Preparation method of hexagonal boron nitride single photon source

Abstract

The invention provides a preparation method of a hexagonal boron nitride single photon source, which can be applied to the technical field of quantum communication, and comprises the following steps: preparing a sapphire substrate; sputtering solid boron films on the first substrate and the third substrate; overlapping the first substrate bearing the solid boron film and the second substrate, and placing the first substrate and the second substrate in a heating furnace to grow a first hexagonal boron nitride single crystal film; performing plasma treatment on the first hexagonal boron nitride single crystal thin film; the third substrate and the second substrate are stacked and placed in the heating furnace, growth of a second hexagonal boron nitride single crystal thin film is carried out, and the first hexagonal boron nitride single crystal thin film is located between the second substrate and the third substrate. The preparation of a large-scale single photon source is realized on a hexagonal boron nitride single crystal film through a plasma treatment process, and efficient passivation protection of the single photon source in a first hexagonal boron nitride single crystal film is realized by using an in-situ cover layer to secondarily grow a second hexagonal boron nitride single crystal film.

Description

Technical Field

[0001] The invention relates to the field of quantum communication technology, and in particular to a method for preparing a hexagonal boron nitride single-photon source. Background Art

[0002] Quantum emitters in solid-state systems have become a key factor in promoting the application of many cutting-edge quantum technologies, such as quantum communication technology, quantum computing, quantum network architecture, and quantum sensing. As the cornerstone of quantum information technology, single-photon sources provide an indispensable basic resource for the realization of these technologies. With the continuous deepening of research, the scope of single-photon emitters (SPE) is no longer limited to the initial single-atom or single-molecule form, but has been successfully expanded to a variety of solid-state materials such as diamond, point defects in silicon carbide, semiconductor quantum dots, and carbon nanotubes.

[0003] Recently, two-dimensional (2D) materials have attracted much attention from the research community due to their excellent ability to host specific SPEs and their inherent advantages in device integration and coupling efficiency with optical devices. Unfortunately, however, most SPEs in 2D transition metal dichalcogenides (TMDs) can only work properly under low temperature conditions, which undoubtedly limits their widespread application under room temperature conditions. In this context, hexagonal boron nitride (h-BN), a 2D layered material with a similar structure to graphene, has successfully demonstrated its ability to host high-brightness, room-temperature stable and strongly linearly polarized SPEs due to the local point defects in its wide bandgap of about 6 eV. In addition, the excellent chemical and thermal stability exhibited by h-BN provides a strong guarantee for the long-term stable operation of SPEs. These remarkable properties make h-BN-based quantum emitters an ideal choice for integrated quantum photonic devices.

[0004] Quantum emitters in h-BN often originate from defects randomly formed during its growth process or when it is peeled off from the bulk crystal. Usually, these emitters can be stabilized without further treatment or with only a simple thermal annealing process. However, this randomness leads to the ubiquity and disordered spatial distribution of emitters, accompanied by low density and inhomogeneous optical properties. To overcome this problem, researchers have explored and adopted a variety of post-processing methods, such as ion / electron irradiation, focused ion beam (FIB) processing, plasma etching, femtosecond laser ablation, and atomic force microscope (AFM) tip nanoindentation, aiming to create high-density and uniform quantum emitters. Among these methods, plasma processing technology is particularly attractive due to its ability to generate optically active defects on a large scale, high scalability, and ease of operation.

[0005] Maintaining good emission stability is the core element for the successful implementation of SPE applications. However, h-BN-based SPEs often encounter flickering and even quenching problems in actual testing and applications. Therefore, it has become a top priority to develop effective suppression and passivation technologies to enhance the stability of the emitter. In view of this, researchers have deeply explored the flickering and quenching mechanisms of h-BN-based SPEs, and have continuously tried various treatment methods to improve their stability. Studies have shown that emitters based on thicker h-BN layers exhibit higher stability, and it is speculated that luminescent flickering may be related to the chemical reaction between the h-BN emitter and surface impurities or adsorbed molecules. Similarly, there are also views that attribute flickering to photochemical reactions triggered by oxygen adsorption on the h-BN surface. Although there is still controversy about the specific mechanism of flickering and quenching of h-BN-based SPEs, the industry has reached a consensus: isolating h-BN emitters from the environment can significantly improve their stability. Based on this consensus, researchers have tried a variety of isolation methods. For example, some researchers have effectively isolated the sample from the environment by spin-coating a polymethyl methacrylate (PMMA) film on the surface of h-BN, thereby significantly improving the stability of the emitter. Other researchers have used transfer technology to cover the upper and lower surfaces of h-BN with another layer of h-BN as a protective layer. This method significantly suppressed the quenching phenomenon of the emitter and extended its half-life by two orders of magnitude. In addition, some researchers have used atomic layer deposition technology to grow an Al2O3 layer on h-BN, achieving effective passivation and significantly reducing the spectral diffusion caused by the substrate.

[0006] However, it is worth noting that the two-dimensional h-BN material itself has an atomically flat surface without dangling bonds, which is an ideal protective layer for the emitter. However, covering by transferring h-BN film is not the best choice, because contamination and damage will inevitably be introduced during the peeling and transfer process, which may generate electron traps and affect the stability of the emitter. Therefore, it is particularly urgent to explore a method that is simple, effective, pollution-free, and can perfectly cover the h-BN surface to protect the emitter. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] In order to solve the technical problem in the prior art that additional contamination is easily introduced when covering other material films or transferring h-BN during the passivation protection process of the hexagonal boron nitride emitter surface, an embodiment of the present invention provides a method for preparing a hexagonal boron nitride single-photon source, which realizes the preparation of large-scale single-photon sources on h-BN single crystal thin films through a plasma treatment process, and uses an in-situ capping layer to secondary grow h-BN single crystal thin films to achieve efficient passivation protection of the underlying single-photon source. The prepared single-photon source has the characteristics of high brightness, high purity, room temperature operation, stable luminescence properties, and low preparation cost.

[0009] (II) Technical solution

[0010] In view of the above technical problems, an embodiment of the present invention provides a method for preparing a hexagonal boron nitride single-photon source.

[0011] According to a first aspect of the present invention, a method for preparing a hexagonal boron nitride single-photon source is provided, comprising: preparing three single-sided polished sapphire substrates, respectively serving as a first substrate, a second substrate and a third substrate; sputtering and depositing a first solid boron film on the polished surface of the first substrate; stacking a second substrate on the surface of the first solid boron film to obtain a first stacked body, wherein the first solid boron film contacts the polished surface of the second substrate; processing the first stacked body according to first process parameters in a nitrogen atmosphere to convert the first solid boron film into a first hexagonal boron nitride single crystal film; peeling the first substrate from the first stacked body to obtain a second substrate carrying the first hexagonal boron nitride single crystal film; and stacking the second substrate carrying the first hexagonal boron nitride single crystal film. The substrate is placed in a radio frequency plasma generator for treatment to controllably introduce a single photon source into the first hexagonal boron nitride single crystal film; a layer of a second solid boron film is sputtered and deposited on the polished surface of the third substrate; the third substrate is stacked on the surface of the first hexagonal boron nitride single crystal film introduced with the single photon source to obtain a second stacked body, wherein the first hexagonal boron nitride single crystal film introduced with the single photon source is in contact with the second solid boron film; the second stacked body is treated according to second process parameters under a nitrogen atmosphere to convert the second solid boron film into a second hexagonal boron nitride single crystal film; and the third substrate is peeled off from the second stacked body to obtain a second substrate carrying the first hexagonal boron nitride single crystal film and the second hexagonal boron nitride single crystal film, which serves as a hexagonal boron nitride single photon source.

[0012] In some exemplary embodiments, the method further includes: annealing the second substrate carrying the first hexagonal boron nitride single crystal thin film and the second hexagonal boron nitride single crystal thin film.

[0013] In some exemplary embodiments, preparing three single-side polished sapphire substrates includes sequentially placing the sapphire substrates in acetone, isopropanol, and ethanol for ultrasonic cleaning and drying them with nitrogen.

[0014] In some exemplary embodiments, the thickness of the first solid boron film and the second solid boron film is related to the sputtering deposition time; the deposition time of the first solid boron film is 5 min-60 min; and the deposition time of the second solid boron film is 5 min-60 min.

[0015] In some exemplary embodiments, the first process parameters include the following process procedures: adjusting the nitrogen gas flow to 400 sccm and maintaining it; the first target growth temperature is not higher than 1600°C, and the temperature in the heating furnace is increased to the first target growth temperature at a heating rate not exceeding 5°C / min; or the first target growth temperature is higher than 1600°C, and the temperature in the heating furnace is increased to 1600°C at a heating rate not exceeding 5°C / min, and then increased to the first target growth temperature at a rate not exceeding 2°C / min; keeping at the first target growth temperature for 1min-120min; reducing the temperature of the heating furnace tube to 500°C at a cooling rate not exceeding 3°C / min; and naturally cooling to room temperature.

[0016] In some exemplary embodiments, the second process parameters include the following process procedures: adjusting the nitrogen flow to 400 sccm and maintaining it; the second target growth temperature is not higher than 1600°C, and the temperature in the heating furnace is increased to the second target growth temperature at a heating rate not exceeding 5°C / min; or the second target growth temperature is higher than 1600°C, and the temperature in the heating furnace is increased to 1600°C at a heating rate not exceeding 5°C / min, and then increased to the second target growth temperature at a rate not exceeding 2°C / min; keeping at the second target growth temperature for 1min-30min; reducing the temperature of the heating furnace tube to 500°C at a cooling rate not exceeding 3°C / min; and naturally cooling to room temperature.

[0017] In some exemplary embodiments, the first target growth temperature is 1350° C.-1750° C.; the second target growth temperature is 1350° C.-1650° C.; and the second target growth temperature is lower than the first target growth temperature.

[0018] In some exemplary embodiments, the second substrate carrying the first hexagonal boron nitride single crystal film is placed in a radio frequency plasma generator for treatment with plasma treatment parameters as follows: the plasma treatment atmosphere includes at least one of argon, oxygen, nitrogen, hydrogen, methane and ammonia; the plasma treatment time is 1 min-20 min; and the plasma treatment power is 20 W-250 W.

[0019] In some exemplary embodiments, the method of peeling the first substrate from the first stacked body includes purging with nitrogen; and the method of peeling the third substrate from the second stacked body includes purging with nitrogen.

[0020] In some exemplary embodiments, during the annealing process, the annealing atmosphere includes one of air, oxygen, nitrogen or argon; the annealing temperature is 700°C-900°C; the annealing time is 30min-60min; and the temperature rise and fall rates do not exceed 10°C / min.

[0021] (III) Beneficial effects

[0022] It can be seen from the above technical solutions that the method for preparing a hexagonal boron nitride single-photon source provided by the embodiment of the present invention has at least the following beneficial effects:

[0023] Based on the plasma treatment process, large-scale single-photon sources are prepared on h-BN single crystal films. The in-situ capping layer is used to secondary grow h-BN single crystal films to achieve efficient passivation protection of the underlying single-photon source. The prepared single-photon source has the characteristics of high brightness, high purity, room temperature operation, stable luminescence properties, and low preparation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above contents and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0025] Figure 1 A schematic diagram of a process for preparing a hexagonal boron nitride single-photon source according to an embodiment of the present invention is shown;

[0026] Figure 2 A schematic diagram of a hexagonal boron nitride cap layer growth structure according to an embodiment of the present invention is shown;

[0027] Figure 3 A schematic diagram of the atomic force microscope surface morphology of a hexagonal boron nitride capping layer growth structure according to an embodiment of the present invention is shown;

[0028] Figure 4 A schematic diagram of a Raman scattering spectrum of a hexagonal boron nitride capping layer growth structure according to an embodiment of the present invention is shown;

[0029] Figure 5 A photoluminescence scanning diagram of a single photon source in a hexagonal boron nitride capping layer growth structure according to an embodiment of the present invention is schematically shown;

[0030] Figure 6 A schematic diagram showing the test results of the second-order correlation characteristics of a single photon source in a hexagonal boron nitride capping layer growth structure according to an embodiment of the present invention is shown;

[0031] Figure 7 Schematically showing an emission spectrum-time correlation diagram of a single photon source in a first hexagonal boron nitride single crystal thin film structure according to an embodiment of the present invention;

[0032] Figure 8 Schematically shows an emission spectrum-time correlation diagram of a single photon source in a hexagonal boron nitride capping layer growth structure according to an embodiment of the present invention;

[0033] Fig. 9A schematic diagram schematically shows the emission stability test results of a single photon source in a first hexagonal boron nitride single crystal thin film structure according to an embodiment of the present invention; and

[0034] Fig.10 The figure schematically shows the emission stability test results of a single photon source in a hexagonal boron nitride capping structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Figure 1 The flowchart of a method for preparing a hexagonal boron nitride single-photon source according to an embodiment of the present invention is schematically shown.

[0037] like Figure 1 As shown, a method for preparing a hexagonal boron nitride single-photon source according to an embodiment of the present invention includes steps S101 to S110.

[0038] In step S101 , three single-side polished sapphire substrates are prepared as a first substrate, a second substrate and a third substrate, respectively.

[0039] For example, a 2-inch single-sided polished sapphire single crystal is prepared as a sapphire substrate, and the sapphire single crystal is sequentially placed in acetone, isopropanol, and ethanol for ultrasonic cleaning and blown dry with nitrogen. Optionally, the sapphire single crystal is cleaned twice in each solvent, each cleaning time is 30 minutes, and the sapphire single crystal is blown dry with nitrogen, wherein the purity of the nitrogen is 99.9%.

[0040] In step S102, a first solid boron film is sputter-deposited on the polished surface of the first substrate, wherein the thickness of the first solid boron film is related to the sputtering deposition time, and optionally, the deposition time of the first solid boron film is 5 min-60 min.

[0041] For example, fix the clean sapphire substrate with the polished surface facing outward on the sample holder, and put the sample holder on a rotatable heating furnace in the sputtering chamber; turn on the vacuum pump to reduce the vacuum degree in the sputtering chamber to 5×10 -5Pa or less. Turn on the heating furnace to heat up in stages. When the substrate temperature rises to 1100℃-1410℃, adjust the distance between the substrate and the boron sputtering target to 7cm-11cm; turn on the sample holder to rotate at a speed of 10r / min; turn on the boron sputtering target in the cavity to rotate at a speed of 15r / min. This process does not require the introduction of any gas to maintain a high vacuum environment; start the krypton fluoride (KrF) excimer laser power supply, adjust the laser light path so that the laser is focused through the lens and emitted from the transparent optical window. The laser is irradiated onto the boron sputtering target in the sputtering chamber, the laser pulse width is set to 20ns, the frequency is set to 1-20Hz, the energy of a single pulse laser is set to 200-700mJ, the spot diameter is 4mm, and the excitation voltage is 22kV; the substrate temperature is maintained unchanged, and the sputtering deposition is continuously performed for 5-60min; after the sputtering is completed, the sample holder rotation and the target rotation are turned off, the distance between the substrate and the boron sputtering target is restored to the maximum, and the substrate temperature is slowly reduced to room temperature, and a high-purity solid boron film can be obtained. Optionally, the purity of the boron sputtering target is not less than 99.9%.

[0042] In step S103, a second substrate is stacked on the surface of the first solid boron film to obtain a first stacked body, wherein the first solid boron film is in contact with the polished surface of the second substrate.

[0043] In step S104, the first stacked body is processed according to first process parameters under a nitrogen atmosphere to transform the first solid boron film into a first hexagonal boron nitride single crystal film.

[0044] In some exemplary embodiments, the first process parameters include the following process procedures: adjusting the nitrogen flow to 400sccm and maintaining it; the first target growth temperature is not higher than 1600°C, and the temperature in the heating furnace is increased to the first target growth temperature at a heating rate not exceeding 5°C / min; or the first target growth temperature is higher than 1600°C, and the temperature in the heating furnace is increased to 1600°C at a heating rate not exceeding 5°C / min, and then increased to the first target growth temperature at a rate not exceeding 2°C / min; the first target growth temperature is 1350°C-1750°C, and the first target growth temperature is kept at the first target growth temperature for 1min-120min; the temperature of the heating furnace tube is reduced to 500°C at a cooling rate not exceeding 3°C / min; and naturally cooled to room temperature.

[0045] In step S105, the first substrate is peeled off from the first stacked body to obtain a second substrate carrying the first hexagonal boron nitride single crystal thin film.

[0046] In some exemplary embodiments, the method of peeling the first substrate from the first stack includes purging with nitrogen gas.

[0047] For example, two stacked substrates are placed in a customized marble tray to fix their positions, and then the marble tray is placed horizontally in the furnace tube of a high-temperature tubular heating furnace and slowly pushed into the center of the furnace tube, and the two sides of the furnace tube are sealed with flanges and rubber rings. A vacuum pump is used to pump the pressure in the furnace tube from one end of the heating furnace to below 1Pa and maintain it for 5-10 minutes, and then the vacuum pump is turned off and nitrogen is introduced from the other end of the furnace tube to raise the pressure in the furnace tube to atmospheric pressure. After repeating the evacuation-inflation steps 4-6 times, the nitrogen gas flow is adjusted to 400sccm and maintained, and then the temperature in the heating furnace is increased to the growth target temperature (1350-1750℃) in stages at a heating rate not exceeding 5℃ / min; if the target temperature is higher than 1600℃, the temperature in the heating furnace is increased to 1600℃ in stages at a heating rate not exceeding 5℃ / min, and increased to the target temperature at a rate not exceeding 2℃ / min, and then kept at the target temperature for 1-120min, and then the temperature of the heating furnace tube is reduced to 500℃ at a cooling rate not exceeding 3℃ / min, and then it is naturally cooled to room temperature. After taking out the marble tray, a nitrogen gun is used to purge between the first substrate and the second substrate to separate the two substrate sheets, and finally a high-quality hexagonal boron nitride two-dimensional atomic crystal is obtained on the second substrate sheet.

[0048] In step S106, the second substrate carrying the first hexagonal boron nitride single crystal thin film is placed in a radio frequency plasma generator for treatment, so as to controllably introduce a single photon source into the first hexagonal boron nitride single crystal thin film.

[0049] In some exemplary embodiments, the second substrate carrying the first hexagonal boron nitride single crystal film is placed in a radio frequency plasma generator for treatment with plasma treatment parameters as follows: the plasma treatment atmosphere includes at least one of argon, oxygen, nitrogen, hydrogen, methane and ammonia; the plasma treatment time is 1 min-20 min; and the plasma treatment power is 20 W-250 W.

[0050] For example, the obtained second substrate with a h-BN single crystal film is placed in the chamber of the radio frequency plasma generator, and then the chamber is sealed and the chamber pressure is pumped to below 0.5Pa using a vacuum pump and maintained for 5 minutes, and then the vacuum pump is turned off and argon is introduced into the chamber to purge the chamber. After repeating the vacuum-purging step 2-3 times, argon, nitrogen, oxygen, hydrogen, methane or ammonia are introduced into the chamber according to the selected different treatment effects, and the chamber pressure is adjusted to 20-150Pa by adjusting the gas flow rate and the tightness of the chamber bypass valve, and the plasma excitation power is adjusted to 20-250W, and then the plasma generator is turned on and the capacitance of the matching device is adjusted so that the plasma forward power reaches the set excitation power and the reverse power is reduced to 0. After the plasma glow in the chamber is stable, the h-BN single crystal film on the second substrate is processed, and the processing time is set to 1-20min. After the processing is completed, the plasma generator power supply and the gas valve are turned off, and then the vacuum pump is turned off, and the processed second substrate is taken out of the chamber.

[0051] In step S107, a second solid boron film is sputter-deposited on the polished surface of the third substrate. The thickness of the second solid boron film is related to the time of sputtering deposition; the deposition time of the second solid boron film is 5 min-60 min. Optionally, the method of depositing the second solid boron film is the same as the method of depositing the first solid boron film in step S102.

[0052] In step S108, a third substrate is stacked on the surface of the first hexagonal boron nitride single crystal film introduced with the single photon source to obtain a second stacked body, wherein the first hexagonal boron nitride single crystal film introduced with the single photon source is in contact with the second solid boron film.

[0053] In step S109 , the second stacked body is processed according to second process parameters under a nitrogen atmosphere to transform the second solid boron film into a second hexagonal boron nitride single crystal film (cap layer).

[0054] In some exemplary embodiments, the second process parameters include the following process: adjusting the nitrogen gas flow to 400 sccm and maintaining it; the second target growth temperature is not higher than 1600°C, and the temperature in the heating furnace is increased to the second target growth temperature at a heating rate of no more than 5°C / min; or the second target growth temperature is higher than 1600°C, and the temperature in the heating furnace is increased to 1600°C at a heating rate of no more than 5°C / min, and then increased to the second target growth temperature at a rate of no more than 2°C / min; keeping the temperature at the second target growth temperature for 1min-30min; reducing the temperature of the heating furnace tube to 500°C at a cooling rate of no more than 3°C / min; and cooling naturally to room temperature. Optionally, the second target growth temperature is 1350°C-1650°C; and the second target growth temperature is lower than the first target growth temperature.

[0055] In step S110, the third substrate is peeled off from the second stacked body to obtain a second substrate carrying the first hexagonal boron nitride single crystal film and the second hexagonal boron nitride single crystal film, which is used as a hexagonal boron nitride single photon source. Optionally, the method of peeling the third substrate from the second stacked body includes purging with nitrogen.

[0056] For example, the polished surfaces of the third substrate and the second substrate are stacked face to face, the solid boron film and the plasma-treated h-BN single crystal film are located between the two substrates, the two stacked substrates are placed in a customized marble tray to fix their positions, and then the marble tray is horizontally placed in the furnace tube of the high-temperature tubular heating furnace and slowly pushed into the center of the furnace tube, and the two sides of the furnace tube are sealed with flanges and rubber rings. Use a vacuum pump to pump the pressure in the furnace tube from one end of the heating furnace to below 1Pa and maintain it for 5-10 minutes, then turn off the vacuum pump and introduce nitrogen from the other end of the furnace tube to raise the pressure in the furnace tube to atmospheric pressure. After repeating the evacuation-inflation steps 4-6 times, the nitrogen gas flow is adjusted to 400 sccm and maintained, and then the temperature in the heating furnace is increased to the growth target temperature (1350-1650°C, the secondary growth temperature is slightly lower than the primary growth temperature) in stages at a heating rate not exceeding 5°C / min; if the target temperature is higher than 1600°C, the temperature in the heating furnace is increased to 1600°C in stages at a heating rate not exceeding 5°C / min, and increased to the target temperature at a rate not exceeding 2°C / min, and then kept at the target temperature for 1-30 minutes, and then the temperature of the heating furnace tube is reduced to 500°C at a cooling rate not exceeding 3°C / min, and then it is naturally cooled to room temperature. After taking out the marble tray, a nitrogen gun is used to purge between the third substrate and the second substrate to separate the two substrate sheets, and finally an in-situ capping layer growth of an h-BN single crystal thin film on the h-BN-based single photon source is achieved on the second substrate.

[0057] In an embodiment of the present invention, a large-scale single-photon source is prepared on an h-BN single crystal film based on a plasma treatment process, and an in-situ capping layer is used to secondary grow a second hexagonal boron nitride single crystal film to achieve efficient passivation protection of the single-photon source in the first hexagonal boron nitride single crystal film. The prepared single-photon source has the characteristics of high brightness, high purity, room temperature operation, stable luminescence properties, and low preparation cost.

[0058] In order to further improve the quality of hexagonal boron nitride single crystal films, Figure 1 Based on the method shown, the method may further include annealing the second substrate carrying the first hexagonal boron nitride single crystal film and the second hexagonal boron nitride single crystal film.

[0059] Optionally, during the annealing process, the annealing atmosphere includes one of air, oxygen, nitrogen or argon; the annealing temperature is 700°C-900°C; the annealing time is 30min-60min; and the temperature rise and fall rates do not exceed 10°C / min.

[0060] Figure 2 The figure schematically shows a schematic diagram of the growth structure of a hexagonal boron nitride cap layer according to an embodiment of the present invention.

[0061] like Figure 2 As shown, the single photon source in the hexagonal boron nitride capping layer growth structure according to the embodiment of the present invention is covered by the second hexagonal boron nitride single crystal film.

[0062] Figure 3 The schematic diagram of the atomic force microscope surface morphology of the hexagonal boron nitride capping layer growth structure according to the embodiment of the present invention is schematically shown.

[0063] like Figure 3 As shown, the hexagonal boron nitride film according to the embodiment of the present invention is distributed in a lamellar stack and has good surface roughness.

[0064] Figure 4 A schematic diagram of the Raman scattering spectrum of a hexagonal boron nitride capping layer growth structure according to an embodiment of the present invention is schematically shown.

[0065] like Figure 4 As shown in the figure, the E of h-BN 2g The characteristic peak spectrum shows that both the first hexagonal boron nitride single crystal film and the second hexagonal boron nitride single crystal film have excellent crystal quality. The Raman intensity of the second hexagonal boron nitride single crystal film is significantly higher than that of the first hexagonal boron nitride single crystal film, indicating that the h-BN film has been significantly thickened after the second growth.

[0066] Figure 5 The photoluminescence scanning diagram of a single photon source in a hexagonal boron nitride capping layer growth structure according to an embodiment of the present invention is schematically shown.

[0067] like Figure 5 As shown in the figure, the luminous points circled by the marked square pattern are single-photon sources. From the density results, it can be seen that the surface density of single-photon sources exceeds 0.1 counts / μm², indicating that the h-BN cap layer growth structure can carry a higher single-photon source surface density.

[0068] Figure 6 The figure schematically shows the test results of the second-order correlation characteristics of a single photon source in a hexagonal boron nitride capping layer growth structure according to an embodiment of the present invention.

[0069] like Figure 6As shown, the second-order correlation of the hexagonal boron nitride capping layer according to the embodiment of the present invention is much smaller than 0.5 at time zero, from which it can be known that a single photon source is obtained through processing, and the single photon purity is relatively high.

[0070] Figure 7 The emission spectrum-time correlation diagram of the single photon source in the first hexagonal boron nitride single crystal thin film structure according to an embodiment of the present invention is schematically shown.

[0071] like Figure 7 As shown, due to the lack of the passivation effect of the second h-BN single crystal film, the single photon source exhibits obvious flickering or even quenching during the test.

[0072] Figure 8 The emission spectrum-time correlation diagram of a single photon source in a hexagonal boron nitride capping layer growth structure according to an embodiment of the present invention is schematically shown.

[0073] like Figure 8 As shown, compared Figure 7 The single-photon source in the structure in which the first hexagonal boron nitride single crystal film does not cover the second hexagonal boron nitride single crystal film, and the stability of the single-photon source in the growth structure containing the second hexagonal boron nitride single crystal film (cover layer) is significantly improved during the test, and no obvious flickering or quenching occurs.

[0074] Fig. 9 The figure schematically shows the emission stability test results of a single photon source in a first hexagonal boron nitride single crystal thin film structure according to an embodiment of the present invention.

[0075] like Fig. 9 As shown in the figure, the emission stability test of the single photon source in the first hexagonal boron nitride single crystal film (without cap layer) structure according to the embodiment of the present invention uses a wide-field fluorescence microscope to observe the single photon source in a large area of ​​the sample, and counts the time distribution of all single photon sources from the first light emission to the last light emission, that is, the "lifetime". It can be seen from the figure that the "lifetime" of most single photon sources is around 0, indicating that they are quenched in a short time after light emission, and the emission stability is poor.

[0076] Fig.10 The figure schematically shows the emission stability test results of a single photon source in a hexagonal boron nitride capping structure according to an embodiment of the present invention.

[0077] like Fig.10 As shown, compared Fig. 9 The single photon source in the structure where the first hexagonal boron nitride single crystal film is not covered by the second hexagonal boron nitride single crystal film, and the single photon source in the structure containing the second hexagonal boron nitride single crystal film (capping layer) has a significantly increased "lifetime" and significantly improved emission stability compared to the single photon source in the uncapped structure.

[0078] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a hexagonal boron nitride single-photon source, characterized in that: The method comprises: Prepare three single-side polished sapphire substrates, which are used as a first substrate, a second substrate and a third substrate respectively; sputtering and depositing a first solid boron film on the polished surface of the first substrate; stacking a second substrate on the surface of the first solid boron film to obtain a first stacked body, wherein the first solid boron film is in contact with the polished surface of the second substrate; In a nitrogen atmosphere, processing the first stacked body according to first process parameters to convert the first solid boron film into a first hexagonal boron nitride single crystal film; peeling the first substrate from the first stacked body to obtain a second substrate carrying the first hexagonal boron nitride single crystal thin film; placing the second substrate carrying the first hexagonal boron nitride single crystal thin film into a radio frequency plasma generator for treatment, so as to controllably introduce a single photon source into the first hexagonal boron nitride single crystal thin film; sputtering and depositing a second solid boron film on the polished surface of the third substrate; The third substrate is stacked on the surface of the first hexagonal boron nitride single crystal film introduced with the single photon source to obtain a second stacked body, wherein the first hexagonal boron nitride single crystal film introduced with the single photon source is in contact with the second solid boron film; processing the second stacked body according to second process parameters in a nitrogen atmosphere to convert the second solid boron film into a second hexagonal boron nitride single crystal film; and The third substrate is peeled off from the second stacked body to obtain a second substrate carrying the first hexagonal boron nitride single crystal film and the second hexagonal boron nitride single crystal film, which is used as a hexagonal boron nitride single photon source.

2. The method according to claim 1, characterized in that The method further comprises: The second substrate carrying the first hexagonal boron nitride single crystal thin film and the second hexagonal boron nitride single crystal thin film is annealed.

3. The method according to claim 1, characterized in that The preparation of three single-sided polished sapphire substrates includes sequentially placing the sapphire substrates in acetone, isopropanol, and ethanol for ultrasonic cleaning and drying them with nitrogen.

4. The method according to claim 1, characterized in that: The thickness of the first solid boron film and the second solid boron film is related to the sputtering deposition time; The deposition time of the first solid boron film is 5 min-60 min; and The deposition time of the second solid boron film is 5 min-60 min.

5. The method according to claim 1, characterized in that The first process parameters include the following process: Adjust nitrogen gas flow to 400 sccm and maintain; The first target growth temperature is not higher than 1600°C, and the temperature in the heating furnace is raised to the first target growth temperature at a heating rate not exceeding 5°C / min; or the first target growth temperature is higher than 1600°C, and the temperature in the heating furnace is raised to 1600°C at a heating rate not exceeding 5°C / min, and then raised to the first target growth temperature at a rate not exceeding 2°C / min; Keeping the temperature at the first target growth temperature for 1 min to 120 min; Lower the temperature of the heating furnace tube to 500°C at a cooling rate not exceeding 3°C / min; and Cool naturally to room temperature.

6. The method according to claim 5, characterized in that The second process parameters include the following process: Adjust nitrogen gas flow to 400 sccm and maintain; The second target growth temperature is not higher than 1600°C, and the temperature in the heating furnace is raised to the second target growth temperature at a heating rate not exceeding 5°C / min; or the second target growth temperature is higher than 1600°C, and the temperature in the heating furnace is raised to 1600°C at a heating rate not exceeding 5°C / min, and then raised to the second target growth temperature at a rate not exceeding 2°C / min; Keeping the temperature at the second target growth temperature for 1 min to 30 min; Lower the temperature of the heating furnace tube to 500°C at a cooling rate not exceeding 3°C / min; and Cool naturally to room temperature.

7. The method according to claim 6, characterized in that The first target growth temperature is 1350°C-1750°C; The second target growth temperature is 1350° C.-1650° C.; and The second target growth temperature is lower than the first target growth temperature.

8. The method according to claim 1, characterized in that The plasma treatment parameters for placing the second substrate carrying the first hexagonal boron nitride single crystal thin film into a radio frequency plasma generator for treatment are as follows: The plasma treatment atmosphere includes at least one of argon, oxygen, nitrogen, hydrogen, methane and ammonia; The plasma treatment time is 1 min to 20 min; and The plasma treatment power is 20W-250W.

9. The method according to claim 1, characterized in that: The method of peeling the first substrate from the first stacked body includes purging with nitrogen; and The method of peeling the third substrate from the second stacked body includes purging with nitrogen.

10. The method according to claim 2, characterized in that During the annealing process, the annealing atmosphere includes one of air, oxygen, nitrogen or argon; Annealing temperature is 700℃-900℃; The annealing time is 30min-60min; and The temperature rise and fall rate shall not exceed 10℃ / min.

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