A liquid-based photodetector based on a mixed liquid of polar quantum dots and a preparation method thereof

Abstract

The application relates to the field of photoelectric sensing, and discloses a liquid-based photoelectric detector based on a polar quantum dot mixed liquid. The liquid-based photoelectric detector based on the polar quantum dot mixed liquid comprises an N-type semiconductor, a polar quantum dot mixed liquid, graphene, a first electrode and a second electrode. The liquid-based photoelectric detector based on the polar quantum dot mixed liquid of the application utilizes the Fermi level difference of the graphene and the N-type semiconductor to polarize the polar liquid. Under the irradiation of a light source, the quantum dots are excited by light to generate electron-hole pairs, the electron-hole pairs jump to the surface of the quantum dots, and the polar liquid molecules around the quantum dots are polarized. The quantum dots are uniformly distributed in the polar liquid, connect the short-range ordered polar liquid molecules to form long-range ordered electron / hole transmission channels, and therefore generate internal liquid optical polarization current to improve the output optical polarization current.

Description

Technical Field

[0001] This invention relates to the field of photoelectric sensing, and more particularly to a liquid-based photodetector based on a polar quantum dot mixed liquid and its preparation method. Background Technology

[0002] The increasing informatization of society further promotes the development of the sensing information field. As a key component in the conversion of optical signals to electrical signals, photoelectric sensors play an indispensable role in fields such as spectroscopy, optical communication, and environmental monitoring. High-performance, novel photoelectric detectors are a crucial link in the development of informatization, contributing to further enhancing the level of informatization.

[0003] Currently, photodetectors are mainly classified according to their operating principles into photomultiplier tubes, photodiodes, phototransistors, photoresistive photodetectors, and photoconductive photodetectors. Among these, van der Waals heterojunction photodiodes are the most widely used. However, traditional van der Waals heterojunction photodiodes face challenges in many aspects, including assembly technology, doping control, metal-semiconductor contact, and stability.

[0004] Liquid-based photodetectors, based on the traditional van der Waals heterojunction photodiode structure, introduce polar liquids between semiconductors, overcoming problems such as semiconductor lattice mismatch caused by traditional assembly processes. Further improving their performance is a key area of ​​research. Summary of the Invention

[0005] The purpose of this invention is to provide a liquid-based photodetector based on polar quantum dot mixed liquid and its fabrication method, based on existing interfacial water polarization theory, by introducing polar quantum dot mixed liquid to further introduce water polarization within the liquid. This photodetector testing method is convenient to operate and significantly improves performance.

[0006] The present invention discloses a liquid-based photodetector based on a polar quantum dot mixed liquid. The photodetector includes an N-type semiconductor, a polar quantum dot mixed liquid, and graphene. It also includes a first electrode and a second electrode disposed on the N-type semiconductor and the graphene, respectively. Both the N-type semiconductor and the graphene are in contact with the polar quantum dot mixed liquid. By adjusting the size of the quantum dots to customize the absorption peak wavelength of the polar quantum dot mixed liquid, the detection performance of the photodetector at the absorption peak wavelength can be selectively improved.

[0007] The first and second electrodes are independently selected from one or more composite electrodes made of gold, titanium, chromium, nickel, and silver, with a thickness of 50-300 nm.

[0008] The N-type semiconductor is a semiconductor layer selected from one of the semiconductors such as gallium nitride, gallium arsenide, and silicon.

[0009] The polar quantum dot mixed liquid is a quantum dot mixed solution based on a polar liquid solvent, such as an aqueous solution of molybdenum disulfide quantum dots, an aqueous solution of tungsten disulfide quantum dots, or a toluene solution of cadmium selenide quantum dots.

[0010] The method for fabricating the photodetector includes:

[0011] A first electrode is prepared on one side of an N-type semiconductor, with the other side facing upwards. A polar quantum dot mixture is placed on the semiconductor, and graphene is laid on the mixture. A second electrode is prepared on the upper surface of the graphene. During testing, the current between the first electrode and the second electrode is directly detected.

[0012] To test the effect of the photodetector designed in this invention, a laser light source and a current detection device are required. The laser wavelength can be 300-1000nm, and the current detection device can be an instrument suitable for current measurement, such as a Keithley 6514 electrometer.

[0013] To test the effectiveness of the liquid-based photodetector based on polar quantum dot mixed liquid described above, the testing method in this invention includes the following steps:

[0014] 1) Measure the photopolarization current of a fixed-power laser of the same wavelength directly irradiated onto an N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction and an N-type semiconductor / polar liquid / graphene heterojunction using a current detection device;

[0015] 2) Measure the photopolarization current on the N-type semiconductor / polar quantum dot hybrid liquid / graphene heterojunction and the N-type semiconductor / polar liquid / graphene heterojunction directly irradiated by lasers of different wavelengths using a current detection device, and compare the output current growth rate.

[0016] 3) Measure the photopolarization current at the absorption peak wavelength of the N-type semiconductor / different absorption peak polar quantum dot mixed liquid / graphene heterojunction and the N-type semiconductor / polar liquid / graphene heterojunction directly irradiated by the laser using a current detection device.

[0017] The beneficial effects of this invention compared to the prior art are:

[0018] Traditional van der Waals heterojunction photodiodes face challenges in assembly technology, doping control, metal-semiconductor contact, and stability. Liquid-based photodetectors, however, overcome problems such as semiconductor lattice mismatch caused by traditional assembly processes. This invention presents a liquid-based photodetector based on a polar quantum dot mixed liquid. Based on an N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction and existing interfacial water polarization theory, the invention introduces a polar quantum dot mixed liquid to further introduce water polarization within the liquid, thereby improving the photocurrent and responsivity detectivity of the photodetector. By controlling the size of the quantum dots to customize the polar quantum dot mixed liquid with a specific absorption peak wavelength, the resulting N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction exhibits significantly improved detection performance at the absorption peak wavelength. The testing method for this liquid-based photodetector based on a polar quantum dot mixed liquid is convenient to operate and offers significant performance improvements, making it applicable to various special needs scenarios. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a photodetector based on an N-type gallium arsenide / polar quantum dot hybrid liquid / graphene.

[0020] Figure 2 This is a schematic diagram illustrating the principle of polarization of internal polar liquid molecules in a photodetector based on an N-type gallium arsenide / polar quantum dot mixed liquid / graphene.

[0021] Figure 3 A comparison of the output current of a photodetector based on N-type gallium arsenide / molybdenum disulfide quantum dot aqueous solution / graphene (820nm) and a photodetector based on N-type gallium arsenide / deionized water / graphene (820nm);

[0022] Figure 4 The graph shows the output current of an N-type gallium arsenide / tungsten disulfide quantum dot aqueous solution / graphene photodetector (820nm) as a function of time.

[0023] Figure 5 The optical absorption spectra of cadmium selenide quantum dot toluene solutions with different absorption peak wavelengths (494nm, 527nm, 563nm, 582nm, 600nm);

[0024] Figure 6 The graph shows the relationship between the output current growth rate and wavelength for N-type gallium arsenide / cadmium selenide quantum dot toluene solution (494nm, 527nm, 563nm, 582nm, 600nm) / graphene photodetectors and N-type gallium arsenide / toluene / graphene photodetectors (494nm, 527nm, 563nm, 582nm, 600nm).

[0025] Figure 7 This is a comparison of the output current at the absorption peaks of a photodetector based on N-type gallium arsenide / cadmium selenide quantum dots in toluene solution (494nm, 527nm, 563nm, 582nm, 600nm) / graphene and a photodetector based on N-type gallium arsenide / toluene / graphene (494nm, 527nm, 563nm, 582nm, 600nm). Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Reference Figure 1 As a specific example of the present invention, the structure of the liquid-based photodetector device based on polar quantum dot mixed liquid is as follows: Figure 1 As shown, from top to bottom, these are: first electrode 1, N-type semiconductor 2, polar quantum dot mixed liquid 3, graphene 4, and second electrode 5. The liquid-based photodetector of this invention, based on a polar quantum dot mixed liquid, utilizes the Fermi level difference between graphene and the N-type semiconductor to polarize the polar liquid. Under illumination, the quantum dots are photoexcited, generating electron-hole pairs. These electrons and holes transition to the surface of the quantum dots, polarizing the surrounding polar liquid molecules. The quantum dots are uniformly distributed in the polar liquid, connecting short-range ordered polarized liquid molecules to form long-range ordered electron / hole transport channels, thus generating an internal photopolarization current that enhances the output photopolarization current. To more comprehensively test the effect of the liquid-based photodetector based on polar quantum dot mixed liquid of the present invention, the testing process includes the following test steps: (1) Measure the photopolarization current of N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction and N-type semiconductor / polar liquid / graphene heterojunction directly irradiated by a fixed-power laser of the same wavelength using a detection device; (2) Measure the photopolarization current of N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction and N-type semiconductor / polar liquid / graphene heterojunction directly irradiated by lasers of different wavelengths using a detection device, and compare the output current growth rate; (3) Measure the photopolarization current of N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction and N-type semiconductor / polar liquid / graphene heterojunction directly irradiated by lasers at the absorption peak wavelength using a detection device. When the absorption peaks of the polar quantum dot mixed liquid are different, the dynamic exciton effect of the quantum dots is enhanced at the absorption peak, the number of freely migratable charge carriers increases, and more polar liquid molecules are polarized, thereby causing a significant increase in the instantaneous photopolarization current. Therefore, the performance of photodetectors in a corresponding band can be selectively improved by customizing the absorption peak wavelength of quantum dots.

[0028] Example 1:

[0029] 1) Gold-plated electrode on one side of N-type gallium arsenide with a resistivity of 10 Ω·cm;

[0030] 2) Take a piece of polyethylene terephthalate (PET) flexible substrate of appropriate size, and clean the substrate surface in acetone solution and ethanol solution in turn to remove impurities attached to the surface, and then blow dry with N2.

[0031] 3) Select one side of the PET flexible substrate as the front side and transfer the monolayer graphene to the front side of the PET substrate;

[0032] 4) Electrodes were fabricated on the graphene surface using 50nm silver electrodes;

[0033] 5) A working window is formed on the other side of the N-type gallium arsenide with a resistivity of 10 Ω·cm using UV adhesive, and 10 μL of molybdenum disulfide quantum dot aqueous solution is dropped into it;

[0034] 6) Flip the PET substrate so that the back side faces up, thereby covering the graphene side on the working window and bringing the graphene into close contact with the molybdenum disulfide quantum dot aqueous solution, thereby forming an N-type gallium arsenide / molybdenum disulfide quantum dot aqueous solution / graphene heterojunction structure.

[0035] 7) Connect the silver electrode on the graphene to the positive terminal of the ammeter, and connect the gold electrode on the N-type gallium arsenide to the negative terminal of the ammeter.

[0036] 8) Illuminate the N-type gallium arsenide / molybdenum disulfide quantum dot aqueous solution / graphene with a light source, and measure the peak current when the light source is directly irradiated onto the N-type gallium arsenide / molybdenum disulfide quantum dot aqueous solution / graphene heterojunction structure.

[0037] 9) Replace the molybdenum disulfide quantum dot aqueous solution with 10 μL of deionized water, control the irradiation under the same light source conditions, and measure the peak current of the N-type gallium arsenide / deionized water / graphene heterojunction structure directly irradiated by the light source for comparison; 10) Replace the molybdenum disulfide quantum dot aqueous solution with tungsten disulfide quantum dot aqueous solution, control the irradiation under the same light source conditions, and measure the peak current of the N-type gallium arsenide / tungsten disulfide quantum dot aqueous solution / graphene heterojunction structure directly irradiated by the light source.

[0038] Taking an N-type gallium arsenide / molybdenum disulfide quantum dot aqueous solution / graphene photodetector as an example, the principle diagram of polar liquid molecule polarization inside the solution is as follows: Figure 2As shown, in the absence of light, graphene and N-type gallium arsenide exhibit a Fermi level difference, polarizing water molecules. When a light source illuminates the semiconductor surface, the semiconductor absorbs photons, exciting a large number of minority carriers and further polarizing the surface water molecules. Molybdenum disulfide quantum dots, excited by photons, experience electron-hole pairs due to internal carrier transitions, which migrate to the quantum dot surface. Hydrogen atoms within water molecules carry a positive charge, while oxygen atoms carry a negative charge. Therefore, electrons on the quantum dot surface attract positively charged hydrogen atoms, while holes attract negatively charged oxygen atoms. Taking electron transport channels as an example, when positively charged hydrogen atoms contact electrons on the quantum dot surface, the positive charge state on the hydrogen atom surface decreases, while the negative charge state on the oxygen atom surface becomes abundant. This excess negative charge state is transferred through hydrogen bonds to the corresponding positively charged hydrogen atoms in neighboring water molecules, forming short-range ordered water-polarized electron transport channels. Molybdenum disulfide (MoD) quantum dots are uniformly distributed in deionized water, connecting with surrounding short-range ordered polarized water molecules to form long-range ordered water-polarized electron / hole transport channels. These channels transport electrons / holes to the semiconductors on either side, generating internal polarization current and further enhancing the output polarization current. For N-type gallium arsenide (GaAs), it exhibits good light absorption intensity and excellent photoelectric performance under 820nm illumination. MoD quantum dots also possess a certain light absorption intensity at 820nm; therefore, the introduction of MoD quantum dots further enhances the photocurrent of the GaAs-based liquid photodetector. By measuring the photocurrent of an N-type GaAs / deionized water / graphene photodetector and comparing it with an N-type GaAs / MoD quantum dot aqueous solution / graphene photodetector, the following results can be obtained... Figure 3 The output photocurrent of the N-type gallium arsenide / deionized water / graphene photodetector reached 3.76 μA, and the output photocurrent of the N-type gallium arsenide / molybdenum disulfide quantum dot aqueous solution / graphene photodetector reached 11.5 μA, representing an effective increase of 3.06 times. Meanwhile, tungsten disulfide quantum dots at 820 nm also exhibit a certain light absorption intensity. The photocurrent measurement of the N-type gallium arsenide / tungsten disulfide quantum dot aqueous solution / graphene photodetector yielded... Figure 4 The output photocurrent of the N-type gallium arsenide / tungsten disulfide quantum dot aqueous solution / graphene photodetector reached 10.4 μA, which is 2.77 times higher than that of the N-type gallium arsenide / deionized water / graphene photodetector. This verifies that the introduction of polarized quantum dot mixed liquid can provide a certain photocurrent enhancement at the effective absorption wavelength of N-type semiconductor.

[0039] Example 2:

[0040] 1) Gold electrode is plated on one side of an N-type gallium arsenide electrode with a resistivity of 10 Ω·cm;

[0041] 2) Take a piece of polyethylene terephthalate (PET) flexible substrate of appropriate size, and clean the substrate surface in acetone solution and ethanol solution in turn to remove impurities attached to the surface, and then blow dry with N2.

[0042] 3) Select one side of the PET flexible substrate as the front side and transfer the monolayer graphene to the front side of the PET substrate;

[0043] 4) Electrodes were fabricated on the graphene surface using 50nm silver electrodes;

[0044] 5) The absorption spectra of different cadmium selenide quantum dots were measured using an absorption spectrometer to obtain the absorption peak wavelengths;

[0045] 6) A working window was formed on the other side of the N-type gallium arsenide with a resistivity of 10 Ω·cm using UV adhesive, and 10 μL of cadmium selenide quantum dot toluene solution with an absorption peak at 494 nm was dropped in.

[0046] 7) Flip the PET substrate so that the graphene side directly covers the working window and makes the graphene in close contact with the cadmium selenide quantum dot toluene solution, thereby forming an N-type gallium arsenide / cadmium selenide quantum dot toluene solution (494nm) / graphene heterojunction structure.

[0047] 8) Connect the silver electrode on the graphene to the positive terminal of the ammeter, and connect the gold electrode on the N-type gallium arsenide to the negative terminal of the ammeter.

[0048] 9) Irradiate the N-type gallium arsenide / cadmium selenide quantum dot toluene solution (494nm) / graphene with a light source, and measure the peak current I when directly irradiated by the light source. s494nm ;

[0049] 10) Measure the peak output current I of the N-type gallium arsenide / cadmium selenide quantum dot toluene solution / graphene photodetector with absorption peaks at 527 nm, 563 nm, 582 nm, and 600 nm, respectively. s527nm I s563nm I s582nm I s600nm ;

[0050] 11) Replace the cadmium selenide quantum dot toluene solution with 10 μL of toluene, and control the irradiation under the same light source conditions. Measure the peak current IA of the N-type gallium arsenide / toluene / graphene heterojunction structure at wavelengths of 494 nm, 527 nm, 563 nm, 582 nm, and 600 nm. 494nm ,I s527nm ,I s563nm ,I s582nm and I s600nm Comparison with the output photocurrent of graphene / cadmium selenide quantum dot toluene solution / N-type gallium arsenide;

[0051] 12) Based on the absorption peak wavelength of cadmium selenide quantum dot toluene solution, a wavelength scanning step of ±10 nm was selected, and five wavelengths were scanned for each wavelength. The output photocurrent I of N-type gallium arsenide / cadmium selenide quantum dot toluene solution / graphene was measured at different wavelengths. s The output photocurrent I of N-type gallium arsenide / toluene / graphene is obtained through I... s The / i output calculates the photocurrent growth rate.

[0052] Absorption spectra of different cadmium selenide quantum dot toluene solutions were obtained using an absorption spectrometer, as shown below. Figure 5 As shown in the figure, different sizes of cadmium selenide quantum dots in toluene solution exhibit different absorption peaks, with distinct absorption peaks at 494 nm, 527 nm, 563 nm, 582 nm, and 600 nm, respectively, demonstrating that the absorption intensity of cadmium selenide quantum dots is highest at these wavelengths. Using a wavelength scan step of ±10 nm, five wavelengths were scanned, and the photocurrent growth rate of cadmium selenide quantum dot toluene solution at different absorption peak wavelengths was measured as a function of wavelength, as shown in the figure. Figure 6 As shown, with the change of scanning wavelength, the photocurrent growth rate reaches its maximum at the absorption peak wavelength and shows a certain decreasing trend at other wavelengths, exhibiting a similar trend to the absorption spectrum curve of cadmium selenide quantum dot toluene solution. For N-type gallium arsenide, the absorption intensity is weak at wavelengths of 400nm-600nm. The introduction of cadmium selenide quantum dot toluene solution enhances the dynamic exciton effect at the absorption peak wavelength, increases the number of mobile free carriers, and further causes a significant increase in the instantaneous photopolarization current, effectively improving the photocurrent of the N-type gallium arsenide-based liquid photodetector. The output photocurrents of N-type gallium arsenide / cadmium selenide quantum dot toluene solution / graphene and N-type gallium arsenide / toluene solution / graphene at the absorption peak wavelength were measured, as shown in the figure. Figure 7 As shown, the comparison reveals that the output photocurrent of N-type gallium arsenide / cadmium selenide quantum dot toluene solution / graphene is significantly enhanced at the absorption peak wavelength. Specifically, the output photocurrent of N-type gallium arsenide / cadmium selenide quantum dot toluene solution / graphene photodetectors based on absorption peak wavelengths of 494nm, 527nm, 563nm, 582nm, and 600nm increases by 3.14, 2.35, 2.24, 2.49, and 3.63 times respectively compared to N-type gallium arsenide / toluene solution / graphene photodetectors.

Claims

1. A liquid-based photodetector based on a mixture of polar quantum dots in a liquid, characterized in that, include: The system comprises an N-type semiconductor (2), a polar quantum dot mixed liquid (3), and graphene (4), and also includes a first electrode (1) and a second electrode (5) disposed on the N-type semiconductor and graphene respectively. The N-type semiconductor (2) and graphene (4) are both in contact with the polar quantum dot mixed liquid (3). The N-type semiconductor (2) is a semiconductor layer, independently selected from gallium nitride, gallium arsenide, and silicon. The polar quantum dot mixed liquid (3) is a quantum dot mixed solution based on a polar liquid solvent, selected from molybdenum disulfide quantum dot aqueous solution, tungsten disulfide quantum dot aqueous solution, and cadmium selenide quantum dot toluene solution. By adjusting the size of the quantum dots, the absorption peak wavelength of the polar quantum dot mixed liquid (3) is customized, thereby selectively improving the detection performance of the photodetector at the absorption peak wavelength. The system utilizes graphene and N-type semiconductors. The Fermi level difference of the semiconductor polarized polar liquid allows quantum dots to be uniformly distributed in the polar liquid and connected to form long-range ordered electron / hole transport channels by connecting short-range ordered polarized liquid molecules, thereby generating an internal optically polarized current to enhance the output optically polarized current.

2. The liquid-based photodetector based on polar quantum dot mixed liquid as described in claim 1, characterized in that, The first electrode (1) and the second electrode (5) are independently selected from one or more of gold, titanium, chromium, nickel and silver composite electrodes, with a thickness of 50-300 nm.

3. The design method of a liquid-based photodetector based on a polar quantum dot mixed liquid as described in any one of claims 1-2, characterized in that, By adjusting the size of the quantum dots, the absorption peak wavelength of the polar quantum dot mixture (3) can be customized, thereby selectively improving the detection performance of the photodetector at the absorption peak wavelength.

4. A method for preparing a liquid-based photodetector based on a polar quantum dot mixed liquid as described in any one of claims 1-2, characterized in that, include: A first electrode (1) is prepared on one side of an N-type semiconductor (2), and a polar quantum dot mixture (3) is placed on the other side with the surface facing upward. Graphene (4) is laid on the polar quantum dot mixture (3), and a second electrode (6) is prepared on the upper surface of the graphene (4). During testing, the current between the first electrode and the second electrode is directly detected.

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