A direct directional epitaxial fabrication method for wafer-level two-dimensional In2S3 / MoS2 heterojunctions

Abstract

This invention belongs to the technical field of semiconductor materials and devices, and discloses a direct directional epitaxial growth method for wafer-level two-dimensional In2S3 / MoS2 heterostructures. The method uses a single-crystal monolayer MoS2 film as the epitaxial substrate and In2O3 powder and elemental sulfur powder as reaction precursors. Chemical vapor phase epitaxy is performed in a mixed carrier gas atmosphere containing H2. By introducing H2 into the reaction atmosphere to in-situ regulate the gas-phase decomposition of the precursors, an active reaction intermediate with specific adsorption characteristics, In2O, is generated. The adsorption advantage of this intermediate on the MoS2 surface is utilized to suppress the local aggregation of In2S3, achieving direct epitaxial growth of a wafer-level van der Waals heterostructure with uniform thickness and low interface defects. The photodetector device built based on this heterostructure exhibits significant rectification characteristics and excellent photoelectric response, and has application value in the field of photoelectric detection.

Description

Technical Field

[0001] This invention belongs to the technical field of semiconductor materials and devices, and more specifically, relates to a direct directional epitaxial fabrication method for wafer-level two-dimensional In2S3 / MoS2 heterojunctions. Background Technology

[0002] Van der Waals heterojunctions based on two-dimensional transition metal chalcogenides (TMDCs) have great potential in ultrathin optoelectronic devices that continue Moore's Law due to the absence of dangling bonds and atomically abrupt interfaces. However, their large-scale fabrication faces several bottlenecks: mechanical transfer methods are prone to introducing interface impurities and cracks and are not suitable for mass production; while conventional vapor deposition methods for directly growing other two-dimensional materials on MoS2 substrates are prone to generating unevenly thick island-like crystals and disordered grain boundaries due to uncontrolled reaction kinetics, which cannot meet the stringent requirements for thin film uniformity and crystal quality in wafer-level device manufacturing.

[0003] Therefore, there is an urgent need to design a direct directional epitaxial growth method for wafer-level two-dimensional In2S3 / MoS2 heterojunctions, which can directly grow two-dimensional heterostructures with uniform surface, consistent orientation and clean interface at the wafer scale. Summary of the Invention

[0004] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a direct directional epitaxial growth method for wafer-level two-dimensional In2S3 / MoS2 heterojunctions. The aim is to introduce H2 into the reaction atmosphere to in-situ regulate the gas-phase decomposition of the precursor to generate an active reaction intermediate, In2O, with specific adsorption characteristics. The adsorption advantage of this intermediate on the MoS2 surface is used to suppress the local aggregation of In2S3, thereby achieving direct epitaxial growth of van der Waals heterostructures with uniform thickness and low interface defects at the wafer scale.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for direct directional epitaxy fabrication of a wafer-level two-dimensional In2S3 / MoS2 heterojunction is provided, comprising the following steps: S1: Provides a single-crystal MoS2 thin film as an epitaxial growth substrate; S2: Place an In2O3 source in temperature zone I of the CVD reaction chamber, place a single-element S source in temperature zone II, and place the epitaxial growth substrate downstream of the In2O3 source. S3: Introduce a mixed carrier gas containing H2 into the reaction chamber; S4: The reaction chamber is heated to allow H2 to react in situ with vaporized In2O3 to generate gaseous reaction intermediates In2O clusters. The In2O clusters are then controlled to adsorb on the surface of the MoS2 film and react with a sulfur source to undergo epitaxial growth, resulting in a wafer-level In2S3 / MoS2 van der Waals heterojunction.

[0006] Preferably, the single-crystal MoS2 thin film in step S1 is a single-crystal monolayer film epitaxially grown on a single-crystal sapphire with the C-plane and the A-plane aligned.

[0007] Preferably, the mixed carrier gas in step S3 is a mixture of Ar and H2, wherein the volume percentage of H2 is 5% to 15%, which is used to catalyze and regulate the reduction conversion rate of In2O3 to the gas-phase reaction intermediate In2O.

[0008] Preferably, in step S4, the adsorption energy of the gas-phase reaction intermediate In2O on the surface of the MoS2 film is lower than its formation energy at the edge of the grown In2S3 film, thereby forming a thermodynamically self-limiting mode to grow In2S3 with uniform thickness layer by layer.

[0009] Preferably, the parameters of the epitaxial reaction in step S4 are: temperature zone I is set at 600-700℃, temperature zone II is set at 170-190℃, and the epitaxial isothermal time is 20-30 min.

[0010] Preferably, the crystal lattice of In2S3 is aligned with the orientation of MoS2 at 0° or 60°.

[0011] According to another aspect of the present invention, a wafer-level two-dimensional In2S3 / MoS2 van der Waals heterojunction thin film prepared by the above method is provided. The heterojunction is formed by vertically stacking a single-crystal monolayer of MoS2 and multiple layers of In2S3. The In2S3 is directly epitaxially grown on the surface of the MoS2. The interlayer of the heterojunction is an atomically steep abrupt van der Waals interface with no atomic diffusion at the interface.

[0012] Preferably, the thickness of the In2S3 is less than 2.0 nm, and the surface thickness uniformity of the heterojunction film is greater than 99.5%.

[0013] According to another aspect of the present invention, a photodetector is provided, which uses the above-mentioned wafer-level two-dimensional In2S3 / MoS2 van der Waals heterojunction thin film as the photoelectric active region; the device includes a substrate, a bottom electrode and a top electrode, the bottom electrode forming an electrical contact with the MoS2, and the top electrode forming an electrical contact with the In2S3, so as to construct a photogenerated carrier transport channel in a direction perpendicular to the van der Waals interface.

[0014] Preferably, the In2S3 / MoS2 van der Waals heterojunction has a vertical Type-II band arrangement.

[0015] In summary, compared with the prior art, the direct directional epitaxial fabrication method for wafer-level two-dimensional In2S3 / MoS2 heterojunctions provided by this invention has the following advantages: 1. This invention introduces H2 into the reaction atmosphere and utilizes the gas-phase reaction intermediate In2O clusters, whose adsorption energy on the MoS2 surface is lower than its formation energy at the edge of the In2S3 film, effectively suppressing the local aggregation and longitudinal disordered stacking of In2S3, thereby obtaining a wafer-level heterojunction film with a thickness uniformity greater than 99.5%.

[0016] 2. This invention achieves directional epitaxial growth of In2S3 through the lattice template effect of a single-crystal MoS2 substrate (the crystal lattice is aligned with MoS2 at 0° or 60°). The resulting heterojunction has atomically steep abrupt van der Waals interfaces between layers, with no atomic diffusion at the interfaces and a sulfur vacancy concentration below 8.3 × 10¹¹ cm⁻¹. - ², possesses excellent crystal quality.

[0017] 4. The photodetector device constructed based on the heterojunction thin film of the present invention exhibits significant rectification characteristics (rectification ratio of approximately 300) and excellent photoelectric response (average responsivity of 6.28 × 10³ A / W and detectivity of 1.76 × 10¹² Jones), and has broad application prospects in the field of photoelectric detection. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a wafer-level two-dimensional In2S3 / MoS2 heterojunction provided by the present invention.

[0019] Figure 2 This is a photograph of the two-dimensional In2S3 / MoS2 heterojunction under an optical microscope in Embodiment 1 of the present invention.

[0020] Figure 3 This is a Raman scan of the two-dimensional In2S3 / MoS2 heterojunction in Embodiment 1 of the present invention.

[0021] Figure 4 This is a schematic diagram of the photodetector structure in Embodiment 2 of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0023] Please see Figure 1-2 This invention provides a direct directional epitaxial fabrication method for wafer-level two-dimensional In2S3 / MoS2 heterojunctions, comprising the following steps: S1: Provides a single-crystal MoS2 thin film as an epitaxial growth substrate; S2: Place an In2O3 source in temperature zone I of the CVD reaction chamber, place a single-element S source in temperature zone II, and place the epitaxial growth substrate downstream of the In2O3 source. S3: Introduce a mixed carrier gas containing H2 into the reaction chamber; S4: The reaction chamber is heated to allow H2 to react in situ with vaporized In2O3 to generate gaseous reaction intermediates In2O clusters. The In2O clusters are then controlled to adsorb on the surface of the MoS2 film and react with a sulfur source to undergo epitaxial growth, resulting in a wafer-level In2S3 / MoS2 van der Waals heterojunction.

[0024] Specifically, the single-crystal MoS2 thin film mentioned in step S1 is a single-crystal monolayer film epitaxially grown on a single-crystal sapphire with the C-plane and the A-plane aligned.

[0025] Specifically, the mixed carrier gas in step S3 is a mixture of Ar and H2, wherein the volume percentage of H2 is 5% to 15%, which is used to catalyze and regulate the reduction conversion rate of In2O3 to the gas-phase reaction intermediate In2O.

[0026] Specifically, in step S4, the adsorption energy of the gas-phase reaction intermediate In2O on the surface of the MoS2 film is lower than its formation energy at the edge of the grown In2S3 film, thereby forming a thermodynamically self-limiting mode to grow In2S3 with uniform thickness layer by layer.

[0027] Specifically, the parameters of the epitaxial reaction in step S4 are as follows: temperature zone I is set at 600-700℃, temperature zone II is set at 170-190℃, and the epitaxial isothermal time is 20-30 min.

[0028] Specifically, the crystal lattice of In2S3 is aligned with the orientation of MoS2 at 0° or 60°.

[0029] Example 1 This embodiment provides a direct directional epitaxial fabrication method for 2-inch wafer-level In2S3 / MoS2 heterojunctions, mainly including the following steps: (1) Preparation of first-layer single-crystal MoS2 wafer: A 2-inch high-quality single-crystal single-layer MoS2 thin film wafer was obtained by epitaxial growth of a sapphire substrate with A-plane and C-plane orientation aligned by metal-organic chemical vapor deposition (MOCVD).

[0030] (2) Precursor loading and positioning: The sapphire substrate containing the MoS2 thin film is placed in the downstream temperature zone of the dual-temperature zone tube furnace; a ceramic boat loaded with 1 g of high-purity In2O3 powder (99.99% purity) is placed flat in the central temperature zone (temperature zone I) of the tube furnace; 2 g of high-purity S powder is placed on the heating belt upstream of the tube furnace (temperature zone II), and the local temperature at this position is maintained by an independent auxiliary heating temperature controller.

[0031] (3) Control of reaction gas and atmosphere conditioning: The furnace is evacuated and flushed three times with high-purity protective gas. Then, a flowing mixed gas is introduced to serve as the carrier gas and reaction gas source. The parameters of the flowing gas source are: total flow rate 100 sccm, which contains high-purity argon gas with a flow rate of 90 sccm and high-purity hydrogen gas with a flow rate of 10 sccm (i.e., H2 volume percentage is 10%).

[0032] (4) Two-step chemical vapor phase epitaxy: The furnace body is heated to 650°C in the middle section of the tube furnace at a rate of about 20°C / min. The temperature zone II then stabilizes at 630-640°C, which is the orientation epitaxial growth window. When the middle zone approaches 650°C, the upstream heating belt is turned on to heat the sulfur powder to 180°C. The vaporized sulfur vapor is carried into the middle and downstream zones with the Ar / H2 mixed carrier gas. The in-situ reaction lasts for 25 min. At this time, hydrogen partially reduces In2O3 to produce volatile In2O reactive clusters. These clusters flow through the downstream single crystal MoS2 surface to nucleate and react with sulfur vapor to transform into In2S3. After the reaction is completed, the heating power is cut off, and the furnace body is allowed to cool rapidly to room temperature under the flow of protective gas. The prepared In2S3 / MoS2 heterojunction thin film wafer is then taken out.

[0033] (5) The surface of the sample grown under these conditions is a uniform translucent gray tone. Optical microscopy and atomic force microscopy measurements revealed that the top layer is a uniform multilayer In2S3 (about 3 layers thick, about 2.0 nm), attached to the monolayer bottom layer MoS2.

[0034] Please see Figure 3 Full-area Raman scanning confirmed that the positions of its main characteristic peaks were not significantly distorted, and the Raman vibration peak fluctuations were controlled within 0.5 cm. - Within ¹, the intensity fluctuation is within 2% of the average value. XRD and selected area electron diffraction analysis show that the crystal lattice of In2S3 is aligned with MoS2 at 0°. Cross-sectional high-resolution transmission electron microscopy characterization shows that the heterojunction layers have abrupt van der Waals interfaces at the atomic level, with no atomic diffusion at the interface.

[0035] Example 2 Please see Figure 3 This embodiment provides a vertical photodetector based on a two-dimensional In2S3 / MoS2 van der Waals heterojunction, mainly including the following steps: (1) Bottom electrode processing: On a heavily doped silicon wafer with a thermal oxide layer (300 nm SiO2), a layer of heavy metal Cr / Au electrode is deposited by ultraviolet lithography and stripping process to serve as the cable and bottom electrode connected to the underlying MoS2.

[0036] (2) Two-dimensional heterojunction film transfer and patterning: The heterojunction film epitaxially prepared on the sapphire substrate in Example 1 was completely transferred and released onto the silicon wafer with the processed bottom electrode by using a high-temperature transfer method mediated by polymethyl methacrylate (PMMA).

[0037] (3) Top electrode construction: Secondary photolithography is performed on the surface of In2S3 / MoS2 heterojunction, and the top Cr / Au (10 nm / 50 nm) contact electrode is deposited by electron beam evaporation process. This electrode forms a good ohmic contact with the uppermost In2S3 surface layer of the active region.

[0038] (4) Electrical characterization and photoelectric response: Parameters were measured using a Keysight B1500A parameter analyzer on a probe stage. Under 532nm laser excitation and different applied gate voltage modulation, the device exhibited a strong rectification effect (rectification ratio approximately 300); the effective hole / electron carrier mobility of the material was calculated to be 26.3 cm²V using multi-channel conductivity modulation. - ¹s - ¹; Under green light illumination, the photodetector generates a strong photocurrent gain, achieving an average photoresponsivity of 6.28 × 10³ A / W on 30 array test units, with a maximum extrapolation detectivity of 1.76 × 10¹² Jones.

[0039] Example 3 The difference between this embodiment and Embodiment 1 is that the volume percentage of H2 in the mixed carrier gas is 5%. Specifically, the flow source parameters are: a total flow rate of 100 sccm, containing high-purity argon at a flow rate of 95 sccm and high-purity hydrogen at a flow rate of 5 sccm. Temperature zone I is set to 600℃, temperature zone II is set to 170℃, and the epitaxial isothermal time is 30 min. The remaining steps are the same as in Embodiment 1. The results show that the obtained In2S3 / MoS2 heterojunction film is still within the parameter window of this invention, with uniform surface thickness and a clear heterojunction interface without diffusion.

[0040] Example 4 The difference between this embodiment and Embodiment 1 is that the volume percentage of H2 in the mixed carrier gas is 15%. Specifically, the flow source parameters are: a total flow rate of 100 sccm, containing high-purity argon at a flow rate of 85 sccm and high-purity hydrogen at a flow rate of 15 sccm. Temperature zone I is set to 700℃, temperature zone II is set to 190℃, and the epitaxial isothermal time is 20 min. The remaining steps are the same as in Embodiment 1. The obtained In2S3 / MoS2 heterojunction film also exhibits excellent thickness uniformity and crystal quality, with Raman vibration peak fluctuations controlled within 0.5 cm. - ¹Within.

[0041] Example 5 The difference between this embodiment and Embodiment 1 is that the epitaxially grown MoS2 substrate is a single-crystal monolayer film epitaxially grown on a single-crystal sapphire with the C-plane and A-plane aligned using a large-area CVD method. The remaining steps are the same as in Embodiment 1. The crystal quality and electrical properties of the resulting heterojunction film are essentially the same as in Embodiment 1.

[0042] Comparative Example To verify the beneficial effects of the technical solution of the present invention, the following comparative examples are set up: Comparative Example 1: Except for the absence of H2 in the mixed carrier gas (i.e., only 100 sccm of high-purity Ar is introduced), the other process parameters are exactly the same as in Example 1. The results show that In2O3 cannot be effectively reduced to the active intermediate In2O, and In2S3 grows in an island-like disorder on the MoS2 surface, resulting in poor film thickness uniformity and the inability to obtain a continuous wafer-level heterojunction film.

[0043] Comparative Example 2: Except for replacing the In2O3 source with the In2S3 source (i.e., using conventional solid In2S3 as the indium and sulfur source), the other process parameters were exactly the same as in Example 1. The results showed that the adsorption and binding force of the gaseous InxSy species obtained by sublimation on the MoS2 surface was weaker than that at the domain edge, and the growth turned into an island-like mode. In2S3 formed a large number of locally aggregated thick domain regions on the MoS2 surface, the film surface was rough, and uniform layer-by-layer growth could not be achieved.

[0044] The comparative examples above demonstrate that the present invention introduces H2 into the reaction atmosphere to generate In2O gas-phase reaction intermediate in situ, and utilizes the adsorption advantage of this intermediate on the MoS2 surface, which is a key technical means to achieve direct directional epitaxial growth of uniform In2S3 / MoS2 heterojunctions at the wafer level.

[0045] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for direct directional epitaxy fabrication of a wafer-level two-dimensional In2S3 / MoS2 heterojunction, characterized in that, Includes the following steps: S1: Provides a single-crystal MoS2 thin film as an epitaxial growth substrate; S2: Place an In2O3 source in temperature zone I of the CVD reaction chamber, place a single-element S source in temperature zone II, and place the epitaxial growth substrate downstream of the In2O3 source. S3: Introduce a mixed carrier gas containing H2 into the reaction chamber; S4: The reaction chamber is heated to allow H2 to react in situ with vaporized In2O3 to generate gaseous reaction intermediates In2O clusters. The In2O clusters are then controlled to adsorb on the surface of the MoS2 film and react with a sulfur source to undergo epitaxial growth, resulting in a wafer-level In2S3 / MoS2 van der Waals heterojunction.

2. The method as described in claim 1, characterized in that: The single-crystal MoS2 thin film mentioned in step S1 is a single-crystal monolayer film epitaxially grown on a single-crystal sapphire with the C-plane and the A-plane orientation aligned.

3. The method as described in claim 1, characterized in that: The mixed carrier gas mentioned in step S3 is a mixture of Ar and H2, wherein the volume percentage of H2 is 5% to 15%.

4. The method as described in claim 1, characterized in that: In step S4, the adsorption energy of the gas-phase reaction intermediate In2O on the surface of the MoS2 film is lower than its formation energy at the edge of the grown In2S3 film, so that In2S3 with uniform thickness is grown layer by layer in a thermodynamically self-limiting mode.

5. The method as described in claim 1, characterized in that: The parameters for the epitaxial reaction in step S4 are as follows: temperature zone I is set at 600–700°C, temperature zone II is set at 170–190°C, and the epitaxial isothermal time is 20–30 min.

6. The method as described in claim 1, characterized in that: In step S4, the crystal lattice of In2S3 is aligned with the orientation of MoS2 at 0° or 60°.

7. A wafer-level two-dimensional In2S3 / MoS2 van der Waals heterojunction thin film prepared by the method according to any one of claims 1 to 6, characterized in that: The heterojunction is formed by vertically stacking a single layer of MoS2 and multiple layers of In2S3. The In2S3 is directly epitaxially grown on the surface of the MoS2. The interlayer of the heterojunction is an atomically steep abrupt van der Waals interface with no atomic diffusion at the interface.

8. The wafer-level two-dimensional In2S3 / MoS2 van der Waals heterojunction thin film as described in claim 7, characterized in that: The thickness of the In2S3 is less than 2.0 nm, and the surface thickness uniformity of the heterojunction film is greater than 99.5%.

9. A photoelectric detection device, characterized in that: The wafer-level two-dimensional In2S3 / MoS2 van der Waals heterojunction thin film as described in claim 7 or 8 is used as the photoelectric active region; the device includes a substrate, a bottom electrode and a top electrode, the bottom electrode forms an electrical contact with the MoS2, and the top electrode forms an electrical contact with the In2S3, so as to construct a photogenerated carrier transport channel in a direction perpendicular to the van der Waals interface.

10. The photodetector device as described in claim 9, characterized in that: The In2S3 / MoS2 van der Waals heterojunction has a vertical Type-II band arrangement.

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