Dispersion method for locatable and density-adjustable gallium nitride quantum dots

Abstract

The invention provides a positioning and density-adjustable gallium nitride quantum dot dispersion method. The method comprises the following steps: obtaining a gallium nitride nanowire substrate on which gallium nitride quantum dots grow; performing ultrasonic treatment in a dispersion solvent, and regulating and controlling the concentration of the quantum dot dispersion liquid by controlling the ultrasonic duration; dispensing the dispersion liquid onto a target substrate with a photoetching patterning mark, and drying to enable the quantum dots to be positioned in a mark area; and scanning and verifying quantum dot distribution by adopting a fluorescence microscopy technology to obtain a positioned and density-controllable gallium nitride quantum dot sample. According to the method, accurate positioning and flexible density regulation and control of the gallium nitride quantum dots on the substrate can be simultaneously realized, the technical problems of random distribution and uncontrollable density of the quantum dots in a traditional method are effectively solved, and the integration level and the performance consistency of the quantum dot device are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, and more particularly to a method for dispersing gallium nitride quantum dots that can be positioned and have adjustable density. Background Technology

[0002] Gallium nitride (GaN) quantum dots, as a typical representative of third-generation semiconductor materials, have shown great application potential in constructing high-performance optoelectronic devices, such as quantum dot light-emitting diodes (QLEDs), low-threshold lasers, and single-photon detectors, due to their wide direct bandgap, excellent optical stability, high exciton binding energy, and outstanding physicochemical stability. The performance of quantum devices largely depends on the quality of the quantum dot material and its spatial arrangement in the device structure: on the one hand, the density of quantum dots directly affects key parameters such as the luminescence intensity and carrier injection efficiency of the device; on the other hand, precisely placing quantum dots in specific functional regions of the device (such as the location of maximum field strength in an optical microcavity or between electrodes in an electrical structure) is a prerequisite for achieving efficient opto-electric coupling and improving device integration and performance consistency.

[0003] However, the mainstream gallium nitride quantum dot preparation and dispersion methods in existing technologies have significant limitations. Currently, quantum dots are mostly prepared by self-assembly growth on planar substrates using molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD). Although their density and position can be controlled to some extent by growth parameters, it is difficult to achieve large-scale, precise control across scales. In the process of transferring and dispersing quantum dots from the growth substrate to the target device substrate, physical methods such as mechanical stirring, ultrasonic disruption, or simple spin coating and drop coating are commonly used. Although these methods are simple to operate, they have two fundamental drawbacks: First, the concentration of quantum dots in the dispersion solution is difficult to control precisely, resulting in large fluctuations in the density of quantum dots deposited on the substrate and poor repeatability, which cannot meet the differentiated and precise requirements of quantum dot density for different device structures; second, the deposition process of quantum dots on the substrate depends entirely on random physical adsorption, exhibiting a random Poisson distribution and lacking effective spatial positioning methods. This random distribution characteristic severely restricts the uniformity and order of quantum dot arrays, resulting in inconsistent performance, low integration, and difficulty in guaranteeing yield of devices built based on such materials. This has become a key technological bottleneck hindering gallium nitride quantum dots from the laboratory to industrial applications. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a gallium nitride quantum dot dispersion method with tunable density and positionability to solve the problems of uncontrollable quantum dot density and low positioning accuracy in existing dispersion methods.

[0005] On one hand, the present invention provides a method for dispersing gallium nitride quantum dots with tunable density and a locatable position, the method comprising: A gallium nitride nanowire substrate is obtained, on which gallium nitride-containing quantum dots are grown; The gallium nitride nanowire substrate is placed in a dispersion solvent and subjected to ultrasonic treatment to detach the quantum dots from the gallium nitride nanowire substrate and disperse them in the dispersion solvent to form a quantum dot dispersion. The quantum dot dispersion is drop-coated onto a target substrate pre-patterned with markings. After drying, the quantum dots are positioned within the area defined by the patterned markings. The dried target substrate was scanned using fluorescence microscopy. By detecting the fluorescence emitted by the quantum dots, their distribution within the patterned marking area was verified, and gallium nitride quantum dot samples were obtained. Specifically, by controlling the duration of the ultrasonic treatment, the concentration of quantum dots in the quantum dot dispersion is adjusted, thereby controlling the final density of quantum dots deposited on the target substrate.

[0006] In some embodiments, the gallium nitride-containing quantum dot is a core-shell quantum dot, with a gallium nitride core and an aluminum nitride shell.

[0007] In some embodiments, the quantum dots are grown on the gallium nitride nanowire substrate by molecular beam epitaxy.

[0008] In some embodiments, the dispersing solvent is isopropanol.

[0009] In some embodiments, the duration of the ultrasonic treatment ranges from 0.2 to 10 minutes, wherein the longer the duration of the ultrasonic treatment, the higher the density of quantum dots is obtained.

[0010] In some embodiments, the patterned markings are fabricated on the target substrate using a photolithography process.

[0011] In some embodiments, the spacing between the areas defined by the patterned markers ranges from 1 to 100 micrometers.

[0012] In some embodiments, the drying process employs either natural drying or drying based on a preset temperature.

[0013] In some embodiments, the method uses a laser with a wavelength range of 100~300nm as an excitation source to perform fluorescence scanning on the target substrate.

[0014] In some embodiments, the target substrate is made of silicon.

[0015] This invention provides a method for the localizable and density-tunable dispersion of gallium nitride quantum dots. By simply adjusting the single variable of ultrasonic treatment duration, the number of quantum dots detached from the gallium nitride nanowire substrate can be precisely controlled, thereby achieving linear control of the concentration of the quantum dot dispersion. This method is simple to operate, has good repeatability, and can flexibly prepare quantum dot samples with different densities from sparse to dense, effectively meeting the differentiated quantum dot density requirements of various optoelectronic devices, and overcoming the problems of large quantum dot density fluctuations and poor controllability in traditional methods.

[0016] Micrometer-scale patterned markers are pre-fabricated on a substrate using photolithography, and then gallium nitride quantum dots are deposited within pre-defined functional regions using a drop-coating process. Fluorescence microscopy is then used for verification to ensure the precision of the quantum dot positions. This method solves the problem of random quantum dot distribution in traditional dispersion processes, significantly improving the uniformity and order of the quantum dot array, and laying a solid foundation for the fabrication of highly integrated, high-performance, and consistent quantum devices.

[0017] Meanwhile, the entire process only includes routine operations such as ultrasonic dispersion, drop-coating positioning, and fluorescence detection, eliminating the need for expensive and complex nanofabrication equipment and avoiding harsh processing conditions such as electron beam lithography. This method offers mild experimental conditions, simple operation, low cost, and strong process compatibility and reproducibility, providing a practical technical path for the large-scale fabrication and industrial application of gallium nitride quantum dot-based devices.

[0018] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows, and will also become apparent in part to those skilled in the art upon studying the description, or may be learned by practice of the invention. The objects and other advantages of the invention can be realized and obtained by means of the structures specifically pointed out in the description and drawings.

[0019] Those skilled in the art will understand that the objectives and advantages achievable with the present invention are not limited to those specifically described above, and that the above and other objectives achievable with the present invention will become clearer from the following detailed description. Attached Figure Description

[0020] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, are not intended to limit the scope of the invention. In the drawings: Figure 1 This is a schematic diagram illustrating the steps of a gallium nitride quantum dot dispersion method with locatable and density-tunable distribution in one embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of the structure of gallium nitride quantum dots grown on a gallium nitride nanowire substrate in one embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the illustrative embodiments and descriptions of this invention are used to explain the invention, but are not intended to limit the invention.

[0023] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0024] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, element, step, or component, but does not exclude the presence or addition of one or more other features, elements, steps, or components.

[0025] It should also be noted that, unless otherwise specified, the term "connection" in this article can refer not only to a direct connection, but also to an indirect connection involving an intermediary.

[0026] In the following description, embodiments of the invention will be illustrated with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or similar parts, or the same or similar steps.

[0027] It should be emphasized here that the step markers mentioned below are not a limitation on the order of the steps, but should be understood as meaning that the steps can be executed in the order mentioned in the embodiments, or in a different order than in the embodiments, or several steps can be executed simultaneously.

[0028] To address the problems of uncontrollable quantum dot density and low positioning accuracy in existing dispersion methods, this invention provides a gallium nitride quantum dot dispersion method with adjustable positioning and density, such as... Figure 1 As shown, the method includes the following steps S101~S104: Step S101: Obtain a gallium nitride nanowire substrate. The gallium nitride nanowire substrate has gallium nitride-containing quantum dots grown on it.

[0029] Step S102: Place the gallium nitride nanowire substrate in a dispersion solvent and perform ultrasonic treatment to detach the quantum dots from the gallium nitride nanowire substrate and disperse them in the dispersion solvent to form a quantum dot dispersion.

[0030] Step S103: The quantum dot dispersion is drop-coated onto the target substrate with pre-prepared patterned markings. After drying, the quantum dots are positioned in the area defined by the patterned markings.

[0031] Step S104: Scan the dried target substrate using fluorescence microscopy. By detecting the fluorescence emitted by the quantum dots, verify their distribution within the patterned marking area to obtain gallium nitride quantum dot samples.

[0032] In this method, the concentration of quantum dots in the quantum dot dispersion is adjusted by controlling the duration of ultrasonic treatment, thereby controlling the final density of quantum dots deposited on the target substrate.

[0033] In step S101, gallium nitride nanowire substrates are first obtained, which is the material basis of this invention.

[0034] Among them, gallium nitride nanowire substrate is a nanostructure array, which is a series of highly ordered micro-wire crystals with gallium nitride (GaN) as the main component, which are vertically grown on a certain basic substrate (such as silicon wafer, sapphire, etc.) through methods such as chemical vapor deposition.

[0035] In this invention, gallium nitride nanowire substrates are selected, and their main advantages are as follows: Compared to planar substrates, nanowire arrays have an extremely high surface area to volume ratio, providing more space for quantum dots to grow; nanowire structures have excellent stress release capabilities; quantum dots are grown on the surface of nanowires, and during subsequent ultrasonic processing, mechanical vibrations more easily shake these quantum dots attached to the nanowire surface off, thereby achieving efficient separation and dispersion.

[0036] In some embodiments, quantum dots containing gallium nitride are grown on gallium nitride nanowire substrates using molecular beam epitaxy.

[0037] In some embodiments, the quantum dots grown on the gallium nitride nanowire substrate are core-shell quantum dots, with gallium nitride as the core and aluminum nitride as the shell.

[0038] The main advantages of using aluminum nitride / gallium nitride / aluminum nitride are as follows: The bandgap of aluminum nitride (~6.2 eV) is much larger than that of gallium nitride (~3.4 eV). When the two are combined, a significant bandgap is formed at the interface, that is, the energy band of gallium nitride is sandwiched between the higher energy bands of the two layers of aluminum nitride, forming a potential barrier.

[0039] Due to the high-energy barrier formed above, when this quantum dot is excited, the generated electrons and holes (charge carriers) are effectively confined within the gallium nitride nucleus in the middle.

[0040] Through the aforementioned limiting effect, the probability of charge carriers running to the surface or defects of quantum dots and undergoing nonradiative recombination (non-luminescence) is reduced, which significantly improves the photoluminescence efficiency and stability of quantum dots and meets the requirements of high-performance optoelectronic devices.

[0041] It should also be noted that in the aforementioned core-shell structure, the luminescent core, the part that generates optical and electrical functions, is a gallium nitride (GaN) core with a size that achieves the quantum confinement effect. Although the entire particle is composed of three elements, its essential properties (such as emission wavelength) are determined by the GaN core. Furthermore, in the semiconductor field, core-shell quantum dots are usually named after the material of their luminescent core. Therefore, by depositing aluminum nitride / gallium nitride / aluminum nitride, a quantum dot containing gallium nitride is formed, or simply called a gallium nitride quantum dot.

[0042] like Figure 2 The diagram shown is a schematic diagram of gallium nitride quantum dots grown on a gallium nitride nanowire substrate in one embodiment of the present invention.

[0043] In step S102, the gallium nitride nanowire substrate obtained in step S101 is placed in a dispersion solvent and subjected to ultrasonic treatment to detach the quantum dots from the gallium nitride nanowire substrate and uniformly disperse them in the dispersion solvent to form a quantum dot dispersion.

[0044] Ultrasound, a high-frequency mechanical vibration wave, disrupts the chemical bonds or physical adsorption forces between quantum dots and nanowires through cavitation, causing the quantum dots to detach from the gallium nitride nanowire substrate. Simultaneously, the ultrasonic energy prevents the detached quantum dots from re-aggregating into large particles due to van der Waals forces. The intense disturbance makes it difficult for the quantum dots to approach and adhere, thus maintaining the uniformity and stability of the dispersion.

[0045] In some embodiments, isopropanol is used as the dispersion solvent. Isopropanol is a polar organic solvent that effectively wets the surface of polar semiconductor materials such as gallium nitride and aluminum nitride, contributing to the stable suspension of quantum dots and preventing their aggregation due to hydrophobic interactions. Simultaneously, it possesses high stability, is not prone to chemical reactions with gallium nitride or aluminum nitride, ensuring that the optical properties and structure of the quantum dots are not damaged during dispersion. Furthermore, it has suitable volatility, allowing for rapid evaporation during the subsequent drop-coating and drying steps, enabling the quantum dots to quickly adhere to the target substrate without causing uneven distribution due to excessively rapid evaporation.

[0046] In this invention, the adjustable quantum dot density is achieved by controlling a variable (ultrasonic processing time), which is the core difference between this invention and traditional dispersion methods. Specifically: Ultrasonic processing is a process of energy and damage accumulation. The longer the ultrasonic treatment time, the greater the total energy acting on the gallium nitride nanowire substrate, and the more cavitation effects are generated.

[0047] That is, a longer ultrasonic treatment time means that: (1) more quantum dots are successfully stripped from the nanowires; and (2) the nanowire structure itself is more thoroughly destroyed, which may release deeper or more tightly bound quantum dots. Therefore, under the premise of a fixed volume of dispersion solvent, the ultrasonic treatment time is positively correlated with the concentration of quantum dots in the dispersion.

[0048] In some embodiments, the duration of ultrasonic treatment ranges from 0.2 to 10 minutes. Preferably, the duration of ultrasonic treatment is set to 5 minutes to obtain a high-concentration gallium nitride quantum dot isopropanol solution.

[0049] In step S103, the quantum dot dispersion obtained in step S102 is drop-coated onto a target substrate pre-patterned with markings. After drying, the quantum dots are positioned within the region defined by the patterned markings. This step enables the controlled deposition of quantum dots from solution to solid, achieving the most crucial positioning function of this invention.

[0050] In some embodiments, photolithography is used to create micron-scale physical or chemical patterns on a target substrate, forming hydrophilic / hydrophobic differences (i.e., some areas are hydrophilic and other areas are hydrophobic) or tiny physical trenches / steps.

[0051] When a quantum dot dispersion (such as isopropanol) is dropped onto a patterned substrate, the liquid tends to spread in the hydrophilic regions and avoid the hydrophobic regions due to surface tension; alternatively, the liquid may be confined to flow within physical trenches. These pre-fabricated marked regions guide and restrict the flow of the liquid and the final deposition area.

[0052] In some embodiments, the target substrate is a silicon wafer.

[0053] In some embodiments, the spacing between the areas defined by the patterned markers ranges from 1 to 100 micrometers.

[0054] In some embodiments, a drop-coating method is used, such as using a pipette, to uniformly drop quantum dots onto a pre-prepared patterned target substrate. Preferably, 1 mL of a high-concentration gallium nitride quantum dot isopropanol solution is drawn up with a pipette for each drop-coating.

[0055] In some embodiments, after drop application, the quantum dot solution is fixed in the area defined by the patterned markings by drying treatment such as natural air drying or low-temperature drying.

[0056] In step S104, the gallium nitride quantum dot samples obtained based on steps S101 to S103 are verified using fluorescence microscopy.

[0057] Gallium nitride (GaN) is a direct bandgap semiconductor. When GaN quantum dots with a core-shell structure are irradiated with photons whose energy exceeds their bandgap width, electrons in the valence band absorb the photon energy and transition to the conduction band, leaving holes. Therefore, using lasers with wavelengths in the range of 100–300 nm as excitation sources, such as a 266 nm laser with a photon energy of approximately 4.66 eV, which is much greater than the GaN bandgap (~3.4 eV), is sufficient to efficiently excite the quantum dots and bring them into an excited state.

[0058] Electrons in the excited state are unstable and relax back to the valence band through radiative recombination, recombinating with holes. During recombination, excess energy is released as a photon. This photon has slightly lower energy than the absorbed photon (as some energy is consumed through lattice vibrations, etc.), and therefore its wavelength is longer than the excitation light. For gallium nitride quantum dots, the emitted fluorescence is typically located in the ultraviolet to blue light region.

[0059] Fluorescence microscopes / scanners are equipped with a sophisticated filter system that filters out powerful excitation lasers (such as 266nm lasers), allowing only the longer-wavelength fluorescence emitted by the quantum dots to pass through. Detectors (such as CCD or CMOS) receive these fluorescence signals and convert them into electrical signals. On a computer, each luminescent quantum dot is displayed as a bright spot, and the collection of countless quantum dots forms a fluorescence image.

[0060] The positioning function can be verified by comparing this fluorescence image with a pre-fabricated photolithographic marking pattern on the substrate. Specifically, if the fluorescence signal appears only in the marked pattern (such as a square shape) area and the background (unmarked area) is dark, it proves that the precise positioning of the quantum dot has been achieved.

[0061] Meanwhile, by observing whether the distribution of quantum dots in the marked pattern area is uniform and whether the density meets expectations (whether it is high-density coverage or sparse distribution), the effectiveness of density control in step S102 can be indirectly verified.

[0062] Only after confirming that the gallium nitride quantum dot samples prepared above meet the positioning and density requirements can they be officially recognized as gallium nitride quantum dot samples that meet the requirements and can be used for subsequent device fabrication or scientific research.

[0063] In summary, this invention successfully achieves precise control over both the density and spatial position of gallium nitride quantum dots by combining ultrasonic duration-based quantum dot concentration regulation with photolithographic pattern guidance and positioning. This fundamentally solves the common problems of random distribution and uneven density of quantum dots in traditional processes, providing a reliable technical path for the controllable fabrication and integrated application of high-performance quantum dot optoelectronic devices.

[0064] It should be clarified that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0065] In this invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or in place of features of other embodiments.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, various modifications and variations can be made to the embodiments of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for dispersing gallium nitride quantum dots with tunable density and positionability, characterized in that, The method includes: A gallium nitride nanowire substrate is obtained, on which gallium nitride-containing quantum dots are grown; The gallium nitride nanowire substrate is placed in a dispersion solvent and subjected to ultrasonic treatment to detach the quantum dots from the gallium nitride nanowire substrate and disperse them in the dispersion solvent to form a quantum dot dispersion. The quantum dot dispersion is drop-coated onto a target substrate pre-patterned with markings. After drying, the quantum dots are positioned within the area defined by the patterned markings. The dried target substrate was scanned using fluorescence microscopy. By detecting the fluorescence emitted by the quantum dots, their distribution within the patterned marking area was verified, and gallium nitride quantum dot samples were obtained. Specifically, by controlling the duration of the ultrasonic treatment, the concentration of quantum dots in the quantum dot dispersion is adjusted, thereby controlling the final density of quantum dots deposited on the target substrate.

2. The method for dispersing gallium nitride quantum dots with tunable density according to claim 1, characterized in that, The gallium nitride-containing quantum dot is a core-shell structure quantum dot, with gallium nitride as the core and aluminum nitride as the shell.

3. The method for dispersing gallium nitride quantum dots with tunable density according to claim 1, characterized in that, The quantum dots are grown on the gallium nitride nanowire substrate by molecular beam epitaxy.

4. The method for dispersing gallium nitride quantum dots with tunable density according to claim 1, characterized in that, The dispersing solvent is isopropanol.

5. The method for dispersing gallium nitride quantum dots with tunable density according to claim 1, characterized in that, The duration of the ultrasonic treatment ranges from 0.2 to 10 minutes, wherein the longer the duration of the ultrasonic treatment, the higher the density of quantum dots obtained.

6. The method for dispersing gallium nitride quantum dots with tunable density according to claim 1, characterized in that, The patterned markings are fabricated on the target substrate using a photolithography process.

7. The method for dispersing gallium nitride quantum dots with tunable density according to claim 1, characterized in that, The interval range of the area defined by the patterned marker is 1 to 100 micrometers.

8. The method for dispersing gallium nitride quantum dots with tunable density according to claim 1, characterized in that, The drying process employs either natural drying or drying based on a preset temperature.

9. The method for dispersing gallium nitride quantum dots with tunable density according to claim 1, characterized in that, The method uses a laser with a wavelength range of 100~300nm as an excitation source to perform fluorescence scanning on the target substrate.

10. The method for dispersing gallium nitride quantum dots with tunable density according to claim 1, characterized in that, The target substrate is made of silicon.

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