JP2004165683A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain light emitting devices with different luminous wavelengths even if the stimulation light source layer is the same, and to provide a light emitting device by which polychromatic light can be obtained from a single device. <P>SOLUTION: In a light emitting device provided with a stimulation light source layer, a luminous layer, and a photo-degradation prevention layer, the stimulation light source layer is made of inorganic compound semiconductor light emitting devices, the luminous layer comprises multiple organic compounds which present different stimulation luminous colors according to the light from the stimulation light source layer, and the photo-degradation prevention layer works to prevent the photo-degradation of the organic compounds. Also, the luminous layer adjoins the photo-degradation prevention layer in the device structure. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a light-emitting element, and more particularly to a light-emitting element including an organic compound exhibiting photoexcitation light emission and an excitation light source layer using an inorganic compound semiconductor for photoexcitation and emission of the organic compound.

  Among the various light-emitting phenomena, the fluorescent and phosphorescent phenomena exhibited by organic compounds have the potential to be multicolored as light-emitting materials in that they exhibit emission colors and color tones that reflect the molecular structure of each organic compound. . These light emission mechanisms are known as phenomena comprising excitation of electrons to emission light levels by light and a process of relaxing energy as light emission. When the excitation to the electronic level is caused by electric energy and involves a light emission relaxation process, this phenomenon falls into the category of the electroluminescence phenomenon. Above all, in the case of light emission of an organic compound, it is known as so-called organic electroluminescence. Organic electroluminescence has long been observed in anthracene crystals and the like, but since the mid-1980s, it has been observed using thin-film formed luminescent activities, particularly organic compounds that have fluorescence, and as thin-film organic electroluminescent devices Research and development of application to light emitting devices have been performed.

  In the organic electroluminescent element, light is emitted by injecting an electric charge from the outside into an organic compound that is luminescent by electric energy and forming an excited state in which luminescence is allowed. Therefore, in the application of the element, based on the present light-emitting mechanism, devices and attempts have been made to improve the light-emitting efficiency, and measures have been sought. That is, this is a method in which light-permissible electrons and holes are recombined in a light-emitting organic compound layer. As a typical element structure, the light-emitting layer injects electrons into an electron injection layer and holes injects. It has a structure sandwiched between two layers with a hole injection layer, or has a mode in which it is bonded to one of the injection layers. This form is determined by the charge mobility of the light emitting layer and the size of the energy barrier at the interface of the injection layer, and the optimum form differs depending on the type of the light emitting layer and the injection layer. Such a charge injection layer and a light emitting layer are formed between a transparent substrate on which a transparent electrode represented by ITO (indium tin oxide) is deposited and an electrode made of a metal having a low work function. It is customary to obtain light emission by injecting charges. FIG. 5 shows an example of such an element. In the figure, a hole injection layer (111), a luminescent organic compound layer (104), an electron injection layer (110), and a hole injection layer (111) are formed on a transparent electrode (117) deposited on the surface of a substrate (101) such as glass. , Electrodes (107) are sequentially stacked.

In the case of an organic electroluminescent device, it is relatively easy to make the light emitting device multicolor. That is, the luminescent color can be easily selected by changing the luminescent organic compound, and can be newly created by a synthesis method. This is one of the advantages of the element using an organic compound for the light emitting layer. Also, an organic electroluminescent device that emits white light by appropriately mixing a plurality of organic compounds that emit light has been reported recently (for example, see Non-Patent Document 1). Shows superiority. The typical performance of the element formed as described above exhibits light emission of several hundreds to several thousand Cd / m ² at several volts. However, its long life is about several thousand hours even if it is long.

  On the other hand, a typical example of a light emitting element made of an inorganic compound material is a light emitting diode (LED), which is used for a display device, an optical communication device, and the like. Various compound semiconductor materials are used for the LED depending on the emission wavelength. For example, AlGaAs is used for a visible red LED, and a compound semiconductor material in which P and As are combined as a Group III element and a Group V element of the periodic table such as Al and Ga is used for a visible green LED such as GaP. Have been. Further, recently, mixed crystals of GaN, AlGaN, GaInN, etc., which are a kind of group III-V compound semiconductor, have been used as blue LED materials of high luminance (for example, see Non-Patent Document 2 or Non-Patent Document 3). .

Red, green, and blue light emission is important in that, if these inorganic LEDs can emit light of three primary colors, the LED can be applied from a light emitting element to a display element to expand a wider application range. In particular, short-wavelength green and blue LEDs are expected. As an example, FIG. 6 shows a schematic diagram of a conventional structure of a blue LED using GaInN, which is a mixed crystal of GaN, as a light emitting layer (see, for example, Non-Patent Documents 4 and 5). As the substrate (101), a transparent sapphire single crystal is used (for example, see Non-Patent Document 6). GaN is provided directly above the substrate as a buffer layer (102). In some cases, the buffer layer is made of AlN (for example, see Non-Patent Document 7, Non-Patent Document 8, and Non-Patent Document 9). A lower cladding layer (103) made of AlGaN is provided on the GaN buffer layer (102). A light emitting layer (104) made of GaInN is provided on the lower cladding layer (103). Other is as a light emitting layer _{material, Al u In v Ga w N} (u + v + w = 1, u ≠ 0, u> 0) has been disclosed (e.g., see Patent Document 1.).

As shown in FIG. 6, in a visible LED that emits blue light, Ga _x In _{1 -x} N (x is a composition ratio), which is an example of a mixed crystal of GaN composed of three elements instead of a binary compound, is used as a light emitting layer material. And 0 <x <1) are used. The reason why mixed crystal Ga _x In _1-x N is used instead of GaN is to reduce the band gap by mixing In. The forbidden band width (E _g , unit: eV) and the emission wavelength (λ, unit: nm) have a relationship of (Equation 1).
λ = 1.24 × 10 ³ / E _g (Equation 1)

The band gap of GaN at room temperature is 3.4 eV (for example, see Non-Patent Document 10). Therefore, according to (Equation 1), λ is about 365 nm. Therefore, GaN is a light emitting layer material for an LED that emits ultraviolet light, but is not a light emitting layer material for a visible LED. In Ga _x In _1-x N obtained by adding In to GaN, the band gap is changed from 3.4 eV of GaN to 1.9 eV of InN (for example, see Non-Patent Document 11), depending on (x). Can be changed with. For example, in order to obtain blue light emission with a wavelength of 460 nm, E _g needs to be about 2.7 eV according to (Equation 1). From the (x) dependency of E _g of Ga _x In _1-x N (for example, see Non-Patent Document 12), (x) needs to be about 0.3. That is, in order to obtain blue light emission of 460 nm, it is necessary to use a layer having a composition of Ga _0.7 In _0.3 N as a light emitting layer.

However, in practice, it is difficult to reduce (x), that is, to increase the composition ratio of In, due to the technology of crystal growth. In practice, it is difficult to increase the composition ratio of In beyond 0.2 to 0.3 because crystallinity is deteriorated. In the sense that the band gap is changed, conventionally, (x) of the Ga _x In ₁ -xN layer is practically suppressed to about 0.8 and zinc (element symbol: Zn) An operation of adding such impurities to the Ga _x In _1-x N mixed crystal layer and apparently reducing the forbidden band width using an impurity level formed by Zn is performed. When Zn is added, the forbidden band width is reduced by about 0.5 eV (for example, see Non-Patent Document 13).

  The level formed between the valence band and the conduction band of the semiconductor by the impurity is generally not unique. Therefore, light having wavelengths corresponding to the levels of various impurities coexist from the light emitting layer to which an impurity such as Zn is added. When light emission having different wavelengths coexist, the emission spectrum becomes wider as a result. In fact, secondary light emission adjacent to main light emission is observed in Zn-doped GaInN (Shunji Nakamura, “InGaN high-brightness blue light-emitting diode” (JSPS 125th Committee, No. 148, 148). Meeting (May 27, 1994))). It has been reported that, even when Zn is added to GaN, the emission spectrum of the LED is expanded with an increase in the amount of Zn added (T. Kawabata et al., J. Appl. Phys., 56 (8) ( 1984), 2367). Therefore, the conventional method of increasing the emission wavelength using the impurity level has a difficulty in obtaining monochromatic emission having a narrow half width of the emission spectrum.

One of the three primary colors of light is green, which has a longer wavelength than blue. According to (Equation 1), it is necessary to further reduce E _g in order to obtain emission of a longer wavelength. When a Ga _x In _1-x N layer is used as a light emitting layer material, the composition ratio of In must be further increased. For example, the wavelength to obtain a green light emission of 550nm, it is necessary that the E _g and 2.25 eV. The E _g in a 2.25eV should increase to about 0.6 to the composition ratio of In (S.SAKAI other, Jpn.J.Appl.Phys., 32 (1993) , 4413. See). As described above, it is not easy to increase the composition ratio of In without deteriorating the crystallinity. Even if Zn is added as a light emitting impurity and the band gap is reduced to about 0.5 eV, (x) needs to be about 0.6, that is, the In composition ratio is about 0.4. This composition ratio exceeds the practical upper limit of 0.2 to 0.3 of the In composition ratio that does not impair the crystallinity of Ga _x In ₁ -xN.
"Applied Physics" Vol. 63, No. 10 (1994), p. 1026 Shuji Nakamura, Journal of the Institute of Electronics, Information and Communication Engineers, Vol. 76, No. 9 (1993), p. 913 Masabe Katsuhide, "Toyoda Gosei Giho," Vol. 35, No. 4, April 1993, p. 68 NIKKEI MATERIALS & TECHNOLOGY 94.4 (No. 140), p. 48 NIKKIEELECTRONICS 1994.1.3 (No. 598), p. 59 H. M. Manasevit et al. Electrochem. Soc. , 118 (1971), 1864. Yasuko KOIDE et al., Jpn. J. Appl. Phys. , 27 (7) (1988), p. p. 1156-161 H. Amano et al., Thin Solid Films, 163 (1988), 415. Yasuo Koide et al., "Journal of Japan Society for Crystal Growth", Vol. 13, No. 4 (1986), p. 8 Japanese Patent Publication No. 6-14564 Edited by Isamu Akasaki, "III-V Group Compound Semiconductor" (published on May 20, 1994 by Baifukan), p. 150 K. Kubota et al. Appl. Phys. , 66 (1989), 2984 S. SAKAI et al., Jpn. J. Appl. Phys. , 32 (1993), 4413. Shuji Nakamura, “JSPS Photoelectric Interconversion 125th Committee, 148th Meeting, May 27, 1994”

In general, an LED that includes a light-emitting layer material made of an inorganic compound and that is made of an inorganic compound has a higher luminance than a light-emitting element that has a layer made of an organic dye compound or has a layer containing it as a light-emitting layer. It has become. However, in order to obtain a short-wavelength visible LED that emits blue or green light, for example, in the case of using Ga _x In _1-x N for the light emitting layer, it is necessary to obtain a high-quality mixed crystal layer as described above. There is a difficulty in the growth technique, and there is a problem that even if Zn is added as a light-emitting impurity, the light-emitting spectrum broadens and the spectrum does not become a sharp monochromatic spectrum.

On the other hand, if an inorganic compound semiconductor material composed of two elements such as GaN, which can be more easily grown, is used instead of a mixed-crystal light-emitting layer such as the conventional Ga _x In _1-x N, the LED can be relatively easily manufactured. You can also get. However, when the GaN light-emitting layer emits ultraviolet light for GaN of E _g is 3.4 eV, does not emit visible light.

  On the other hand, light emission from the light-emitting layer of an organic electroluminescent device using a conventional organic compound can be made polychromatic due to the selectivity of the organic compound, but the light emission itself is brought about by injection of electric energy. Have been. For this reason, electric energy is converted into heat energy in an organic compound layer such as a light emitting layer and an injection layer, and there is a problem that deterioration of the organic compound layer due to heat, that is, a change in an electronic state due to heat energy impairs light emission allowance. The problem is how to efficiently convert the injected energy into light energy to obtain high-brightness light emission and extend the life of the device, thereby improving efficiency.

Organic compounds exhibit color even upon injection of light energy. It was mentioned earlier that fluorescence and phosphorescence are examples. In this case, light energy is generally injected with energy larger than the energy corresponding to the emission wavelength. That is, in order to obtain light emission in the visible light region, light having energy larger than that, for example, visible light or ultraviolet light having a short wavelength may be appropriately used. The wavelength (λ) of light and the magnitude (E) of its energy have a relationship represented by (Equation 2) when a Planck constant is h and a light speed C is used.
E = h · C / λ ··· (Equation 2)

  Therefore, a light-emitting element made of an inorganic compound semiconductor can be used as a light-emitting source of an organic compound that emits light by light excitation. For example, it is also possible to use the ultraviolet light emitted from the above-mentioned excitation light source layer made of GaN as a light source for photo-exciting the organic dye compound, thereby obtaining light emission of the organic compound.

In the light-emitting element having such a configuration, the light-emitting layer does not need to intentionally require a mixed crystal such as Ga _x In _1-x N, and thus it is necessary to increase the composition ratio of In intended to increase the wavelength. Disappears. Ultraviolet light emission from GaN is convenient for photoexcitation of organic compounds, and therefore, the light emitting layer is made of a material having a larger band gap (E _g ) such as GaN than Ga _x In ₁ -xN. It is good to configure. However, for example, a light-emitting element that supplies such an optical excitation light and includes both an excitation light source layer made of an inorganic compound and a light-emitting layer made of an organic compound is not known.

  In addition, light emission can also be obtained by disposing a resin or the like made of an organic compound or a resin containing the same around an excitation light source layer that emits an excitation light source, for example, an inorganic compound. However, a light-emitting element having a simple structure in which such an organic compound is arranged around the excitation light source layer is not known.

  The present inventor has achieved the present invention as a result of efforts to solve the above problems. That is, the present invention provides a light emitting layer comprising an organic compound exhibiting photoexcited light emission or comprising an organic compound exhibiting photoexcited light emission, and an excitation light source layer having an inorganic compound semiconductor for emitting light by light excitation of the organic compound as a light emitting element. It is a light emitting element provided. Further, a compound comprising an organic compound exhibiting photoexcited light emission or comprising an organic compound exhibiting photoexcited light emission, and an excitation light source layer for causing the organic compound to emit light by photoexcitation are provided. Is a light emitting element which is surrounded by a compound containing and sealed. In these light-emitting elements, an excitation light source layer for causing an organic compound to emit light by photoexcitation can be made of a material that emits light of a wavelength whose center is 400 nm or less. The excitation light source layer that emits light of a wavelength whose center is 400 nm or less is made of, for example, AlN, GaN, or a mixed crystal of these and InN. Further, the organic compound can be an organic compound exhibiting a photoexcited light emission phenomenon by light having a wavelength of 400 nm or less at the center.

  Emission comprising a layer comprising an organic compound or a layer containing an organic compound of the present invention (hereinafter referred to as an organic compound layer) and an excitation light source layer which emits excitation light for photoexcitation of the organic compound layer to obtain emission. The element can be formed simply by providing an organic compound layer above an excitation light source layer made of a pn junction such as GaN provided on a substrate. If the material used for the substrate is optically transparent or translucent, it may be provided, for example, on the back side of the substrate located below the excitation light source layer. If the substrate material is insulative and it is not possible to form an electrode on one surface of the substrate, an organic compound layer can be inserted in the middle of the laminated structure provided on the front surface side of the substrate. If the buffer layer provided on the insulating substrate is a high resistance layer, an organic compound layer can be provided on the buffer layer. Further, a part or the whole of the side surface of the laminated structure including the excitation light source generating layer may be covered with the organic compound layer. When configured based on these examples, a light-emitting element including the organic compound layer according to the present invention and an excitation light source layer for photo-exciting and emitting light from the organic compound is formed.

  The conductivity and conductivity of the organic compound layer are not particularly limited. If the organic compound layer is a high-resistance layer, for example, the organic compound layer may be provided so as to cover a region other than the region where the electrode is formed of the inorganic compound layer on which the electrode is mounted. In the case of an organic compound layer having conductivity, the organic compound layer itself may be used as an electrode, or a portion where the metal electrode and the organic compound are in contact may be covered with an insulating material having a property of transmitting light. Further, it may be inserted between layers of the laminated structure including the excitation light source layer which are required to be conductive, for example, between the cladding layer and the contact layer. In short, the organic compound layer does not hinder the flow of operation drive current for obtaining light emission from the excitation light source layer, and can receive excitation light for exciting the organic compound emitted from the excitation light source layer over a wide range. Place it in the same way.

FIGS. 1 and 2 each show an example of a cross-sectional view and a schematic plan view of a light-emitting element including an organic compound layer and an excitation light source layer. In this structural example, a light-transmitting aluminum nitride (AlN) is used for the substrate (101). The substrate material is not limited to AlN, but when an organic compound layer is provided on the back surface side of the substrate material, it does not absorb light having a wavelength emitted from the excitation light source layer, that is, is larger than the material constituting the excitation light source layer. Preferably, it is composed of a material having E _g . This is because the intensity of the excitation light for exciting the organic compound layer disposed on the back side of the substrate is not reduced. The back surface side of the substrate refers to the surface of the substrate opposite to the surface of the substrate on which the laminated structure including the excitation light source layer is deposited. When the back surface side of the substrate is also coated with the organic compound layer, as an example of a preferable combination of the excitation light source layer and the substrate material from the viewpoint of E _g of the material, the excitation light source layer is made of GaN, and the substrate is made of E _g. There is an example in which a quartz glass material or AlN having a large value is used.

As shown in FIG. 1, on the AlN substrate (101), Al _y Ga _1-y N (y represents a composition ratio, where 0 <y ≦ 1) exhibiting p-type conduction as a lower cladding layer. ) Is deposited as a lower cladding layer (103). An excitation light source layer (104) made of p-type GaN is provided on the lower cladding layer (103). On the excitation light source layer (104), there is an upper cladding layer (105) made of n-type Al _y Ga _1-y N. Need not consist together the upper and lower clad layers Al _y Ga _1-y N. However, the upper and lower cladding layers ((103) and (105)) are provided for efficiently confining electrons and holes in the excitation light source layer (104), that is, for efficiently performing “light emission confinement”. For this reason, it is necessary to form the excitation light source layer from a material having a larger E _g than the material forming the excitation light source layer. For example, in the case where Al _0.2 Ga _0.8 N having an Al composition ratio of 0.2 is used as the excitation light source layer, this example corresponds to a case where the cladding layer is made of a higher Al composition ratio, for example, Al _0.4 Ga _0.6 N. . Is In Al _y Ga _1-y N mixed crystal, by increasing the composition ratio of Al, is because it is enhanced E _g (S.SAKAI other, Jpn.J.Appl.Phys., 32 (1993 ), 4413.). Other examples of preferable material combinations of the excitation light source layer / cladding layer include Ga _0.85 In _0.15 N / GaN and GaN / AlN. Desirably, the combination of the excitation light source layer and the cladding layer material has a band discontinuity between conduction bands of about 10 times thermionic energy (about 0.026 eV) at room temperature when both materials are heterojunctioned. The resulting combination is good. Also, the upper and lower cladding layers need not be made of the same material.

  An electrode (107) having a circular planar shape is provided on a central portion of the upper cladding layer (105). The other electrode (108) is provided on the lower cladding layer (103). The electrode (108) on the lower cladding layer (103) is provided concentrically with the electrode (107) around the upper cladding layer (105) as viewed in plan as shown in FIG. The shape and arrangement of the electrodes are not limited to the configurations illustrated in FIGS. 1 and 2.

  The constituent layers of the laminated structure made of the inorganic compound as described above are formed by a metalorganic thermal decomposition vapor deposition method (referred to as MOCVD method, MOVPE method, OMVPE method, or the like), a vapor phase growth method (VPE method), or a molecule. It can be formed by using a vapor phase growth method such as a line epitaxial method (MBE method). For example, the MOCVD method is roughly classified into a normal pressure (atmospheric pressure) method and a reduced pressure method depending on the pressure at which a vapor phase growth reaction for growing a layer is performed. It can be obtained regardless of the method. In addition, the MBE method includes a gas source MBE (GS-MBE) and an organic metal MBE (MO-MBE) depending on the type and form of the raw material used, and any of these methods can be used. Also, a chemical beam growth method (CBE method) can be used.

  The periphery of the electrode (107) on the upper clad layer (105) is covered with an organic compound layer (106). With such a structure, a light-emitting element including an inorganic compound and an organic compound can be formed. The electrode (107) is not covered with the organic compound layer (106) for connection. The surface of the organic compound layer (106) may be flat, and the surface may be uneven in order to scatter light emitted from the same layer (106).

  The luminescent organic compound layer that is photoexcited by the excitation light source is formed of the compound itself or a composition containing the compound. The content of the compound in the luminescent active organic compound layer is basically good as long as the compound can emit light, and can be set in the range of 0.0001 to 100 mol%. In the case of forming the layer with the former photoexcited light-emitting active organic compound itself, it can be formed by vapor deposition of a compound or a method of preparing a Langmuir-Blodgett film, or can be used by dissolving the compound in a solvent. In particular, dissolution in this solvent is effective in the case of a soluble polymer. In the case of using a composition, a simple method is to disperse the compound in a substance which does not absorb light emitted by photoexcitation of the compound. As the method, a material obtained by physically dispersing the compound in a high molecular polymer having light transmittance in a visible light region is simple and useful in the process. Examples of the high-molecular polymer include polymethyl methacrylate, polycarbonate, and polystyrene. Further, as a dispersion method of this method, the luminescent active organic compound and the high molecular polymer are dissolved in a common solvent or dissolved in a mutually compatible solvent, and a solution obtained by mixing the solutions is mixed with the compound. Can be used to form layers. When the layer is formed from a solution by dissolving in a solvent, a coating method can be used. A spray method in which the solution is sprayed on a surface on which a light emitting element provided with the layer is to be provided, or a spin coating method in which the surface is rotated around a rotation axis perpendicular to the surface and the solution is dropped and applied, for example. The layer can be easily formed by forming a layer on the surface by using a screen printing technique or the like and then solidifying the layer. The application of such a solution is useful because the process can be simplified since a coating layer containing the compound can be formed relatively easily over a large area. In addition, a method for laminating an organic compound layer includes a method of directly forming a light-emitting active organic compound or a composition containing the compound on a surface where a light-emitting element provided with an excitation light source is to be provided, and laminating the layer. A method in which the layer is formed into a self-supporting film and bonded and attached to a surface on which the light emitting element is to be provided, or the like may be used.

  The organic compound layer does not need to be composed of an organic compound exhibiting one type of color. For example, organic compounds exhibiting red and green colors may be mixed and included. When organic compounds exhibiting red and green colors are mixed in the same layer, both lights are mixed, and as a result, an orange light-emitting element can be obtained. Alternatively, a region to be covered may be divided, and an organic compound layer which emits different light for each region may be provided. In this manner, a multi-color light emitting element composed of only a single light excitation source can be easily obtained. For example, if a combination of an organic compound layer that emits light of each of the three primary colors of red, green, and blue and a GaN excitation light source layer serving as a single light excitation source is used, a white light emitting element can also be obtained. This is one of the advantages of combining the excitation light source layer and the organic compound layer.

  When mixing organic compound layers exhibiting different colors, when the obtained color intensity is relatively different for each organic compound layer, for example, the area occupied by the organic compound layer having a relatively weak color intensity is increased. On the contrary, they are arranged so as to reduce the area occupied by the organic compound layer having relatively high color intensity. In this way, it is possible to mix luminescence having substantially the same intensity without depending on the original luminescence intensity difference due to the difference in emitted color. It is also an advantage that a multicolor light-emitting element which is excellent in harmony of light by mixing colors having almost the same intensity can be obtained only by appropriately adjusting the area of the organic compound layer which emits light.

  Even if the light emitting element including the excitation light source layer is sealed with the organic compound including the organic compound or the like without directly applying the organic compound to the position where the laminated structure is located or the substrate material, a light emitting element having a new configuration can be obtained. it can.

  For example, an organic compound is contained in a general epoxy resin or the like conventionally used as an LED sealing material. Thereby, the LED provided with the excitation light source layer for optically exciting the organic compound made of the ultraviolet light emitting material such as GaN is sealed. Due to the ultraviolet light emitted from the LED, for example, the organic compound in the epoxy resin exhibits a color unique to the compound. Thus, a light emitting element that emits visible light can be formed by a simple method in which the excitation source is not visible light but is sealed with a sealing resin containing an organic compound. That is, originally, it is not necessary to use a binary compound material, which is a material that emits ultraviolet light, as a multi-element mixed crystal with difficulty in crystal growth in order to obtain light emission on a longer wavelength side. A light-emitting element that emits visible light can be obtained without causing an increase in the half-value width of an emission spectrum due to an increase in wavelength due to addition.

  The organic compound may be uniformly dispersed in the sealing resin. In the case where the light emitted from the excitation light source layer is condensed and projected onto a part of the region, the organic compound is concentrated on the region of the sealing resin corresponding to the part of the region. You may make it contain. The number of organic compounds to be mixed with the sealing resin is not limited to one, and it is considered as one application to include various kinds of organic compounds exhibiting different colors. Even in such a configuration, for example, ultraviolet light emitted from the GaN excitation light source layer optically excites the organic compound in the sealing material, and emits visible light. That is, it is not necessary to use a mixed crystal in which it is difficult to grow a crystal in order to obtain visible light as in the related art.

  A conventional sealing technique can be used to seal a light emitting element having an excitation light source layer with the substance containing an organic compound according to the present invention. The sealing can be performed simply by changing the conventional sealing material to the sealing material containing the organic compound according to the present invention. For example, a light emitting element having an excitation light source layer is impregnated with a sealing epoxy resin containing an organic compound according to the present invention, which is poured into a mold or the like that gives a desired outer shape, and is heated and melted. If the sealing material is cooled and solidified, the light emitting element can be sealed. The light emitting element can be sealed by placing the light emitting element inside an appropriate mold and dropping and solidifying a sealing resin containing an organic compound into the mold.

  In the present invention, a light emitting element is obtained by photoexciting an organic compound using a laminated structure composed of an inorganic compound as excitation light. For this purpose, it is preferable that the photoexcitation energy is higher than the light emission energy. Light energy is related to wavelength by (Equation 2), and the shorter the wavelength, the greater the light energy. In the present invention, in order to excite the organic compound efficiently, as a desirable example, the emission wavelength of the excitation light source layer is specified. Specifically, the light emitted from the excitation light source layer has a center wavelength of 400 nm or less. In other words, the excitation light source layer is made of a material that emits light having a center wavelength of 400 nm or less. The center wavelength refers to the wavelength that gives the maximum emission intensity among the emission having a certain wavelength width.

  The reason for setting the center wavelength to 400 nm or less is that the shorter the wavelength of the light, the higher the energy according to (Equation 2). In particular, ultraviolet light having a wavelength of 400 nm or less has an excitation energy sufficient to optically excite an organic compound exhibiting photoexcited light emission and to emit light in the visible light region.

Materials satisfying the requirement of the center wavelength include, for example, III-V compound semiconductors such as GaN. The emission wavelength of GaN calculated by (Equation 1) is 365 nm. In addition to GaN, AlN (emission wavelength = 207 nm) or Al _z Ga _1-z N (z represents a composition ratio and ≦ z ≦ 1) that can emit ultraviolet light from 207 nm to 360 nm depending on the Al composition ratio. .) Is suitable. Also, Ga _x In ₁ -xN mixed crystals having an E _g of 3.1 eV or more are suitable.

  The photoexcited light emitting active organic compound according to the present invention may be any of organic molecule monomers, polymers, aggregates and the like, and basically, any organic compound exhibiting photoexcited light emission may be used. The photoexcitation light emission here is a phenomenon that emits light by light irradiation, and for example, phenomena such as fluorescence and phosphorescence are naturally included. Specific examples thereof include, in the case of monomers, condensed six-membered rings such as anthracene and perylene, and para-oligophenylene derivatives, oxazole derivatives, oxodiazole derivatives, stilbene derivatives, coumarin derivatives, and rhodamine dyes. Examples thereof include a xanicene-based dye and an oxazine-based dye. Polymers can be broadly classified into those whose main chain has luminescence activity and those whose side chains have luminescence activity. Basically, some or all of the polymers have luminescence activity. Just think. Examples of the former include a polyparaphenylene derivative, a polyparaphenylenevinylene derivative, an arylenevinylene derivative represented by a polynaphthovinylene derivative, a polythiophene derivative represented by poly (3-alkylthiophene), a polyfluorene derivative, and the like. be able to. Further, a polymer in which a monomer of the above-mentioned luminescent organic compound is chemically bonded to a side chain of a high molecular polymer such as polymethyl methacrylate, polycarbonate, or polystyrene is an example of the latter. Furthermore, a polymer in which a part of the crosslinked product has photoexcited luminescence activity is also included in the polymer. Further, for example, a complex formed by associating an 8-quinolinol derivative with a metal ion, a metal complex such as an azomethine complex, an aggregate of a cyanine dye (J-aggregate), and the like are also compounds referred to herein.

  When these photoexcited light emitting active organic compounds are used, for example, red light having a wavelength of about 630 nm from rhodamine B, green light having a wavelength of about 510 nm from coumarin 153, and polyparaphenylene vinylene having a wavelength of about 510 nm, Coumarin 1 emits blue light with a wavelength near 430 nm, and coumarin 120 emits blue light with a wavelength near 450 nm. Light emission from an organic compound is generally obtained by irradiating excitation light having a wavelength shorter than the emission wavelength of the organic compound. Therefore, it is sufficient that the wavelength of the excitation light is 400 nm to obtain at least three primary colors of light.

  A substance having a sensitizing effect of light emission which promotes light emission from a light-emitting organic compound may be added to the layer made of the organic compound exemplified above or the light-emitting layer made of a compound containing them. In this case, the specific additive substance and the amount thereof may be selected so as to maintain the sensitization of the luminescence of the luminescent organic compound.

  The light-emitting layer may contain a compound that prevents or reduces the deterioration of the light-emitting characteristics of the light-emitting active organic compound. In this case, the specific additive substance and the amount added can be selected within a range where the emission of the luminescent active organic compound is not inhibited.

  Contains a substance that can prevent or reduce photodeterioration of the organic compound that constitutes the light emitting layer, and that prevents light from deteriorating in the light emitting layer having the property of reducing ultraviolet light as excitation light and transmitting light emitted from the light emitting layer. For example, it is also useful to provide a light deterioration preventing layer between the light emitting layer and the excitation light source layer. In this case, as the light deterioration preventing layer, for example, a salicylic acid derivative, a benzophenone derivative, a benzotriazole derivative, or a cyanoacrylate derivative is used as an ultraviolet absorber in a light-transmitting polymer material such as polymethyl methacrylate or polycarbonate. For example, an organic composition formed by dispersing a single or plural kinds of light stabilizers made of a hindered amine or the like for stabilizing the light emission characteristics can be used.

  Further, in the case where ultraviolet light from the outside of the light emitting device according to the present invention prevents light deterioration of the organic compound layer due to being incident on the light emitting device, the light deterioration preventing layer is used to extract light emitted from the light emitting layer. What is necessary is just to form. This is because, for example, there is a high probability that light will enter from the outside through the sealing outer layer in the direction in which light is emitted from the light emitting layer. For example, in the case of an element for extracting light emitted from a light-emitting layer to the upper part, the element is preferably provided above the light-emitting layer. The light deterioration preventing layer provided in the direction of extracting light emission also has an effect of preventing and reducing excitation light from the excitation light source layer of the light emitting element from being emitted simultaneously with visible light emitted from the light emitting layer.

  Even if a light-transmitting inorganic layer made of a light-transmitting inorganic material typified by silicon oxide or the like is applied to the organic compound light-emitting layer, it is effective in preventing deterioration of the characteristics of the light-emitting element. Such a light-transmitting inorganic layer can prevent, for example, water, oxygen, and the like from directly adsorbing to the surface of the organic compound light-emitting layer, thereby improving the characteristics such as the life characteristics of the device.

  The light emitted from the excitation light source is incident on the organic compound layer or the sealing resin containing the organic compound, so that the organic compound emits light by light excitation. The wavelength of light emitted from the organic compound is longer than the wavelength of light emitted from the excitation light source layer.

(Example 1) The present invention will be described in detail based on examples. FIG. 3 is a schematic sectional view of a light emitting device according to the present invention. An n-type GaP single crystal to which sulfur (element symbol: S) was added was used for a substrate (101) for forming a laminated structure made of an inorganic compound. The plane orientation of the substrate (101) was <111> ± 2 °. The shape of the substrate (101) was a circle having a diameter of about 50 mm and a thickness of about 200 μm.

On the surface (101-1) of the substrate (101), an n-type AlN layer having a thickness of 0.2 μm was deposited as a lower cladding layer (103). The carrier concentration of the lower cladding layer (103) was about 1 × 10 ¹⁸ cm ⁻³ . An excitation light source layer (104) made of p-type GaN was provided on the lower cladding layer (103). The carrier concentration of the excitation light source layer (104) was about 9 × 10 ¹⁶ cm ⁻³ , and the film thickness was about 0.1 μm. On the excitation light source layer (104), a p-type Al _0.2 Ga _0.8 N layer was deposited as an upper cladding layer (105). The layer (105) had a thickness of 0.2 μm and a carrier concentration of 2 × 10 ¹⁸ cm ⁻³ . Each of the constituent layers ((102) to (105)) of the laminated structure was grown by MOCVD under normal pressure. The growth temperature was 750 ° C. irrespective of the constituent layers.

  On the upper cladding layer (105), coumarin 1 which is an organic compound which emits blue light and a high molecular weight polymer which is light-transmissive in the visible light region, polymethyl methacrylate methyl ester, are added to a solvent chloroform at a weight ratio of 1: 5. : 125, and the solution was quantified at room temperature using a commercially available microdispenser, dropped, and applied by spin coating. After dropping, the temperature was raised from room temperature to 70 ° C., which is a solidification temperature, to evaporate the solvent and solidify. The organic compound to be used is not limited to the compound of the present embodiment, and it is needless to say that the solute may be changed according to the desired color development, and the solvent may be selected according to the solute. The solidification was performed under a reduced pressure of about 200 Torr in a nitrogen gas stream as an inert gas to prevent oxidation. When the solidification is performed under a certain degree of reduced pressure environment, the diffusion of the gas component dissolved in the solution is promoted, and therefore, a dense insulating organic compound layer (106) which is well defoamed and has few bubbles can be obtained. Was. The thickness of the organic compound layer (106) was about 0.3 μm.

The surface of the solidified organic compound layer (106) was once coated with a silicon dioxide (SiO ₂ ) film by ordinary plasma CVD deposition. Thereafter, a photoresist agent generally used for patterning the element shape was applied. Thereafter, through a conventional general exposure step, patterning was performed into the shape of the electrode (107) provided on the upper clad layer (105). After patterning, the exposed SiO ₂ film and organic compound layer (106) in the region where the electrode (107) was to be formed were removed by etching with an organic solvent to expose the surface of the upper cladding layer (105). In this embodiment, since the shape of the electrode was circular, the region from which the organic compound layer (106) was removed was a circular region similar to the shape of the electrode.

  After patterning, high-purity aluminum of 99.999% purity as an electrode material was deposited on the remaining photoresist and on a part of the surface of the upper cladding layer (105) exposed by patterning by a normal vacuum deposition method. After the vapor deposition, the photoresist agent was stripped off using a resist stripping chemical. As a result, the Al film deposited on the resist material was simultaneously removed as the resist material was peeled off from the upper cladding layer (105). In the region where the electrode (107) was formed, the photoresist agent was not present immediately below the deposited Al film, so that it was not removed by the lift-off method and remained in a circle in the region where the electrode was formed. A so-called "solid" electrode (108) made of high-purity Al was provided on the back surface (101-2) of the substrate (101). Thereafter, the elements formed on the entire surface of the substrate (101) are individually divided into chips to form an excitation light source layer composed of an inorganic compound having a sectional structure as shown in FIG. 3 and a layer containing an organic dye compound. Was formed.

A driving current of 20 mA was passed between the electrodes ((107) and (108)) to cause the organic compound layer (106) to emit light by photoexcitation. The resulting emission wavelength was blue emission at about 430 nm. The half-width of the emission spectrum was about 70 nm, which was markedly monochromatic compared to that of a conventional blue LED using a Ga _x In ₁ -xN mixed crystal as a light-emitting layer.

Example 2 First, a light emitting element chip as shown in FIG. 3 was obtained. An n-type GaP single crystal was used as the substrate (101). A lower cladding layer (103) made of n-type Al _0.8 Ga _0.2 N, a p-type excitation light source layer (104) and an upper cladding layer (105) made of p-type Al _0.7 Ga _0.3 N are sequentially formed on a substrate (101). , Deposited. Excitation light source layer (104) is constructed from theory, p-type wavelength emits ultraviolet approximately 253nm Al _0.6 Ga _0.4 N. The carrier concentration and the film thickness of each layer were almost the same as the numerical values described in Example 1.

Al _0.7 Ga _0.3 N upper cladding layer on the (105) was deposited organic compound layer (106) containing coumarin 153 resulting in green light. The organic compound (106) was provided so as not to cover the surface of the electrode (107), but to cover the surface of the surrounding upper clad layer (105). The organic compound layer (106) was not provided on the back side (101-2) of the substrate (101). Since a large number of light-emitting elements are arranged on the substrate, the light-emitting elements are cut into individual light-emitting element chips.

  Next, a light emitting element sealed with a resin was manufactured using the light emitting element chip. FIG. 4 shows the cross-sectional structure. The light emitting element chip (112) was mounted on a commercially available stem (113), and the electrode (108) on the back surface side (101-2) of the substrate (101) was electrically connected to the stem (113). Next, the electrode (107) was connected to the lead terminal portion (115-1) by a bonding wire (114).

  After the electrical connection, the light emitting element chip (112) mounted on the stem (113) is surrounded with an epoxy resin (116) for encapsulating a semiconductor element containing coumarin 153, which is one of the organic compounds according to the present invention. Sealed. The epoxy resin (116) contained about 2% by weight of the above-mentioned organic compound which emits green light. At the time of sealing, the light emitting element chip (112) was impregnated in an epoxy resin poured into a mold maintained at a temperature of about 190 ° C. After cooling, the periphery was molded with an epoxy resin (116) to form a light-emitting element surrounded by a substance containing an organic compound. FIG. 4 shows a sectional view of the structure in a sealed state according to the present embodiment.

  A driving current was passed through the lead terminals (115-1 and 115-2), and a light-emitting element emitting green light having a wavelength of about 535 nm was obtained. The half width was about 40 nm. Also, the emission intensity was superior to that of the same color obtained by attaching a color filter to a conventional white EL device.

By providing a layer made of or containing an organic compound that emits light by photoexcitation, it is possible to use a binary compound that is easy to grow, instead of a multi-element mixed crystal, which is difficult to grow as in the related art. In obtaining a light-emitting element that emits visible light, a crystal growth layer that can stably grow can be used as a generation layer of a photoexcitation source, so that the light-emitting element can be provided stably, There is also an economic effect that enables pricing. Further, in the conventional LED, in order to obtain light emission of a specific wavelength, it is necessary to use a crystal layer corresponding to the wavelength or a mixed crystal layer whose composition is specified each time as a light emitting layer. That is, it was required that the emission wavelength correspond to the material and composition of the emission layer in a ratio of 1: 1. However, according to the present invention, near-ultraviolet light or ultraviolet light having a center wavelength of 400 nm or less was used as an emission excitation source. There is no need to change the material of the light-emitting layer depending on the desired emission wavelength as long as the material emits light. Even if the same light excitation source is used, the desired light emission or multicolor light emission can be obtained by changing the kind of the organic dye compound. Is obtained. In addition, unlike a conventional multicolor light emitting device using a combination of a white EL device and a color filter, the organic compound emits light based on photoexcitation by ultraviolet light having a large light energy, so that a light emitting device having more excellent intensity is provided.

FIG. 2 is a schematic cross-sectional view illustrating an example of a light emitting device according to the present invention. FIG. 2 is a schematic plan view of the light emitting device shown in FIG. 1. FIG. 2 is a schematic diagram illustrating a cross-sectional structure of a light emitting device according to the present invention described in Example 1. FIG. 3 is a schematic cross-sectional view of a light emitting device according to the present invention described in Example 2. It is a cross section showing an example of the structure of the conventional organic EL element. It is a schematic diagram of the conventional structure.

Explanation of reference numerals

Reference Signs List 101 substrate 101-1 substrate front surface 101-2 substrate back surface 102 buffer layer 103 lower cladding layer 104 excitation light source layer 105 upper cladding layer 106 organic compound light emitting layer 107 electrode 108 electrode 110 electron injection layer 111 hole (hole) injection layer 112 Chip 113 Stem 114 Bonding wire 115 Lead terminal 116 Epoxy resin 117 containing an organic dye compound Transparent electrode

Claims (20)

A light-emitting element including an excitation light source layer, a light-emitting layer, and a light deterioration prevention layer, wherein the excitation light source layer is formed of an inorganic compound semiconductor light-emitting element, and the light-emitting layer is formed of a plurality of organic light-emitting layers that exhibit different excitation emission colors depending on light from the excitation light source layer. A light-emitting element including a compound, wherein the light-deterioration preventing layer has an action of preventing light deterioration of the organic compound. The light emitting device according to claim 1, wherein the light emitting layer and the light deterioration preventing layer are in contact with each other. The light emitting device according to claim 1, wherein a plurality of organic compounds in the light emitting layer are provided in different regions in the layer. The area of each region when a plurality of organic compounds are provided in different regions is increased for organic compounds having low color intensity and narrow for organic compounds with high color intensity. Light emitting element. The light emitting device according to any one of claims 1 to 4, wherein the excitation light source layer is a group III-V compound semiconductor light emitting device. The excitation light source layer is made of Al _z Ga _{1 -z} N (z represents a composition ratio, and 0 ≦ z ≦ 1) or Ga _x In _{1 -x} N (x is a composition ratio) of 3.1 eV or more. And 0 ≦ x ≦ 1). 6. The light-emitting device according to claim 1, wherein The excitation light source layer has a double heterojunction structure in which aluminum / gallium nitride (composition formula: Al _X Ga _Y N: 0 ≦ X, Y ≦ 1, X + Y = 1) is used as an upper and lower cladding layer. The light emitting device according to claim 1. The light emitting device according to any one of claims 1 to 7, wherein the excitation light source layer has an asymmetric band structure. The light emitting device according to any one of claims 1 to 8, wherein the light emitting layer is coated around an electrode on the upper clad layer. The light emitting device according to any one of claims 1 to 9, wherein the light emitting layer has irregularities on a surface thereof. The light emitting device according to any one of claims 1 to 10, wherein the excitation light source layer is surrounded by a resin material containing an organic compound and is sealed. The light emitting device according to any one of claims 1 to 11, wherein the organic compound is a monomer, a polymer, or an aggregate of organic molecules. The monomer of the organic molecule is a condensed six-membered ring of anthracene or perylene, a para-oligophenylene derivative, an oxazole derivative, an oxodiazole derivative, a stilbene derivative, a coumarin derivative, a xanicene-based dye represented by a rhodamine-based dye, or an oxazine-based dye. The light emitting device according to claim 12, wherein the light emitting device is a dye. 14. The light emitting device according to claim 12, wherein the polymer of the organic molecule is a substance whose main chain is a luminescent active substance or whose side chain is a luminescent active substance. Substances whose main chain is luminescent are polyparaphenylene derivatives, polyparaphenylene vinylene derivatives, arylene vinylene derivatives represented by polynaphthovinylene derivatives, polythiophene derivatives represented by poly (3-alkylthiophene), and polyfluorene derivatives The light emitting device according to claim 14, wherein: A substance whose side chain has luminescence activity is a polymer or a crosslinked body in which a monomer of a luminescence active organic compound is chemically bonded to the side chain of a high molecular polymer of polymethyl methacrylate, polycarbonate, or polystyrene. Wherein the moiety is a photoexcited luminescent activity, or a complex formed by associating an 8-quinolinol derivative with a metal ion, a metal complex such as an azomethine complex, or an aggregate of a cyanine dye (J-aggregate). The light emitting device according to claim 14, wherein: The light-emitting device according to any one of claims 1 to 16, wherein the light degradation prevention layer is made of a light-transmitting polymer material. A translucent polymer material disperses at least one selected from the group consisting of a salicylic acid derivative, a benzophenone derivative, a benzotriazole derivative, a cyanoacrylate derivative, and a hindered amine-based material in polymethyl methacrylate or polycarbonate. The light-emitting device according to claim 17, wherein the light-emitting device is provided. An excitation light source layer, a light-emitting layer, and a light deterioration prevention layer are provided on a substrate, and the substrate is made of an optically transparent or translucent material. The light-emitting layer is provided on the opposite side of the excitation light source layer and the substrate. The light-emitting device according to any one of claims 1 to 18, wherein: 20. The light emitting device according to claim 19, wherein the substrate is made of a material having a larger band gap than a material of the excitation light source layer.

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