CN115207259B - Single photon source based on quantum dots and preparation method thereof - Google Patents
Single photon source based on quantum dots and preparation method thereof Download PDFInfo
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Abstract
The invention provides a single photon source based on quantum dots and a preparation method thereof, wherein the single photon source based on the quantum dots sequentially comprises the following components from bottom to top: the device comprises a substrate, a positive electrode, a hole injection layer, an aluminum oxide layer containing silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots, an electron injection layer and a negative electrode; the aluminum sesquioxide layer containing the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots consists of an aluminum sesquioxide film and the silver selenide/silver sulfide/silver selenide sulfide/shell quantum dots dispersed in the aluminum sesquioxide film; the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot is composed of a silver selenide core, a silver sulfide shell coated on the surface of the silver selenide core and a silver selenide sulfide alloy shell coated on the surface of the silver sulfide shell. The invention can obtain the electrically-driven single photon source with ultrahigh purity, strong warning drive, high efficiency, low background noise and environment friendliness, and works in communication wavelength.
Description
Technical Field
The invention relates to the technical field of semiconductor photoelectronic devices, in particular to a single photon source based on quantum dots and a preparation method thereof.
Background
Single photon sources are core components in quantum communication and quantum computing systems, and have also achieved excellent research results in the field. The development trend of quantum communication and quantum computation requires that a single photon source has the advantages of high purity, high efficiency, high isotropy and the like. Quantum dots can be used as excellent single photon emission materials due to their atomic-like discrete energy level mechanisms and high emission efficiency. However, due to the multiple degeneracy of the lowest energy levels at which the quantum dots participate in emission (multiple electron-hole pairs can be accommodated), there is multiple exciton emission in the quantum dots, which affects the purity of the single photon source. At present, the main means of the prior art is to avoid generating multiple excitons as much as possible by reducing the driving strength; however, multiple exciton emissions inevitably occur due to fluctuations in the driving light or electrical signal; in addition, too low a drive strength can result in very low emission efficiency from a single photon source.
In view of the above, there is a need for a single photon source based on quantum dots and a method for preparing the same to obtain an electrically driven single photon source with ultra-high purity, cautionable overdrive, high efficiency, operation at communication wavelengths, low background noise, and environmental friendliness.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a single photon source based on quantum dots to obtain an electrically driven single photon source with ultra-high purity, cautionable over-drive, high efficiency, operating within the communication wavelength, low background noise and environmental friendliness.
In order to achieve the above objects and other related objects, the present invention provides a single photon source based on quantum dots, which comprises, in order from bottom to top:
the device comprises a substrate, a positive electrode, a hole injection layer, an aluminum oxide layer containing silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots, an electron injection layer and a negative electrode;
the aluminum sesquioxide layer internally containing the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots consists of an aluminum sesquioxide film and the silver selenide/silver sulfide/silver selenide sulfide/shell quantum dots dispersed in the aluminum sesquioxide film;
the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot consists of a silver selenide core, a silver sulfide shell coated on the surface of the silver selenide core and a silver selenide sulfide alloy shell coated on the surface of the silver sulfide shell.
Optionally, the single-photon source based on quantum dots further comprises an oil immersion objective lens and a prism which are sequentially arranged below the substrate.
Optionally, the silver sulfide shell has a shell thickness in a range of 2 to 4 atomic layers.
Optionally, the ratio of sulfur element in the silver selenide sulfide alloy shell to the sum of sulfur and selenium elements is 70% to 90%, and the shell thickness of the silver selenide sulfide alloy shell ranges from 6 atomic layers to 8 atomic layers.
Optionally, the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots are distributed in a single layer in the aluminum oxide film; the distance between the centers of two adjacent silver selenide/silver sulfide/silver selenide sulfide cores/shells of quantum dots is more than 5 mu m.
Optionally, the distance between the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot and the electron injection layer is from 2nm to 4nm.
Optionally, the positive electrode is an indium tin oxide distributed feedback grating, the hole injection layer is made of tris (4-carbazol-9-ylphenyl) amine, the electron injection layer is made of zinc oxide, and the negative electrode is made of aluminum.
Optionally, the product of the grating period and the effective refractive index of the ito dfb grating is equal to the emission peak wavelength of the core/shell quantum dots of silver selenide/silver sulfide/silver selenide sulfide.
The invention also provides a preparation method of the single photon source based on the quantum dots, which is used for preparing the single photon source based on the quantum dots and comprises the following steps:
s1: preparing a silver selenide core;
s2: coating a silver sulfide shell on the surface of the silver selenide core, and coating a silver selenide sulfide alloy shell on the surface of the silver sulfide shell to obtain silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots;
s3: providing a substrate, and forming a positive electrode on the substrate;
s4: forming a hole injection layer on the positive electrode;
s5: dispersing the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots obtained in the step S2 in toluene, then diluting the dispersion liquid with toluene, and spin-coating the diluted dispersion liquid on the hole injection layer to obtain a dispersed quantum dot single layer;
s6: depositing aluminum oxide on the hole injection layer to obtain an aluminum oxide layer containing the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots;
s7: and sequentially forming an electron injection layer and a negative electrode on the aluminum oxide layer containing the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots.
Optionally, in step S7, after the electron injection layer and the negative electrode are formed, a step of sequentially disposing an oil immersion objective lens and a prism under the substrate is further included.
As described above, the single photon source based on quantum dots of the present invention has the following beneficial effects: when the silver selenide core 1 does not contain excitons, electrons and holes injected into the silver selenide sulfide alloy shell 3 through the electron injection layer 8 and the hole injection layer 6 can efficiently penetrate through the silver sulfide shell 2 and be injected into the silver selenide core 1 through a quantum tunneling effect to form a singlet exciton; when the silver selenide core 1 contains a single exciton, electrons and holes injected into the silver selenide sulfide alloy shell 3 cannot be injected into the silver selenide core 1 under the common obstruction of exciton coulomb repulsion force in the silver sulfide shell 2 and the silver selenide core 1, and only can be compounded in the silver selenide sulfide alloy shell 3, wherein the silver sulfide shell 2 is used as a barrier for the electrons and the holes in the movement of the electrons and the holes, the silver selenide/silver sulfide/silver selenide sulfide/core/shell quantum dots are of a quasi-two-type structure, and the coulomb action between excitons is mainly used as repulsion force.
Therefore, due to the huge energy level difference between the silver selenide sulfide and the silver selenide, the emission of the silver selenide sulfide alloy shell 3 and the single photon emission of the silver selenide core 1 can be completely separated in space, wherein the emission of the silver selenide sulfide alloy shell 3 can be used as a warning signal with over-strong driving, so that an operator can monitor and adjust the driving strength, or the driving strength is directly adjusted through a feedback circuit, thereby reducing background noise and energy loss; the core/shell of the silver selenide/silver sulfide/silver selenide sulfide/shell quantum dot well passivates the core of the quantum dot, the influence of external environment is isolated, ultrahigh-purity single photon emission irrelevant to driving strength can be realized, and the quantum dot emission efficiency is high and stable; the emission wavelength of the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots is adjustable along with the size of the silver selenide core in a near infrared second window, and the quantum dots can work in a communication wavelength; the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot does not contain toxic heavy metal elements and is environment-friendly.
Drawings
Fig. 1 shows a schematic structural diagram of a silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot of a single photon source based on quantum dots according to the present invention.
Fig. 2 is a schematic diagram showing the energy levels corresponding to the quantum dots of the silver selenide/silver sulfide/silver selenide sulfide core/shell of the single-photon source based on quantum dots.
FIG. 3 is a schematic diagram of a single photon source based on quantum dots according to the present invention.
FIG. 4 is a flow chart of a single photon source manufacturing method based on quantum dots according to the present invention.
Fig. 5 to 11 are schematic structural views showing steps of a single photon source manufacturing method based on quantum dots according to the present invention.
Description of the element reference numerals
1, silver selenide core; 2, silver sulfide shells; 3, silver selenide sulfide alloy shell; 4, a substrate; 5, a positive electrode; 6, a hole injection layer; 7, an aluminum sesquioxide layer containing silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots; 8, an electron injection layer; 9, a negative electrode; 10, an oil immersion objective lens; 11, a prism.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1 to 11. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than being drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of each component in actual implementation may be changed arbitrarily, and the layout of the components may be more complicated.
Example one
As shown in fig. 1 to fig. 3, this embodiment provides a single photon source based on quantum dots, which is characterized in that the single photon source based on quantum dots sequentially includes, from bottom to top:
as shown in fig. 3, a substrate 4, a positive electrode 5, a hole injection layer 6, an aluminum oxide layer 7 containing silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots, an electron injection layer 8 and a negative electrode 9;
the aluminum sesquioxide layer 7 containing the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots consists of an aluminum sesquioxide film and silver selenide/silver sulfide/silver selenide sulfide/shell quantum dots dispersed in the aluminum sesquioxide film;
as shown in fig. 1, the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot is composed of a silver selenide core 1, a silver sulfide shell 2 coated on the surface of the silver selenide core 1, and a silver selenide sulfide alloy shell 3 coated on the surface of the silver sulfide shell 2.
As shown in fig. 1 and fig. 2, the working principle of the present embodiment is: when the silver selenide core 1 does not contain excitons, electrons and holes injected into the silver selenide sulfide alloy shell 3 through the electron injection layer 8 and the hole injection layer 6 can efficiently penetrate through the silver sulfide shell 2 and be injected into the silver selenide core 1 through a quantum tunneling effect to form a singlet exciton; when the silver selenide core 1 already contains a single exciton, electrons and holes injected into the silver selenide sulfur alloy shell 3 cannot be injected into the silver selenide core 1 under the common hindrance of exciton coulomb repulsion force in the silver sulfide shell 2 and the silver selenide core 1, and only can be recombined in the silver selenide sulfur alloy shell 3, wherein the silver sulfide shell 2 is used as a barrier for electrons and holes in the movement of electrons and holes, the silver selenide/silver sulfide/silver selenide sulfur core/shell quantum dots are of a quasi-two-type structure, and the coulomb action between excitons is mainly repulsive force. Due to the large energy level difference between silver selenide sulfide and silver selenide, the emission of the silver selenide sulfide alloy shell 3 and the single photon emission of the silver selenide core 1 can be completely separated spatially.
The silver selenide sulfide alloy shell 3 of the embodiment emits a warning signal which can be used as an over-driving warning signal for an operator to monitor and adjust the driving strength, or the driving strength is directly adjusted through a feedback circuit, so that the background noise and the energy loss are reduced; the core/shell of the silver selenide/silver sulfide selenide core/shell quantum dot well passivates the core of the quantum dot, the influence of external environment is isolated, ultra-high-purity single photon emission irrelevant to driving strength can be realized, and the emission efficiency of the silver selenide/silver sulfide selenide core/shell quantum dot is high and stable; the emission wavelength of the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots is adjustable along with the size of the silver selenide core 1 in a near infrared second window and can work in a communication wavelength; the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot does not contain toxic heavy metal elements and is environment-friendly.
The substrate 4 used in this embodiment is a quartz substrate, which is cheap and has good compatibility with the structure on the substrate, and is preferable as an example.
As shown in fig. 3, the single photon source based on quantum dots further includes an oil immersion objective lens 10 and a prism 11, which are sequentially disposed under the substrate 4, as an example.
The single photon source based on quantum dots collects signals from the lower surface of the substrate 4 by using the oil immersion objective lens 10, and completely separates the warning signal with over-strong driving from the single photon output in space through the prism 11 (as shown by an arrow at the lower part of fig. 3).
By way of example, the silver sulfide shell 2 has a shell thickness in the range of 2 to 4 atomic layers.
The shell thickness of the silver sulfide shell 2, namely the number of atomic layers determines the width of electron and hole barriers, and excessive atomic layers can reduce the injection efficiency of a first pair of electrons and a first pair of holes, so that the single photon emission efficiency is reduced; too few atomic layers together with the coulomb repulsion cannot completely block the injection of multiple excitons, thereby reducing single photon emission purity. As an exemplary preference, the silver sulfide shell 2 has a shell thickness of 3 atomic layers.
For example, the ratio of sulfur element in the silver selenide sulfide alloy shell 3 to the sum of sulfur and selenium elements is 70% to 90%, and the shell thickness of the silver selenide sulfide alloy shell 3 is in a range of 6 to 8 atomic layers.
The proportion of sulfur element in the sum of sulfur and selenium elements, namely the forbidden bandwidth of the silver selenide alloy and the forbidden bandwidth of silver sulfide determine the height of electron and hole potential barriers, and the injection of a first pair of electrons and a first pair of holes can be reduced by the excessively low proportion of sulfur element, namely the forbidden bandwidth difference is too large, and the potential barrier is too high, so that the single-photon emission efficiency is reduced; too high proportion means that the difference of forbidden band widths is too small, the potential barrier is too low, and the injection of multiple excitons can not be completely blocked together with the Coulomb repulsive force, so that the single photon emission purity is reduced. The silver selenide sulfide alloy shell 3 is too thick and thin to isolate the influence of external environment, and the emission stability is low; the excessively thick shell can reduce the dispersibility of the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots, and the preparation quality of the device is affected. As an example, it is preferable that the ratio of the sulfur element to the sum of the sulfur and selenium elements in the silver selenide sulfide alloy shell 3 is 80%, and the shell thickness of the silver selenide sulfide alloy shell 3 is 7 atomic layers.
As an example, the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots are distributed in a monolayer in the aluminum sesquioxide film; the distance between the centers of two adjacent silver selenide/silver sulfide/silver selenide sulfide cores/shells of quantum dots is more than 5 mu m.
The single-layer distribution of the silver selenide/silver sulfide selenide core/shell quantum dots and the distance between the centers of two adjacent silver selenide/silver sulfide selenide core/shell quantum dots ensure that the fluorescence of the surrounding quantum dots cannot be collected during signal collection, and ensure the purity of single photon emission.
As shown in fig. 3, the structure of the positive electrode 5 is an indium tin oxide distributed feedback grating, the material of the hole injection layer 6 is tris (4-carbazol-9-ylphenyl) amine, the material of the electron injection layer 8 is zinc oxide, and the material of the negative electrode 9 is aluminum.
Here, it should be noted that the thickness of the hole injection layer 6 of the tris (4-carbazol-9-ylphenyl) amine material in the present embodiment is 50nm; the thickness of the electron injection layer 8 of zinc oxide material is 60nm.
By way of example, the distance between the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot and the electron injection layer 8 ranges from 2nm to 4nm.
As a preferred example, the distance between the silver selenide/silver sulfide selenide core/shell quantum dot and the electron injection layer 8 of zinc oxide material is about 2nm, electrons are injected into the silver selenide/silver sulfide selenide core/shell quantum dot through the electron injection layer 8 of 2nm by a tunneling effect, in other areas, because the aluminum oxide film is too thick and the tunneling effect is very weak, the composite current is concentrated in the area of the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot, the emission efficiency is increased, the direct exchange of carriers between the hole injection layer 6 and the electron injection layer 8 is slowed down, so that a large amount of carriers are prevented from being recombined at the hole injection layer 6 or the electron injection layer 8 and the interface thereof, and the background noise is reduced, that is, in this embodiment, the direct exchange of carriers between the tris (4-carbazol-9-ylphenyl) amine layer and the zinc oxide layer is slowed down, so that a large amount of carriers are prevented from being recombined at the tris (4-carbazol-9-ylphenyl) amine layer or the zinc oxide layer and the interface thereof, and the background noise is reduced.
As a preferred example, when the structure of the positive electrode 5 is an indium tin oxide distributed feedback grating, the product of the grating period and the effective refractive index of the indium tin oxide distributed feedback grating is equal to the emission peak wavelength of the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot.
It should be noted here that the resonant wavelength of the ito distributed feedback grating is the same as the peak wavelength of the emission of the quantum dots of the core/shell of the silver selenide/silver sulfide/silver selenide sulfide, that is, the product of the grating period and the effective refractive index is equal to the peak wavelength of the emission of the quantum dots, so that the collection efficiency and the isotropy of the device can be increased.
Example two
This example provides a method for preparing a single photon source based on quantum dots, which can be used to prepare the single photon source based on quantum dots described in the first example, and the method for preparing the single photon source based on quantum dots in the second example will be described in detail below with reference to the accompanying drawings (as shown in fig. 4 to 11).
As shown in fig. 4 and 5, first, step S1 is performed to prepare a silver selenide core 1.
In this embodiment, the silver selenide core 1 having an emission wavelength located in a communication band is prepared by controlling a reaction time using a metal organic preparation method, where the size of the silver selenide core 1 is controllable.
As shown in fig. 4 and 6, step S2 is performed next, a silver sulfide shell 2 is coated on the surface of the silver selenide core 1, and a silver selenide sulfide alloy shell 3 is coated on the surface of the silver sulfide shell 2, so as to obtain a silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot.
In this embodiment, the shell thickness of the silver sulfide shell 2 is 3 atomic layers, and the silver sulfide shell 2 is coated on the surface of the silver selenide core 1 by controlling the injection amount of the precursor by using a continuous ion-layer adsorption reaction method; in the silver selenide sulfide alloy shell 3, the proportion of sulfur element in the sum of sulfur and selenium elements is 80%, the shell thickness is 7 atomic layers, and the silver selenide sulfide alloy shell 3 is coated on the surface of the silver sulfide shell 2 by controlling the proportion and the injection amount of the precursor, so that the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots are obtained.
As shown in fig. 4 and 7, step S3 is performed to provide a substrate 4, and form a positive electrode 5 on the substrate 4.
In this embodiment, the structure of the positive electrode 5 is selected to be an indium tin oxide distribution feedback grating, and when the indium tin oxide distribution feedback grating is formed, an indium tin oxide film is deposited on the substrate 4 by using a magnetron sputtering method, and then the indium tin oxide film is etched into the indium tin oxide distribution feedback grating by using a reactive ion etching method, so as to form the positive electrode 5 of the quantum dot-based single photon source.
As shown in fig. 4 and 8, step S4 is performed to form a hole injection layer 6 on the positive electrode 5.
In this embodiment, the material of the hole injection layer 6 is selected to be tris (4-carbazol-9-ylphenyl) amine, that is, the hole injection layer 6 is a tris (4-carbazol-9-ylphenyl) amine layer, and the tris (4-carbazol-9-ylphenyl) amine layer is deposited on the ito dfb by using a thermal evaporation method, wherein the thickness of the tris (4-carbazol-9-ylphenyl) amine layer 6 is 50nm.
As shown in fig. 4, step S5 is then performed, the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots obtained in step S2 are dispersed in toluene, then the dispersion is diluted with toluene, and the diluted dispersion is spin-coated on the hole injection layer 6, so as to obtain a dispersed quantum dot monolayer.
In this embodiment, the silver selenide/silver sulfide selenide core/shell quantum dots obtained in step S2 are dispersed in toluene, then quantum dots or toluene are added to adjust the optical density of the quantum dot toluene dispersion to 0.1 at 800nm excitation light, then the adjusted dispersion is diluted 200000 times with toluene, and then the diluted dispersion is spin-coated onto the hole injection layer 6, i.e., the tris (4-carbazol-9-ylphenyl) amine layer, at a rotation speed of 4000 rpm, to obtain the dispersed silver selenide/silver sulfide selenide core/shell quantum dot monolayer.
As shown in fig. 4 and 9, step S6 is performed to deposit aluminum oxide on the hole injection layer 6, so as to obtain an aluminum oxide layer 7 containing silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots.
In this embodiment, aluminum oxide is deposited on the hole injection layer 6, i.e., the tris (4-carbazol-9-ylphenyl) amine layer, by using an atomic layer deposition method, wherein the thickness of the aluminum oxide is 12nm, and the aluminum oxide layer 7 containing the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots is obtained.
As shown in fig. 4 and 10, step S7 is finally performed to sequentially form an electron injection layer 8 and a negative electrode 9 on the aluminum oxide layer 7 containing the silver selenide/silver sulfide/silver sulfoselenide core/shell quantum dots.
In this embodiment, the material of the electron injection layer 8 is selected to be zinc oxide, and the material of the negative electrode 9 is selected to be aluminum; spin-coating 15mg/ml of zinc oxide ethanol sol onto the aluminum oxide layer 7 containing the silver selenide/silver sulfide/silver sulfoselenide core/shell quantum dots at a rotation speed of 5000 rpm to obtain the electron injection layer 8, namely the zinc oxide layer, wherein the thickness of the zinc oxide layer is 60nm; and depositing aluminum on the electron injection layer 8 by using a thermal evaporation method to obtain a negative electrode 9 of the quantum-dot-based single photon source.
As shown in fig. 11, after the electron injection layer 8 and the negative electrode 9 are formed in step S7, a step of sequentially disposing an oil immersion objective lens 10 and a prism 11 under the substrate 4 is further included, and the collection efficiency of the oil immersion objective lens 10 and the spectroscopic position of the prism 11 are optimally adjusted.
In the present embodiment, the single photon source based on quantum dots collects signals from the lower surface of the substrate 4 by using the oil immersion objective lens 10, and completely separates the warning signal with too strong driving from the single photon output from space by using the prism 11 (as shown by the arrow below fig. 11).
In summary, the invention provides a single photon source based on quantum dots and a preparation method thereof, wherein the single photon source based on quantum dots sequentially comprises the following components from bottom to top: the device comprises a substrate 4, a positive electrode 5, a hole injection layer 6, an aluminum oxide layer 7 containing silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots, an electron injection layer 8 and a negative electrode 9; the aluminum sesquioxide layer containing the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots consists of an aluminum sesquioxide film and the silver selenide/silver sulfide/silver selenide sulfide/shell quantum dots dispersed in the aluminum sesquioxide film; the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot is composed of a silver selenide core 1, a silver sulfide shell 2 coated on the surface of the silver selenide core, and a silver selenide sulfide alloy shell 3 coated on the surface of the silver sulfide shell.
When the silver selenide core 1 does not contain excitons, electrons and holes injected into the silver selenide sulfide alloy shell 3 through the electron injection layer 8 and the hole injection layer 6 can efficiently penetrate through the silver sulfide shell 2 and be injected into the silver selenide core 1 through a quantum tunneling effect to form a singlet exciton; when the silver selenide core 1 contains a single exciton, electrons and holes injected into the silver selenide sulfide alloy shell 3 cannot be injected into the silver selenide core 1 under the common obstruction of exciton coulomb repulsion force in the silver sulfide shell 2 and the silver selenide core 1, and only can be compounded in the silver selenide sulfide alloy shell 3, wherein the silver sulfide shell 2 is used as a barrier for the electrons and the holes in the movement of the electrons and the holes, the silver selenide/silver sulfide/silver selenide sulfide/core/shell quantum dots are of a quasi-two-type structure, and the coulomb action between excitons is mainly used as repulsion force.
Therefore, due to the huge energy level difference between silver selenide sulfide and silver selenide, the emission of the silver selenide sulfide alloy shell 3 and the single photon emission of the silver selenide core 1 can be completely separated in space, wherein the emission of the silver selenide sulfide alloy shell 3 can be used as an over-driving warning signal for an operator to monitor and adjust the driving strength, or the driving strength is directly adjusted through a feedback circuit, so that the background noise and the energy loss are reduced; the core/shell of the silver selenide/silver sulfide/silver selenide sulfide/shell quantum dot well passivates the core of the quantum dot, the influence of external environment is isolated, ultra-high-purity single photon emission irrelevant to driving strength can be realized, and the emission efficiency of the silver selenide/silver sulfide/silver selenide core/shell quantum dot is high and stable; the emission wavelength of the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots is adjustable along with the size of the silver selenide core in a near infrared second window, and the quantum dots can work in a communication wavelength; the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot does not contain toxic heavy metal elements and is environment-friendly. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Those skilled in the art can modify or change the above-described embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (10)
1. A single photon source based on quantum dots is characterized in that the single photon source based on quantum dots sequentially comprises the following components from bottom to top:
the device comprises a substrate, a positive electrode, a hole injection layer, an aluminum oxide layer containing silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots, an electron injection layer and a negative electrode;
the aluminum sesquioxide layer internally containing the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots consists of an aluminum sesquioxide film and the silver selenide/silver sulfide/silver selenide sulfide/shell quantum dots dispersed in the aluminum sesquioxide film;
the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot is composed of a silver selenide core, a silver sulfide shell coated on the surface of the silver selenide core and a silver selenide sulfide alloy shell coated on the surface of the silver sulfide shell.
2. A single photon source based on quantum dots according to claim 1 wherein: the single photon source based on the quantum dots further comprises an oil immersion objective lens and a prism which are sequentially arranged below the substrate.
3. A single photon source based on quantum dots according to claim 1 wherein: the shell thickness range of the silver sulfide shell is 2-4 atomic layers.
4. A single photon source based on quantum dots according to claim 1 wherein: the proportion of sulfur element in the silver selenide sulfide alloy shell to the sum of sulfur and selenium elements is 70-90%, and the shell thickness of the silver selenide sulfide alloy shell ranges from 6 atomic layers to 8 atomic layers.
5. A single photon source based on quantum dots as claimed in claim 1 wherein: the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots are distributed in a single layer in the aluminum oxide film; the distance between the centers of two adjacent silver selenide/silver sulfide/silver selenide sulfide cores/shells of quantum dots is more than 5 mu m.
6. A single photon source based on quantum dots according to claim 1 wherein: the distance range between the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dot and the electron injection layer is 2nm to 4nm.
7. A single photon source based on quantum dots as claimed in claim 1 wherein: the positive electrode is structured by indium tin oxide distributed feedback gratings, the hole injection layer is made of tri (4-carbazole-9-phenyl) amine, the electron injection layer is made of zinc oxide, and the negative electrode is made of aluminum.
8. A single photon source based on quantum dots according to claim 7 wherein: the product of the grating period and the effective refractive index of the indium tin oxide distributed feedback grating is equal to the emission peak wavelength of the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots.
9. A preparation method of a single photon source based on quantum dots is characterized by comprising the following steps:
s1: preparing a silver selenide core;
s2: coating a silver sulfide shell on the surface of the silver selenide core, and coating a silver selenide sulfide alloy shell on the surface of the silver sulfide shell to obtain silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots;
s3: providing a substrate, and forming a positive electrode on the substrate;
s4: forming a hole injection layer on the positive electrode;
s5: dispersing the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots obtained in the step S2 in toluene, then diluting the dispersion liquid with toluene, and spin-coating the diluted dispersion liquid on the hole injection layer to obtain a dispersed quantum dot single layer;
s6: depositing aluminum oxide on the hole injection layer to obtain an aluminum oxide layer containing silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots;
s7: and sequentially forming an electron injection layer and a negative electrode on the aluminum oxide layer containing the silver selenide/silver sulfide/silver selenide sulfide core/shell quantum dots.
10. A method of preparing a single photon source based on quantum dots as claimed in claim 9 wherein: in step S7, after the electron injection layer and the negative electrode are formed, a step of sequentially disposing an oil immersion objective lens and a prism under the substrate is further included.
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