Quantum dot infrared light multiplication detector, preparation method and application thereof

Abstract

The application belongs to the technical field of infrared photoelectric detection, and particularly relates to a quantum dot infrared light multiplication detector and a preparation method and application thereof. The application discloses a quantum dot infrared light multiplication detector and a preparation method and application thereof. 60 Compared with a device without a C interface layer, the device disclosed by the application has reduced dark current, stable photoelectric current polarity, and can obtain a light multiplication response with an external quantum efficiency greater than 100% under infrared light. The detector is suitable for short-wave infrared weak light detection, infrared imaging, and image sensors integrated with a CMOS readout circuit.

Description

Technical Field

[0001] This invention belongs to the field of infrared photoelectric detection technology, specifically relating to a quantum dot infrared light multiplication detector, its preparation method, and its application. Background Technology

[0002] Short-wave infrared detection has applications in night vision imaging, machine vision, semiconductor inspection, biomedical imaging, spectral recognition, and optical communication. Existing high-performance short-wave infrared detectors mostly use epitaxial semiconductor materials such as InGaAs and HgCdTe, which have good device performance, but the material and fabrication costs are high, and there are also certain limitations to their large-area low-temperature integration with silicon-based readout circuits.

[0003] Colloidal quantum dot materials possess advantages such as tunable bandgap, solution processing, low-temperature film formation, and ease of heterogeneous integration. Among them, quantum dots such as PbS, PbSe, HgTe, and InAs can achieve absorption in the near-infrared to short-wave infrared bands through size control, making them suitable for constructing low-cost infrared detectors.

[0004] Quantum dot infrared detectors typically include photoconductive, photodiode, and phototransistor structures. Photoconductive devices can achieve high photoelectric gain, but their dark current and noise are usually high, and their response speed is easily affected by trapped states. Photodiode devices have low dark current, but their external quantum efficiency is usually limited by light absorption and carrier collection efficiency, making it difficult to achieve significant photomultiplication.

[0005] For quantum dot infrared photomultiplier detectors, the key challenge lies in achieving high gain by opening the carrier injection channel under illumination while simultaneously preventing significant leakage current in the dark. In existing devices, defects, Fermi level pinning, or uncontrolled band bending easily occur at the interface between the quantum dot layer and the electron transport layer or metal electrodes, leading to increased dark current, unstable photocurrent polarity, or decreased device repeatability.

[0006] Therefore, a quantum dot infrared photomultiplier detector that can simultaneously control dark-state injection, light-state injection, and contact polarity is needed. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a quantum dot infrared light multiplication detector, its preparation method and application. The detector can be used for short-wave infrared weak light detection, infrared imaging, spectral detection and infrared image sensor integrated with CMOS readout circuit.

[0008] To achieve the aforementioned objective, the present invention provides a quantum dot infrared photomultiplier detector, comprising a bottom electrode, a first electron transport layer, a quantum dot infrared absorption layer, a molecular interface layer, a second electron transport layer, and a top electrode arranged sequentially from bottom to top along a vertical direction; the molecular interface layer is used to reduce the interface leakage current caused by direct contact between the quantum dot infrared absorption layer and the second electron transport layer, and to maintain the photocurrent polarity of the device; the quantum dot infrared absorption layer is used to generate photogenerated charges under infrared illumination, and the photogenerated charges form a restricted electron injection contact with the first electron transport layer, thereby enhancing electron injection and generating a photomultiplier response.

[0009] Furthermore, the bottom electrode is one of ITO, FTO, IZO, AZO, graphene, and metal nanowire transparent electrodes; the top electrode is one or more of Ag, Al, Au, Cu, ITO, IZO, and AZO.

[0010] Furthermore, the first electron transport layer is one or more of ZnO, ZnMgO, SnO2, TiO2, In2O3, and Nb2O5, preferably ZnO. The thickness of the first electron transport layer is 5 nm to 50 nm.

[0011] Furthermore, the quantum dot infrared absorption layer is one or more of PbS, PbSe, HgTe, Ag2Se, Ag2Te, InAs, and InSb, preferably a PbS quantum dot thin film.

[0012] Furthermore, the molecular interface layer is C 60 Layer; the C 60 The layer thickness is 1 nm to 50 nm, preferably 3 nm to 30 nm, and more preferably 5 nm to 20 nm.

[0013] Furthermore, the second electron transport layer is one or more of SnO2, ZnO, TiO2, In2O3, and Nb2O5, preferably SnO2.

[0014] Furthermore, this includes the following steps: 1) The first electron transport layer is prepared on the bottom electrode by solution spin coating, spraying, blade coating, atomic layer deposition or magnetron sputtering; 2) A quantum dot infrared absorption layer is fabricated on the first electron transport layer; 3) Perform ligand exchange, halogen treatment, annealing or surface passivation on the quantum dot infrared absorption layer; 4) A molecular interface layer is deposited on the quantum dot infrared absorption layer by thermal evaporation; 5) A second electron transport layer is deposited on the molecular interface layer by magnetron sputtering; 6) Deposit the top electrode on the second electron transport layer.

[0015] Furthermore, in step 3), the ligand exchange or surface passivation treatment uses one or more of halide salts, short-chain organic ligands, and bidentate ligands; the halide salts include one or more of iodide salts, bromide salts, or chloride salts; the short-chain organic ligands include one or more of 1,2-ethylenedithiol, 3-mercaptopropionic acid, and mercaptoacetic acid.

[0016] Furthermore, the quantum dot infrared absorption layer is a PbS quantum dot thin film, and it is prepared by spin coating, blade coating, spray coating, inkjet printing, slot coating, or layer-by-layer deposition; the PbS quantum dot solution for forming the PbS quantum dot thin film is prepared by hot injection; the PbS quantum dot solution includes lead oxide, oleic acid, octadecene solution, and thiourea, and the first exciton absorption peak of the PbS quantum dot thin film is from 1000 nm to 2000 nm. By changing the amount of oleic acid in the PbS quantum dot solution, the size of the final PbS quantum dot film can be altered, thereby changing the first exciton absorption peak of the PbS quantum dot film.

[0017] Preferably, an application of a quantum dot infrared light multiplication detector is characterized in that the detector is applied in an infrared image sensor.

[0018] An infrared image sensor includes a CMOS readout circuit; the quantum dot infrared light multiplier detector is disposed on the CMOS readout circuit and electrically connected to the pixel readout node in the CMOS readout circuit.

[0019] The beneficial effects of this invention are reflected in: (1) The detector provided by the present invention forms an asymmetric Nin structure through a first electron transport layer, a quantum dot infrared absorption layer, a molecular interface layer, and a second electron transport layer. In this structure, the first electron transport layer and the quantum dot infrared absorption layer form a confined electron injection contact, and the molecular interface layer and the second electron transport layer form an electron extraction and hole blocking contact. In the dark state, due to the confined electron injection contact at the bottom and the molecular interface layer C 60 Together, they suppress dark current. Under infrared illumination, the quantum dot infrared absorption layer generates photogenerated charges, which modulate the bottom electron injection barrier, enhancing electron injection and thus producing a photomultiplication response. The molecular interface layer isolates the direct contact between the quantum dot infrared absorption layer and the second electron transport layer, reducing interface leakage and stabilizing the photocurrent direction of the device, thereby interacting with C-free... 60 Compared to devices with an interface layer, the device of this invention has reduced dark current, maintained stable photocurrent polarity, and achieved a photomultiplication response with an external quantum efficiency greater than 100% under infrared illumination.

[0020] (2) The detector provided by the present invention can further adjust the dark state injection barrier and the injection enhancement under illumination by adjusting the size of PbS quantum dots, ligands or the n-type degree of thin film, so that the device can obtain higher photoelectric gain under low dark current conditions. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the quantum dot infrared light multiplication detector of the present invention; Figure 2 For ITO / ZnO / PbS quantum dots / C 60 Schematic diagram of the energy level structure of the / SnO2 / Ag device; Figure 3 A schematic diagram of the photomultiplication response of PbS quantum dots with an external quantum efficiency greater than 100%; Figure 4 When PbS quantum dots with an absorption wavelength of 1800 nm are used as the light-absorbing layer, the light-dark current curve of the device is shown. Figure 5 The EQE curve of the device when PbS quantum dots with an absorption wavelength of 1800 nm are used as the light-absorbing layer; Figure 6 When PbS quantum dots with an absorption wavelength of 1550 nm are used as the light-absorbing layer, the light-dark current curve of the device is shown. Figure 7 For containing C 60 Layer devices and C-free 60 A schematic diagram comparing the dark current of layer devices; Figure 8 This is a schematic diagram of the integrated structure of a quantum dot infrared light multiplication detector array and a CMOS readout circuit. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] like Figure 1-8 As shown, this invention provides a quantum dot infrared light multiplication detector, its fabrication method, and its application. It includes a bottom electrode, a first electron transport layer, a quantum dot infrared absorption layer, a molecular interface layer, a second electron transport layer, and a top electrode, arranged sequentially.

[0024] The first electron transport layer forms a confined electron injection contact with the quantum dot infrared absorption layer, and the molecular interface layer (is C) 60A layer is disposed between the quantum dot infrared absorption layer and the second electron transport layer to reduce interface leakage and stabilize the photocurrent polarity of the device.

[0025] The Fermi level position or n-type prevalence of the quantum dot infrared absorption layer can be tuned by quantum dot size, surface ligands, halogen treatment, Pb / S stoichiometry, annealing temperature, or surface passivation. The quantum dot infrared absorption layer is tuned to a state where electron injection is limited in the dark and enhanced under infrared illumination by photogenerated charge modulation. This detector can be applied in infrared image sensors. Specific implementation details are as follows: Example 1 Preparation of ITO / ZnO / PbS quantum dots / C 60 An infrared light multiplier detector with a SnO2 / Ag structure. Its device structure and band structure diagram are shown below. Figure 1 and Figure 2 As shown.

[0026] First, the purchased commercial ITO transparent conductive glass (bottom electrode) is cleaned and then treated with ultraviolet ozone.

[0027] A ZnO thin film is then deposited on ITO as the first electron transport layer. ZnO can be prepared by solution spin coating, spraying, blade coating, atomic layer deposition, or magnetron sputtering. In actual preparation, the thickness of the first electron transport layer is 5-50 nm.

[0028] Then, a PbS quantum dot film was deposited on the ZnO layer. The PbS quantum dot solution was prepared using the classic hot injection method, specifically by injecting 20 mL of thiourea into a solution of 0.903 g lead oxide, 2.45 mL oleic acid, and 30 mL octadecene at 135 °C under vacuum, holding for 20 minutes, and then cooling to room temperature.

[0029] The first exciton absorption peak of the PbS quantum dot film prepared from the above PbS quantum dot solution is located at 1500 nm.

[0030] PbS quantum dot films can be prepared by spin coating or layer-by-layer deposition, with ligand exchange and surface passivation treatments performed during or after deposition. A combination of iodide and bromide salts is used as the ligand exchange agent.

[0031] Subsequently, C was deposited on the PbS quantum dot film by thermal evaporation. 60 The layer serves as the molecular interface layer. In actual preparation, C... 60 The layer thickness is 1-50 nm. Then, in C... 60 A SnO2 layer is deposited on top of the layer as a second electron transport layer.

[0032] Finally, an Ag top electrode is deposited to obtain an infrared photomultiplier detector.

[0033] Figure 1 The silver electrode on the ITO glass is the final thermally vapor-deposited top electrode, deposited on the exposed ITO, with the aim of better drawing out the current. The performance of the device obtained in Example 1 was tested using a source table. The results showed that the device had a low dark current in the dark state due to electron injection being restricted by the ZnO / PbS contact. Under infrared illumination, the PbS quantum dots absorbed photons to generate photogenerated charges. These photogenerated charges modulated the bottom electron injection barrier, enhancing electron injection into the external circuit. The injected electrons passed through C... 60 / SnO2 top contact extraction forms a photomultiplication response with an external quantum efficiency greater than 100%. The external quantum efficiency testing system measures its EQE as follows: Figure 3 As shown, the maximum EQE is 750%, and the EQE at the 1500 nm absorption peak can also reach 200%, far exceeding that of traditional diode-structured detection devices. Comparative Example 1 The energy levels and n-type degree of the PbS quantum dot film were controlled. The same device structure as in Example 1 was used, except that a different size of PbS quantum dot film was selected.

[0034] The quantum dot size control is specifically achieved by increasing the amount of oleic acid in the octadecene solution from 2.45 mL to 2.8 mL when preparing PbS quantum dot solution using the classic hot injection method, resulting in a PbS quantum dot film with a first exciton absorption peak of 1800 nm.

[0035] Ultraviolet photoelectron spectroscopy (UVP) analysis of the obtained PbS quantum dot thin film revealed that its semiconductor properties, becoming more n-type, are more conducive to electron transport. Therefore, the device's dark current increases; simultaneously, electron injection is more easily initiated under illumination, leading to a corresponding increase in photocurrent, as shown in its JV curve and EQE curve. Figure 4 , Figure 5 As shown: Under a bias voltage of -1 V, its photocurrent density reaches as high as 300 mA / cm². 2 The maximum EQE can reach 900%.

[0036] The quantum dot size control is specifically achieved by increasing the amount of oleic acid in the octadecene solution from 2.45 mL to 2.5 mL when preparing PbS quantum dot solution using the classic hot injection method, resulting in a first exciton absorption peak of 1550 nm for the final PbS quantum dot film.

[0037] The current level of the obtained device was detected by source meter. The test results show that when PbS quantum dots with an absorption wavelength of 1550 nm are used as the light-absorbing layer, the electron injection barrier of the thin film is increased, the dark current of the device is lower, but the photomultiplication under illumination is weaker, as shown in the JV curve. Figure 6As shown: Under a bias voltage of -1 V, its dark current density decreases to 8 × 10⁻⁶. -4 mA / cm 2 However, the photocurrent density will also decrease to 80 mA / cm². 2 Although it still has a multiplier effect, the effect is weakened.

[0038] This indicates that the energy level states of PbS quantum dot films need to be within a moderate range to suppress dark-state electron injection while allowing for significant injection enhancement under illumination.

[0039] Comparative Example 2 Comparison of C 60 Molecular interface layer and C-free 60 Devices at the molecular interface layer. Two sets of devices were fabricated using the same process as in Example 1. The first set had a structure of ITO / ZnO / PbS quantum dots / C. 60 / SnO2 / Ag; where C 60 The first layer has a thickness of 20 nm; the second structure is ITO / ZnO / PbS quantum dots / SnO2 / Ag; the absorption peak of the PbS quantum dots is 1000 nm and the thickness of the ZnO is 50 nm.

[0040] like Figure 7 As shown, the JV curve test indicates that: without C 60 The molecular layer devices not only saw their dark current density surge to 0.7 mA / cm² at -1 V. 2 Much higher than C 60 The standard device at the molecular level exhibits a reversal of dark current polarity.

[0041] This result indicates that C 60 The layer not only assists in electron transport but also reduces interfacial leakage caused by direct contact between the PbS quantum dot layer and the SnO2 layer, and helps stabilize the photocurrent polarity at the top contact. Therefore, a C layer is placed between the PbS quantum dot layer and the SnO2 layer. 60 The molecular interface layer is beneficial for obtaining infrared light multiplication response with low dark current and stable polarity.

[0042] Example 2 The quantum dot infrared light multiplier detector is integrated into the CMOS readout circuit.

[0043] A first electron transport layer, a PbS quantum dot infrared absorption layer, and a C layer are sequentially fabricated on the pixel electrode of the CMOS readout circuit. 60 A molecular interface layer, a second electron transport layer, and a common top electrode form a quantum dot infrared photomultiplier detector array. Each detector pixel is electrically connected to a corresponding CMOS pixel readout node. A schematic diagram of its structure is shown below. Figure 8As shown: depending on the specifications of the customized CMOS readout circuit, it is easy to fabricate a high-quality, high-pixel detection imaging array.

[0044] Because the detector exhibits a photomultiplication response, the readout signal can be improved under weak infrared illumination conditions; simultaneously, the suppression of dark current reduces the impact of dark noise on image quality. Therefore, devices fabricated using this structure can be used as short-wave infrared image sensors under weak light conditions.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A quantum dot infrared light multiplication detector, characterized in that, The device comprises, from bottom to top, a bottom electrode, a first electron transport layer, a quantum dot infrared absorption layer, a molecular interface layer, a second electron transport layer, and a top electrode, arranged vertically. The molecular interface layer is used to reduce the interface leakage current caused by the direct contact between the quantum dot infrared absorption layer and the second electron transport layer, and to maintain the photocurrent polarity of the device. The quantum dot infrared absorption layer is used to generate photogenerated charges under infrared light, and the photogenerated charges form a restricted electron injection contact with the first electron transport layer, thereby enhancing electron injection and generating a photomultiplication response.

2. The quantum dot infrared light multiplication detector according to claim 1, characterized in that, The bottom electrode is one of ITO, FTO, IZO, AZO, graphene, and metal nanowire transparent electrodes; the top electrode is one or more of Ag, Al, Au, Cu, ITO, IZO, and AZO.

3. The quantum dot infrared light multiplication detector according to claim 1, characterized in that, The first electron transport layer is one or more of ZnO, ZnMgO, SnO2, TiO2, In2O3, and Nb2O5.

4. The quantum dot infrared light multiplication detector according to claim 1, characterized in that, The quantum dot infrared absorption layer is one or more of PbS, PbSe, HgTe, Ag2Se, Ag2Te, InAs, and InSb.

5. A quantum dot infrared light multiplication detector according to claim 1, characterized in that, The molecular interface layer is C. 60 layer.

6. A quantum dot infrared light multiplication detector according to claim 1, characterized in that, The second electron transport layer is one or more of SnO2, ZnO, TiO2, In2O3, and Nb2O5.

7. A method for fabricating a quantum dot infrared light multiplication detector according to any one of claims 1-6, characterized in that, Includes the following steps: 1) Fabricate the first electron transport layer on the bottom electrode; 2) A quantum dot infrared absorption layer is fabricated on the first electron transport layer; 3) Perform ligand exchange, halogen treatment, annealing or surface passivation on the quantum dot infrared absorption layer; 4) A molecular interface layer was prepared on the quantum dot infrared absorption layer by thermal evaporation. 5) A second electron transport layer was prepared on the molecular interface layer by magnetron sputtering; 6) Deposit the top electrode on the second electron transport layer.

8. The method for fabricating a quantum dot infrared light multiplication detector according to claim 7, characterized in that, In step 3), the ligand exchange or surface passivation treatment uses one or more of halide salts, short-chain organic ligands, and bidentate ligands; the halide salts include one or more of iodide salts, bromide salts, or chloride salts; the short-chain organic ligands include one or more of 1,2-ethanedithiol, 3-mercaptopropionic acid, and mercaptoacetic acid.

9. The method for fabricating a quantum dot infrared light multiplication detector according to claim 8, characterized in that, The quantum dot infrared absorption layer is a PbS quantum dot thin film, and it is prepared by spin coating, blade coating, spray coating, inkjet printing, slot coating or layer-by-layer deposition; the PbS quantum dot solution for forming the PbS quantum dot thin film is prepared by hot injection method; the first exciton absorption peak of the PbS quantum dot thin film is 1000 nm to 2000 nm.

10. The application of a quantum dot infrared light multiplication detector according to any one of claims 1-6, characterized in that, The detector is used in an infrared image sensor.

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