METHOD FOR MANUFACTURING GALLIUM NITRIDE QUANTUM DOTS DOPED WITH METAL IONS

Abstract

The present invention relates to a method of manufacturing gallium nitride quantum dots, and more particularly, to a method of manufacturing gallium nitride quantum dots doped with metal ions, which uses a wet-based synthesis method capable of lowering the fluorescence energy of pure gallium nitride by introducing metal ions into pure gallium nitride.

Claims

1. A method of manufacturing gallium nitride quantum dots doped with metal ions, comprising: preparing a first solution comprising a first precursor including a group III element, a second precursor including a metal, and a compound for a ligand; performing a reaction between the first precursor and the second precursor in the first solution; controlling a temperature of the first solution within a first temperature range; and allowing the first solution to react with a second solution in which a nitrogen-based compound is dissolved in a solvent to form gallium nitride quantum dots doped with metal ions.

2. The method of claim 1, wherein the first precursor comprises a gallium halide.

3. The method of claim 2, wherein the gallium halide comprises one selected from the group consisting of gallium trichloride (GaCl.sub.3), gallium tribromide (GaBr.sub.3), and gallium triiodide (GaI.sub.3).

4. The method of claim 1, wherein the second precursor comprises one selected from the group consisting of zinc (Zn), magnesium (Mg), and indium (In).

5. The method of claim 1, wherein the compound for a ligand comprises oleylamine.

6. The method of claim 1, wherein the first temperature range is in a range of 200° C. to 280° C.

7. The method of claim 1, wherein the first solution is allowed to react with the second solution for 1 hour to 3 hours.

8. The method of claim 1, wherein the second solution comprises lithium hexamethyldisilazide dissolved in anhydrous hexane.

9. The method of claim 1, wherein the second solution comprises oleylamine and a mixture of n-butyllithium and tetramethylethylenediamine.

10. The method of claim 1, further comprising, after the formation of the gallium nitride quantum dots doped with metal ions: removing impurities from a solution comprising the gallium nitride quantum dots doped with metal ions using a centrifugation method; mixing ethanol with the solution from which the impurities are removed; and separating the gallium nitride quantum dots doped with metal ions from the solution with which ethanol is mixed, using a centrifugation method.

11. A gallium nitride quantum dot doped with metal ions, which has a ligand bound to a surface thereof, wherein the gallium nitride quantum dot is doped with metal ions to lower the bandgap transition energy of the gallium nitride.

12. The gallium nitride quantum dot of claim 11, wherein the metal ions comprise ions of one selected from the group consisting of zinc (Zn), magnesium (Mg), and indium (In).

13. The gallium nitride quantum dot of claim 11, wherein the ligand comprises oleylamine.

14. An electronic device comprising the quantum dot defined in claim 11.

Description

DESCRIPTION OF DRAWINGS

[0030] FIG. 1 is a flowchart of a method of manufacturing gallium nitride quantum dots doped with metal ions according to one embodiment of the present invention.

[0031] FIG. 2 is a graph showing the absorption spectra according to a reaction time and an amount of a zinc precursor.

[0032] FIG. 3 is a graph showing the emission spectra according to the reaction time and the amount of the zinc precursor.

[0033] FIG. 4 is a graph showing the fluorescence excitation spectra according to the reaction time and the amount of the zinc precursor.

[0034] FIG. 5 is a graph showing an X-ray diffraction pattern.

[0035] FIG. 6 is an electron microscope image of gallium nitride quantum dots doped with zinc. The size of the gallium nitride quantum dots are shown in the graph.

[0036] FIG. 7 is a graph showing the energy dispersion spectrum of the gallium nitride quantum dots doped with zinc.

[0037] FIG. 8 is a graph showing the X-ray photoelectron spectrum of a gallium region of the gallium nitride quantum dots doped with zinc.

[0038] FIG. 9 is a graph showing the X-ray photoelectron spectrum of a nitrogen region of the gallium nitride quantum dots doped with zinc.

[0039] FIG. 10 is a graph showing the Raman spectrum of the gallium nitride quantum dots doped with zinc.

[0040] FIG. 11 is a graph showing the UV-Vis absorbance of the gallium nitride quantum dots in which a ligand is substituted with bromine ions.

[0041] FIG. 12 is a graph showing the IR absorbance of the gallium nitride quantum dots in which the ligand is substituted with bromine ions.

[0042] FIG. 13 is a graph showing the absorption spectrum of the gallium nitride quantum dots doped with zinc, which has oleylamine and oleic acid ligands bound thereto.

[0043] FIG. 14 is a graph showing the emission spectrum of the gallium nitride quantum dots doped with zinc, which has the oleylamine ligand bound thereto.

[0044] FIG. 15 is a graph showing the emission spectrum of the gallium nitride quantum dots doped with zinc, which has the oleic acid ligand bound thereto.

[0045] FIG. 16 is a graph of normalizing and comparing the emission spectra of the gallium nitride quantum dots doped with zinc in a solution state and the gallium nitride quantum dot doped with zinc coated onto a glass substrate.

BEST MODE

[0046] The terminology used herein is used for the purpose of only describing particular embodiments and is not intended to be limiting of exemplary embodiments. The singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features and/or components thereof, but do not preclude the presence or addition of one or more other features and/or components thereof.

[0047] Unless defined otherwise, all terms used herein (including technical or scientific terms) have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. It should be understood that the terms defined in generally used dictionaries are interpreted as including meanings identical to contextual meanings of the related art unless clearly defined otherwise in the present invention, and are not interpreted with being ideal or excessively formal meanings.

[0048] Hereinafter, a method of manufacturing gallium nitride quantum dots doped with metal ions according to the present invention will be described in detail with reference to the accompanying drawings. However, it should be understood that the accompanying drawings are provided for the purpose of illustration only, and are not intended to limit the method of manufacturing gallium nitride quantum dots doped with metal ions according to the present invention.

[0049] FIG. 1 is a flowchart of a method of manufacturing gallium nitride quantum dots doped with metal ions according to one embodiment of the present invention.

[0050] As shown in FIG. 1, the method of manufacturing gallium nitride quantum dots doped with metal ions according to one embodiment of the present invention includes: preparing a first solution including a first precursor including a group III element, a second precursor including a metal, and a compound for a ligand (S110); performing a reaction between the first precursor and the second precursor in the first solution (S120); controlling a temperature of the first solution within a second temperature range (S130); and allowing the first solution to react with a second solution including a nitrogen-based compound and a solvent to form gallium nitride quantum dots doped with metal ions (S140).

[0051] Hereinafter, each step of the present invention will be described in detail.

[0052] The present invention relates to a method of manufacturing gallium nitride quantum dots using a chemical wet method. First, a first solution, which includes a first precursor including a group III element, a second precursor including a metal, and a compound for a ligand, is prepared (S110).

[0053] For example, the group III element is gallium (Ga), and the first precursor includes gallium and halogen elements. Preferably, the first precursor is a gallium halide, and more preferably includes one selected from the group consisting of gallium trichloride (GaCl.sub.3), gallium tribromide (GaBr.sub.3), and gallium triiodide (GaI.sub.3). Here, when considering the binding energy of the gallium halides, GaCl.sub.3, GaBr.sub.3, and GaI.sub.3 have better reactivity in the given order. Hereinafter, the present invention will be described based on gallium trichloride (GaCl.sub.3), but the present invention is not limited thereto.

[0054] According to one embodiment, the second precursor includes one selected from the group consisting of zinc (Zn), magnesium (Mg), and indium (In). According to one embodiment, the second precursor may also be one selected from a zinc halide, a magnesium halide, and an indium halide. Here, the halogen element is one selected from chlorine (Cl), bromine (Br), and iodine (I).

[0055] Hereinafter, the present invention will be described based on zinc chloride as a second precursor, but the present invention is not limited to zinc chloride and zinc ion dopants. When the above-described metal ions are included, the fluorescence energy of pure gallium nitride may be lowered. In this way, blue emission may be obtained from a gallium nitride semiconductor material doped with metal ions.

[0056] According to one embodiment, the contents of gallium and the metal (Zn) may be adjusted to a weight ratio of 1:0.5 to 3.5. When blue emission is required, the contents of Ga and Zn may be adjusted to 1:1. When strong ultraviolet emission is required, the contents of Ga and Zn may be adjusted to 1:3.

[0057] Here, the degree to which gallium nitride is doped with zinc varies depending on an amount of the zinc precursor and the reaction conditions. Specifically, the reaction temperature rises with an increasing amount of the zinc precursor, and an amount of zinc introduced into the gallium nitride increases with a longer reaction time and a higher reaction temperature. That is, the amount of the zinc precursor, the reaction temperature, and the reaction time may be properly controlled according to an intended purpose of the present invention to control an amount of zinc to be doped. In this way, a range of fluorescence energy of gallium nitride may be properly lowered from the ultraviolet region to the visible region.

[0058] According to one embodiment, the compound for a ligand includes oleylamine. The biggest characteristic of chemically synthesized quantum dots is that the physical properties of a core region are changed by an organic or inorganic ligand surrounding the quantum dots. Accordingly, various relative intensities of luminous energy of the quantum dots vary according to the type of ligand atoms binding to the gallium nitride quantum dots. That is, the type of ligand atom may be controlled according to an intended purpose of the present invention to control the intensity of luminous energy of the gallium nitride quantum dots.

[0059] Next, a reaction between the first precursor and the second precursor in the first solution is performed (S120).

[0060] According to one embodiment, the above-described reaction is a step for removing moisture and impurities in the reactants immediately before the main reaction, and is performed under vacuum. The reaction temperature is sufficient as long as moisture can be evaporated. According to one embodiment, the reaction may be performed at a temperature in the range of 100° C. to 120° C. The reaction occurs in this temperature range to synthesize a gallium-oleylamine precursor. Here, the synthesized precursor may be used for reaction without any particular separation process.

[0061] Then, the temperature of the first solution is controlled in a first temperature range (S130). According to one embodiment, the first temperature range is in a range of 200 to 280° C. Also, the second temperature range is higher than the temperature range of the above-described reaction.

[0062] When the first temperature is less than 200° C., the reaction does not proceed. When the second temperature is greater than 280° C., a solvent may evaporate as the temperature further increases to reach a boiling point (approximately 350° C.) of the solvent. In this case, the advantages from the chemical wet synthesis may be lost due to the excessively high temperature.

[0063] In this process, a reaction-ready state may be realized.

[0064] After preparing for the reaction, the first solution is allowed to react with the second solution including a nitrogen-based compound and a solvent to form gallium nitride quantum dots doped with metal ions (S140).

[0065] For example, the second solution includes lithium hexamethyldisilazide dissolved in anhydrous hexane. As another example, the reaction may also be performed using a second solution including a mixture of n-butyllithium and tetramethylethylenediamine. Here, oleylamine is used as the solvent.

[0066] The first solution may be allowed to react with the second solution to obtain gallium nitride quantum dots doped with metal ions as intended in the present invention. As the reaction proceeds, it can be seen that a clear solution changes to an opaque white color. According to one embodiment of the present invention, the first solution is allowed to react with the second solution for 1 to 3 hours.

[0067] Next, a heat source is removed to stop the reaction.

[0068] Then, impurities are removed from the solution including the gallium nitride quantum dots doped with metal ions using a centrifugation method. Also, the solution from which the impurities are removed is mixed with ethanol to reduce solubility of the quantum dots. Then, the gallium nitride quantum dots doped with metal ions are separated from the solution with which ethanol is mixed using a centrifugation method.

[0069] The gallium nitride quantum dots doped with metal ions may be obtained through such a series of processes.

[0070] A gallium nitride quantum dot doped with metal ions according to another embodiment of the present invention is a gallium nitride quantum dot having a ligand bound to a surface thereof. In this case, the gallium nitride quantum dot is doped with metal ions to lower the bandgap transition energy of gallium nitride.

[0071] According to one embodiment, the metal ions include ions of one selected from the group consisting of zinc (Zn), magnesium (Mg), and indium (In).

[0072] According to one embodiment, the ligand includes oleylamine.

[0073] An electronic device according to still another embodiment of the present invention includes the above-described quantum dots.

[0074] Hereinafter, the present invention will be described in further detail with reference to experimental examples thereof.

MODE FOR INVENTION

Experimental Example 1

[0075] To determine whether quantum dots of gallium nitride doped with zinc were formed by the above-described manufacturing method, an experiment was performed as follows.

[0076] Gallium chloride (GaCl.sub.3) and zinc (II) chloride (ZnCl.sub.2) were mixed at 1:1, and oleylamine was added to synthesize a gallium-oleylamine precursor. The precursor synthesized here was used for reaction without any particular separation process. Thereafter, a reaction-ready state was realized by adjusting a temperature of a gallium precursor solution to 200° C. After the reaction preparation was completed, a solution in which lithium hexamethyldisilazide was dissolved in anhydrous hexane was placed in a reaction vessel to initiate the reaction. The reaction proceeded for an hour, and a heat source was removed to stop the reaction. After the reaction was completed, the impurities which were not soluble in the solution were first removed from the solution in the reaction vessel using a centrifuge. The clear solution from which the impurities were removed was set aside. Thereafter, the clear solution was mixed with ethanol to reduce the solubility of colloidal quantum dots, and gallium nitride quantum dots doped with zinc were separated from the resulting mixture using a centrifuge, thereby manufacturing the zinc-doped gallium nitride quantum dots of Example 1.

[0077] Also, zinc-doped gallium nitride quantum dots of Example 2 were manufactured in the same manner as in Example 1, except that gallium chloride (GaCl.sub.3) and zinc (II) chloride (ZnCl.sub.2) were mixed at 1:2 to perform the reaction. In addition, zinc-doped gallium nitride quantum dots of Example 3 were manufactured in the same manner as in Example 1, except that gallium chloride (GaCl3) and zinc (II) chloride (ZnCl.sub.2) were mixed at 1:3, and the reaction was performed at 250° C. Zinc-doped gallium nitride quantum dots of Example 4 were manufactured in the same manner as in Example 1, except that gallium chloride (GaCl.sub.3) and zinc (II) chloride (ZnCl.sub.2) were mixed at 1:3, and the reaction was performed at 280° C. Zinc-doped gallium nitride quantum dots of Example 5 were manufactured in the same manner as in Example 1, except that gallium chloride (GaCl.sub.3) and zinc (II) chloride (ZnCl.sub.2) were mixed at 1:3, and the reaction was performed at 280° C. for 3 hours.

[0078] Absorption spectra of the zinc-doped gallium nitride quantum dots of Examples 1 to 5 were measured. The results are shown in FIG. 2. As shown in FIG. 2, it can be seen that the bandgap transition absorption energy of the synthesized zinc-doped gallium nitride quantum dots was reduced as the synthesis conditions were changed from Example 1 to Example 5. This directly shows a quantum confinement effect of the quantum dots whose absorption energy decreased as the reaction proceeded. Also, it can be seen that the zinc ions served to promote a quantum dot reaction when the zinc-doped gallium nitride quantum dots of Examples 1 and 2 were compared.

[0079] Also, emission spectra of the zinc-doped gallium nitride quantum dots of Examples 1 to 5 were measured. The results are shown in FIG. 3. As shown in FIG. 3, it can be seen that the energy of bandgap transition emission of the synthesized gallium nitride quantum dots was red-shifted as the reaction proceeded. This change was due to the red shifting of the absorption spectra as shown in FIG. 2. In addition, it is characteristic that the bandgap transition of ultraviolet rays and blue emission occurred in the zinc-doped gallium nitride quantum dots of Examples 1 and 2, indicating that the zinc ions were generated at an impurity level. Also, it can be seen that this blue emission was blue-shifted as a content of zinc in the gallium nitride increased. Because zinc strongly served to protect surfaces of the zinc-doped gallium nitride quantum dots rather than serve as a blue emission source as the content of zinc increased, blue emission decreased and ultraviolet emission became stronger. Therefore, stronger ultraviolet emission could be observed as shown in Example 5.

[0080] Further, the fluorescence excitation spectrum of the zinc-doped gallium nitride quantum dots of Example 5 was measured. The results are shown in FIG. 4. As shown in FIG. 4, it can be seen that the fluorescence excitation spectrum of the zinc-doped gallium nitride quantum dots of Example 5 was coincident with the absorption spectrum of Example 5 clearly shown in FIG. 2. This verifies that the fluorescence of Example 5 is originated from an electrical structure of the gallium nitride quantum dots.

Experimental Example 2

[0081] An X-ray diffraction pattern of the sample of Example 1 was measured. The results are shown in FIG. 5. The diffraction pattern of the zinc-doped gallium nitride quantum dots of Example 1 of the present invention was not significantly different from the diffraction pattern of the gallium nitride quantum dots which were not doped with metal ions, which were used as a control. This indicates that the zinc ions did not damage a structure of the gallium nitride quantum dots because the zinc ions were present on surfaces of the gallium nitride quantum dots. However, because the pattern became wide due to the characteristics of the nano-sized particles, it was difficult to differentiate the diffraction spectrum of this example from that of γ-gallium oxide that was likely to be present as an impurity of the reaction.

Experimental Example 3

[0082] Each of the samples of Examples 1 to 5 was photographed using an electron microscope. The respective images are shown in FIG. 6, and the zinc ions were counted according to the size of the individual zinc ions, and shown in a graph. As shown in FIG. 6, it can be seen that the mean size of the particles increased as the reaction proceeded from Example 1 to Example 5. When this was examined with reference to FIGS. 2 and 3, the presence of the quantum confinement effect in the zinc-doped gallium nitride quantum dots could be directly explained.

Experimental Example 4

[0083] The energy dispersion spectrum of the zinc-doped gallium nitride quantum dots of Example 1 was measured. The results are shown in FIG. 7. As shown in FIG. 7, peaks for zinc, gallium, and nitrogen were observed. Based on the results, it can be seen that the zinc-doped gallium nitride quantum dots were formed.

Experimental Example 5

[0084] The X-ray photoelectron spectrum of the zinc-doped gallium nitride quantum dots of Example 1 was measured after a film was formed on a silicon wafer. Graphs for the gallium region and the nitrogen region are shown in FIGS. 8 and 9, respectively.

[0085] As shown in FIGS. 8 and 9, the binding energy of gallium and nitrogen regions on the X-ray photoelectron spectrum was analyzed. As a result, it can be seen that gallium and nitrogen elements were bound to each other in the reaction product of Example 1 to form crystals. Specifically, the results of measurement of the X-ray photoelectron spectrum showed that the reaction product of Example 1 had a binding energy of 19.78 eV in a 3d region of gallium and a binding energy of 397.3 eV in a is region of nitrogen, indicating that the binding energy values were exactly coincident with the values measured for bulk gallium nitride semiconductors material known in the related art.

Experimental Example 6

[0086] The Raman spectrum of the zinc-doped gallium nitride quantum dots of Example 1 was measured after a film was formed on an aluminum oxide wafer using spin-coating. The results are shown in FIG. 10. As shown in FIG. 10, the measured spectrum showed that γ-gallium oxide was not present and only gallium nitride was present in the material of Example 1. Based on the fact that the data of the measured spectrum was identical to that of undoped gallium nitride, it can also be seen that a crystal structure was not distorted by the introduced zinc ions.

Experimental Example 7

[0087] To check the characteristics of gallium nitride quantum dots bound to another ligand, an experiment was further performed, as follows.

[0088] To observe the innate optical properties of the quantum dots having no organic ligand, a film manufactured from zinc-doped gallium nitride was treated with cetyltrimethylammonium bromide (CTAB) so that oleylamine and oleic acid ligands present in the film were both replaced with bromine ions. Graphs showing the UV-Vis absorbance and IR absorbance of gallium nitride quantum dots in which the ligand was replaced with bromine ions are shown in FIGS. 11 and 12, respectively.

[0089] As shown in FIGS. 11 and 12, it could be determined whether the ligand was replaced by determining whether there was a peak corresponding to the vibration energy of C—H on the FT-IR spectrum, and the optical properties were confirmed using an ultraviolet-visible spectrophotometer. It can be seen that the absorbance of the quantum dot film was still maintained even after the ligand was replaced with bromine ions. This verifies that the absorbance of the ultraviolet region observed in a solution state was not due to a π-bond of the ligand but arises from the quantum dots themselves.

[0090] To replace oleylamine as the ligand with oleic acid, replacement of the ligand was promoted using an ultrasonic disperser while applying heat to the zinc-doped gallium nitride synthesized in Example 1 in 10% by volume of an oleic acid-hexane solution. After the replacement of the ligand was completed, ethanol was added to the corresponding solution again to reduce the solubility of quantum dots. Thereafter, the quantum dots bound to the oleic acid ligand were separated using a centrifuge.

[0091] The absorption spectra of the zinc-doped gallium nitride quantum dots bound to the oleylamine and oleic acid ligands, respectively, were measured. The results are shown in FIG. 13. Also, the emission spectrum of the zinc-doped gallium nitride quantum dots bound to the oleylamine ligand was measured. The results are shown in FIG. 14. The emission spectrum of the zinc-doped gallium nitride quantum dots bound to the oleic acid ligand was measured. The results are shown in FIG. 15.

[0092] However, there was a significant difference in fluorescence when an amine-based ligand and an acid-based ligand were used. Specifically, when the amine ligand was used, exciton fluorescence intensity was weak, and the fluorescence associated with a deep trap level was observed in a low energy region. On the other hand, when the acid ligand was used, low energy fluorescence was not observed, and only exciton peaks were strongly observed.

[0093] As shown in FIG. 16, it can also be seen that the zinc-doped gallium nitride quantum dots could express the inherent properties exhibited in a solution phase even when in a state of a thin film coated onto a substrate. This suggests that the zinc-doped gallium nitride quantum dots provided in the present invention are directly applicable to various engineering applications through existing knowledge.

[0094] As shown in these Experimental Examples, it can be seen that the zinc-doped gallium nitride quantum dots could be provided by the manufacturing method of the present invention.

[0095] Although the present invention has been described in detail with reference to embodiments and examples thereof, the present invention is not limited to the embodiments, and may be embodied in various forms. Therefore, it will be apparent that various changes and modifications may be made by those skilled in the art without departing from the scope of the present invention. Also, it should be understood that various substitutions, changes, and modifications are possible by those skilled in the art without departing from the scope of the present invention defined in the claims, and these also fall within the scope of the present invention.