CN120364745B - A dry preparation method for PbS quantum dot film and a phototransistor forming a heterojunction with silicon - Google Patents
A dry preparation method for PbS quantum dot film and a phototransistor forming a heterojunction with siliconInfo
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Abstract
The invention discloses a preparation method of a PbS quantum dot film, which is formed by taking a PbI 2 uniform continuous film as a Pb source and reacting an S source at 220-300 oC in a mixed atmosphere of hydrogen and inert gas, and realizes the controllable preparation of the PbS quantum dot film without an organic ligand. The invention also discloses a heterojunction photoelectric transistor constructed by the PbS quantum dot film prepared by the preparation method and silicon, and the response, specific detection rate and other photoelectric property performances of the constructed heterojunction photoelectric transistor are obviously improved along with the improvement of the coverage rate of the PbS quantum dot film on the surface of the substrate.
Description
Technical Field
The invention relates to the field of photoelectric technology and photoelectric detectors, in particular to a method for preparing a PbS quantum dot film, and a photoelectric transistor with heterojunction formed by the PbS quantum dot film and silicon.
Background
The quantum dot has unique photoelectric property and wide application value including luminescence, detection, sensing and the like. The photoelectric detector is a core element for converting optical signals into electric signals and plays a key role in various optical detection scenes. The photoelectric effect of special materials is utilized, and light with different intensities and frequencies is accurately perceived. The photoelectric detector is widely applied to the fields of environment detection, security monitoring, imaging, optical communication and the like, and is an essential part of modern optoelectronic technology. The traditional photoelectric detector is difficult to meet development requirements in the aspects of sensitivity, response speed and the like. In this context, photodetectors based on novel functional materials have been developed as a focus.
PbS quantum dots (PbS quats or PbS QDs) are zero-dimensional semiconductor nanomaterials composed of lead (Pb) and sulfur (S) elements, and have significant quantum confinement effects and large bohr exciton radii, which impart unique optical and electrical properties thereto. The band gap of the PbS quantum dot can be regulated by precisely controlling the size of the quantum dot, so that the precise regulation and control of the absorption and emission spectrum in the near infrared band can be realized, and the advantages of the PbS quantum dot are obvious in the near infrared light detection field. Meanwhile, the PbS quantum dot has high extinction coefficient and strong light absorption capacity, and can effectively improve photoelectric conversion efficiency. These characteristics make it possible to show great potential for application in the field of photodetectors.
In the field of synthesis of PbS quantum dots, wet preparation methods are used, wherein the reaction is performed in a solution, and the method is performed in a specific solution system synthesis process, namely reactants are chemically reacted in a liquid solvent, and in order to control the size of the quantum dots and prevent agglomeration of the quantum dots in the solution, one key feature of the method is that organic molecules must be added, and the organic molecules coated on the surfaces of the quantum dots are called surface ligands (ligands), and known surface ligands are tetrabutylammonium iodide (TBAI) and ethanedithiol (ethanedithiol) [ ACS Photonics (2020), 7 (8), 1932-1941], mercaptopropionic acid (mercaptopropionic acid) [ ACS APPLIED MATERIALS & Interfaces (2018), 10 (36), 30283-30295], picolinic acid (picolinic acid), 2,6-dipicolinic acid (2, 6-dipicolinic acid), salicylic acid (SALICYLIC ACID), thiourea (thiourea), and thiosemicarbazide (thiosemicarbazide) [ CHEMISTRY OF MATERIALS (2011), 23 (18), 4158-4169] and the like. PbS in turn forms core-shell structures, dumbbell structures, or other more complex structures, such as PbS-ligands, with these organic compounds, and such quantum dots are referred to as colloidal quantum dots. However, this core-shell encapsulation structure increases the van der Waals interaction distance at the interface between the quantum dots. For application to optoelectronic devices, the organic ligands on the quantum dot surface can severely affect the carrier transport characteristics, thereby affecting device performance and stability. The wet-process PbS quantum dot product necessarily contains surface ligand, and the colloid chemical synthesis method is one of common means. On the other hand, for quantum dots to be used in photovoltaic device applications, it is desirable that the individual quantum dots be capable of forming a complete continuous film rather than separate quantum dots, so that the continuous, complete quantum dot film can enhance light absorption, facilitate carrier transport, and enhance the properties of the photovoltaic device as compared to the individual separate quantum dots.
In the prior art, no research report related to the preparation method of the PbS quantum dot film which has the participation of hydrogen in the preparation process and does not contain surface ligand is found.
Disclosure of Invention
Aiming at the problems in the field, in particular the fundamental problems of hindered carrier transportation and poor device performance caused by the existence of organic ligands in the chemical preparation, the invention provides a dry preparation method of a PbS quantum dot film, the surface of the PbS quantum dot prepared by the method has no organic ligand, and the nucleation density is obviously improved, so that the controllable preparation of quantum dots with smaller size and more uniform distribution is realized, and the efficient carrier transportation can be realized.
Solution system
A Solution System (Solution System) refers to a synthesis process environment in which reactants react chemically in a liquid solvent to produce a product. In the field of quantum dot preparation, this is generally referred to as conventional colloidal chemical synthesis. One key feature of this system is that in order to control the size of the quantum dots and prevent their agglomeration in the liquid medium, specific organic molecules must be added as surface ligands during the reaction. The preparation method proposed in the patent is carried out in a Non-solution System (Non-solution System) which is fundamentally different from the preparation method
Surface free ligands
The no surface ligand (Without Surface Ligands) is a core feature describing the PbS quantum dots prepared by the present patent, meaning that the surface of the quantum dots is clean and not encapsulated by organic molecules. This is in sharp contrast to quantum dots prepared by conventional methods, which must rely on surface ligands (ligands), i.e., organic molecules that are encapsulated on the surface of the quantum dot in order to control size and prevent agglomeration in colloidal synthesis. However, these surface ligands can form a layer of insulating core-shell structure on the surface of the quantum dots, increasing the distance between the quantum dots, thereby severely impeding the efficient transport of carriers and ultimately affecting the performance and stability of the device. Therefore, the quantum dots without surface ligands are prepared by the method, the insulating barrier is eliminated, efficient carrier transport between the quantum dots is promoted, and the responsivity, specific detection rate and other key performances of the photoelectric device are obviously improved.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the invention provides a dry preparation method of a PbS quantum dot film, which comprises the step of reacting a PbI 2 uniform continuous film serving as a Pb source with an S source in a mixed atmosphere of hydrogen and inert gas to form the PbS quantum dot film.
In complete contrast to the wet process, the reaction system of the dry process of the present invention does not involve surface ligands nor does it use solvents. The reaction system of the preparation method is a reaction system without surface ligand participation.
Specifically, the reaction involved in the preparation method of the invention has the following reaction formula:
the reaction is a free radical reaction process, and the principle schematic diagram is as follows:
among them, the use of H 2 is important to improve PbS synthesis efficiency. In pure inert gas such as argon or nitrogen systems, the decomposition of PbI 2 is dependent primarily on thermodynamic driving. Since PbI 2 has a high chemical bond energy (Pb-I bond energy is about 200 kJ/mol), it is difficult to efficiently release Pb atoms only by thermal activation, and PbI 2 may have a surface that is locally broken, resulting in a limited number of released Pb atoms and poor dispersibility, and such inefficient decomposition directly limits the nucleation site density of the quantum dot, forcing the limited Pb atoms to aggregate into large-sized particles by surface diffusion, and it is difficult to obtain quantum dots having quantum effects. And after H 2 is inserted, the decomposition path is changed through functional reaction. H 2 can accelerate the decomposition of PbI 2 to generate Pb-containing free radicals and volatile HI. Meanwhile, H 2 reacts with I 2 (generated by directly reacting PbI 2 with S) to generate HI, so that the concentration of I 2 in a gas phase is reduced, pbI 2 is pushed to directly react with S, pbI 2 is also pushed to continuously decompose, and more Pb is released to participate in the reaction. The function of H 2 is beneficial to the increase of the generation rate of Pb atoms, so that a large number of Pb clusters which are uniformly distributed are formed on the surface of the substrate, dense nucleation sites are provided for subsequent sulfur combination reaction, and finally the quantum dot film is formed. Thus, the proper hydrogen accelerates the decomposition of PbI 2, the local concentration of Pb atoms in the reaction system is obviously improved, the critical free energy required by nucleation is reduced, and the nucleation density is greatly increased. meanwhile, the high-density initial nucleation sites can rapidly consume Pb atoms in the system and inhibit subsequent secondary nucleation, so that quantum dots with uniform sizes are formed. In pure inert gas such as argon or nitrogen, pb atoms which do not participate in nucleation have higher surface mobility due to low nucleation density, and tend to combine with the existing quantum dots through diffusion, so that large particles continuously grow through phagocytizing small particles, and a coarsening structure with larger radius is finally formed.
Further, the preparation method satisfies at least one of the following features:
1) In the mixed atmosphere of the hydrogen and the inert gas, the ratio of the hydrogen to the inert gas is 2:1-2:5.
2) The PbI 2 uniform continuous film is prepared on a substrate by a physical vapor deposition method (such as thermal evaporation), and the thickness of the PbI 2 film on the substrate is not more than 5nm, preferably, the thickness of the PbI 2 film on the substrate is 1-5nm, and more preferably, the thickness of the PbI 2 film on the substrate is 1-2nm.
3) The S source is solid sulfur powder or H 2 S. Wherein the solid S source is sulfur powder, gaseous sulfur is formed by adopting heat treatment, and H 2 S is used as the gaseous S source, and is more uniform and higher in reaction activity than the solid S.
Wherein, sulfur powder generates gaseous S 8 annular molecules at high temperature, but the chemical combination reaction of the sulfur powder and Pb needs to overcome higher energy barrier. In pure inert gas such as argon or nitrogen systems, the reaction rate of sulfur vapor with Pb is limited by the degree of sulfur activation, resulting in slow and uneven reaction progress, and partial regions forming "starved growth" due to insufficient sulfur supply. The introduction of hydrogen optimizes the sulfur activation process by sulfur chain cleavage catalysis (H 2 can react with S 8 molecules to generate HS radical, such as S 8+H2→2HS4. Reduce the energy required by sulfur chain cleavage, promote sulfur to participate in the reaction in a more active small molecular form (such as S 2、S4) and surface reaction acceleration (HI generated by the reaction of H 2 with PbI 2 can serve as an acidic medium, enhance the adsorption capacity of sulfur vapor on Pb surface, enable sulfur atoms to be covered on Pb cluster surface more uniformly, and form compact PbS crystal lattice). Inert gas mainly plays a role in physical mass transfer and thermal balance, while hydrogen becomes a reaction leading factor through chemical activity and dynamic regulation. Therefore, the hydrogen plays multiple roles in the preparation of the PbS quantum dots, wherein the chemical activity of the hydrogen directly promotes the decomposition of the precursor, the kinetic regulation and control inhibit the coarsening of crystals, and simultaneously, the activation and the surface reaction of sulfur are optimized. In contrast, pure inert systems suffer from thermodynamic equilibrium due to the lack of chemically active components, resulting in low nucleation density and uncontrolled growth.
Further, the temperature condition of the reaction is 220-300 ℃.
The invention also provides a PbS quantum dot film, which is prepared by the method, and the coverage rate of the PbS quantum dot on the surface of the substrate is not lower than 50%. The bS quantum dot surface prepared by the invention does not contain surface ligand.
Preferably, the substrate is selected from insulating materials or semiconductor materials, including one or a combination of more than two of glass, siO 2、SiC、Si3N4、Al2O3, sapphire, mica, mgO, si, two-dimensional materials such as MoS 2, etc.
The invention also provides a heterojunction photoelectric transistor formed by the PbS quantum dot film and silicon, which is characterized by comprising a silicon layer and the PbS quantum dot film prepared by the method.
Preferably, the heterojunction phototransistor is formed by the PbS quantum dot film and silicon, and the heterojunction phototransistor is characterized in that a two-dimensional layered material layer is arranged between the silicon layer and the PbS quantum dot film, and the layered material film comprises one or more of graphene, transition metal chalcogenide such as MoS 2、PtSe2、CrS2 and the like.
Preferably, the heterojunction phototransistor is formed by the PbS quantum dot film and silicon, and is characterized in that an insulating layer is arranged between the silicon layer and the PbS quantum dot film, the insulating layer comprises SiO 2, HfO2、Hf(1-x)ZrxO2(HZO) 、Al2O3、TiO2、ZrO2、Ta2O5 with high dielectric constant and Bi 2SeO5, and the thickness of the insulating layer is 2-20 nm.
Further preferably, the heterojunction phototransistor is formed by the PbS quantum dot film and silicon, and is characterized in that a two-dimensional layered material layer is arranged between the insulating layer and the PbS quantum dot film, and the layered material film comprises one or more than one of graphene and transition metal chalcogenide.
Compared with the prior art, the invention has the advantages that:
In the invention, the PbI 2 film is used as a Pb source, hydrogen participates in the reaction, promotes the reaction of the Pb source and the S source to be converted into the PbS quantum dots, and can regulate the density of the growing PbS quantum dots to form the PbS quantum dot film. The method for preparing the PbS quantum dot film is simple, the surface of the prepared quantum dot does not contain an organic ligand layer, the preparation of the PbS quantum dot and the coverage rate of the surface of a substrate are easy to control, the preparation efficiency and the material quality are improved, and the method is beneficial to being applied to preparing high-performance photoelectric devices.
Drawings
FIG. 1 is a schematic diagram of a method for preparing a PbS quantum dot film according to the invention;
FIG. 2 is a scanning electron microscope image of the PbS quantum dot film prepared in example 2;
FIG. 3 is an x-ray photoelectron spectrometer of the PbS quantum dot film prepared in example 2;
FIG. 4 is a scanning electron microscope image of the PbS quantum dot film prepared in example 3;
FIG. 5 is a scanning electron microscope image of the PbS quantum dot film prepared in example 4;
FIG. 6 is a scanning electron microscope image of the PbS quantum dot film prepared in example 5;
FIG. 7 is an x-ray photoelectron spectrometer of the PbS quantum dot film prepared in example 5;
FIG. 8 is a scanning electron microscope image of the PbS quantum dot film prepared in comparative example 1;
Fig. 9 is a statistical analysis of the sizes of PbS quantum dots prepared in example 3 (fig. 9 b) and comparative example 1 (fig. 9 a);
FIG. 10 is a graph showing the current-voltage relationship of a photodetector constructed using the PbS quantum dot films prepared in example 2 (device 2), example 3 (device 3), and comparative example 1 (device 1), wherein the different color curves are shown as different incident light intensities (mW cm -2);
FIG. 11 is a graph showing the current-voltage relationship of a photodetector constructed from PbS (quantum dot film)/MoS 2/SiO2 (20 nm)/Si, as shown in example 8, wherein the different color curves are different incident light intensities (mW cm -2);
Fig. 12 is a scanning electron microscope image of PbS colloidal quantum dots used in comparative example 2.
Fig. 13 is an X-ray photoelectron spectroscopy characterization result of PbS quantum dots prepared in comparative example 3, (a) S 2p, (b) Pb4f and (c) I 3d spectra.
FIG. 14 is a scanning electron microscope image of PbS quantum dots prepared in comparative example 2
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments.
Example 1
The invention relates to a dry preparation method of a PbS quantum dot film, which comprises the following steps (the schematic diagram is shown in fig. 1):
1) PbI 2 uniform continuous film is adopted as Pb source to react with S source in inert gas atmosphere to form PbS quantum dot;
2) In the step 1), hydrogen participates in the reaction;
3) In the step 1), the reaction temperature is 220-300 ℃;
4) The ratio of the hydrogen to the inert gas is 2:1-2:5;
5) The PbS quantum dot film is a film with the coverage rate of the PbS quantum dot on the surface of the substrate not lower than 50%, and the coverage rate result is obtained by calculating particles in an SEM image.
The preparation method of the PbS quantum dot film does not have the participation of surface ligands and does not use solvents.
The reaction formula of the reaction is as follows:
The PbI 2 film is prepared on a substrate by thermal evaporation, the thickness is not more than 5: 5 nm, and the thickness in the range has no obvious difference on the subsequent formation of the PbS quantum dot film. The substrate is selected from insulating material or semiconductor material, including one or more of glass, siO 2、SiC、Si3N4、Al2O3, sapphire, mica, mgO, si, two-dimensional material such as MoS 2, etc.
The S source can be solid sulfur powder or H 2 S, the solid sulfur powder can be heated to form gaseous sulfur, and the basic chemical conversion process is that the solid sulfur (S) is evaporated into S 8,H2 at high temperature to react with S to generate high-activity HS. free radicals and the like. H 2 S is more uniform and more reactive than solid S as a gaseous S source.
When the chemical reaction is carried out, the substrate is subjected to constant temperature rising and constant temperature treatment, and the constant temperature is 220-300 ℃.
Example 2
Which has the implementation content of the above embodiment, wherein reference is made to the foregoing description for the implementation of the above embodiment, the embodiment is not repeated here in detail, but in embodiment 2, it is different from the foregoing embodiment in that:
In this example, a 10mm ×10mm wafer was first rinsed with acetone/isopropanol/ethanol/deionized water in sequence and dried with dry nitrogen for later use. A2. 2 nm thick film of PbI 2 was deposited on the above substrate using thermal evaporation plating at a rate of 0.02 nm/s as a source of Pb, fed into a CVD (chemical vapor deposition) system and placed at the downstream end of the carrier gas. Sulfur powder 300 mg was weighed into a quartz boat, fed into a CVD system and placed at the upstream end of the carrier gas. The background vacuum of the system was brought to below 1.0X10 -1 Pa using a mechanical pump.
The participation of hydrogen is to introduce a certain flow of mixed gas of H 2 (20 sccm) and Ar (10 sccm), and after the gas flow is stable, the CVD system starts to heat. The temperature rising rate is 25 ℃ per minute, and when the system temperature is heated to 250 ℃, 100 min is maintained until the reaction is finished.
After the reaction is finished, the CVD system is slowly cooled to 170 ℃, the flow of inert gas is increased during the reaction, and then the system is quickly cooled to room temperature, so that the denser quantum dot film can be obtained. The obtained quantum dot film is subjected to scanning electron microscope characterization (figure 2), and a more uniform quantum dot structure can be seen. The prepared quantum dot film is subjected to X-ray photoelectron spectroscopy (XPS) characterization, and the XPS characterization verifies that the formed quantum dot sample is PbS quantum dot (figure 3).
Example 3
Which has the implementation content of the above embodiment, wherein reference is made to the foregoing description for the implementation of the above embodiment, the embodiment is not repeated here in detail, but in embodiment 3, it is different from the foregoing embodiment in that:
In this example, a 10mm ×10mm wafer was first rinsed with acetone/isopropanol/ethanol/deionized water in sequence and dried with dry nitrogen for later use. A1. 1 nm thick film of PbI 2 was deposited on the above substrate using thermal evaporation plating at a rate of 0.02 nm/s as a Pb source, fed into the CVD system and placed at the downstream end of the carrier gas. Sulfur powder 300 mg was weighed into a quartz boat, fed into a CVD system and placed at the upstream end of the carrier gas. The background vacuum of the system was brought to below 1.0X10 -1 Pa using a mechanical pump.
And (3) introducing an H 2/Ar mixed gas, wherein the flow rate of H 2 is 20 sccm, the flow rate of Ar is 20 sccm, and after the gas flow is stable, heating the CVD system. The temperature rising rate is 25 ℃ per minute, and when the system temperature is heated to a certain temperature of 300 ℃, 100 min is maintained until the reaction is finished.
After the reaction is finished, the CVD system is slowly cooled to 170 ℃, the flow of inert gas is increased during the reaction, and then the system is quickly cooled to room temperature, so that the compact quantum dot film can be obtained. The prepared quantum dot film was subjected to XPS characterization, and the XPS results are consistent with the above-described FIG. 3. And (4) carrying out scanning electron microscope characterization (figure 4) on the obtained PbS quantum dot film to obtain the PbS quantum dots with uniform sizes. As can be seen from SEM, the density of PbS quantum dots in the quantum dot film prepared in example 3 is higher than that in example 2, relative to example 2.
Example 4
Which has the implementation content of the above embodiment, wherein reference is made to the foregoing description for the implementation of the above embodiment, the embodiment is not repeated here in detail, but in embodiment 4, it is different from the foregoing embodiment in that:
In this example, a 10 mm ×10 mm wafer was first rinsed with acetone/isopropanol/ethanol/deionized water in sequence and dried with dry nitrogen for later use. A PbI 2 film (5 nm) was deposited on the above substrate at a rate of 0.02 nm/s as a Pb source using thermal evaporation plating, fed into the CVD system and placed at the downstream end of the carrier gas. H 2 S is selected as an S source. The background vacuum of the system was brought to below 1.0X10 -1 Pa using a mechanical pump.
And (3) introducing an H 2/Ar mixed gas, wherein the flow rate of H 2 is 20 sccm, the flow rate of Ar is 30 sccm, and after the gas flow is stable, heating the CVD system. The temperature rising rate is 25 ℃ per minute, and when the system temperature is heated to 220 ℃,100 min is maintained until the reaction is finished. After the reaction is finished, the CVD system is slowly cooled to 170 ℃, the flow rate of inert gas is increased during the reaction, and then the system is quickly cooled to room temperature, so that the compact PbS quantum dot film (shown in figure 5) can be obtained.
Example 5
Which has the implementation content of the above embodiment, wherein reference is made to the foregoing description for the implementation of the above embodiment, the embodiment is not repeated here in detail, but in embodiment 5, it is different from the foregoing embodiment in that:
In this example, moS 2/SiO2 (20 nm)/Si was used as a substrate to prepare PbS quantum dot films on the two-dimensional MoS 2 surface. A2. 2 nm thick film of PbI 2 was deposited on the above substrate using thermal evaporation plating at a rate of 0.02 nm/s as a Pb source, fed into the CVD system and placed at the downstream end of the carrier gas. Sulfur powder 300 mg was weighed into a quartz boat, fed into a CVD system and placed at the upstream end of the carrier gas. The background vacuum of the system was brought to below 1.0X10 -1 Pa using a mechanical pump.
And (3) introducing an H 2/Ar mixed gas, wherein the flow rate of H 2 is 20 sccm, the flow rate of Ar is 50 sccm, and after the gas flow is stable, heating the CVD system. The temperature rising rate is 25 ℃ per minute, and when the system temperature is heated to 250 ℃,100 min is maintained until the reaction is finished. After the reaction is finished, the CVD system is slowly cooled to 170 ℃, the flow rate of inert gas is increased during the reaction, and then the system is quickly cooled to room temperature, so that the compact PbS quantum dot film can be obtained (fig. 6 and 7).
Comparative example 1
In this example, comparative example 1 did not use hydrogen gas in the reaction as compared with example 2. In this example, a 10mm ×10mm wafer was first rinsed with acetone/isopropanol/ethanol/deionized water in sequence and dried with dry nitrogen for later use. A2. 2 nm thick film of PbI 2 was deposited on the above substrate using thermal evaporation plating at a rate of 0.02 nm/s as a Pb source, fed into the CVD system and placed at the downstream end of the carrier gas. Sulfur powder 300 mg was weighed into a quartz boat, fed into a CVD system and placed at the upstream end of the carrier gas. The background vacuum of the system was brought to below 1.0X10 -1 Pa using a mechanical pump.
The flow rate of the inert gas Ar is 20 sccm, and after the gas flow is stable, the CVD system starts to heat up. The temperature rising rate is 25 ℃ per minute, and when the system temperature is heated to 250 ℃, 100 min is maintained until the reaction is finished.
After the reaction is finished, the CVD system is slowly cooled to 170 ℃, the flow of inert gas is increased during the reaction, and then the system is quickly cooled to room temperature to obtain sparse quantum dots. The prepared quantum dots were characterized by XPS, and the XPS results are consistent with the above-mentioned FIG. 3, which shows that PbS quantum dots were obtained. Characterization of the resulting PbS quantum dots by scanning electron microscopy, as shown in fig. 8, reduced the PbS quantum dot density (compared to using H 2) by a factor of about 20, prepared in CVD conditions in the absence of H 2.
Further, analyzing the size distribution of the PbS quantum dots prepared in example 3 and comparative example 1 revealed that in the Ar inert atmosphere system, the PbS quantum dot density was about 13/μm 2, the quantum dot radius was concentrated between 40-60 nm (fig. 9 a), and after H 2(H2 to Ar ratio 1:1) was introduced, the quantum dot density was significantly increased to about 261/μm 2, while the size concentration was significantly reduced to radius 10-20 nm (fig. 9 b), and the size was smaller and more uniform. This significant difference stems from the synergistic regulatory effect of hydrogen on reaction kinetics, nucleation processes, and crystal growth mechanisms.
Example 6
The invention also discloses a heterojunction photoelectric transistor formed by the PbS quantum dot film and silicon, which comprises a silicon layer and the PbS quantum dot film prepared by the method.
Optionally, the heterojunction phototransistor is formed by the PbS quantum dot film and silicon, and is characterized in that an insulating layer is arranged between the silicon layer and the PbS quantum dot film, the insulating layer comprises SiO 2, HfO2、Hf(1-x)ZrxO2(HZO) 、Al2O3、TiO2、ZrO2、Ta2O5 and Bi 2SeO5 with high dielectric constants, and the thickness of the insulating layer is 2-20 nm.
Optionally, the heterojunction phototransistor is formed by the PbS quantum dot film and silicon, and the heterojunction phototransistor is characterized in that a two-dimensional layered material layer is arranged between the silicon layer and the PbS quantum dot film, and the layered material film comprises one or a combination of more than one of graphene, transition metal chalcogenide such as MoS 2、PtSe2、CrS2 and the like.
Example 7
Heterojunction phototransistors (hereinafter referred to as photodetectors) are fabricated based on the prepared PbS quantum dot films with different coverage rates, and the device structure is PbS quantum dot film/SiO 2 (5 nm)/Si. In this example, the PbS quantum dot films of comparative example 1, example 2, and example 3 were used, and photodetectors corresponding to device 1, device 2, and device 3 were prepared using Au (30 nm)/Cr (5 nm) as electrodes (source and drain electrodes) in contact with the PbS quantum dot films. The test was performed using 1550 nm band different incident light intensities (0.8 mW/cm 2、1.8 mW/cm2、3.2 mW/cm2 and 5.6 mW/cm 2) source-drain bias voltage V ds = V, as shown in fig. 10, under the same test conditions, the current of the PbS quantum dot device prepared by comparative example 1 (device 1) was the smallest, and thus the corresponding photodetector responsivity (R) and specific detection rate (D) could be calculated. For example, at 1550 nm band incident light intensity of 0.8 mW cm -2, source drain bias voltage V ds =1V, the responsivity and specific detection rate of device 1 are 1.07A/W and 6.1×10 10 Jones, respectively, while the responsivity and specific detection rate of device 2 are 54. 54A/W and 4.56×10 11 Jones, respectively, and the responsivity and specific detection rate of device 3 are 95.1A/W and 6.39×10 11 Jones, respectively. The results show that the performance of the photodetector is improved as the density of PbS quantum dots is increased.
Example 8
This example uses the technical method of example 5 to prepare a PbS quantum dot film, i.e., a PbS quantum dot film is prepared on MoS 2/SiO2 (20 nm)/Si substrate, and then a heterojunction phototransistor is prepared with Au (30 nm)/Cr (5 nm) as the electrode (source, drain electrode) in contact with the PbS quantum dot film. Fig. 11 is a current-voltage curve of the photodetector prepared in this example. The test conditions were 1550 nm bands of different incident light intensities (0.8 mW/cm 2、1.8 mW/cm2、3.2 mW/cm2 and 5.6 mW/cm 2), source drain bias voltage V ds =1V (no gate voltage applied). From this, the responsivity (R) and specific detection rate (D) of the photodetector at different light intensities can be calculated, for example, when the incident light intensity at 1550 nm band is 0.8 mW cm -2, the responsivity and specific detection rate are 93.4A/W and 5.49×10 11 Jones, respectively.
Comparative example 2
Compared to the PbS quantum dots of the present invention (without organic ligand coating), comparative example 2 employed PbS colloidal quantum dots (i.e., pbS quantum dots surface coated with organic ligands, available from scintillant nanotechnology limited) to construct photodetectors (colloid-PbS/SiO 2/Si). Under the same test conditions as in example 7, the responsivity of the photodetector of comparative example 2 was about 16.25A/W and the specific detection rate was 1.35×10 11 Jones at 1550 nm band incident light intensity of 0.8 mW cm -2 and bias voltage V ds =1V, which is significantly lower than that of devices 2 and 3 of example 7 (i.e., pbS quantum dot devices without organic ligands when the PbS density is high). Therefore, the performance of the photoelectric detector of the organic ligand-free PbS quantum dot film prepared by the invention is superior to that of a device with ligand PbS quantum dots. Fig. 12 is an SEM image (5 μm×5 μm) of PbS quantum dots with ligands.
Comparative example 3
In this example, comparative example 3 uses PbI 2 having a thickness of more than 5 nm as a Pb source, as compared with example 2.
In this comparative example, a 10 mm ×10 mm wafer was first rinsed with acetone/isopropanol/ethanol/deionized water in sequence and dried using dry nitrogen for later use. A6. 6 nm thick PbI 2 film was deposited on the above substrate using thermal evaporation plating at a rate of 0.02 nm/s as a Pb source, fed into a CVD (chemical vapor deposition) system and placed at the downstream end of the carrier gas. Sulfur powder 300 mg was weighed into a quartz boat, fed into a CVD system and placed at the upstream end of the carrier gas. The background vacuum of the system was brought to below 1.0X10 -1 Pa using a mechanical pump.
The participation of hydrogen is to introduce a certain flow of mixed gas of H 2 (20 sccm) and Ar (10 sccm), and after the gas flow is stable, the CVD system starts to heat. The temperature rising rate is 25 ℃ per minute, and when the system temperature is heated to 250 ℃, 100 min is maintained until the reaction is finished.
After the reaction is finished, the CVD system is slowly cooled to 170 ℃, the flow of inert gas is increased during the reaction, and then the system is quickly cooled to room temperature. The resulting material was characterized by X-ray photoelectron spectroscopy (XPS), which confirmed the presence of both PbS and unreacted complete PbI 2 in the resulting material (fig. 13). The resulting sample was subjected to scanning electron microscope characterization (FIG. 14), and it was seen that the nanowire material was in the form of a thin film in addition to the quantum dot. Therefore, when a PbI 2 thin film of more than 5 nm is used as a precursor of Pb, it is difficult to completely convert it into PbS quantum dots.
The photodetector performance parameters are also characterized by response times, responses at different wavelengths, etc., which are described in the relevant literature [ SCIENCE CHINA MATERIALS, 66, 193 (2023); adv. Opt. Mate. 11, 2300910 (2023) ], and are not described in detail herein. However, the photodetectors of PbS quantum dot films prepared by the present invention have a broad spectral response characteristic at uv to near ir wavelengths, determined on the one hand by the different dimensions (forbidden bandwidths) of PbS quantum dots prepared as shown in fig. 9, and on the other hand by the device structure of the heterojunction formed by PbS quantum dot films and silicon.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.
Claims (11)
1. A dry preparation method of a PbS quantum dot film is characterized in that a PbI 2 uniform continuous film is used as a Pb source to react with an S source to form the PbS quantum dot film in a mixed atmosphere of hydrogen and inert gas, the PbI 2 uniform continuous film is prepared on a substrate by a physical vapor deposition method, and the thickness of the PbI 2 film on the substrate is not more than 5 nm.
2. The method of manufacture of claim 1, wherein the method of manufacture meets at least one of the following characteristics:
1) In the mixed atmosphere of the hydrogen and the inert gas, the ratio of the hydrogen to the inert gas is 2:1-2:5;
2) The S source is solid sulfur powder or H 2 S, wherein the solid S source is sulfur powder, and gaseous sulfur is formed by adopting heating treatment.
3. The method according to claim 2, wherein the reaction temperature is 220 to 300 ℃.
4. A PbS quantum dot film, characterized in that it is produced by the method according to any one of claims 1 to 3.
5. The PbS quantum dot film of claim 4, wherein the PbS quantum dot film has a coverage rate of the PbS quantum dots in the PbS quantum dot film on the surface of the substrate of not less than 50%.
6. The PbS quantum dot film of claim 4, wherein the substrate is selected from an insulating material or a semiconductor material, and comprises one or a combination of more than two of glass, siO 2、SiC、Si3N4、Al2O3, sapphire, mica, mgO, si, and two-dimensional materials.
7. The PbS quantum dot film of claim 6, wherein the two-dimensional material is selected from MoS 2.
8. A heterojunction phototransistor formed by the PbS quantum dot film and silicon is characterized in that the heterojunction phototransistor is composed of a silicon layer and the PbS quantum dot film as claimed in claim 4.
9. The PbS quantum dot film and silicon heterojunction phototransistor of claim 8, wherein an insulating layer is provided between the silicon layer and the PbS quantum dot film, wherein:
The insulating layer material comprises SiO 2, HfO2、Hf(1-x)ZrxO2 (HZO) 、Al2O3、TiO2、ZrO2、Ta2O5 with high dielectric constant and Bi 2SeO5;
the thickness of the insulating layer is 2-20 nm.
10. The heterojunction phototransistor formed by the PbS quantum dot film and the silicon according to claim 8, wherein a two-dimensional lamellar material layer is arranged between the silicon layer and the PbS quantum dot film, and the lamellar 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 of claim 9, wherein a two-dimensional layered material layer is provided between the insulating layer and the PbS quantum dot film, and the layered material film comprises one or a combination of more than one of graphene and transition metal chalcogenide.
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