JP2007103513A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device comprising a light emitting element, and a wavelength conversion layer having a phosphor and capable of emitting light with high efficiency. <P>SOLUTION: The light emitting device comprises a light emitting element 3 formed on a substrate 2 and emitting excitation light having a peak wavelength in a range exceeding 450 nm, and a wavelength conversion layer 4 formed to cover the light emitting element and converting the excitation light into visible light, and outputs a part of the excitation light together with the visible light wherein the wavelength conversion layer 4 contains semiconductor ultrafine particles 5 having mean particle size of 10 nm or less. On the surface of semiconductor ultrafine particle 5, a compound consisting of a repetition structure of silicon-oxygen having the number of bonding units of 5-500 is preferably coordinated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  INDUSTRIAL APPLICABILITY The present invention is suitably used for a light-emitting device that converts the wavelength of light emitted from a light-emitting element such as an LED (Light Emitting Diode) and extracts it to the outside, in particular, a backlight power source for an electronic display, a fluorescent lamp, and the like. The present invention relates to a light emitting device.

  A light emitting element made of a semiconductor material (hereinafter sometimes referred to as “LED chip”) is small in size, has high power efficiency, and vividly develops color. LED chips have excellent characteristics such as long product life, strong on / off lighting repeatability, and low power consumption, so they are expected to be applied to backlight sources such as liquid crystals and lighting sources such as fluorescent lamps. Has been.

  The application of the LED chip to the light emitting device is that the wavelength of part of the light of the LED chip is converted with a phosphor, and the wavelength-converted light and the light of the LED that is not wavelength-converted are mixed and emitted, thereby It has already been manufactured as a light emitting device that emits a color different from that of light.

Specifically, in order to emit white light, a light emitting device in which a wavelength conversion layer containing a phosphor is provided on the surface of an LED chip has been proposed. For example, in a light emitting device in which a wavelength conversion layer containing a YAG phosphor expressed by a composition formula of (Y, Gd) ₃ (Al, Ga) ₅ O ₁₂ is formed on a blue LED chip using an nGaN-based material, Since blue light is emitted from the LED chip and a part of the blue light is changed to yellow light in the wavelength conversion layer, a light emitting device in which blue and yellow light are mixed and white is proposed (see Patent Document 1). ).

  An example of such a light emitting device is shown in FIG. 4, the light-emitting device includes a substrate 102 on which an electrode 101 is formed, a light-emitting element 103 including a semiconductor material that emits light having a central wavelength of 470 nm on the substrate 102, and a light-emitting element 103 on the substrate 102. The wavelength conversion layer 104 is provided so as to cover it, and the wavelength conversion layer 104 contains the phosphor 105.

  In this light emitting device, when the phosphor 105 is irradiated with light emitted from the light emitting element 103, the phosphor 105 is excited to emit visible light, and this visible light is used as an output. However, the light emitting device having the above configuration has the following problems because it is affected by the shape and dispersion state of the phosphor 105 particles contained in the matrix in the wavelength conversion layer 104.

  Since the average particle diameter of conventional phosphor 105 particles is several μm or more, excitation light and visible light converted by the phosphor are absorbed and scattered by the phosphor 105 particles. When such absorption and scattering are received, the entire phosphor 105 particles are not irradiated with the excitation light, so that there is a problem that the use efficiency of the excitation light is reduced and the light emission efficiency is lowered.

Thus, the conventional light emitting device has a problem that a light emitting device that emits light with high efficiency cannot be obtained.
JP 11-261114 A

  An object of the present invention is to provide a light-emitting device that includes a light-emitting element and a wavelength conversion layer having a phosphor and can emit light with high efficiency.

  The present inventor has found that if semiconductor ultrafine particles having a specific particle diameter are used, non-uniform dispersion of the phosphor due to the precipitation of the phosphor particles can be suppressed and highly efficient light emission can be performed. The invention has been completed.

That is, the light emitting device of the present invention has the following configuration.
(1) A light emitting element that emits excitation light having a peak wavelength in a range exceeding 450 nm and a wavelength conversion layer that is formed so as to cover the light emitting element and converts the excitation light into visible light are provided on a substrate. A light-emitting device that outputs both of the excitation light and the visible light, wherein the wavelength conversion layer includes semiconductor ultrafine particles having an average particle diameter of 10 nm or less.
(2) The light-emitting device according to (1), wherein the surface of the semiconductor ultrafine particles is coordinated with a compound having a repeating unit structure of silicon-oxygen having 5 to 500 bonding units.
(3) The light-emitting device according to (1) or (2), wherein the semiconductor ultrafine particles absorb the excitation light and emit visible light having a wavelength of 520 nm to 700 nm.
(4) A semiconductor composition in which the semiconductor ultrafine particles are composed of at least two kinds of elements belonging to Group Ib, Group II, Group III, Group IV, Group V, and Group VI of the Periodic Table The light-emitting device according to any one of (1) to (3), wherein
(5) The light emitting device according to any one of (1) to (4), wherein the semiconductor ultrafine particles include two or more kinds of particles having different average particle diameters in a wavelength conversion layer.
(6) The light emitting device according to any one of (1) to (5), wherein the wavelength conversion layer includes a plurality of layers including semiconductor ultrafine particles.
(7) The light emitting device according to any one of (1) to (6), wherein a reflection member that emits light emitted from the light emitting element forward is provided around the light emitting element.

  According to (1) above, by containing semiconductor ultrafine particles having an average particle diameter of 10 nm or less in the wavelength conversion layer, non-uniform dispersion caused by sedimentation of the phosphor particles is suppressed, and highly efficient light emission is achieved. Obtainable.

  According to the above (2), the dispersibility of the semiconductor ultrafine particles with respect to the polymer resin, in particular, the silicone-based polymer resin is improved, so that a highly efficient light-emitting device can be easily obtained, and the light resistance and heat resistance. A light emitting device having excellent transparency can be obtained.

  According to the above (3), emission of light (white light) that expresses a broad spectrum and has excellent color rendering properties by synthesizing a part of excitation light and visible light of 520 nm to 700 nm converted by semiconductor ultrafine particles. can get.

  According to (4) above, if the average particle diameter of the particles composed of the semiconductor composition is 10 nm or less, the fluorescence quantum efficiency can be drastically improved due to the quantum confinement effect.

According to the above (5), by using a mixture of two or more kinds of particles having different average particle diameters, the wavelength from yellow to red can be covered, and excellent color rendering can be realized.
According to the above (6), a self-absorption between semiconductor ultrafine particles having different average particle diameters can be suppressed, and a light emitting device with excellent luminous efficiency can be obtained.
According to the above (7), the light emission efficiency can be improved by emitting the light from the light emitting element that has been emitted in the lateral direction or the substrate side to the front surface.

  The light emitting device of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an embodiment of a light emitting device of the present invention. According to FIG. 1, the light emitting device of the present invention is formed so as to cover the light emitting element 3 on the substrate 2, the light emitting element 3 provided on the substrate 2, the substrate 2 on which the electrode 1 is formed. And includes a wavelength conversion layer 4 that converts excitation light into visible light and a reflecting member 6 that reflects light, and outputs a part of the excitation light and visible light together to produce white light. Is output.

  The electrode 1 has a function as a conductive path for electrically connecting the light emitting element 3 and is connected to the light emitting element 3 with a conductive bonding material. As the electrode 1, for example, a metallized layer containing a metal powder can be used. This electrical connection pattern is formed by forming a lead terminal such as an Fe-Ni-Co alloy on the substrate 2 by forming a metallized layer of metal powder such as W, Mo, Cu, or Ag on the surface or inside of the substrate 2, for example. It is provided by burying or by fitting an input / output terminal made of an insulator on which a wiring conductor is formed into a through hole provided in the substrate 2. It should be noted that a metal having excellent corrosion resistance such as Ni or gold (Au) is preferably deposited on the exposed surface of the pattern for electrical connection in a thickness of about 1 to 20 μm. Can be effectively prevented, and the connection between the light emitting element 5 and the electrical connection pattern can be strengthened. Therefore, for example, an Ni plating layer having a thickness of about 1 to 10 μm and an Au plating layer having a thickness of about 0.1 to 3 μm are sequentially coated on the exposed surface of the electrical connection pattern by an electrolytic plating method or an electroless plating method. More preferably it is worn.

  As the substrate 2, a substrate having excellent thermal conductivity and a large total reflectance is used. As the substrate 2, for example, a polymer resin in which metal oxide fine particles are dispersed in addition to a ceramic material such as alumina and aluminum nitride is preferably used.

  As the light-emitting element 3, an element that emits excitation light having a peak wavelength exceeding 450 nm, preferably in a wavelength range of 450 nm to 470 nm can be used. The structure of the light-emitting element 3 is not particularly limited, and any known GaN-based light-emitting element may be used, but one that can obtain a higher output with the same current is preferable. Note that the structure of the light-emitting element 3 suitable for the present invention will be described later. Examples of the semiconductor material include various semiconductors such as ZnSe and nitride semiconductor (GaN, etc.), but the type of the semiconductor material is not particularly limited as long as the emission wavelength is in the above wavelength range. A stacked structure having a light emitting layer made of a semiconductor material may be formed on the light emitting element substrate 7 by crystal growth methods such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy using these semiconductor materials.

The light emitting element substrate 7 can be selected in consideration of the combination with the light emitting layer. For example, when a light emitting layer made of a nitride semiconductor is formed on the surface, sapphire, spinel, silicon carbide (SiC), silicon (Si), It can be composed of zinc oxide (ZnO), zirconium diboride (ZrB ₂ ), gallium nitride (GaN), quartz, ceramic material, polymer resin, and the like. In the present invention, it is preferable to select the material of the light emitting element substrate 7 in consideration of the combination with the light emitting layer of the light emitting element 3. For example, when forming a light emitting layer made of a nitride semiconductor on the surface, alumina, spinel, SiC Materials such as Si, ZnO, ZrB ₂ , GaN, and quartz are preferably used. In order to form a nitride semiconductor with good crystallinity with high productivity, it is preferable to use sapphire as the light emitting element substrate 7.

  The wavelength conversion layer 4 contains semiconductor ultrafine particles 5 having an average particle diameter of 10 nm or less, preferably 2 nm to 5 nm. If such semiconductor ultrafine particles 5 (phosphor particles) are used, light scattering in the wavelength conversion layer 4 is reduced, so that the entire semiconductor ultrafine particles 5 are easily irradiated with excitation light, and the use efficiency of excitation light is improved. Thus, the luminous efficiency is improved. Furthermore, since the semiconductor ultrafine particles 5 can be uniformly dispersed in the wavelength conversion layer 4, the occurrence of light scattering by the semiconductor ultrafine particles 5 can be suppressed, and the occurrence of light emission variation can be suppressed, so that uniform light emission can be obtained. .

  The thickness of the wavelength conversion layer 4 is preferably 0.1 to 5 mm, particularly preferably 0.5 to 1 mm. Within this range, the excitation light emitted from the light emitting element 3 can be converted into output light with high efficiency, and the converted output light can be transmitted to the outside with high efficiency.

  In the present invention, it is preferable to use, as the semiconductor ultrafine particles 5, fine particles that absorb excitation light having a peak wavelength exceeding 450 nm and emit visible light of 520 nm to 700 nm. If such semiconductor ultrafine particles 5 are used, by synthesizing a part of excitation light and visible light of 520 nm to 700 nm converted by the semiconductor ultrafine particles, a wide spectrum is expressed and an excellent color rendering property is obtained. A light emitting device can be obtained. In the light emitting device shown in FIG. 1, as the semiconductor ultrafine particles 5, the yellow phosphor 5a that absorbs excitation light of 430 to 500 nm and emits fluorescence of 540 nm to 600 nm and the excitation light of 430 to 500 nm are absorbed and 590 nm to 700 nm. And a red phosphor 5b that emits the above fluorescence.

  As the semiconductor ultrafine particles 5, it is preferable to use two or more kinds of particles having different average particle diameters. Compared to the case where only semiconductor ultrafine particles having the same particle diameter are used, if a mixture of two or more types of semiconductor ultrafine particles having different average particle diameters is used, for example, by covering the wavelength from yellow to red region, the longer wavelength side Therefore, excellent color rendering properties can be realized. For example, the light emitting device shown in FIG. 1 contains two types of yellow phosphor 5a and red phosphor 5b.

The semiconductor ultrafine particles 5 contained in the wavelength conversion layer 4 are not particularly limited as long as the average particle diameter is 10 nm or less, preferably 2 nm to 5 nm, but for example, the periodic table Tables Ib and II It is preferably a semiconductor ultrafine particle composed of at least two kinds of elements belonging to Group III, Group III, Group IV, Group V, and Group VI. For example, III-V group compound semiconductors such as BN, BP, BAs, AlN, AlP, AlSb, GaN, GaP, GaSb, InN, InP, and InSb, II-VI group compound semiconductors such as CdSe, ZnO, and ZnS, CuInS ₂ CuGaS ₂ , CuAlS ₂ , Cu (In _1-x Al _x ) S ₂ (0 ≦ x ≦ 1), CuInS ₂ , CuIn _x Ga _1-x S ₂ (0 ≦ x ≦ 1), AgInS ₂ , AgGaS ₂ AgAlS ₂ , Ag (In _1-x Al _x ) S ₂ , AgInS ₂ , Ag (In _1-x Ga _x ) S ₂ , ZnAgInS ₂ (0 ≦ x ≦ 1), ZnCuInS _{2 and the} like are preferably used.

Of the above semiconductors, the yellow phosphor 5a includes CdSe (average particle diameter of 2.0 to 3.5 nm, preferably 3.0 nm), CuInS ₂ (average particle diameter of 2.0 to 5.0 nm, preferably 4.0 nm), ZnCuInS ₂ (average particle size of 2.0 to 5.0 nm, preferably 3.5 nm), and ZnAgInS ₂ (average particle size of 2.0 to 4.0 nm, preferably 3.0 nm) are used. Good. Of these, ZnCuInS ₂ is most preferred.

Among the above semiconductors, as the red phosphor 5b, CdSe (average particle size 3.0 to 5.0 nm, preferably 4.0 nm), CuInS ₂ (average particle size 3.0 to 6.0 nm, preferably 5.0 nm), ZnCuInS ₂ (average particle size 3.0 to 6.0 nm, preferably 4.5 nm), and ZnAgInS ₂ (average particle size 3.0 to 5.0 nm, preferably 4.0 nm) are used. Good. Of these, ZnCuInS ₂ is most preferred.
The average particle diameter can be measured using a method in which the average particle diameter of the semiconductor ultrafine particles (yellow phosphor 5a, red phosphor 5b) is measured in Examples described later.

  In the light emitting device of the present invention, it is preferable to use, as the semiconductor ultrafine particles 5, fine particles in which a compound having a repeating unit structure of silicon-oxygen having 5 to 500 bond units is coordinated on the surface. For example, in the case of semiconductor ultrafine particles in which triphenylphosphine oxide, a long-chain hydrocarbon-based amine, or a long-chain hydrocarbon-based carboxylic acid is coordinated on the surface, dispersion into the polymer resin may be insufficient. On the other hand, the semiconductor ultrafine particles in which the compound having a number of bond units of 5 to 500 and having a repeating structure of silicon-oxygen is coordinated on the surface is a polymer resin, particularly a silicone-based resin having excellent light resistance and heat resistance. High dispersibility in polymer resin. By using such highly dispersible semiconductor ultrafine particles, dispersion of the ultrafine semiconductor particles 5 in the wavelength conversion layer 4 into a polymer resin (for example, a resin excellent in light resistance and heat resistance such as a silicone-based polymer resin). Can be improved. Moreover, the light resistance, heat resistance, and transparency of the wavelength conversion layer 4 can be improved by using such a resin excellent in light resistance and heat resistance and the above-described highly dispersible semiconductor ultrafine particles. As a result, a light emitting device having excellent light resistance, heat resistance, and transparency can be obtained.

  In order to fabricate the semiconductor ultrafine particles 5 in which a compound having a bond unit number of 5 to 500 and a silicon-oxygen repeating structure is coordinated on the surface, for example, silicon that can be coordinated to the semiconductor ultrafine particles A process of mixing a compound having a repeating structure of two or more oxygen bonds and stirring while heating may be mentioned.

  The semiconductor ultrafine particles 5 preferably have a band gap energy of a compound semiconductor in a bulk state of a semiconductor composition constituting the semiconductor fine particles 5 in a range of 1.5 to 2.5 eV at a temperature of 300K.

  The semiconductor ultrafine particles 5 in the present invention may have a so-called core-shell structure composed of an inner core (core) and an outer shell (shell). The core-shell type semiconductor nanoparticles may be suitable for applications using an exciton absorption / emission band. In this case, it is generally effective to form an energy barrier by using a shell semiconductor particle having a forbidden band width (band gap) larger than that of the core. This is presumed to be due to a mechanism that suppresses the influence of an undesirable surface level or the like due to the influence of the outside world or crystal lattice defects on the crystal surface.

  The composition of the semiconductor material suitably used for the shell depends on the band gap of the core semiconductor crystal, but the band gap in the bulk state is 2.5 eV or more at a temperature of 300 K, such as BN, BAs, GaN, GaP, etc. III-V group compound semiconductors, II-VI group compound semiconductors such as ZnO and ZnS, and compounds of Group 2 elements of the periodic table and Group 16 elements of the periodic table such as MgS and MgSe are preferably used.

  Moreover, the semiconductor ultrafine particles 5 in the present invention may be covered with surface modifying molecules made of organic ligands. By covering the surface modification molecules, aggregation of the semiconductor ultrafine particles can be suppressed, and the function of the semiconductor ultrafine particles can be expressed to the maximum. Surface modifying molecules are n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, octyl, decyl, dodecyl, hexadecyl, octadecyl Examples thereof include molecules having a hydrocarbon group containing an aromatic hydrocarbon group such as an alkyl group having about 3 to 20 carbon atoms such as a group, a phenyl group, a benzyl group, a naphthyl group, and a naphthylmethyl group, among which n-hexyl A molecule having a linear alkyl group having about 6 to 16 carbon atoms, such as a group, an octyl group, a decyl group, a dodecyl group, a hexadecyl group, is more preferable. Also, sulfur atom-containing functional groups such as mercapto group, disulfide group, thiophene ring, nitrogen atom-containing functional groups such as amino group, pyridine ring, amide bond, nitrile group, carboxyl group, sulfonic acid group, phosphonic acid group, phosphinic acid Using molecules having acidic functional groups such as groups, phosphorus atom-containing functional groups such as phosphine groups and phosphine oxide groups, or oxygen atom-containing functional groups such as hydroxyl groups, carbonyl groups, ester bonds, ether bonds, polyethylene glycol chains, etc. Also good.

  The semiconductor ultrafine particles 5 in the present invention are manufactured by a general manufacturing method. Gas phase chemical reaction methods such as flame process, plasma process, electric heating process, laser process, physical cooling method, sol-gel method, alkoxide method, coprecipitation method, hot soap method, hydrothermal synthesis method, spray pyrolysis method, etc. A phase method, a mechanochemical bonding method, a microreactor method, a microwave heating method, and the like are used.

  In order to produce the wavelength conversion layer 4, first, the yellow phosphor 5a and the red phosphor 5b are mixed with an uncured matrix resin. As the matrix resin, for example, an epoxy resin, a polycarbonate resin, an acrylic resin, or a polymer resin (silicone resin or the like) mainly composed of a silicon-oxygen bond is preferable in terms of transmittance.

  In particular, a polymer resin mainly composed of a silicon-oxygen bond has an excellent heat resistance and light resistance because it has a very large silicon-oxygen bond energy and does not deteriorate by absorbing light at around 400 nm. . As a result, by dispersing and mixing phosphors in a polymer resin mainly composed of silicon-oxygen bonds, the light conversion, heat resistance and transparency of the wavelength conversion layer can be improved, and the long life of the light emitting device is ensured. can do. Therefore, a silicone resin is most preferable because it has both transmittance and heat resistance. In addition, it is desirable to use a dispersant that is chemically coupled to the matrix resin in terms of stability after curing.

  Next, a mixture of the yellow phosphor 5a, the red phosphor 5b and the uncured matrix resin is formed into a sheet shape. Examples of the molding method include a molding method capable of forming a sheet such as a doctor blade method, a die coater method, an extrusion method, a spin coating method, a dip method, and in particular, if a doctor blade method or a die coater method is used, productivity Can be improved. In order to uniformly disperse the yellow phosphor 5a and the red phosphor 5b in the sheet, it is preferable to optimize the manufacturing conditions. For example, a dimethyl silicone resin is used as the matrix resin, and the yellow phosphor 5a and the red phosphor It is preferable to mix the body 5b in the resin, set the viscosity of the matrix resin to 1 to 5 Pa · s, set the curing temperature of the matrix resin to 130 to 170 ° C., and leave it for 1 to 5 hours.

  The addition amount when the yellow phosphor 5a and the red phosphor 5b are added to the resin may be determined in consideration of the light emission intensity of the light emitting element, the size of the light emitting element, and the film thickness of the wavelength conversion layer 4. It is preferable to add 1 to 10% by weight of the yellow phosphor 5a and 1 to 10% by weight of the red phosphor 5b with respect to the total amount of the wavelength conversion layer 4.

  The reflecting member 6 is provided around the light emitting element, specifically around the light emitting element 3 and the wavelength conversion layer 4, and reflects light escaping to the side surface and the substrate 2 side to the front to increase the intensity of the output light. Can be increased. Examples of the material of the reflecting member 6 include aluminum (Al), nickel (Ni), silver (Ag), chromium (Cr), titanium (Ti), copper (Cu), gold (Au), iron (Fe), and these. These laminated structures and alloys, ceramics such as alumina ceramics, or resins such as epoxy resins can be used.

  FIG. 2 is a diagram showing another embodiment of the light emitting device according to the present invention, and is a schematic cross-sectional view of a light emitting device having a wavelength conversion layer 40 having a two-layer structure. In FIG. 2, the same members as those of the light emitting device shown in FIG. 1 are denoted by the same reference numerals as those in FIG.

  In the light emitting device shown in FIG. 2, the wavelength conversion layer 40 has a plurality of layers (sheet structure) of a first conversion layer 41 and a second conversion layer 42, and the conversion layer 42 is a surface of the light emitting element 3. In addition, the conversion layer 41 is laminated on the surface of the conversion layer 42.

  When semiconductor ultrafine particles 5 having different average particle diameters are dispersed and mixed in the same layer, absorption between the semiconductor ultrafine particles 5 may occur, and conversion efficiency (quantum yield) may be reduced. On the other hand, as shown in FIG. 2, the wavelength conversion layer 40 has a structure composed of a plurality of conversion layers such as a two-layer structure, for example, a sheet shape and a structure of a plurality of layers, and different types of semiconductor ultrafine particles for each layer. If the structure containing 5 is used, self-absorption between the semiconductor ultrafine particles 5 can be suppressed, so that a light-emitting device with excellent light emission efficiency can be obtained. In the light emitting device shown in FIG. 2, the conversion layer 41 contains a yellow phosphor 5a, and the conversion layer 42 contains a red phosphor 5b.

  The wavelength conversion layer 40 preferably has a thickness of 0.1 to 5 mm, the conversion layer 41 has a thickness of 0.05 to 3 mm, and the conversion layer 42 has a thickness of 0.05 to 3 mm. Within this range, the excitation light emitted from the light emitting element 3 can be converted into output light with high efficiency, and the converted output light can be transmitted to the outside with high efficiency.

  FIG. 3 is an example of a light-emitting element 3 that is preferably used in the present invention, and shows an element structure of a GaN-based LED. On the light emitting element substrate 7 which is a crystal substrate such as a sapphire substrate, an n-type contact layer 31 and a light emitting part 35 (n-type clad layer 32 / MQW light emitting layer (details) are arranged in order via a GaN-based low temperature growth buffer layer 30. 33 / p-type cladding layer 34) and p-type contact layer (which may be a multi-layer structure, but not shown in detail) 36 are stacked by vapor phase growth. Each contact layer is provided with an n electrode and a p electrode (not shown).

  In FIG. 3, the light emitting element substrate 7 is drawn on the lower side for the sake of explanation. However, the mounting (so-called flip) is performed with the p electrode facing the mounting substrate side and directly connected to the circuit so that the light emitting element substrate 7 faces upward. It may be configured to perform chip mounting, extract light from the back surface of the substrate, and irradiate the phosphor with the light.

  In the example of FIG. 3, irregularities 37 are processed on the upper surface (surface on which the GaN-based crystal layer grows) of the light emitting element substrate 7 as a preferred embodiment. The unevenness 37 reduces the dislocation density of the GaN-based crystal layer and further increases the light emission efficiency in the light emitting portion 35 (improves internal quantum efficiency). Further, the irregularities 37 do not keep the light generated in the element confined but show more action to the outside (improvement of external quantum efficiency). Combined with these actions, a high-power GaN-based LED can be obtained. In the case of such an element structure, from the viewpoint of extracting more light to the outside through the surface of the irregularities 37, the above-described element for flip chip mounting is a preferable aspect.

  For the light-emitting element substrate 7, the buffer layer 30, the crystal growth technique on the light-emitting element substrate 7, the structure of the light-emitting element 3, and the mounting technique for constituting the GaN-based light-emitting element, a conventionally known technique may be referred to. .

[Examples 1 to 4]
The light emitting device of FIG. 1 was produced. First, a light emitting element 3 made of a nitride semiconductor was formed on a light emitting element substrate made of sapphire by a metal organic vapor phase epitaxy method. The structure of the light-emitting element 3 includes an n-type GaN layer that is an undoped nitride semiconductor on a light-emitting element substrate, a GaN layer that is formed with an Si-doped n-type electrode and serves as an n-type contact layer, and an undoped nitride semiconductor. A n-type GaN layer, a GaN layer that forms the next light emitting layer, an InGaN layer that forms the well layer, and a GaN layer that forms the barrier layer as a set of five InGaN layers sandwiched between the GaN layers A multi-quantum well structure was obtained.

  The light-emitting element 3 is mounted by a flip-chip mounting method in a package that forms an insulating substrate on which a wiring pattern for arranging near-ultraviolet LEDs is formed and a frame-shaped reflecting member surrounding the near-ultraviolet LEDs. . The light emitting element 3 was mounted on the wiring pattern in the package via an Ag paste.

Subsequently, the package was filled with a silicone resin to cover the light emitting element 3, and the resin was further cured by heating to form an inner layer. The silicone resin was filled by a coating method using a dispenser.
Semiconductor ultrafine particles (yellow phosphor 5a, red phosphor 5b) were synthesized by a hot soap method. The semiconductor ultrafine particles having different emission wavelengths were synthesized by changing the reaction time, reaction temperature, and post-treatment method.
The average particle diameter of the semiconductor ultrafine particles (yellow phosphor 5a, red phosphor 5b) obtained by the above method was measured using a transmission electron microscope (TEM). The transmission electron microscope used was JEOL JEM2010F, and an acceleration voltage of 200 kV was observed according to the following procedure. The semiconductor ultrafine particles obtained above were placed in a sample bottle, and IPA or toluene in an amount such that the particle concentration was in the range of 0.002 to 0.02 mol / liter was added and dispersed. This was scooped with a TEM observation microgrid, dried, and then set on a transmission electron microscope. The average particle diameter was measured by confirming the particles from the lattice image. First, the part where the particles adhered to the mesh was searched at a low magnification. At this time, the portion where a lot of ultrafine semiconductor particles are attached is not suitable for measuring the average particle diameter because the particles overlap in the direction of the electron beam. Also, the semiconductor ultrafine particles adhering to the Cu mesh part of the microgrid are not suitable for observation of the average particle diameter because the lattice image cannot be observed. Therefore, the semiconductor ultrafine particles for measuring the average particle diameter were selected by selecting a portion having as little overlap as possible in the resin portion of the microgrid. Next, this portion is enlarged to about 1,000,000 times to confirm the lattice image.
At this time, if a large amount of organic components used in the synthesis remain around the semiconductor ultrafine particles, the lattice image is blurred, so that the average particle diameter cannot be measured correctly. In such a case, observation was performed by changing the location, or in some cases, a sample was prepared by repeatedly removing organic components during synthesis, and observation was performed.
Removal of organic components during synthesis is achieved by adding chloroform, toluene, or hexane to the precipitated semiconductor ultrafine particles and dispersing with ultrasound, then adding alcohol (for example, ethanol) to this and centrifuging it. Can be done. Organic components at the time of synthesis are dissolved in the supernatant ethanol, and the semiconductor ultrafine particles are precipitated. This operation was repeated as necessary. Thus, after searching for semiconductor ultrafine particles with less organic component adhesion used during synthesis, a lattice image was photographed at a magnification of 4,000,000. At this time, if the electron beam was kept on for a long time, the semiconductor ultrafine particles moved, and thus the image was taken promptly.
The average particle diameter of the semiconductor ultrafine particles was determined by processing according to the following method based on the diameter of 200 photographed lattice images.
A length average diameter was calculated by creating a histogram and statistically processing the diameter of the measured lattice image. The length average diameter was calculated by counting the number belonging to the diameter section and dividing the sum of the product of the center value and the number of the diameter section by the total number of measured grid images (average Particle shape and calculation formula, “Ceramic manufacturing process” p.11-12, edited by ceramic industry association editorial committee lecture subcommittee). The length average diameter thus calculated was regarded as the average particle diameter of the semiconductor ultrafine particles.

  Next, the semiconductor ultrafine particles (yellow phosphor 5a and red phosphor 5b) synthesized by the above method are dispersed and mixed with the silicone resin having a dimethyl silicone skeleton under the conditions shown in Table 1 to produce a phosphor-containing resin paste. did. The phosphor-containing resin paste was prepared by adding 5 parts by weight of yellow phosphor 5a and 5 parts by weight of red phosphor 5b to 100 parts by weight of silicone resin.

  The obtained phosphor-containing resin paste was applied and formed on a smooth substrate 2 with a dispenser, and this was heated on a hot plate at 150 ° C. for 5 minutes to prepare a temporarily cured film. Then, this was put into a 150 degreeC dryer for 5 hours, and the 4 types of fluorescent substance containing films (wavelength conversion layer 4) shown in Table 1 were produced (Examples 1-4). This film was attached to the upper surface of the inner layer to obtain four types of light emitting devices.

The luminous efficiency of the light emitting devices (Examples 1 to 4) provided with the respective phosphor-containing films was measured using a light emitting characteristic evaluation device manufactured by Otsuka Electronics Co., Ltd.
The dispersion state and average particle diameter of the phosphor inside the phosphor-containing film were confirmed by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). First, the dispersed state was determined by dividing the phosphor-containing film, and the fracture surface was observed by SEM at 500 to 100,000 times. At this time, when the semiconductor ultrafine particles are uniformly dispersed, the particles cannot be found in the resin because the magnification is low. Therefore, the phosphor-containing film was processed into a thin slice with a microtome with a thickness of 30 to 200 nm as a guide. . It is desirable that the thickness of the slice is properly used depending on the average particle diameter of the semiconductor ultrafine particles. When the average particle diameter is 5 to 10 times as a guide, the semiconductor ultrafine particles can be clearly observed. At this time, when the phosphor-containing film was soft, a thin slice could not be obtained, and the slice processing was performed with a target of 50 nm in thickness by cooling with liquid nitrogen. The section of the semiconductor ultrafine particles in this section was observed with a transmission electron microscope, and the lattice image was photographed at a magnification of 4,000,000. As the transmission electron microscope, JEOL JEM2010F was used, and observation was performed under the condition of an acceleration voltage of 200 kV. After confirming the presence or absence of aggregation of the semiconductor ultrafine particles again at 500,000 times, the lattice image of the semiconductor ultrafine particles was observed at a magnification of 4,000,000 times. At this time, because the semiconductor ultrafine particles are completely fixed by the resin, the particles did not move even when the electron beam was applied for a longer time than when the synthesized semiconductor ultrafine particles were observed.
Further, 200 semiconductor ultrafine particles having a confirmed lattice image were selected, and the diameter of the lattice image of each semiconductor ultrafine particle was measured. A histogram was created and statistically processed for the diameter of the measured lattice image in the same manner as described above to calculate the average length diameter, and this was regarded as the average particle diameter of the semiconductor ultrafine particles.
At this time, all the lattice images were measured in the same direction with respect to the photographic paper so that the length of the lattice image was not measured with a bias toward a long portion or a short portion. The average particle size of the ultrafine semiconductor particles of the phosphor-containing film thus obtained did not change from the average particle size of the ultrafine semiconductor particles at the time of synthesis.

[Comparative Example 1]
As a comparative example, a phosphor (La ₂ O ₂ S: Eu, Y ₂ SuO ₅ : Ce, Te) having an average particle diameter of 1 μm or more is used in the same manner as in Examples 1 to 4 instead of the semiconductor fine particles. A wavelength conversion layer was produced. By heating a resin in which 20 parts by weight of La ₂ O ₂ S: Eu and 20 parts by weight of Y ₂ SuO ₅ : Ce, Te are mixed with 100 parts by weight of a silicone resin at 150 ° C. for 5 hours, a sheet is obtained. A wavelength conversion layer in a state was prepared. The obtained wavelength conversion layer was mounted on the light emitting element similar to Examples 1-4, and luminous efficiency was evaluated. The results are shown in Table 1.

  According to Table 1, in Examples 1-4, all showed high luminous efficiency of 50 lm / W or more. On the other hand, in Comparative Example 1, a very low value of 20 lm / W was obtained.

It is a schematic sectional drawing which shows an example of the light-emitting device of this invention. It is a schematic sectional drawing which shows an example of the light-emitting device which has a wavelength conversion layer of the 2 layer structure in this invention. It is a schematic diagram which shows an example of the light emitting element suitable for the light-emitting device of this invention. It is a schematic sectional drawing which shows the structure of the conventional light-emitting device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Substrate 3 ... Light emitting element 4 ... Wavelength conversion layer 5 ... Semiconductor ultrafine particle 6 ... Reflective member 7 ... Light emitting element substrate 40 ... Wavelength conversion layer

Claims (7)

A light emitting element that emits excitation light having a peak wavelength in a range exceeding 450 nm and a wavelength conversion layer that converts the excitation light into visible light are formed on the substrate so as to cover the light emitting element. A light-emitting device that outputs both a part of light and the visible light,
The wavelength conversion layer contains semiconductor ultrafine particles having an average particle diameter of 10 nm or less.   2. The light emitting device according to claim 1, wherein a compound of a silicon-oxygen repeating structure having 5 to 500 bond units is coordinated on the surface of the semiconductor ultrafine particles.   The light emitting device according to claim 1, wherein the semiconductor ultrafine particles absorb the excitation light and emit visible light having a wavelength of 520 nm to 700 nm.   The semiconductor ultrafine particle is a semiconductor composition comprising at least two kinds of elements belonging to Group Ib, Group II, Group III, Group IV, Group V, and Group VI of the periodic table. The light-emitting device according to claim 1.   The light emitting device according to any one of claims 1 to 4, wherein the semiconductor ultrafine particles include two or more kinds of particles having different average particle diameters in a wavelength conversion layer.   The light emitting device according to claim 1, wherein the wavelength conversion layer includes a plurality of layers containing semiconductor ultrafine particles. The light emitting device according to claim 1, wherein a reflection member that emits light emitted from the light emitting element forward is provided around the light emitting element.

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