JP7284043B2 - semiconductor light emitting device - Google Patents

Description

The present invention relates to a semiconductor light emitting device.

In recent years, a light emitting diode (LED) with improved directivity has been provided (see Patent Document 1).

In Patent Document 1, at least a barrier layer of a first conductivity type, an active layer serving as a light-emitting layer, and a barrier layer of a second conductivity type are provided, and the surface on the light extraction side has one flat surface and at least two inclined surfaces. A light emitting diode with a structured ridge structure is disclosed. In the light-emitting diode, the width of the upper flat surface of the ridge structure is 2λ (λ: emission wavelength) or less, the active layer is formed in a striped shape narrower than the width of the upper flat surface of the ridge structure, and the active layer is crystal-grown. It is arranged at a location corresponding to the upper flat surface of the ridge structure in the in-plane direction (perpendicular to the crystal growth direction) of the substrate for the substrate. Moreover, the overall external shape of this light-emitting diode is a substantially rectangular parallelepiped.

Japanese Patent No. 6041265

By the way, a light-emitting diode that emits ultraviolet rays includes a pGaN layer made of GaN doped with p-type impurities as a p-type contact layer on the opposite side of the substrate for crystal growth. This pGaN layer has the property of absorbing ultraviolet rays. Therefore, a light-emitting diode that emits ultraviolet rays is mounted by a flip-chip method so that a substrate for crystal growth is used as a light-emitting surface and light can be extracted from the substrate side.

However, since the conventional light-emitting diode described in Patent Document 1 has a substantially rectangular parallelepiped shape, the light that can be extracted from the substrate side is the light that can pass through the upper surface of the base material, which is the emission surface. Since it is restricted, there is a possibility that the amount of radiant flux may decrease.

Even if the light-emitting diode is mounted by the flip-chip method, total reflection and Fresnel reflection occur near the interface due to the difference in refractive index between the substrate and air and between the substrate and the light-emitting layer. Reflected light generated by these reflections is absorbed by the pGaN layer, which may reduce the light extraction efficiency.

For such problems related to total reflection and Fresnel reflection, for example, an antireflection film such as an AR (Anti-Reflection) coat, or a microprojection structure (that is, a moth-eye structure) is provided to alleviate the above-mentioned difference in refractive index. Therefore, it is possible to take measures to reduce the reflection at each interface.

However, although the AR coating and moth-eye methods are suitable for optimizing the direction of travel for light traveling in one direction, the light from the light-emitting layer, such as the light present in a flip-chip mounted light-emitting diode, may It may not be suitable for optimizing the traveling direction of random light in the substrate where emitted light and reflected light coexist, and the decrease in light extraction efficiency cannot be sufficiently suppressed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconductor light emitting device capable of improving light extraction efficiency.

In order to solve the above problems, the present invention provides a transparent substrate that transmits ultraviolet light and is formed of sapphire (Al ₂ O ₃ ), an n-cladding layer on the transparent substrate, a semiconductor layer having a structure in which a light-emitting layer and a p-cladding layer are sequentially stacked; the transparent substrate has a bottom surface located on the semiconductor layer side and a side surface connected to the bottom surface; a semiconductor light-emitting device, wherein an outer angle formed by a surface in contact with the side surface at a position connected to the bottom surface and the bottom surface is an acute angle, and the transparent substrate has a truncated cone shape; I will provide a.
Further, for the purpose of solving the above problems, the present invention provides a transparent substrate that is transparent to ultraviolet light and is formed of aluminum nitride (AlN), an n-cladding layer on the transparent substrate, a semiconductor layer having a structure in which a light-emitting layer and a p-cladding layer are sequentially stacked; the transparent substrate has a bottom surface located on the semiconductor layer side and a side surface connected to the bottom surface; a semiconductor light-emitting device, wherein an outer angle formed by a surface in contact with the side surface at a position connected to the bottom surface and the bottom surface is an acute angle, and the transparent substrate has a truncated cone shape; I will provide a.

ADVANTAGE OF THE INVENTION According to this invention, the semiconductor light-emitting device which can improve light extraction efficiency can be provided.

1 is a schematic diagram showing an example of a configuration of a semiconductor light emitting device according to a first embodiment of the invention; FIG. 1. It is a schematic diagram which shows an example of the simulation model of the semiconductor light-emitting device shown in FIG. 1, (a) is a side view, (b) is a bottom view, (c) is a bird's-eye view. It is a figure which shows an example of the light-receiving range of the light emitted from the semiconductor light-emitting device. FIG. 10 is a graph showing an example of a result of radiant flux simulation; FIG. 10 is a graph showing an example of a result of radiant flux simulation; FIG. 10 is a graph showing an example of a result of radiant flux simulation; FIG. 10 is a graph showing an example of a result of radiant flux simulation; FIG. 10 is a schematic diagram showing an example of a simulation model of a semiconductor light emitting device according to a modified example of the present invention, where (a) is a side view, (b) is a bottom view, and (c) is a bird's-eye view. is. It is a schematic diagram which shows an example of dicing. FIG. 10 is a schematic diagram showing an example of a simulation model of a semiconductor light emitting device according to a modified example of the present invention, where (a) is a side view, (b) is a bottom view, and (c) is a bird's-eye view. is. FIG. 10 is a front view schematically showing an example of the configuration of a semiconductor light emitting device according to one modification of the present invention;

[Embodiment]
An embodiment of the present invention will be described with reference to the drawings. It should be noted that the embodiments described below are shown as preferred specific examples for carrying out the present invention, and there are portions that specifically illustrate various technically preferable matters, but the present invention The technical scope of the invention is not limited to this specific embodiment.

[First embodiment]
[Structure of Semiconductor Light Emitting Device]
FIG. 1 is a schematic diagram showing an example of the configuration of a semiconductor light emitting device according to a first embodiment of the invention. In this embodiment, as the semiconductor light emitting element 2, a light emitting diode that emits light with a wavelength in the ultraviolet region (for example, deep ultraviolet light with a center wavelength of 300 nm or less) will be described as an example. In addition, the semiconductor light emitting element 2 is not limited to a light emitting diode, and may be a laser diode (LD), for example.

The semiconductor light emitting device 2 comprises a transparent substrate 21, a buffer layer 22 made of AlN, an n-cladding layer 23 made of n-type AlGaN, a light-emitting layer 24 made of AlGaN, a p-cladding layer 25 made of p-type AlGaN, and p-type GaN. The contact layer 26 is formed sequentially. The n-cladding layer 23, the light emitting layer 24, the p-cladding layer 25 and the contact layer 26 are semiconductor layers.

The semiconductor light-emitting device 2 also has an anode-side electrode portion (p-electrode) 27 formed on the contact layer 26 and a cathode-side electrode portion (n-electrode) 28 formed on the n-cladding layer 23 . ing. The transparent substrate 21 has a truncated cone shape with an outer periphery that expands outward from the buffer layer 22 side in the height direction of the semiconductor light emitting device 2 (vertical direction in FIG. 1). .

The semiconductor light emitting device 2 is placed on a package electrode (not shown) formed in a package (not shown) with the transparent substrate 21 facing upward so that the anode side electrode portion 27 and cathode side electrode portion 28 sides face the package electrode side. (i.e. flip-chip mounting). In such a configuration, the ultraviolet light emitted by the light emitting layer 24 is guided outside the semiconductor light emitting element 2 through the transparent substrate 21 . Therefore, as the transparent substrate 21, it is desirable to use a substrate having a transmittance as high as possible for emitted ultraviolet light. In the present embodiment, the semiconductor light emitting device 2 may use a sapphire substrate made of sapphire glass (Al ₂ O ₃ ) as the transparent substrate 21 .

[Simulation model]
FIG. 2 is a schematic diagram showing an example of a simulation model of the semiconductor light emitting device 2, where (a) is a side view, (b) is a bottom view, and (c) is a bird's-eye view. FIG. 3 is a diagram showing an example of a light receiving range of light emitted from the semiconductor light emitting element 2. As shown in FIG. In this simulation, when the light emitted from the semiconductor light emitting device 2 shown in FIG. 2 spreads radially and propagates in the air, a numerical calculation is performed to estimate the radiant flux received by the light receiving area 3 having a substantially hemispherical shape. do.

As a simulation model, detailed conditions were set especially for the transparent substrate 21 of the semiconductor light emitting device 2 shown in FIG. Specifically, as shown in FIG. 2, the upper surface 21a of the transparent substrate 21 is used as an emission surface for extracting light. It is assumed that the side surface 21b is inclined outward from the bottom surface 21c toward the top surface 21a. In other words, the transparent substrate 21 has a shape that widens from the bottom surface 21c side toward the top surface 21a side in the side view shown in FIG. 2(a). Further, the bottom surface 21 c is used as an incident surface on which the light emitted from the light emitting layer 24 is incident on the transparent substrate 21 . In this embodiment, the side surface b has a planar shape.

Hereinafter, the exterior angle (hereinafter also referred to as "side angle") formed by the side surface 21b and the bottom surface 21c is assumed to be θ (hereinafter the unit is "deg"). Further, the width of the bottom surface 21c in side view shown in FIG. 2A is _L1 , the width of the top surface 21a in side view shown in FIG. 2A is _L2 , and the height of the transparent substrate 21 is h. .

で与えられる。ここで、底面２１ｃの形状が円形の場合、底面２１ｃの側面視における幅Ｌ_１は、底面２１ｃの直径に相当し、上面２１ａの形状が円形の場合、上面２１ａの側面視における幅Ｌ_２は、上面２１ａの直径に相当する。 The side angle θ is expressed by the following equation (1) using the width L ₁ of the bottom surface 21c when viewed from the side, the width L ₂ of the top surface 21a when viewed from the side, and the height h of the transparent substrate 21.

is given by Here, when _the shape of the bottom surface 21c is circular, the width _L1 of the bottom surface 21c in side view corresponds to the diameter of the bottom surface 21c. , corresponds to the diameter of the upper surface 21a.

Note that the side surface 21b may not necessarily be flat and may be curved. The side surface 21b may have, for example, a curved shape with a predetermined curvature. In this case, the side angle θ may be an angle (external angle) formed between a plane (virtual plane) in contact with the side surface 21b at the position where it is connected to the bottom surface 21a and the bottom surface 21a.

〔simulation〕
The inventors performed a simulation for calculating the radiant flux using the simulation model described above. Also, three wavelengths of light of 260 nm, 280 nm and 300 nm were used.

In addition, in order to reduce the influence of the difference in light distribution due to the direction of observation, a light source having a circular shape was used. Optical design software (Optic Studio (registered trademark)) was used for the simulation. The conditions of the semiconductor light emitting device 2 used in this simulation are summarized in Table 1 below.

(1) Result 1A
FIG. 4 is a graph showing an example of simulation results. The horizontal axis of the graph shown in FIG. 4 indicates the side angle θ (deg), and the vertical axis indicates the radiant flux ratio. Note that the radiant flux ratio on the vertical axis is the ratio to the radiant flux in the comparative example.

Here, in the "comparative example", a light-emitting element having a side surface angle θ of 90 degrees, that is, a substantially rectangular parallelepiped shape in which the side surface 21b and the top surface 21a and the bottom surface 21c are orthogonal to each other was used. The solid line shows the results for UV light with a wavelength of 260 nm, the dashed-dotted line shows the results for UV light with a wavelength of 280 nm, and the double-dotted line shows the results for UV light with a wavelength of 300 nm. Similar descriptions are omitted below.

As shown in the graph of FIG. 4, at any of the three wavelengths, the radiant flux ratio is 1.10 or more in the range of the side angle θ = 48 to 81 deg, and in the range of the side angle θ = 60 to 70 deg. is 1.40 or more, and is 1.45 or more in the range of the side angle θ=63 to 65 degrees.

In other words, in order to obtain a light extraction efficiency 1.10 times or more as compared with the configuration of the comparative example (that is, the side angle θ=90 deg), the side angle θ should be in the range of 48 deg≦θ≦81 deg. Preferably, in order to obtain a light extraction efficiency of 1.40 times or more, the side angle θ is more preferably in the range of 60deg≦θ≦70deg. A range of θ≦65 deg is optimal.

Although not shown, the inventors confirmed that even when the shape of the light source is square, the highest light extraction efficiency can be obtained in the range of the side angle θ = 63 to 65 deg, as in the above results. are doing. Therefore, the shape of the light source is believed to be less dependent on optimizing the light extraction efficiency than the range of side angles θ. In addition, as shown in the above results, substantially the same profile of the radiant flux is obtained at any of the three wavelengths. It is believed to be less dependent on optimizing efficiency.

(2) Result 1B
FIG. 5 is a graph showing an example of simulation results. The purpose of this result is to optimize the height h of the transparent substrate 21, and the height h of the transparent substrate 21 is changed as a parameter under the condition where the light extraction efficiency is the highest in the result 1A shown in FIG. It is the result of the executed simulation. This simulation was performed with the side angle θ fixed at 63.4 degrees. The horizontal axis of the graph shown in FIG. 5 indicates the height h (mm) of the transparent substrate 21, and the vertical axis indicates the radiant flux ratio.

As shown in the graph of FIG. 5, at any of the three wavelengths, the radiant flux ratio increases with h in the range of 0.2 mm≦h≦0.6 mm, and in the range of h≧0.5 mm, The radiant flux ratio is 1.0 or more, and in the range of h≧0.6 mm, the radiant flux ratio is stable at 1.1 or more.

In other words, in order to improve the radiant flux ratio compared to the configuration of the comparative example, it is preferable to set h>0.5× _L1 , and in order to stabilize the radiant flux ratio, h>0.6× L ₁ is more preferable. That is, the height h of the transparent substrate 21 is preferably larger than half the width _L1 of the bottom surface 21c in side view.

[Second embodiment]
Next, a second embodiment of the invention will be described. The second embodiment differs from the first embodiment in that an AlN substrate is provided as the transparent substrate 21 instead of the sapphire substrate. The following description focuses on points that differ from the first embodiment.

A semiconductor light emitting device 2 according to the second embodiment includes an AlN substrate made of aluminum nitride (AlN) as a transparent substrate 21 . Other configurations are the same as the configuration shown in FIG.

Next, a simulation for estimating the radiant flux was performed using a simulation model in the same manner as in the first embodiment described above. In addition, the wavelength of light was set to two types, 260 nm and 280 nm. Regarding the conditions of the semiconductor light emitting device 2 used in this simulation, those different from the conditions of the simulation performed in the first embodiment are summarized in Table 2 below.

(1) Result 2A
FIG. 6 is a graph showing an example of simulation results. As in FIG. 4 described above, the radiant flux on the vertical axis is the reference value (that is, the radiant flux ratio = 1). As shown in FIG. 6, the radiant flux ratio is 1.7 to 1.8 in the range of θ = 53 to 68 deg, and when an AlN substrate is provided, the radiant flux ratio is the highest in the range of θ = 53 to 68 deg. It can be seen that the bundle is large and efficiently emitted.

Further, when comparing the result 2A shown in FIG. 6 with the result 1A shown in FIG. is also getting bigger. From this comparison result, it can be seen that the configuration provided with an AlN substrate made of AlN as the transparent substrate 21 has a higher light extraction efficiency effect than the configuration provided with a sapphire substrate made of Al ₂ O ₃ .

(2) Result 2B
FIG. 7 is a graph showing an example of simulation results. This simulation, like the result 1B shown in FIG. 5, is a numerical calculation performed with the side angle θ fixed at 63.4 degrees in order to optimize the height h of the transparent substrate 21 . As shown in the graph of FIG. 7, the radiant flux ratio is greater than 1.0 in the range of 0.6 mm<h<0.8 mm. That is, it can be seen that the radiant flux is expected to improve when the height h of the transparent substrate 21 is greater than 0.6 mm and less than 0.8 mm.

<Modification 1>
FIG. 8 is a schematic diagram showing an example of a simulation model of a semiconductor light emitting device 2 according to a modified example of the present invention, where (a) is a side view, (b) is a bottom view, and (c) is a side view. ) is an overhead view. FIG. 9 is a diagram showing a dicing image. As shown in FIGS. 8 and 9, a shape for dicing may be left in order to improve workability.

The wafer 4 shown in FIG. 9 is part of the transparent substrate 21 . As an example, the transparent substrate 21 is lowered into the shape shown in FIG. 9, and then the wafer 4 is separated by dicing at the positions of cutting lines 40 (see broken lines) shown in FIG. The inventors confirmed that when the surface area of the inclined side surface 21b is unchanged, the same effect of improving the radiant flux as that of the semiconductor light emitting device 2 according to the first embodiment described above can be obtained.

<Modification 2>
10A and 10B are schematic diagrams showing an example of a simulation model of a semiconductor light emitting device 2 according to a modified example of the present invention, where (a) is a side view, (b) is a bottom view, and (c) is a side view. ) is an overhead view. The shape of the light emitting surface of the semiconductor light emitting element 2 is not necessarily limited to a circular shape, and may be, for example, a square shape as shown in FIGS.

A quadrangle may be a shape surrounded by four sides, such as a square, a rectangle, a rhombus, or a trapezoid. Also, although not shown, the shape of the light emitting surface of the semiconductor light emitting element 2 is not limited to the circular or square shape described above, and may be, for example, a special shape such as a triangle, polygon, ellipse, or star shape. good.

<Modification 3>
FIG. 11 is a front view schematically showing an example of a semiconductor light emitting device 2 according to one modification of the invention. For example, as shown in FIG. 11, the sapphire substrate has a circular shape in front view, and the semiconductor layers (that is, the buffer layer 22, the n-cladding layer 23, the light-emitting layer 24, the p-layer) formed on the sapphire substrate. The cladding layer 25 and contact layer 26) may have a circular shape.

Although the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the scope of claims. Also, it should be noted that not all combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

(Summary of embodiment)
Next, technical ideas understood from the embodiments described above will be described with reference to the reference numerals and the like in the embodiments. However, each reference numeral and the like in the following description do not limit the constituent elements in the claims to the members and the like specifically shown in the embodiment.

[1] A transparent substrate (21) transparent to ultraviolet light, and an n-cladding layer (23), a light-emitting layer (24), and a p-cladding layer (25) on the transparent substrate (21) and a semiconductor layer having a sequentially laminated structure, wherein the transparent substrate (21) has a bottom surface (21c) located on the semiconductor layer side and a side surface (21b) connected to the bottom surface (21c). , the side surface (21b) is inclined such that an outer angle formed by a surface in contact with the side surface (21b) at a position connecting to the bottom surface (21c) and the bottom surface (21c) is an acute angle; A semiconductor light emitting device (1).
[2] The semiconductor light emitting device according to [1], wherein the side surface has a planar shape.
[3] The semiconductor light-emitting device (1) according to [2], wherein the exterior angle is in the range of 48 degrees or more and 81 degrees or less.
[4] The semiconductor light emitting device according to any one of [1] to [3], wherein the height of the semiconductor light emitting device (1) is larger than half of the width of the bottom surface (21c) in a side view. (1).
[5] The semiconductor light emitting device (1) according to any one of [1] to [4], wherein the transparent substrate ( ₂₁ ) is made of sapphire ( _Al2O3 ).
[6] The semiconductor light emitting device (1) according to any one of [1] to [4], wherein the transparent substrate (21) is made of aluminum nitride (AlN).

2 Semiconductor light emitting device (LED)
21a upper surface 21b side surface 21c bottom surface 21 transparent substrate 22 buffer layer 23 n-cladding layer 24 light-emitting layer 25 p-cladding layer 26 contact layer 27 anode electrode portion 28 cathode electrode portion 3 light receiving area 4 wafer

Claims (5)

a transparent substrate having transparency to ultraviolet light and made of sapphire (Al ₂ O ₃ );
a semiconductor layer having a structure in which an n-cladding layer, a light-emitting layer, and a p-cladding layer are sequentially stacked on the transparent substrate;
The transparent substrate has a bottom surface located on the semiconductor layer side and a side surface connected to the bottom surface,
The side surface is inclined so that an outer angle formed between a surface in contact with the side surface at a position connected to the bottom surface and the bottom surface is an acute angle,
The transparent substrate has a truncated cone shape,
Semiconductor light emitting device. a transparent substrate that is transparent to ultraviolet light and made of aluminum nitride (AlN);
a semiconductor layer having a structure in which an n-cladding layer, a light-emitting layer, and a p-cladding layer are sequentially stacked on the transparent substrate;
The transparent substrate has a bottom surface located on the semiconductor layer side and a side surface connected to the bottom surface,
The side surface is inclined so that an outer angle formed between a surface in contact with the side surface at a position connected to the bottom surface and the bottom surface is an acute angle,
The transparent substrate has a truncated cone shape,
Semiconductor light emitting device. The side surface has a planar shape,
3. The semiconductor light emitting device according to claim 1 or 2 . The size of the exterior angle is in the range of 48 degrees or more and 81 degrees or less,
4. The semiconductor light emitting device according to claim 3 . The height of the transparent substrate is greater than half the width of the bottom surface in a side view,
5. The semiconductor light emitting device according to claim 1.

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