JP2022057384A - Nitride semiconductor nanoparticles and method for producing the same - Google Patents

Abstract

To provide high quality nitride semiconductor nanoparticles which suppress the generation of metallic by-products and are obtained in high yield in nanoparticles which are expected to be used for applications such as a phosphor, a self-luminous material and a solar cell and to provide a method for producing the same.SOLUTION: There is provided a method for producing nitride semiconductor nanoparticles which comprises: a first step of reacting a solution containing a nitrogen raw material containing an alkali metal and nitrogen, a metal halide and a solvent at a first temperature to form a solid precursor; and a second step of reacting the solution at a second temperature higher than the first temperature.SELECTED DRAWING: Figure 1

Description

The present invention relates to nanoparticles, particularly nitride semiconductor nanoparticles and a method for producing the same.

In recent years, nanoparticles have been attracting attention for use in applications such as phosphors, self-luminous materials, and solar cells. Conventionally, nanoparticles have been produced by a chemical synthesis method such as a solvothermal method, a hot injection method, or a liquid phase synthesis method.

Japanese Unexamined Patent Publication No. 2007-1536662

Patent Document 1 discloses a method for producing metal nitride nanoparticles by a liquid phase synthesis method. However, when metal nitride nanoparticles are produced by such a conventional chemical synthesis method, a large amount of metal impurities are generated as by-products, and one problem is that almost no metal nitride nanoparticles can be obtained. It can be given as one.

The present invention has been made in view of the above points, and an object of the present invention is to provide high-quality nitride semiconductor nanoparticles obtained by suppressing the generation of metal by-products and obtaining high yields, and a method for producing the same. And.

In the method for producing nitride semiconductor nanoparticles of the present invention, a solution containing a nitrogen raw material containing an alkali metal and nitrogen, a metal halide and a solvent is reacted at a first temperature to form a solid precursor. It is characterized by having one step and a second step of reacting the solution at a second temperature higher than the first temperature.

It is a flow figure which shows the process of the manufacturing method of the nitride semiconductor nanoparticles which is Example 1 of this invention. It is sectional drawing which shows an example of the manufacturing apparatus used in the manufacturing method of the nitride semiconductor nanoparticles which is Example 1 of this invention. It is a figure which shows the change of the solution until the precursor is formed. It is a graph which shows the indium concentration in a solution. 3 is a graph showing the ratio of indium metal to the nitride semiconductor nanoparticles produced by the method of Example 1 and the ratio of indium metal to the nitride nanoparticles produced by the method of Comparative Example. 6 is a TEM image of the nitride nanoparticles produced by the method for producing nitride semiconductor nanoparticles according to the first embodiment of the present invention. 3 is a graph showing the ratio of indium metal to the nitride semiconductor nanoparticles produced by the method of Example 2 and the ratio of indium metal to the nitride nanoparticles produced by the method of Comparative Example.

Hereinafter, examples of the present invention will be described in detail with reference to the drawings. In the following description, a synthetic solution consisting of a raw material for a metal halide containing indium (In) (hereinafter, also referred to as an indium raw material), a raw material containing nitrogen (N) (hereinafter, also referred to as a nitrogen raw material), and a solvent is heated. To obtain III-V semiconductor nanoparticles, specifically, indium nitride (InN) nitride semiconductor nanoparticles, a case will be described.

FIG. 1 is a flow chart showing a process of a method for producing nitride semiconductor nanoparticles of the present invention.

First, a group III material, that is, an indium raw material, and a group V raw material, that is, a nitrogen raw material, which are raw materials for nitride semiconductor nanoparticles, are mixed with a solvent to generate a solution (step S1).

As a group III material, that is, an indium raw material, a metal halide such as indium iodide, indium chloride, and indium bromide can be used. As the group V material, that is, the nitrogen raw material, an alkali metal-based material such as sodium amide, cesium amide, or lithium amide can be used. Further, as the solvent, trioctylphosphine, diphenyl ether, diethyl ether and benzene can be used.

Next, while stirring the solution obtained in step S1, the solution is heated to a predetermined temperature equal to or lower than the decomposition temperature of the indium raw material using a heater to form a precursor of nanoparticles of indium nitride, which is the final product (step). S2). In step S2, the solution is reacted at a temperature of 140 ° C. to 160 ° C. for a predetermined time, for example, about 5 minutes to precipitate a solid precursor. In this step, the solution is maintained in a predetermined temperature range for a certain period of time, which is lower than the temperature at which the nanoparticles of indium nitride, which are the final product of the nitride semiconductor nanoparticles, are grown. The structure and composition of this solid precursor cannot be investigated due to the circumstances described below, and the details are unknown. Probably, the group III material melted at a temperature lower than the precursor formation temperature forms a solid precursor together with the group V material, and is considered to be an amide-based complex containing a group III element, a halogen, and an alkali metal. Since the precursor of this solid is precipitated due to its low solubility in a solvent, it is preferable to make the distribution of the precursor uniform in the synthetic solution by an operation such as stirring.

After the precursor is formed, the solution is heated to a temperature at which the final product, indium nitride nanoparticles, is grown, for example, 200 ° C. or higher, and reacted for a predetermined time, for example, about 1 hour (step S3).

After the growth step of the indium nitride nanoparticles, the solution is cooled and centrifuged to recover the indium nitride nanoparticles (step S4). That is, in the method for producing nitride semiconductor nanoparticles of the present invention, a solution containing a nitrogen raw material, a metal halide and a solvent is predetermined at a predetermined first temperature (precursor formation temperature) so that a solid precursor is deposited. It has a first step of reacting only for the time of the above, and a second step of reacting the solution at a second temperature higher than the precursor formation temperature.

Thus, the inventors of the present invention have a temperature lower than the temperature at which nanoparticles of indium nitride, which is the final product of the nitride semiconductor nanoparticles, are grown in the production of group III-V nitride semiconductor nanoparticles. It has been found that high-quality nitride nanoparticles can be synthesized in a single phase by growing nitride semiconductor nanoparticles, which are the final products, through a step of precipitating a solid precursor at a temperature.

It is considered that this is partly because it is possible to suppress the vaporization of nitrogen from the solution in the solution by forming a stable precursor that takes in nitrogen before forming the final nitride semiconductor nanoparticles. .. On the contrary, when the solution is heated to the nanoparticle formation temperature without using the group V material as a solid precursor, the nitrogen raw material is decomposed and released from the solution as ammonia gas, so that the group III metal is sufficiently nitrided. It is thought that it cannot be done. That is, under high temperature conditions of 200 ° C. or higher to produce the final nitride semiconductor nanoparticles, more indium reacts with nitrogen in the solution due to the residual nitrogen in the solution than in the conventional method. However, it is considered that high-quality nitride nanoparticles can be obtained in good yield without residual indium.

Hereinafter, a method for producing nitride semiconductor nanoparticles according to the first embodiment of the present invention will be described with reference to the drawings.

[manufacturing device]
FIG. 2 is a cross-sectional view of the synthesizer 10 used in the manufacturing method of the first embodiment. The solution container 11 is a cylindrical container including a cylindrical container portion 11A and a disk-shaped lid portion 11B. The solution container 11 is a cylindrical container made of a platinum group element material such as platinum or iridium. In Example 1, nanoparticles are produced by putting a solution LQ containing a raw material for nanoparticles into a solution container 11 and reacting the solution LQ.

Further, in Example 1, a stirrer SB for stirring the solution LQ is put into the solution container 11. The stirrer SB is formed by sealing a rod-shaped magnet with glass, Teflon (registered trademark), or the like. Therefore, the stirrer SB can perform an operation such as rotation by the action of a magnetic force from the outside of the solution container 11. In this example, CM1219 manufactured by Isis was used as the stirrer SB.

The pressure vessel 13 includes a cylindrical container portion 13A and a closed lid portion 13B capable of forming a closed space SS capable of accommodating the solution container 11 together with the container portion 13A. In this example, No. 4740 manufactured by Parr was used as the pressure vessel. The pressure vessel 13 may be a container that can withstand high temperature or high pressure inside the vessel. In this embodiment, the pressure vessel 13 may withstand, for example, a container internal temperature of about 500 ° C. or a container internal pressure of about 1 MPa.

The heater 15 has a cylindrical container shape that can accommodate the pressure vessel 13. The heater 15 is a heating device capable of heating the pressure vessel 13 housed therein, and is, for example, a mantle heater. In this embodiment, MS-ESB manufactured by AS ONE was used as the heater 15.

In the first embodiment, the heater 15 has a built-in stirrer ST at the bottom, which generates a magnetic force for rotating the stirrer ST. That is, when the stirrer ST generates a magnetic force, the stirrer SB rotates and the solution LQ is agitated. The stirrer ST may be separate from the heater 15. For example, the heater may be arranged on a stirrer separate from the heater such as a mantle heater.

[Manufacturing procedure]
Hereinafter, the process of the manufacturing method of Example 1 will be described with reference to FIG. 1 described above again. First, an indium raw material as a group III material, a nitrogen raw material as a group V material, and a solvent were mixed and filled in a solution container 11 as a solution LQ (step S1). At this time, the stirrer SB for stirring the solution LQ was also put into the solution container 11. After filling the solution container 11 with the solution LQ, the solution container 11 was housed in the pressure vessel.

As the indium raw material, indium iodide (manufactured by Aldrich, purity 99.998%) was used. As a nitrogen raw material, sodium amide (manufactured by Aldrich, hydrogen-storage grade) was used. As the solvent, trioctylphosphine (manufactured by Aldrich, purity 97%) was used.

In this example, indium iodide 89.2 mg (0.18 mmol), sodium amide 149.5 mg (3.84 mmol) and trioctylphosphine 6 ml (13.44 mmol) were mixed to prepare a solution LQ. The solution LQ was filled in the solution container 11 in a glove box in which the oxygen / water concentration was controlled to 1 ppm or less.

Next, the pressure vessel 13 is housed in the heater 15, and while stirring the solution LQ, the solution LQ is heated to the precursor formation temperature using the heater 15, and the nitride semiconductor nanoparticles of indium nitride, which is the final product, are heated. (Step S2). In this example, in step S2, the solution LQ was heated from 25 ° C. to 5 ° C./min and maintained at 150 ° C. for 5 minutes to react the solution. Further, in this embodiment, the stirring speed in step S2 was set to 600 rpm.

FIG. 3 is a photograph showing the state of the solution that changes from the heating of the solution LQ until the precursor is formed. In addition, each photograph of FIG. 3 was taken by using a transparent glass container so that the state of the solution LQ could be seen.

3A shows the solution LQ at 25 ° C., FIG. 3B shows the solution LQ at 100 ° C., and FIG. 3C shows the solution LQ at 120 ° C. Further, FIG. 3D shows the state after the solution LQ has been heated to 150 ° C. and 5 minutes have passed.

As shown in FIG. 3, until the temperature of the solution LQ reaches 120 ° C., the solution is slightly colored, but the solid does not appear to precipitate in the solution. However, after the temperature of the solution LQ was raised to 150 ° C. and 5 minutes had passed, black precipitates were generated in the solution LQ. It is difficult to analyze the components of this black precipitate because of its high reactivity and, specifically, its property of burning immediately when exposed to air.

FIG. 4 shows the In concentration in the sample solution collected at each temperature when the solution was heated to 150 ° C., 165 ° C., 200 ° C., and 250 ° C. while performing step S2 as the measured value of fluorescent X-ray measurement. It is a graph which shows the value calculated based on. The sample of the solution in which the presence of the precursor was visually confirmed was collected by waiting until the precursor settled in the lower part of the solution container so that the precursor would not be mixed with the sample.

As can be seen from this graph, when the solution temperature exceeds 150 ° C., the In concentration sharply decreases, and when the solution temperature exceeds 165 ° C., In cannot be detected. From this, it is expected that indium iodide dissolved in the solvent forms a precursor and solidifies at a temperature of about 150 ° C. In addition, Na which is an alkali metal and iodine which is a halogen also showed the same tendency. Further, it is presumed that the precursor, which is a black precipitate, is an amide-based complex containing a group III material and a group V material.

In the above description, a case where a precursor is formed by maintaining the solution LQ at 150 ° C. has been described. However, since it has been experimentally confirmed that the precursor is formed in the temperature range of 140 to 160 ° C., the formation of the precursor is to react the solution LQ at a temperature between 140 and 160 ° C. for a certain period of time. But it is feasible. In the present application, this temperature will be referred to as a precursor formation temperature.

Further, in the step S2 for forming the precursor, the solution LQ was reacted with stirring in order to make the constituent composition of the precursor to be formed uniform. Specifically, the alkali metal-based material of the group V raw material has low solubility in a solvent, and the concentration in the solvent tends to be non-uniform. When the concentration of the alkali metal-based material in the solvent becomes non-uniform, the constituent composition of the precursor to be formed becomes non-uniform, and the nitriding of the group III metal varies. The formation of precursors that are not sufficiently nitrided causes the generation of by-products other than nitride nanoparticles, especially the generation of Group III metals.

Further, if the constituent substances of the precursor are non-uniform, the nitrogen raw material may remain unreacted. In that case, in processes such as particle cleaning and processing after particle synthesis, the remaining nitrogen raw material reacts, leading to oxidation of the particles and deterioration of the nitride nanoparticles due to an unexpected reaction. Therefore, in the precursor formation process, it is preferable to homogenize the material in the reaction solution by stirring the reaction solution or vibrating the reaction vessel with ultrasonic waves to sufficiently take in nitrogen and form a homogeneous precursor.

After the precursor was formed, the temperature was further increased and the reaction was carried out at the growth temperature of the nitride semiconductor nanoparticles for 1 hour (step S3). In this example, the growth temperature was set to three patterns of 200 ° C, 250 ° C, and 300 ° C.

After the above step S3, the pressure vessel 13 was taken out from the heater 15, and the pressure vessel 13 was cooled with cold water to cool the solution (step S4). The reason for cooling with cold water is to quickly stop the reaction in the solution.

Then, the solution container 11 was taken out from the pressure vessel 13, the solution LQ in the solution container 11 was taken out, and the solution LQ was centrifuged (step S4). This centrifugation was performed by an ultracentrifuge. Specifically, first, ethanol was added to the synthetic solution for centrifugation, the supernatant after centrifugation was removed, and then ethanol was added again for centrifugation. Then, after further removing the supernatant after centrifugation, ethanol was added again and centrifugation was performed. In this step, each centrifuge was separated for 30 minutes at a rotation speed of 28,000 rpm. Then, hexane was added and the mixture was further centrifuged. Finally, ethanol was added and centrifugation was performed to recover the nanoparticles of indium nitride.

[evaluation]
The nitride semiconductor nanoparticles produced and recovered by the production method of the above example were evaluated in comparison with the nitride semiconductor nanoparticles produced and recovered by the production method of Comparative Example. The manufacturing method of the comparative example is different from the manufacturing method of the first embodiment in that the step S2 is not performed. That is, in the production method of the comparative example, the solution is heated to 200 ° C., 250 ° C., or 300 ° C., which is the growth temperature of the nanoparticles, to produce nitride semiconductor nanoparticles.

The ratio of In metal contained in the nitride semiconductor nanoparticles produced by the production method of Example 1 and the nitride semiconductor nanoparticles produced by the production method of Comparative Example was measured by an X-ray diffractometer (XRD). Calculated using. Specifically, the peak of the XRD measurement result was subjected to precision structural analysis, for example, Rietveld analysis, and the Wt% of indium (In) metal with respect to the recovered material was calculated.

FIG. 5 is a graph showing the calculated content ratio of indium (In) metal. The horizontal axis represents the growth temperature in step S3, and the vertical axis represents the ratio of In metal. As shown in FIG. 5, the content of indium (In) metal in the nitride semiconductor nanoparticles produced by the production method of Example 1 was produced by the production method of Comparative Example at any growth temperature. It was lower than the nitride semiconductor nanoparticles and had a content of almost 0%.

As mentioned above, this low indium metal content causes nitrogen to vaporize from solution in solution by forming a stable precursor that incorporates nitrogen before forming the final nitride semiconductor nanoparticles. It is thought that one of the reasons is that it can suppress this. That is, under high temperature conditions of 200 ° C. or higher to produce the final nitride semiconductor nanoparticles, more indium reacts with nitrogen in the solution due to the residual nitrogen in the solution than in the conventional method. However, it is considered that high-quality nitride nanoparticles can be obtained in good yield without residual indium.

FIG. 6 is a TEM image (× 100,000) of nitride semiconductor nanoparticles produced by the production method of Example 1. FIG. 6A is a product generated with a growth temperature of 200 ° C., FIG. 6B is a product produced with a growth temperature of 250 ° C., and FIG. 6C is a product produced with a growth temperature of 300 ° C. Is.

As can be seen from FIG. 6, when the growth temperature is 200 ° C., the particle size is 5-7 nm, when the growth temperature is 250 ° C., the particle size is 7-10 nm, and when the growth temperature is 300 ° C., the particle size is 7-15 nm. Particles were formed.

Based on the above, in the production of nitride semiconductor nanoparticles, nitride semiconductor nanoparticles are formed by using an alkali metal-based material as the Group V material and forming a precursor at a temperature equal to or lower than the growth temperature of the nitride semiconductor nanoparticles. It was found that uniform nitride can be promoted, and high-quality nitride nanoparticles having a low content of Group III metal and a uniform particle size can be obtained with high yield.

In Example 1 above, trioctylphosphine was used as a solvent. Trioctylphphosphine also has properties as a surface modifier for nitride semiconductor nanoparticles. Therefore, the nitride semiconductor nanoparticles produced in Example 1 can omit the step of surface modification in the subsequent steps.

The manufacturing method of Example 2 will be described below. The production method of Example 2 is different from the production method of Example 1 only in that diphenyl ether is used as a solvent instead of trioctylphosphine in the preparation of the solution, and the other steps are exactly the same. Therefore, the description is omitted except for the preparation of the solution.

In Example 2, indium iodide (manufactured by Aldrich, purity 99.998%) was used as the indium raw material. As a nitrogen raw material, sodium amide (manufactured by Aldrich, hydrogen-storage grade) was used. Further, as a solvent, diphenyl ether (manufactured by Aldrich, purity 99.9%) was used.

In Example 2, 89.2 mg (0.18 mmol) of indium iodide, 149.5 mg (3.84 mmol) of sodium amide, and 6 ml (13.44 mmol) of diphenyl ether were mixed to prepare a solution LQ. The solution LQ was filled in the solution container 11 in a glove box in which the oxygen / water concentration was controlled to 1 ppm or less.

The nitride semiconductor nanoparticles produced by the production method of Example 2 were evaluated in comparison with the nitride semiconductor nanoparticles produced by the production method of Comparative Example. The manufacturing method of the comparative example is different from the manufacturing method of the second embodiment in that the step S2 is not performed, as described above in the first embodiment. That is, in the production method of the comparative example, the solution is heated to 200 ° C., 250 ° C., or 300 ° C., which is the growth temperature of the nanoparticles, to produce nitride semiconductor nanoparticles.

The ratio of indium (In) contained in the nitride semiconductor nanoparticles produced by the production method of Example 2 and the nitride semiconductor nanoparticles produced by the production method of the comparative example is measured by an X-ray diffractometer (XRD). Calculated using the results. Specifically, the peak of the XRD measurement result was subjected to precision structural analysis, for example, Rietveld analysis, and the Wt% of indium (In) with respect to the recovered material was calculated.

FIG. 7 is a graph showing the measured indium (In) content ratio. The horizontal axis represents the growth temperature in step S3, and the vertical axis represents the ratio of indium (In). As shown in FIG. 7, the In content of the nitride semiconductor nanoparticles produced by the production method of Example 2 is the nitride semiconductor nanoparticles produced by the production method of Comparative Example at any growth temperature. Was lower than.

Based on the above, in the production of nitride semiconductor nanoparticles, nitride semiconductor nanoparticles are formed by using an alkali metal-based material as the Group V material and forming a precursor at a temperature equal to or lower than the growth temperature of the nitride semiconductor nanoparticles. It was found that uniform nitride can be promoted, and high-quality nitride nanoparticles having a low content of Group III metal and a uniform particle size can be obtained with high yield.

In the above example, in step 2, the solution was reacted at 150 ° C. for 5 minutes to form a precursor. However, the precursor formation time is not limited to this. It is preferable to grow the nitride semiconductor nanoparticles in step S3 after the formation of the precursor is completed, that is, after the reaction for producing the precursor is saturated. Therefore, it is preferable to raise the temperature to the growth temperature of the nitride semiconductor nanoparticles after the precipitation of the precursor has converged at a temperature of about 140 to 160 ° C. to grow the nitride semiconductor nanoparticles.

In the above embodiment, it is assumed that the temperature of the solution is raised at 5 ° C./min in step S2, but the heating rate is not limited to this. For example, the temperature may be raised at a heating rate of 5 ° C. or less per minute.

Further, in the above embodiment, the nitride semiconductor nanoparticles having different particle sizes were produced by changing the growth temperature in step S3. However, the particle size of the nitride semiconductor nanoparticles to be produced may be adjusted by not only changing the growth temperature but also adding an additive to the solution to inhibit the growth of the nitride semiconductor nanoparticles.

Further, in the above examples, indium iodide, which is an iodide, was used as the material for Group III, but in addition to iodide, halides of Group III elements including chlorides or bromides can also be used. That is, it is also possible to use indium halide other than indium iodide.

Further, in the above embodiment, InN nitride semiconductor nanoparticles were produced using a material containing In as a group III raw material. However, a halide containing Ga as a group III element is used as a material, and mixed-crystal nitride semiconductor nanoparticles such as GaN, AlN, InGaN, InAlN, AlGaN, and AlInGaN are obtained in the same step as the step of the above embodiment. It is also possible to manufacture. It is also possible to produce nitride semiconductor nanoparticles using halides of other Group III elements.

In the above embodiment, the solution LQ is stirred by the stirrer SB and the stirrer ST, but a shaft having a stirring blade is inserted from the outside of the pressure vessel and the shaft and the stirring blade are rotated by a motor or the like. The solution may be stirred with. Further, the solution LQ may be agitated by vibrating the solution LQ using an ultrasonic vibration device.

The material of the stirrer and the stirrer blade may be any material other than glass, such as quartz, teflon, platinum, gold, iridium, rhodium, and sapphire, which is not easily affected by being dissolved in a solution.

The various numerical values, dimensions, materials, etc. in the above-mentioned examples are merely examples, and can be appropriately selected depending on the intended use, the semiconductor nanoparticles to be manufactured, and the like.

10 Synthesizer 11 Solution vessel 13 Pressure vessel 15 Heater

Claims (12)

The first step of reacting a nitrogen raw material containing an alkali metal and nitrogen, a solution containing a metal halide and a solvent at a first temperature to form a solid precursor, and the first step.
A second step of reacting the solution at a second temperature higher than the first temperature, and
A method for producing nitride semiconductor nanoparticles. The method for producing nitride semiconductor nanoparticles according to claim 1, wherein the first step includes a step of maintaining the solution at the first temperature for a certain period of time. The method for producing nitride semiconductor nanoparticles according to claim 2, wherein the temperature range of the first temperature is 140 ° C to 160 ° C. The production of nitride semiconductor nanoparticles according to any one of claims 1 to 3, wherein the rate of temperature rise at the time of forming the precursor in the first step is 5 ° C./min or less. Method. The method for producing nitride semiconductor nanoparticles according to any one of claims 1 to 4, wherein the formation of the precursor in the first step is performed while stirring the solution. The method for producing nitride semiconductor nanoparticles according to any one of claims 1 to 5, wherein the solid precursor is black. The method for producing nitride semiconductor nanoparticles according to any one of claims 1 to 6, wherein the nitride semiconductor nanoparticles are group III-V semiconductors. The metal halide is a halide of a Group III element including chlorides, bromides or iodides.
The nitrogen raw material is a compound of nitrogen and an alkali metal, and is
The method for producing nitride semiconductor nanoparticles according to claim 7, wherein the solvent is diphenyl ether, trioctylphosphine or benzene. The method for producing nitride semiconductor nanoparticles according to claim 8, wherein the metal halide is indium halide. The method for producing nitride semiconductor nanoparticles according to claim 9, wherein the nitrogen raw material is sodium amide, and the metal halide is indium iodide. The method for producing nitride semiconductor nanoparticles according to any one of claims 1 to 10, wherein the precursor contains an amide-based complex. Nitride semiconductor nanoparticles produced by the method for producing nitride semiconductor nanoparticles according to any one of claims 1 to 11.

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