High-speed photoelectric detector based on mixed surface plasma slit waveguide and preparation method thereof

Abstract

The invention discloses a high-speed photoelectric detector based on a mixed surface plasma slit waveguide and a preparation method of the high-speed photoelectric detector, and belongs to the technical field of integrated optoelectronic devices. Comprising a substrate, a mixed surface plasma slit waveguide, metal gates on the two sides, a Van der Waals heterostructure and metal source and drain electrodes on the two sides. The Van der Waals heterojunction is composed of an upper hexagonal boron nitride layer, a lower hexagonal boron nitride layer and a middle two-dimensional material. According to the invention, the hexagonal boron nitride is used for packaging the two-dimensional material, so that the carrier mobility of the two-dimensional material can be improved, and the photoelectric response of the detector is enhanced; according to the invention, the distance between the metal gate and the optical waveguide is shortened, a transverse electric mode transmitted in the waveguide is regulated and controlled, a hybrid surface plasma slit mode with a strong local area is formed, the interaction between an optical field and a two-dimensional material layer is enhanced, and the responsivity of the detector is remarkably improved; the Fermi level of the two-dimensional material can be dynamically regulated and controlled by introducing the grid bias voltage, the photo-generated current separation efficiency is enhanced, and the responsivity and the signal-to-noise ratio of the detector can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated optoelectronic devices, and more specifically, relates to a high-speed photodetector based on a hybrid surface plasmon slit waveguide and a preparation method thereof. Background Art

[0002] In an integrated optoelectronic circuit, a photodetector is one of the core devices at the receiving end. By utilizing the photoelectric effect of materials, it converts an optical signal into an electrical signal, and then detects attributes such as the intensity, wavelength, and phase of light. Common photodetector material systems include III-V materials, germanium silicon, and two-dimensional materials, etc.

[0003] Two-dimensional materials (graphene, transition metal sulfides, black phosphorus, etc.) with their atomic layer thickness (0.3 - 3 nm), tunable bandgap (black phosphorus, molybdenum disulfide), and strong light-matter interaction (molybdenum disulfide) provide a breakthrough solution for new photodetectors: graphene can achieve an ultra-wide spectral response from terahertz to ultraviolet due to its zero bandgap, and at the same time, its ultrafast carrier mobility is expected to achieve an ultra-high photoelectric response bandwidth (theoretically up to 500 GHz); transition metal sulfides can accurately cover the near-infrared communication band (1310 / 1550 nm) through layer number regulation (1 - 3 layers).

[0004] Although photodetectors based on these material systems have achieved good performance, there are still some deficiencies, such as low responsivity, low signal-to-noise ratio, relatively complex preparation processes, and high costs, etc. Summary of the Invention

[0005] Aiming at the defects of the prior art, the purpose of the present invention is to provide a high-speed photodetector based on a hybrid surface plasmon slit waveguide and a preparation method thereof, aiming to solve the problems of low responsivity and low signal-to-noise ratio of the detector.

[0006] The high-speed photodetector based on a hybrid surface plasmon slit waveguide proposed by the present invention includes a substrate, a hybrid surface plasmon slit waveguide disposed on the substrate, and a van der Waals heterojunction disposed on the hybrid surface plasmon slit waveguide;

[0007] The hybrid surface plasmon slit waveguide includes a waveguide, a first metal electrode and a second metal electrode respectively located on both sides of the waveguide. The first metal electrode and the second metal electrode are the gates. The first metal electrode and the second metal electrode respectively maintain the same and unchanged spacing from the waveguide, and respectively form a first air slit and a second air slit; the width of the waveguide changes gradually as decreasing, remaining unchanged, and gradually increasing along the axial direction, respectively forming a first tapered waveguide region, a straight waveguide region, and a second tapered waveguide region;

[0008] The van der Waals heterojunction includes, from bottom to top, a first hexagonal boron nitride layer, a two-dimensional material layer, and a second hexagonal boron nitride layer. The range of the hybrid surface plasma slit waveguide covered by the van der Waals heterojunction includes at least a straight waveguide region and a first metal electrode and a second metal electrode adjacent thereto. A third metal electrode and a fourth metal electrode are provided at both ends of the two-dimensional material layer, which are a source and a drain, respectively.

[0009] The present invention also provides a method for preparing the hybrid surface plasmon slit waveguide photodetector, which comprises the following steps:

[0010] A waveguide is prepared on a substrate by electron beam exposure and inductive plasma etching; a metal film is deposited by electron beam evaporation, and a first metal electrode and a second metal electrode are prepared by maintaining a first air slit and a second air slit on both sides of the waveguide, respectively, to form a hybrid surface plasma slit waveguide; the stacked van der Waals heterojunction is transferred to the hybrid surface plasma slit waveguide by a dry method to form a first hexagonal boron nitride layer, a two-dimensional material layer and a second hexagonal boron nitride layer; the van der Waals heterojunction is processed by electron beam exposure, reactive ion etching or inductive plasma etching to expose the two-dimensional material layer, and a metal film is deposited by electron beam evaporation to prepare a third metal electrode and a fourth metal electrode.

[0011] Compared with the prior art, the above technical solutions conceived by the present invention can achieve the following

[0012] Beneficial effects:

[0013] (1) The hybrid surface plasmon slit waveguide structure proposed in the present invention regulates the transverse electric mode transmitted in the waveguide by shortening the distance between the metal gate and the optical waveguide, and utilizes the hybrid slit waveguide mode to form a strongly localized hybrid surface plasmon slit mode, which is mainly distributed in the two air slits, which is beneficial to enhance the interaction between light and the two-dimensional material layer and significantly improve the responsiveness of the detector.

[0014] (2) The first metal electrode and the second metal electrode on both sides of the waveguide can act as the gate of the detector, while the first hexagonal boron nitride layer serves as the gate dielectric. This design can not only achieve multi-dimensional control of the electronic structure and carrier transport properties of two-dimensional materials, but also achieve precise control of the local Seebeck coefficient, so that the detector can work on the photothermoelectric effect and thus significantly improve the signal-to-noise ratio of the detector.

[0015] (3) The use of hexagonal boron nitride to encapsulate two-dimensional materials can significantly improve the electrical properties (carrier mobility), optical properties (charge uniformity) and environmental stability of two-dimensional materials through atomic-level interface protection, scattering suppression and environmental isolation, thereby enhancing the photoelectric response of the detector, making it possible to achieve high-performance photoelectric detectors with high speed, high response and high repeatability. Brief Description of the Drawings

[0016] Figure 1 The side view of the photodetector based on the hybrid surface plasmon slit waveguide provided by the present invention.

[0017] Figure 2 The top view of the photodetector based on the hybrid surface plasmon slit waveguide provided by the present invention.

[0018] Figure 3 The simulated mode field distribution diagram of the hybrid surface plasmon slit.

[0019] Figure 4 The simulation diagram of the absorption rate of the photodetector based on the hybrid surface plasmon slit waveguide provided in Embodiment 1 of the present invention; (a) is the metal absorption loss diagram, (b) is the graphene absorption loss diagram, and (c) is the absorption ratio diagram of monolayer graphene.

[0020] Figure 5 The metallographic microscope diagram of the photodetector based on the hybrid surface plasmon slit waveguide provided in Embodiment 2 of the present invention.

[0021] Figure 6 The flowchart of the preparation method of the photodetector based on the hybrid surface plasmon slit waveguide provided in Embodiment 2 of the present invention.

[0022] Reference Numerals: 1, substrate; 2, waveguide; 3, first air slit; 4, second air slit; 5, first metal electrode; 6, second metal electrode; 7, first hexagonal boron nitride layer; 8, two-dimensional material layer; 9, second hexagonal boron nitride layer; 10, third metal electrode; 11, fourth metal electrode. Detailed Description of the Invention

[0023] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present 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 only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0024] The photodetector based on the hybrid surface plasmon slit waveguide provided in the embodiment of the present invention has a structural schematic diagram as shown in Figure 1 and 2 shown. The photodetector includes a substrate, on which a hybrid surface plasmon slit waveguide is provided for enhancing the interaction between light and two-dimensional materials; above the hybrid surface plasmon slit waveguide is a van der Waals heterojunction, and a source electrode and a drain electrode are provided on both sides thereof. Among them, the length, width and height directions are defined as the x, y and z directions respectively.

[0025] Specifically, the hybrid surface plasma slit waveguide is provided by a first metal electrode 5, a first air slit 3, a waveguide 2, a second air slit 4, and a second metal electrode 6 on a substrate 1, which are sequentially arranged along the y direction and sequentially connected;

[0026] Specifically, the hybrid surface plasma slit waveguide is arranged by a first metal electrode 5, a first air slit 3, a waveguide 2, a second air slit 4, and a second metal electrode 6 on a substrate 1, which are arranged in sequence along the y direction and connected in sequence; the van der Waals heterojunction is arranged by a first hexagonal boron nitride layer 7, a two-dimensional material layer 8, and a second hexagonal boron nitride layer 9 on the hybrid surface plasma slit waveguide, which are arranged in sequence along the z direction and connected in sequence; the third metal electrode 10 and the fourth metal electrode 11 are directly connected to the van der Waals heterojunction in the y direction, respectively, as the source and drain of the detector.

[0027] The hybrid surface plasma slit waveguide structure provided by the embodiment of the present invention can provide a strong localized light field, which is mainly distributed in the air slit, which is beneficial to enhancing the interaction between light and the two-dimensional material layer and is used to improve the device responsiveness.

[0028] At the same time, in the embodiment of the present invention, the first metal electrode 5 and the second metal electrode 6 can act as the gate of the detector, and the first hexagonal boron nitride layer 7 is the gate dielectric. This design can not only realize multi-dimensional regulation of the electronic structure and carrier transport characteristics of two-dimensional materials, but also realize precise regulation of the local Seebeck coefficient, significantly improving the signal-to-noise ratio of the detector.

[0029] In addition, the present invention uses hexagonal boron nitride packaging to significantly improve the electrical properties, optical properties and environmental stability of two-dimensional materials through atomic-level interface protection, scattering suppression and environmental isolation, making it possible to achieve high-performance photodetectors with high speed, high response and high repeatability.

[0030] The material of the substrate 1 includes at least one of silicon, silicon dioxide, lithium niobate, lithium tantalate, gallium arsenide, and indium phosphide.

[0031] The material of the waveguide 2 includes at least one of silicon, silicon nitride, lithium niobate, lithium tantalate, gallium arsenide, germanium, and indium phosphide.

[0032] The structures of the first metal electrode 5, the second metal electrode 6, the third metal electrode 10 and the fourth metal electrode 11 are composed of an adhesion layer and a conductive layer, wherein the conductive layer material includes at least one of gold, silver and copper, and the adhesion layer material includes at least one of chromium, nickel, titanium and palladium.

[0033] The material of the two-dimensional material layer 8 includes at least one of graphene, transition metal sulfides (MX2, M = Mo, W, Re; X = S, Se, Te), black phosphorus, MXenes, two-dimensional metal halides, or topological insulator materials.

[0034] The waveguide 2 has a size of 50 - 600 nm in the z direction and a size of 100 - 1000 nm in the y direction.

[0035] The first metal electrode 5 and the second metal electrode 6 have a size of 50 - 600 nm in the z direction and a size of 100 - 600 nm in the y direction.

[0036] The first hexagonal boron nitride layer and the second hexagonal boron nitride layer have a size of 1 - 60 nm in the z direction and a size of 0.7 - 10 μm in the y direction.

[0037] The two-dimensional material layer is a single layer or multiple layers, preferably a twisted bilayer, with a relative twist angle of 1° to 15°, preferably 3° to 5°, and more preferably 4° ± 0.5°; it has a size of 0.34 - 50 nm in the z direction and a size of 1 - 10 μm in the y direction.

[0038] The third metal electrode and the fourth metal electrode have a size of 10 - 200 nm in the z direction.

[0039] As Figure 2 shown, the photodetector further includes two tapered mode converters disposed on the substrate 1, and the main purpose is to achieve the conversion from the transverse electric mode of the strip waveguide layer to the hybrid surface plasmon slit mode; for the waveguide 2, an inverted cone structure is adopted, that is, the width gradually decreases, and the first metal electrode 5 and the second metal electrode 6 on both sides adopt opposite cone structures, with their tapers being adapted to each other and separated by an air slit, and at the same time, a strip structure is used to connect to the electrode pad.

[0040] For ease of understanding, the specific embodiments of the present invention will be described by way of examples.

[0041] Example 1:

[0042] The mode field distribution diagram of the hybrid surface plasmon slit, as Figure 3 shown, is a hybrid plasmonic slit waveguide composed of a silicon waveguide and metal electrodes, where the substrate is silica and the upper cladding is air. Compared with the common strip waveguide, the optical field of the hybrid plasmonic slit waveguide is more concentrated in the slit, which helps to enhance the light-matter interaction and improve the detector responsivity.

[0043] Figure 4Shows the absorption rate spectrum of a photodetector based on a hybrid surface plasmon slit, where the two-dimensional material layer is monolayer graphene, the thickness of the first hexagonal boron nitride layer and the second hexagonal boron nitride layer is 10 nm each, the thickness of the silicon waveguide is 135 nm, W Si is the width of the silicon waveguide, W slot is the width of the air slit, α m is the absorption loss of graphene, α g is the absorption loss of graphene, η g is the absorption ratio of graphene. It can be seen from the figure that as W Si and W slot decrease, the distribution of the mode at this time is mainly concentrated at the four vertices of the metal electrode, corresponding to a stronger surface plasmon mode. The increasing rate of α m is much higher than that of α g , that is, η g is lower. Although the size of the device reaching saturated absorption is small at this time, the low absorption rate will result in a low responsivity; when W Si gradually increases to around 400 nm, the mode is mainly distributed in the air slit at this time, α m is lower, while α g is higher, corresponding to a moderate η g , and the size of the device is also moderate at this time; as W Si further increases, the mode distribution gradually approaches the core layer of the silicon waveguide at this time, which is similar to the transverse electric mode distribution of the strip waveguide. α m is very low, and α g is also small. Although a relatively high η g is achieved at this time, the size of the device is long, and it is difficult to realize a photodetector with a large bandwidth. Therefore, when W Si = 400 nm and W slot = 100 nm are selected, α m = 0.16 dB / μm, α g = 0.20 dB / μm, η g = 55.2%, the size reaching saturated absorption is 36 μm, and the absorption coefficient of graphene is increased by nearly 3 times compared with that of the ordinary strip waveguide. Generally speaking, this scheme is expected to realize a high-speed, high-responsivity and high-stability photodetector.

[0044] Example 2:

[0045] The photodetector based on a hybrid surface plasmon slit waveguide in this embodiment includes a silicon-based substrate and a hybrid surface plasmon slit waveguide structure disposed thereon. The waveguide is composed of a strip-shaped silicon with a width of 400 nm and a height of 135 nm and symmetrically distributed metal gates on both sides. The metal gate is made of 5 nm chromium and 130 nm gold, with a spacing of 100 nm from the strip-shaped silicon, and the total length of the waveguide is 30 μm. An upper layer of 15 nm hexagonal boron nitride, twisted bilayer graphene with a twist angle of 4°, and an upper layer of 20 nm h-BN are sequentially stacked above the waveguide to form a van der Waals heterojunction. A source electrode and a drain electrode are provided on both sides of the heterojunction. The electrodes are prepared by electron beam evaporation of 5 nm chromium and 50 nm gold. The metallographic microscope image of the photodetector based on the hybrid surface plasmon slit waveguide provided in this embodiment is shown in Figure 5 .

[0046] See Figure 6 As shown, this embodiment of the present invention provides a method for preparing a photodetector based on a hybrid surface plasmon slit waveguide, including the following steps:

[0047] S1: Pattern the high refractive index layer 2 on the substrate 1 by electron beam lithography and inductively coupled plasma etching to prepare the waveguide.

[0048] S2: Deposit a metal thin film by electron beam evaporation to prepare the first metal electrode 5 and the second metal electrode 6.

[0049] S3: Transfer the stacked van der Waals heterojunction to the waveguide 2, the first air layer 3, the second air layer 4, the first metal electrode 5, and the second metal electrode 6 by dry transfer to form the first hexagonal boron nitride layer 7, the two-dimensional material layer 8, and the second hexagonal boron nitride layer 9.

[0050] S4: Process the van der Waals heterojunction by electron beam lithography, reactive ion etching, or inductively coupled plasma etching to expose the two-dimensional material layer 8, and deposit a metal thin film by electron beam evaporation to prepare the third metal electrode 10 and the fourth metal electrode 11.

[0051] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-speed optoelectronic detector based on a hybrid surface plasmon slit waveguide, characterized in that It includes a substrate (1), a hybrid surface plasmon slit waveguide, and a van der Waals heterojunction, which are sequentially arranged from bottom to top; The hybrid surface plasmon slit waveguide includes a waveguide (2), a first metal electrode (5), and a second metal electrode (6) located on both sides of the waveguide (2) respectively. The first metal electrode (5) and the second metal electrode (6) are respectively kept at the same and unchanged spacing from the waveguide (2), and a first air slit (3) and a second air slit (4) are respectively formed; the width of the waveguide (2) changes gradually decreasing, remaining unchanged, and gradually increasing along the axial direction, forming a first tapered waveguide region, a straight waveguide region, and a second tapered waveguide region respectively; The van der Waals heterojunction sequentially includes a first hexagonal boron nitride layer (7), a two-dimensional material layer (8), and a second hexagonal boron nitride layer (9) from bottom to top. The range where the van der Waals heterojunction covers the hybrid surface plasmon slit waveguide includes at least the straight waveguide region and the adjacent first metal electrode (5) and second metal electrode (6); third metal electrodes (10) and fourth metal electrodes (11) are respectively provided at both ends of the two-dimensional material layer (8).

2. The high-speed photodetector according to claim 1, characterized in that, The width and thickness directions of the substrate (1) are respectively defined as the y and z directions. The size of the waveguide (2) in the z direction is 50 - 600 nm, and the size in the y direction is 100 - 1000 nm; the sizes of the first air slit (3) and the second air slit (4) in the y direction are 10 - 200 nm.

3. The high-speed photodetector according to claim 2, characterized in that, The sizes of the first metal electrode (5) and the second metal electrode (6) in the z direction are 50 - 600 nm, and the sizes in the y direction are 100 - 600 nm.

4. The high-speed photodetector according to claim 2, wherein The sizes of the first hexagonal boron nitride layer (7) and the second hexagonal boron nitride layer (9) in the z direction are 1 - 60 nm, and the sizes in the y direction are 1 - 10 μm.

5. The high-speed photodetector according to claim 1, characterized in that The two-dimensional material layer (8) is monolayer or multilayer.

6. The high-speed photodetector according to claim 1, characterized in that, The sizes of the third metal electrode (10) and the fourth metal electrode (11) in the z direction are 10 - 200 nm.

7. The high-speed photodetector according to claim 1, wherein Both the third metal electrode (10) and the fourth metal electrode (11) include an adhesion layer and a conductive layer. The material of the conductive layer includes at least one of gold, silver, and copper, and the material of the adhesion layer includes at least one of chromium, nickel, titanium, and palladium.

8. The high-speed photodetector according to claim 1, characterized in that, The material of the two-dimensional material layer (8) includes at least one of graphene, transition metal sulfides, black phosphorus, MXenes, two-dimensional metal halides, or topological insulator materials.

9. The high-speed photodetector according to claim 1, characterized in that, The material of the substrate (1) includes at least one of silicon, silicon dioxide, lithium niobate, lithium tantalate, gallium arsenide, and indium phosphide; the material of the waveguide (2) includes at least one of silicon, silicon nitride, lithium niobate, lithium tantalate, gallium arsenide, germanium, and indium phosphide.

10. A method for fabricating a high-speed photodetector based on a hybrid surface plasmon slit waveguide according to any one of claims 1 to 9, characterized in that, It includes the following steps: Prepare the waveguide (2) on the substrate (1); Prepare the first metal electrode (5) and the second metal electrode (6) on both sides of the waveguide (2) while keeping the first air slit (3) and the second air slit (4) respectively, to form a hybrid surface plasmon slit waveguide; Transfer the stacked van der Waals heterojunction onto the hybrid surface plasmon slit waveguide to successively form a first hexagonal boron nitride layer (7), a two-dimensional material layer (8), and a second hexagonal boron nitride layer (9); process the van der Waals heterojunction by electron beam lithography, reactive ion etching, or inductively coupled plasma etching to expose the two-dimensional material layer (8), and fabricate a third metal electrode (10) and a fourth metal electrode (11) at both ends of the two-dimensional material layer (8).

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