A dry preparation method for PbS quantum dot film and a phototransistor forming a heterojunction with silicon

Abstract

The present invention discloses a method for preparing a PbS quantum dot film. The PbS quantum dot film is formed by reacting a uniform, continuous thin film of PbI2 as a Pb source with a S source at a temperature of 220-300°C in a mixed atmosphere of hydrogen and inert gas. This method achieves the controllable preparation of an organic ligand-free PbS quantum dot film. The preparation method is simple, highly reliable, and has good results. The prepared PbS quantum dot film has a coverage rate of at least 50% on the substrate surface. The present invention also discloses a heterojunction phototransistor constructed by combining the PbS quantum dot film prepared by the preparation method with silicon. As the coverage rate of the PbS quantum dot film on the substrate surface increases, the photoelectric properties of the constructed heterojunction phototransistor, such as responsivity and specific detectivity, are significantly improved.

Description

Technical Field

[0001] The present invention relates to the fields of photoelectric technology and photoelectric detectors, and in particular to a method for preparing a PbS quantum dot film, and a phototransistor with a heterojunction formed by the PbS quantum dot film and silicon. Background Art

[0002] Quantum dots possess unique optoelectronic properties and have a wide range of applications, including luminescence, detection, and sensing. Photodetectors, core components for converting optical signals into electrical signals, play a crucial role in various optical detection scenarios. They utilize the photoelectric effect of specialized materials to accurately sense light of varying intensities and frequencies. Widely used in environmental monitoring, security monitoring, imaging, and optical communications, photodetectors are an indispensable component of modern optoelectronics technology. However, conventional photodetectors are increasingly unable to meet development demands in terms of sensitivity and response speed. Against this backdrop, the development of photodetectors based on novel functional materials has become a key focus.

[0003] PbS quantum dots (PbS QDs) are a zero-dimensional semiconductor nanomaterial composed of lead (Pb) and sulfur (S). They exhibit significant quantum confinement and a large Bohr exciton radius, which endow them with unique optical and electrical properties. Precise control of quantum dot size allows for tuning of their band gap, enabling precise regulation of their absorption and emission spectra in the near-infrared region. These advantages make PbS QDs particularly advantageous in near-infrared light detection. Furthermore, PbS QDs have a high extinction coefficient and strong light absorption, effectively improving photoelectric conversion efficiency. These properties give them enormous potential for application in photodetectors.

[0004] In the field of synthesis of PbS quantum dots, the wet preparation method is used. The wet preparation method refers to the reaction carried out in solution. In the specific solution system synthesis process, the reactants undergo chemical reactions in a liquid solvent. In order to control the size of quantum dots and prevent them from agglomerating in solution, a key feature of this method is that organic molecules must be added. These organic molecules wrapped on the surface of quantum dots are called surface ligands. The known surface ligands include tetrabutylammonium iodide (TBAI) and ethanedithiol [ACS Photonics (2020), 7(8), 1932-1941], mercaptopropionic acid [ACS Applied Materials&Interfaces(2018), 10(36), 30283-30295], picolinic acid, 2,6-dipicolinic acid, salicylic acid, etc. acid), thiourea and thiosemicarbazide [Chemistry of Materials (2011), 23(18), 4158-4169]. PbS then forms core-shell structures, dumbbell structures or other more complex structures with these organic compounds, such as PbS-ligand; such quantum dots are called colloidal quantum dots. However, this core-shell encapsulation structure increases the van der Waals interaction distance at the interface between quantum dots. For applications in optoelectronic devices, the organic ligands on the surface of quantum dots will seriously affect the transport characteristics of carriers, thereby affecting the performance and stability of the device. The PbS quantum dot products prepared by the wet method must contain surface ligands, and colloidal chemical synthesis is one of the commonly used methods. On the other hand, for quantum dots, when applied to optoelectronic devices, it is expected that independent quantum dots can form a complete continuous film rather than separated quantum dots; thus, compared with independent separated quantum dots, the continuous and complete quantum dot film can improve light absorption, facilitate carrier transport, and enhance the characteristics of optoelectronic devices.

[0005] There are no related research reports in the prior art on the preparation method of PbS quantum dot thin films that involve hydrogen in the preparation process and do not contain surface ligands. Summary of the Invention

[0006] To address existing problems in this field, especially the fundamental difficulty of hindered carrier transport and poor device performance caused by the presence of organic ligands during chemical preparation, the present invention proposes a dry-process preparation method for PbS quantum dot films. The PbS quantum dots prepared by the present invention have no organic ligands on their surface, significantly improving the nucleation density, thereby achieving the controllable preparation of quantum dots with smaller size and more uniform distribution, and realizing efficient carrier transport.

[0007] Solution system

[0008] A solution system refers to a synthetic process environment in which reactants undergo chemical reactions in a liquid solvent to produce products. In the field of quantum dot preparation, this usually refers to the traditional colloidal chemical synthesis method. A key feature of this system is that in order to control the size of quantum dots and prevent them from agglomerating in the liquid medium, specific organic molecules must be added as surface ligands during the reaction. The preparation method proposed in this patent is carried out in a non-solution system, which is fundamentally different from the conventional method.

[0009] No surface ligands

[0010] "Without Surface Ligands" is a core characteristic of the PbS quantum dots prepared in this patent, meaning that the surface of the quantum dots is clean and not coated by organic molecules. This is in stark contrast to quantum dots prepared by traditional methods, which must rely on surface ligands—organic molecules that are coated on the surface of the quantum dots during colloidal synthesis to control size and prevent agglomeration. However, these surface ligands form an insulating core-shell structure on the surface of the quantum dots, increasing the distance between the quantum dots, thereby severely hindering the effective transport of carriers and ultimately affecting the performance and stability of the device. Therefore, the preparation of quantum dots without surface ligands through this patented method eliminates this insulating barrier, promotes efficient carrier transport between quantum dots, and significantly improves key performance of optoelectronic devices, such as responsiveness and specific detectivity.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] The present invention provides a dry method for preparing a PbS quantum dot film. The preparation method comprises the following steps: using a uniform and continuous PbI2 film as a Pb source to react with an S source to form the PbS quantum dot film in a mixed atmosphere of hydrogen and an inert gas.

[0013] Completely different from the wet preparation method, the dry preparation method of the present invention does not involve surface ligands or solvents in the reaction system. The reaction system of the preparation method of the present invention is a reaction system without surface ligands.

[0014] Specifically, the reaction formula of the reaction involved in the preparation method of the present invention is as follows:

[0015]

[0016] The reaction of the present invention is a free radical reaction process, and its principle diagram is as follows:

[0017]

[0018] The use of H₂ is crucial for improving the efficiency of PbS synthesis. In pure inert gases such as argon or nitrogen, the decomposition of PbI₂ is primarily driven by thermodynamics. Due to the high chemical bond energy of PbI₂ (Pb-I bond energy is approximately 200 kJ / mol), efficient release of Pb atoms through thermal activation alone is difficult. Instead, the PbI₂ surface may only undergo localized breakage, resulting in a limited number of released Pb atoms and poor dispersion. This inefficient decomposition directly limits the density of quantum dot nucleation sites, forcing the limited Pb atoms to diffuse and aggregate through the surface to form large particles, making it difficult to obtain quantum dots with quantum effects. However, the addition of H₂ alters the decomposition pathway through functional reactions. H₂ accelerates the decomposition of PbI₂, generating Pb-containing free radicals and volatile HI. Furthermore, H₂ reacts with I₂ (generated by the direct reaction of PbI₂ with S) to generate HI, reducing the I₂ concentration in the gas phase, promoting the direct reaction of PbI₂ with S, and promoting the continued decomposition of PbI₂, releasing more Pb for the reaction. The function of H2 helps to increase the generation rate of Pb atoms, thereby forming a large number of evenly distributed Pb atomic clusters on the substrate surface, providing dense nucleation sites for subsequent sulfurization reactions and ultimately forming a quantum dot film. In this way, appropriate hydrogen accelerates the decomposition of PbI2, significantly increases the local concentration of Pb atoms in the reaction system, reduces the critical free energy required for nucleation, and leads to a substantial increase in the nucleation density. At the same time, the high-density initial nucleation sites will quickly consume the Pb atoms in the system, inhibiting subsequent secondary nucleation, thereby forming quantum dots of uniform size. In pure inert gas systems such as argon or nitrogen, due to the low nucleation density, Pb atoms that do not participate in nucleation have a high surface mobility and tend to combine with existing quantum dots through diffusion, resulting in large particles continuing to grow by "swallowing" small particles, ultimately forming a coarsened structure with a larger radius.

[0019] Furthermore, the preparation method satisfies at least one of the following characteristics:

[0020] 1) In the mixed atmosphere of hydrogen and inert gas, the ratio of hydrogen to inert gas is 2:1 to 2:5.

[0021] 2) The PbI2 uniform continuous thin film is prepared on the substrate by a physical vapor deposition method (such as thermal evaporation), and the thickness of the PbI2 film on the substrate does not exceed 5 nm. Preferably, the thickness of the PbI2 film on the substrate is 1-5 nm; more preferably, the thickness of the PbI2 film on the substrate is 1-2 nm.

[0022] 3) The sulfur source is solid sulfur powder or H2S. The solid sulfur source is sulfur powder, which is heated to form gaseous sulfur. H2S, as a gaseous sulfur source, is more uniform and more reactive than solid sulfur.

[0023] Sulfur powder generates gaseous S8 cyclic molecules at high temperatures, but its chemical reaction with Pb requires overcoming a high energy barrier. In pure inert gases such as argon or nitrogen, the reaction rate of sulfur vapor with Pb is limited by the degree of sulfur activation, resulting in a slow and uneven reaction process. Some areas experience "starved growth" due to insufficient sulfur supply. The introduction of hydrogen optimizes the sulfur activation process by catalyzing sulfur chain scission (H2 reacts with S8 molecules to form HS· radicals, such as S8+H2→2HS4·, reducing the energy required for sulfur chain scission and promoting the participation of more active sulfur molecules (such as S2 and S4) in the reaction) and accelerating surface reactions (HI generated by the reaction of H2 with PbI2 acts as an acidic medium, enhancing the adsorption of sulfur vapor on the Pb surface and ensuring a more uniform coverage of sulfur atoms on the Pb cluster surface, forming a dense PbS lattice). Inert gases primarily contribute to physical mass transfer and thermal equilibrium, while hydrogen dominates the reaction through its chemical activity and kinetic regulation. Therefore, hydrogen plays multiple roles in the preparation of PbS quantum dots: its chemical activity directly promotes precursor decomposition, kinetically controls crystal coarsening, and optimizes sulfur activation and surface reactions. In contrast, purely inert systems lack chemically active components, limiting reactions to thermodynamic equilibrium, resulting in low nucleation density and uncontrollable growth.

[0024] Furthermore, the reaction temperature is between 220°C and 300°C.

[0025] The present invention also provides a PbS quantum dot film, wherein the PbS quantum dot film is prepared by the aforementioned method, and the coverage of the PbS quantum dots on the substrate surface is not less than 50%. The PbS quantum dots prepared by the present invention do not contain surface ligands.

[0026] Preferably, the substrate is selected from insulating materials or semiconductor materials, including one or a combination of two or more of glass, SiO2, SiC, Si3N4, Al2O3, sapphire, mica, MgO, Si, two-dimensional materials such as MoS2, etc.

[0027] The present invention also provides a heterojunction phototransistor formed by a PbS quantum dot film and silicon, which is characterized in that the heterojunction phototransistor is composed of a silicon layer and the PbS quantum dot film prepared by the above method.

[0028] Preferably, the PbS quantum dot film and silicon form a heterojunction phototransistor, which is characterized by having a two-dimensional layered material layer between the silicon layer and the PbS quantum dot film, and the layered material film includes one or more combinations of graphene, transition metal chalcogenides such as MoS2, PtSe2, CrS2, etc.

[0029] Preferably, the PbS quantum dot film and silicon form a heterojunction phototransistor, which is characterized by an insulating layer between the silicon layer and the PbS quantum dot film, and the insulating layer material includes SiO2 and high dielectric constant HfO2, Hf (1-x) ZrxO2(HZO), Al2O3, TiO2, ZrO2, Ta2O5 and Bi2SeO5; the thickness of the insulating layer is 2-20 nm.

[0030] Further preferably, the PbS quantum dot film and silicon form a heterojunction phototransistor, characterized in that there is a two-dimensional layered material layer between the insulating layer and the PbS quantum dot film, and the layered material film includes one or more combinations of graphene and transition metal chalcogenides.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] In the present invention, a PbI2 thin film is used as a Pb source, and hydrogen participates in the reaction, promoting the reaction between the Pb source and the S source to convert them into PbS quantum dots. The density of the grown PbS quantum dots can be controlled to form a PbS quantum dot film. The present invention provides a simple method for preparing a PbS quantum dot film, and the surface of the prepared quantum dots does not contain an organic ligand layer. This makes it easy to control the preparation of the PbS quantum dots and their coverage on the substrate surface, improving preparation efficiency and material quality. This method is useful for the preparation of high-performance optoelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the preparation method of PbS quantum dot film of the present invention;

[0034] Figure 2 This is a scanning electron microscope image of the PbS quantum dot film prepared in Example 2;

[0035] Figure 3 An X-ray photoelectron spectrometer for the PbS quantum dot film prepared in Example 2;

[0036] Figure 4This is a scanning electron microscope image of the PbS quantum dot film prepared in Example 3;

[0037] Figure 5 This is a scanning electron microscope image of the PbS quantum dot film prepared in Example 4;

[0038] Figure 6 This is a scanning electron microscope image of the PbS quantum dot film prepared in Example 5;

[0039] Figure 7 An X-ray photoelectron spectrometer for the PbS quantum dot film prepared in Example 5;

[0040] Figure 8 This is a scanning electron microscope image of the PbS quantum dot film prepared in Comparative Example 1;

[0041] Figure 9 For Example 3 ( Figure 9 b) and Comparative Example 1 ( Figure 9 a) Size statistical analysis of the prepared PbS quantum dots;

[0042] Figure 10 The results of Example 7 are the current-voltage relationships of the photodetectors constructed using the PbS quantum dot films prepared in Example 2 (device 2), Example 3 (device 3), and Comparative Example 1 (device 1). The different colored curves in the figure represent different incident light intensities (mW cm -2 );

[0043] Figure 11 The results of Example 8 are the current-voltage relationship of the photodetector constructed with PbS (quantum dot film) / MoS2 / SiO2 (20 nm) / Si. The different color curves in the legend represent different incident light intensities (mW cm -2 );

[0044] Figure 12 This is a scanning electron microscope image of the PbS colloidal quantum dots used in Comparative Example 2.

[0045] Figure 13 The X-ray photoelectron spectroscopy results of the PbS quantum dots prepared in Comparative Example 3, (a) S 2p , (b)Pb 4f and (c) I 3d Score.

[0046] Figure 14 Scanning electron microscope image of PbS quantum dots prepared in Comparative Example 2 DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0048] Example 1

[0049] The present invention provides a dry process for preparing a PbS quantum dot film, wherein the reactants include PbI2, S and H2, and the preparation method comprises the following steps (see the schematic diagram for details). Figure 1 ):

[0050] 1) In an inert gas atmosphere, a uniform continuous PbI2 film is used as a Pb source to react with a S source to form PbS quantum dots;

[0051] 2) In the above step 1), hydrogen participates in the reaction;

[0052] 3) In step 1), the reaction temperature is 220-300°C;

[0053] 4) The ratio of hydrogen to inert gas is 2:1 to 2:5;

[0054] 5) The PbS quantum dot film is a film in which the coverage of PbS quantum dots on the substrate surface is not less than 50%, and the coverage result is obtained by calculating the particles in the SEM image.

[0055] The preparation method of the PbS quantum dot film of the present invention does not involve the participation of surface ligands and does not use solvents.

[0056] The reaction formula of the reaction is as follows:

[0057]

[0058] The PbI2 film is deposited on a substrate by thermal evaporation, with a thickness of no more than 5 nm. This thickness range does not significantly affect the subsequent formation of the PbS quantum dot film. The substrate is selected from insulating or semiconductor materials, including one or a combination of two or more of glass, SiO2, SiC, Si3N4, Al2O3, sapphire, mica, MgO, Si, and two-dimensional materials such as MoS2.

[0059] The sulfur source can be solid sulfur powder or H2S. Solid sulfur powder can be heated to form gaseous sulfur. The basic chemical conversion process is as follows: solid sulfur (S) evaporates at high temperature to form S8, and H2 reacts with S to form highly reactive HS• radicals. As a gaseous sulfur source, H2S is more uniform and more reactive than solid sulfur.

[0060] During the chemical reaction, the substrate is heated at a uniform rate and kept at a constant temperature of 220-300°C.

[0061] Example 2

[0062] It has the implementation content of the above embodiment, wherein, for the specific implementation of the above embodiment, reference can be made to the above description, and the embodiment here will not be repeated in detail; and in Example 2, it differs from the above embodiment in that:

[0063] In this example, a 10 mm × 10 mm silicon wafer was first cleaned sequentially with acetone, isopropanol, ethanol, and deionized water, then dried with dry nitrogen. A 2 nm thick PbI2 film was deposited on the substrate using thermal evaporation at a rate of 0.02 nm / s as a Pb source. This film was then fed into a CVD (chemical vapor deposition) system and placed downstream of the carrier gas. 300 mg of sulfur powder was weighed and placed into a quartz boat, which was then fed into the CVD system and placed upstream of the carrier gas. A mechanical pump was used to evacuate the system to a base vacuum of less than 1.0 × 10 -1 Pa.

[0064] Hydrogen is introduced by introducing a mixture of H2 (20 sccm) and Ar (10 sccm). Once the flow stabilizes, the CVD system begins heating at a rate of 25°C / min. When the system temperature reaches 250°C, it is maintained for 100 minutes until the reaction is complete.

[0065] After the reaction is completed, the CVD system is slowly cooled to 170 °C, during which the inert gas flow rate is increased, and then the system is quickly cooled to room temperature to obtain a denser quantum dot film. The obtained quantum dot film is characterized by scanning electron microscopy ( Figure 2 ), it can be seen that a relatively uniform quantum dot structure is formed. The prepared quantum dot film is characterized by X-ray photoelectron spectroscopy (XPS). XPS characterization verifies that the quantum dot sample formed is PbS quantum dots ( Figure 3 ).

[0066] Example 3

[0067] It has the implementation content of the above embodiment, wherein, for the specific implementation of the above embodiment, reference can be made to the above description, and the embodiment here will not be repeated in detail; and in Example 3, it is different from the above embodiment in that:

[0068] In this example, a 10 mm × 10 mm silicon wafer was first cleaned sequentially with acetone, isopropanol, ethanol, and deionized water, then dried with dry nitrogen. A 1 nm thick PbI2 film was deposited on the substrate using thermal evaporation at a rate of 0.02 nm / s as a Pb source. This film was then fed into a CVD system and placed downstream of the carrier gas. 300 mg of sulfur powder was weighed and loaded into a quartz boat, which was then fed into the CVD system and placed upstream of the carrier gas. A mechanical pump was used to evacuate the system to a base vacuum of less than 1.0 × 10 -1 Pa.

[0069] An H2 / Ar gas mixture was introduced, with an H2 flow rate of 20 sccm and an Ar flow rate of 20 sccm. Once the gas flow stabilized, the CVD system began to heat up at a rate of 25°C / min. When the system temperature reached a constant temperature of 300°C, it was maintained for 100 minutes until the reaction was complete.

[0070] After the reaction is completed, the CVD system is slowly cooled to 170 °C, during which the inert gas flow rate is increased, and then the system is quickly cooled to room temperature to obtain a dense quantum dot film. The prepared quantum dot film is characterized by XPS, and its XPS results are consistent with the above Figure 3 The obtained PbS quantum dot film was characterized by scanning electron microscopy ( Figure 4 ), obtaining PbS quantum dots of relatively uniform size. Compared with Example 2, it can be seen from SEM that the density of PbS quantum dots in the quantum dot film prepared in Example 3 is higher than that in Example 2.

[0071] Example 4

[0072] It has the implementation content of the above embodiment, wherein, for the specific implementation of the above embodiment, reference can be made to the above description, and the embodiment here will not be repeated in detail; and in Example 4, it is different from the above embodiment in that:

[0073] In this example, a 10 mm × 10 mm silicon wafer was first cleaned sequentially with acetone, isopropanol, ethanol, and deionized water, then dried with dry nitrogen. A PbI2 film (5 nm thick) was deposited on the substrate using thermal evaporation at a rate of 0.02 nm / s. This film was then fed into a CVD system and placed downstream of the carrier gas. H2S was selected as the sulfur source. A mechanical pump was used to evacuate the system to a base vacuum of less than 1.0 × 10 -1 Pa.

[0074] A H2 / Ar mixture was introduced, with an H2 flow rate of 20 sccm and an Ar flow rate of 30 sccm. After the gas flow stabilized, the CVD system began to heat up. The heating rate was 25°C / min. When the system temperature reached 220°C, it was maintained for 100 minutes until the reaction was completed. After the reaction was completed, the CVD system was slowly cooled to 170°C. During this period, the inert gas flow rate was increased, and the system was then quickly cooled to room temperature to obtain a dense PbS quantum dot film (such as Figure 5 shown).

[0075] Example 5

[0076] It has the implementation content of the above embodiment, wherein, for the specific implementation of the above embodiment, reference can be made to the above description, and the embodiment here will not be repeated in detail; and in Example 5, it is different from the above embodiment in that:

[0077] In this example, a PbS quantum dot film was prepared on a two-dimensional MoS2 surface using MoS2 / SiO2 (20 nm) / Si as a substrate. A 2 nm thick PbI2 film was deposited on the substrate using thermal evaporation at a rate of 0.02 nm / s as a Pb source. This film was then fed into a CVD system and placed downstream of the carrier gas. 300 mg of sulfur powder was weighed and placed into a quartz boat, which was then fed into the CVD system and placed upstream of the carrier gas. A mechanical pump was used to evacuate the system to a base vacuum of less than 1.0 × 10 -1 Pa.

[0078] A H2 / Ar mixture was introduced, with an H2 flow rate of 20 sccm and an Ar flow rate of 50 sccm. After the gas flow stabilized, the CVD system began to heat up. The heating rate was 25°C / min. When the system temperature reached 250°C, it was maintained for 100 minutes until the reaction was complete. After the reaction was complete, the CVD system was slowly cooled to 170°C, during which the inert gas flow rate was increased. The system was then quickly cooled to room temperature to obtain a dense PbS quantum dot film ( Figure 6 and Figure 7 ).

[0079] Comparative Example 1

[0080] In this embodiment, compared with Example 2, Comparative Example 1 does not use hydrogen during the reaction. In this embodiment, a 10 mm × 10 mm silicon wafer is first cleaned with acetone / isopropanol / ethanol / deionized water in sequence, and blown dry with dry nitrogen for later use. A 2 nm thick PbI2 film is deposited on the above substrate at a rate of 0.02 nm / s as a Pb source using thermal evaporation coating, which is then fed into a CVD system and placed at the downstream end of the carrier gas. 300 mg of sulfur powder is weighed and loaded into a quartz boat, which is then fed into a CVD system and placed at the upstream end of the carrier gas. A mechanical pump is used to evacuate the system so that the background vacuum is lower than 1.0 × 10-1 Pa.

[0081] The inert gas Ar was introduced at a flow rate of 20 sccm. Once the flow stabilized, the CVD system began to heat up at a rate of 25°C / min. When the system temperature reached 250°C, it was maintained for 100 minutes until the reaction was complete.

[0082] After the reaction is completed, the CVD system is slowly cooled to 170 °C, during which the inert gas flow rate is increased, and then the system is quickly cooled to room temperature to obtain sparse quantum dots. The prepared quantum dots are characterized by XPS, and the XPS results are consistent with the above Figure 3 The obtained PbS quantum dots were characterized by scanning electron microscopy. Figure 8 As shown, the density of PbS quantum dots prepared under CVD conditions in the absence of H2 is reduced by about 20 times (compared to those using H2).

[0083] Further, the size distribution of the PbS quantum dots prepared in Example 3 and Comparative Example 1 was analyzed and found to be ( Figure 9 ), in an Ar inert atmosphere system, the density of PbS quantum dots is about 13 / μm 2 , the quantum dot radius is concentrated between 40-60 nm ( Figure 9 a); After the introduction of H2 (H2 to Ar ratio 1:1), the quantum dot density increased significantly to about 261 / μm 2 , while the size is drastically reduced to a radius of 10-20 nm ( Figure 9 b) Smaller and more uniform size. This significant difference stems from the synergistic regulation of hydrogen on reaction kinetics, nucleation process, and crystal growth mechanism.

[0084] Example 6

[0085] The invention also discloses a PbS quantum dot film and silicon heterojunction phototransistor, comprising a silicon layer and the PbS quantum dot film prepared by the invention.

[0086] Optionally, a PbS quantum dot film and silicon form a heterojunction phototransistor, which is characterized by providing an insulating layer between the silicon layer and the PbS quantum dot film, and the insulating layer material includes SiO2 and high dielectric constant HfO2, Hf (1-x) Zr x O2(HZO), Al2O3, TiO2, ZrO2, Ta2O5 and Bi2SeO5; the thickness of the insulating layer is 2-20 nm.

[0087] Optionally, a PbS quantum dot film and silicon form a heterojunction phototransistor, which is characterized by having a two-dimensional layered material layer between the silicon layer and the PbS quantum dot film, and the layered material film includes one or more combinations of graphene, transition metal chalcogenides such as MoS2, PtSe2, CrS2, etc.

[0088] Example 7

[0089] Based on the prepared PbS quantum dot films with different coverage, heterojunction phototransistors (hereinafter referred to as photodetectors) were prepared. The device structure was PbS quantum dot film / SiO2 (5 nm) / Si. This embodiment uses the PbS quantum dot films of the above-mentioned comparative example 1, embodiment 2 and embodiment 3, and uses Au (30 nm) / Cr (5 nm) as electrodes (source and drain electrodes) in contact with the PbS quantum dot films to prepare photodetectors, which are device 1, device 2 and device 3 respectively. Different incident light intensities (0.8 mW / cm 2 , 1.8 mW / cm 2 , 3.2 mW / cm 2 and 5.6 mW / cm 2 ) Source-drain bias voltage V ds = 1 V for testing, such as Figure 10 As shown in the figure, under the same test conditions, the current of the PbS quantum dot device prepared by comparative example 1 (device 1) is the smallest; from this, the corresponding photodetector responsivity (R) and specific detectivity (D) can be calculated. For example, in the 1550 nm band, the incident light intensity is 0.8 mW cm -2 , source-drain bias voltage V ds = 1 V, the responsivity and specific detectivity of device 1 are 1.07 A / W and 6.1×10 10 Jones, while the responsivity and specific detectivity of device 2 are 54 A / W and 4.56×10 11 Jones, the responsivity and specific detectivity of device 3 are 95.1 A / W and 6.39×10 11 Jones. The results show that as the density of PbS quantum dots increases, the performance of the photodetector improves.

[0090] Example 8

[0091] This embodiment adopts the technical method of the above-mentioned embodiment 5 to prepare the PbS quantum dot film, that is, the PbS quantum dot film is prepared on the MoS2 / SiO2 (20nm) / Si substrate, and then the Au (30nm) / Cr (5nm) is used as the electrode (source and drain electrode) in contact with the PbS quantum dot film to prepare a heterojunction phototransistor. Figure 11 The current-voltage curve of the photodetector prepared in this example. The test conditions are: different incident light intensities in the 1550 nm band (0.8 mW / cm 2 , 1.8 mW / cm 2 , 3.2 mW / cm 2 and 5.6 mW / cm 2 ), source-drain bias voltage V ds = 1 V (no gate voltage applied). From this, the responsivity (R) and specific detectivity (D) of the photodetector under different light intensities can be calculated. For example, in the 1550 nm band, the incident light intensity is 0.8 mW cm -2 When the responsivity and specific detectivity are 93.4 A / W and 5.49×10 11 Jones.

[0092] Comparative Example 2

[0093] Compared with the PbS quantum dots (without organic ligand coating) of the present invention, Comparative Example 2 uses PbS colloidal quantum dots (i.e., PbS quantum dots with organic ligand coating on their surface, purchased from Suzhou Xingshuo Nanotechnology Co., Ltd.) to construct a photodetector (colloid-PbS / SiO2 / Si). Under the same test conditions as Example 7, the incident light intensity at 1550 nm is 0.8 mW cm -2 , bias voltage V ds = 1 V, the responsivity of the photodetector in Example 2 is about 16.25 A / W, and the specific detectivity is 1.35×10 11 Jones; this performance is significantly lower than that of devices 2 and 3 in Example 7 (i.e., PbS quantum dot devices without organic ligands when the PbS density is high). Therefore, the performance of the photodetector based on the organic ligand-free PbS quantum dot film prepared by the present invention is superior to that of the device with ligand-containing PbS quantum dots. Figure 12 SEM image of PbS quantum dots with ligands (5 µm × 5 µm).

[0094] Comparative Example 3

[0095] In this embodiment, compared with Example 2, Comparative Example 3 uses PbI2 with a thickness greater than 5 nm as the Pb source.

[0096] In this comparative example, a 10 mm × 10 mm silicon wafer was first cleaned sequentially with acetone, isopropanol, ethanol, and deionized water, then dried with dry nitrogen. A 6 nm thick PbI2 film was deposited on the substrate using thermal evaporation at a rate of 0.02 nm / s as a Pb source. This film was then fed into a CVD (chemical vapor deposition) system and placed downstream of the carrier gas. 300 mg of sulfur powder was weighed and loaded into a quartz boat, which was then fed into the CVD system and placed upstream of the carrier gas. A mechanical pump was used to evacuate the system to a base vacuum of less than 1.0 × 10 -1 Pa.

[0097] Hydrogen is introduced by introducing a mixture of H2 (20 sccm) and Ar (10 sccm). Once the flow stabilizes, the CVD system begins heating at a rate of 25°C / min. When the system temperature reaches 250°C, it is maintained for 100 minutes until the reaction is complete.

[0098] After the reaction is completed, the CVD system is slowly cooled to 170 °C, during which the inert gas flow rate is increased, and then the system is quickly cooled to room temperature. The prepared material is characterized by X-ray photoelectron spectroscopy (XPS). XPS characterization verifies that both PbS and unreacted PbI2 ( Figure 13 The obtained samples were characterized by scanning electron microscopy ( Figure 14 ), it can be seen that: in addition to quantum dots, there are also nanowire-like substances and thin-film substances. Therefore, when using PbI2 films larger than 5nm as Pb precursors, it is difficult to completely convert them into PbS quantum dots.

[0099] The performance parameters of photodetectors include response time, response at different wavelengths, etc., which can be referred to in relevant literature. Science China Materials 66, 193 (2023); Adv. Opt. Mater. 11,2300910 (2023)], which will not be described in detail here. However, the photodetector of the PbS quantum dot film prepared by the present invention has a wide spectral response characteristic from ultraviolet to near infrared wavelengths, which is due to the following reasons: Figure 9 The prepared PbS quantum dots shown have different sizes (bandgap widths), which are determined by the device structure in which the PbS quantum dot film forms a heterojunction with silicon.

[0100] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A dry process for preparing a PbS quantum dot film, characterized in that: The preparation method comprises the following steps: using a uniform continuous PbI2 film as a Pb source to react with an S source in a mixed atmosphere of hydrogen and inert gas to form a PbS quantum dot film; The PbI2 uniform continuous thin film is prepared on a substrate by a physical vapor deposition method, and the thickness of the PbI2 thin film on the substrate does not exceed 5 nm.

2. The preparation method according to claim 1, characterized in that The preparation method satisfies at least one of the following characteristics: 1) In the mixed atmosphere of hydrogen and inert gas, the ratio of hydrogen to inert gas is 2:1 to 2:5; 2) The S source is solid sulfur powder or H2S, wherein the solid S source is sulfur powder, which is heated to form gaseous sulfur.

3. The preparation method according to claim 2, characterized in that: The reaction temperature is between 220°C and 300°C.

4. A PbS quantum dot film, characterized in that Prepared by the method of any one of claims 1 to 3.

5. The PbS quantum dot thin film according to claim 4, characterized in that The PbS quantum dot film has the following characteristics: the coverage rate of the PbS quantum dots in the PbS quantum dot film on the substrate surface is not less than 50%.

6. The PbS quantum dot thin film according to claim 4, characterized in that The substrate is selected from insulating materials or semiconductor materials, including one or a combination of two or more of glass, SiO2, SiC, Si3N4, Al2O3, sapphire, mica, MgO, Si, and two-dimensional materials.

7. The PbS quantum dot thin film according to claim 6, characterized in that The two-dimensional material is selected from MoS 2。 8. A PbS quantum dot film and silicon heterojunction phototransistor, characterized by: The heterojunction phototransistor is composed of a silicon layer and the PbS quantum dot thin film according to claim 4.

9. The PbS quantum dot film and silicon heterojunction phototransistor according to claim 8, wherein the characteristics include: An insulating layer is provided between the silicon layer and the PbS quantum dot film, wherein: The insulating layer materials include SiO2 and high dielectric constant HfO2, Hf (1-x) Zr x O2 (HZO), Al2O3, TiO2, ZrO2, Ta2O5 and Bi2SeO5; The thickness of the insulating layer is 2-20 nm.

10. The PbS quantum dot film and silicon heterojunction phototransistor according to claim 8, wherein the characteristics include: A two-dimensional layered material layer is provided between the silicon layer and the PbS quantum dot film. The layered material film comprises one or a combination of more than one of graphene and transition metal chalcogenide.

11. The PbS quantum dot film and silicon heterojunction phototransistor according to claim 9, characterized in that: There is a two-dimensional layered material layer between the insulating layer and the PbS quantum dot film, and the layered material film includes one or a combination of more than one of graphene and transition metal chalcogenides.

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