Quantum dot photoelectric detector based on Van der Waals epitaxy and preparation method thereof

Abstract

The invention provides a quantum dot photoelectric detector based on Van der Waals epitaxy, which can be applied to the technical field of semiconductors. The detector comprises a supporting substrate, a lower conducting layer, a quantum dot active layer, an upper conducting layer, an upper electrode and a lower electrode, wherein the upper electrode and the lower electrode are isolated from each other and form a vertical sandwich structure. Wherein the lower conductive layer is a lower-layer two-dimensional material with a Van der Waals surface, and the quantum dot active layer directly grows on the lower conductive layer through Van der Waals epitaxy; and the upper conductive layer is an upper-layer two-dimensional material which is transferred and covered by a dry method. The preparation method comprises the following steps: preparing a lower-layer two-dimensional material with a Van der Waals surface as an epitaxial substrate; growing a quantum dot material in molecular beam epitaxy equipment in a Van der Waals epitaxy mode; an upper-layer two-dimensional material is transferred through a dry method to form a sandwich structure; and finally, respectively preparing mutually staggered electrodes on the upper-layer two-dimensional material and the lower-layer two-dimensional material in a graphical manner.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically to a quantum dot photodetector based on van der Waals epitaxy and its fabrication method. Background Technology

[0002] Quantum dots, as typical artificial quantum structures, exhibit unique photoelectric properties closely related to their size and shape due to the quantum confinement effect caused by their confinement in three-dimensional space. They hold significant application value in cutting-edge fields such as infrared detection, single-photon sources, and quantum computing. The realization of high-performance quantum dot photodetectors hinges on the precise control of the energy level structure of the quantum dots and the heterojunction interface characteristics formed with the surrounding barrier layer, which directly determines the excitation, separation, and collection efficiency of charge carriers. Current quantum dot fabrication and device integration technologies mainly follow two routes: epitaxial growth and chemical synthesis. However, both face fundamental challenges in achieving high-performance, customizable quantum dot photodetectors.

[0003] In traditional epitaxial growth methods, strain-driven self-assembly, exemplified by the Stranski-Krastanov model, dominates. This method typically involves epitaxially growing materials like InAs with a certain lattice mismatch onto III-V single-crystal substrates such as GaAs and InP, forming size-controllable quantum dots through strain accumulation and release. While this technique can yield quantum dots with high crystal quality and uniform size distribution, its development is fundamentally limited by two factors: First, the stringent lattice matching requirements severely restrict the freedom of material selection. The quantum dot material, barrier layer material, and substrate material must meet extremely demanding lattice constant matching conditions (typically a mismatch of less than 7%), limiting the available material combinations to a few III-V systems (such as the classic AlGaAs / InAs / AlGaAs structure). This limitation results in extremely low freedom in bandgap engineering design, making it difficult to flexibly select barrier materials to control key parameters such as barrier height and quantum dot energy level positions, thus hindering precise control over detector response wavelength, dark current, and detectivity. Secondly, this method relies on lattice mismatch to generate strain. Although this intrinsic strain field drives the formation of quantum dots, it is also very easy to introduce defects such as dislocations and stacking faults inside the quantum dots and at the heterojunction interface, which become nonradiative recombination centers and impair carrier lifetime and long-term stability of the device.

[0004] Unlike the strictly epitaxial route, the colloidal chemical synthesis route offers a non-epitaxial solution. This method synthesizes colloidal quantum dots such as PbS and CdSe through solution-phase chemical reactions, and then assembles these quantum dots into thin films using processes such as spin coating and drop casting to construct devices. Its advantages include low synthesis cost, precise control of quantum dot size to match the target absorption wavelength by changing reaction conditions, and the convenience of solution processing. However, detectors constructed using this method have significant performance limitations: First, the quantum dot films formed by spin coating are typically on the micrometer scale, and the physical connections and electronic coupling between quantum dots rely on long-chain organic ligands, resulting in extremely low carrier mobility, severely limiting the device's response speed and external quantum efficiency. Second, the light absorption mechanism of such devices mainly depends on the intrinsic interband transitions of individual quantum dots; the device structure is essentially a simple thin-film resistive or Schottky junction type, lacking in-depth design of the band structure. It is difficult to construct efficient heterojunctions with specific band alignments such as type-I and type-II to achieve effective spatial separation of photogenerated carriers, thus limiting the improvement of key indicators such as detector gain and specific detectivity.

[0005] In recent years, the rise of two-dimensional layered materials, represented by graphene and transition metal chalcogenides (such as MoS2 and WSe2), has provided a revolutionary new approach to heterogeneous integration. These materials have no dangling bonds and possess atomically flat van der Waals surfaces, theoretically serving as "universal" substrates. This allows any material to be epitaxially grown on them through weak van der Waals forces, thus completely eliminating dependence on lattice matching; this mode is known as van der Waals epitaxy. This characteristic opens up unprecedented material selection space for heterogeneous material integration. Currently, van der Waals epitaxy has achieved success in growing two-dimensional materials, one-dimensional nanowires, and some three-dimensional thin films. However, how to creatively apply this paradigm to the controllable preparation of zero-dimensional quantum dot materials, and further synergistically design it with the rich band structure characteristics of two-dimensional materials (such as tunable band gaps and variable band edge positions) to construct a novel, highly tunable "two-dimensional material / quantum dot / two-dimensional material" sandwich-type photodetector structure, remains an unresolved technical challenge. Existing technologies do not yet provide a systematic method to grow high-quality quantum dots using the van der Waals surface of two-dimensional materials as an ideal epitaxial template, and on this basis, to achieve precise and flexible "bottom-up" control of the device's built-in electric field, carrier transport path and final photoelectric response characteristics by selecting two different two-dimensional materials as designable barrier layers.

[0006] In summary, existing technologies have failed to effectively address the core challenges in quantum dot photodetectors, such as limited material selection, low freedom in bandgap engineering, and difficulty in synergistically optimizing interface quality and device performance. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] To address at least one of the aforementioned problems, this invention provides a quantum dot photodetector based on van der Waals epitaxy and its fabrication method. By using the van der Waals surface of a two-dimensional layered material as a universal epitaxial substrate, the strict limitations of lattice matching in traditional heteroepitaxial methods are overcome, expanding the selection range of quantum dots and barrier layer materials. Furthermore, by combining van der Waals epitaxy technology with dry transfer processes, a vertical sandwich heterostructure consisting of a lower two-dimensional material, a quantum dot active layer, and an upper two-dimensional material is constructed. Utilizing the rich tunable band structure of the upper and lower two-dimensional materials as a designable carrier barrier, precise artificial control of the generation, separation, and transport processes of photogenerated carriers within the quantum dot is achieved. Ultimately, a high-performance quantum dot photodetector with highly customizable response wavelength, barrier height, and band structure is obtained.

[0009] (II) Technical Solution

[0010] To address the aforementioned technical problems, embodiments of the present invention propose a quantum dot photodetector based on van der Waals epitaxy and its fabrication method.

[0011] According to a first aspect of the present invention, a quantum dot photodetector based on van der Waals epitaxy is provided. The photodetector has a layered vertical structure and includes, from bottom to top, the following: a supporting substrate; a lower conductive layer comprising a lower two-dimensional material having an atomically flat van der Waals surface without dangling bonds; a quantum dot active layer composed of multiple discrete quantum dots grown on the van der Waals surface of the lower two-dimensional material via van der Waals epitaxy; an upper conductive layer comprising an upper two-dimensional material coated on the quantum dot active layer by a dry transfer process, thereby completely encapsulating the quantum dot active layer between the lower and upper conductive layers to form a van der Waals heterojunction; an upper electrode forming an ohmic contact with the upper conductive layer; and a lower electrode forming an ohmic contact with the lower conductive layer; wherein the upper and lower electrodes are offset from each other in planar projection so that when a bias voltage is applied between the upper and lower electrodes, the current channel is perpendicular to the layered structure and penetrates the quantum dot active layer.

[0012] In some exemplary embodiments, the lower two-dimensional material and the upper two-dimensional material are independently selected from transition metal chalcogenides or group IV-VI two-dimensional semiconductor materials including MoS2, MoSe2, WS2, WSe2, GeSe or SnSe.

[0013] In some exemplary embodiments, the material of the quantum dot active layer is selected from group III-V or IV-VI compound semiconductors including InAs, InSb, GaAs, GaSb or SnTe.

[0014] In some exemplary embodiments, the supporting substrate is an insulator or a semiconductor substrate with an insulating layer on its surface, including a silicon substrate with a SiO2 layer on its surface.

[0015] In some exemplary embodiments, the metal materials of the upper and lower electrodes are independently selected from Au, Pt / Au, Ti / Au, Cr / Au, or Bi / Au.

[0016] According to a second aspect of the present invention, a method for fabricating the above-mentioned quantum dot photodetector is provided, comprising: step S1, providing a lower two-dimensional material having a van der Waals surface as a lower conductive layer, and placing the lower two-dimensional material on a support substrate to form a composite substrate; step S2, placing the composite substrate in a molecular beam epitaxy apparatus, using the van der Waals surface of the lower two-dimensional material as an epitaxial substrate, growing quantum dot material in van der Waals epitaxy mode to obtain a quantum dot active layer, wherein the lower conductive layer and the quantum dot active layer constitute a heterojunction; step S3, removing the composite substrate with the heterojunction grown from the molecular beam epitaxy apparatus, and precisely covering the quantum dot material with an independently prepared upper conductive layer containing an upper two-dimensional material using a dry transfer process, forming a vertical sandwich structure including the lower two-dimensional material, quantum dots, and the upper two-dimensional material; step S4, patterning an upper electrode and a lower electrode on the upper conductive layer and the lower conductive layer, respectively, wherein the upper electrode forms electrical contact only with the upper conductive layer, the lower electrode forms electrical contact only with the lower conductive layer, and the upper electrode and the lower electrode are spatially offset from each other.

[0017] In some exemplary embodiments, in step S1, the lower two-dimensional material is prepared by mechanical exfoliation, chemical vapor deposition, or molecular beam epitaxy.

[0018] In some exemplary embodiments, in step S2, the size, areal density, and crystallinity of the quantum dot material are controlled by independently or jointly adjusting the temperature of the composite substrate, the beam intensity of the molecular beam source, and the growth time.

[0019] In some exemplary embodiments, in step S3, the dry transfer process includes a pick-and-release process using a polydimethylsiloxane stamp or a two-dimensional material transfer stage.

[0020] In some exemplary embodiments, in step S4, the upper and lower electrodes are patterned using any one of photolithography combined with thermal metal evaporation deposition, electron beam lithography, or laser direct writing technology.

[0021] (III) Beneficial Effects

[0022] As can be seen from the above technical solutions, the quantum dot photodetector based on van der Waals epitaxy and its fabrication method provided by the embodiments of the present invention have at least the following beneficial effects:

[0023] (1) Using the van der Waals surface of a two-dimensional layered material as the epitaxial substrate for quantum dots, this surface has the characteristics of no dangling bonds and atomic-level flatness, which enables the epitaxial growth of quantum dots through van der Waals forces. This method eliminates the requirement for lattice matching between the substrate, quantum dots and barrier layer materials in traditional epitaxy, thereby expanding the range of selectable quantum dot and barrier layer materials and providing more material combination possibilities for the design of device band structure.

[0024] (2) Based on the above material selection freedom, this method provides a triple regulation mechanism: ① Quantum dot energy level is tunable: by controlling the growth parameters of van der Waals epitaxy, the size and density of quantum dots can be regulated, thereby adjusting their quantum confinement energy level and absorption wavelength; ② Barrier height is tunable: by selecting two-dimensional materials with different band gaps and band edge positions as upper and lower barrier layers, the band alignment and barrier height of the heterojunction can be regulated, thereby affecting the separation and transport of charge carriers; ③ Overall performance is tunable: by combining the regulation of quantum dot energy level and two-dimensional material barrier, the device band structure and built-in electric field can be optimized, thereby adjusting the detector's response wavelength, dark current and photoresponse and other parameters.

[0025] (3) The van der Waals epitaxial mode avoids bulk defects introduced by lattice mismatch. At the same time, the interface bonding between the upper two-dimensional material and the quantum dot layer is achieved through dry transfer process, which can form a clean and low-stress van der Waals heterojunction. This is beneficial to reduce interface states and nonradiative recombination, improve the separation and collection efficiency of charge carriers, and thus improve the response speed and quantum efficiency of the device.

[0026] (4) The molecular beam epitaxy, dry transfer, and patterning processes used in this preparation method are all mature micro-nano fabrication technologies with good repeatability and controllability. This method provides a feasible technical path for the fabrication of high-performance, customizable quantum dot photodetectors and can be used in fields such as infrared detection and imaging sensing. Attached Figure Description

[0027] The above-described features, other objects, and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0028] Figure 1 The schematic diagram illustrates the structure of a quantum dot photodetector based on van der Waals epitaxy according to an embodiment of the present invention;

[0029] Figure 2 A flowchart illustrating a method for fabricating a quantum dot photodetector based on van der Waals epitaxy according to an embodiment of the present invention is shown.

[0030] Figure 3A schematic diagram illustrating the fabrication process of a quantum dot photodetector based on van der Waals epitaxy according to an embodiment of the present invention is shown; and

[0031] Figure 4 An optical micrograph of a quantum dot photodetector obtained according to Embodiment 1 of the present invention is shown schematically.

[0032] Figure label:

[0033] 1-Supporting substrate; 2-Lower conductive layer; 3-Quantum dot active layer; 4-Upper conductive layer; 5-Lower electrode; 6-Upper electrode. Detailed Implementation

[0034] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0035] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0036] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0037] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0038] Figure 1 The schematic diagram illustrates the structure of a quantum dot photodetector based on van der Waals epitaxy according to an embodiment of the present invention.

[0039] like Figure 1As shown, according to an embodiment of the present invention, a quantum dot photodetector based on van der Waals epitaxy is provided. The photodetector has a layered vertical structure and includes, from bottom to top, the following: a supporting substrate 1; a lower conductive layer 2, comprising a lower two-dimensional material having an atomically flat van der Waals surface without dangling bonds; a quantum dot active layer 3, composed of multiple discrete quantum dots, grown on the van der Waals surface of the lower two-dimensional material via van der Waals epitaxy; an upper conductive layer 4, comprising an upper two-dimensional material, covered on the quantum dot active layer 3 by a dry transfer process, thereby completely encapsulating the quantum dot active layer 3 between the lower conductive layer 2 and the upper conductive layer 4, forming a van der Waals heterojunction; an upper electrode 6 forming an ohmic contact with the upper conductive layer 4; and a lower electrode 5 forming an ohmic contact with the lower conductive layer 2. The upper electrode 6 and the lower electrode 5 are offset from each other in planar projection so that when a bias voltage is applied between the upper electrode 6 and the lower electrode 5, the current channel is perpendicular to the layered structure and penetrates the quantum dot active layer 3.

[0040] In embodiments of the present invention, the lower two-dimensional material serves as the epitaxial substrate and the bottom electrode conductive channel; the quantum dot active layer 3 serves as the light absorption and carrier generation center; the upper two-dimensional material serves as the top electrode conductive channel and the encapsulation layer; and the upper electrode 6 and the lower electrode 5 are staggered to guide the electric field to penetrate the active layer vertically. This structure establishes a carrier transport path perpendicular to the device plane, which facilitates the efficient and rapid separation of photogenerated electron-hole pairs under the action of an applied electric field and their collection by the upper electrode 6 and the lower electrode 5, respectively, thereby achieving photoelectric detection with high response speed and low dark current.

[0041] In some exemplary embodiments, the lower two-dimensional material and the upper two-dimensional material can be any two-dimensional layered material known to date. Preferably, the lower two-dimensional material and the upper two-dimensional material are independently selected from transition metal chalcogenides or group IV-VI two-dimensional semiconductor materials such as MoS2, MoSe2, WS2, WSe2, GeSe or SnSe.

[0042] Understandably, the upper two-dimensional material can be the same type of two-dimensional material as the lower two-dimensional material, or it can be a different type of two-dimensional material, depending on the pre-design of the barrier height and width. This ultimately results in a sandwich structure of two-dimensional material / quantum dot / two-dimensional material.

[0043] The band structure (such as band gap and band edge position) of two-dimensional materials is determined by their type, number of layers, and stacking method. By independently selecting the types of upper and lower two-dimensional materials, the band alignment (such as Type-I and Type-II) and barrier height of the heterojunction formed by them and the intermediate quantum dot layer can be directly controlled. This provides the freedom to design "band engineering" for the built-in electric field, carrier injection, and extraction barriers of the device. Through flexible selection of material combinations, the separation efficiency of photogenerated carriers can be optimized, and dark current can be suppressed (by increasing the barrier), thereby achieving customized control of key performance parameters such as detector response wavelength, detectivity, and operating voltage.

[0044] In some exemplary embodiments, the quantum dot material can be any non-layered elemental or compound semiconductor material that can be grown using an existing beam source in a molecular beam epitaxy system. Preferably, the material of the quantum dot active layer 3 is selected from group III-V or IV-VI compound semiconductors, including InAs, InSb, GaAs, GaSb, or SnTe. The light absorption characteristics of quantum dots are determined by both their size and the bulk band gap of the material itself. Under strong quantum confinement effects, the effective band gap of quantum dots blue-shifts as the size decreases. Group III-V and IV-VI compound semiconductors have suitable bulk band gaps in the infrared band, making them ideal active materials for constructing infrared photodetectors.

[0045] In some exemplary embodiments, the support substrate 1 is an insulator or a semiconductor substrate with an insulating layer on its surface, including a silicon substrate with a SiO2 layer on its surface. The support substrate 1 mainly serves a mechanical support function. Selecting an insulating substrate or a semiconductor substrate with an insulating layer (such as SiO2 / Si) can effectively isolate the active region of the device from the substrate electrically, prevent leakage current channels, and ensure that the applied bias voltage is mainly applied to the vertical sandwich structure.

[0046] In some exemplary embodiments, the metal materials of the upper electrode 6 and the lower electrode 5 are independently selected from Au, Pt / Au, Ti / Au, Cr / Au, or Bi / Au. The selection of electrode materials must consider their ability to form low-resistance ohmic contacts with specific two-dimensional materials. Au is often used to form good contacts with a variety of two-dimensional materials due to its high conductivity and work function characteristics. Introducing adhesion layers such as Ti and Cr (e.g., Ti / Au) can enhance the adhesion and interface stability between the metal and the two-dimensional material. By optimizing the electrode materials and their structure (e.g., by introducing adhesion layers), contact resistance can be reduced, Joule heat loss can be decreased, and efficient injection and extraction of electrical signals can be ensured, thereby improving the overall photoelectric conversion efficiency and reliability of the detector.

[0047] Figure 2 A flowchart illustrating a method for fabricating a quantum dot photodetector based on van der Waals epitaxy according to an embodiment of the present invention is shown.

[0048] like Figure 2 As shown, the fabrication method of the quantum dot photodetector based on van der Waals epitaxy according to an embodiment of the present invention includes steps S1 to S4.

[0049] In step S1, a lower two-dimensional material with a van der Waals surface is provided as the lower conductive layer 2, and the lower two-dimensional material is placed on the supporting substrate 1 to form a composite substrate. The resulting structure is shown in [reference needed]. Figure 3 (a) in the middle.

[0050] Optionally, in step S1, the lower two-dimensional material is prepared by mechanical exfoliation, chemical vapor deposition, or molecular beam epitaxy. The lower two-dimensional material can be any known two-dimensional layered material, preferably a common and typical two-dimensional material such as MoS2, MoSe2, WS2, WSe2, GeSe, or SnSe.

[0051] Two-dimensional materials have atomically flat surfaces free of dangling bonds, forming ideal van der Waals epitaxial interfaces that avoid stress and defects introduced by lattice mismatch. Different fabrication methods can control the crystal quality, number of layers, and area of ​​two-dimensional materials to meet various application requirements. This enables precise control over the surface properties of epitaxial substrates, providing a stress-free, dangling-bond-free clean surface for subsequent high-quality quantum dot epitaxial growth, while also broadening the range of substrate material choices.

[0052] In step S2, the composite substrate is placed in a molecular beam epitaxy apparatus, using the van der Waals surface of the lower two-dimensional material as the epitaxial substrate. Quantum dot material is grown in van der Waals epitaxy mode to obtain quantum dot active layer 3. The lower conductive layer 2 and the quantum dot active layer 3 form a heterojunction. The resulting structure is described in [reference needed]. Figure 3 (b) in the middle.

[0053] Optionally, in step S2, the size, areal density, and crystal quality of the quantum dot material are controlled by independently or jointly adjusting the temperature of the composite substrate, the beam intensity of the molecular beam source, and the growth time.

[0054] In van der Waals epitaxy, quantum dot materials are bonded to a two-dimensional substrate via weak van der Waals forces, requiring no lattice matching. The growth process is dominated by surface diffusion and nucleation kinetics. By adjusting temperature, beam current, and time, the nucleation density, size distribution, and crystal integrity of the quantum dots can be precisely controlled. This enables flexible control over the size, density, and mass of quantum dots, thereby allowing for adjustment of their quantum confinement energy levels and optical absorption characteristics. This provides a foundation for the designability of device response wavelengths while avoiding the mismatch defects found in traditional epitaxy.

[0055] In step S3, the composite substrate with the heterojunction grown is removed from the molecular beam epitaxy equipment. Using a dry transfer process, a separately prepared upper conductive layer 4 containing the upper two-dimensional material is precisely coated onto the quantum dot material, forming a vertical sandwich structure comprising the lower two-dimensional material, quantum dots, and the upper two-dimensional material. The resulting structure is described in [reference needed]. Figure 3 (c) in the middle.

[0056] Optionally, in step S3, the dry transfer process includes a pick-and-release process using a polydimethylsiloxane stamp or a two-dimensional material transfer stage.

[0057] The dry transfer process allows for the precise bonding of pre-prepared upper two-dimensional materials to the surface of a quantum dot layer under solvent-free and pollution-free conditions, forming a clean van der Waals interface. This interface relies on van der Waals forces for bonding, eliminating the need for epitaxial growth and avoiding thermal damage or chemical contamination to the quantum dot layer. This achieves non-destructive encapsulation of the quantum dot active layer 3, forming a structurally complete and clearly defined vertical heterojunction. This facilitates longitudinal carrier transport and interfacial recombination suppression, while also providing selectivity for the upper barrier layer in bandgap engineering.

[0058] In step S4, an upper electrode 6 and a lower electrode 5 are patterned and fabricated on the upper conductive layer 4 and the lower conductive layer 2, respectively. The upper electrode 6 forms electrical contact only with the upper conductive layer 4, and the lower electrode 5 forms electrical contact only with the lower conductive layer 2. The upper electrode 6 and the lower electrode 5 are spatially offset from each other. The resulting structure is shown in [reference needed]. Figure 3 (d) in the middle.

[0059] Optionally, in step S4, the upper electrode 6 and the lower electrode 5 are patterned using any one of photolithography combined with metal thermal evaporation deposition, electron beam lithography, or laser direct writing technology.

[0060] The patterned fabrication of the electrodes ensures precise positioning and spatial isolation of the electrical contacts, allowing the electric field under applied bias to penetrate the sandwich structure vertically, driving photogenerated carriers to separate longitudinally and be collected by the corresponding electrodes. Different patterning techniques offer flexible options in terms of accuracy, efficiency, and applicable scale. This achieves low-resistance, high-precision ohmic contacts, optimizing the electrical injection and signal extraction efficiency of the device. The spatially staggered electrode design ensures a uniform distribution of the electric field in the active region, which is beneficial for improving photoelectric conversion efficiency and response consistency, and facilitates device integration and testing.

[0061] Example 1:

[0062] A method for fabricating a MoS2 / InAs / MoS2 quantum dot photodetector on a SiO2 / Si supported substrate 1, the specific process of which is as follows:

[0063] First, MoS2 nanosheets were obtained on a SiO2 / Si support substrate 1. SiO2 / Si serves only as the support substrate 1. The MoS2 nanosheets have lateral micrometer-scale dimensions and longitudinal nanometer-scale thickness, and were placed on the SiO2 / Si support substrate 1 using mechanical exfoliation and dry transfer techniques.

[0064] Secondly, InAs quantum dots were prepared in a molecular beam epitaxy system using MoS2 nanosheets on a SiO2 / Si support substrate 1 as the epitaxial substrate. Specifically, the MoS2 nanosheets on the SiO2 / Si support substrate 1 were loaded into the buffer chamber of the molecular beam epitaxy equipment and degassed at, for example, 200°C for 1 hour. After degasing, the substrate was loaded into the growth chamber. The In source and As source temperatures were set at, for example, 650°C and 170°C, respectively, in the growth chamber. After the baffle was opened while the substrate was rotating, it was maintained for, for example, 2-3 minutes, to obtain a 2D / 0D mixed-dimensional heterojunction of MoS2 / InAs.

[0065] Next, the MoS2 / InAs mixed-dimensional heterojunction is removed and another MoS2 nanosheet is transferred onto it using a dry transfer method. Specifically, in an atmospheric environment, a two-dimensional material transfer platform is used to dry transfer mechanically exfoliated MoS2 nanosheets onto the MoS2 / InAs mixed-dimensional heterojunction using PDMS adhesive, constructing a MoS2 / InAs / MoS2 sandwich structure. In this structure, the upper MoS2 layer does not completely cover the lower MoS2 layer, leaving electrode positions on the lower MoS2 layer.

[0066] Next, the upper electrode 6 and the lower electrode 5 are fabricated on the upper / lower MoS2 using a patterning process. Specifically, the electrodes at both ends can be fabricated on the MoS2 / InAs / MoS2 sandwich structure using processes such as spin-coating photoresist, masking, ultraviolet lithography, development, thermal evaporation of metal, and lift-off, thus constructing a quantum dot photodetector.

[0067] Figure 4 An optical micrograph of a quantum dot photodetector obtained according to Embodiment 1 of the present invention is shown schematically.

[0068] like Figure 4As shown, the quantum dot photodetector obtained according to Embodiment 1 of the present invention exhibits a clear device morphology under an optical microscope. The figure reveals a sandwich heterojunction structure in the central region, formed by encapsulation of two layers of two-dimensional materials, with clear boundaries, indicating that the dry transfer process achieves precise coverage of the upper two-dimensional material on the quantum dot layer. Independent metal upper electrodes 6 and lower electrodes 5 are fabricated on both sides of this sandwich structure. The electrodes have regular morphologies and good contact with the target two-dimensional material layer, and are spatially offset, meeting the design requirements of a vertical device structure. The entire device is constructed on a silicon support substrate 1 with a SiO2 layer on its surface, exhibiting a complete structure and demonstrating the good process controllability of this fabrication method.

[0069] Those skilled in the art will understand that the features described in the various embodiments of the present invention can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments of the present invention can be combined and / or combined in various ways without departing from the spirit and teachings of the present invention. All such combinations and / or combinations fall within the scope of the present invention.

Claims

1. A quantum dot photodetector based on van der Waals epitaxy, characterized in that, The photodetector has a layered vertical structure, comprising the following components arranged sequentially from bottom to top: Support substrate; The lower conductive layer includes a lower two-dimensional material having an atomically flat van der Waals surface free of dangling bonds. The quantum dot active layer is composed of multiple discrete quantum dots, which are grown on the van der Waals surface of the underlying two-dimensional material via van der Waals epitaxy. The upper conductive layer, comprising an upper two-dimensional material, is coated on the quantum dot active layer by a dry transfer process, thereby completely encapsulating the quantum dot active layer between the lower conductive layer and the upper conductive layer to form a van der Waals heterojunction. The upper electrode forms an ohmic contact with the upper conductive layer; The lower electrode forms an ohmic contact with the lower conductive layer; The upper and lower electrodes are staggered in planar projection so that when a bias voltage is applied between the upper and lower electrodes, the current channel is perpendicular to the layered structure and penetrates the quantum dot active layer.

2. The quantum dot photodetector based on van der Waals epitaxy according to claim 1, characterized in that, The lower two-dimensional material and the upper two-dimensional material are independently selected from transition metal chalcogenides or group IV-VI two-dimensional semiconductor materials including MoS2, MoSe2, WS2, WSe2, GeSe or SnSe.

3. The quantum dot photodetector based on van der Waals epitaxy according to claim 1, characterized in that, The material of the quantum dot active layer is selected from group III-V or IV-VI compound semiconductors including InAs, InSb, GaAs, GaSb or SnTe.

4. The quantum dot photodetector based on van der Waals epitaxy according to claim 1, characterized in that, The supporting substrate is an insulator or a semiconductor substrate with an insulating layer on its surface, including a silicon substrate with a SiO2 layer on its surface.

5. The quantum dot photodetector based on van der Waals epitaxy according to claim 1, characterized in that, The metal materials of the upper and lower electrodes are independently selected from Au, Pt / Au, Ti / Au, Cr / Au, or Bi / Au.

6. A method for fabricating a quantum dot photodetector as described in any one of claims 1 to 5, characterized in that, include: Step S1: Provide a lower two-dimensional material with a van der Waals surface as a lower conductive layer, and place the lower two-dimensional material on a support substrate to form a composite substrate; Step S2: Place the composite substrate in a molecular beam epitaxy apparatus, use the van der Waals surface of the lower two-dimensional material as the epitaxial substrate, grow quantum dot material in van der Waals epitaxy mode to obtain a quantum dot active layer, and the lower conductive layer and the quantum dot active layer form a heterojunction. Step S3: The composite substrate with the heterojunction grown is removed from the molecular beam epitaxy equipment. A separately prepared upper conductive layer containing the upper two-dimensional material is precisely covered on the quantum dot material by a dry transfer process to form a vertical sandwich structure including the lower two-dimensional material, quantum dots and the upper two-dimensional material. Step S4: Pattern an upper electrode and a lower electrode are fabricated on the upper conductive layer and the lower conductive layer, respectively. The upper electrode forms electrical contact only with the upper conductive layer, and the lower electrode forms electrical contact only with the lower conductive layer. The upper electrode and the lower electrode are spatially offset from each other.

7. The preparation method according to claim 6, characterized in that, In step S1, the lower two-dimensional material is prepared by mechanical exfoliation, chemical vapor deposition, or molecular beam epitaxy.

8. The preparation method according to claim 6, characterized in that, In step S2, the size, areal density, and crystal quality of the quantum dot material are controlled by independently or jointly adjusting the temperature of the composite substrate, the beam intensity of the molecular beam source, and the growth time.

9. The method according to claim 6, characterized in that, In step S3, the dry transfer process includes a pick-and-release process using a polydimethylsiloxane stamp or a two-dimensional material transfer stage.

10. The method according to claim 6, characterized in that, In step S4, the upper and lower electrodes are patterned using any one of photolithography combined with metal thermal evaporation deposition, electron beam lithography, or laser direct writing technology.

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