JP4942996B2 - Light emitting diode - Google Patents

Description

  The present invention relates to a compound semiconductor light emitting device, and more particularly, to a light emitting diode with excellent heat dissipation and high brightness.

Conventionally, for the purpose of increasing the brightness of a light-emitting diode, a method for improving light extraction efficiency by using an element shape has been used. In an element structure in which electrodes are formed on the front surface and the back surface of a semiconductor light emitting diode, a method for increasing brightness by using a side surface shape has been proposed (see Patent Documents 1 to 3).
Japanese Examined Patent Publication No. 63-28508 USP 6229160 Specification JP-A-3-227078

In the prior art, many shapes have been proposed for an element having a structure in which electrodes are formed on the front and back surfaces of a light emitting diode, but heat dissipation when used at a high current has not been studied. In particular, in a light-emitting diode including AlGaInP and a gallium nitride-based light-emitting layer having two electrodes on the light extraction surface, an electrode is not provided on the back surface, so heat dissipation is inferior to an element structure in which an electrode is provided on the back surface. It is known that when the heat dissipation is poor, the temperature of the light emitting layer increases, leading to a decrease in luminous efficiency and a decrease in luminance.
The structure of the device that uses the AlGaInP light emitting layer in a transparent substrate type and forms two electrodes on the light extraction surface is complicated in shape, and the side surface state, the light emitting layer, and the back surface of the device have not been optimized. There is a problem that sufficient heat dissipation characteristics are not obtained with brightness.

  The present invention has been proposed in view of the above problems, and an object of the present invention is to provide a light-emitting diode that is high in luminance and excellent in heat dissipation with the element having the above structure.

The inventor has comprehensively studied the shape and the back surface of the light emitting diode, and has reached an element structure of a light emitting diode that has high light extraction efficiency and excellent heat dissipation.
It is clear from the prior art that the side surface shape of the light emitting diode is related to light extraction, but in the structure where the light emitting surface is at the top, the area of the back surface is increased when the inclination angle is increased in order to make the side surface shape effective. It becomes smaller, heat dissipation is reduced, and the luminance characteristics in the high current region are reduced. Further, in order to improve heat dissipation, when the light emitting layer is made small and the area of the back surface is made large, the loss is large with respect to the expensive light emitting layer, and there is a problem in cost. Further, when the light emitting layer is close to the back surface, the structure having two electrodes on one side cannot be assembled in a normal wire bonding process.
The present inventor discovered that the structure and area of the back surface, the area of the light emitting layer, the side surface shape, and the roughening of the back surface were important, and found the optimum device structure and a stable manufacturing method, and reached the present invention. That is, the present invention comprises the following inventions.

(1) In a transparent substrate type light emitting diode having a light emitting layer made of a compound semiconductor, the first electrode and the first electrode are formed on the area (A) of the light extraction surface where the second electrode having a different polarity is formed. A light emitting diode characterized in that the relationship between the area (B) of the light emitting layer and the area (C) of the back surface of the light emitting diode satisfies the relationship of the expression (1).
A>C> B (1)
(2) the light emitting layer is made of composition formula _{(Al X Ga 1-X)} Y In 1-Y P (0 ≦ X ≦ 1,0 <Y ≦ 1), the thermal conductivity of the transparent substrate, 100W / The light-emitting diode according to (1), wherein the light-emitting diode is m · K or more.
(3) The side surface has a first side surface close to the light emitting layer and a second side surface close to the back surface, and the inclination angle of the first side surface is smaller than the inclination angle of the second side surface. The light-emitting diode according to (1) or (2).
(4) The light-emitting diode according to (3) above, wherein the first side surface is vertical and the second side surface is inclined.

(5) The light emitting diode according to any one of (1) to (4) above, wherein the inclination angle of the second side surface is not less than 10 degrees and not more than 30 degrees.
(6) The light emitting diode according to any one of (1) to (5) above, wherein the inclination angle of the second side surface is 10 degrees or more and 20 degrees or less. The length is 50 μm or more and 100 μm or less, and the length of the second side surface is 100 μm or more and 250 μm or less.
(8) The light-emitting diode according to any one of (1) to (7), wherein the transparent substrate is gallium phosphide (GaP).
(9) The light-emitting diode according to any one of (1) to (7), wherein the transparent substrate is silicon carbide (SiC).

(10) The light-emitting diode according to any one of (1) to (9), wherein the back surface of the transparent substrate is a rough surface on which light is scattered.
(11) The light-emitting diode according to any one of (1) to (10), wherein a metal film is formed on the back surface of the transparent substrate.
(12) The light-emitting diode according to (11), wherein the metal film on the back surface of the transparent substrate contains a metal having a melting point of 400 ° C. or lower.
(13) The light-emitting diode according to any one of (11) to (12), wherein the metal film is an AuSn alloy.
(14) The light-emitting diode according to any one of (1) to (13) above, wherein the area of the back surface of the light-emitting diode is 0.6 mm ² or more and is used with a power of 1.5 W or more.
(15) The light-emitting diode according to any one of (8) and (10) to (14), wherein the back surface is a GaP substrate treated with hydrochloric acid.
(16) The light-emitting diode according to any one of (1) to (15), wherein the side surface of the transparent substrate is formed by a dicing method.

  In the light-emitting diode of the present invention, by optimizing the relationship between the area of the light-emitting layer and the area of the back surface and the shape of the side surface, it is possible to provide a light-emitting diode with high brightness, high heat dissipation and suitable for high current use.

Hereinafter, the present invention will be described in detail with reference to the drawings.
The light emitting diode of the present invention includes a light emitting layer of a compound semiconductor. Usually, in addition to the light emitting layer, a clad layer, a contact layer, and the like are laminated to form a light emitting portion. These are laminated on the substrate by an epitaxial method as shown in FIG. A known structure such as a double hetero structure or a multiple quantum well structure can be used for the light emitting layer.
As the light emitting layer, known light emitting layers such as GaAlAs, InGaN, and AlInGaP can be applied. In particular, thin InGaN and AlInGaP based epitaxial layers are easy to produce. These light emitting portions are effective for a wide wavelength from ultraviolet to infrared.
As shown in FIG. 2, both the first electrode (for example, n-type) and the second electrode (for example, p-type) having a different polarity are formed on the light extraction surface as shown in FIG. Both are structures that allow wire bonding.

The second electrode is formed by etching a part of the laminate from the surface to below the light emitting layer and connecting it to a semiconductor layer or a conductive transparent substrate.
The light emitting diode of the present invention is a so-called transparent substrate type light emitting diode having a transparent substrate on the side opposite to the light extraction surface. The transparent substrate can be made of a material that is transparent with respect to the emission wavelength, such as GaP, SiC, zinc oxide, sapphire, alumina, and GaN.
Of these, GaP and SiC are preferable. The thermal conductivity of GaP is 110 W / m · K. Single crystals are mass-produced and have excellent processability. As the main surface of GaP, general plane orientations such as (111) plane and (100) plane can be used, but the (111) plane which is easy to roughen is more preferable. SiC has a thermal conductivity of 167 W / m · K. Single crystals are mass-produced. Although it is difficult to process, it is an optimal material for heat dissipation.
This transparent substrate is bonded onto the semiconductor layer 135 as indicated by reference numeral 14 in FIG.

  In the light-emitting diode as described above, the area of the light extraction surface (A), the area of the light-emitting layer (B), and the area of the back surface of the light-emitting diode (surface opposite to the electrode forming side of the transparent substrate) (C) are specified. One characteristic is that they are in the relationship. The light emitting diode is generally covered with a transparent resin around the element. Transparent resins such as epoxy resins have poor heat conduction and cannot be expected to release heat from the device. Therefore, most of the heat generated in the element is dissipated from the substrate of the package that is in contact with the back surface of the element. The back surface (C), which is a heat radiating surface, the light emitting layer (B), which is a heat generating surface, and the element upper surface (A), which is a light extraction surface, have an optimum relationship for luminance and heat dissipation.

Considering only the heat dissipation surface, the relationship of C>A> B is desirable, but the area of the light extraction surface and the light emitting layer is small, and high brightness cannot be achieved. Further, the removal area of the expensive epitaxial layer is large and the cost is increased.
In order to increase the brightness, the area of the light emitting layer and the light extraction surface is maximized with the side surfaces inclined. The light emitting layer is near the light extraction surface, diffuses the heat generated in the light emission layer to a large area A of the light extraction surface, releases the heat of the light emission layer, and smoothly conducts the heat through the element. The heat is dissipated to the back surface, which is the heat dissipating surface.

In order to increase the brightness, the side surface needs to be inclined, and in order to perform heat dissipation satisfactorily, the area (B) of the light emitting layer and the area (A) near the light emitting layer are increased. It is desirable not to provide. In order to spread heat easily, it is better that the volume of the semiconductor near the light emitting layer is large. An inclined surface is provided near the back surface far from the light emitting layer. In the vicinity of the back surface, since it is in contact with a material with good heat dissipation, even if it is slightly smaller than the area A, the heat escape is good and the heat dissipation is not rate-limiting. Desirable conditions for maintaining these balances are shown below.
0.95 × A>C> 0.6 × A
0.9 × A>B> 0.7 × A
C>B> 0.8 × C
∴ A>C> B
The area of the back surface of the light emitting diode is preferably 0.6 mm ² or more. The most demanded heat dissipation is a light emitting diode of 0.5 W or more and a large size used with a high power of 1.5 W or more. The effect is large for applications with a chip size of 0.4 mm ² or more, and further, there is a remarkable effect for applications with a chip size of 0.7 mm ² or more.

When the transparent substrate is GaP, it is preferable to treat the back surface with hydrochloric acid. In particular, the processing method using the plane orientation (111) plane is suitable.
Another feature of the light emitting diode of the present invention is that at least one of its side surfaces, usually the side surface of the transparent substrate, is inclined. The transparent substrate preferably has a first side surface 21 and a second side surface 22 as shown in FIGS. The inclination angle of the first side surface is smaller than the inclination angle of the second side surface. In this case, the inclination angle of the first side surface is preferably zero, that is, perpendicular to the transparent substrate. The inclination angle is represented by an inclination angle (20 in the figure) with respect to the perpendicular of the transparent substrate. The inclination angle of the second side surface is preferably in the range of 10 degrees to 30 degrees, more preferably 10 degrees to 20 degrees. The angle of the second side surface may be constant, a plurality of angles, or an inclined curved surface. In the case of a plurality of surfaces, the angle is represented by an average, and in the case of a curved surface, the angle is represented by an angle between a line connecting the start point and the end point of the curved surface.

These angles take brightness and heat dissipation into consideration, and are particularly excellent in characteristics in a high current region. A large angle is advantageous in terms of light extraction, but the above range is optimal because the area of the back surface is small and the thermal resistance is high.
As shown in the above document, it is known to increase the light extraction efficiency by inclining the side surface of the light emitting diode.
In the present invention, the light emitting layer is formed by having the first side surface 21 and the second side surface 22 as described above, and the inclination angle of the first side surface is smaller than the inclination angle of the second side surface. There is an effect of enlarging the area in the vicinity to promote heat dissipation and increasing the brightness on the second side.
Regarding the length of the side surface, the length (L) of the first side surface is preferably 50 μm or more and 100 μm or less, and the length (L) of the second side surface is preferably 100 μm or more and 250 μm or less. M / L is preferably in the range of 0.5 to 5.

The first side surface and the second side surface of the transparent substrate of the light emitting diode can be formed by a dicing method. In addition, the side surface can be produced by combining wet etching, dry etching, scribing, laser processing, and the like, but a dicing method with high shape controllability and high productivity is the optimum manufacturing method.
The back surface of the transparent substrate of the light emitting diode can be a rough surface on which light is scattered. The back surface of the light emitting diode is a surface connected to the package to be assembled. In order to increase the luminance, the connection surface is generally adhered with a highly reflective Ag paste or fixed on a highly reflective metal such as silver or aluminum with a transparent adhesive. By scattering light on the back surface, light having an incident angle that is difficult to be extracted from the side surface or the top surface is also scattered, resulting in a reflection angle at which light can be extracted, which contributes to improvement in luminance. In addition, even on the heat radiating surface, there is an effect that the surface area becomes large and heat easily escapes to the package side.

A metal film can be formed on the back surface of the transparent substrate of the light emitting diode. The metal film has the above-described function of enhancing the reflection effect and heat conduction on the light emitting diode side, and can broaden the selection of the material of the package. The metal film preferably contains a metal having a melting point of 400 ° C. or lower. As a method for connecting to the package, there is a technique using solder or eutectic bonding. The light emitting diode is connected to the package with a metal, and the above metal is optimal in terms of heat dissipation. By adding a bonding metal to the back surface of the light emitting diode, assembly can be simplified. Bonding conditions at 400 ° C or lower are desirable due to the package material.
The metal film is preferably an AuSn alloy. AuSn is widely used as a eutectic metal, and since the melting point of Sn 20 wt% of the eutectic point is about 283 ° C., it is an optimal material that can be bonded at a low temperature.

Other light-emitting diode manufacturing methods can use known light-emitting diode manufacturing techniques, and manufacture light-emitting diodes through ohmic electrode formation, separation, inspection and evaluation processes. Further, a light emitting diode (lamp) can be manufactured by incorporating the light emitting diode into a package.
Other light-emitting diode manufacturing methods can use known light-emitting diode manufacturing techniques, and manufacture light-emitting diodes through ohmic electrode formation, separation, inspection and evaluation processes. Further, a light emitting diode (lamp) can be manufactured by incorporating the light emitting diode into a package.

In this example, an example in which a light-emitting diode according to the present invention is manufactured will be specifically described.
1 and 2 are diagrams showing a semiconductor light-emitting diode manufactured in this example. FIG. 1 is a plan view of the semiconductor light-emitting diode, and FIG. 2 is a cross-sectional view taken along the line II of FIG. FIG. 3 is a cross-sectional view of a layer structure of a semiconductor epitaxial wafer used for a semiconductor light emitting diode.
The semiconductor light emitting diode 10 manufactured in this example is a red light emitting diode (LED) having an AlGaInP light emitting portion.
In the first embodiment, the present invention will be specifically described with reference to an example in which a light emitting diode is manufactured by bonding an epitaxial multilayer structure (epiwafer) provided on a GaAs substrate and a GaP substrate.

The light-emitting diode 10 uses an epitaxial wafer including a semiconductor layer 13 sequentially stacked on a semiconductor substrate 11 made of a GaAs single crystal having a plane inclined by 15 ° from an n-type (100) plane doped with Si. Produced. The stacked semiconductor layers are Si-doped n-type (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P 130, Si-doped n-type GaAs contact layer 131, Si-doped n-type ( Al _0.7 Ga _{0.3) 0.5} in _0.5 the lower cladding layer 132 composed of P, undoped _{(Al 0.2 Ga 0.8) 0.5 in} 0.5 P / Al 0.7 Ga 0.3) 0.5 in 0.5 emitting layer 133 composed of P of 20 pairs, and Mg An upper clad layer 134 made of doped p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, an intermediate layer 134 made of a thin film (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P, and an Mg-doped p-type GaP layer 135.

In this embodiment, each of the semiconductor layers 130 to 135 is made of trimethylaluminum ((CH ₃ ) ₃ Al), trimethyl gallium ((CH ₃ ) ₃ Ga), and trimethylindium ((CH ₃ ) ₃ In) as a group III. An epitaxial wafer was formed by laminating on the GaAs substrate 11 by a low pressure metal organic chemical vapor deposition method (MOCVD method) used as a constituent element material. Biscyclopentadiethyl magnesium (bis- (C ₅ H ₅ ) ₂ Mg) was used as the Mg doping material. Disilane (Si ₂ H ₆ ) was used as a Si doping material. Further, phosphine (PH ₃ ) or arsine (AsH ₃ ) was used as a raw material for the group V constituent elements. The GaP layer 135 was grown at 750 ° C., and the other semiconductor layers 130 to 134 forming the semiconductor layer 13 were grown at 730 ° C.

The carrier concentration of the (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P etching stop layer 130 was about 2 × 10 ¹⁸ cm ⁻³ , and the layer thickness was about 0.2 μm. The contact layer 131 is made of GaAs, the carrier concentration is about 2 × 10 ¹⁸ cm ⁻³ , and the layer thickness is about 0.2 μm. The n-cladding layer 132 has a carrier concentration of about 8 × 10 ¹⁷ cm ⁻³ and a layer thickness of about 2 μm. The light emitting layer 133 was undoped 0.8 μm. The carrier concentration of the p-cladding layer 134 was about 2 × 10 ¹⁷ cm ⁻³ and the layer thickness was 1 μm. The carrier concentration of the GaP layer 135 was about 3 × 10 ¹⁸ cm ⁻³ and the layer thickness was 9 μm.
The p-type GaP layer 135 was polished and mirror-finished in a region reaching a depth of about 1 μm from the surface. Depending on the mirror finish, the surface roughness of the p-type GaP layer 135 was set to 0.18 nm.

On the other hand, an n-type GaP substrate 14 to be attached to the mirror-polished surface of the p-type GaP layer 135 was prepared. For this bonding GaP substrate 14, a single crystal having a plane orientation of (111) to which Si was added so that the carrier concentration was about 1 × 10 ¹⁷ cm ⁻³ was used. The diameter of the bonding GaP substrate 14 was 50 millimeters (mm) and the thickness was 250 μm. The surface of the GaP substrate 14 was polished to a mirror surface before being bonded to the p-type GaP layer 135, and finished to a square average square root value (rms) of 0.12 nm.
The GaP substrate 14 and the epitaxial wafer were carried in, and the inside of the apparatus was evacuated to 3 × 10 ⁻⁵ Pa. Thereafter, in order to remove contamination on the surface, the surface of the GaP substrate 14 and the epi-wafer surface was irradiated with an accelerated Ar beam to perform pre-bonding processing. Then, both were joined at room temperature in vacuum.

Next, the GaAs substrate 11 was selectively removed from the bonded wafer with an ammonia-based etchant. Thereafter, the etching stop layer 130 was removed with hydrochloric acid.
An n-type ohmic electrode was formed as a first ohmic electrode 15 on the surface of the contact layer 131 by a vacuum vapor deposition method so that the thickness of AuGe and Ni alloy was 0.2 μm. Patterning was performed using general photolithography means to form an electrode 15. Thereafter, the contact layer other than the electrode forming portion was removed.
Next, the epi layers 131 to 134 including the light emitting layer in the region for forming the p electrode were selectively removed to expose the GaP layer 135. A p-type ohmic electrode 16 was formed on the surface of the GaP layer by vacuum deposition so that AuBe was 0.2 μm and Au was 1 μm. At this time, the area of the light emitting layer was 0.72 mm ² .
Heat treatment was performed at 450 ° C. for 10 minutes, and alloyed to form low resistance p-type and n-type ohmic electrodes.

Thereafter, a bonding pad was formed on the ohmic electrode by vacuum deposition so that Au was 1 μm. Further, the semiconductor layer was covered with a SiO ₂ film so as to have a thickness of 0.3 μm to form a protective film.
Next, using a dicing saw, a V-shaped grooving is performed so that the length of the second side surface is about 180 μm from the back surface of the GaP substrate 14 so that the angle 20 of the inclined surface is 15 degrees. Went. A roughening treatment was carried out with hydrochloric acid.

Next, it cut | disconnected by 1 mm space | interval using the dicing saw from the surface side, and was chipped. The length of the first side surface was approximately perpendicular to the light emitting layer so as to be about 80 μm.
The crushing layer and dirt due to dicing were removed with a sulfuric acid / hydrogen peroxide mixed solution to produce a semiconductor light emitting diode (chip) 10. The area of the chip back surface was 0.8 mm ² .
The LED chip 10 manufactured as described above was assembled into a light emitting diode lamp 42 as schematically shown in FIGS. This LED lamp 42 is fixed and supported (mounted) with a silver (Ag) paste on a mounting substrate 45, and an n-type ohmic electrode 15 of the LED chip 10 and an n-electrode terminal 43 provided on the surface of the mounting substrate 45 are Further, the p-type ohmic electrode 16 and the p-electrode terminal 44 were wire-bonded with a gold wire 46 and then sealed with a general epoxy resin 41.

The mounting substrate 45 is made of aluminum nitride having good heat dissipation, and a current is passed between the n-type and p-type ohmic electrodes 15 and 16 via the n-electrode terminal 43 and the p-electrode terminal 44 provided on the surface. Then, red light having a dominant wavelength of 620 nm was emitted. The forward voltage (Vf) when a current of 500 milliamperes (mA) is passed in the forward direction has a low resistance at the junction interface between the GaP layer 315 and the GaP substrate 316 and the ohmic electrodes 15, 16. Reflecting good ohmic characteristics, it was about 2.4 volts (V). In addition, the emission intensity when the forward current is 500 mA reflects the improvement of the extraction efficiency to the outside, such as the structure of the light emitting part with high emission efficiency and the removal of the crushing layer generated when cutting into chips. As a result, the luminance became 5500 mcd.
(Example 2)

  An element shape similar to that of Example 1 was prepared, AuSn eutectic (melting point 283 ° C.) was formed to 1 μm on the back surface, and fixed to the package with AuSn without using Ag paste. Table 1 shows the results of fabricating light-emitting diodes that are made into chips and having different back-surface connection states and evaluated in the same manner as in Example 1. The forward voltage (Vf) when a current of 500 mA (mA) was passed in the forward direction was 2.4V. The emission intensity was 6430 mcd high brightness reflecting further improvement in heat dissipation and light absorption by Ag paste.

(Comparative Example 1)
The side surface shape was changed in the same process as in Example 1. The first side surface was approximately vertical and 10 μm long, the second side surface was 30 degrees in angle, and the length was 300 μm. The area of the back surface was 0.5 mm ² . The light emitting layer was 0.72 mm ² as in the example. The results evaluated in the same manner as in Example 1 are shown in Table 1. The forward voltage (Vf) when a current of 500 mA (mA) was passed in the forward direction was 2.4V. The emission intensity remained at a luminance of 3290 mcd due to the small area of the back surface and insufficient heat dissipation.

(Comparative Example 2)
A rectangular parallelepiped light-emitting diode having no inclined surface was manufactured in the same process as in Example 1.
The area of the back surface was 0.9 mm2. The light emitting layer was 0.72 mm 2 as in the example. The results evaluated in the same manner as in Example 1 are shown in Table 1. The forward voltage (Vf) when a current of 500 mA (mA) was passed in the forward direction was 2.4V. The light emission intensity was slightly low because there was no inclined surface, and the luminance was only 4270 mcd.

  The light emitting diode of the present invention has good heat dissipation and high brightness. Because of its good heat dissipation, it can be used with high power and can be used widely as various lamps.

1 is a plan view of a semiconductor light emitting diode of Example 1. FIG. It is sectional drawing along the II line | wire of FIG. It is a figure which shows the cross section of the epi wafer in this invention. It is sectional drawing which joined the board | substrate to the epitaxial wafer in this invention. 6 is a sectional view of a semiconductor light emitting diode of Example 2. FIG. 6 is a cross-sectional view of a light emitting diode of Comparative Example 1. FIG. 10 is a cross-sectional view of a light emitting diode of Comparative Example 2. FIG. It is a top view of the semiconductor light emitting diode lamp of an Example and a comparative example. It is sectional drawing of the semiconductor light emitting diode lamp of an Example and a comparative example.

Explanation of symbols

10 Semiconductor Light Emitting Diode 11 Semiconductor Substrate (GaAs)
12 Light Emitting Section 13 Epitaxial Growth Layer 130 Etching Stop Layer
131 Contact layer
132 Lower cladding layer 133 Light emitting layer
134 Upper cladding layer 135 GaP layer 141 Junction interface 14 GaP substrate 15 First electrode (n-type ohmic)
16 Second electrode (p-type ohmic)
20 Inclination angle 21 First side surface 22 Second side surface 23 Back surface 24 Metal layer (AuSn)
41 Epoxy resin 42 Light-emitting diode 43 First electrode terminal 44 Second electrode terminal 45 Insulating substrate (AlN)
46 gold wire

Claims (16)

In the compounds transparent substrate light-emitting diode having a light emitting layer made of semiconductor, and the first electrode and the first electrode and a second different electrode polarity is formed on the light extraction surface side, the light emitting layer on the light extraction surface The relationship between the area (A) of the upper surface of the element that is the light extraction surface, the area (B) of the light emitting layer, and the area (C) of the back surface of the light emitting diode satisfies the relationship of the formula (1). A light emitting diode having an upper surface area (A) of 0.7 mm ² or more and an rear surface area (C) of 0.6 mm ² or more .
A>C> B (1) The light emitting layer is made of composition formula _{(Al X Ga 1-X)} Y In 1-Y P (0 ≦ X ≦ 1,0 <Y ≦ 1), the thermal conductivity of the transparent substrate, 100W / m · K It is the above, The light emitting diode of Claim 1 characterized by the above-mentioned. The side surface of the light emitting diode has a first side surface close to the light emitting layer and a second side surface close to the back surface, and an inclination angle of the first side surface is smaller than an inclination angle of the second side surface. Item 3. The light emitting diode according to Item 1 or 2.     4. The light emitting diode according to claim 3, wherein the first side surface is vertical and the second side surface is inclined. 5. The light emitting diode according to claim 3, wherein an inclination angle of the second side surface is not less than 10 degrees and not more than 30 degrees. 6. The light emitting diode according to claim 3, wherein an inclination angle of the second side surface is 10 degrees or more and 20 degrees or less. 7. The light emitting diode according to claim 3, wherein a length of the first side surface is 50 μm or more and 100 μm or less, and a length of the second side surface is 100 μm or more and 250 μm or less.     The light-emitting diode according to claim 1, wherein the transparent substrate is gallium phosphide (GaP).     The light-emitting diode according to claim 1, wherein the transparent substrate is silicon carbide (SiC).     The light-emitting diode according to claim 1, wherein the back surface of the transparent substrate is a rough surface on which light is scattered.     The light emitting diode according to claim 1, wherein a metal film is formed on a back surface of the transparent substrate.     The light emitting diode according to claim 11, wherein the metal film on the back surface of the transparent substrate contains a metal having a melting point of 400 ° C or lower.     The light emitting diode according to claim 11, wherein the metal film is an AuSn alloy. 14. The light emitting diode according to claim 1, wherein an area of a back surface of the light emitting diode is 0.6 mm ² or more and is used with a power of 1.5 W or more.     15. The light emitting diode according to claim 8, wherein the back surface is obtained by treating a GaP substrate with hydrochloric acid.     16. The light emitting diode according to claim 1, wherein the side surface of the transparent substrate is formed by a dicing method.