Double-end ultraviolet photoelectric detector based on barrier height control and preparation method thereof

Abstract

The invention belongs to the technical field of optoelectronic devices, and particularly relates to a double-end ultraviolet photoelectric detector based on barrier height regulation and control and a preparation method. The structure of the detector sequentially comprises a substrate, an electrode, a functional layer, a dielectric layer and a transparent electrode layer from bottom to top, based on a metal or semiconductor / insulator medium / transparent electrode structure, ultraviolet spectrum selection is realized; two layers of semiconductors or metal layer materials are separated through the insulating dielectric layer to reduce dark current of the device, and when the energy of non-equilibrium hot electrons generated by ultraviolet irradiation is higher than the barrier height, hot electron emission is generated, so that light current is formed to realize light detection. According to the invention, the spectral response of the double-end device is regulated and controlled by using the tunneling barrier height, the dependence on a wide bandgap semiconductor is avoided, and the material selection is rich; according to the two-end structure and the three-end ultraviolet photoelectric detector provided in the earlier stage and regulated by the potential barrier, the structure is simpler, and the light response speed is higher.

Description

Technical Field

[0001] The invention belongs to the technical field of optoelectronic devices, and in particular relates to a double-terminal ultraviolet photoelectric detector and a preparation method thereof. Background Art

[0002] Ultraviolet light is widely used in many scenarios, and accurate ultraviolet light detection is an important part of modern optoelectronic technology. Ultraviolet radiation is divided into three main spectral regions: UVA (400 nm-320 nm) radiation, which can penetrate the atmospheric clouds to reach the ground, and large doses can cause skin damage; UVB (320 nm-280 nm) radiation, most of which is absorbed by the atmosphere, but the 2% that reaches the earth's surface can cause harm to the human body and cause skin diseases; and UVC (280 nm-100 nm) radiation, which is completely absorbed by the ozone layer and cannot reach the ground, so there is very little background radiation in this area of ​​the earth's surface. The deep ultraviolet region generally refers to radiation <280 nm, and ultraviolet radiation <200 nm, called vacuum ultraviolet (10-200 nm), is easily absorbed by molecules and cannot be transmitted in the air. And the effects of ultraviolet radiation of different wavelengths on organisms and materials vary greatly. [Nat Rev Mater 8,587-603(2023); Nat. Photonics 13,233-244(2019)]

[0003] With the development of sensing technology, the field of photodetectors has attracted widespread attention. Its performance indicators usually include responsiveness, response speed, dark current, detection rate and spectral selectivity. The working mechanism includes processes such as photon absorption, photogenerated carrier generation and charge transfer. In practical applications, the performance of the detector often determines the sensitivity and reliability of the system. Due to the wide application of ultraviolet light, ultraviolet photodetectors have important application prospects. For example, in space environment monitoring, highly sensitive ultraviolet photodetectors can accurately capture weak ultraviolet radiation and provide key data for atmospheric composition analysis and astronomical observation; in flame detection, ultraviolet photodetectors with high response speed can quickly identify the source of fire and improve the response efficiency of fire warning systems.

[0004] In terms of material selection for detector preparation, traditional photomultiplier tubes have excellent detection performance, but their large size and high operating voltage bring instability to their application. Si photodiodes are also commonly used in the field of ultraviolet light detection, but because the Si band gap is only 1.12eV, a high-pass optical filter is required, which is expensive, and the device performance decreases with increasing temperature, making it difficult to meet the needs of multiple scenarios. In order to achieve good ultraviolet spectral selectivity, people place their hopes on wide bandgap semiconductor materials such as GaN and SiC, but to achieve day-blind ultraviolet light detection, they still rely on ultra-wide bandgap semiconductor materials such as GaOx and AlGaN. However, the current growth and doping processes of ultra-wide bandgap semiconductor materials are still immature, so their ultraviolet detection performance is still limited and cannot meet the needs of multiple scenarios.

[0005] In order to solve the above problems, the present invention proposes a new type of ultraviolet photodetector structure - a double-terminal ultraviolet photodetector based on barrier regulation. The detector relies on a metal (or semiconductor) / insulator medium / transparent electrode structure to achieve ultraviolet spectrum selection, has high quantum efficiency and responsivity, and can achieve solar-blind ultraviolet light detection. Summary of the invention

[0006] The purpose of the present invention is to provide a double-terminal ultraviolet photodetector structure based on barrier height control and a preparation method thereof, so as to achieve high-sensitivity ultraviolet light detection.

[0007] The double-end barrier-regulated ultraviolet photodetector proposed in the present invention separates two layers of semiconductor or metal materials through an insulating dielectric layer to reduce the dark current of the device; when the energy of non-equilibrium hot electrons generated by ultraviolet light irradiation is higher than the barrier height, hot electron emission will occur, thereby forming a photocurrent to achieve light detection. Its structure includes multiple layers of materials, from bottom to top: substrate 1, electrode 2, functional layer 3, dielectric layer 4, transparent electrode layer 5; among which:

[0008] The substrate 1 is a silicon substrate;

[0009] The electrode 2 is a Cr and Au electrode, the thickness of Cr is 5-10 nanometers, and the thickness of Au is 50-100 nanometers;

[0010] The functional layer 3 is graphene or a metal film (such as Al, Pd, etc. film); the thickness is 5-15 nanometers;

[0011] The dielectric layer 4 is hexagonal boron nitride (h-BN) or Al 2 O 3 or HfO 2 etc., with a thickness of 8-10 nm;

[0012] The transparent electrode 5 is a graphene material or a semi-transparent metal (such as Al, Au) or a two-dimensional semiconductor material (such as MoS 2 ) etc.; thickness is 5-10 nanometers;

[0013] The functional layer 3 and the transparent electrode 5 are separated by a dielectric layer and are insulated in a dark state; the functional layer 3 and the electrode 1 form an ohmic contact;

[0014] The present invention also provides a method for preparing a double-terminal ultraviolet photodetector based on tunneling barrier regulation, the specific steps of which are:

[0015] (1) Cleaning of substrate:

[0016] The substrate was ultrasonically cleaned in acetone, isopropanol, and deionized water for 15-20 minutes in sequence, and then cleaned in a UV-ozone cleaning machine for 120-150 seconds.

[0017] (2) Preparation of bottom electrode:

[0018] The bottom electrode is prepared on the substrate by using a coating and electron beam exposure method combined with evaporation and lift-off processes to prepare metal layer electrodes such as Cr / Au.

[0019] (3) Preparation of functional layer:

[0020] When the functional layer is graphene, a uniform multi-layer graphene material is placed on the bottom electrode by mechanical exfoliation and dry transfer technology;

[0021] When the functional layer is metal, a functional layer material with a suitable work function can be prepared on the bottom electrode, such as Al, Pd and other thin films. If Au is also used in the functional layer, it can be shared with the electrode. The metal film is prepared by coating and electron beam lithography combined with evaporation and stripping processes.

[0022] (4) Preparation of dielectric layer

[0023] Growth of Al by Atomic Layer Deposition 2 O 3 , HfO 2 Materials, or h-BN thin films are prepared by mechanical exfoliation and transferred to the functional layer;

[0024] (5) Preparation of top transparent electrode

[0025] MoS was mechanically exfoliated 2 Or graphene is cleaved to 4-8nm and then transferred to the dielectric layer, or semi-transparent metal electrodes are prepared using evaporation and photolithography processes with a thickness of 5-10nm.

[0026] The present invention also proposes a working method of a double-terminal ultraviolet photodetector based on potential barrier regulation, the specific steps of which are:

[0027] Apply voltage to one electrode and ground the other end to form an electric field in the dielectric layer. Monitor the current change between the two electrodes under light irradiation:

[0028] (1) When irradiated with light of different wavelengths, if the photon energy is greater than the tunneling barrier height, a significant current change occurs, enabling the detection of optical signals;

[0029] (2) When exposed to light of different intensities, the photocurrent increases with the increase of light intensity.

[0030] Compared with traditional photodetectors, the double-terminal ultraviolet photodetector based on potential barrier regulation has the following advantages:

[0031] (1) The spectral response of the two-terminal device is regulated by the tunnel barrier height, avoiding the reliance on wide-bandgap semiconductors and providing a wide range of material options;

[0032] (2) The two-terminal structure is simpler and has a faster light response speed than the barrier-controlled three-terminal ultraviolet photodetector proposed earlier. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the overall structure of a double-terminal ultraviolet photodetector based on potential barrier regulation.

[0034] Figure 2 Graphene is the functional layer, hBN is the barrier layer, and MoS 2 Schematic diagram of the transparent electrode layer device's response to 254nm ultraviolet light.

[0035] Figure 3 is the spectral response of the device.

[0036] Figure 4 The working principle diagram of the device is shown in Figure 2.

[0037] In the figure, the numbers are: 1 is the substrate, 2 is the electrode, 3 is the functional layer, 4 is the dielectric layer, and 5 is the transparent electrode layer. DETAILED DESCRIPTION

[0038] The present invention is further described below by way of embodiments in conjunction with the accompanying drawings.

[0039] The double-terminal ultraviolet photodetector based on barrier height regulation provided by the present invention controls the spectral response of the device by controlling the barrier height of photothermal electron emission. The device has the advantages of low dark current, fast response speed, etc.

[0040] The preparation of a double-terminal ultraviolet photodetector based on barrier height regulation is as follows:

[0041] (1) Substrate cleaning

[0042] A heavily doped p-type Si substrate with a thickness of 0.5 mm was selected as the substrate. The surface of the substrate contained 285 ± 15 nm of SiO 2 The substrate was ultrasonically cleaned in acetone, isopropanol, and deionized water for 15 minutes in sequence, and then cleaned in a UV-ozone cleaner for 120 seconds.

[0043] (2) Preparation of bottom electrode

[0044] When the functional layer is a non-metal such as graphene, it is necessary to prepare the bottom electrode on the substrate (below the functional layer) first. Place the substrate (0.5×0.5 cm) containing the curing layer on a glue spreader and adsorb it with a pump. Use a rubber-tipped dropper to absorb a small amount of polymethyl methacrylate (PMMA) solution, spread it at 600 rpm for 10 seconds, then spread it at 4000 rpm for 40 seconds, and then bake it on a hot plate at 180°C for 3 minutes. Then, by electron beam exposure, use KLayout software to draw the bottom electrode pattern, and expose this bottom electrode pattern under an electron beam current of 10 nanoamperes. After the exposure is completed, place it in a developer for 10 seconds, then place it in isopropanol to clean the developer, and then blow it dry with an air gun. The developed substrate and oxide layer are placed in a thermal evaporation system, and Cr / Au (thickness 5 / 15 nanometers) is evaporated on the substrate as the bottom electrode.

[0045] (3) Preparation of functional layer

[0046] When the functional layer is a metal: functional layer materials with suitable work functions can be prepared, such as Al, Pd and other thin films. First, place the substrate (0.5×0.5 cm) containing the curing layer on a coating machine and adsorb it with a pump. Use a rubber-tipped dropper to absorb a small amount of polymethyl methacrylate (PMMA) solution and drop it on the surface. Use 600 rpm to coat for 10 seconds and then 4000 rpm to coat for 40 seconds, and then bake on a hot plate at 180°C for 3 minutes. Use KLayout software to draw the electrode pattern, and then perform electron beam exposure to expose the required electrode pattern under a 10 nanoampere electron beam flow. After the exposure is completed, place it in a developer for 10 seconds, then place it in isopropanol to clean the developer, and then blow it dry with an air gun. Place the developed substrate and oxide layer in a thermal evaporation system and evaporate the metal layer at a speed of 1 angstrom per second to control the thickness to 5-15 nanometers. For example, metal films such as Al and Pd can be evaporated.

[0047] When the functional layer is graphene: through mechanical exfoliation, use blue tape to mechanically exfoliate the graphene flakes into a two-dimensional uniform multilayer structure, use polydimethylsiloxane (PDMS) to transfer the material on the tape to PDMS using dry transfer technology, find the required uniform multilayer large-area graphene (thickness of 5-15 nanometers, transparent and whitish color) under an optical microscope, and then transfer it to the bottom electrode with the help of a transfer table.

[0048] (4) Preparation of dielectric layer

[0049] Mechanical stripping and dry transfer technology are used to mechanically strip the flaky hexagonal boron nitride (h-BN) into a uniform few-layer structure with blue tape. The hexagonal boron nitride on the tape is then transferred to PDMS. The required uniform few-layer large-area hexagonal boron nitride (thickness of 8-10 nanometers, transparent and bluish in color) is found under an optical microscope. It is then transferred to the functional layer at a fixed point with the help of a transfer table, and the contact area between the two is kept as large as possible to ensure that the device has a stronger light absorption ability.

[0050] Al can also be grown by atomic layer deposition 2 O 3 , HfO 2 Material, covering above the functional layer.

[0051] (5) Preparation of top transparent electrode layer

[0052] When the top transparent electrode is a semi-transparent metal:

[0053] The process is almost the same as the preparation method of the metal functional layer in step 3. The difference is that the evaporated metal must meet the requirement of high light transmittance, and the top metal electrode cannot be in direct contact with the functional layer. At the same time, it is necessary to ensure that there is a large area of ​​overlap between the functional layer, the dielectric layer, and the top translucent metal electrode, so that the effective area of ​​the device is larger and greater light absorption can be achieved.

[0054] When the top electrode layer is a two-dimensional semiconductor material such as graphene, molybdenum disulfide, etc.:

[0055] Use blue tape to cleave the flake graphene or flake molybdenum disulfide into about 5nm, transfer the tape to polydimethylsiloxane (PDMS) with the help of PDMS, find the required uniform large-area graphene under an optical microscope, and transfer it to the top of the dielectric layer hexagonal boron nitride (h-BN) with the help of a transfer table. This layer of graphene or molybdenum disulfide cannot be in direct contact with the functional layer, that is, the functional layer 3 and the transparent electrode 5 are separated by the dielectric layer and are insulated in the dark state. At the same time, it is necessary to ensure that there is a large area overlap between the functional layer, the dielectric layer, and the transparent electrode layer to ensure that the device has a large light absorption capacity.

[0056] After the device is fabricated, the photoelectric performance of the two-terminal device is tested using a 4200 probe station. First, the tunneling current of the device is tested in the dark state and under light. Figure 4 The carrier transport process in the device when irradiated with ultraviolet light and visible light respectively) is used to find the operating voltage value that makes the device responsive. Then, under this voltage, the device is mainly used to detect the ultraviolet light of different wavelengths, such as 222nm, 254nm, etc. ( Figure 2 The photocurrent of the device at different light power densities is tested, and then the important parameters of the photodetector such as responsivity and quantum efficiency are calculated to characterize the photoelectric performance of the device.

[0057] Finally, the cutoff wavelengths of two-terminal devices with different structures were tested. By fixing the optical power density to 0.11mW / cm 2 ( Figure 3 Gr / h-BN / MoS 2 Structural device at P = 0.11mW / cm 2 The cut-off wavelength at the time of the device is determined, and the photocurrent values ​​of the device at different wavelengths are tested under the same voltage. The wavelengths cover the range from ultraviolet light to visible light, such as 222nm, 254nm, 310nm, 365nm, 405nm and 520nm.

Claims

1. A double-terminal ultraviolet photodetector based on barrier height control, characterized in that: An insulating dielectric layer is used to separate two layers of semiconductor or metal materials to reduce the dark current of the device. When the energy of non-equilibrium hot electrons generated by ultraviolet light is higher than the barrier height, hot electron emission will occur, thereby forming a photocurrent to achieve light detection. Its structure from bottom to top is: substrate, electrode, functional layer, dielectric layer, transparent electrode layer; among which: The substrate is a silicon substrate; The electrode is a Cr / Au electrode, the thickness of Cr is 5-10 nanometers, and the thickness of Au is 50-100 nanometers; The functional layer is graphene or a metal film with a thickness of 5-15 nanometers; The dielectric layer is hexagonal boron nitride or Al2O3 or HfO2, and has a thickness of 8-10 nanometers; The transparent electrode is a graphene material or a semi-transparent metal or a two-dimensional semiconductor material, and has a thickness of 5-10 nanometers; The functional layer and the transparent electrode are separated by a dielectric layer and are insulated in a dark state; the functional layer and the electrode form an ohmic contact.

2. The double-ended ultraviolet photodetector according to claim 1, characterized in that: The functional layer is an Al or Pd thin film.

3. The double-ended ultraviolet photodetector according to claim 1, characterized in that: The transparent electrode is selected from molybdenum disulfide, Al, and Au.

4. The method for preparing a double-terminal ultraviolet photodetector according to any one of claims 1 to 3, characterized in that: The specific steps are: (1) Cleaning of substrate: The substrate was ultrasonically cleaned in acetone, isopropanol, and deionized water for 15-20 minutes in sequence, and then cleaned in a UV-ozone cleaning machine for 120-150 seconds. (2) Preparation of bottom electrode: The bottom electrode is prepared on the substrate by using a coating and electron beam exposure method, combined with evaporation and lift-off processes. (3) Preparation of functional layer: When the functional layer is graphene, a uniform multi-layer graphene material is placed on the bottom electrode by mechanical exfoliation and dry transfer technology; When the functional layer is a metal film, a functional layer material with a suitable work function is prepared on the bottom electrode, and the metal film is prepared by using a coating and electron beam lithography method combined with evaporation and stripping processes; (4) Preparation of dielectric layer Use atomic layer deposition to grow Al2O3 and HfO2 materials, or use mechanical exfoliation to prepare h-BN films and transfer them to the functional layer; (5) Preparation of top transparent electrode MoS2 or graphene is cleaved to 4-8nm by mechanical stripping and then transferred to the dielectric layer, or semi-transparent metal electrodes are prepared by evaporation and photolithography with a thickness of 5-10nm.

5. The operating method of the double-terminal ultraviolet photodetector according to any one of claims 1 to 3, characterized in that: The specific steps are: Apply voltage to one electrode and ground the other end to form an electric field in the dielectric layer. Monitor the current change between the two electrodes under light irradiation: (1) When irradiated with light of different wavelengths, if the photon energy is greater than the tunneling barrier height, a significant current change occurs, enabling the detection of optical signals; (2) When exposed to light of different intensities, the photocurrent increases with the increase of light intensity.

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