JP2009071337A - Light emitting device, and illuminating device using the same - Google Patents

Light emitting device, and illuminating device using the same Download PDF

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JP2009071337A
JP2009071337A JP2008335798A JP2008335798A JP2009071337A JP 2009071337 A JP2009071337 A JP 2009071337A JP 2008335798 A JP2008335798 A JP 2008335798A JP 2008335798 A JP2008335798 A JP 2008335798A JP 2009071337 A JP2009071337 A JP 2009071337A
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light
phosphor
gan
emitting device
based
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Yoshiyuki Imada
Hiroaki Okagawa
Yoichiro Ouchi
Kazuyuki Tadatomo
Tsunemasa Taguchi
Takashi Tsunekawa
Masahiko Yoshino
善之 今田
一行 只友
正彦 吉野
洋一郎 大内
広明 岡川
高志 常川
常正 田口
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Kasei Optonix Co Ltd
Mitsubishi Chemicals Corp
三菱化学株式会社
化成オプトニクス株式会社
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<P>PROBLEM TO BE SOLVED: To provide a light emitting device in which variation in color tones is suppressed by improving a light emitting device configured to output visible light through the combination of a LED and a phosphor, and to provide an illuminating device using the same. <P>SOLUTION: A GaN-based LED 1 is combined with the phosphor 2 which is excited by light L1 emitted from the LED 1 and emits fluorescence (visible light) L2, to thereby compose the light emitting device using the fluorescence L2 as output light. The LED 1 and the phosphor 2 are selected and combined such that variation in the chromaticity of the output light falls within 0.05 on the x-y chromaticity diagram when the amount of driving currents injected into the LED 1 is varied from 0.1 A/cm<SP>2</SP>to 70.0 A/cm<SP>2</SP>per unit light-emitting area. A white lighting fixture in which variation in color tones is suppressed can be obtained by using a high-efficiency InGaN-based ultraviolet LED as the LED 1, and a white phosphor as the phosphor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light-emitting device that includes a combination of a light-emitting diode (LED) and a phosphor that emits fluorescence when excited by light emitted from the LED, and emits visible light as output light.

Conventionally, a light source that emits light of various wavelengths is collected and arranged to constitute a color image display device, electrical decoration, signal lamp, lighting device, and the like.
As the light source, a semiconductor light emitting element such as an LED or a semiconductor laser (LD) (hereinafter also simply referred to as a light emitting element) or a combination of a light emitting element and a phosphor is used. The phosphor is selected so as to be excited by light from the light emitting element and emit fluorescence of various wavelengths.

  Among the light sources described above, a combination of an LED and a phosphor, in particular, a so-called white LED configured to output white light is important as a lighting fixture. As a conventional white LED, first, a combination of a blue LED and a yellow phosphor can be mentioned. This white LED has a structure in which a blue LED chip is covered with a first resin in which a yellow phosphor (a phosphor that is excited by blue light and emits yellow light) is dispersed, and then a second transparent resin is used to form a shell or the like. Is molded into With such a configuration, blue light that is not absorbed by the phosphor and passes through the first and second resin regions is mixed with yellow light from the phosphor in a complementary color relationship, and white light is output. looks like. However, since such white light does not completely contain the three primary colors of light, color purity and color rendering are poor.

  On the other hand, an attempt has been made to generate white light with good color purity and color rendering by combining an LED light source that emits light from purple to near-ultraviolet and a white phosphor. The white phosphor includes a phosphor component that emits fluorescence of three primary colors (three wavelengths of red, green, and blue) when excited by main light emission from the LED light source. White light produced by mixing the three primary colors has high color rendering properties and can be a preferable illumination light source.

  However, as described above, the present inventors have studied in detail a conventional light emitting device in which an LED and a phosphor are combined. As a result, any device increases the color tone (color balance) when the amount of current supplied to the LED is increased. Was found to change significantly.

  For example, in the case of a device capable of emitting white light (a so-called white LED) in which a blue LED and a yellow phosphor are combined, yellow light contained in white light (blue light converted by the phosphor) and blue light ( The ratio with respect to the light transmitted through the phosphor changes greatly depending on the light emission output of the blue LED. In addition, the light emission output of the blue LED does not increase in proportion to the injection current because the external quantum efficiency decreases as the injection current increases, and the conventional rated current (for example, 350 μm × 350 μm LED chip is normal) Saturation tendency is shown from around 20 mA). Even when the current is close to the rated current, the temperature of the LED chip rises. First, the conversion efficiency decreases due to the temperature rise of the phosphor. Second, the blue emission wavelength shifts longer, and the phosphor is excited. There is a phenomenon that efficiency changes. When a current exceeding the rated current is passed, this tendency becomes stronger, and in such a white LED, the color tone changes as the injection current into the blue LED increases.

In addition, in the case of a white LED that combines a purple to near-ultraviolet LED and a white phosphor, white is constituted only by red, green, and blue light fluorescence, and the light from the LED light source is not directly output. The change in color tone due to the loss of the color balance between the LED light emission and the phosphor light emission as described in the white LED can be suppressed. However, when a conventional near-ultraviolet LED with a low output or a phosphor with low conversion efficiency is used, the following phenomenon occurs due to the temperature rise of the LED light source due to energization, and the color tone also changes.
First, the light emission wavelength of the light source changes due to the temperature rise of the LED light source, thereby changing the conversion efficiency for each phosphor of each color, resulting in a change in color tone.
Second, the temperature of the phosphor changes due to the temperature rise of the LED light source, thereby changing the conversion efficiency of the phosphors of the respective colors, resulting in a change in color tone.

  The problem of color tone change as described above is a problem that occurs not only in a light emitting device combining an LED and a phosphor, but also in a light emitting device combining an LD and a phosphor. Accordingly, an object of the present invention is to improve the above problem, improve a light emitting device configured to output visible light by combining a light emitting element and a phosphor, and the light emitting device in which a change in color tone is suppressed, And it is providing the illuminating device using the same.

The present invention has the following features.
(1) A light-emitting device that combines a GaN-based light-emitting element and a phosphor that emits visible light when excited by light emitted from the light-emitting element, and uses the fluorescence as output light,
The GaN-based light emitting device is a GaN-based light emitting diode, and the amount of driving current injected into the light emitting diode is changed from 0.1 (A / cm 2 ) to 70.0 (A / cm 2 ) per unit light emitting area. A light-emitting device characterized in that when it is made, the amount of change in chromaticity of the output light is within 0.05 on the xy chromaticity diagram.
(2) The GaN-based light-emitting diode has a light-emitting portion configured to include a light-emitting layer made of an InGaN-based material, and the light-emitting portion has a single quantum well structure, a multiple quantum well structure, Alternatively, it has a double hetero structure, an emission peak wavelength of 430 nm or less, and 5% when a drive current of 30 (A / cm 2 ) per unit emission area is injected in a bare chip state.
The light-emitting device according to (1), which has the above external quantum efficiency.
(3) The GaN-based light emitting diode is configured to emit photoluminescence light having a wavelength different from that of main light emission, and the photoluminescence light is output together with the fluorescence. The light-emitting device of description.
(4) A light-emitting device in which a GaN-based light emitting element and a phosphor that emits visible light when excited by light emitted from the light-emitting element are combined, and uses the fluorescence as output light. A GaN-based semiconductor laser having an emission peak wavelength of 360 nm to 430 nm and an external quantum efficiency of 10% or more of the total emission energy. The laser output of the semiconductor laser is 10 times the laser output from the laser output when the oscillation threshold current is applied. A light emitting device characterized in that when the laser output is changed, the amount of change in chromaticity of the output light is within 0.05 on the xy chromaticity diagram.
(5) light-emitting portion of the GaN-based light emitting device is a multiple quantum well structure composed of In A Ga 1-A N ( 0 <A ≦ 1) well layer and a GaN-based barrier layer, emission peak wavelength 360nm The light emitting device according to any one of the above (1) to (4), wherein the composition ratio A of the In A Ga 1-A N well layer is determined to be ˜430 nm.
(6) The element structure of the GaN-based light-emitting element is such that the GaN-based crystal layer covers the unevenness directly or via a low-temperature buffer layer made of a GaN-based semiconductor on a crystal substrate with unevenness processed on the surface. The light-emitting device according to any one of (1) to (5), wherein the light-emitting device is laterally grown or faceted and has a structure in which a light-emitting portion is formed on the GaN-based crystal.
(7) The visible light according to any one of (1) to (6), wherein the visible light is light having one or more peaks of emission intensity within a wavelength range from a wavelength of light emitted from the light emitting diode to a wavelength of 800 nm. The light-emitting device in any one.
(8) The light emitting device according to (7), wherein the visible light is white light including three primary color lights including red light, green light, and blue light.
(9) The phosphor is a white phosphor composed of a mixture of a red phosphor, a green phosphor, and a blue phosphor,
The red phosphors are [Ln 2 O 2 S: Eu (Ln = Y, La, Gd, Lu, Sc)] and [(Zn a , Cd 1-a ) S: Ag, Cl, (0.5> a > 0.2)] including one or more kinds of phosphors selected from
The green phosphor is [(Zn a , Cd 1-a ) S: Cu, Al, (1 ≧ a> 0.6)], [(
Zn a , Cd 1-a ) S: Au, Al, (1 ≧ a> 0.6)], [(Zn a , Cd 1-a ) S: Ag, Cl, (1 ≧ a> 0.6) And one or more phosphors selected from [(Ba, Sr) MgAl 10 O 17 : Eu, Mn],
The blue phosphor is [(Sr, Ca, Ba, Mg) 10 (PO 4 ) 6 Cl 2 : Eu], [
(Ba, Sr) MgAl 10 O 17 : Eu, Mn] and the above (1) to (8)
The light emitting device according to any one of the above.
(10) A lighting device having a configuration in which a plurality of light emitting devices according to any one of (1) to (9) are gathered.

  According to the present invention, it is possible to provide a light emitting device in which the color tone hardly changes even when the amount of current changes, and thus it is possible to provide a preferable lighting device that stably emits white light with good color rendering properties.

The light-emitting device according to the present invention includes a light-emitting element and a phosphor. In the following description, the present invention will be specifically described by taking a GaN-based LED as an example of the light-emitting element.
In the configuration example of FIG. 1, the light emitting device is configured by combining a GaN-based LED 1 and a phosphor 2. The phosphor 2 is excited by the light L1 emitted from the GaN-based LED 1 and emits fluorescence (visible light) L2, and the fluorescence L2 is output light of the light emitting device.

The GaN-based in the present invention, In A Ga B Al C N (0 ≦ A ≦ 1,0 ≦ B ≦ 1,0 ≦ C ≦
1, A + B + C = 1), and for example, AlN, GaN, AlGaN, InGaN and the like are important compounds.

As shown in the xy chromaticity diagram of FIG. 2, an important feature of the light emitting device when configured using a GaN-based LED is that the amount of drive current injected into the GaN-based LED is determined per unit light emitting area. when changing from 0.1 a / cm 2 up to 70A / cm 2, the amount of change in chromaticity of the output light (the amount of change from point m1 in diagram the x-y chromaticity to the point m @ 2 Delta] m) is 0. It is configured to be within 05, more preferably within 0.03.
By selecting and combining the GaN-based LED and the phosphor so as to satisfy this condition, a change in color tone is suppressed even when the drive current is increased.

Here, the amount of change Δm is given by the square root of (x2−x1) 2 + (y2−y1) 2 where the coordinates of the point m1 are (x1, y1) and the coordinates of the point m2 are (x2, y2). .
The xy chromaticity diagram used in the present invention is defined by the CIE 1931 xyz color system (JISZ8701).

When the same change in the drive current amount as described above is given to the conventional light emitting device, the change amount of the chromaticity of the output light exceeds the value 0.05 defined by the present invention. For example, it is 0.054 for a light emitting device composed of a blue LED and a yellow phosphor, and 0.052 even for a conventional product using an ultraviolet LED and a white phosphor. Not considered.

The amount of drive current injected into the LED to evaluate the amount of change in chromaticity is [current amount per unit light emission area A / cm 2] so that it does not vary depending on the shape of the LED. Stipulate.
The light emitting area means the effective total area in the lateral direction of the light emitting layer, but approximately, if the p electrode covers almost the front surface of the p layer, the area of the p layer may be substituted. good. In addition, when the p-electrode covers only a part of the p-layer, light is emitted substantially directly under the electrode, so that the electrode area may be used as the light-emitting area.
For example, in the device structure of a GaN-based light emitting diode formed on a sapphire substrate as shown in FIG. 3, when the device outer shape is a square of about (350 μm × 350 μm) to (5 mm × 5 mm), the light emitting area is reduced by etching for n-type electrode formed the 7 × 10 -4 cm 2 ~0.24cm 2 about. Among these, for example, when a light emitting area of 7.2 × 10 −4 cm 2 is used, the change in the amount of drive current injected for evaluating the change in chromaticity is 0.072 mA to 50 mA. Up to.

  As other measurement conditions for evaluating the amount of change in chromaticity, the ambient temperature is [15 to 35 ° C.], and the mounting state is [flip chip mounting is preferable for increasing luminous efficiency, Is a so-called p-side-up die bonding with the GaN-based light-emitting layer on the upper side, [epoxy-based resin] as a sealing (second mold resin) material, and a phosphor coating method [fluorescence mixed at an appropriate blending ratio] The mounted light-emitting element is coated (molded) with a silicon resin containing a body].

In order to achieve the above chromaticity change amount condition, the GaN-based LED used, the phosphor, and the combination thereof are important.
First, for a GaN-based LED, the following limitations are necessary for the emission peak wavelength, emission output, and external quantum efficiency.

  The emission peak wavelength of the GaN-based LED is an important factor related to the excitation efficiency of the phosphor, and thus the conversion efficiency of the phosphor from the excitation light to the fluorescence, and is preferably 450 nm or less, and more preferably 360 nm to 430 nm. . Moreover, 380 nm is mentioned as an example of a particularly preferable emission peak wavelength. This is because, in an LED using InGaN as the light emitting layer, the light emission efficiency is high and the excitation efficiency of the phosphor is generally high.

  The light emission output (value measured for the peak wavelength) of the GaN-based LED and the external quantum efficiency are important factors for suppressing the temperature rise of the LED accompanying energization. The electric power injected by energization is finally converted into light or heat. Therefore, an element with lower external quantum efficiency has a higher ratio of being converted into heat, and the temperature of the element increases, resulting in a decrease in the conversion efficiency of the phosphor and a deterioration of the light emitting element and the phosphor.

The light emission output of the GaN-based LED preferably has an external quantum efficiency of 5% or more, more preferably 7% or more when a drive current of 30 (A / cm 2 ) per unit light emitting area is injected in a bare chip state. .
As described in the evaluation of the amount of change in chromaticity, the light emission output is obtained by applying a silver paste or eutectic alloy with the substrate side down in a so-called p-side-up measurement environment at an ambient temperature of 15 ° C. to 35 ° C. Used as a metal material for bonding, for example, mounted on a metal stem known as a TO18 can and used as a test sample, which is inserted into an integrating sphere as it is, and measured with a standard measurement system that measures the total emission intensity. Measured as luminescence output.

The external quantum efficiency can be measured from the total light emission output by the following formula. The light emission output varies greatly depending on the shape of the element and the mounting method, but here the above evaluation method is the measurement method in a standard bare chip state.
The external quantum efficiency η e is calculated by η e = P O / ( IF · E g ).
P O [W] is the total light emission output, and I F [A] is the energization amount. E g [eV] is a value obtained by converting the emission peak wavelength λ p [μm] into an energy value, and is calculated by E g = 1.2398 / λ p .

In the present invention, it is recommended that the external quantum efficiency of the GaN-based LED is 5% or more, and particularly preferably 7% or more.
For example, in the device structure shown in FIG. 3, when the element outline and (350μm × 350μm) ~ (5mm × 5mm) of about rectangular, the light emitting area becomes 7 × 10 -4 cm 2 ~0.24cm 2 about. Among these, for example, the emission area is 7.2 × 10 −4 cm 2 and the emission peak wavelength is 380 n.
When an LED element of m is used, it is preferable that the light emission output is 3.3 mW (external quantum efficiency 5%) or more when a current of 20 mA is applied, and 4.6 mW (external quantum efficiency 7%) or more is more preferable.

  By limiting the light emission output and the external quantum efficiency of the GaN-based LED as described above, the temperature rise of the LED is suppressed as compared with the conventional light emitting device. Therefore, the change in the emission wavelength of the LED itself is also suppressed, and the change in the conversion efficiency of each phosphor on the wavelength plane is reduced. At the same time, the temperature rise of the phosphor due to heating is reduced, and the change in conversion efficiency of each phosphor is also reduced. These contribute to suppression of color tone change.

As shown in FIG. 3, the GaN-based LED that satisfies the conditions of the emission peak wavelength, the light emission output, and the external quantum efficiency includes a light-emitting portion 13 that includes a light-emitting layer made of an InGaN-based material. It is done.
The light-emitting portion is configured to have a p-type layer and an n-type layer so that light can be generated by current injection, such as (n-type clad layer / quantum well structure / p-type clad layer). It has a layer (light emitting layer). The light emitting layer is a well layer in a quantum well structure. As a preferable structure of the light emitting portion, a single quantum well (SQW) structure, a multiple quantum well (MQW) structure, or a double hetero (DH) structure can be cited. Among them, the MQW structure has a high output and high efficiency. Particularly preferred.

In the example of the element structure shown in FIG. 3A, an n-type contact layer 11 and a light emitting portion 13 (n-type cladding layer 12 / MQW / p) are sequentially formed on a sapphire substrate 10 via a GaN-based low-temperature growth buffer layer 10b. Type cladding layer 14) and p-type contact layer 15 are deposited by vapor phase growth, and an n-electrode P1 and a p-electrode P2 are provided in each contact layer.
Moreover, in FIG.3 (b), the unevenness | corrugation S for implementing the below-mentioned LEPS method is further added to the upper surface of a sapphire substrate.

The InGaN-based material used as the material of the light emitting layer is a compound semiconductor that essentially includes an In composition and a Ga composition among the GaN-based materials described above, and is represented by In A Ga 1-A N (0 <A <1). In addition to those described above, an Al composition may be further added thereto. The composition of In A Ga 1 -A N may be determined so as to obtain the above emission peak wavelength, but In A Ga 1 -A N (0.005 ≦ A ≦ 0.22, emission wavelength at this time is 360 nm) (˜430 nm) is a preferable material having a large output.

In view of the above, an MQW-structured LED (InGaN UV LED) having a well layer of In A Ga 1-A N whose emission peak wavelength is determined to be 360 nm to 430 nm is the most preferable LED for the light emitting device. It is. Furthermore, among the MQW structures using In A Ga 1-A N as a well layer, the MQW structure consisting of an In A Ga 1-A N well layer and a GaN barrier layer is a structure that provides high output and high efficiency. is there.

  In order to suppress a change in color tone, the light emitted from the light emitting device is basically based on fluorescence from a phosphor. However, the GaN-based LED may be configured to emit photoluminescence light (PL light) in addition to the main light emission, and the PL light may be output together with the fluorescence to correct the fluorescence balance. In order to generate such PL light, a GaN-based crystal layer whose composition is determined so as to emit main PL light and emit target PL light may be added to the element structure of the GaN-based LED.

  The light emitting device according to the present invention can also use a GaN LD as the GaN light emitting element. In that case, as the conditions for the LD, those having an emission peak wavelength of 360 nm to 430 nm and an external quantum efficiency of 10% or more are used. Further, in the case of using an LD, when the laser output of the LD is changed from the laser output when the oscillation threshold current is energized to the laser output 10 times the laser output, the amount of change in chromaticity of the output light is changed. What is within 0.05 on the xy chromaticity diagram is the light emitting device according to the present invention.

  Examples of the growth method of the GaN crystal layer for forming the GaN light emitting device include HVPE method, MOVPE method, MBE method and the like. The HVPE method is preferable when forming a thick film, but the MOVPE method or MBE method is preferable when forming a thin film.

  The crystal substrate used as the base of the element structure of the GaN-based light-emitting element may be any substrate that can grow GaN-based crystals. Preferable crystal substrates include, for example, sapphire (C plane, A plane, R plane), SiC (6H, 4H, 3C), GaN, AlN, Si, spinel, ZnO, GaAs, NGO, and the like. Moreover, the base material which has these crystals as a surface layer may be sufficient. The plane orientation of the substrate is not particularly limited, and may be a just substrate or a substrate with an off angle.

  When growing an element structure made of a GaN-based crystal layer on a crystal substrate, a buffer layer may be interposed as necessary. As a preferable buffer layer, a GaN-based low-temperature growth buffer layer made of GaN, AlN, InN, or the like can be given.

In order to further increase the output and efficiency of the GaN-based light emitting device, a structure for reducing the dislocation density of the GaN-based crystal layer grown on the crystal substrate may be introduced as appropriate. Examples of the structure for reducing the dislocation density include the following.
(Ii) A structure in which a mask layer (SiO 2 or the like is used) is formed as a stripe pattern on a crystal substrate so that a conventionally known selective growth method (ELO method) can be performed.
(B) A structure in which dots and stripes are formed on the crystal substrate so that the GaN-based crystal can be laterally grown or faceted.
These structures and the buffer layer may be appropriately combined.

  Among the structures for reducing the dislocation density, the above (b) is a preferable structure that does not use a mask layer, and contributes to higher output and higher efficiency of the GaN-based LED. Obtainable. Hereinafter, the dislocation density reducing structure (b) will be described.

  As a method for processing irregularities on a crystal substrate, for example, a method for obtaining desired irregularities by patterning according to a desired irregularity mode using an ordinary photolithographic technique and performing etching using an RIE technique or the like Etc. are exemplified.

Convex and concave arrangement patterns include a pattern in which dot-shaped concave portions (or convex portions) are arranged, a linear or curved concave groove (or convex ridge) arranged in a regular or indefinite interval, and stripes or concentric Pattern. A pattern in which convex ridges intersect in a lattice shape can be regarded as a pattern in which dot-shaped (square hole-shaped) concave portions are regularly arranged. In addition, examples of the cross-sectional shape of the unevenness include a rectangular (including trapezoidal) wave shape, a triangular wave shape, a sine curve shape, and the like.

  Among these various concavo-convex forms, the stripe-shaped concavo-convex pattern (rectangular cross-sectional shape) in which linear grooves (or convex ridges) are arranged at regular intervals can simplify the manufacturing process and produce the pattern. Is easy and preferable.

  When the longitudinal direction of the stripe is set to the <1-100> direction for a GaN-based crystal that is embedded and grown, as shown in FIG. 4B, the GaN-based crystal layer 11b tends to be formed in a state where the recess remains as a cavity, as shown in FIG. 4B. Such a method using unevenness in the <1-100> direction is also called a LEPS method (Lateral Epitaxy on the Patterned Substrate). However, the same effect as in the <11-20> direction described below can be obtained by selecting growth conditions in which facet surfaces are easily formed.

  On the other hand, when the longitudinal direction of the stripe is set to the <11-20> direction for the growing GaN-based crystal, the lateral growth is suppressed, and an oblique facet such as a {1-101} plane is easily formed. As shown in a), first, the crystal grows into a ridge-line crystal 11a having a triangular cross section, and as shown in FIG. 5B, it tends to become a GaN-based crystal layer 11b without leaving a cavity in the recess. As a result, the dislocation propagated in the C-axis direction from the substrate side is bent in the lateral direction at the facet surface, and is difficult to propagate upward, which is particularly preferable in that a low dislocation density region can be formed. Such a method using unevenness in the <11-20> direction can also be referred to as a facet LEPS method in contrast to the LEPS method.

  The preferred dimensions when the concavo-convex cross section has a rectangular wave shape as shown in FIG. 6 are as follows. The width W1 of the concave groove is preferably 1 μm to 20 μm, particularly preferably 2 μm to 20 μm. The width W2 of the convex portion is preferably 1 μm to 20 μm, particularly preferably 1 μm to 10 μm. The amplitude of the unevenness (the depth of the groove) d should be 0.2 μm or more. These dimensions, the pitches calculated from the dimensions, and the like are the same for the unevenness of other cross-sectional shapes.

  In addition to the above-mentioned structure for reducing dislocation density, various structures for taking out more light generated in the light emitting layer (electrode structure, reflective layer structure, flip chip structure that can be mounted upside down, etc.) ) And the like are preferably provided as appropriate.

  The fluorescence used as the output light of the light-emitting device may be visible light, and the emission intensity peak is within the wavelength range from the emission peak wavelength (450 nm or less, 360 nm to 430 nm) to 800 nm of the GaN-based LED that is the excitation light source. It is sufficient that the light has one or more. Among them, white light is useful for lighting applications, and in order to have good color rendering properties, white light (RGB white color) that is produced by including three primary colors consisting of red light, green light, and blue light are essential. (Also referred to as light).

A material that emits visible light when excited by a GaN-based LED that is an excitation light source may be used as the phosphor.
As a phosphor capable of generating white light (a white phosphor composed of a mixture of a red phosphor, a green phosphor, and a blue phosphor), a known material may be used, but a light emitting device with little color tone change is configured. Preferred white phosphors for this purpose include red phosphors such as [Ln 2 O 2 S: Eu (Ln = Y, La, Gd, Lu, Sc)] and [(Zn a , Cd 1-a ) S: One or more phosphors selected from Ag, Cl, (0.5>a> 0.2)], and as a green phosphor, [(Zn a , Cd 1-a ) S: Cu, Al, (1 ≧ a> 0.6)], [(Zn a , Cd 1-a ) S: Au, Al, (1 ≧ a> 0.6)], [(Zn a , Cd 1-a ) S: Ag, Cl, ( 1 ≧ a> 0.6)], and [
It contains one or more phosphors selected from (Ba, Sr) MgAl 10 O 17 : Eu, Mn], and as a blue phosphor, [(Sr, Ca, Ba, Mg) 10 (PO 4 ) 6 Cl 2 : Eu] and [
Examples include (Ba, Sr) MgAl 10 O 17 : Eu, Mn].

  The phosphor material described above is a substance that emits fluorescence. When a light-emitting device is actually combined with the light-emitting element as a phosphor, an applicable fluorescent paint or a phosphor component that can be assembled is used. It is a preferable aspect to make it. For this purpose, the phosphor material may be subjected to various processes such as mixing with various base materials, compounding, loading on a substrate, and solidification. For a bonding method and a bonding structure itself for combining a light emitting element and a phosphor to form one light emitting device, known techniques may be referred to.

  The use of the light-emitting device is not limited, and may be a traffic light, a display device, an electrical decoration, etc., but the feature that the change in color tone is suppressed is most remarkable when the light emission is RGB white light as output light. This is an illumination device that constitutes a device and is a collection of a plurality of such devices.

Using an InGaN ultraviolet LED and a white phosphor, a white LED in which a change in color tone was suppressed was actually manufactured.
The main specifications of the InGaN ultraviolet LED are as follows.
Emission peak wavelength: 380 nm.
Structure of light emitting part: MQW structure in which 6 pairs of In 0.03 Ga 0.97 N well layer / GaN barrier layer are stacked.
Dislocation density reduction method: facet LEPS method.
Bare chip outline: 350 μm × 350 μm square.
Mounting method: Flip chip Light emission output in bare chip state: 7.8 mW (12.5 mW by resin molding) at a current of 20 mA.

(Production of InGaN UV LED)
Striping patterning with a photoresist was performed on a C-plane sapphire substrate, and etching was performed with a RIE apparatus so as to have a square cross section up to a depth of 1.5 μm, thereby obtaining a substrate having a striped pattern on the surface.
The specifications of the pattern were a convex part width of 3 μm, a period of 6 μm, and the longitudinal direction of the stripes in the <11-20> direction for the GaN-based crystal grown on the substrate.

After removing the photoresist, the substrate was mounted on a normal horizontal atmospheric pressure metalorganic vapor phase epitaxy (MOVPE), and the temperature was raised to 1100 ° C. in a nitrogen gas main component atmosphere to perform thermal cleaning. Lower the temperature to 500 ° C and use trimethylgallium (hereinafter TMG) as a Group III material
Then, ammonia was allowed to flow as an N raw material to grow a GaN low-temperature growth buffer layer having a thickness of 30 nm.

Subsequently, the temperature was raised to 1000 ° C., a raw material (TMG, ammonia) and a dopant (silane) were passed, and an n-type GaN layer (contact layer) was grown. The growth of the GaN layer at this time has a mountain-shaped cross section from the top surface of the convex portion and the bottom surface of the concave portion as shown in the document Jpn. J. Appl. Phys. 40 (2001) L583 disclosed by Tadatomo et al. After generating as a ridge-like crystal including a facet plane, the growth was embedded without forming a cavity in the recess.

A flat GaN buried layer is grown via the facet structure, and then an n-type AlGaN cladding layer, an InGaN light emitting layer (MQW structure), a p-type AlGaN cladding layer, and a p-type GaN contact layer are formed in this order, and the emission wavelength An epi substrate for an ultraviolet LED of 380 nm,
Etching for exposing the n-type contact layer, electrode formation, and element separation into 350 μm × 350 μm chips were performed to obtain InGaN ultraviolet LEDs in a bare chip state.

A so-called flip chip mounting was performed on a submount pedestal using a Si substrate with the sapphire substrate side as the upper surface. The Si submount on which the ultraviolet LED was mounted was fixed in the lead frame cup. When the total light emission output of the LED chip in this state was measured with an integrating sphere, 7.8 mW was observed when 20 mA was applied. The same measurement was performed with an LED lamp molded with an epoxy resin as it was, and a total light emission output of 12.5 mW was observed. The light emitting area of this light emitting device was 7.18 × 10 −4 cm 2 .
This luminous efficiency corresponds to an external quantum efficiency of 12% at a current amount of 27.9 (A / cm 2 ) per unit luminous area.
The light emitting element did not saturate the light emission output even when energized at least 50 mA, and a light emission output proportional to the energization amount was obtained.

(Preparation of white phosphor)
A phosphor mainly composed of BaMgAl 10 O 17 : Eu, Mn is used as a blue phosphor material, and Y 2 SiO 5 : Ce and Tb (Y, Gd) A phosphor mainly composed of Al 5 O 12 : (Ce, Tb), and as a phosphor material that outputs red light, Ln 2 O 2 S: Eu (Ln = Y, La, Gd, A phosphor mainly composed of Lu and Sc) was used.
These phosphors of each color were blended and dispersed in a thermosetting silicone resin to obtain a white phosphor.

(Assembly of light emitting device)
The white phosphor was applied so as to cover the ultraviolet LED mounted on the flip chip. The coating thickness of the phosphor is about 100 μm. The optimum value of the thickness varies depending on the content of the white phosphor. After the silicon resin was sufficiently solidified, a bullet-shaped mold was performed using an epoxy resin to finish the light emitting device (white LED lamp) of the present invention.

(Evaluation)
With respect to the obtained light emitting device, the LED driving current amount is changed from 0.072 mA to 50 mA (corresponding to a change from 0.1 (A / cm 2 ) to 70 (A / cm 2 ) per unit light emitting area). As shown in FIG. 2, the chromaticity of the output light when it is generated is from the point m1 (x = 0.3, y = 0.34) to the point m2 (on the chromaticity coordinates of the xy chromaticity diagram. x = 0.28, y = 0.32).
The amount of change Δm between the two points at this time is about 0.028, which satisfies the regulation of the color tone change according to the present invention.

It is a schematic diagram which shows the structure of the light-emitting device of this invention. Hatching is performed for the purpose of distinguishing the areas. The same applies to the other figures. In this invention, it is an xy chromaticity diagram which prescribes | regulates the variation | change_quantity of chromaticity of output light. It is a figure which shows an example of the element structure of GaN-type LED used for the structure of the light-emitting device of this invention. FIG. 3 is a schematic diagram showing a concavo-convex structure provided on a crystal substrate and a growth state of a GaN-based crystal in order to reduce the dislocation density of a GaN-based crystal layer constituting the GaN-based LED. In the example of the figure, the unevenness is a striped pattern with grooves and convex ridges extending perpendicularly to the paper surface, and the direction perpendicular to the paper surface is the <1-100> direction of the growing GaN-based crystal. . FIG. 5 is a schematic diagram showing the concavo-convex structure provided on the crystal substrate and the growth of the GaN-based crystal in order to reduce the dislocation density of the GaN-based crystal layer constituting the GaN-based LED, as in FIG. 4. In the example of the figure, the longitudinal direction (direction perpendicular to the paper surface) of the grooves / ridges is the <11-20> direction of the growing GaN-based crystal. It is a figure for showing the dimension of the unevenness | corrugation provided in a crystal substrate upper surface.

Explanation of symbols

1 GaN-based light emitting diode 2 phosphor L1 light from light emitting diode L2 fluorescence (= output light)

Claims (12)

  1. A GaN-based light-emitting element and a phosphor that emits visible light when excited by light emitted from the light-emitting element, and a light-emitting device that uses the fluorescence as output light,
    The GaN-based light emitting device is a GaN-based light emitting diode, and the drive current amount injected into the light emitting diode is from 0.1 (A / cm 2 ) to 70.0 (A / cm 2 ) per unit light emitting area. When you change
    A light emitting device characterized in that the amount of change in chromaticity of output light is within 0.05 on the xy chromaticity diagram.
  2. The GaN-based light emitting diode has a light-emitting portion configured to include a light-emitting layer made of an InGaN-based material, and the light-emitting portion has a single quantum well structure, a multiple quantum well structure, or a double heterostructure. The structure has an emission peak wavelength of 430 nm or less and an external quantum efficiency of 5% or more when a drive current of 30 (A / cm 2 ) per unit emission area is injected in a bare chip state. The light-emitting device of description.
  3.   2. The light emitting device according to claim 1, wherein the GaN-based light emitting diode is configured to emit photoluminescence light having a wavelength different from that of the main light emission, and the photoluminescence light is output together with the fluorescence. .
  4. A GaN-based light-emitting element and a phosphor that emits visible light when excited by light emitted from the light-emitting element, and a light-emitting device that uses the fluorescence as output light,
    The GaN-based light emitting element is a GaN-based semiconductor laser having an emission peak wavelength of 360 nm to 430 nm and an external quantum efficiency of 10% or more of the total emission energy, and the laser output of the semiconductor laser is calculated from the laser output when the oscillation threshold current is applied. When changing the laser output to 10 times the laser output,
    A light emitting device characterized in that the amount of change in chromaticity of output light is within 0.05 on the xy chromaticity diagram.
  5. Emitting portion of the GaN-based light emitting device is a multiple quantum well structure composed of In A Ga 1-A N ( 0 <A ≦ 1) well layer and a GaN-based barrier layer, and the emission peak wavelength 360nm~430nm The light-emitting device according to claim 1, wherein the composition ratio A of the In A Ga 1-A N well layer is determined so as to be.
  6.   The element structure of the GaN-based light-emitting element is laterally grown on a crystal substrate having a concavo-convex processed surface through a low-temperature buffer layer made of a GaN-based semiconductor or directly over the GaN-based crystal layer. The light-emitting device according to claim 1, wherein the light-emitting device has facet growth and has a structure in which a light-emitting portion is formed on the GaN-based crystal.
  7.   The said visible light is light which has one or more peaks of emitted light intensity in the wavelength range from the wavelength of the light emitted from the said light emitting diode to wavelength 800nm, The any one of Claims 1-6. Light emitting device.
  8.   The light-emitting device according to claim 7, wherein the visible light is white light including three primary color lights including red light, green light, and blue light.
  9. The phosphor is a white phosphor composed of a mixture of a red phosphor, a green phosphor, and a blue phosphor,
    The red phosphor is
    [Ln 2 O 2 S: Eu (Ln = Y, La, Gd, Lu, Sc)] and [(Zn a , Cd 1-a ) S: Ag, Cl, (0.5>a> 0.2)]
    One or more phosphors selected from:
    The light emitting device according to claim 1.
  10. The phosphor is a white phosphor composed of a mixture of a red phosphor, a green phosphor, and a blue phosphor,
    The green phosphor is
    [(Zn a , Cd 1-a ) S: Cu, Al, (1 ≧ a> 0.6)],
    [(Zn a , Cd 1-a ) S: Au, Al, (1 ≧ a> 0.6)],
    [(Zn a , Cd 1-a ) S: Ag, Cl, (1 ≧ a> 0.6)] and [(Ba, Sr) MgAl 10 O 17 : Eu, Mn]
    One or more phosphors selected from:
    The light emitting device according to claim 1.
  11. The phosphor is a white phosphor composed of a mixture of a red phosphor, a green phosphor, and a blue phosphor,
    The blue phosphor contains [(Sr, Ca, Ba, Mg) 10 (PO 4 ) 6 Cl 2 : Eu].
    The light-emitting device of any one of Claims 1-10.
  12.   The illuminating device which has the structure which the light-emitting device in any one of Claims 1-11 gathered.
JP2008335798A 2008-12-29 2008-12-29 Light emitting device, and illuminating device using the same Pending JP2009071337A (en)

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