JP7274163B2 - Semiconductor nanoparticles and wavelength conversion member - Google Patents

Description

The present invention relates to semiconductor nanoparticles made of a nitride-based semiconductor material, and wavelength conversion members using the semiconductor nanoparticles.

A substance that has been reduced to a few nanometers to ten and several nanometers exhibits physical properties different from those in a bulk state. Such phenomena and effects are called carrier confinement effects, quantum size effects, and the like, and substances exhibiting such effects are called quantum dots. By changing the size (overall size) of quantum dots, the bandgap (light absorption wavelength and emission wavelength) can be adjusted.

Fluorescent substances are one of the applications of quantum dots (semiconductor nanoparticles) containing semiconductor materials. It is possible to emit fluorescence of a predetermined wavelength upon receiving high-energy light or particle beams. A surface light source can be obtained by evenly distributing semiconductor nanoparticles and generating fluorescence. Some semiconductor nanoparticles have a core-shell structure in which a core (nucleus) is covered with a shell (for example, Patent Documents 1 to 3).

JP 2016-148028 A JP 2016-145328 A JP 2016-135863 A

A main object of the present invention is to obtain semiconductor nanoparticles with excellent long-term stability.

According to a main aspect of the present invention, a plurality of GaInN-containing cores having a particle size of 10 nm or less, and an AlInN-containing shell connecting body covering and interconnecting each of the plurality of cores are provided. Semiconductor nanoparticles are provided.

Semiconductor nanoparticles with excellent long-term stability can be obtained.

FIG. 2 is a cross-sectional view showing semiconductor nanoparticles according to a conventional example; 2a and 2b are cross-sectional views showing semiconductor nanoparticles according to embodiments. FIG. 3a is a graph showing _the relationship between the lattice constant and the energy gap of the ZnOS mixed crystal system, the GaInN mixed crystal system, and the AlInN _mixed crystal system, and _FIG. 4 is a graph showing changes in lattice constant with respect to composition x of an In _x N mixed crystal system and an Al _1-x In _x N mixed crystal system. 4a-4d are cross-sectional views schematically showing semiconductor nanoparticles according to an embodiment during the manufacturing process. 1 is a diagram showing a light source device using semiconductor nanoparticles according to an embodiment;

FIG. 1 is a cross-sectional view showing semiconductor nanoparticles 90 according to a conventional example. A semiconductor nanoparticle 90 comprises a core 92 and a shell 94 covering the core 92 .

CdSe, InP, or the like is used for the core 92, and ZnS, ZnSe, or the like is used for the shell 94, for example. A nitride-based semiconductor material (AlGaInN) or the like may also be used for the core 92 or shell 94 . In general, the grain size of the core 92 is about 2 nm to 5 nm, and the thickness of the shell 94 is 1 nm or less (about two or three atomic layers).

The semiconductor nanoparticles 90, particularly the cores 92, exhibit a quantum size effect, absorb irradiated light, and emit light. Shell 94 constitutes an energy barrier and confines excited carriers within core 92 . Shell 94 also serves to protect core 92 .

When the particle diameter of core 92 is extremely small (for example, 10 nm or less) and the thickness of shell 94 is extremely thin (several atomic layers), the surface state of semiconductor nanoparticles 90 (especially core 92) is generally chemically stable. long-term reliability is reduced. In addition, when the thickness of the shell 94 is increased to stabilize the surface state of the semiconductor nanoparticles 90 (especially the core 92), the optical action (especially the light emission characteristics) by the shell 94 becomes dominant, and the core 92 Optical effects (especially light emission properties) are relatively reduced.

In general, semiconductor nanoparticles preferably have excellent long-term stability. Moreover, depending on the application of the semiconductor nanoparticles, there are cases where it is desired to utilize the optical action mainly due to the core. The present inventors have investigated semiconductor nanoparticles that can solve these problems.

FIG. 2a is a cross-sectional view showing a basic example 10 of a semiconductor nanoparticle according to an embodiment. A semiconductor nanoparticle 10 includes a plurality of core particles 12 made of GaInN and having an extremely small particle size (for example, 10 nm or less), and a matrix 14 made of AlInN containing the plurality of core particles 12 . . Note that the matrix 14 can be regarded as a shell connecting body in which the shells covering the cores 12 are connected to each other.

The compositions of core 12 (GaInN) and matrix 14 (AlInN) are chosen to be mutually lattice-matched. For example, the composition of core 12 is _Ga0.5In0.5N and the composition _{of matrix} 14 is _Al0.4In0.6N . At this time, the lattice constants of core 12 and matrix 14 are approximately 0.337 nm. The matrix 14 is composed of single crystal AlInN.

The grain size of each core 12 is, for example, 4 nm. Note that the particle size of the core does not have to be uniform. For example, cores having a particle size of about 2 nm to 6 nm may be mixed. For the sake of convenience, the core 12 is shown in a spherical shape, but actually the core 12 has a somewhat distorted granular shape.

The particle size of the entire matrix 14 (the entirety of the semiconductor nanoparticles 10) including the core 12 is, for example, about 7 nm to 40 nm. Matrix 14 includes a plurality of cores 12, eg, on the order of 5-1000 cores 12. FIG. For the sake of convenience, the semiconductor nanoparticles 10 are illustrated in a spherical shape, but in reality, the semiconductor nanoparticles 10 have a slightly distorted granular shape.

When a plurality of cores are collectively covered with a matrix (shell linking body), compared to the case where each individual core is covered with a shell (that is, a conventional semiconductor nanoparticle, see FIG. 1), The particle diameter/size of the entire particle can be increased, and the surface state of the semiconductor nanoparticles (or individual cores) becomes chemically more stable. Specifically, by adjusting the size of the entire particle to include at least 5 or more cores, the chemical stability of the particle surface is significantly improved, and the long-term reliability is improved.

If the cores 12 are sparsely distributed in the matrix 14, the optical action of the cores 12 is relatively small, and the optical action of the matrix 14 is dominant. Conversely, when the cores 12 are densely distributed in the matrix 14, the optical effect of the matrix 14 is relatively small and the optical effect of the cores 14 is dominant.

If the optical action of the cores 12 is to be dominant, the distribution of the cores 12 should be dense. Specifically, it is preferable that the cores 12 are spaced from each other by less than twice the Bohr radius (effective Bohr radius) of the material from which they are constructed.

In the material (Ga _1-x In _x N) constituting the core 12, the composition with the largest Bohr radius is InN (x=1 in Ga _1-x In _x N), and the Bohr radius is about 8.2 nm. In other words, if the optical action of the cores 12 is to be dominant, the spacing between the cores 12 should preferably be at least less than 16.4 nm.

FIG. 2b shows a cross-sectional view of a semiconductor nanoparticle variant 10V according to an embodiment. The matrix 14 may be made of polycrystalline AlInN instead of single crystal AlInN.

Moreover, the particle size of the core 12 does not have to be uniform. For example, cores 12 having a particle size of about 2 nm to 6 nm may be mixed.

A method for manufacturing the semiconductor nanoparticles 10 will be described below. A matrix (AlInN) having a relatively large size and grain size (for example, 10 nm or more) containing a plurality of cores can be formed when lattice-matched with the cores (GaInN). If the GaInN (core) and the AlInN (matrix) enclosing them are not lattice-matched, it will be difficult to form large-sized AlInN (matrix). Consequently, it would be difficult to form semiconductor nanoparticles with stable surface conditions.

FIG. 3a is a graph showing the relationship between the lattice constant and the energy gap of the ZnOS mixed crystal system, the GaInN mixed crystal system, and the AlInN mixed crystal system. "Mixed crystal system" is a term that describes a system that includes both end materials and intermediate mixed crystals. The horizontal axis indicates the lattice constant in units of nm (nanometers), and the vertical axis indicates the energy gap in units of eV (electron volts). The energy gap that determines the emission wavelength is ZnO: 3.2 eV, ZnS: 3.8 eV, AlN: 6.2 eV, GaN: 3.4 eV, and InN: 0.64 eV.

When a hexagonal crystal is grown in the c-axis direction, the lattice constant in the a-axis direction is used as the lattice constant in the growth plane. The lattice constants of ZnO and ZnS are 0.324 nm and 0.382 nm along the a-axis, and the lattice constants of AlN, GaN and InN are 0.311 nm, 0.320 nm and 0.355 nm along the a-axis.

For paired compounds, the closest combination of lattice constants is 0.324 nm for ZnO and 0.320 nm for GaN, with a lattice mismatch of more than 1%. Lattice mismatch distorts the crystal lattice and can be a cause of reduced luminous efficiency and reliability.

FIG. 3b schematically shows the change in lattice constant (a-axis direction) with respect to the composition x of the ZnO _x S _1-x mixed crystal system, the Ga _1-x In _x N mixed crystal system, and the Al _1-x In _x N mixed crystal system. is a graphical representation. The horizontal axis indicates the composition x, and the vertical axis indicates the lattice constant. ZnOS and AlGaInN have the same hexagonal wurtzite crystal structure. By forming a mixed crystal, it is possible to adjust the lattice constant between the two end substances, and achieve lattice matching.

Lattice constants, energy gaps, and compositions are in a fixed relationship, and FIG. 3b basically shows the same content as FIG. 3a. Different graphs are used according to the parameters of interest. For example, a lattice-matched composition is a composition with the same vertical axis (lattice constant) in FIG. 3b. A preferred lattice matching range would be within 1.0% difference in lattice constants with the smaller lattice constant as the reference (100%).

The range in which ZnO _x S _1-x and Ga _1-x In _x N and Al _1-x In _x N can be lattice-matched is indicated by a solid line. Ga1 _{- xInxN} (0.15≤x≤1.00), Al1 _{- yInyN} (0.3≤y≤1.0), _{ZnOzS1 -z} (0.47≤z ≤1.00), lattice matching between ZnOS and GaInN and AlInN is possible.

When ZnOS is used as a base crystal and lattice-matched AlGaInN is grown thereon, strain at the interface can be reduced. By reducing the strain, crystal defects could be prevented and good quality semiconductor nanoparticles could be achieved.

Highly reliable semiconductor nanoparticles can be manufactured by forming base material (substrate) particles using ZnOS, which is easy to manufacture, and then heteroepitaxially growing lattice-matched AlGaInN crystals thereon. Furthermore, it is also possible to layer-grow other AlGaInN crystals thereon.

In the case of forming semiconductor nanoparticles composed of Ga _1-x In _x N and Al _{1-x In x} N, Ga _1-x In x N and Al _1-x In _x N can be lattice-matched. The range is indicated by a dashed line. In the composition range of Ga _1-x In _x N (0.00≦x≦1.00) and Al _1-y In _y N (0.18≦y≦1.00), the lattice matching between GaInN and AlInN is It is possible.

An example of a method for producing semiconductor nanoparticles according to an embodiment will now be described with reference to FIGS. 4a-4d. Although one semiconductor nanoparticle (or core) is shown, many semiconductor nanoparticles (or cores) are produced simultaneously according to the liquid phase synthesis described below. It should be noted that the semiconductor nanoparticles (especially matrices) according to the examples can also be produced by vapor phase synthesis.

The semiconductor nanoparticles according to the embodiment are produced by the steps of forming a substrate particle (ZnOS) for growing a core (GaInN) (Fig. 4a), growing the core on the surface of the substrate particle (Fig. 4b), It is produced by removing the particles (Fig. 4c) and forming a matrix (AlInN) containing the core (Fig. 4d). The semiconductor nanoparticles may be produced by a method of directly synthesizing the core (or matrix) without using the base particles.

First, substrate particles 18 are synthesized as shown in FIG. 4a. In an embodiment, the substrate particles 18 are made of wurtzite-type ZnO _0.78 S _0.22 and have a distorted block shape. Also, the average particle diameter of the substrate particles 18 is about 4 nm, and the lattice constant is about 0.337 nm.

Zinc acetate (2.0 mmol) and sulfur (0.4 mmol) were added to and mixed with oleylamine (10 mL) as a reaction solvent, and the mixed solution was maintained at a temperature of 130° C. for 1 hour under a nitrogen atmosphere. A temperature of 250° C. is maintained for 1 hour. Thereby, the substrate particles 18 are synthesized. Thereafter, centrifugal separation (4000 rpm, 10 minutes) alternately using toluene for dispersing the base particles and ethanol for removing unnecessary raw materials from the base particles is repeated to purify the base particles.

Next, core particles 12 are grown on the surfaces of substrate particles 18, as shown in FIG. 4b. The composition of the core particles 12 is wurtzite-type Ga _0.5 In _0.5 N, the average particle size is about 2.0 nm, and the lattice constant is about 0.337 nm.

GaI ₃ (0.2 mmol), InI ₃ (0.2 mmol), NaNH ₂ (2.0 mmol) and substrate particles (10 mg) were added to benzene (6 mL) as a reaction solvent and mixed, and the mixed solution was A temperature of 300° C. is maintained for 1 hour. As a result, core particles 12 made of GaInN grow. After that, a centrifugal separation process using alternately toluene for dispersing the particles consisting of the substrate and the core and ethanol for removing unnecessary raw materials from the particles is repeated to purify the particles.

Next, as shown in FIG. 4c, the substrate 18 is removed from the particle body composed of the substrate 18 and the core 12, leaving the core 12. As shown in FIG. The substrate can be removed by wet etching. As the etchant, diluted hydrochloric acid having a compounding ratio of hydrochloric acid (36% by volume):pure water=1:100 can be used.

A matrix 14 containing a plurality of cores 12 is then formed, as shown in FIG. 4d. The matrix 14 has a composition of Al _0.4 In _0.6 N and a lattice constant of 0.337 nm. The overall size (particle diameter) of the matrix 14 containing the cores 12 is approximately 10 nm to 30 nm, and the matrix 14 contains approximately 10 to 1000 cores 12, for example.

AlI ₃ (0.14 mmol), InI ₃ (0.2 mmol), NaNH ₂ (2.0 mmol) and core particles (30 mg) are put into and mixed with benzene (6 mL) as a reaction solvent. After that, the mixed solution is heated to a temperature of 375° C. at a heating rate of 30° C./min, and the temperature is maintained for 1 hour. Thereby, the matrix 14 made of single crystal AlInN is synthesized. After that, centrifugal separation using alternately toluene for dispersing the semiconductor nanoparticles 10 composed of the cores 12 and the matrix 14 and ethanol for removing unnecessary raw materials from the semiconductor nanoparticles is repeated to purify the semiconductor nanoparticles. do.

The density of the cores (the number of cores contained per semiconductor nanoparticle) can be controlled by adjusting the amount of core particles to be added and the heating rate for synthesizing the matrix. Further, by increasing the temperature elevation rate for synthesizing the matrix, it is possible to synthesize a matrix made of polycrystalline AlInN. In addition, by adjusting the temperature rise rate for synthesizing the matrix, the matrix growth/synthesis process and the state and quality after growth/synthesis can be changed.

As described above, the semiconductor nanoparticles 10 are manufactured. The grain size of the cores does not have to be uniform. For example, cores having a grain size of about 2 nm to 6 nm may be mixed. Cores with different particle sizes (wide particle size distribution) can be formed, for example, by preparing substrate particles with different particle sizes (wide particle size distribution) and growing cores on the surfaces thereof. Substrate particles with different particle diameters (wide particle diameter distribution) can be produced by adjusting synthesis conditions of the substrate particles (growth temperature/time, temperature increase rate, etc.). Cores with different particle sizes (wide particle size distribution) can also be formed by adjusting core synthesis conditions (growth temperature/time, temperature increase rate, etc.).

FIG. 5 is a diagram showing a light source device 20 using semiconductor nanoparticles. The light source device 20 mainly includes an LED light source 22 and a wavelength conversion film 24 containing semiconductor nanoparticles 10 as a wavelength conversion material (phosphor).

A semiconductor light-emitting element containing a nitride semiconductor, for example, is used for the LED light source 22 and emits blue light. The wavelength conversion film 24 has, for example, a structure in which the semiconductor nanoparticles 10 are uniformly dispersed in a translucent resin film. Semiconductor nanoparticles 10 absorb blue light emitted from light source 22 and emit, for example, green light or red light.

In general, in a system in which particles are dispersed in a base material, increasing the size and particle size of the particles increases the light scattering property and lengthens the optical path length of the dispersion system.

In the wavelength conversion film 24, when semiconductor nanoparticles having a large size and particle size, for example, semiconductor nanoparticles 10 having a particle size of 30 nm or more are used, the optical path length of the wavelength conversion film is significantly increased. As a result, the ratio (wavelength conversion efficiency) of the intensity of wavelength-converted light (green light or red light) to the intensity of incident light (blue light) is relatively high.

When the semiconductor nanoparticles according to the embodiments having relatively high wavelength conversion efficiency are used, the content of the semiconductor nanoparticles is reduced compared to the case of using semiconductor nanoparticles having a small size and particle size (for example, the semiconductor nanoparticles according to the conventional example). A relatively small wavelength conversion film or a wavelength conversion film having a relatively thin thickness can be realized.

Although the present invention has been described along with the examples, the present invention is not limited to these. The range of lattice matching shown in the examples is an example, and the layer structure can be freely selected by adjusting the composition so as to achieve lattice matching. In addition, various members and materials may be appropriately changed according to the production conditions, the application of the semiconductor nanoparticles, and the like. It will be obvious to those skilled in the art that various other changes, improvements, combinations, etc. are possible.

DESCRIPTION OF SYMBOLS 10... Semiconductor nanoparticle (Example), 12... Core (core particle), 14... Shell connection body (matrix), 18... Base particle, 20... Light source device, 22... LED light source, 24... Wavelength conversion film, 90 ... semiconductor nanoparticles (conventional example), 92 ... core, 94 ... shell.

Claims (4)

a plurality of cores containing GaInN having a particle size of 10 nm or less;
In the plurality of cores and the shell link, the difference between the lattice constants of GaInN forming the plurality of cores and AlInN forming the shell link is the smaller one as a reference (100%). Lattice matched within 1.0%,
The plurality of cores are dispersed within a range narrower than twice the Bohr radius from each other.
semiconductor nanoparticles. 2. The semiconductor nanoparticle according to claim 1, wherein five or more of the plurality of cores are included in the shell linking body. The composition of each of the plurality of cores is Ga _1-x In _x N (0.00≦x≦1.00), and the composition of the shell linker is Al _1-y In _y N (0.18≦y≦ 1.00), the semiconductor nanoparticles according to claim 1 or 2. a translucent resin member;
A semiconductor nanoparticle according to any one of claims 1 to 3;
A wavelength conversion member having

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