Solar-blind ultraviolet detector and preparation method therefor

Abstract

A solar-blind ultraviolet detector and a preparation method therefor, which are applied to the technical field of photoelectric detection. The solar-blind ultraviolet detector comprises: a substrate, wherein the material of the substrate is lithium niobate, and the upper surface of the substrate is provided with two opposite vertical trenches; a first electrode, which is disposed in one of the vertical trenches; and a second electrode, which is disposed in the other vertical trench, wherein a voltage bias is applied between the first electrode and the second electrode. The solar-blind ultraviolet detector has the advantages of low dark current, high response performance, ease of large-scale manufacturing, device miniaturization, etc.

Description

Solar-blind ultraviolet detector and its preparation method

[0001] This application claims priority to Chinese Patent Application No. 202411704501.8, filed on November 26, 2024, entitled "Solar-blind Ultraviolet Detector and Preparation Method Thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of photoelectric detection technology, and in particular to a solar-blind ultraviolet detector and its preparation method. Background Technology

[0003] Solar-blind ultraviolet light, also known as UV-C ultraviolet light, refers to light with wavelengths in the range of 200-280 nm. This type of ultraviolet light is needed for detection in various scenarios, including environmental monitoring and pollution control, medical and disinfection equipment, high-speed optical communication, security and monitoring systems, consumer electronics, and wearable devices. Traditional solar-blind ultraviolet detectors suffer from problems such as high dark current, poor response performance, and difficulty in industrial manufacturing. Summary of the Invention

[0004] The purpose of this application is to at least solve one of the aforementioned technical defects, and in particular to provide a solar-blind ultraviolet detector with low dark current, high response performance and suitability for large-scale industrial manufacturing.

[0005] In a first aspect, this application provides a solar-blind ultraviolet detector, comprising:

[0006] The substrate is made of lithium niobate, and two opposing vertical grooves are formed on the upper surface of the substrate.

[0007] The first electrode is disposed in one of the vertical trenches;

[0008] The second electrode is disposed in another vertical trench; a voltage bias is applied between the first electrode and the second electrode.

[0009] In one embodiment, the solar-blind ultraviolet detector further includes an adhesion layer, through which the first electrode and the second electrode are bonded to corresponding vertical trenches.

[0010] In one embodiment, the adhesive layer is made of chromium or titanium and has a thickness of 5 nm to 10 nm.

[0011] In one embodiment, the distance between the first electrode and the second electrode is 5nm-1000nm.

[0012] In one embodiment, the vertical trench has a width of 50nm-100μm, a length of 1μm-1mm, and a depth of 10nm-100μm.

[0013] In one embodiment, the materials of the first electrode and the second electrode include one or more of gold, silver, platinum, palladium, copper, zinc, aluminum, and graphene.

[0014] In one embodiment, the substrate is a 128° Y-cut, X-cut, or Z-cut wafer.

[0015] In one embodiment, the thickness of the substrate is 100μm-1000μm.

[0016] Secondly, this application provides a method for preparing a solar-blind ultraviolet detector, used to prepare the solar-blind ultraviolet detector in any of the above embodiments. The preparation method includes:

[0017] Two opposing vertical trenches were etched on a lithium niobate substrate;

[0018] A first electrode and a second electrode are deposited in a vertical trench, respectively; a voltage bias is applied between the first electrode and the second electrode.

[0019] In one embodiment, a first electrode and a second electrode are deposited respectively within a vertical trench, including:

[0020] Adhesion layers were deposited in the vertical trenches respectively;

[0021] The first electrode and the second electrode are deposited on the adhesion layer, respectively.

[0022] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:

[0023] This solar-blind ultraviolet detector, by using lithium niobate as the substrate material and combining a vertical trench structure with a reasonable electrode design, effectively optimizes the generation and collection of photogenerated carriers. It can not only sensitively detect weak solar-blind ultraviolet light, greatly improving detection sensitivity, but also achieve the expected detection effect without relying on advanced and expensive manufacturing processes. It is highly flexible, efficient and low-cost, which is conducive to industrial-scale production. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 is a schematic diagram of the structure of a solar-blind ultraviolet detector provided in an embodiment of this application;

[0026] Figure 2 is a schematic diagram of the structure of a solar-blind ultraviolet detector in another embodiment of this application;

[0027] Figure 3 is a spectrum obtained by photoluminescence detection using a solar-blind ultraviolet detector according to a specific embodiment of this application;

[0028] Figure 4 shows the current-voltage characteristics of a solar-blind ultraviolet detector provided in a specific embodiment of this application under solar-blind ultraviolet light irradiation of different powers;

[0029] Figure 5(a) is a power-responsivity curve of a solar-blind ultraviolet detector provided in a specific embodiment of this application;

[0030] Figure 5(b) is a power-external quantum efficiency curve of a solar-blind ultraviolet detector provided in a specific embodiment of this application;

[0031] Figure 5(c) is a power-detectivity curve of a solar-blind ultraviolet detector provided in a specific embodiment of this application;

[0032] Figure 5(d) is a power-noise equivalent power curve of a solar-blind ultraviolet detector provided in a specific embodiment of this application;

[0033] Figure 6 is a flowchart illustrating a method for preparing a solar-blind ultraviolet detector according to another embodiment of this application. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] This application provides a solar-blind ultraviolet detector, as shown in Figure 1, including a substrate 10, a first electrode 20, and a third electrode 30. The substrate 10 is made of lithium niobate, and two opposing vertical trenches are formed on the upper surface of the substrate 10. The first electrode 20 is disposed in one of the vertical trenches. The second electrode 30 is disposed in the other vertical trench. A voltage bias is applied between the first electrode 20 and the second electrode 30.

[0036] The substrate 10 plays a fundamental supporting role in this solar-blind ultraviolet detector. It is made of lithium niobate and has two opposing vertical trenches on its upper surface. Lithium niobate is a crystalline material with a variety of excellent properties, exhibiting unique characteristics in optics, electricity, and piezoelectricity. The design of these two opposing vertical trenches serves a specific function, providing specific spatial positions for the subsequent electrode placement.

[0037] As shown in Figure 1, the detection principle of this device is as follows: When solar-blind ultraviolet light passes through to the substrate 10, if the energy of the solar-blind ultraviolet light is higher than the bandgap of lithium niobate (LiNbO3), electron-hole pairs will be generated in the lithium niobate material. These electron-hole pairs can be collected by applying an external electric field. Specifically, in this device, solar-blind ultraviolet light irradiates the substrate 10, causing the substrate 10 to generate electron-hole pairs, i.e., photogenerated carriers. These photogenerated carriers are affected by the electric field generated by the voltage bias applied between the first electrode 20 and the second electrode 30. Driven by the electric field force, electrons move to one side and holes move to the other side, thus forming a current. The detection of solar-blind ultraviolet light is achieved based on the detection of this current. In this embodiment, the electrodes are placed in trenches excavated on the surface of the substrate 10, so that the surfaces with the largest areas of the two electrodes face each other. Compared to the layout where planar electrodes are laid flat on the surface of substrate 10, this structure utilizes space in the vertical direction. This allows for an increase in the effective range of the electrodes without increasing the planar area of ​​substrate 10, through the rational design of parameters such as trench depth. By appropriately deepening the trenches, the electrodes can generate electric field correlations with more substrate material in the vertical direction, expanding the area of ​​influence of the electric field and the space for the generation and collection of photogenerated carriers within the same planar dimensions. This vertical space utilization aligns with the trend of miniaturization in electronic devices, reducing the overall size of the detector in the planar direction while achieving the same or even better detection functions. Furthermore, this approach directly uses lithium niobate as substrate 10, rather than depositing it on silicon-based materials. This allows for the direct use of high-purity lithium niobate crystals, resulting in better overall device performance. Moreover, solar-blind ultraviolet light does not need to penetrate the transparent conductive layer to enter the lithium niobate, reducing complexity and minimizing defects caused by capacitance effects between different material interfaces.

[0038] In one embodiment, referring to Figure 2, the solar-blind ultraviolet detector further includes an adhesion layer 40, through which the first electrode 20 and the second electrode 30 are bonded to the corresponding vertical trenches. When one or more of the following materials are used as electrode materials to form electrodes, such as gold, silver, platinum, palladium, copper, zinc, aluminum, and graphene, the bonding force between lithium niobate and the electrode material is often insufficient. The adhesion layer 40 mainly serves to enhance the bonding force between the electrode and the substrate 10, ensuring that the electrode can be firmly attached to the substrate 10. This prevents problems such as electrode layer detachment, peeling, or poor contact caused by external factors such as temperature changes and mechanical vibrations during subsequent use. It is a key intermediate layer that ensures the structural stability and electrical performance reliability of the entire device. In a specific embodiment, the material of the adhesion layer 40 includes chromium or titanium, with a thickness of 5 nm to 10 nm. Chromium and titanium are two materials that can better connect the substrate 10 and the electrode together. The thickness of the adhesion layer 40 is selected as 5nm to 10nm mainly because they can also fill the tiny pores and defects that may exist on the surface of the substrate 10, so that the electrode has a more uniform and stable adhesion foundation during deposition or subsequent use.

[0039] In one embodiment, the distance between the first electrode 20 and the second electrode 30 is 5 nm to 1000 nm. Lithium niobate material itself has a low electron mobility, meaning that electrons move relatively slowly and difficult within it. When ultraviolet light irradiates the lithium niobate material of the substrate 10, generating photogenerated carriers (electron-hole pairs), these photogenerated carriers need to move to the electrodes under the influence of an electric field to form a current signal that can be collected and detected. Due to the low electron mobility, if the distance between the electrodes is too large, electrons are more likely to recombine with holes during their movement towards the electrodes, resulting in a reduction in the number of photogenerated carriers that ultimately reach the electrodes and form an effective current signal, thus affecting the overall detection sensitivity and accuracy of the detector. When the distance between the first electrode 20 and the second electrode 30 is set to a relatively small value such as 5nm-1000nm, after applying a voltage bias between them, according to the relationship between electric field strength and distance (for example, in a simple model similar to a parallel plate capacitor, the electric field strength is inversely proportional to the distance between the electrodes), a relatively strong electric field will be formed between the two electrodes and in the surrounding substrate 10 region. This will overcome the difficulty of movement caused by low electron mobility to a certain extent, accelerate the movement of photogenerated carriers towards the electrode direction, and reduce the probability of recombination of electrons and holes in the substrate 10.

[0040] In one embodiment, the vertical trench has a width of 50 nm-100 μm, a length of 1 μm-1 mm, and a depth of 10 nm-100 μm. These dimensional parameters are relatively easy to achieve with current microfabrication technology. For example, using conventional microfabrication processes such as photolithography and etching, vertical trenches of this size can be manufactured with relatively high precision, ensuring process stability and product consistency during mass production, facilitating industrial-scale production and improving production efficiency. These dimensional parameters also ensure the normal movement of photogenerated carriers within the substrate 10, ensuring the detectability of the photocurrent.

[0041] In one embodiment, the substrate 10 is a lithium niobate substrate (wafer), which can be a Z-cut, Y-cut, or X-cut wafer. The cutting angle is not limited in this embodiment, and the thickness of the wafer can be 100μm-1000μm.

[0042] In one specific embodiment, as shown in Figure 2, the distance between the first electrode 20 and the second electrode 30 is 1 μm. The materials of the first electrode 20 and the second electrode 30 are gold. The width of the vertical trench is 10 μm, the length is 20 μm, and the depth is 500 nm. The material of the substrate 10 is a 128° Y-cut lithium niobate wafer with a thickness of 350 μm, and the adhesion layer 40 is 10 nm of titanium. When the solar-blind ultraviolet detector with this parameter combination is characterized by photoluminescence (PL), the results shown in Figure 3 can be obtained. The experimental results show that the peak of its photoluminescence spectrum corresponds to light with a wavelength of 320 nm, from which the corresponding bandgap can be calculated to be 3.87 eV.

[0043] As shown in Figure 4, the solar-blind ultraviolet detector of the above specific embodiment was tested under both dark and illuminated conditions. With a 6V bias, the dark current of the device is 30 × 10⁻⁶. -12 A. The photocurrent of the device was determined by irradiating it with 266nm wavelength ultraviolet light under different illumination powers. The formula for measuring photocurrent is: I Photo =I illumination -I Dark

[0044] I Photo For photocurrent, I illumination I is the detection current under light illumination. Dark This is the dark current. Experimental results show that under different power irradiation, at an optical power of 95 mW / cm², 2 The corresponding maximum photocurrent is 87 nA. Furthermore, the responsivity of a device is an important parameter characterizing the efficiency of a photodetector in converting incident light into an electrical signal. Responsivity is defined as the ratio of output photocurrent to incident light power at a specific wavelength.

[0045] R

[0046] Where R is the responsiveness, P light This represents the incident light power.

[0047] For the solar-blind ultraviolet detector of the specific embodiment described above, Figure 5(a) shows the relationship between responsivity and optical power. It is clear from the figure that the responsivity increases with increasing illumination intensity. The maximum responsivity is 11.9 A / W. External quantum efficiency (EQE) is the ratio of the number of charge carriers (electrons or holes) generated and collected by the photodetector to the number of incident photons. Figure 5(b) shows that the external quantum efficiency EQE also exhibits a similar trend to the responsivity under different illumination powers. When the illumination power is 95 mW / cm², the responsivity increases. 2 At that time, the maximum EQE was 5.3 × 10. 3 %. Specific detectivity (D*) is a quality factor indicating the sensitivity of a photodetector. It is the detector's ability to detect weak signals and is normalized by the detector area and bandwidth. The highest specific detectivity in the results shown in Figure 5(c) is 1.2 × 10⁻⁶. 12 Jones. Noise equivalent power (NEP) represents the incident light power required to produce a signal equal to the detector noise level, and it serves as a measure of the minimum detectable power. The minimum noise equivalent power in the results of Figure 5(d) is 8.2 × 10⁻⁶. -13 W / Hz -1 / 2 This indicates that the device can sense very weak light signals.

[0048] This application provides a method for preparing a solar-blind ultraviolet detector, which is used to prepare the solar-blind ultraviolet detector in any of the above embodiments. Please refer to Figure 6. The preparation method includes steps S602 and S604.

[0049] S602, two opposing vertical trenches are etched on a lithium niobate substrate.

[0050] It can be understood that lithium niobate substrate refers to the finished lithium niobate wafer produced in the manufacturing process. Wafers with any cutting method and angle can be selected. A 128° Y-cut lithium niobate wafer is preferred. The thickness can be selected from 100-1000μm, mainly depending on the processing platform supporting the processing technology (2-inch, 4-inch, 6-inch, 8-inch, or 12-inch). In practice, the first step is to obtain high-quality lithium niobate wafers. This is usually purchased from professional crystal growth manufacturers. These manufacturers use crystal growth technologies such as Czochralski and crucible dropping to grow large-sized lithium niobate crystals, and then cut them according to specific cutting angle requirements using high-precision cutting equipment (such as diamond wire saws) to obtain wafers with precise angles and suitable thicknesses as the substrate material.

[0051] This step involves manipulating the lithium niobate substrate. The aim is to selectively remove material from the surface and a certain depth of the lithium niobate substrate using specific physical or chemical methods, thereby forming two opposing vertical trench structures. Vertical trenches mean that their orientation is perpendicular to the substrate surface. These two trenches are positioned opposite each other and play a crucial foundational role in the subsequent device operation, including electrode placement and electric field construction. This is a vital step in the formation of the entire solar-blind ultraviolet detector structure.

[0052] Before starting step S602, the SiO2 / Si substrate must first be pretreated. It is ultrasonically cleaned using an organic solvent (such as acetone or ethanol) to remove surface oil and impurities, and then dried with high-purity nitrogen to ensure the substrate surface is clean and dry. Next, photoresist is coated onto the substrate according to the trench shape, exposed, developed, and vertical trenches are etched. After etching, the photoresist can be removed, and the substrate can be cleaned with deionized water. Dry etching, such as ion beam etching, is preferred here.

[0053] If ion beam etching is chosen, a high-purity, high-quality lithium niobate substrate (e.g., a 128° Y-cut, 350μm thick high-purity wafer) must first be prepared and fixed on the sample stage of the ion beam etching equipment, ensuring the substrate is placed stably and accurately to precisely receive the ion beam bombardment. Then, the etching equipment parameters are set, selecting a suitable ion source, such as an argon ion source, and adjusting the ion beam energy. The specific values ​​are determined based on the desired etching depth and trench sidewall quality requirements. The incident angle of the ion beam should ideally be perpendicular to the substrate surface to facilitate the formation of vertical trenches. Simultaneously, the beam current density must be controlled by adjusting parameters such as the discharge current of the ion source. Too high a beam current density can lead to uneven etching or excessive damage to the substrate, while too low a density results in an excessively slow etching rate. During the etching process, equipment such as optical microscopes and scanning electron microscopes can be used to monitor the trench formation in real time, including parameters such as trench depth, width, and sidewall perpendicularity. Feedback is used to adjust the relevant ion beam parameters to ensure the etching proceeds according to the design requirements. The specific dimensions of the vertical trench can be 10 μm in width, 20 μm in length, and 500 nm in depth.

[0054] S604, a first electrode and a second electrode are deposited in a vertical trench, respectively. A voltage bias is applied between the first electrode and the second electrode.

[0055] It can be understood that deposition here refers to using certain physical or chemical methods to cover the conductive material used to fabricate the electrodes onto the inner surface of the etched vertical trenches, forming a continuous and uniform electrode film, namely the first electrode and the second electrode. As a key part of the entire device's electrical system, the electrodes undertake important functions such as conducting current, constructing an electric field, and collecting photogenerated carriers. Applying a voltage bias between the two electrodes involves using an external power supply to create a potential difference between the first and second electrodes, thereby generating an electric field between and around the electrodes. This electric field plays a crucial driving role in the movement and collection of photogenerated carriers generated during subsequent solar-blind ultraviolet irradiation, and is a core electrical condition for achieving the detection function. Before step S602, an adhesion layer can be deposited on the SiO2 / Si substrate to increase the bonding force between the electrode layer and the substrate. The adhesion layer can be made of chromium or titanium, with a thickness of 5 nm to 10 nm.

[0056] When depositing electrodes, the fabrication of electrodes with specific shapes, sizes, and precise locations often requires steps such as photoresist application, exposure, and development to achieve patterning. For example, to deposit electrodes with regular shapes and precise positions within vertical trenches on a substrate, a layer of photoresist is first spin-coated onto the substrate surface (including the trenches), uniformly covering the substrate to form a thin film. Then, through an exposure operation, a mask with electrode pattern design (usually fabricated using high-precision electronic design and manufacturing processes, with transparent and opaque areas corresponding to the electrodes and non-electrode parts) is used. When light passes through the mask and illuminates the photoresist, the illuminated portions undergo a chemical reaction. Next, a development operation is performed, using a developer to remove the chemically changed photoresist portions, leaving the unchanged photoresist. This creates a photoresist pattern on the substrate surface (especially at the corresponding locations within the trenches) that matches the shape and size of the electrode. When performing physical vapor deposition of electrode materials, only the areas not covered by photoresist (i.e., the areas where the electrode is to be deposited) will be covered by the electrode material, while the areas protected by photoresist will not be deposited. After deposition, the desired electrode structure can be accurately obtained on the substrate by removing the photoresist (e.g., cleaning with suitable reagents such as organic solvents).

[0057] Electrode deposition can be performed using physical vapor deposition (PVD), such as thermal evaporation, sputtering, and electron beam evaporation. Taking sputtering deposition as an example, firstly, a high-quality target material (e.g., a gold target for gold electrodes) is selected based on the required electrode material and installed on the target position of the sputtering equipment. A suitable working gas (argon) is then introduced into the sputtering chamber, and the gas flow rate is adjusted. Finally, the appropriate sputtering power and substrate temperature are set according to the equipment and process requirements. During the deposition process, the electrode size must be adjusted by precisely controlling the sputtering time to achieve the desired design range.

[0058] In this application, lithium niobate was selected as the substrate material to fabricate the device, exhibiting excellent characteristics such as low dark current and good responsivity, and possessing the advantage of being suitable for industrial-scale production. Previously, due to the extremely low carrier mobility of lithium niobate, it was theoretically ruled out as an absorber. However, this application, through a unique structural design and corresponding experimental verification, successfully overcame this technological bias. Although the bandgap of lithium niobate is not as wide as that of gallium oxide, in practical applications, it is fully capable of achieving effective detection in the corresponding wavelength band.

[0059] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0060] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0061] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A solar-blind ultraviolet detector, characterized in that, include: The substrate is made of lithium niobate, and two opposing vertical grooves are formed on the upper surface of the substrate. A first electrode is disposed in one of the vertical trenches; A second electrode is disposed in another of the vertical trenches; a voltage bias is applied between the first electrode and the second electrode.

2. The solar-blind ultraviolet detector according to claim 1, characterized in that, It also includes an adhesive layer through which the first electrode and the second electrode are bonded to the corresponding vertical trench.

3. The solar-blind ultraviolet detector according to claim 2, characterized in that, The adhesive layer is made of chromium or titanium and has a thickness of 5 nm to 10 nm.

4. The solar-blind ultraviolet detector according to claim 1, characterized in that, The distance between the first electrode and the second electrode is 5nm-1000nm.

5. The solar-blind ultraviolet detector according to claim 1, characterized in that, The vertical trench has a width of 50nm-100μm, a length of 1μm-1mm, and a depth of 10nm-100μm.

6. The solar-blind ultraviolet detector according to claim 1, characterized in that, The materials of the first electrode and the second electrode include one or more of gold, silver, platinum, palladium, copper, zinc, aluminum, and graphene.

7. The solar-blind ultraviolet detector according to claim 1, characterized in that, The substrate is a wafer with a 128° Y-cut, X-cut, or Z-cut structure.

8. The solar-blind ultraviolet detector according to claim 7, characterized in that, The thickness of the substrate is 100μm-1000μm.

9. A method for preparing a solar-blind ultraviolet detector, characterized in that, The method for preparing the solar-blind ultraviolet detector according to any one of claims 1-8 comprises: Two opposing vertical trenches were etched on a lithium niobate substrate; A first electrode and a second electrode are deposited in the vertical trench, respectively; a voltage bias is applied between the first electrode and the second electrode.

10. The preparation method according to claim 9, characterized in that, The deposition of the first electrode and the second electrode in the vertical trench includes: An adhesion layer is deposited in each of the vertical trenches; The first electrode and the second electrode are deposited on the adhesion layer, respectively.

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