Method for producing group III nitride semiconductor nanoparticles

Abstract

To provide Group III nitride nanoparticles substantially free from impurities and having high quantum efficiency.SOLUTION: In reacting one or more materials containing a Group III element M in a liquid phase to synthesize Group III nitride semiconductor nanoparticles having a particle size of 16 nm or less, trimethylindium is used as at least one Group III element material among the one or more materials containing a Group III element M; trimethylindium is dissolved in a coordination solvent to form a precursor prior to the synthesis reaction of the nanoparticles; and the precursor is reacted with another Group III element material and a nitrogen source in the solvent at 300°C or higher in an inert atmosphere to synthesize the nanoparticles.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to semiconductor nanoparticles composed of nitrides of group III elements such as Al, Ga, and In, and particularly to a method for producing group III nitride semiconductor nanoparticles without using halogen-based materials.

Background Art

[0002] Nitride nanoparticles are materials expected to be applied to EL devices such as lighting and displays, light-receiving elements such as sensors and solar cells, and photocatalysts such as hydrogen generation. It is known that quantum effects occur when the particle size of nitride nanoparticles becomes 2 times or less of the Bohr radius. Even for nitride nanoparticles of the same composition, the energy gap can be controlled by changing the particle size, and the controllability of the emission wavelength and the light absorption edge is significantly improved.

[0003] Al x Ga y In z The Bohr radius of group III nitrides represented by N(0≦(x, y, z)≦1, x + y + z = 1) is 2.3 nm for AlN, 3.3 nm for GaN, and 8.2 nm for InN. By controlling the composition and particle size, the emission region can be controlled from ultraviolet to infrared. In particular, by including In, nitride nanoparticles that emit light in the visible region can be produced, and the emission efficiency is improved.

[0004] As a method for producing group III nitride nanoparticles, a chemical synthesis method in which a group III element material and a nitrogen material are synthesized in a liquid phase is common, and nanoparticles with a particle size of 16 nm or less that exhibit quantum effects can be produced by the chemical synthesis method. As the group III element material, halogen compounds such as indium iodide and gallium iodide that can maintain stability even during heating in chemical synthesis are used. For example, Patent Document 1 discloses a method for producing nitride nanoparticles using indium iodide and gallium iodide.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2012-515803 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] However, when a halogen compound is used as a synthesis raw material, there is a problem that a trace amount of halogen is incorporated into the generated nitride as an impurity in the particles. Furthermore, in the material manufacturing process of halogen-based materials, transition elements such as iron group and alkali metal elements such as Li and Na remain as residues, and these elements are also incorporated as impurities into the nitride particles in the same manner as halogen. The impurities incorporated into the particles function as non-light-emitting centers for the excited carriers, leading to a decrease in the light-emitting efficiency. In particular, transition elements such as iron group and alkali metal elements such as Li and Na cause a fatal decrease in the light-emitting efficiency even at a trace amount on the order of several ppm.

[0007] As group III compounds other than halogen compounds, there are also organic group III compounds such as trimethylindium (hereinafter referred to as TMIn) and triethylindium. Since these compounds are of high purity and do not contain elements unnecessary for the material itself, there are examples where they are used as materials for vapor phase growth such as MOCVD method in the manufacture of high-quality nitride thin films such as LEDs. However, TMIn has a risk of causing a violent self-decomposition reaction accompanied by explosion when heated to 80 °C or higher. For this reason, it cannot be used in chemical synthesis where it is directly heated for reaction and decomposition. Especially in the chemical synthesis of nitride nanoparticles, high thermal energy is required, so it is necessary to react and decompose the material at least at 100 °C or higher, preferably 150 °C or higher, and TMIn cannot be used as a material. Also, when the self-decomposition reaction occurs, it is precipitated as In metal, so it is impossible to obtain nitride nanoparticles containing In or a nitride with the target element ratio. obtainable or obtain a nitride with the desired element ratio.

[0008] The present invention has been made to solve the above-described conventional problems, and an object thereof is to provide a method for producing group III nitride nanoparticles by chemical synthesis without using a halogen material, and thereby to provide group III nitride nanoparticles not containing halogen.

Means for Solving the Problems

[0009] As a result of intensive studies on the conditions for reacting with an organic group III material that can be used in chemical synthesis in order to solve the above problems, trimethyl M (where M is any one or more of Al, Ga, and In) is used as the group III element material, and by reacting in a coordination solvent, it has been found that self-decomposition can be suppressed and group III nitride nanoparticles having a desired composition and a particle size of 16 nm or less can be produced. The produced group III nitride nanoparticles do not contain impurity elements contained in halogen elements or halogen-based materials, and have a higher quantum efficiency than group III nitride nanoparticles synthesized using halogen-based materials.

Effects of the Invention

[0010] According to the present invention, in the chemical synthesis of nitride nanoparticles, the explosive self-decomposition reaction of TMIn can be suppressed, and nitride nanoparticles can be stably produced. Further, according to the present invention, it is possible to provide nitride nanoparticles having high luminous efficiency and substantially not containing impurities that inhibit the luminous efficiency.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments of the group III nitride nanoparticles and a method for producing the same according to the present invention will be described. The group III nitride nanoparticles of the present invention have the general formula: Al x Ga y In z N (where 0 ≤ (x, y, z) ≤ 1, x + y + z = 1), or the general formula: Al x Ga y In z N (where 0 ≤ (x, y) < 1, 0 < z ≤ 1, x + y + z = 1). The parentheses such as "0 ≤ (x, y, z) ≤ 1" mean that each of x, y, and z is in a relationship represented by the inequality or equality sign before and after it. The group III nitride nanoparticles of the present invention also include core-shell type particles having the nanoparticles represented by the above general formula as core particles and group III nitrides represented by the general formula as shells.

[0013] As shown in Fig. 1, the energy gaps of nitrides of aluminum (Al), gallium (Ga), and indium (In) are within the range of the region formed by connecting the energy gaps of binary nitrides with the curve showing the energy gaps of ternary nitrides, and by changing the ratios of these three elements, they can be arbitrarily changed within this range. Also, the core-shell type has a band structure of Type 1 as shown in Fig. 2, and the ratio of the elements constituting the core particles and the shell is determined such that the energy gap of the core particles (EGcore) and the energy gap of the shell (EGshell) satisfy EGcore < EGshell. As shown in Fig. 1, the higher the proportion of Al, the higher the energy gap, and the higher the proportion of In, the lower the energy gap. Therefore, for example, a Type 1 band structure can be realized by combining core particles containing a relatively large amount of In and a shell containing a relatively large amount of Al. As an example, core-shell type particles with InGaN as the core particles and AlInN as the shell can be mentioned. Not limited to this example, various combinations of compositions are possible as long as the energy gaps of the core particles and the shell satisfy the above relationship, but it is particularly preferable that they are group III nitride nanoparticles containing indium or core-shell particles having such nanoparticles as the core particles. Thereby, the light emission region can be expanded to the visible region, and the light emission efficiency is also improved.

[0014] The ratio of the group III elements in the nitride can be adjusted by using the compounds serving as the raw materials of the group III elements in a stoichiometric ratio such that the molar ratio of the group III elements becomes the desired ratio in the production of the group III nitride nanoparticles described later. In the production method of the present invention, since the precipitation of metals and the incorporation of impurities are suppressed during the reaction, the desired ratio can be realized.

[0015] The nitride nanoparticles of the present invention have a particle size of 16 nm or less. The particle size of 16 nm or less is 2 times or less the Bohr radius (8.2 nm) of InN, whereby a quantum effect is exhibited and a high luminous efficiency can be obtained. Nitride nanoparticles can generally have their particle size reduced to 16 nm or less by chemical synthesis in a suitable solvent under high-temperature conditions. However, in the manufacturing method of the present invention, it can also be achieved by adjusting synthesis conditions such as the synthesis temperature, heating time, solvent, and material concentration during manufacturing. Specific synthesis conditions will be described later.

[0016] Furthermore, the nitride nanoparticles of the present invention are characterized by substantially not containing impurity elements substantially mixed into halogen elements and halogen compounds. Nitride nanoparticles produced by conventional chemical synthesis methods are manufactured using a halogen compound as a group III element material during synthesis, and impurities derived from the halogen compound are inevitably mixed in. Impurities derived from halogen compounds vary depending on the type of halogen compound, and include, in addition to halogen elements such as iodine (I) and bromine (Br), transition elements such as fluorine, iron, manganese, and zinc, and alkali metal elements such as Li and Na. Since the nitride nanoparticles of the present invention are manufactured by chemical synthesis without using a halogen compound, there is no such mixing of impurities, and they exhibit a high quantum efficiency (luminous efficiency).

[0017] The group III nitride nanoparticles / core-shell type group III nitride nanoparticles of the present invention can be widely used in general semiconductor nanoparticle applications. In particular, by utilizing their high quantum efficiency (derived high energy conversion efficiency, luminous efficiency, light absorption efficiency, etc.), they can be suitably used in wavelength conversion materials, photocatalysts, solar cells, EL light-emitting devices, etc.

[0018] Next, the manufacturing method of the above-described group III nitride nanoparticles will be explained.

[0019] The method for manufacturing group III nitride nanoparticles of the present invention involves reacting a material containing one or more group III elements M in a liquid phase to synthesize group III nitride semiconductor nanoparticles with a particle size of 16 nm or less. When using at least one group III material among the materials containing one or more group III elements M, trimethyl M is used. Trimethyl M is pretreated using a coordination solvent.

[0020] The group III nitride semiconductor nanoparticles to be manufactured have the general formula: Al x Ga y In z N (where 0 ≦ (x, y, z) ≦ 1, x + y + z = 1), or nanoparticles represented by the general formula: Al x Ga y In z N (where 0 ≦ (x, y) < 1, 0 < z ≦ 1, x + y + z = 1).

[0021] Hereinafter, the method for manufacturing group III nitride nanoparticles of the present invention will be described in detail. The method for manufacturing group III nitride nanoparticles of the present invention is based on a chemical synthesis method in which a group III material and a nitrogen material are introduced into a solvent and heated to synthesize a nitride.

[0022] As the group III material, compounds of Al, Ga, and In are used. However, when y > 0, that is, when In is included in the above general formula, trimethylindium (TMIn) is used as at least the In material. Among organic In compounds, in addition to TMIn, there are trialkylindiums with long organic chain lengths such as triethylindium with a similar structure. However, these In compounds cause a β - dehydrogenation elimination reaction during the reaction at high temperatures to generate metal hydrides, and further metals are generated as by - products of hydrogen reduction by the metal hydrides. As a result, the stoichiometric ratio of the V element to the III element in the obtained nitride nanoparticles changes, and a nitride with a desired composition cannot be obtained. When TMIn is used, such a hydrogen elimination reaction hardly occurs, so that no precipitation of metallic indium occurs, and nitride nanoparticles with a stable composition can be obtained.

[0023] Prior to the reaction, it is preferable to pre-form TMIn by treatment with a coordination solvent. The coordination solvent suppresses the violent self-decomposition reaction by coordinating to In of TMIn. As the coordination solvent, trioctylphosphine (boiling point: 351 °C), tributylphosphine (boiling point: 150 °C under 6.7 kPa conditions), trioctylamine (boiling point: 367 °C), diphenyl ether (boiling point: 260 °C), etc. can be used. In particular, trioctylphosphine (hereinafter abbreviated as TOP) is preferable.

[0024] Regarding the materials of Al and Ga, it is also preferable to use trimethylaluminum (TMAl) and trimethylgallium (TMGa), but compounds other than trimethylated metals (excluding halogen compounds) may also be used. For example, for Al, aluminum acetonate, etc., and for Ga, gallium acetonate, etc. can be used. However, in order to minimize the impurity elements mixed into the nitride and stoichiometric ratio maintain it, it is most preferable to use trimethylaluminum and trimethylgallium in the same manner as the In material.

[0025] As the nitrogen material, ammonia, metal azide compounds, metal nitrides, hydrazines, amines, metal amides, etc. can be used. In particular, metal amides such as sodium amide and lithium amide are preferable.

[0026] As the reaction solvent, general solvents used for the synthesis of nitrides can be used. Specifically, tetradecylbenzene (boiling point: 356 °C), 1-octadecene (boiling point: 320 °C), TOP, tributylphosphine, trioctylphosphine oxide (boiling point: 238 °C under 0.4 kPa conditions), diphenyl ether, etc. can be mentioned. In particular, tetradecylbenzene is preferable.

[0027] In the manufacturing method of the present invention, first, regarding TMIn among the group III materials, it is dissolved in a coordinating solvent to form a precursor. The precursor is a state in which TMIn is solvated and isolated, and by setting such a state, the self-decomposition reaction is suppressed. Since there is a risk of explosion due to the self-decomposition reaction at 20°C to below the boiling point of the solvent and 88°C (the melting point of TMIn) or higher, the precursor formation treatment is preferably carried out at 80°C or lower. The precursor is considered to have a structure in which P (phosphorus) of TOP is coordinately bonded to a metal (indium) to which a trimethyl group is bonded when, for example, TOP is used. Since the bulky trioctyl group coordinates and isolates the TMIn molecules, the high self-decomposition reaction is inhibited, and relatively stable it is possible to maintain the state for a long time. As a result, it continuously functions as a stable group III source even under heating at 100°C or higher.

[0028] The amount of the coordinating solvent required for precursor formation is preferably such that the molar ratio of P contained in TOP to the metal element of the trimethylated metal introduced as the group III material is 1:1 or more, and more preferably 3:1 or more.

[0029] After performing such a precursor formation treatment, a group III element material other than TMIn, a nitrogen material, and a reaction solvent are added to the reaction system, and the synthesis reaction is advanced. The concentration of the materials is not particularly limited, but the concentration of the metal element (the total amount determined stoichiometrically) in the reaction solvent is preferably about 3 to 36 mol / liter. Also, the nitrogen material is preferably the same as or more than the group III element material, and the concentration in the reaction solvent is preferably about 27 to 720 mol / liter.

[0030] The reaction is carried out under heating at 200°C or higher, preferably 300°C or higher, more preferably 330°C or higher in an inert atmosphere. By reacting at such a temperature, nitride nanoparticles with a particle size of 16 nm or less are produced. The reaction time is about 1 to 5 minutes depending on the scale of the reaction. After the reaction, centrifugation using a predetermined solvent is repeated to wash the particles, and then the particles are recovered as particles or as a solvent dispersion.

[0031] The manufacturing method of core-shell type nanoparticles is the same as that of general core-shell type nanoparticles. Using the group III nitride nanoparticles obtained by the manufacturing method described above as core particles, a group III nitride serving as a shell covering them is synthesized. The compositions of the core particles and the shell are selected such that the energy gap (EGcore) of the core particles and the energy gap (EGshell) of the shell satisfy EGcore < EGshell in order to obtain a Type1 structure. For example, the core particles have a composition containing a relatively large amount of In, and the shell has a composition containing a relatively large amount of Al. Further, as the material of the group III element constituting the shell, a material other than a halogen compound, particularly a trimethylated product, is used.

[0032] For the synthesis reaction to form the shell, the nanoparticles manufactured by the manufacturing method described above, the material of the group III element constituting the shell, and a solvent are added to a reaction vessel, and heated in an inert atmosphere to 200 °C or higher, preferably 300 °C or higher, more preferably 330 °C or higher. As the solvent, the same solvent as the one used for manufacturing the core particles can be used. The method for recovering the core-shell particles after generation is the same as that for recovering the core particles. By repeating centrifugation and washing using a dispersion medium, the core-shell particles are recovered as a dispersion.

[0033] Since the group III nitride nanoparticles / core-shell type group III nitride nanoparticles obtained by the above manufacturing method do not use a halogen-based material containing impurity elements such as iron, they are substantially free of impurities (for example, not detected by powder X-ray measurement), have high purity, and there is no decrease in the luminescence efficiency due to impurities.

Example

[0034] Hereinafter, a manufacturing example of the group III nitride nanoparticles of the present invention will be described. In the following examples and comparative examples, the size of the particles was measured by a transmission electron microscope (TEM) / scanning transmission electron microscope (STEM).

[0035] [Example 1] Trimethylgallium (TMGa) was used as the Ga source, TMIn as the In source, and lithium amide as the Group V source. The general ICP measurement results of TMGa and TMIn used as materials are shown in Fig. 3. For reference, the measurement results of indium iodide and gallium iodide are also shown in Fig. 3. As shown in the figure, transition metals and alkali metals were detected in the iodide, while such impurity elements were not detected in the materials used in this example.

[0036] First, TMIn (0.0675 mmol) was added to TOP (0.5 ml) and heated to 40 °C for precursor formation treatment. Hereinafter, the TMIn after the precursor treatment will be abbreviated as TMIn@TOP.

[0037] Into a glass reaction vessel, 0.0675 mmol of TMIn@TOP as the amount of TMIn, 0.0675 mmol of TMGa, and 2.7 mmol of lithium amide were placed, and 1.0 ml of tetradecylbenzene was added as the reaction solvent. It was heated to 350 °C in an inert atmosphere and reacted for about 3 minutes.

[0038] After the reaction, the product was collected in a centrifuge tube, a mixed solvent in which hexane and ethanol were mixed at a volume ratio of about 3:7 was added, and centrifugation was performed at 10,000 to 30,000 rpm for about 30 minutes, and the supernatant was discarded. The obtained precipitate was dispersed in hexane, ethanol was added, and centrifugation was performed again under the same conditions. This step was repeated 3 to 5 times to wash the particles. Finally, it was dispersed in hexane to obtain a sample of a hexane dispersion. The particle size of the obtained nanoparticles was 3 to 5 nm.

[0039] [Comparative Example 1] When non-precursor-treated TMIn was used as the In source instead of TMIn@TOP, explosive self-decomposition occurred during heating and the product could not be recovered.

[0040] [Comparative Example 2] The reaction was carried out in the same manner as in Example 1, except that triethylindium (TEIn) was used instead of TMIn as the In source, to produce nitride particles. Since TEIn does not undergo a self-decomposition reaction, it was directly introduced into the reaction solvent without any precursor treatment. The particle size of the obtained nanoparticles was 50 - 200 nm.

[0041] [Comparative Example 3] Nitride nanoparticles (hexane dispersion) were obtained in the same manner as in Example 1, except that indium iodide (InI 3 ) and gallium iodide (GaI 3 ) were used instead of TMIn and TMGa as the In source and Ga source, respectively. The particle size of the obtained nanoparticles was 3 - 5 nm.

[0042] Powder X-ray diffraction measurement (XRD) was performed on the nitride particles obtained in Example 1 and Comparative Examples 2 and 3, respectively. The results are shown in Figure 4.

[0043] From the results of the powder X-ray measurement shown in Figure 4, it was confirmed that nitride nanoparticles were generated in all of Example 1 and Comparative Examples 2 and 3. However, it was confirmed that In metal was precipitated in Comparative Example 2. From this, it was found that when the alkyl chain becomes longer, metal precipitation occurs due to the reduction reaction, and nitride particles with good purity cannot be obtained, and the yield also decreases.

[0044] In addition, impurity analysis and quantum efficiency measurement were performed on the nitride nanoparticles of Example 1 and Comparative Example 3. For impurity analysis, iron (Fe) was analyzed by X-ray fluorescence analysis (XRF), iodine (I) was analyzed by X-ray photoelectron spectroscopy (XPS) and ICP. The measurement of the quantum efficiency was carried out using a quantum efficiency measuring instrument (Otsuka Electronics QE-2100), and the excitation light (365 nm) was incident on the particle dispersion solution for measurement. The impurity analysis results are shown in Table 1, and the results of the quantum efficiency measurement are shown in Figure 5. The results of the impurity analysis were calculated as the "amount of impurities relative to Group III (ppm)" using the impurities detected in each measurement and the measured values of Group III.

[0045]

Table 1

[0046] As shown in Table 1, in Comparative Example 3 using a halogen compound as the Group III source material, Fe was detected as an impurity in addition to the halogen element (I), whereas in Example 1, these impurity elements were not detected. From this, it can be seen that impurities such as Fe other than the halogen are impurities derived from the material, and by not using a halogen compound as the material, nitride particles with high purity can be obtained. Also, as shown in Figure 3, the quantum efficiency of the nitride nanoparticles in Example 1 is about 11%, whereas the nitride nanoparticles in Comparative Example 3 have a low quantum efficiency of about 7%, and it was confirmed that the luminescence efficiency decreases due to impurities in the material.

[0047] [Example 2] The following precursor treatment, core particle synthesis, and shell formation were sequentially performed to produce core-shell type nitride particles. Trimethylgallium (TMGa) was used as the Ga source, TMIn as the In source, TMAl as the Al source, and lithium amide as the Group V source.

[0048] In the precursor treatment, as in Example 1, TMIn was added to TOP (0.5 ml), heated to 40 °C for precursor conversion treatment to obtain TMIn@TOP.

[0049] In the core particle synthesis, 0.0675 mmol of TMIn@TOP in terms of the amount of TMIn, 0.0675 mmol of TMGa, 2.7 mmol of lithium amide, and 1.0 ml of tetradecylbenzene as the reaction solvent were added to a glass reaction vessel, heated to 350 °C in an inert atmosphere, and reacted for about 3 minutes.

[0050] The product was collected in a centrifuge tube, and centrifugation and washing were repeated with hexane / ethanol in the same manner as in Example 1 to obtain InGaN nanoparticles dispersed in hexane (particle size 3 - 5 nm).

[0051] Next, tetradecylbenzene was added to the InGaN nanoparticle dispersion, and while diffusing it, the pressure was reduced to perform solvent replacement. The InGaN nanoparticles (core particles) after solvent replacement were placed in a glass reaction vessel, and 0.054 mmol of TMAl and 0.081 mmol of TMIn@TOP were added. The ratio of In in the added materials among group III elements is 60 atomic %. Further, 2.7 mmol of lithium amide was added, and the material was reacted by heating to 350 °C in an inert atmosphere.

[0052] The product was centrifuged and washed repeatedly in the same manner as in the core particle synthesis, and finally, core-shell particles (In 0.5 Ga 0.5 N / Al 0.4 In 0.6 N) dispersed in hexane were obtained. It was confirmed by powder X-ray measurement that they were nitride nanoparticles. The particle size of these core-shell particles was 3 to 6 nm.

[0053] [Comparative Example 4] Core-shell particles were produced in the same manner as in Example 2, except that the In source, Ga source, and Al source were changed to indium iodide, gallium iodide, and aluminum iodide (AlI 3 ), respectively. From the ICP analysis results shown in Table 1 and the quantum efficiency measurement results of Comparative Example 3, it is presumed that the luminescence efficiency of Comparative Example 4 is also lower than that of Example 2.

Industrial Applicability

[0054] According to the present invention, nitride nanoparticles are provided that can improve the performance of wavelength conversion materials, photocatalysts, solar cells, EL light-emitting devices, etc. when used in them.

Claims

1. A first step of dissolving trimethylindium in at least one of trioctylphosphine, tributylphosphine, trioctylamine, and diphenyl ether, which are coordination solvents, to form a precursor; A second step of reacting the precursor trimethylindium with a metal amide, which is a nitrogen source, in a reaction solvent; A method for producing group III nitride semiconductor nanoparticles having a particle size of 16 nm or less, comprising the above steps.

2. The method for producing group III nitride semiconductor nanoparticles according to Claim 1, wherein the second step further comprises a step of reacting in the presence of at least one of trimethylgallium and trimethylaluminum.

3. The method for producing group III nitride semiconductor nanoparticles according to Claim 1, wherein the metal amide is at least one of sodium amide and lithium amide.

4. The Group III nitride semiconductor nanoparticles have the general formula: Al ｘ Ga ｙ In ｚ N (where 0 ≤ (x, y) < 1, 0 < z ≤ 1, x + y + z = 1), and the method for producing Group III nitride semiconductor nanoparticles according to claim 2, characterized in that the nanoparticles are represented by the formula.

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