JP3708730B2 - Light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to the technical field of GaN-based semiconductor light emitting devices and phosphors.
[0002]
[Prior art]
White light sources using light-emitting diodes (LEDs) include a configuration that produces white only by the emission color of the LEDs and a configuration that combines phosphors with LEDs.
In the former configuration, red light (LEDs such as AlGaAs, AlInGaP, and GaN), green light (GaN-based LEDs), and blue light (GaN-based LEDs) are mixed to produce white light.
On the other hand, in the latter configuration, a light-emitting device that produces white light using a GaN-based blue LED as an excitation light source and a phosphor that emits yellowish fluorescence that is complementary to blue is realized. In this light-emitting device, white light is generated by blue light from an excitation light source that leaks through the phosphor and yellowish fluorescence from the phosphor.
[0003]
[Problems to be solved by the invention]
The present inventors examined the performance of a conventional light emitting device using a blue LED and a phosphor, and made a problem that high-luminance light emission was not obtained from the device. Furthermore, when the cause was examined, the light extraction efficiency of the GaN-based blue LED used as the excitation light source is low, and even if an effective amount of phosphor is disposed in actual use, it is not sufficiently excited. I understand. This is also a problem when using a short wavelength LED of 420 nm or less to excite a phosphor capable of emitting multiple colors and realizing an illuminating lamp that replaces the discharge tube fluorescent lamp currently in practical use. In particular, when the LED is a surface emitting type, it has been found that low light extraction efficiency becomes a fatal defect.
[0004]
The present invention has been made in view of such circumstances, and provides a light-emitting device in which a phosphor is sufficiently excited by light having a short wavelength of 450 nm or less, such as blue light and ultraviolet light, to obtain high-luminance light emission. The challenge is to do.
[0005]
[Means for Solving the Problems]
  In order to solve the above problems, the present invention has the following features.
(1)The following (A) GaN-based light-emitting diode that emits light of a wavelength of 450 nm or less is used as an excitation light source, and the phosphor of the following (A) is excited by the light from the excitation light source to emit visible range fluorescence. A light emitting device having at least a configuration disposed in a recess of a GaN-based light emitting diode,The light from the light emitting layer to the upper side of the laminate is blocked by the p-type electrode, so that the light emitted from the light emitting layer is incident on the phosphor and only the fluorescence is emitted to the outside.DepartureOptical device.
(A) A GaN-based light-emitting diode having a structure in which a stack of GaN-based crystals is formed on a crystal substrate so as to include a light-emitting layer, and an electrode is provided on the stack, and the entire top surface of the stack is A GaN-based light-emitting diode that is covered with a p-type electrode, and that the laminate is provided with a recess from its upper surface, and at least the light-emitting portion of the light-emitting layer is exposed on the inner side surface of the recess.
(2(1) The above-mentioned (1), wherein the visible range fluorescence emitted from the phosphor has two or more peaks in the visible range spectrum.)The light-emitting device of description.
(3(1) The GaN-based light-emitting diode of (A) is a GaN-based light-emitting diode array in which a plurality of light-emitting element portions are formed on a wafer as a common crystal substrate.)The light-emitting device of description.
[0015]
As used herein, “GaN-based” refers to the formula In_XGa_YAl_ZIt means a compound semiconductor determined by N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z = 1).
[0016]
[Action]
In the present invention, as one aspect for solving the problem, a GaN-based semiconductor laser that emits laser light having a wavelength of 450 nm or less is used as an excitation light source for a phosphor. As a result, unprecedented strong light is obtained as excitation light having a short wavelength of 450 nm or less, and accordingly, high-intensity fluorescence is obtained. In particular, the low light extraction efficiency of a conventional surface-emitting blue LED is remarkably improved by using a surface-emitting laser, and a preferable surface-emitting light-emitting device is obtained.
[0017]
In the present invention, as another aspect for solving the problem, when a GaN-based LED is used as an excitation light source of a phosphor, as shown in the above (A) and FIG. A GaN-based LED to which is given is used. Furthermore, a phosphor is attached to the LED according to the unique combination of the present invention to form a light emitting device, thereby obtaining a unique method of taking out the fluorescent light, and improving the low light extraction efficiency of the blue LED. A new mode is provided for the combination of LED and phosphor.
[0018]
The structure unique to the present invention provided to the GaN-based LED is a recess, and is a structure in which a main part of light emission is emitted into the recess. Even if a general LED is provided with such a recess, the light emitted into the recess only attenuates. In addition, the unique combination method of the present invention and the unique method of taking out fluorescence are that the phosphor is disposed inside the recess, and that fluorescence is taken out from the inside of the recess.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
First, an apparatus using a GaN-based semiconductor laser (hereinafter also simply referred to as “laser”) as an excitation light source, which is an embodiment of the light-emitting device of the present invention, will be described.
As shown in FIG. 1, the light-emitting device of the present invention has a configuration in which a laser 1 is used as an excitation light source and the laser 1 and a phosphor 2 are combined. The laser 1 emits laser light L1 having a wavelength of 450 nm or less, and the phosphor 2 emits fluorescence L2 in the visible range when excited by the laser light L1.
[0020]
As shown in FIGS. 1A and 1B, the combination of the laser 1 and the phosphor 2 may be in close contact with each other or separated. The phosphor 2 is disposed with respect to the laser 1 so that the laser beam L1 from the laser 1 can be received. As shown to Fig.1 (a), the arrangement | positioning which irradiates a laser beam to the surface which apply | coated or coated fluorescent substance may be sufficient, and it is in the spherical body or optical fiber form with a favorable optical coupling property (coupling) with a laser beam. A processed phosphor may be disposed. As shown in FIG. 1B, the mode in which the phosphor 2 is directly attached to the laser 1 is compact and easy to manufacture and handle the apparatus.
[0021]
The GaN-based semiconductor laser only needs to emit laser light having a wavelength of 450 nm or less, and is a surface-emitting element as shown in FIG. 2, a stripe-type element as shown in FIG. 3, or any of these types. Examples include a laser array in which elements are arranged on a wafer.
[0022]
A part of the laser light may be used together with the fluorescent light through the phosphor. However, when the light emitting device of the present invention is used for illumination or the like, it is not preferable for the human body to emit the laser light to the outside. . In that case, it is preferable that all of the light is absorbed by the phosphor or not emitted to the outside by a filter or the like.
[0023]
The wavelength of the laser light may be 450 nm or less, and a wavelength necessary for excitation of the phosphor is used. Therefore, the wavelength of the laser beam may be determined in consideration of the combination with the following phosphor.
In particular, as mentioned above as a problem to be solved, white light obtained by a device combining a conventional blue LED and a phosphor does not have sufficient light intensity. Therefore, the usefulness of the present invention is particularly remarkable when white light or light of a color close thereto is obtained by a semiconductor light emitting device. In order to obtain white light or light of a color close to it, the emitted fluorescence has two or more peaks in the visible spectrum, for example, light mixed with two colors, light mixed with three colors, etc. What is necessary is just to select a fluorescent substance so that it may become light.
[0024]
The fluorescence referred to in the present invention means luminescence emitted by photoexcitation.
In addition, the phosphor referred to in the present invention includes a mixture of a fluorescent substance and a medium. The phosphor is not particularly limited as long as it is excited by light from an excitation light source and emits fluorescence in the visible range, and a substance that becomes a luminescent center is localized in a transparent medium (especially a solid such as glass or crystal). A known substance such as a substance that exhibits intrinsic luminescence in a pure state may be used. Specific examples include phosphors used in discharge tube fluorescent lamps and phosphors used in color television CRTs. A semiconductor material that is excited by short light of 450 nm or less and emits visible light is included in the phosphor according to the present invention.
[0025]
In order to make fluorescence have light having two or more peaks in the visible spectrum so as to be close to white light, the following modes are exemplified.
(1) A mode in which substances that emit one peak light are collected for a necessary peak to form one phosphor, and a plurality of peak lights are mixed.
{Circle around (2)} A mode in which a phosphor having a plurality of energy levels and two or more peak lights to be emitted from a single substance is used.
(3) A mode in which the above (1) and (2) are combined.
Among the above (1) to (3), (1) and (3) are useful because the color development can be freely adjusted.
[0026]
In the above aspect (1), in order to mix the intrinsic peak light emitted from each substance, each substance is combined and mixed at the raw material level, or each substance is arranged in a matrix on the surface irradiated with excitation light. For example, the layers may be arranged or stacked so that excitation light passes through each substance in order.
[0027]
Examples of the fluorescent material (or fluorescent material) include the fluorescent material described on page 78 of the Institute of Electrical Engineers of Japan, "Illumination Engineering" (revised 20th edition) published by the Institute of Electrical Engineers of Japan, and JP-A-10-163535. One or more phosphors selected from the phosphors described in 1) can be used. Preferred embodiments of the phosphor include a sintered body, a coating applied to a transparent plate-like material such as quartz, a glass-like object, solidified into a sphere, a column, or a fiber, processed, Examples of the molded product are included.
[0028]
As shown in FIG. 1 (a), when the laser 1 and the phosphor 2 are separated and combined, the phosphor becomes a single member or component. For example, the phosphor 2 may be a transparent member coated or coated with a fluorescent material, a glass member in which the fluorescent material is dispersed, etc., and used in combination with a laser element. In this case, the laser is preferably a surface emitting laser.
[0029]
As shown in FIGS. 1B, 2, 3, and 4, when the phosphor is directly provided on the laser emission portion, a method for forming the phosphor on the emission surface is, for example, a sol-gel method. Depending on the material, there are methods such as sputtering, vacuum deposition, etc. depending on the method used for film formation by mixing with a liquid glass precursor material such as Can be mentioned.
[0030]
The example of FIG. 2 is an example of a specific mode of the light-emitting device shown in FIG. 1B, and uses a surface emitting laser as a GaN-based semiconductor laser. In the example of the figure, the phosphor 2 is formed in a film shape on the emission surface of the surface emitting laser 1. The surface emitting laser 1 shown in FIG. 1 includes an n-AlGaN layer (contact layer) S1, a lower reflector H1, a buffer layer (not shown) on a crystal substrate (for example, sapphire crystal substrate) B, A GaN-based crystal layer (n-AlGaN clad layer S2, InGaN active layer S3, p-AlGaN clad layer S4, p-AlGaN contact layer S5) including a light emitting layer is sequentially laminated, and an n-type electrode P2 and a p-type electrode P1 are formed. It has a provided structure.
[0031]
A circular opening is provided in the central portion of the p-type electrode P1, and the p-AlGaN contact layer S5 is exposed in the opening. An upper reflector H2 is provided in this portion, and optical resonance occurs between H1 and H2. The vessel is configured. The phosphor 2 is provided on the upper surface of the upper reflector H2. Although it is a preferable aspect for the reason on the formation process of a conductivity type that the upper side of a laminated body is made into a p-type, it is not limited to this, A n-type may be an upper side.
[0032]
With the configuration shown in FIG. 2, the light emitted from the active layer oscillates in a direction perpendicular to the substrate surface, the laser light is emitted into the phosphor 2, and the fluorescence L2 is emitted to the outside, whereby strong fluorescence is obtained.
[0033]
The material of the light-emitting portion, for example, the material of the active layer in FIG. 2 may be a GaN-based material that can emit light having a wavelength of 450 nm or less, and the composition depends on the wavelength necessary for excitation of the phosphor. Just decide.
[0034]
In the example of FIG. 2, a current confinement structure is provided so that a current flows intensively in a portion of the active layer S3 that is on the optical path of laser oscillation. The current confinement structure has a formation pattern corresponding to the formation pattern of the p-type electrode, for example, a low carrier concentration GaN-based crystal layer or SiO 2₂This is achieved by providing a high resistance layer S6 such as a layer or a reverse conductivity type layer S6 such as an n-GaN layer.
[0035]
The phosphor in the example of FIG. 2 is not particularly limited, but is selected from known or commercially available materials suitable for the target color temperature and color tone. Examples of the forming method include a method of forming a thin film by mixing with a solvent or a resin, applying and drying, and a method of forming a phosphor-containing glass thin film by a sol-gel method.
[0036]
The configuration of the optical resonator is not limited, but the lower reflector is preferably a Bragg reflection layer that can withstand crystal growth of the upper layer and can be formed of a GaN-based crystal layer. The upper reflector may be a Bragg reflection layer, a dielectric multilayer film, or the like.
[0037]
For other structures of the surface emitting laser 1 itself, the shape of each part, the material, and the method of forming each part, known techniques may be referred to. Further, when laser light is emitted from the substrate side, processing may be performed as necessary, such as providing an opening in a portion of the back surface of the crystal substrate that corresponds to the optical path of the emitted light.
[0038]
Further, the surface emitting laser described above may be formed as a GaN-based surface emitting laser array by forming a number of elements in a two-dimensional matrix on a sapphire crystal substrate wafer having an outer diameter of 2 inches. At that time, the phosphors may be individually provided in the individual elements as in the embodiment of FIG. 2, or a large-area plate-like phosphor is attached to the emission side of the array so that all the individual laser beams are 1 It is good also as an aspect received with two fluorescent substance.
[0039]
2, the surface emitting laser element 1 emits intense blue light to the phosphor 2 to obtain a surface-emitting light emitting device that emits white fluorescent light with high brightness, which is not conventional.
[0040]
The example of FIG. 3 is an example of another mode of the light-emitting device shown in FIG. The GaN-based semiconductor laser 1 shown in FIG. 1 has a structure in which resonators by cleavage are formed at both ends of an active layer, and resonates in parallel with the active layer and emits in the same manner as a known stripe structure. In the example of the figure, it is assumed that the resonance direction is perpendicular to the paper surface, and the laser light is emitted from the back of the paper surface in the front direction. Therefore, although the cleavage plane and the phosphor do not appear in the drawing, for the sake of explanation, the center of the beam of the emitted laser light is indicated by “x” in the center of the active layer S3 and formed on the emission surface. The phosphor 2 is represented by a dashed line in a thick line. With this configuration, the laser light oscillates perpendicularly to the paper surface, is emitted into the phosphor 2, and the fluorescence is output to the outside.
[0041]
The laser 1 of FIG. 3 has substantially the same structure as that of FIG. 2 except for the presence of the optical resonator, the p-type electrode, and the mask layer M. The crystal substrate B, buffer layer, n-GaN-based contact layer S1, n A -GaN-based cladding layer S2, a GaN-based active layer S3, a p-GaN-based cladding layer S4, a current confinement structure S6, and a p-GaN-based contact layer S5 are sequentially stacked, and an n-type electrode P2 and a p-type electrode P1 The structure is formed.
[0042]
The phosphor is formed on the cleavage surface on the emission side, and may be larger than the size including the emitted laser beam, or may be formed over the entire side surface of the element. As the structure and formation method of the phosphor material, those described in the description of FIGS. 1 and 2 can be used.
[0043]
The current confinement structure S6 is a structure in which current is concentrated in a stripe-shaped portion perpendicular to the paper surface in the center of the active layer. The active layer emits light intensively in that portion, laser oscillates perpendicular to the paper surface, and laser light is emitted. Is done.
[0044]
The mask layer M provided in the structure of the laser 1 in FIG. 3 is provided for growing the GaN-based crystal layer after the contact layer S1 as a low dislocation crystal layer. The crystal growth method using this mask layer will be schematically described. SiO that does not substantially grow GaN-based crystals.₂A mask pattern is formed on the substrate using a material such as a GaN-based crystal grown from a region where the mask layer is not formed (non-mask region) as a starting surface until the crystal fills and covers the mask layer. It is a method of continuing growth. In the example of FIG. 3, the GaN-based crystal layer that covers and covers the mask layer is used as the n-contact layer S1. Due to the low dislocation structure by the mask layer M and the current confinement structure by the high resistance layer S6, a light emission portion having a low dislocation stripe shape can be generated in the active layer.
[0045]
Further, the laser described in FIG. 3 may be provided as a laser array by providing a large number of adjacent elements on a single crystal substrate having a large area. At that time, the phosphor may be individually provided for each element, or may be attached to the emission side of the array as a plate-like member that receives all the laser beams from adjacent elements in a single sheet. .
[0046]
Next, as another aspect of the present invention, an apparatus using a GaN-based LED as an excitation light source will be described.
In the example of FIG. 4, the GaN-based LED includes a GaN-based crystal layer (n-AlGaN contact layer S1, n-clad layer S2, active layer S3, p) including a light-emitting layer on a crystal substrate B via a buffer layer. -A clad layer S4, p-contact layer S5) is formed, on which an n-type electrode P2 and a p-type electrode P1 are formed, and a recess (u1) reaching from the upper surface of the p-type electrode P1 to the inside of the laminate , U2, u3). A cross section of the active layer S3 is exposed on the inner side surface of the recess, and the light L1 from the active layer is emitted into the recess.
[0047]
In the light emitting device of FIG. 4, phosphors 21, 22, and 23 are filled in the recesses, and phosphors 24 and 25 are also provided on the outer wall surface of the laminate. In the example of FIG. 4, the p-type electrode covers the entire top surface of the multilayer body, and the light traveling from the active layer to the upper side of the multilayer body is blocked by the p-type electrode. With this configuration, the light emitted from the active layer into the recesses excites each phosphor, and the fluorescence L2 emitted from the phosphors is emitted from the recesses toward the outside.
[0048]
The aspect of the phosphor, the number of fluorescence peaks, the wavelength of the fluorescence, the emission wavelength of the LED, and the relationship thereof are the same as described above for the case where the excitation light source is a laser. Further, as a method of providing a phosphor on the element, the method described in the case of using an excitation light source as a laser can be used.
[0049]
The form of the recess is not limited, and even in a form in which holes having various opening shapes such as square holes and round holes are used as the recesses, and this is two-dimensionally arranged, the grooves that divide the laminate portion are used as the recesses. Examples include a striped form.
[0050]
The depth of the recess may be such a depth that at least a portion that emits light (for example, a depletion layer portion in a pn junction or a well portion in a well-type potential structure) is exposed on the inner wall of the recess. In the example of FIG. 4, the depth of the recess reaches the n-AlGaN cladding layer S2, and the active layer S3 is completely exposed on the inner wall of the recess.
[0051]
The size w1 shown in FIG. 4 such as the size of the opening shape of the recess, for example, the diameter in the case of a round hole, one side in the case of a square hole, and the groove width in the case of a groove is not limited, but is preferably about 2 μm to 200 μm. Dimensions.
On the other hand, the width (dimension w2 shown in FIG. 4) of the laminate sandwiched between the two recesses is not limited, but is preferably about 2 μm to 400 μm in consideration of the intensity of light emission.
The ratio between the dimension w1 of the recess and the width w2 of the laminate may be determined so that strong fluorescence is emitted to the outside (upward) most efficiently.
[0052]
The example of FIG. 4 is a mode in which the upper part of the stack is completely covered with a p-type electrode, the light emitted from the light emitting layer is almost incident only on the phosphor, and only the fluorescence is used as a light source to the outside. However, in addition to such an embodiment, the light emitted from the light emitting layer may be directly emitted to the outside world by adjusting the area occupied by the p-type electrode and the transparency of the p-type electrode, and used together with fluorescence.
[0053]
The example of FIG. 4 shows an example in which a concave portion is provided in one element. However, a large number of such elements are formed in a two-dimensional matrix on a single crystal substrate having a large area to form a GaN-based LED array. Also good. In the case of an array, the individual elements are not distinguished, and each GaN-based crystal layer having the same size as the crystal substrate is stacked on one large crystal substrate to form as many recesses as necessary. It may be an aspect.
[0054]
In any of the embodiments shown in FIGS. 2 to 4, the same crystal substrate and electrode material are used. As the crystal substrate, in addition to a sapphire crystal substrate, a known substrate capable of growing a GaN-based crystal such as SiC or quartz can be used.
[0055]
The structure related to light emission may be a structure preferable for laser light emission and oscillation and LED light emission, and a double heterojunction structure, SQW (Single Quantum Well), MQW (Multiple Quantum Well), a structure including quantum dots, and the like are preferable. It is mentioned as a thing. Further, in the case of an LED, a simple two-layer pn junction by homojunction or heterojunction may be used.
[0056]
【Example】
Example 1
In this example, the embodiment shown in FIG. 2, that is, a light emitting device having a surface emitting laser provided with a phosphor was manufactured. In the following description, the unit [cm^-3] Is the carrier concentration.
[Production of surface emitting laser]
As shown in FIG. 2, n-Al is formed on a C-plane sapphire crystal substrate via a low-temperature GaN buffer layer (thickness 30 nm)._0.05Ga_0.95N contact layer S1 (thickness 3 μm, 1 × 10¹⁸cm^-3), Bragg reflection layer H1, n-Al_0.15Ga_0.85N clad layer S2 (thickness 0.4 μm, 8 × 10¹⁷cm^-3), In_0.02Ga_0.98N active layer S3 (thickness 4 nm, 2 × 10¹⁷cm^-3, Emission wavelength 370 nm), p-Al_0.2Ga_0.8N clad layer S4 (thickness 0.2 μm, 5 × 10¹⁷cm^-3), Undoped Al_0.5Ga_0.5N (thickness 80 nm) current confinement structure S6, p-Al_0.05Ga_0.95N contact layer S5 (thickness 0.2 μm, 8 × 10¹⁷cm^-3) Was grown sequentially.
[0057]
The specifications of the Bragg reflection layer H1 are (GaN, thickness 38 nm) and (Al_0.28Ga_0.72N, with a thickness of 43 nm).
[0058]
Next, the n-AlGaN contact layer S1 is partially exposed by etching from the upper layer of the stack by RIE, and an n-type electrode P2 (Ti / Al) is formed in that portion, and the remaining p- A p-type electrode P1 (Ni / Au) was formed on the upper surface of the AlGaN contact layer S5.
[0059]
Further, the central portion of the p-type electrode P1 was removed into a circle having a diameter of 5 μm to expose the p-AlGaN contact layer S5, and an upper reflective layer H2 made of a dielectric multilayer film was formed. The specification of the reflective layer H2 by this dielectric multilayer film is the upper layer side (ZrO₂) And lower layer side (SiO₂) And a set of 40 sets, which were formed by electron beam evaporation. Thus, a surface emitting laser capable of emitting laser light having a wavelength of 370 nm was obtained.
[0060]
[Applying phosphor]
On the upper surface of the reflection layer H2 on the upper side of the surface emitting laser, a glass in which a fluorescent material is dispersed is formed in a film shape (thickness: 3 μm) by a sol-gel method to obtain a light emitting device of the present invention. The phosphor receives laser light having a wavelength of 370 nm and emits fluorescence including blue, green, yellow, and red color components, and visually becomes a color close to white.
[0061]
[Evaluation]
When power was supplied to the laser of the light emitting device to cause laser oscillation, the energy conversion efficiency was 80 [lm / W].
[0062]
Example 2
In this example, the embodiment shown in FIG. 3, that is, a light emitting device combining a stripe type laser and a phosphor was manufactured.
[Laser fabrication]
First, as a stripe-type GaN-based laser 1, on a C-plane sapphire crystal substrate, a low-temperature GaN buffer layer (thickness 30 nm, not shown), a GaN thin film (thickness 4 μm, 8 × 10).¹⁷cm^-3, Not shown) to form a base substrate B. By means of sputtering and patterning technology, on the base substrate B, SiO for reducing dislocations is formed.₂A mask layer M (striped pattern) was formed. Using an MOCVD apparatus, the non-mask region is used as a starting surface for crystal growth, and n-Al_0.05Ga_0.95N (1 × 10¹⁸cm^-3) And grow SiO₂The n-contact layer S1 was grown by covering the mask layer M until it was covered.
[0063]
Furthermore, n-Al_0.15Ga_0.85N clad layer S2 (thickness 0.4 μm, 8 × 10¹⁷cm^-3), Active layer S3 having an MQW structure, p-Al_0.2Ga_0.8N clad layer S4 (thickness 0.1 μm, 7 × 10¹⁷cm^-3) Was formed. The MQW structure is n-Al._0.1Ga_0.9N is a barrier layer and n-In_0.02Ga_0.98N is a well layer.
[0064]
Furthermore, n-Al_0.2Ga_0.8N (thickness 70 nm, 4 × 10¹⁷cm^-3) And a current passing portion of the current confinement structure is formed by p-Al._0.05Ga_0.95N (8x10¹⁷cm^-3The p-contact layer S5 (thickness 0.1 μm) is successively grown to form the p-type electrode P1 (Ni / Au) and the n-type electrode P2 (Ti / Al). A GaN-based laser that oscillates perpendicularly to the paper surface of FIG. 3 and can emit laser light having a wavelength of 370 nm was obtained using the cleavage plane on the side surface of the laminate as an optical resonator.
[0065]
[Applying phosphor]
A spherical lens-like glass (average particle size of 50 to 100 μm) in which the selected phosphor is contained on the emission surface of this laser (the surface in front of the active layer of the element shown in FIG. 3) is coupled with the emission laser light. Thus, the light emitting device of the present invention was obtained. The phosphor receives laser light having a wavelength of 370 nm and emits fluorescence including blue, green, yellow, and red color components, and visually becomes a color close to white.
[0066]
[Evaluation]
When power was supplied to the laser of the light emitting device to cause laser oscillation, the phosphor had an energy conversion efficiency of 90 [lm / W].
[0067]
Example 3
In this example, the embodiment shown in FIG. 4, that is, a light emitting device in which a phosphor is provided on a GaN-based LED was manufactured.
[Production of GaN-based LEDs]
As shown in FIG. 4, a low-temperature GaN buffer layer (thickness 25 μm, not shown), undoped Al on a C-plane sapphire crystal substrate_0.05Ga_0.95N (thickness 3 μm) was formed to form a base substrate B. By means of sputtering and patterning technology, on the base substrate B, SiO for reducing dislocations is formed.₂A mask layer M (striped pattern) was formed. Using an MOCVD apparatus, the non-mask region is used as a starting surface for crystal growth, and n-Al_0.05Ga_0.95N (1 × 10¹⁸cm^-3) And grow SiO₂The n-contact layer S1 was grown by covering the mask layer M until it was covered.
[0068]
Furthermore, n-Al_0.15Ga_0.85N clad layer S2 (thickness 0.3 μm, 1 × 10¹⁸cm^-3), In_0.02Ga_0.98N active layer S3 (thickness 3.5 nm, emission wavelength 370 nm), p-Al_0.2Ga_0.8N clad layer S4 (thickness 0.2 μm, 7 × 10¹⁷cm^-3), P-Al_0.05Ga_0.95N contact layer S5 (thickness 0.1 μm, 1 × 10¹⁸cm^-3) Were sequentially grown to obtain a laminate.
[0069]
Similarly to Example 1, the n-contact layer S1 is partially exposed by etching from the upper layer of the stacked body by RIE to form the n-type electrode P2 (Ti / Al), and the p-contact layer S5. A p-type electrode P1 (material Ni / Au) was formed thereon.
[0070]
The stacked body composed of the GaN-based crystal layer formed as described above is dug down from the upper surface of the p-type electrode by RIE (Reactive Ion Etching) to form groove-like recesses u1 to U3, and used as an excitation light source Got. The groove width w1 of each recess is 15 μm, and the width w2 of the laminate is 50 μm. The depth of each recess was set to a depth (0.8 μm) at which the entire thickness of the active layer appeared completely on the side surface of the recess and the n-cladding layer was exposed on the bottom surface.
[0071]
[Applying phosphor]
The phosphors are applied to the inside of the groove-shaped recesses u1 to u3 of the LED and the wall surface outside the active layer by screen printing, and sintered at a low temperature up to 300 ° C. to form the phosphors 21 to 25. The light emitting device of the present invention was obtained. The phosphor receives light having a wavelength of 370 nm from the LED, and emits fluorescence including blue, green, yellow, and red color components, and visually becomes a color close to white.
[0072]
[Evaluation]
When power was supplied to the LED of the light emitting device to emit light, the energy conversion efficiency was 80 [lm / W].
[0073]
【The invention's effect】
In the light emitting device of the present invention, as a first aspect, a laser is used as an excitation light source. Thus, even if light having a short wavelength of 450 nm or less is used as excitation light, the phosphor is sufficiently excited and has high luminance. Fluorescence is obtained. As a second aspect, when an LED is used as the excitation light source, fluorescence is emitted to the outside as a special structure in which a concave portion is provided in the LED and a phosphor is disposed in the concave portion. This structure improves the low light extraction efficiency of the blue LED.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of a configuration of a light emitting device of the present invention.
FIG. 2 is a diagram showing an embodiment of a light emitting device of the present invention, and shows an example in which a surface emitting laser is used as an excitation light source.
FIG. 3 is a diagram showing one embodiment of a light-emitting device of the present invention, and shows an example in which a stripe laser is used as an excitation light source.
FIG. 4 shows an example in which a GaN-based LED is used as an excitation light source as another embodiment of the light-emitting device of the present invention.
[Explanation of symbols]
1 GaN semiconductor laser
2 Phosphor
L1 laser light
L2 fluorescence

Claims (3)

The following (A) GaN-based light-emitting diode that emits light of a wavelength of 450 nm or less is used as an excitation light source, and the phosphor of the following (A) is excited by the light from the excitation light source to emit visible range fluorescence. A light emitting device having at least a configuration disposed in a recess of a GaN-based light emitting diode,
The light from the light emitting layer to the upper side of the laminate is blocked by the p-type electrode, so that the light emitted from the light emitting layer enters the phosphor and only the fluorescence is emitted to the outside. that light emission devices.
(A) A GaN-based light-emitting diode having a structure in which a stack of GaN-based crystals is formed on a crystal substrate so as to include a light-emitting layer, and an electrode is provided on the stack, and the entire top surface of the stack is A GaN-based light-emitting diode that is covered with a p-type electrode, and that the laminate is provided with a recess from its upper surface, and at least the light-emitting portion of the light-emitting layer is exposed on the inner side surface of the recess. The light-emitting device according to claim 1, wherein fluorescence in the visible range emitted from the phosphor has two or more peaks in the spectrum in the visible range. The light-emitting device according to claim 1, wherein the GaN-based light-emitting diode (A) is a GaN-based light-emitting diode array in which a wafer is used as a common crystal substrate and a plurality of light-emitting element portions are formed on the wafer.

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