Liquid-based photoelectric detector based on polar quantum dot mixed liquid and preparation method thereof

Abstract

The invention relates to the field of photoelectric sensing, and discloses a liquid-based photoelectric detector based on polar quantum dot mixed liquid. The liquid-based photoelectric detector based on the polar quantum dot mixed liquid comprises an N-type semiconductor, the polar quantum dot mixed liquid, graphene, a first electrode and a second electrode. According to the liquid-based photoelectric detector based on the polar quantum dot mixed liquid, the polar liquid is polarized by using the Fermi energy level difference between the graphene and the N-type semiconductor. Under the irradiation of a light source, the quantum dots are excited by light to generate electron hole pairs, and electron holes are transited to the surfaces of the quantum dots to polarize the surrounding polar liquid molecules. The quantum dots are uniformly distributed in the polar liquid and are connected with short-range ordered polarized liquid molecules to form a long-range ordered electron / hole transmission channel, so that optical polarization current in the liquid is generated and output optical polarization current is improved.

Description

Technical Field

[0001] The invention relates to the field of photoelectric sensing, and in particular to a liquid-based photoelectric detector based on a polar quantum dot mixed liquid and a preparation method thereof. Background Art

[0002] The deepening of social information technology has further promoted the development of sensor information. Photoelectric sensors, as key components for converting optical signals into electrical signals, play an indispensable role in spectroscopy, optical communications, environmental monitoring and other fields. High-performance new photoelectric detectors are a key link in the development of informatization, which is conducive to further improving the degree of informatization.

[0003] At present, the types of photodetectors are mainly divided into photomultiplier tubes, photosensitive diodes, photodiodes, phototransistors, photoresistive photodetectors, photoconductive photodetectors, etc. according to their principles. Among them, van der Waals heterojunction photodiodes are the most widely used. However, traditional van der Waals heterojunction photodiodes face many challenges such as assembly technology, doping control, metal-semiconductor contact and stability.

[0004] Liquid-based photodetectors are based on the traditional van der Waals heterojunction photodiode structure, which introduces polar liquids between semiconductors to overcome problems such as semiconductor lattice mismatch caused by traditional process assembly. How to further improve its performance is an issue that needs to be studied in depth. Summary of the invention

[0005] The purpose of the present invention is to provide a liquid-based photoelectric detector based on polar quantum dot mixed liquid and a preparation method thereof, based on the existing interfacial water polarization theory, by introducing polar quantum dot mixed liquid to further introduce water polarization in the liquid. The photoelectric detector testing method is easy to operate and has significant performance improvement.

[0006] The present invention discloses a liquid-based photoelectric detector based on a polar quantum dot mixed liquid. The photoelectric detector comprises: an N-type semiconductor, a polar quantum dot mixed liquid, and graphene. It also comprises a first electrode and a second electrode respectively arranged on the N-type semiconductor and the graphene. The N-type semiconductor and the graphene are both 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 photoelectric detector at the absorption peak wavelength can be selectively improved.

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

[0008] The N-type semiconductor is a semiconductor layer selected from one of 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 a molybdenum disulfide quantum dot aqueous solution, a tungsten disulfide quantum dot aqueous solution, a cadmium selenide quantum dot toluene solution, and the like.

[0010] The method for preparing the photoelectric detector comprises: A first electrode is prepared on one surface of an N-type semiconductor, with the other surface facing upwards, a polar quantum dot mixed liquid is placed on it, graphene is laid on the polar quantum dot mixed liquid, a second electrode is prepared on the upper surface of the graphene, and during testing, the current between the first electrode and the second electrode is directly detected.

[0011] In order to test the effect of the photoelectric detector designed in the present invention, a laser light source and a current detection device are required, wherein the laser wavelength can be 300-1000nm. The current detection device can use an instrument suitable for current measurement such as Keithley 6514 electrometer.

[0012] Using the above-mentioned liquid-based photoelectric detector based on the polar quantum dot mixed liquid, in order to detect its effect, the testing method in the present invention includes the following steps: 1) The photopolarization current of the same wavelength fixed power laser directly irradiated on the N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction and the N-type semiconductor / polar liquid / graphene heterojunction is measured by a current detection device; 2) Using a current detection device, measure the photopolarized current on the N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction and the N-type semiconductor / polar liquid / graphene heterojunction when lasers of different wavelengths are directly irradiated, and compare and obtain the output current growth rate; 3) The photopolarization current of the N-type semiconductor / different absorption peak polarity quantum dot mixed liquid / graphene heterojunction and the N-type semiconductor / polar liquid / graphene heterojunction at the absorption peak wavelength is measured by a current detection device.

[0013] Compared with the prior art, the present invention has the following beneficial effects: Traditional van der Waals heterojunction photodiodes face challenges in many aspects, such as assembly technology, doping control, metal-semiconductor contact and stability, while liquid-based photodetectors overcome problems such as semiconductor lattice mismatch caused by traditional process assembly; the liquid-based photodetector based on polar quantum dot mixed liquid of the present invention is based on N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction and existing interface water polarization theory, and introduces polar quantum dot mixed liquid to further introduce water polarization in the liquid, thereby improving the photocurrent and responsiveness detection rate indicators of the photodetector. By adjusting the size of the quantum dots to customize the polar quantum dot mixed liquid with a specific absorption peak wavelength, the formed N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction has a significant improvement in detection performance at the absorption peak wavelength. The liquid-based photodetector testing method based on polar quantum dot mixed liquid of the present invention is easy to operate and has significant performance improvement, and can be applied to scenarios with different special needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of the structure of a photodetector based on N-type gallium arsenide / polar quantum dot mixed liquid / graphene; Figure 2 A schematic diagram of the principle of polarization of polar liquid molecules inside a photodetector based on N-type gallium arsenide / polar quantum dot mixed liquid / graphene; Figure 3 It is a comparison diagram of the output current based on N-type GaAs / MoS2 quantum dot aqueous solution / graphene photodetector (820nm) and based on N-type GaAs / deionized water / graphene photodetector (820nm); Figure 4 This is a graph showing the relationship between the output current and time of the N-type gallium arsenide / tungsten disulfide quantum dot aqueous solution / graphene photodetector (820nm); Figure 5 The optical absorption spectra of CdSe quantum dots toluene solutions with different absorption peak wavelengths (494nm, 527nm, 563nm, 582nm, 600nm); Figure 6 The relationship between the output current growth rate and wavelength based on N-type GaAs / CdSe quantum dot toluene solution (494nm, 527nm, 563nm, 582nm, 600nm) / graphene photodetector and based on N-type GaAs / toluene / graphene photodetector (494nm, 527nm, 563nm, 582nm, 600nm); Figure 7This is a comparison chart of the output current at the absorption peak based on N-type GaAs / CdSe quantum dot toluene solution (494nm, 527nm, 563nm, 582nm, 600nm) / graphene photodetector and based on N-type GaAs / toluene / graphene photodetector (494nm, 527nm, 563nm, 582nm, 600nm). DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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.

[0016] Reference Figure 1 , is a specific example of the present invention, the structure of the liquid-based photodetector device based on the polar quantum dot mixed liquid of this example is as follows Figure 1 As shown, from top to bottom, the first electrode 1, N-type semiconductor 2, polar quantum dot mixed liquid 3, graphene 4, and second electrode 5 are provided. The liquid-based photodetector based on polar quantum dot mixed liquid of the present invention utilizes the Fermi level difference between graphene and N-type semiconductor to polarize the polar liquid. Under the irradiation of the light source, the quantum dots are excited by light to generate electron-hole pairs, and the electron-hole pairs transition to the surface of the quantum dots, polarizing the surrounding polar liquid molecules. The quantum dots are evenly distributed in the polar liquid, connecting the short-range ordered polarized liquid molecules to form a long-range ordered electron / hole transmission channel, thereby generating a photopolarized current inside the liquid to increase the output photopolarized current. In order to more comprehensively detect the effect of the liquid-based photodetector based on the polar quantum dot mixed liquid of the present invention, the test process includes the following test steps: (1) measuring the photopolarization current of the same wavelength fixed power laser directly irradiated on the N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction and the N-type semiconductor / polar liquid / graphene heterojunction through a detection device; (2) measuring the photopolarization current of different wavelength lasers directly irradiated on the N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction and the N-type semiconductor / polar liquid / graphene heterojunction through a detection device, and comparing to obtain the output current growth rate; (3) measuring the photopolarization current of the laser directly irradiated on the N-type semiconductor / polar quantum dot mixed liquid / graphene heterojunction with different absorption peaks and the N-type semiconductor / polar liquid / graphene heterojunction at the absorption peak wavelength through a detection device. When the absorption peaks of the polar quantum dot mixed liquid are different, the quantum dots are at the absorption peak, the dynamic exciton effect is enhanced, the mobile free carriers increase, and more polar liquid molecules are polarized, thereby causing a significant increase in the instantaneous photopolarization current. Therefore, the performance of photodetectors in the corresponding band can be selectively improved by customizing the absorption peak wavelength of quantum dots.

[0017] Embodiment 1: 1) Plate a gold electrode on one side of N-type GaAs with a resistivity of 10Ω·cm; 2) Take a piece of polyethylene terephthalate (PET) flexible substrate of appropriate size, put the substrate into acetone solution and ethanol solution in turn to clean the surface of the substrate, remove impurities attached to the surface, and blow dry with N2; 3) Select one side of the PET flexible substrate as the front side, and transfer the single-layer graphene to the front side of the PET substrate; 4) Making electrodes on the graphene surface, made of 50nm silver electrodes; 5) A working window is formed on the other side surface of the N-type gallium arsenide with a resistivity of 10 Ω·cm using ultraviolet glue, and 10 μL of molybdenum disulfide quantum dot aqueous solution is dripped into the window; 6) turning the PET substrate over so that the back side faces upwards, thereby covering the graphene side on the working window, and making the graphene in 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; 7) Connect the silver electrode on the graphene to the positive pole of the ammeter, and connect the gold electrode on the N-type gallium arsenide to the negative pole of the ammeter; 8) irradiating a light source onto the N-type gallium arsenide / molybdenum disulfide quantum dot aqueous solution / graphene, and measuring the peak current of the N-type gallium arsenide / molybdenum disulfide quantum dot aqueous solution / graphene heterojunction structure when the light source is directly irradiated; 9) The molybdenum disulfide quantum dot aqueous solution was replaced with 10 μL deionized water, and the same light source conditions were controlled for irradiation. The peak current of the N-type gallium arsenide / deionized water / graphene heterojunction structure was measured for comparison; 10) The molybdenum disulfide quantum dot aqueous solution was replaced with a tungsten disulfide quantum dot aqueous solution, and the same light source conditions were controlled for irradiation. The peak current of the N-type gallium arsenide / tungsten disulfide quantum dot aqueous solution / graphene heterojunction structure was measured. Taking the N-type GaAs / MoS2 quantum dot aqueous solution / graphene photodetector as an example, the principle diagram of the polarization of polar liquid molecules inside the solution is as follows: Figure 2As shown in the figure, when there is no light, there is a Fermi level difference between graphene and N-type gallium arsenide, polarizing water molecules. When the light source shines on the surface of the semiconductor, the semiconductor absorbs photons, a large number of minority carriers are excited, and the surface water molecules are further polarized. MoS2 quantum dots are excited by photons, and internal carrier transitions produce electron-hole pairs, which migrate to the surface of the quantum dots. The surface of hydrogen atoms inside water molecules is positively charged, and the surface of oxygen atoms is negatively charged. Therefore, the electrons on the surface of the quantum dots attract the positively charged hydrogen atoms, and at the same time, the holes on the surface of the quantum dots attract the negatively charged oxygen atoms. Taking the electron transmission channel as an example, the positively charged hydrogen atoms contact the electrons on the surface of the quantum dots, the positive charge state of the hydrogen atoms on the surface is reduced, and the negative charge state of the oxygen atoms on the surface is surplus, which is transmitted to the corresponding positively charged hydrogen atoms of the connected adjacent water molecules through hydrogen bonds, forming a short-range ordered water polarization electron transmission channel. MoS2 quantum dots are evenly distributed in deionized water, connecting the surrounding short-range ordered polarized water molecules to form long-range ordered water-polarized electron / hole transmission channels, transmitting electrons / holes to the semiconductors on both sides, forming internal polarization currents to further increase the output polarization current. For N-type GaAs, it has good light absorption intensity under 820nm illumination and excellent photoelectric performance. MoS2 quantum dots also have a certain light absorption intensity at 820nm. Therefore, the introduction of MoS2 quantum dots further improves the photocurrent of GaAs-based liquid photodetectors. By introducing the photocurrent test of N-type GaAs / deionized water / graphene photodetector and comparing it with N-type GaAs / MoS2 quantum dot aqueous solution / graphene photodetector, it can be obtained. Figure 3 , the output photocurrent of N-type GaAs / deionized water / graphene photodetector reached 3.76μA, and the output photocurrent of N-type GaAs / molybdenum disulfide quantum dot aqueous solution / graphene reached 11.5μA, which effectively increased the output photocurrent by 3.06 times. At the same time, tungsten disulfide quantum dots 820nm also have a certain light absorption intensity. When introducing the photocurrent test of N-type GaAs / tungsten disulfide quantum dot aqueous solution / graphene photodetector, we get Figure 4 The output photocurrent of the N-type gallium arsenide / tungsten disulfide quantum dot aqueous solution / graphene photodetector reached 10.4μA, which was effectively increased by 2.77 times compared with the output current of the N-type gallium arsenide / deionized water / graphene photodetector, verifying that the introduction of polarized quantum dot mixed liquid can provide a certain photocurrent enhancement at the effective absorption wavelength of the N-type semiconductor.

[0018] Embodiment 2: 1) Plate a gold electrode on one side of the N-type GaAs with a resistivity of 10Ω·cm; 2) Take a piece of polyethylene terephthalate (PET) flexible substrate of appropriate size, put the substrate into acetone solution and ethanol solution in turn to clean the surface of the substrate, remove impurities attached to the surface, and blow dry with N2; 3) Select one side of the PET flexible substrate as the front side, and transfer the single-layer graphene to the front side of the PET substrate; 4) Making electrodes on the graphene surface, made of 50nm silver electrodes; 5) measuring the absorption spectra of different cadmium selenide quantum dots by an absorption spectrometer to obtain the absorption peak wavelength; 6) A working window is formed on the other side surface of the N-type gallium arsenide with a resistivity of 10 Ω·cm by using UV glue, and 10 μL of a toluene solution of cadmium selenide quantum dots with an absorption peak at 494 nm is dropped into the window; 7) Flipping the PET substrate so that the graphene side directly covers the working window and the graphene is 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; 8) Connect the silver electrode on the graphene to the positive pole of the ammeter, and connect the gold electrode on the N-type gallium arsenide to the negative pole of the ammeter; 9) Irradiate the light source onto the N-type GaAs / CdSe quantum dot toluene solution (494nm) / graphene and measure the peak current I when the light source is directly irradiated s494nm ; 10) Measure the output peak current I of the N-type GaAs / CdSe quantum dot toluene solution / graphene photodetector with absorption peaks of 527nm, 563nm, 582nm, and 600nm respectively s527nm , I s563nm , I s582nm , I s600nm ; 11) Replace the CdSe quantum dot toluene solution with 10 μL toluene, control the same light source conditions for irradiation, and measure the peak current I when the light source directly irradiates the N-type GaAs / 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 Compare with the output photocurrent of graphene / cadmium selenide quantum dot toluene solution / N-type gallium arsenide; 12) Based on the absorption peak wavelength of CdSe quantum dot toluene solution, a wavelength scanning step of plus or minus 10 nm was selected, and five wavelengths were scanned respectively to measure the output photocurrent I of N-type GaAs / CdSe quantum dot toluene solution / graphene at different wavelengths. s and the output photocurrent I of N-type GaAs / toluene / graphene, through I s / i outputs the calculated photocurrent growth rate. The absorption spectra of different cadmium selenide quantum dot toluene solutions were measured by absorption spectrometer. Figure 5As shown in the figure, it can be seen that the absorption peaks of toluene solutions of cadmium selenide quantum dots of different sizes are different, with obvious absorption peaks at 494nm, 527nm, 563nm, 582nm and 600nm, respectively, proving that the absorption intensity of cadmium selenide quantum dots is the largest at this wavelength. Select a wavelength scanning step of plus or minus 10nm and scan five wavelengths respectively, and measure the change curve of the photocurrent growth rate of toluene solutions of cadmium selenide quantum dots with different absorption peak wavelengths as shown in the figure below. Figure 6 As shown, with the change of scanning wavelength, the photocurrent growth rate reaches the maximum value at the absorption peak wavelength, and shows a certain decreasing trend at other wavelengths, which is the same trend as the absorption spectrum curve of CdSe quantum dot toluene solution. For N-type GaAs, the absorption intensity is weak at wavelengths of 400nm-600nm. The introduction of CdSe 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 photopolarized current, effectively improving the photocurrent of N-type GaAs-based liquid photodetector. The output photocurrents of N-type GaAs / CdSe quantum dot toluene solution / graphene and N-type GaAs / toluene solution / graphene were tested at the absorption peak wavelength, as shown in Figure 7 As shown, after comparison, it can be obtained that the output photocurrent of N-type GaAs / CdSe quantum dot toluene solution / graphene is significantly enhanced at the absorption peak wavelength. Among them, the output photocurrent of N-type GaAs / CdSe quantum dot toluene solution / graphene photodetector based on CdSe quantum dot toluene solution with absorption peak wavelengths of 494nm, 527nm, 563nm, 582nm and 600nm is increased by 3.14, 2.35, 2.24, 2.49 and 3.63 times respectively compared with the N-type GaAs / toluene solution / graphene photodetector.

Claims

1. A liquid-based photoelectric detector based on a polar quantum dot mixed liquid, characterized in that: The invention comprises: an N-type semiconductor (2), a polar quantum dot mixed liquid (3), and graphene (4), and also comprises a first electrode (1) and a second electrode (5) respectively arranged on the N-type semiconductor and the graphene, wherein the N-type semiconductor (2) and the graphene (4) are both in contact with the polar quantum dot mixed liquid (3), and the absorption peak wavelength of the polar quantum dot mixed liquid (3) is customized by adjusting the size of the quantum dots, thereby selectively improving the detection performance of the photodetector at the absorption peak wavelength.

2. The liquid-based photoelectric detector based on polar quantum dot mixed liquid according to 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, and have a thickness of 50-300 nm.

3. The liquid-based photoelectric detector based on polar quantum dot mixed liquid according to claim 1, characterized in that: The N-type semiconductor (2) is a semiconductor layer independently selected from one of gallium nitride, gallium arsenide and silicon.

4. The liquid-based photoelectric detector based on polar quantum dot mixed liquid according to claim 1, characterized in that: The polar quantum dot mixed liquid (3) is a quantum dot mixed solution based on a polar liquid solvent, selected from a molybdenum disulfide quantum dot aqueous solution, a tungsten disulfide quantum dot aqueous solution, and a cadmium selenide quantum dot toluene solution, and the quantum dot absorption peak wavelength is customized by regulating the size of the quantum dots.

5. The method for designing a liquid-based photodetector based on a polar quantum dot mixed liquid according to any one of claims 1 to 4, characterized in that: The absorption peak wavelength of the polar quantum dot mixed liquid (3) is customized by regulating the size of the quantum dots, thereby selectively improving the detection performance of the photodetector at the absorption peak wavelength.

6. A method for preparing a liquid-based photodetector based on a polar quantum dot mixed liquid as claimed in any one of claims 1 to 4, characterized in that: include: A first electrode (1) is prepared on one surface of an N-type semiconductor (2), and the other surface faces upward. A polar quantum dot mixed liquid (3) is arranged on the first surface. Graphene (4) is laid on the polar quantum dot mixed liquid (3). 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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