JPH10270754A - Semiconductor light-emitting device and light-emitting lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting device having improved optical output. SOLUTION: There are formed on a sapphire substrate 1, in the following order, an AlGaN buffer layer 21, an n-type GaN clad layer 2 which also serves as an n-side contact layer, an n-type InGaN active layer 3, a p-type AlGaN clad layer 4 and a p-type GaN contact layer 5. A portion of layers covering from the p-type GaN contact layer 5 to a predetermined depth of the n-type GaN clad layer 2 is removed to permit the n-type GaN clad layer 2 to be exposed. An n-side electrode 6 is formed on the exposed n-type GaN clad layer 2, while a p-side electrode 7 is formed on the p-type GaN contact layer 5. Then, a metal reflection film 8 is formed on the reverse side of the sapphire substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor light emitting device and a light emitting lamp using the same.

[0002]

2. Description of the Related Art Gallium nitride (GaN) having a direct transition type band structure has attracted attention as a material for semiconductor light emitting devices such as light emitting diodes and semiconductor laser devices that emit blue or violet light. However, since there is no GaN substrate, when fabricating a GaN-based semiconductor light emitting device, each layer is epitaxially grown on an insulating substrate such as sapphire (Al ₂ O ₃ ).

FIG. 12 is a schematic sectional view showing the structure of a conventional GaN-based light emitting diode. In FIG. 12, an AlGaN buffer layer 1a, an n-type GaN cladding layer 2 also serving as an n-side contact layer, an n-type In
A GaN active layer (light emitting layer) 3, a p-type AlGaN cladding layer 4, and a p-type GaN contact layer 5 are sequentially formed. Part of the region from the p-type GaN contact layer 5 to a predetermined depth of the n-type GaN cladding layer 2 is removed, and the n-type GaN
The cladding layer 2 is exposed. An n-side electrode 6 is formed on the exposed n-type GaN cladding layer 2, and a p-side electrode 7 is formed on the p-type GaN contact 5.

FIG. 13 is a schematic sectional view showing the structure of an LED lamp using the light emitting diode of FIG. In the LED lamp of FIG. 13, the back surface of the sapphire substrate 1 of the light emitting diode chip 10a is formed of an adhesive 11 such as a silver paste or a resin.
And the n-side electrode 6 is connected to the lead frame 12 by a wire 13 and
The side electrode 7 is connected to the positive terminal 15 by a wire 14. Further, the light emitting diode chip 10a, the lead frame 12, and the positive terminal 15 are sealed with a resin lens 16.

[0005]

In the conventional light emitting diode shown in FIG. 12, an n-side electrode 6 is formed on an n-type GaN cladding layer 2.
Therefore, the area of the layer above the n-type GaN cladding layer 2 needs to be smaller than the area of the sapphire substrate 1. Therefore, the area of the n-type InGaN active layer 3 is reduced, so that the light emitting area is small and the light output is low.
Therefore, the LED lamp using the light emitting diode of FIG. 12 cannot obtain high light emission intensity.

Further, of the light emitted from the n-type InGaN active layer 3, the light emitted toward the sapphire substrate 1 is not effectively used because it is absorbed by the adhesive 11.

An object of the present invention is to provide a semiconductor light emitting device having an improved light output. Another object of the present invention is to provide a light emitting lamp having an improved light emission intensity.

[0008]

According to a first aspect of the present invention, there is provided a semiconductor light emitting device in which a plurality of semiconductor layers including a light emitting layer are laminated on a light transmitting substrate, and light is emitted on the back surface of the light transmitting substrate. A reflection layer for reflecting light generated by the layer is formed.

In the semiconductor light emitting device according to the present invention,
Of the light generated by the light emitting layer, light transmitted through the light transmitting substrate is reflected by the reflective layer. Thereby, the light emitted by the light emitting layer is efficiently emitted upward, so that the light output is improved.

[0010] The light emitting layer may contain gallium and nitrogen. In this case, purple to green light is generated from the light emitting layer. Therefore, purple to green light with high light output is obtained.

[0011] The reflection layer may be made of a metal film. Alternatively, the reflection layer may be formed of a dielectric reflection film formed by laminating a plurality of dielectric layers. The dielectric reflection film is formed by alternately stacking first dielectric layers having a first refractive index and second dielectric layers having a second refractive index larger than the first refractive index. Thereby, light generated from the light emitting layer is efficiently reflected.

Further, the reflection layer may have an uneven shape.
In this case, since the light generated by the light emitting layer is reflected in various directions, the light emitting area increases, the amount of light emitted from the upper surface increases, and the light output increases.

A light-emitting lamp according to a second aspect of the present invention is a light-emitting lamp in which a semiconductor light-emitting element is adhered on a lead frame. The semiconductor light-emitting element has a plurality of semiconductor layers including a light-emitting layer laminated on a light-transmitting substrate. In addition, a reflection layer that reflects light generated by the light emitting layer is formed on the back surface of the light transmitting substrate.

In this case, of the light generated by the light emitting layer, the light transmitted through the light transmitting substrate is reflected by the reflective layer.
Thereby, the light generated by the light emitting layer is efficiently emitted upward, so that the light emission intensity of the light lamp is improved.

[0015]

FIG. 1 is a schematic sectional view showing the structure of a GaN-based light emitting diode according to a first embodiment of the present invention.

In FIG. 1, on a sapphire substrate 1 having a thickness of 300 μm, an AlGaN buffer layer 1 a having a thickness of about 200 ° and an n-type Ga serving also as an n-side contact layer having a thickness of 4 μm.
An N-clad layer 2, an n-type InGaN active layer (light-emitting layer) 3 having a thickness of 0.1 μm, a p-type AlGaN cladding layer 4 having a thickness of 0.15 μm, and a p-type GaN contact layer 5 having a thickness of 0.3 μm are formed in this order. Have been. Part of the region from the p-type GaN contact layer 5 to a predetermined depth of the n-type GaN cladding layer 2 is removed, exposing the n-type GaN cladding layer 2. An n-side electrode 6 made of Al is formed on the exposed n-type GaN cladding layer 2, and a p-side electrode 7 made of Au is formed on the p-type GaN contact layer 5.

On the back surface of the sapphire substrate 1, a metal reflection film 8 made of Al is formed. As a method for forming the metal reflection film 8, a vacuum evaporation method or a sputtering method is used. When using the vacuum deposition method, the degree of vacuum is set to 2 × 10 ^−6.
When the sputtering method is used, the degree of vacuum is set to about 1 × 10 ⁻³ to 1 × 10 ⁻² Torr.

The thickness of the metal reflection film 8 is not less than 1000.degree.
μm or less is preferred. Accordingly, light hardly transmits through the metal reflection film 8 and the metal reflection film 8 does not peel off.

In the light emitting diode of this embodiment, the n-type In
Of the light generated by the GaN active layer 3, the light traveling downward passes through the sapphire substrate 1 and is reflected upward by the metal reflection film 8. Thereby, light is efficiently emitted from the upper surface of the light emitting diode, and the light output is improved.

FIG. 2 shows an LE using the light emitting diode of FIG.
It is a schematic sectional drawing which shows the structure of D lamp.

In the LED lamp of FIG. 2, the back surface of the metal reflection film 8 of the light emitting diode chip 10 is adhered to the lead frame 12 with an adhesive 11 made of silver paste.
The n-side electrode 6 is connected to the lead frame 12 by a wire 13, and the p-side electrode 7 is connected to a positive terminal 15 by a wire 14. Further, the light emitting diode chip 10, the lead frame 12, and the positive terminal 15 are
Enclosed.

In the LED lamp of FIG. 2, since light is efficiently emitted from the upper surface of the light emitting diode chip 10, high light emission intensity is obtained.

Here, the light emitting diode of the example having the structure of FIG. 1 and the light emitting diode of the comparative example having the structure of FIG. 12 were manufactured, and the light output was measured. In the light-emitting diode of the example, the thickness of the metal reflection film 8 was 3000 °. In the light emitting diode of the comparative example, no treatment was performed on the back surface of the sapphire substrate 1. Table 1 shows the measurement results of the light output of the light emitting diodes of the example and the comparative example.

[0024]

[Table 1]

As shown in Table 1, the light emitting diode of the embodiment has a light output of 50 times that of the light emitting diode of the comparative example.
Up to 60%.

Next, the LED of the embodiment having the structure of FIG.
A lamp and an LED lamp of a comparative example having the structure of FIG. 13 were produced, and the light emission intensity was measured. In the LED lamp of the embodiment, a light emitting diode chip 10 having a metal reflection film 8 having a thickness of 3000 ° was bonded onto a lead frame 12 with a silver paste 11. In the LED lamp of the comparative example, the light emitting diode chip 10 a was bonded on the lead frame 12 with the silver paste 11. Table 2 shows the measurement results of the emission intensity of the LED lamps of the examples and the comparative examples.

[0027]

[Table 2]

As shown in Table 2, the LED lamp of the embodiment has an emission intensity of 30 to 30 compared with the LED lamp of the comparative example.
40% improvement. The reason why the emission intensity of the LED lamp of the comparative example is lower than that of the LED lamp of the embodiment is that the n-type I
This is because light from the nGaN active layer 3 cannot be effectively reflected by the silver paste. In contrast, the LED of the present embodiment
Since the lamp has the film-shaped metal reflective film 8 on the back surface of the sapphire substrate 1, light can be reflected effectively.

The material of the metal reflection film 8 is Al
And Na, Au, Ag, K, Cu, Cr, Rb, M
Metals such as g, Pd, Al, Ni, and Ti can also be used.

FIG. 3A is a schematic sectional view of a GaN-based light emitting diode according to a second embodiment of the present invention. FIG.
1 is different from the light emitting diode of FIG. 1 in that a dielectric reflection film 9 having a multilayer structure is formed on the back surface of the sapphire substrate 1 instead of the metal reflection film 8.

As shown in FIG. 3B, the dielectric reflection film 9
It includes a second dielectric layer 9b made of a first dielectric layer 9a and TiO ₂ of SiO ₂ is laminated on the plurality of sets alternately. In this embodiment, ten pairs of first dielectric layers 9a and second dielectric layers 9b are used. As a method for forming the dielectric reflection film 9, an evaporation method, a CVD method (chemical vapor deposition), a sputtering method, or the like is used.

FIG. 4 is a view for explaining the principle of light reflection on the dielectric reflection film 9. FIG. 4A shows the sapphire substrate 1 and the dielectric reflection film 9, and FIG.
2 shows light generated by a type InGaN active layer 3. FIG. 4C shows light reflected by the dielectric reflection film 9 toward the sapphire substrate 1, and FIG. 4D shows light transmitted through the dielectric reflection film 9.

As shown in FIG. 4 (a), the refractive index of the sapphire substrate 1 and n _s, a refractive index of the first dielectric layer 9a and n _a, the refractive index of the second dielectric layer 9b and n _b.
Here, n _s > n _a and n _b > n _a . Further, λ is the emission wavelength of the n-type InGaN active layer 3, the thickness of the first dielectric layer 9a is λ / 4, and the thickness of the second dielectric layer 9b is λ / 4.

Light traveling in a region having a small refractive index has a phase of λ / λ when reflected at an interface with a region having a large refractive index.
2 off. Conversely, light traveling in a region with a large refractive index is
The phase does not shift when reflected at the interface with the region having a small refractive index.

In FIG. 4C, when the light L1 transmitted through the sapphire substrate 1 is reflected at the interface 91, the phase of the reflected light is 0 because the phase is not shifted. The light L2 transmitted through the sapphire substrate 1 and the first dielectric layer 9a
2, the phase of the reflected light is (3λ) / 4 at the interface 92 and λ at the interface 91 because the phase is shifted by λ / 2.
Becomes When the light L3 transmitted through the sapphire substrate 1, the first dielectric layer 9a, and the second dielectric layer 9b is reflected at the interface 93, the phase does not shift. Therefore, the phase of the reflected light is λ / 2 at the interface 93. And (3λ) / 4 at the interface 92,
It becomes λ at the interface 91. Thus, the phase of the light reflected on the sapphire substrate 1 is 0 or λ, and is always the same.

In FIG. 4D, the phase of the light L4 transmitted through the sapphire substrate 1, the first dielectric layer 9a and the second dielectric layer 9b becomes λ / 2 at the interface 93. When the light L5 transmitted through the sapphire substrate 1 and the first dielectric layer 9a is reflected at the interface 92, the phase shifts by λ / 2, so that the phase of the reflected light becomes (3λ) / 4 at the interface 92, and the reflection When the light is reflected at the interface 91, the phase is shifted by λ / 2.
The phase of the reflected light is (3λ) / 2 at the interface 91 and (7λ) / 4 at the interface 92. When the light further passes through the second dielectric layer 9b, its phase becomes 2λ at the interface 93. In this case, the light L4 and the light L5 cancel each other, and no light passes through the dielectric reflection film 9.

Therefore, if the refractive indices of the first dielectric layer 9a and the second dielectric layer 9b are not considered,
By setting the thicknesses of the dielectric layer 9a and the second dielectric layer 9b to ４ of the wavelength λ of the light generated by the n-type InGaN active layer 3, the light is converted to the dielectric reflection film 9 Can be reflected.

The refractive index n of the first dielectric layer 9a_aAnd the first
Refractive index n of the second dielectric layer 9b_bIs considered, the first
Layer thickness d of dielectric layer 9a_aAnd the layer of the second dielectric layer 9b
Thickness d _bIs set to satisfy the following equation.

[0039] _{d a = λ / (4n a} ) ··· (1) d b = λ / (4n b) ··· (2) the emission wavelength due to n-type InGaN active layer 3 lambda is 470n
m, the refractive index n _s of the sapphire substrate 1 is 1.78, the refractive index n _a of the first dielectric layer 9a is 1.47, the refractive index n _b of the second dielectric layer 9b is a 2.36 In the case, the above equation (1),
(2), the layer thickness d _a of the first dielectric layer 9a is approximately 800
Å, and the layer thickness d _b of the second dielectric layer 9b about 500Å
Becomes

FIG. 5 is a diagram showing a calculation result of the reflectance of the dielectric reflection film 9 described above. As shown in FIG.
When one set of the dielectric layer 9a and the second dielectric layer 9b is one set, the reflectance is about 41%, and when two sets, the reflectance is 71%.
It becomes 88% in the case of three sets, and becomes 95% in the case of four sets. That is, by providing three or four sets of the first dielectric layer 9a and the second dielectric layer 9b,
Almost the same reflectance as the metal reflective film 8 made of Al can be obtained. As described above, as the number of sets of the first dielectric layer 9a and the second dielectric layer 9b increases, the reflectance of light propagating from the sapphire substrate 1 to the dielectric reflection film 9 increases.

In the above embodiment, the first dielectric layer 9
As a, SiO ₂ having a refractive index of 1.47 is used, and TiO ₂ having a refractive index of 2.36 is used as the second dielectric layer 9b. However, as the first dielectric layer 9a, a refractive index of 1.39 is used. Mg
O, Al ₂ O ₃ having a refractive index of 1.63 may be used.
As the dielectric layer 9b, ZnO having a refractive index of 2.1 may be used. Further, as the first dielectric layer 9a, MgF ₂ ,
LaF ₃ , NdF ₃ , CeF ₃ , BaF ₂ , CaF ₂ ,
LiF can also be used, and as the second dielectric layer 9b, ZrO ₂ , CeO ₂ , TiO ₂ , ZnS, Bi ₂ O
₃ , LiNbO ₃ , LiTaO ₃ , BaTiO ₃ , Sr
TiO ₃ and KTaO ₃ can also be used.

FIG. 6A is a schematic sectional view of a GaN-based light emitting diode according to a third embodiment of the present invention. FIG.
1A is different from the light emitting diode of FIG. 1 in that the back surface of the sapphire substrate 1 is processed into a symmetrical triangular wave (sawtooth wave) uneven shape, and a metal reflection film 18 is formed on the back surface of the sapphire substrate 1. This is a point formed in an uneven shape.

In order to process the back surface of the sapphire substrate 1 into an irregular shape, dry etching using CF ₄ gas,
A chemical processing method such as wet etching using a phosphoric acid-based etching solution or a mechanical processing method using a cutting tool for dicing is used.

In the light emitting diode of this embodiment, the n-type In
Among the light generated by the GaN active layer 3, the light transmitted through the sapphire substrate 1 is a metal reflection film 8 formed in an uneven shape.
Are reflected in various directions. Accordingly, the light emitting area increases, the amount of light emitted from the side surface of the light emitting diode decreases, and the amount of light emitted from the upper surface increases.
As a result, the light output is improved.

Here, the light output of the light emitting diode of FIG. 6A was compared with the light output of the light emitting diode of FIG. In the light emitting diode of the present example, the back surface of the sapphire substrate 1 was processed into a symmetrical triangular wave-shaped unevenness as shown in FIG. The groove angle θ is 45 ° and the groove width W is 40μ.
m. The width D of the light emitting diode in FIGS. 1 and 6A was 400 μm. As a result, the light output of the light emitting diode of FIG. 6A was improved by 20% as compared with the light emitting diode of FIG.

The concave and convex shape on the back surface of the sapphire substrate 1 may be a shape in which a plurality of grooves are formed in one direction, as shown in FIG. In addition, as shown in FIG. 7B, pyramid-shaped projections may be two-dimensionally arranged. Further, as shown in FIG. 7C, hexagonal pyramid-shaped projections may be two-dimensionally arranged.

FIG. 8 shows Ga in the fourth embodiment of the present invention.
FIG. 3 is a schematic sectional view of an N-based light emitting diode. The light emitting diode of FIG. 8 differs from the light emitting diode of FIG. 6 in that the metal reflection film 8 formed on the back surface of the sapphire substrate 1 has an asymmetric triangular wave shape (saw blade shape).

In the light emitting diode of this embodiment, as shown by arrows in FIG. 8, of the light generated from the n-type InGaN active layer 3, the light transmitted through the sapphire substrate 1 is reflected by the metal reflection film 8. In this case, the amount of light reflected in the direction of the n-side electrode 6 increases. Thereby, the region of the n-side electrode, which was a non-light emitting region in the conventional light emitting diode, becomes a light emitting region, and light is uniformly emitted from the entire upper surface of the light emitting diode.

FIG. 9 shows an LE using the light emitting diode of FIG.
It is a schematic sectional drawing of D lamp. FIG. 10 shows the LE of FIG.
It is a figure showing the directivity of a D lamp.

As shown in FIG. 9, the light emitting diode chip 10 is disposed at the center inside the resin lens 16. When the light emitting diode of FIG. 8 is used, the light is uniformly emitted from the entire upper surface of the light emitting diode chip 10, and the distribution of the emitted light is symmetric with respect to the central axis S. Thereby, as shown by a solid line in FIG. 10, light emission from the light emitting diode chip 10 becomes symmetric with respect to the central axis. On the other hand, when a conventional light emitting diode is used, no light is emitted from the n-side electrode 6 of the light emitting diode chip 10a. Not symmetric.

FIG. 11 shows G in the fifth embodiment of the present invention.
FIG. 2 is a schematic sectional view of an aN-based light emitting diode. The difference between the light emitting diode of FIG. 11 and the light emitting diode of FIG.
The point is that the metal reflection film 8 formed on the back surface of the sapphire substrate 1 has a concave lens shape.

In the light emitting diode of this embodiment, the n-type In
Of the light generated by the GaN active layer 3, the light transmitted through the sapphire substrate 1 is reflected upward by the metal reflection film 8. In this case, since the metal reflection film 8 has a concave lens shape, most of the reflected light is concentrated on the upper surface of the light emitting diode, and the amount of light emitted from the side surface is reduced. Thereby, the light output of the light emitting diode is improved.

The light output of the light emitting diode of FIG. 11 was compared with the light output of the light emitting diode of FIG. The light emitting diode of FIG. 11 has a light output of 4 compared to the light emitting diode of FIG.
0% improvement.

In the above embodiment, the case where the present invention is applied to a GaN-based light-emitting diode has been described. However, the present invention is applicable to a light-emitting diode and a semiconductor laser device of another material formed on a light-transmitting substrate. The present invention can be applied to a semiconductor light emitting device.

As the transparent substrate, an SiC substrate or an MgO substrate may be used in addition to the sapphire substrate.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a GaN-based light emitting diode according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of an LED lamp using the light emitting diode of FIG.

FIG. 3 is a schematic sectional view of a GaN-based light emitting diode according to a second embodiment of the present invention.

FIG. 4 is a diagram for explaining the principle of light reflection on a dielectric reflection film.

FIG. 5 is a diagram showing a calculation result of light reflectance of a dielectric reflection film.

FIG. 6 is a schematic cross-sectional view of a GaN-based light-emitting diode and a diagram showing an uneven shape on the back surface of a sapphire substrate according to a third embodiment of the present invention.

FIG. 7 is a plan view showing an example of an uneven shape of a metal reflection film in the light emitting diode of FIG.

FIG. 8 is a schematic sectional view of a GaN-based light emitting diode according to a fourth embodiment of the present invention.

FIG. 9 is a schematic sectional view of an LED lamp using the light emitting diode of FIG.

FIG. 10 is a diagram showing the directional characteristics of the LED lamp of FIG. 9;

FIG. 11 is a schematic sectional view of a GaN-based light emitting diode according to a fifth embodiment of the present invention.

FIG. 12 is a schematic sectional view of a conventional GaN-based light emitting diode.

FIG. 13 is a schematic sectional view of an LED lamp using the light emitting diode of FIG.

[Explanation of symbols]

 Reference Signs List 1 sapphire substrate 1a AlGaN buffer layer 2 n-type GaN cladding layer 3 n-type InGaN active layer 4 p-type AlGaN cladding layer 5 p-type GaN contact layer 6 n-side electrode 7 p-side electrode 8 metal reflection film 9 dielectric reflection film 9a 1 dielectric layer 9b 2nd dielectric layer 10 Light emitting diode chip 11 Silver paste 12 Lead frame 15 Positive terminal 16 Resin lens

Claims (7)

[Claims] 1. A plurality of semiconductor layers including a light-emitting layer are laminated on a light-transmitting substrate, and a reflection layer for reflecting light generated by the light-emitting layer is formed on a back surface of the light-transmitting substrate. A semiconductor light emitting device characterized by the above-mentioned. 2. The semiconductor light emitting device according to claim 1, wherein said light emitting layer contains gallium and nitrogen. 3. The semiconductor light emitting device according to claim 1, wherein said reflection layer is a metal film. 4. The reflection layer according to claim 1, wherein the reflection layer is a dielectric reflection film formed by laminating a plurality of dielectric layers.
Or the semiconductor light emitting device according to 2. 5. The dielectric reflection film includes a first dielectric layer having a first refractive index and a second dielectric layer having a second refractive index larger than the first refractive index. The semiconductor light emitting device according to claim 4, wherein the semiconductor light emitting device is alternately stacked. 6. The semiconductor light emitting device according to claim 1, wherein said reflection layer has an uneven shape. 7. A light-emitting lamp in which a semiconductor light-emitting element is adhered on a lead frame, wherein the semiconductor light-emitting element has a structure in which a plurality of semiconductor layers including a light-emitting layer are laminated on a light-transmitting substrate, and A light-emitting lamp, wherein a reflective layer for reflecting light generated by the light-emitting layer is formed on a back surface of the conductive substrate.