here, the lateral dimensions associated with the trench geometry limit the growth of the second nucleus (132) to the second single-domain monolayer (134) of the third material, where the first single-domain monolayer (124) and the second single-domain monolayer (134) form a double layer.

[0017] In one embodiment, the third material comprises one of graphene, carbon nanotubes (CNT), hexagonal boron nitride (h-BN), metallic transition-metal dichalcogenides (e.g., vanadium disulfide (VS2), vanadium diselenide (VSe2), cobalt sulfide (CoS2), cobalt selenide (CoSe2), titanium disulfide (TiS2), or titanium diselenide (TiSe2)), semiconductor transition-metal dichalcogenides (e.g., molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), or tungsten diselenide (WSe2)), or high-k materials.

[0018] In one embodiment, the bilayer is a heterojunction bilayer in which the second material and the third material are different from each other. In another embodiment, the bilayer is a homojunction bilayer in which the second material and the third material are similar to each other.

[0019] In one embodiment, l and w Each is selected to have a value equal to the product of the incubation time of another nucleus of the second material on the single-domain monolayer and the growth rate of the second material. In another embodiment, l and w Each is selected to be 2 micrometers.

[0020] In another embodiment, the method further comprises the step of forming a semiconductor device (valitetronics device, forksheet field-effect transistor (FET), or complementary FET) comprising a single-domain monolayer.

[0021] In one embodiment, before depositing a mask material on a substrate, the method comprises the step of forming a substrate by depositing at least one of hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HZO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO) on silicon.

[0022] In another embodiment, the present invention comprises: (a) providing a substrate (100) of a first material having a first Gibbs free energy; (b) depositing a mask material (110) having a second Gibbs free energy higher than the first Gibbs free energy on the substrate (100); and (c) forming a trench array on the mask material (110), wherein the trench array comprises a plurality of trenches (102), and each trench (102) l x w It has a trench geometry having lateral dimensions, where l andw (d) a step in which each trench (102) is selected to have a maximum dimension of 2 μm and each trench (102) has an exposed portion of the substrate (100) surrounded by a sidewall (112) formed of a mask material (110); (e) a step in which the adsorbed atoms (120) of the second material are selectively nucleated into a first nucleus (122) within each trench (102) of the trench array; (f) a step in which the first nucleus (122) is grown within each trench (102) of the trench array, wherein the lateral dimension related to the trench geometry limits the growth of the first nucleus (122) to a first single-domain monolayer (124) of the second material; (g) a step of waiting for an incubation period; (h) a step of depositing another adsorbed atom (130) of a third material on top of a first single-domain monolayer (124) of at least one trench of a trench array; (i) a step of enabling the other adsorbed atom (130) of the third material to selectively nucleate into a second nucleus (132) on top of the first single-domain monolayer (124) within at least one trench of a trench array; and (j) a step of growing the nucleus (132) within at least one trench of a trench array, wherein lateral dimensions related to the trench geometry restrict the growth of the second nucleus (132) to a second single-domain monolayer (134) of the third material, wherein the first single-domain monolayer (124) and the second single-domain monolayer (134) form a double layer.

[0023] In one embodiment, the first material comprises one of hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HZO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO).

[0024] In one embodiment, the second or third material is graphene, carbon nanotubes (CNT), hexagonal boron nitride (h-BN), metallic transition-metal dichalcogenides (e.g., vanadium disulfide (VS2), vanadium diselenide (VSe2), cobalt sulfide (CoS2), cobalt selenide (CoSe2), titanium disulfide (TiS2), or titanium diselenide (TiSe2)), semiconductor transition-metal dichalcogenides (e.g., molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), or tungsten diselenide (WSe2)), or high-k materials (e.g., Bi2SeO5 or It includes one of Sb2O3.

[0025] In one embodiment, the mask material is amorphous silicon dioxide (a-SiO2), amorphous silicon (a-Si), and amorphous silicon nitride (a-SiN). x It includes at least one of amorphous carbon (α-carbon), hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HfZrO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO).

[0026] All combinations of the above concepts and additional concepts discussed in more detail below (unless such concepts conflict with one another) are part of the subject matter of the invention disclosed herein. In particular, all combinations of the claimed subject matter appearing at the end of this disclosure are part of the subject matter of the invention disclosed herein. Any terms used herein that may also appear in any disclosure incorporated by reference shall have the meaning most consistent with the specific concepts disclosed herein. Brief explanation of the drawing

[0027] Those skilled in the art will understand that the drawings are intended primarily for illustrative purposes and are not intended to limit the scope of the subject matter of the invention as described herein. The drawings are not necessarily to scale; in some cases, various aspects of the subject matter of the invention disclosed herein may be exaggerated or enlarged in the drawings to facilitate understanding of various features. In the drawings, similar reference numerals generally refer to similar features (e.g., functionally similar and / or structurally similar elements). FIG. 1a illustrates a conventional process for the growth of transition metal dichalcogenides (TMDs). FIG. 1b illustrates a limited-growth process of the present invention for the selective single-domain synthesis of single-domain ML TMDs that resolves the limitations of conventional TMD growth processes. FIG. 1c illustrates the fabrication of a single-domain MoS2-WSe2 heterostructure by the limited growth of a second MoS2 layer on WSe2ML in each trench of an array of trenches. Figure 1d shows the calculation of the binding energies of W3O9, Se2, and W3Se6 clusters on c-Al2O3, a-HfO2, and a-SiO2 substrates. Figures 2a-2d show the selective single-domain synthesis and ML-by-ML limited growth of WSe2 in 10 μm (Figs 2a and 2b) and 2 μm (Figs 2c and 2d) pockets on a sapphire substrate with SiO2 sidewalls. Figures 2e-2h show Raman and photoluminescence (PL) mapping images of confined ML-WSe2 (Figures 2e and 2f) and bilayer (BL)-WSe2 (Figures 2g and 2h) in a 2 μm pocket on a sapphire substrate. Figure 2i is a cross-sectional, high-resolution (HR) transmission electron microscope (TEM) image of ML-WSe2 confined in a pocket on a sapphire substrate. Figure 2j is a cross-sectional HR TEM image of BL-WSe2 confined in a pocket on a sapphire substrate. Figure 3a is a photograph of an integrated confined BL-WSe2 field-effect transistor (FET) array on a SiO2 / Si wafer measuring 5.1-cm × 5.1-cm. The inset shows a micrograph of an individual FET array with 20 integrated FETs (scale bar: 10 μm). Fig. 3b shows the channel length L CH drain-source voltage V where α is 0.7 μm DS = represents the transfer characteristics of the BL-WSe2 FET limited at -1 V. The result is up to 155.8 μA μm -1 It exhibits the maximum on-current density of and a maximum of 103.5 cm 2 V -1 s -1 It represents the electric field-effect mobility. Figure 3c shows the output characteristics of a limited BL-WSe2FET. FIG. 3d shows the on-current densities for different WSe2FETs, including the FET of the present invention (asterisk; top right) and the FET having a chemical vapor deposition (CVD) grown single crystal 1-3 ML-WSe2 (filled dark square), a CVD grown polycrystalline 1-3 ML-WSe2 film (empty square), and WSe2 flakes in an exfoliated state (pentagon). I on Effective mobility μ eff It represents. The drain-source voltage and channel length are -1 V and about 1 μm, respectively. Figure 3e shows the on-current density for FETs fabricated with peeled ML / BL-WSe2 flakes and confined ML / BL-WSe2 films. I on (Left) and effective mobility μ eff This is the histogram on the (right). Figure 3f is a plot of the statistical distribution of on-current density and effective mobility for a confined BL-WSe2FET array (different triangles indicate the location of the BL-WSe2 film on the wafer). Figure 4a shows a photograph and schematic image of HfO2 deposited on a Si wafer in a pocket with a lateral dimension of 1 μm (scale bar: 5 μm). Figure 4b shows the nucleation of single-domain MoS2 in a 1 μm HfO2 pocket with SiO2 sidewalls. Figure 4c shows an array of confined single-domain MoS2 within a 1 μm HfO2 pocket having SiO2 sidewalls. Figure 4d is a plot of the transfer characteristics of 16 FETs fabricated with limited ML-MoS2 (8 FETs, bottom locus) or BL-MoS2 (8 FETs, top locus) on an HfO2 substrate. Figure 4e shows the on-current density for ML-MoS2 and BL-MoS2FETs I on (Left) and effective mobility μ eff This is a histogram of the average and maximum values ​​(on the right). Figure 4f is a cross-sectional high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the heterointerface [MoS2 (upper layer) and WSe2 (lower layer)] with superimposed energy-dispersive X-ray (EDX) spectra for Mo Kα (upper left peak), S Kα (upper right peak), W Lα (lower left peak), and Se Kα (lower right peak). Figure 4g is a plot of the time-resolved circular dichroism (CD) response of ML-WSe2 (lower locus) at 300 K, and hetero-BL (MoS2 / WSe2) at 300 K (middle locus) and 77 K (upper locus). Figure 5 illustrates a plot showing the relationship between the lateral growth rate and the secondary nucleation time for limited growth. FIGS. 6a to 6e illustrate a comparison of the formation of a second layer of WSe2 with increasing H2 content. Specific details for implementing the invention

[0028] Description of preferred embodiments

[0029] FIG. 1a illustrates a conventional growth process of transition metal dichalcogenides (TMDs). Initially, a first set of TMD adsorbed atoms (12) is introduced onto the surface of a substrate (10) (left). The TMD adsorbed atoms (12) nucleate to form nuclei (14) on the substrate (10). The orientation of these nuclei (14) is random because the nuclei (14) are not typically aligned with the substrate (10). The nuclei (14) grow laterally to meet each other (center), but they merge to form granules (16), creating a continuous polycrystalline layer due to the random orientation of the nuclei (14). This polycrystalline growth eventually degrades the intrinsic properties of the TMD. Additionally, further nucleation (18) may occur on some of the granules (16) (right). If there is no additional control of nucleation, this process is repeated, and the TMD layer grows to an irregular thickness due to the overlapping granules (16), and a second set of nuclei (18) is nucleated on the initial layer of granules (16).

[0030] FIG. 1b illustrates a limited-growth process that solves these problems by precisely controlling the thickness and crystallinity of the TMD growth. First, a c-planar Al2O3, HfO2, or another material having a relatively low Gibbs free energy, such as an amorphous or crystalline metal oxide, is deposited on a Si wafer to form a substrate (100), and a TMD is grown thereon. Other suitable substrate materials include graphene, hexagonal boron nitride (hBN), hafnium zirconium oxide (HZO), TiO2, ZnO, Fe2O3, SnO2, NiO, CuO, or TMD-coated materials.

[0031] Subsequently, a thin layer of mask material (e.g., 5 nm, 10 nm, 50 nm, 100 nm, or even hundreds of nanometers thick; possibly up to 250 nm, 500 nm, 750 nm, or 1 μm thick) (110) is coated on the c-plane Al2O3 or HfO2 surface of the substrate (100). Suitable mask materials are amorphous SiO2 (a-SiO2), a-Si, and a-SiN. x It includes materials with relatively high Gibbs free energy, such as , and α-carbon.

[0032] Next, a limited growth area (102), also called a recess, pocket, trench, well, or cavity, having lateral dimensions of tens of nanometers to about 2 micrometers, is patterned in a thin layer (110) of a-SiO2. The patterned a-SiO2 layer (110) is also called a mask or mask layer. These pockets (102) can be any suitable shape (e.g., square, rectangular, triangular, or circular) and can be formed as a 1D or 2D array (e.g., square, rectangular, or hexagonal array). The pockets (102) can pass completely through the a-SiO2 layer (110) to expose a portion of the Al2O3 or HfO2 surface of the substrate (100) surrounded by a-SiO2 sidewalls (112). The pocket (102) can even extend to some extent (e.g., several nanometers) into the c-planar Al2O3 or HfO2 (Fig. 1b, left).

[0033] When pockets (102) are formed in the a-SiO2 layer (110), 2D material adsorbed atoms (120) are introduced into each pocket (left). For example, it was recognized that 42 (W and Se) adsorbed atoms exist within a 1 nm x 1 nm area. Thus, for each pocket, within a 2 μm x 2 μm trench, 84,000 adsorbed atoms are required in the monolayer, and 168,000 adsorbed atoms are required in the bilayer. Suitable 2D materials include semiconductor TMDs, such as WSe2 (this example), MoS2, MoSe2, and WS2. Other suitable 2D materials include, but are not limited to, graphene, carbon nanotubes (CNT), hBN, metallic TMDs (e.g., VS2, VSe2, CoS2, CoSe2, TiS2, TiSe2), and high-k 2D materials (e.g., Bi2SeO5, Sb2O3).

[0034] The size of each pocket (102) is small enough so that only a single nucleation (indicated as a single triangle in FIG. 1b) (122) appears in each pocket (center). Each nucleation (122) grows on the exposed c-plane Al2O3 or HfO2 at the bottom of its pocket (102) until it reaches the a-SiO2 sidewall (112) and fills the entire trench (102) to form a TMD film (124) (right). Each TMD film (124) is a single-domain and is also ML (right, inset).

[0035] FIG. 1c illustrates a method in which the steps of adsorbed atom introduction, nucleation, and single-crystal growth of the process in FIG. 1b are repeated to obtain a single-domain MoS2 / WSe2 heterostructure or a single-domain homo-bilayer (BL) of WSe2. (The BL can be thought of as two MLs combined by van der Waals interactions.) When the ML (124) of WSe2 is formed in the pocket (102), MoS2 adsorbed atoms (130) are introduced into the cavity (102) on the WSe2ML (124) (Fig. 1c, left). These MoS2 adsorbed atoms (130) undergo nucleation to form nuclei (132) (center) and grow to form single-crystal MoS2ML (134) on WSe2ML (124) (right, inset), which creates MoS2 / WSe2 heterostructures (140) in each pocket (102). DFT calculations confirm the selectivity of this growth. Alternatively, WSe2 adsorbed atoms can be deposited on WSe2ML and undergo nucleation and growth to form a single-domain BL of WSe2.

[0036] Figure 1d shows the binding energies of WSe2 precursor WO3 and Se, as well as product WSe2 clusters, on c-Al2O3, a-HfO2, and a-SiO2, calculated from DFT. These DFT calculations show that WO3 clusters (W3O9, left), Se clusters (Se2, center), and WSe2 clusters (W3Se6, right) have stronger binding interactions with c-Al2O3 and a-HfO2 than with the surface of SiO2. This indicates that the clusters preferentially bind to the substrate surface at the bottom of the pocket rather than the a-SiO2 sidewalls of the pocket, leading to selective WSe2 growth within the pocket.

[0037] The simultaneous growth of WSe2 on Al2O3, HfO2, and SiO2 substrates under the same CVD growth conditions confirms this selectivity. Atomic force microscopy (AFM) images show that WSe2 nucleates only on Al2O3 and HfO2 instead of SiO2 during 20 minutes of growth. This led to the successful selective and confined growth of WSe2 on the exposed substrate surface of a micropatterned SiO2 trench array.

[0038] The trench size is selected to enable the formation of only a single-domain, ML WSe2 and depends on the lateral growth rate of WSe2 and the incubation period for the second nucleation. The measured lateral growth rate of WSe2 and the incubation period for the second nucleation are approximately 0.4 μm / min and 5 min, respectively. This suggests that each trench should be about 2 μm or less in width to avoid nucleation of the second layer of WSe2. It is possible to control the lateral growth rate or the incubation period (and consequently the maximum trench width) by varying the content of TMD powder, the gas ratio (Ar / H2), and the growth temperature. For example, such control can be achieved by varying the content of S / Se powder from 100 mg to 1500 mg, or by varying the content of MoO3 / WO3 powder from 10 mg to 100 mg. In addition, the gas ratio of the percentage of argon (Ar) to the percentage of hydrogen (H2) can be adjusted from Ar-100% / H2-0% to Ar-0% / H2-100%. In addition, the growth temperature can be adjusted from 200°C to 1000°C.

[0039] Figure 5 illustrates a plot showing the relationship between the lateral growth rate and the secondary nucleation time for restricted growth. In this non-restricted example, after an initial incubation time of 5 minutes, WSe2 was laterally grown up to 10 minutes, and secondary nucleation occurred after the restricted monolayer (ML) was maintained for an additional 2 minutes (i.e., a second incubation time of 2 minutes from the 10-minute point).

[0040] Figures 6a through 6e illustrate a comparison of the formation of the second layer of WSe2 with increasing H2 content. Scanning electron microscope images of the second layer WSe2 before (see Figure 6a) and after (see Figure 6b) a 15% increase in H2 content. Figure 6c shows an optical microscope image of the AA' stacking structure in Figure 6b. The increase in H2 saturates the nucleation density on the first ML-WSe2, allowing the second layer WSe2 to initiate nucleation at the center of the first ML. Accordingly, the scanning electron microscope morphology of the limited ML was compared with the bilayer (BL) after ML-by-ML limited growth of WSe2 at different H2 contents (see Figures 6a and 6b). Compared to polycrystalline WSe2, the surface of the confined WSe2 was extremely smooth, and the contrast between the confined ML (see Fig. 6(d)) and the confined BL (see Fig. 6(e)) was similar.

[0041] In one embodiment, the present invention comprises: (a) providing a substrate (100) of a first material; (b) depositing a mask material (110) on the substrate (100); and (c) forming a trench array on the mask material (110), wherein the trench array comprises a plurality of trenches (102), and each trench (102) l x w It has a trench geometry having lateral dimensions, where l and w(d) a step in which each trench (102) is selected to have a maximum dimension of 2 μm and each trench (102) has an exposed portion of the substrate (100) surrounded by a sidewall (112) formed of a mask material (110); (d) a step of depositing adsorbed atoms (120) of a second material on the exposed portion of the substrate (100), wherein the first binding energy between the first material and the second material is greater than the second binding energy between the mask material (110) and the second material; (e) a step of enabling the adsorbed atoms (120) to selectively nucleate into nuclei (122) within each trench (102) of the trench array; and (f) a step of growing nuclei (122) within each trench (102) of the trench array; Here, the lateral dimensions associated with the trench geometry provide a method of limiting the growth of the nucleus (122) to a single-domain monolayer (124) of the second material.

[0042] In one embodiment, the first material comprises one of hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HZO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO). In one embodiment, the second material is graphene, carbon nanotubes (CNT), hexagonal boron nitride (h-BN), metallic transition-metal dichalcogenides (e.g., vanadium disulfide (VS2), vanadium diselenide (VSe2), cobalt sulfide (CoS2), cobalt selenide (CoSe2), titanium disulfide (TiS2), or titanium diselenide (TiSe2)), semiconductor transition-metal dichalcogenides (e.g., molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), or tungsten diselenide (WSe2)), or high-k materials (e.g., Bi2SeO5 or It includes one of Sb2O3). In one embodiment, the mask material is amorphous silicon dioxide (a-SiO2), amorphous silicon (a-Si), and amorphous silicon nitride (a-SiN). x It includes at least one of amorphous carbon (α-carbon), hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HfZrO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO).

[0043] In one extended embodiment in which the nucleus (122) is the first nucleus (122) and the single-domain monolayer (124) is the first single-domain monolayer (124), the method further comprises: (g) a step of waiting for an incubation period; (h) a step of depositing another adsorbed atom (130) of the third material on top of the first single-domain monolayer (124) in at least one trench of the trench array, wherein the third binding energy between the second material and the third material is greater than the second binding energy between the mask material (110) and the third material; (i) a step of enabling the other adsorbed atom (130) of the third material to selectively nucleate into a second nucleus (132) on top of the first single-domain monolayer (124) within at least one trench of the trench array; and (j) a step of growing the nucleus (132) within at least one trench of the trench array; Here, the lateral dimensions associated with the trench geometry limit the growth of the second nucleus (132) to the second single-domain monolayer (134) of the third material, where the first single-domain monolayer (124) and the second single-domain monolayer (134) form a double layer.

[0044] In one embodiment, the third material comprises one of graphene, carbon nanotubes (CNT), hexagonal boron nitride (h-BN), metallic transition-metal dichalcogenides (e.g., vanadium disulfide (VS2), vanadium diselenide (VSe2), cobalt sulfide (CoS2), cobalt selenide (CoSe2), titanium disulfide (TiS2), or titanium diselenide (TiSe2)), semiconductor transition-metal dichalcogenides (e.g., molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), or tungsten diselenide (WSe2)), or high-k materials.

[0045] In one embodiment, the bilayer is a heterojunction bilayer in which the second material and the third material are different from each other. In another embodiment, the bilayer is a homojunction bilayer in which the second material and the third material are similar to each other.

[0046] In one embodiment, l and w is selected to have a value equal to the product of the incubation time of another nucleus of the second material on the single-domain monolayer and the growth rate of the second material, respectively. For example, if the measured lateral growth rate of WSe2 and the incubation time of the second nucleation are ~0.4 μm / min and 5 min, respectively, l and w is selected to have a value such as 5 min x 0.4 μm / min = 2 μm. In this embodiment, l and w Each is selected to be 2 micrometers.

[0047] In another embodiment, the method further comprises the step of forming a semiconductor device (valitetronics device, forksheet field-effect transistor (FET), or complementary FET) comprising a single-domain monolayer.

[0048] In one embodiment, before depositing a mask material on a substrate, the method comprises the step of forming a substrate by depositing at least one of hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HZO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO) on silicon.

[0049] In another embodiment, the present invention comprises: (a) providing a substrate (100) of a first material having a first Gibbs free energy; (b) depositing a mask material (110) having a second Gibbs free energy higher than the first Gibbs free energy on the substrate (100); and (c) forming a trench array on the mask material (110), wherein the trench array comprises a plurality of trenches (102), and each trench (102) l x w It has a trench geometry having lateral dimensions, where l and w(d) a step in which each trench (102) is selected to have a maximum dimension of 2 μm and each trench (102) has an exposed portion of the substrate (100) surrounded by a sidewall (112) formed of a mask material (110); (e) a step in which the adsorbed atoms (120) of the second material are selectively nucleated into a first nucleus (122) within each trench (102) of the trench array; (f) a step in which the first nucleus (122) is grown within each trench (102) of the trench array, wherein the lateral dimension related to the trench geometry limits the growth of the first nucleus (122) to a first single-domain monolayer (124) of the second material; (g) a step of waiting for an incubation period; (h) a step of depositing another adsorbed atom (130) of a third material on top of a first single-domain monolayer (124) of at least one trench of a trench array; (i) a step of enabling the other adsorbed atom (130) of the third material to selectively nucleate into a second nucleus (132) on top of the first single-domain monolayer (124) within at least one trench of a trench array; and (j) a step of growing the nucleus (132) within at least one trench of a trench array, wherein lateral dimensions related to the trench geometry restrict the growth of the second nucleus (132) to a second single-domain monolayer (134) of the third material, wherein the first single-domain monolayer (124) and the second single-domain monolayer (134) form a double layer.

[0050] In one embodiment, the first material comprises one of hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HZO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO).

[0051] In one embodiment, the second or third material is graphene, carbon nanotubes (CNT), hexagonal boron nitride (h-BN), metallic transition-metal dichalcogenides (e.g., vanadium disulfide (VS2), vanadium diselenide (VSe2), cobalt sulfide (CoS2), cobalt selenide (CoSe2), titanium disulfide (TiS2), or titanium diselenide (TiSe2)), semiconductor transition-metal dichalcogenides (e.g., molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), or tungsten diselenide (WSe2)), or high-k materials (e.g., Bi2SeO5 or It includes one of Sb2O3.

[0052] In one embodiment, the mask material (110) is amorphous silicon dioxide (a-SiO2), amorphous silicon (a-Si), and amorphous silicon nitride (a-SiN). x It includes at least one of amorphous carbon (α-carbon), hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HfZrO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO).

[0053] All combinations of the above concepts and additional concepts discussed in more detail below (unless such concepts conflict with one another) are part of the subject matter of the invention disclosed herein. In particular, all combinations of the claimed subject matter appearing at the end of this disclosure are part of the subject matter of the invention disclosed herein. Any terms used herein that may also appear in any disclosure incorporated by reference shall have the meaning most consistent with the specific concepts disclosed herein.

[0054] Figures 2a-2d are images of WSe2 grown in arrays of limited regions (trenches) of different widths for different periods using the process of Figure 1b. Figures 2a and 2b show WSe2 grown in 10 μm-wide trenches for 20 minutes and 30 minutes, respectively. Figures 2c and 2d show WSe2 grown in 2 μm-wide trenches for 7 minutes and 10 minutes, respectively.

[0055] As shown in Fig. 2a, WSe2 grown in 10 μm-wide trenches for 20 minutes (much longer than the 5-minute second nucleation incubation time) generated multiple nuclei in some trenches. In Fig. 2a, approximately 70% of the trenches contained only a single WSe2 triangle, while other trenches contained multiple nuclei. As shown in Fig. 2b, when the growth time was increased to 30 minutes, multi-domain polycrystalline WSe2 was formed. A significant decrease in photoluminescence (PL) intensity was observed in the multi-domain region compared to the single-domain region. Among the trenches with multiple nuclei, 25% contained more than two nuclei in the periphery, while the remainder had nuclei in the center. However, as shown in Figures 2c and 2d, when the trench width was reduced to 2 μm, only a single nucleus was generated per trench, regardless of the nucleation location for homogeneous nucleation in the center or heterogeneous nucleation in the periphery.

[0056] Without being bound by any specific theory, confined growth effectively suppresses additional heterogeneous nucleation in the trenches by reducing the size of the possible nucleation region. Further nucleation growth produces single-crystal MLs that fill the corresponding entire trenches, as shown in Figures 2c and 2d. Since each confined WSe2ML originates from a single nucleus, all WSe2MLs in the array of trenches are single-crystal across the wafer. Approximately 97% of the 2-μm-wide trenches were completely filled by WSe2 during the incubation period for the second nucleus at the top of the first layer of WSe2.

[0057] Figures 2e and 2f show E of WSe2 grown in a 2-micrometer-wide trench. 1 2g Raman mapping at the peak position and photoluminescence (PL) mapping at 1.65 eV are shown, respectively. The height of each trench can be 5 to 100 nm. These measurements confirm that the WSe2 grown in these trenches is indeed ML WSe2. The average full width at half maximum (FWHM) of the PL spectrum of the single-domain WSe2 in the trenches was measured to be about 55 meV at room temperature, which is similar to that of high-quality, single-domain WSe2 flakes mechanically isolated from bulk WSe2.

[0058] Measurements demonstrate that it is possible to obtain a uniform homo-BL that is electrically superior to ML by growing another layer of WSe2 on these single ML-WSe2 arrays. Each trench was designed so that only a single domain could be filled in each pocket, as shown in Fig. 1b. Further increasing the growth time resulted in the formation of single-domain BL-WSe2 that completely filled the trenches. In each trench, only a single additional WSe2 nucleus was present regardless of the nucleation mode; that is, approximately 60% of the secondary nuclei were heterogeneous nuclei seeded from the sidewalls of the SiO2 mask. This indicates that A for a limited ML 1g Peak (approx. 259.6 cm) -1 B for BL limited from ) 1 2g Peak (approx. 308.5 cm) -1 This was further confirmed by a Raman spectral shift to ). Additionally, a PL spectral peak shift from 1.65 eV to 1.6 eV confirms the transition from the direct-gap to the indirect-gap.

[0059] B shown in Figures 2g and 2h, respectively 1 2gRaman mapping at the peak and PL mapping at 1.6 eV confirm the presence of uniform wafer-scale BL-2D material in trenches across the entire wafer. Figures 2i and 2j show high-resolution transmission electron microscopy (HRTEM) images of 0.8 nm-thick ML-WSe2 and 1.6 nm-thick BL-WSe2, respectively. Scanning tunneling electron microscopy (STEM) images confirm that BL-WSe2 grew without deformation in the center or periphery of the SiO2 trenches. Additionally, topographic HAADF-STEM analysis revealed that BL-WSe2 was epitaxially aligned as AA' stacking.

[0060] The confined growth of single-domain, TMD homo- or hetero-BL at precisely defined locations on a wafer enables the use of TMDs as CMOS channel materials. FIG. 3a shows an array of field-effect transistors (FETs) on BL-WSe2 grown on a 2-inch wafer using the confined growth method exemplified in FIG. 1b and 1c. The wafer in FIG. 3a is a sapphire wafer having a back-gating device created using metal-induced transfer. Other substrates, including Si wafers with suitable masking materials, and other top-gating solutions are also possible.

[0061] FIG. 3b shows a representative drain-source current-gate-source voltage (I) measured from one of the BL-WSe2FET arrays. ds -V gs ) exhibits characteristics. FETs are >10 8 On / off current ratio, subcritical swing (SS) of 240.5 mV / dec, max 155.8 μA μm -1 The maximum on-current of ( I on ) Density and maximum 103.5 cm 2 V -1 s -1 field-effect mobility of ( μ eff = ,C g = 11.6 nF cm -2 ) ( V ds = at -1 V). Fig. 3c shows a maximum of 465 μAμm -1 It represents the saturation current.

[0062] Figure 3d shows the turn-on current / effective mobility characteristics of the array of WSe2FETs in Figure 3a benchmarked against WSe2FETs fabricated using a different method. The electrical characteristics of the FETs fabricated with confined-growth ML- / BL-WSe2 are similar to the best characteristics reported for single-crystal WSe2-based FETs and are similar to (or better than) those of the flake-based ML / BL-WSe2FETs in the exfoliated state as shown in Figure 3e.

[0063] Figure 3f shows the turn-on current per width. I on and effective mobility μ eff This represents a statistical analysis on the FET array for. The FET is per width I on and μ eff Both exhibited a Gaussian distribution; the mean and variation values ​​were, respectively I on Regarding density, 89.9 μAμm -1 and 17.3% and μ eff 79.1 cm 2 V -1 s -1 and 24.1%. 213 FETs fabricated with limited BL-WSe2 were manufactured with an estimated yield of 93.9%. Additionally, FETs fabricated with limited ML-WSe2 have similar electrical performance to FETs fabricated with limited BL-WSe2. FETs fabricated with limited BL-WSe2 exhibited performance similar to that of flake-based FETs uniformly across the entire array.

[0064] The limited growth technique of the present invention can also be used to fabricate logic and memory. FIG. 4a shows a single-crystal TMD (here, MoS2) fabricated on a 10 nm layer of amorphous HfO2 deposited on a Si wafer with a SiO2 mask defining a trench approximately 1 μm wide. DFT calculations confirm that the TMD has a higher binding energy on HfO2 than on SiO2. However, the difference in binding energy between sapphire and SiO2 is greater than the difference in binding energy between HfO2 and SiO2. This can result in a shorter incubation time between the first and second nucleation when growing TMDs on a SiO2 mask on an HfO2 surface. The reduced incubation time can be mitigated by reducing the trench size to 1 μm and further improving selectivity between HfO2 and SiO2 by adjusting the carrier gas and growth conditions.

[0065] As shown in Figures 4b and 4c, only a single nucleation event appears in each 1 μm trench. Further growth successfully fills the trench, generating single-crystal ML-MoS2 in a confined region of the amorphous HfO2 surface. Layer-by-layer growth is also possible. The confined ML- / BL-MoS2 on the HfO2 substrate was used to fabricate FETs to demonstrate the electrical characteristics of the confined ML- / BL-MoS2. Figure 4d shows the transfer characteristics measured from these fabricated ML / BL-MoS2 FETs ( I ds - V ds It represents ). The FET has a maximum of 86.7 μA μm -1 (ML-MoS2) and 129.3 μA μm -1 (BL-MoS2) maximum I on Density, maximum 62.2 cm 2 V -1 s -1 and 88.61 cm 2 V -1 s -1 of μeff (Fig. 4e) is shown, where C g_HfO2 = 600 nF cm -2 and V ds = 1 V. These MoS2FETs have electrical characteristics similar to those of single-crystal MoS2-based FETs made using other technologies.

[0066] The continuous confined growth of single-domain ML can be used to fabricate hetero-BL TMD semiconductors. For example, ML-MoS2 can be grown on an array of single-domain ML-WSe2. A single MoS2 nucleus is confined within a trench filled with WSe2 with full area coverage and can be grown to form a single-domain MoS2 / WSe2 hetero-BL. Raman mapping and PL spectra confirmed the uniform formation of the MoS2 / WSe2 hetero-BL. Additionally, the cross-sectional HAADF-STEM image in Fig. 4f shows a sharp van der Waals (vdW) heterointerface between confined ML-MoS2 and ML-WSe2 without any alloying. A uniform heterointerface without secondary nucleation can be observed in the low-magnification HAADF-STEM image.

[0067] Figure 4g illustrates the valleytronic performance of a MoS2 / WSe2 hetero-BL array. Specifically, Figure 4g shows the valley-polarization carrier dynamics of confined ML-WSe2 and hetero-BL (MoS2 / WSe2) arrays characterized by ultrafast circular dichroism (CD) based on time-resolved pump-probe spectroscopy. In confined-grown ML-WSe2, a valley lifetime (e.g., approximately tens of picoseconds) was observed due to rapid valley polarization extinction caused by exchange interactions, whereas in confined hetero-BL, a longer valley lifetime (e.g., approximately hundreds of picoseconds) was observed at 300 K due to ultrafast charge splitting. Additionally, an increased valley lifetime (approximately nanoseconds) due to reduced phonon scattering at 77 K was also confirmed.

[0068] Confined-growth techniques can be used to synthesize arrays of single-domain 2D TMDs at the wafer scale. These confined-growth techniques enable ML-by-ML synthesis with critical Gibbs free energy differences, allowing for the fabrication of homo-BL (WSe2 / WSe2) and hetero-BL (MoS2 / WSe2) array structures. Additionally, arrays of confined-growth BL-WSe2 transistor devices exhibited wafer-scale performance similar to that of devices made from exfoliated WSe2. Thus, confined-growth techniques overcome the difficulty of controlling 2D material dynamics at the wafer scale, which has been a major obstacle for 2D TMDs. This can be utilized for large-scale single-crystal vdW integration, providing a new pathway for constructing 2D material-based electronics platforms.

[0069] Simulation, fabrication, and measurement

[0070] DFT calculation for selective limited growth of TMDs. DFT calculations were performed using the Vienna Ab initio Simulation Package (VASP) with projector augmented wave (PAW) pseudopotentials and plane wave basis sets. Electron exchange-correlation interactions were described using the Generalized Gradient Approximation (GGA) of the Perdew-Burke-Ernzerhof (PBE) function. The valence electron configurations of W, Se, O, Al, and Si are 6, respectively. s 2 5 d 4 , 4 s 2 4 p 4 , 2 s 2 2 p 4 , 3 s 2 3 p 1 , and 3 s 2 3 p 2The energy cutoff for plane wave expansion was set to 420 eV. Since a large cell (lattice constant > 10 Å) was used for the DFT calculation, Γ - Points only k Brillouin bands were sampled using a point grid. Surface bonding interactions were investigated by placing WO3, Se, and WSe2 clusters on top of a-HfO2, Al2O3(0001), and a-SiO2 slabs, respectively. The surfaces of HfO2, SiO2, and Al2O3 were passivated by H atoms to mimic an Ar / H2 surrounding growth environment. Amorphous HfO2 and SiO2 atomic structures were obtained by applying crystal structures to a melt-quenching process simulated by ab-initio molecular dynamics. The structures were optimized by relaxing the top adsorbent atoms with immobilized substrate atoms. The criterion for structural relaxation was a force applied to the east atoms of less than 0.01 eV / Å. The system energy difference between two consecutive iterations was 10 -5 Electron minimization occurred when it was smaller than eV. The surface binding energy for adsorbent A on substrate B is E b = E A / B - E A - E B It was calculated as, where E A / B , E A , and E B is the energy of the adsorption system A / B, isolated adsorbent A, and substrate B, respectively.

[0071] Limited pattern production.To achieve limited growth of TMDs, LOR 3A and photoresist (PR; S1805) were coated onto a sapphire substrate and patterned using an AS200 i-line stepper (AutoStep 200). An approximately 25-nm-thick layer of a-SiO2 was deposited onto the PR-patterned sapphire substrate using an e-beam evaporator. Subsequently, to fabricate sapphire pockets (trenches), the SiO2 pattern was lifted with Remover PG (Kayaku Advanced Materials) and rinsed in acetone and isopropanol for 15 minutes each.

[0072] WSe 2 and MoS 2 Synthesis of. A limited TMD was synthesized in a quartz tube with a diameter of 4 inches. 300 mg of Se or S powder was placed in band I and 30 mg of WO3 or MoO3 powder was placed in band II, with the distance between bands fixed at 33 cm. A sapphire substrate patterned with SiO2 was loaded vertically 6 cm behind the WO3 or MoO3 powder, and the front and back of the substrate were covered with quartz plates to reduce or minimize direct reactions.

[0073] To synthesize limited ML-WSe2, air was removed from the quartz tube using a vacuum pump. After closing the vacuum valve, the tube was filled using an Ar (50 sccm) / H2 (50 sccm) ratio as the carrier gas before opening the atmospheric valve. The Ar / H2 ratio was continuously maintained. The growth temperatures for (Band I) and (Band II) were set at 15°C min⁻¹, respectively. -1 and 30℃ min -1 It was heated at a ramp rate, then maintained at 450°C (Band I) and 890°C (Band II) for 10 minutes, and then naturally cooled to room temperature.

[0074] For the limited BL-WSe2, the synthesis of the second WSe2 layer was performed using a carrier gas with an Ar (35 sccm) / H2 (65 sccm) ratio. For the limited heterostructure (MoS2 / WSe2), MoS2 synthesis was performed at 8°C min -1 and 30℃ min -1 The process was carried out at 200°C (Band I) and 750°C (Band II) at ramp rates. In particular, to improve growth selectivity on HfO2 substrates, the size of the SiO2 trench was reduced to 1 μm, and the total flow rate of Ar / H2 was increased from 100 sccm [Ar (50 sccm) / H2 (50 sccm)] to 200 sccm [Ar (100 sccm) / H2 (100 sccm)]. All reactions were performed at atmospheric pressure, and the TMD powder had a purity of over 99.99%.

[0075] Characterization of limited TMDs. Raman and PL spectra were measured using a Renishaw InVia Reflex micro-spectrometer equipped with a 532 nm pump laser. Light was applied to 2,400 wells mm -1The sample was dispersed by a holographic grating. For Raman and PL mapping images, the sample was scanned on an xy piezo stage equipped with laser illumination. SEM images were measured using a high-resolution scanning electron microscope (ZEISS Merlin) with an in-lens detector. The working distance was 6 mm at an acceleration voltage of 2 kV and a probe current of 70 pA. TEM characterization was performed using a JEOL JEM-2100F with an acceleration voltage of 200 kV and a Titan Themis Z G3 Cs-Corrected with an acceleration voltage of 60 kV. EDX line profiles were obtained in STEM mode using Velox software with characteristic Mo Kα, S Kα, W Lα, and Se Kα X-ray signals. XPS spectra were measured using a magnesium Kα source (MultiLab 2000, Thermo VG) and the peak energy was corrected by the C 1s peak at 284.8 eV. AFM morphology analysis was performed using XE 100 (Park Systems Corp).

[0076] Device fabrication and electrical measurement. To fabricate a device using confined ML- / BL-WSe2, a 600 nm-thick Au film was deposited onto confined WSe2 / sapphire by E-beam evaporation. The Au / WSe2 stack was exfoliated using thermal release tape as a handling layer and transferred onto a 300 nm-thick SiO2 / high-concentration p-doped silicon wafer. After removing the thermal release tape from a hot plate at 120 °C, the tape residue was removed from the Au film by oxygen plasma treatment. Subsequently, the Au film was etched with an Au etchant and rinsed with deionized water (to compare electrical characteristics, several layers of WSe2 flakes were transferred in the same manner).

[0077] After the delivery of a limited ML- / BL-WSe2 onto a SiO2 substrate, alignment marks for electron-beam lithography (EBL) were patterned on the SiO2 substrate using an optical lithography process, and then 2.5 nm-thick Ti and 7.5 nm-thick Au layers were deposited using an electron-beam evaporator. Subsequently, drain and source contact regions with a width of 2 μm were patterned using EBL. For the EBL photoresist, polymethyl methacrylate (PMMA) A4 and PMMA A6 were spin-coated at 3000 rpm and baked at 180°C for 150 s. After PMMA development, 10 nm-thick Pt and 80 nm-thick Au layers were deposited using an electron-beam evaporator. Finally, the regions excluding the source / drain contact metal regions were removed by a lift-off process. For the fabrication of a device using confined ML- / BL-MoS2 on HfO2, the same process was performed from alignment mark patterning for EBL to PMMA development. Subsequently, 10 nm-thick Ni and 80 nm-thick Au layers were deposited using an electron beam evaporator and then lifted off.

[0078] Current-voltage characteristics were measured using an Agilent B2900A source / measure unit. All measurements were performed in air at room temperature. Additionally, a 2-inch confined BL-WSe2 was 5.1 × 5.1 cm 2 It was transferred onto a 300-nm-thick SiO2 / Si substrate having a size. Kelvin probe force microscopy (KPFM) confirmed a highly uniform distribution of the work function (5.08 eV) on the confined BL-WSe2. Subsequently, a channel length of 0.7 μm ( L CH Source and drain electrodes having ) were integrated using platinum; and a Hall barrier height of 0.31 eV was estimated through modified Richardson plotting.

[0079] Time-resolved pump-probe spectroscopy.Valley-polarized carrier dynamics were investigated by measuring ultrafast CDs using time-resolved pump-probe spectroscopy. A 100 kHz Yb-based regenerative amplifier system (Light Conversion PHAROS) provided femtosecond laser pulses, and a sequential optical parameter amplifier (ORPHEUS) produced wavelength-tunable pump and probe pulses resonating with the A-exciton resonance of WSe2, with a pulse duration of 50 fs and a spectral bandwidth of 50 meV. Samples in a cryogenic reservoir were illuminated by the pump-excitation pulses using a 40× objective lens. Pump-induced changes in probe reflectance were recorded as a function of time delays produced by a mechanical conversion stage and a lock-in amplifier. The polarization profiles of the pump and probe pulses were controlled individually by half-wave and quarter-wave plates. Signals were measured for pump and probe pulses exhibiting the same spiral of circular polarization (co-polarization) and the opposite spiral of circular polarization (cross-polarization). The valley-dependent ultrafast CD response shown in Figures 4f and 4g was obtained by the difference between the co-polarized and cross-polarized pump-probe responses.

[0080] conclusion

[0081] Although various embodiments of the present invention have been described and illustrated herein, a person skilled in the art will readily conceive of various other means and / or structures to perform a function or obtain one or more of the results and / or advantages described herein, and such variations and / or modifications are each considered to be within the scope of the embodiments of the present invention described herein. More generally, a person skilled in the art will readily understand that all parameters, dimensions, materials, and configurations described herein are intended to be exemplary, and that actual parameters, dimensions, materials, and / or configurations will vary depending on the specific application or applications in which the teachings of the present invention are used. A person skilled in the art will be able to recognize or identify many equivalents to the specific embodiments of the present invention described herein by using only routine experimentation. Accordingly, it should be understood that the embodiments are presented merely as examples, and that within the scope of the appended claims and their equivalents, embodiments of the present invention may be practiced differently from those specifically described and claimed. The embodiments of the present invention in this disclosure relate to each individual feature, system, article, material, kit, and / or method described herein. Additionally, any combination of two or more of these features, systems, articles, materials, kits, and / or methods is included within the scope of the invention of this disclosure, provided that these features, systems, articles, materials, kits, and / or methods do not conflict with one another.

[0082] Furthermore, various concepts of the present invention may be implemented in one or more ways, and an example thereof has been provided. Actions performed as part of the method may be ordered in any suitable manner. Accordingly, embodiments in which actions are performed in a different order than illustrated may be constructed, which may include performing some actions simultaneously, even if they appear as sequential actions in the exemplary embodiments.

[0083] All definitions as defined and used herein shall be understood to take precedence over dictionary definitions, definitions in the literature included by reference, and / or the general meaning of the defined terms.

[0084] As used herein in the specification and claims, the indefinite articles "a" and "an" should be understood to mean "at least one" unless explicitly indicated otherwise.

[0085] As used herein in the specification and claims, the phrase “and / or” should be understood to mean “one or both” of the elements thus combined, that is, elements that exist combined in some cases and separately in others. Multiple elements listed together with “and / or” should be interpreted in the same way, that is, “one or more” of the elements thus combined. In addition to the elements specifically identified by the “and / or” clause, other elements may arbitrarily exist, whether or not they are related to the specifically identified elements. Accordingly, as a non-limiting example, when used with open language such as “comprising,” a reference to “A and / or B” may refer, in one embodiment, only A (optionally including elements other than B); in another embodiment, only B (optionally including elements other than A); and in yet another embodiment, both A and B (optionally including other elements); and so on.

[0086] As used herein in the specification and claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items from a list, “or” or “and / or” should be interpreted as inclusive, that is, not only including at least one but also more than one element, a number of elements or a list of elements, and, optionally, additional unlisted items. Terms that are explicitly indicated contrary, such as “only one of” or “exactly one of,” or, when used in claims, “consisting of,” will refer to the inclusion of exactly one element among a number of elements or a list of elements. In general, as used herein, the term “or” should be interpreted to indicate an exclusive alternative (i.e., “one of the two or the other but not both”) only when followed by terms of exclusivity such as “one of the two,” “one of the two,” “only one of the two,” or “exactly one of the two.” When used in a claim, "essentially consisting of" has its ordinary meaning as used in the field of patent law.

[0087] As used herein in the specification and claims, the phrase “at least one” in reference to a list of one or more elements means at least one element selected from any one or more of the elements in the list of elements, but should be understood as not necessarily including at least one of each and all of the elements specifically listed in the list of elements, and not excluding any combination of elements in the list of elements. This definition also allows that elements other than the specifically identified elements in the list of elements referred to by the phrase “at least one” may arbitrarily exist, whether or not related to the specifically identified elements. Accordingly, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B”, or, equivalently, “at least one of A and / or B”) is, in one embodiment, at least one (or optionally more than one) of A that is absent from B (and optionally includes elements other than B); in another embodiment, at least one (or optionally more than one) of B that is absent from A (and optionally includes elements other than A); In addition, in another embodiment, at least one (optional including more than one) of A and at least one (optional including more than one) of B (also optionally including other elements); etc. may be referred to.

[0088] In the claims as well as in the specification above, all transition phrases such as “comprising,” “including,” “having,” “having,” “containing,” “accompanying,” “possessing,” and “consisting of” should be understood as open-ended, meaning that they include but are not limited. Only the transition phrases “consisting of” and “essentially consisting of” are closed or semi-closed transition phrases, respectively, as specified in Section 2111.03 of the U.S. Patent and Trademark Office Manual of Patent Examination Procedure.

Claims

Claim 1 (a) a step of providing a substrate (100) of a first material; (b) a step of depositing a mask material (110) on the substrate (100); (c) a step of forming a trench array on the mask material (110), wherein the trench array comprises a plurality of trenches (102), and each trench (102) l x w It has a trench geometry having lateral dimensions, where l and w The method comprises: (d) a step in which each trench (102) is selected to have a maximum dimension of 2 μm and each trench (102) has an exposed portion of the substrate (100) surrounded by a sidewall (112) formed of a mask material (110); (e) a step of depositing adsorbed atoms (120) of the second material on the exposed portion of the substrate (100), wherein the first binding energy between the first material and the second material is greater than the second binding energy between the mask material (110) and the second material; (f) a step in which the adsorbed atoms (120) can selectively nucleate into nuclei (122) within each trench (102) of the trench array; and (f) a step of growing nuclei (122) within each trench (102) of the trench array, wherein the lateral dimension associated with the trench geometry limits the growth of the nuclei (122) to a single-domain monolayer (124) of the second material, l and w A method in which each is selected to have a value equal to the product of the incubation time of another nucleus of the second material on the single-domain monolayer and the growth rate of the second material. Claim 2 The method of claim 1, wherein the first material comprises one of hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HZO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO). Claim 3 The method of claim 1, wherein the second material comprises one of graphene, carbon nanotubes (CNT), hexagonal boron nitride (h-BN), metallic transition-metal dichalcogenides, semiconductor transition-metal dichalcogenides, or high-k materials. Claim 4 A method according to paragraph 3, wherein the metallic transition-metal dichalcogenide is one of vanadium disulfide (VS2), vanadium diselenide (VSe2), cobalt sulfide (CoS2), cobalt selenide (CoSe2), titanium disulfide (TiS2), or titanium diselenide (TiSe2). Claim 5 A method according to paragraph 3, wherein the semiconductor transition-metal dichalcogenide is one of molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), or tungsten diselenide (WSe2). Claim 6 In paragraph 3, the high-k material is Bi2SeO5 or One of the methods for Sb2O3. Claim 7 In claim 1, the mask material (110) is amorphous silicon dioxide (a-SiO2), amorphous silicon (a-Si), or amorphous silicon nitride (a-SiN). x A method comprising at least one of amorphous carbon (α-carbon), hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HfZrO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO). Claim 8 In claim 1, the nucleus (122) is the first nucleus (122), the single-domain monolayer (124) is the first single-domain monolayer (124), and the method (g) is the step of waiting for an incubation period; (h) the step of depositing another adsorbed atom (130) of the third material on top of the first single-domain monolayer (124) of at least one trench of the trench array, wherein the third binding energy between the second material and the third material is greater than the second binding energy between the mask material (110) and the third material; (i) the step of enabling the other adsorbed atom (130) of the third material to selectively nucleate into the second nucleus (132) on top of the first single-domain monolayer (124) within at least one trench of the trench array; and (j) the step of growing the nucleus (132) within at least one trench of the trench array; A method in which the lateral dimensions associated with the trench geometry here limit the growth of the second nucleus (132) to the second single-domain monolayer (134) of the third material, wherein the first single-domain monolayer (124) and the second single-domain monolayer (134) form a double layer. Claim 9 A method according to claim 8, wherein the third material comprises one of graphene, carbon nanotubes (CNT), hexagonal boron nitride (h-BN), metallic transition-metal dichalcogenides, semiconductor transition-metal dichalcogenides, or high-k materials. Claim 10 The method of claim 9, wherein the metallic transition-metal dichalcogenide is one of vanadium disulfide (VS2), vanadium diselenide (VSe2), cobalt sulfide (CoS2), cobalt selenide (CoSe2), titanium disulfide (TiS2), or titanium diselenide (TiSe2). Claim 11 A method according to claim 9, wherein the semiconductor transition-metal dichalcogenide is one of molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), or tungsten diselenide (WSe2). Claim 12 In claim 8, the method wherein the double layer is a heterojunction double layer in which the second material and the third material are different from each other. Claim 13 In claim 8, the method wherein the double layer is a homojunction double layer in which the second material and the third material are similar to each other. Claim 14 A method according to claim 1, wherein the formation of the trench (102) involves passing through the mask material (110) and etching into the substrate (100) to some extent. Claim 15 In paragraph 1, l and w A method in which each is selected to be 2 micrometers. Claim 16 A method according to claim 1, further comprising the step of forming a semiconductor device including a single-domain monolayer (124). Claim 17 In paragraph 16, the semiconductor device comprises one of a valleyronics device, a fork sheet field-effect transistor (FET), or a complementary FET. Claim 18 A method according to claim 1, further comprising the step of forming a substrate (100) by depositing at least one of hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HZO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO) on silicon before depositing a mask material (110) on the substrate (100). Claim 19 (a) a step of providing a substrate (100) of a first material having a first Gibbs free energy; (b) a step of depositing a mask material (110) having a second Gibbs free energy higher than the first Gibbs free energy on the substrate (100); (c) a step of forming a trench array on the mask material (110), wherein the trench array comprises a plurality of trenches (102), and each trench (102) l x w It has a trench geometry having lateral dimensions, where l and w Steps in which each trench (102) is selected to have a maximum dimension of 2 μm and each trench (102) has an exposed portion of the substrate (100) surrounded by a sidewall (112) formed of a mask material (110); (e) depositing adsorbed atoms (120) of the second material on the exposed portion of the substrate (100); (f) enabling the adsorbed atoms (120) to selectively nucleate into a first nucleus (122) within each trench (102) of the trench array; (g) growing the first nucleus (122) within each trench (102) of the trench array, wherein the lateral dimensions associated with the trench geometry limit the growth of the first nucleus (122) to a first single-domain monolayer (124) of the second material; (h) waiting for an incubation period; (i) the first single-domain of at least one trench of the trench array A method comprising the steps of: (j) depositing another adsorbed atom (130) of a third material on top of a monolayer (124); (k) enabling the other adsorbed atom (130) of the third material to selectively nucleate into a second nucleus (132) on top of a first single-domain monolayer (124) within at least one trench of a trench array; and (k) growing the nucleus (132) within at least one trench of a trench array, wherein the lateral dimensions associated with the trench geometry restrict the growth of the second nucleus (132) to a second single-domain monolayer (134) of the third material, wherein the first single-domain monolayer (124) and the second single-domain monolayer (134) form a double layer. Claim 20 The method of claim 19, wherein the first material comprises one of hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HZO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO). Claim 21 A method according to claim 19, wherein the second or third material comprises one of graphene, carbon nanotubes (CNT), hexagonal boron nitride (h-BN), metallic transition-metal dichalcogenides, semiconductor transition-metal dichalcogenides, or high-k materials. Claim 22 A method according to claim 21 in which the metallic transition-metal dichalcogenide is one of vanadium disulfide (VS2), vanadium diselenide (VSe2), cobalt sulfide (CoS2), cobalt selenide (CoSe2), titanium disulfide (TiS2), or titanium diselenide (TiSe2). Claim 23 A method according to claim 21 in which the semiconductor transition-metal dichalcogenide is one of molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), tungsten disulfide (WS2), or tungsten diselenide (WSe2). Claim 24 In paragraph 21, the high-k material is Bi2SeO5 or One of the methods for Sb2O3. Claim 25 In claim 19, the mask material (110) is amorphous silicon dioxide (a-SiO2), amorphous silicon (a-Si), and amorphous silicon nitride (a-SiN). x A method comprising at least one of amorphous carbon (α-carbon), hafnium oxide (HfO2), aluminum oxide (Al2O3), hafnium zirconium oxide (HfZrO), titanium dioxide (TiO2), zinc oxide (ZnO), iron oxide (Fe2O3), tin oxide (SnO2), nickel oxide (NiO), or copper oxide (CuO). Claim 26 In paragraph 19, a method in which the double layer is a heterojunction double layer in which the second material and the third material are different from each other. Claim 27 In paragraph 19, a method in which the double layer is a homojunction double layer in which the second material and the third material are similar to each other. Claim 28 delete

Images