JPH05167101A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To provide a semiconductor light emitting element which can effectively utilize light by improving its light emitting efficiency. CONSTITUTION:The title light emitting element has a light scattering layer 10 formed on the surface of the element on the side from which the light is taken out from a light emitting layer 2. The light scattering layer 10 is formed on the surface of a current diffusing layer 3 formed on the light emitting layer 2 by using a material having a lattice constant which is different from that the layer 3 has. After the layer 10 is grown on the layer 3, the surface of the layer 10 is roughened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device having a structure with increased brightness, and more particularly to a display light source, for example, an indoor information display board such as a station yard, an outdoor building advertisement board or a road display. The present invention relates to a semiconductor light emitting element used for a board, a stop lamp of an automobile, a traffic signal, and the like.

[0002]

2. Description of the Related Art As a light emitting device using a semiconductor crystal,
Light emitting diodes (LEDs, Light Emitting Diodes), laser diodes (LDs, Laser Diodes), electroluminescence (EL, Electro-Luminescence) and the like are known. The former two apply a forward voltage to the semiconductor junction,
In this device, minority carriers are injected to cause recombination with majority carriers at the junction, and the light emitted at this time is used. Electroluminescence is a phenomenon in which light is emitted when an electric field is applied to a crystal body. The applied voltage is direct current,
Either exchange is possible. Among these semiconductor light emitting devices, a light emitting diode, in particular, a high-brightness LED is used as a display light source, for example, an information display board for indoors or in stations, a road display information board, an automobile stop lamp, and a traffic signal. There is. Further, since it has high brightness even at low current, it is used as an energy-saving type display light source as compared with the conventional one. The LEDs used in such fields are as follows. First, as the red light emitting element, there are GaAsP red LED having a peak wavelength of about 630 nm and GaAlAs red LED having a peak wavelength of about 660 nm, and as the orange light emitting element, a peak wavelength is 610 nm.
About GaAsP orange LED and yellow light emitting element,
GaAsP yellow LED with peak wavelength of about 590 nm
However, as a green light emitting element, the peak wavelength is 565n.
GaP green LEDs of about m are used. The brightness of each element is about 300 mcd for GaAsPLED, G
The aAlAs red LED has a single hetero (SH) structure of about 500 mcd, the double hetero (DH) structure without the GaAs substrate has a structure of about 3000 mcd, and the GaP green LED has a structure of about 500 mcd. As a main means for forming a semiconductor light emitting element, a vapor phase growth method (VPE) or a liquid phase growth method (LPE), which is an epitaxial crystal growth method known as a thick film forming method, is known. , GaAsP formation, LPE
Are suitable for forming GaAlAs, GaP, etc., respectively. In addition, VPE (MOVPEMeta using organic metal)
l Organic Vapor Phase Epitaxy) and MBE (Molecula)
r Beam Epitaxy) and other methods are known.

An example of the prior art will be described with reference to FIG. As the semiconductor substrate 1, an n-GaAs substrate having an impurity concentration of about 3 × 10 ¹⁸ cm ⁻³ is used. On this n-GaAs substrate 1, an n-I having a thickness of 1 μm and an impurity concentration of 5 × 10 ¹⁷ cm ⁻³ was formed.
n _0.5 (Ga _1-x Al _x ) _0.5 P cladding layer 21, 0.6 μm thick undoped In _0.5 (Ga _1-y Al _y ).
_0.5 P active layer 20, thickness 1 μm, impurity concentration 5 × 10 ¹⁷
cm ⁻³ p-In _0.5 (Ga _1-z Al _z ) _0.5 P cladding layer 22, further having a thickness of 7 μm and an impurity concentration of 1 × 10 ^18.
The cm ⁻³ p-Ga _{1 -u} Al _u As current diffusion layer 3 is sequentially grown by, for example, the MOVPE method. Next, on the other surface of the substrate 1, an n-side electrode 4 such as Au-Ge is opened.
Mic contact, and on the opposite side of the current diffusion layer 3,
For example, the p-side electrode 5 such as Au-Zn is brought into ohmic contact. Ga _1-u Al _u As which is the current diffusion layer 3
The layer is provided for diffusing the current from the p-side electrode 5 over the entire surface of the LED chip, but it is not always necessary as a light emitting element, and some layers do not use it. The figure shows the case where u is 0.7. The presence of this layer enables light emission over the entire active layer, so that the light extraction efficiency from the chip can be significantly improved. These various growth layers are lattice-matched with the GaAs substrate and have a double hetero structure. When y of the active layer is changed from 0 to 0.7, red emission of about 660 nm to green emission of about 555 nm are emitted. High emission efficiency can be obtained by obtaining a direct transition band structure in the range and by using a double hetero structure. In this example, since the light is extracted from the current diffusion layer side, the p-side electrode 5 serves as the light extraction-side electrode. The light extraction side electrode is usually connected to an external wiring by a bonding pad.

In this type of light emitting device, the portion that directly contributes to light emission is sandwiched between the active layer 20 and this active layer 1.
Since the clad layers 21 and 22 are a pair, these layers are collectively defined as the light emitting layer 2 here. In this element, the pn junction in the light emitting layer 2 has a double hetero structure, but hereinafter, even in the case of an element having another structure such as a single hetero or a homo junction, a portion directly contributing to light emission is referred to as a light emitting layer.

By the way, for example, in the case of an outdoor display light source, a luminance of 1 cd or more is required in each emission color region. GaAlAs, which is a direct transition type in the red region
Although LEDs with a brightness of 1 cd or more are easily obtained, GaAsPLE is an indirect transition type in the wavelength range shorter than red.
Since D and GaPLED are used, the limit is about 500 mcd, and the current situation is that they do not function sufficiently for outdoor use. Therefore, LEDs of these colors
When using the LED for outdoor use, only one GaAlAs red LED is required, but it is necessary to use a plurality of LEDs, which increases the cost. As will be described later, sufficient brightness cannot be obtained even in the InGaAlPLED which is a direct transition type. One of the causes is that the emitted light is not effectively used. Due to the presence of the current diffusion layer described above, light can be efficiently emitted, but the light cannot be fully utilized. A part of the light emitted from the light emitting layer 2 goes out from the surface on the light extraction side as it is. On the other hand, when the semiconductor substrate is transparent, the light traveling downward on the opposite side is reflected on the substrate surface other than the polka dot electrode if the n-side electrode is shaped like a polka dot, and is reflected from the upper light extraction side surface. Since light is emitted to the outside and is also emitted to the outside from the side surface of the substrate, the light directed downward can be effectively extracted to the outside.

However, considering a light emitting element using an InGaAlP mixed crystal semiconductor having a large band gap as an active layer in the light emitting layer, when the semiconductor substrate 1 is made of a material such as GaAs having a small band gap, the light emitting layer is short. Since it emits a wavelength, most of the emitted light is absorbed by this substrate. Therefore, the light directed downward cannot be extracted to the outside. For that reason, it is necessary to select a semiconductor substrate that absorbs less light.
Materials are limited. Conventionally, a light reflecting layer is formed between a light emitting layer and a semiconductor substrate in order to prevent light from being absorbed by the semiconductor substrate, improve luminous efficiency, and at the same time widen the range of substrate material selection. The light emitted from the light emitting layer 2 is reflected by this light reflecting layer even in the direction of the semiconductor substrate 1 below, and the absorption of light by the semiconductor substrate is prevented.
This light reflection layer is formed, for example, by directly laminating two or more kinds of substances having different refractive indexes directly below the light emitting layer to a thickness equivalent to ¼ times the wavelength of light or an equivalent thickness. .. A Ga _1-u Al _u As layer is a well-known material for the current spreading layer. On the other hand, as a method of extracting the light directed downward without providing the light reflection layer, for example, Ga is used.
IuGaAlP using GaP substrate instead of As substrate
-There is an LED. GaP substrate is InGaAlP-LED
Since it is transparent to the emission color (green to red), it is not necessary to provide a reflective layer. However, in this case, the GaP substrate and the In
_{Since many} lattice defects occur due to lattice mismatch with _0.5 (Ga _1-x Al _x ) _0.5 P, the luminous efficiency is reduced and an LED with high brightness cannot be obtained effectively. In _0.5 (G
By a _1-x Al x) composition ratio on first GaP substrate before growing _0.5 P is grown the In _1-v Ga v P gradient composition layer gradually changes (v = 1 → 0.5) GaP
A method of absorbing a difference in lattice constant between the substrate and In _0.5 (Ga _1-x Al _x ) _0.5 P is adopted. In _1-v
Instead of the Ga _v P composition gradient layer, In _1-v (Ga _1-w A
1 _w ) _v P composition gradient layer (v = 1 → 0.5). The inventors of the present invention have also developed a semiconductor light emitting device in which a light reflection layer is provided between the light emitting layer and the light extraction electrode to effectively extract the light reflected by the light extraction electrode ( Japanese Patent Application No. 3-163359).

[0007]

As described above, light is emitted due to the presence of the light reflection layer and the current diffusion layer inserted between the active layer and the semiconductor substrate or between the electrode on the light extraction side and the active layer. Efficiency goes up and light utilization goes up, but
It is still not sufficient to obtain LEDs of 1 cd or more in the range from orange to green. In _1-v G on the GaP substrate
a _v P composition gradient layer or In _1-v (Ga _1-w Al _w ) _v
The light utilization rate is also improved by the method of growing the P composition gradient layer and then forming the light emitting layer, but in this case, the lattice constant of the lattice constant between the GaP substrate and In _0.5 (Ga _1-x Al _x ) _0.5 P is increased. The difference cannot be completely absorbed, so that the number of crystal defects increases and the internal luminous efficiency decreases, resulting in 1
LED of more than cd cannot be obtained.

The present invention has been made under the above circumstances, and is a semiconductor light emitting device capable of increasing light emission efficiency and effectively utilizing light, for example, InGaAlP.
LE having a brightness of 1 cd or more by using a material that emits light of a short wavelength as an active layer as in the case of using a quaternary mixed crystal
It is intended to provide D.

[0009]

A semiconductor light emitting device of the present invention comprises a light emitting layer including an active layer, a light scattering layer formed on the light emitting layer and having a light extraction surface, the light emitting layer or the light emitting layer. The first feature is that the light extraction side electrode is formed on the scattering layer. In addition, a light emitting layer including an active layer, a current diffusion layer formed on the light emitting layer, a light scattering layer formed on the current diffusion layer and having a light extraction surface, the current diffusion layer or the The second characteristic is that the light extraction side electrode is formed on the light scattering layer. The light emitting layer has a single heterojunction, a double heterojunction, or a homojunction. In the semiconductor light emitting device in which the light emitting layer includes an InGaAlP-based mixed crystal semiconductor as an active layer, the light scattering layer includes GaP, ZnS, ZnSe, and ZnSe-.
A material selected from ZnS can be used. The thickness of the light scattering layer is 0.5 μm or more, and the lattice constant of the semiconductor crystal of the light scattering layer is different from the lattice constant of the semiconductor crystal in contact with the bottom surface by 0.3% or more. it can. A semiconductor substrate is provided on the surface of the light emitting layer opposite to the surface on which the light scattering layer is formed, and on the surface of the semiconductor substrate opposite to the surface on which the light emitting layer is formed. When the semiconductor substrate material is selected such that the substrate side electrode is provided and the band gap of the semiconductor substrate is substantially the same as or larger than the band gap of the active layer, the substrate side is selected. The electrodes can be polka dot shaped. further,
It is also possible to form a light reflection layer directly below the light extraction side electrode.

[0010]

[Function] The light emitted from the light emitting layer toward the light extraction surface is easily emitted to the outside due to the effect of the light scattering surface of the light scattering layer, and when the reflection layer is below the light emitting layer, the light is emitted from the light emitting layer. Light directed to the reflective layer is reflected by the reflective layer and directed to the light extraction surface, and more light is emitted to the outside due to the effect of the light scattering surface. The effect of this light scattering layer is, for example, when the light extraction surface is a mirror surface (InG
In the case of aAlP-LED, it is usually a mirror surface)
Compared with Assuming that the refractive index of the crystal below the light extraction surface is n and the refractive index of air is 1, the light extraction efficiency η _{c in} the case of a mirror surface is η _c = 1/2 [1-cos (s
in ⁻¹ 1 / n)] [1- (n−1 / n + 1) ² ], where n = 3.4, η _c = 0.0155 =
It becomes 1.55%. In the case of a perfect light scattering surface, η _c is
η _c = 1/2 (1 / n) ² f (n), where n =
At the time of 3.4, since f (n) = 0.685, η _c =
It becomes 0.0296 = 2.96%. Here, it is assumed that light is emitted from the light emitting layer to the light extraction surface side (upper side) and the opposite side (lower side), and the light directed downward is completely absorbed. As can be seen from the calculation result of the above equation, the light extraction effect is improved about twice when the light extraction surface is formed in the light scattering layer. Similar effects can be obtained when the reflective layer is provided below the light emitting layer and when the light reflective layer is provided immediately below the light extraction electrode.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a schematic structure of a light emitting diode which is a semiconductor light emitting element according to the first embodiment. As shown in the figure, the basic structure includes a compound semiconductor substrate 1 having one electrode, a light reflection layer 6, a light emitting layer 2, a current diffusion layer 3, a light scattering layer 10 and a light extraction side electrode 5 on this substrate. Is included. The light reflection layer avoids light absorption by the substrate as much as possible, and the light scattering layer improves the rate of light out. In the figure, the compound semiconductor substrate 1 is n-GaA.
s is used. On this substrate 1, a light reflection layer 6 having a multi-layer structure in which n-InAlP and n-InGaAlP having a thickness of about ½ of the emission wavelength are alternately laminated is grown. An n-InAlP cladding layer 21, an InGaAlP active layer 20 and a p-InAlP layer are formed on the light reflection layer 6.
The light emitting layer 2 having a double hetero structure composed of the cladding layer 22 is grown and formed. On the p-InAlP clad layer 22, a p-GaAlAs current diffusion layer 3 is grown and formed so that a current flows in the entire light emitting layer so that light is emitted in the entire light emitting layer. Furthermore, this current spreading layer 3
In addition, the light-scattering layer which is a feature of the present invention (in this embodiment,
A P-GaP layer) 10 is grown and formed. An n-side ohmic electrode 7 (substrate-side electrode) is formed on the substrate 1 side, and a p-type ohmic electrode (light-extraction-side electrode) 5 is formed on the light-scattering layer 10 side. The p-side ohmic electrode 5 is formed into a predetermined shape by ordinary photoetching. In the example of FIG. 1, since the surface of the light scattering layer 10 is rough, only the light extraction electrode (p-side ohmic electrode) is removed by etching. However, the light scattering layer 10
It is also possible to form the light extraction electrode directly on the above.

Next, a method for manufacturing the above semiconductor light emitting device will be specifically described. Each semiconductor layer was grown by a metal organic chemical vapor deposition method (MOVPE method). Trimethyl indium (TMI), trimethyl gallium (TMG), and trimethyl aluminum (TMA) are used as raw materials.
Arsine (AsH ₃ ) and phosphine (PH ₃ ) were used as sources of group V elements as sources of group V elements. Zn as a P-type dopant and S as an n-type dopant
i was used, and these are dimethyl zinc (DM
Z) and silane (SiH ₄ ) as a source.
This reactive gas was transported to a quartz reaction tube using hydrogen as a carrier gas, and crystal growth was performed on an n-GaAs substrate placed on a SiC-coated graphite susceptor. The pressure inside the reaction tube is 30 to 100 Torr,
The substrate is heated to about 800 ° C. The n-GaAs substrate was doped with Si and had a carrier concentration of about 3 × 10 ¹⁸ cm ^-3 . The plane orientation of the substrate is (100).
First, on the n-GaAs substrate 1, n-In _0.5 Al
A light-reflecting layer 6 formed by alternately laminating a plurality of _0.5 P and n-In _0.5 Ga _0.2 Al _0.3 P is grown to a thickness of about 4.3 μm. Each semiconductor layer is Si-doped and has a carrier concentration of 1
It is × 10 ¹⁸ cm ^-3 , and in order to reflect light efficiently, the layers are alternately stacked at a stacking cycle of about ½ (about 86 nm) of the emission wavelength. Then, on the light reflection layer 6, n having a thickness of 1 μm is formed.
-In _0.5 Al _0.5 P (Si-doped, carrier concentration 5 ×
10 ¹⁷ cm ⁻³ ) 21, 0.6 μm thick undoped In
_0.5 Ga _0.21 Al _0.29 P active layer 20, p-In _0.5 Al
_0.5 P (Zn-doped, carrier concentration 5 × 10 ¹⁷ cm ⁻³ )
A light emitting layer 2 having a double hetero structure composed of the clad layer 22 is formed. Then, p-Ga which is transparent to the emission wavelength
_{A 0.2} Al _0.8 As (Zn-doped, 4 × 10 ¹⁸ cm ⁻³ ) current diffusion layer 3 is grown to about 7 μm. Next, a Zn-doped p-GaP light-scattering layer 10 having an impurity concentration of 4 × 10 ¹⁸ / cm ³ is grown to about 1 μm. Since the lattice constant of p-GaP is not the same as that of GaAlAs, imperfect growth due to lattice mismatch occurs, so the p-GaP growth surface becomes a rough surface and a light scattering layer is formed.

In order to form an electrode on the thus obtained green LED wafer, first, the p-GaP light scattering layer 10 is partially removed by etching to remove the light extraction electrode (p.
The portion where the side electrode) 5 is to be formed is exposed. Next, an AuGe alloy layer 4 of 0.5 μm and a p-GaP light-scattering layer 1 were formed on the n-GaAs substrate 1 side of this wafer by vacuum deposition.
480 after depositing a 0.3 μm AuBe alloy layer on the 0 side
Sintering is performed in an Ar atmosphere at 10 ° C. for 10 minutes to form an ohmic contact. Then, pure gold was deposited again on the AuBe alloy layer of this wafer by vacuum evaporation to a thickness of about 1 μm, and the p-GaAlAs current diffusion layer 3 formed on the p-GaP light-scattering layer was exposed by photolithography. The AuBe alloy layer and the pure gold layer are removed except for the portion. In this way, the p-side electrode 5 is formed on the glossy surface of the p-GaAlAs current diffusion layer 3. The reason why such a complicated process is adopted is that the electrode surface needs to have a gloss in order to detect the electrode during automatic wire bonding. Then, finally, it is diced at a predetermined pitch to be separated into individual pellets. In this way, a high-efficiency green LED having the p-side electrode 5 side as the light extraction side is completed. Since the light generated in the light emitting layer 2 is extracted to the outside from the surface on which the p-side electrode 5 is formed, this electrode becomes the light extraction-side electrode. That is, in this LED, the light generated in the active layer of the double hetero structure section goes to the p-side electrode 5 side, the substrate 1 side and the side surface. The light directed to the substrate 1 side is efficiently reflected by the light reflection layer 6 and directed to the light extraction side, and a part thereof is extracted from the light extraction surface, and the light directed to the p-type electrode 5 is also the same part. Are taken out from the light extraction surface. At this time, since the light extraction surface of the device is a light scattering layer, the light extraction efficiency is improved by about 2 times as compared with the conventional case where the light is extracted from the glossy surface of the current diffusion layer. To be realized. As described above, according to the embodiment, a high-brightness LED that emits light in the green region using a high-quality and inexpensive GaAs substrate can be manufactured without using a special substrate. Low cost green L
It can be said that mass production of EDs makes a great contribution to the information industry such as displays and optical communications.

The light scattering layer used here is not limited to GaP, has a lattice constant different from the lattice constant of the material of the current diffusion layer formed in contact therewith, and has an energy rather than an emission color. A light-scattering layer can be used as long as it has a high band gap. That is, by depositing materials having a lattice constant different by 0.3% or more on the semiconductor layer of the light emitting element by 0.5 μm or more, the light scattering layer, which is a feature of the present invention, can be formed. Originally, unless the respective semiconductor layers were grown with good crystallinity, the crystal plane was roughened and the characteristics were deteriorated. Therefore, the adjacent two semiconductor layers were made to have the crystal lattice constants matched as much as possible. But,
Here, conversely, the feature is that the lattice constant is shifted, and by doing so, the surface of the semiconductor layer is roughened. In the case of the InGaAlP-based LED, a material such as ZnSe, ZnS or ZnSe-ZnS is used in addition to GaP. In this example, the lattice constant of the GaAlAs current spreading layer differs from that of the InGaAlP light emitting layer by only about 0.13% or less, so that the GaAlAs
The surface of the current diffusion layer is a mirror surface, but G which grows on it
Since the lattice constant of aP is different from about 3.5% GaAlAs, irregularities are formed on the surface of the GaP light scattering layer. Therefore, the GaP crystal can effectively scatter light. Here, the lattice constant of the semiconductor crystal is given. GaP
Is 5.4512 angstrom (hereinafter, abbreviated as A), GaAs is, 5.6533A, Ga _{0. 3} Al _0.7
As is 5.6588A, Ga _0.2 Al _0.8 As is
5.6595 A and In _0.5 (Ga _1-x Al _x ).
_0.5 P is almost the same as the lattice constant of GaAs. Although the green LED has been described in the embodiment, InG
By appropriately changing the composition of the aAlP active layer, it can be easily applied to yellow, orange, red, infrared LEDs and the like.

Next, a second embodiment will be described with reference to FIG. N-G with an impurity concentration of about 3 × 10 ¹⁸ / cm ³
1 μm thick on aAs semiconductor substrate 1, impurity concentration 5 × 1
0 ¹⁷ / cm ³ n-In _0.5 (Ga _1-x Al _x ) _0.5 P
Clad layer 21, 0.6 μm thick And-In In _{0.5
(Ga 1-y Al y)} 0.5 P active layer 20, a thickness of 1 [mu] m, the impurity concentration of 5 × 10 ¹⁷ / cm ³ of _{p-In 0.5 (Ga 1-} z
Al _z ) _0.5 P clad layer 22, further having a thickness of 7 μm,
Impurity concentration 1 × 10 ¹⁸ / cm ³ of p-Ga _0.3 Al _0.7
The As current diffusion layer 3 is sequentially grown by the MOVPE method or the like. Next, on the other surface of the semiconductor substrate 1, n such as Au-Ge is formed.
The side electrode 4 is brought into ohmic contact. Next, the impurity concentration of Zn doped on the current diffusion layer 3 is 5 ×.
The p-GaP light scattering layer 10 of about 10 ¹⁷ / cm ³ is 1 μm thick.
Grow to a degree. Since the lattice constant of p-GaP does not match the lattice constant of p-GaAlAs of the current diffusion layer, p-GaP is incompletely grown due to lattice mismatch, and its growth surface becomes a rough surface. The light scattering layer 10 is formed. Then, the light scattering layer 10 is partially removed by etching to partially expose the surface of the current diffusion layer 3. Then, an AuBe alloy layer is vapor-deposited on the exposed surface of the current diffusion layer 3, and pure gold is deposited to a thickness of about 1 μm to form a light extraction side electrode (p side electrode) 5. Of course, the light extraction side electrode 5 can also be formed directly on the light scattering layer 10.

Next, a third embodiment will be described with reference to FIG. The semiconductor substrate used here is transparent to the light from the light emitting layer, and therefore, no light reflecting layer is provided on the substrate side. For example, n-GaP is used for the semiconductor substrate 1, and InGaAlP is used for the active layer. This Ga
Since the P substrate is transparent to the emission color (green to red) of InGaAlP-LED, it is not necessary to provide a reflective layer. G
No problem occurs in the case of an LED having GaP as a light emitting layer on an aP substrate. However, when InGaAlP is used as a light emitting layer on a GaP substrate, the light emitting efficiency is lowered due to frequent occurrence of lattice defects due to lattice mismatch in the light emitting layer. And, as a result, LE with high brightness
I can't get D. Therefore, in this embodiment, GaP substrate 1 and the _{n-In 0.5 (Ga 1-} x Al x) 0.5 P cladding layer 21, and - flop _{In 0.5 (Ga 1-y Al} y) 0.5 P active layer 20, p- In _0.5 (Ga _{1- z} Al _z ) _0.5 P, the In _1-v Ga _v
A method is adopted in which the difference in lattice constant between the substrate and the light emitting layer is absorbed by growing the P composition gradient layer 7 (v = 1 → 0.5). As the composition gradient layer, In
_{1- v (Ga 1-w Al} w) V P (v = 1 → 0.5) can also be used. On this light emitting layer 2, a p-Ga _0.2 Al _0.8 As current diffusion layer 3 transparent to the emission wavelength is formed. The light extraction side electrode 5 and the p-GaP light scattering layer 10 formed on this current diffusion layer are formed by the same method as in the second embodiment. An electrode is also formed on the substrate side,
In order to efficiently reflect light on the bottom surface of the substrate, the substrate-side electrode 4 has a polka dot pattern. Since the light absorption at the electrodes cannot be ignored, the light is reflected uniformly on the bottom surface of the substrate in such a shape. Further, the shape is not limited to the polka dot shape, and may be an arbitrary shape such as a polygonal shape.

Next, a fourth embodiment will be described with reference to FIG. In this embodiment, a light-reflecting layer is provided immediately below the light-extraction-side electrode so that the light emitted from the light-emitting layer toward this electrode is effectively extracted. As shown in the figure, the same first light reflection layer 6 as that used in the first embodiment is formed on the n-GaAs substrate 1 on which the substrate side electrode 4 is formed, and the n-GaAlAs clad layer is formed thereon. 21, Ando Ga
AlAs active layer 20, p-GaAlAs clad layer 22
The light emitting layer 2 is formed. Here, the clad layer 21
Is about 1 μm and the active layer 20 is about 0.6 μm in thickness, but the cladding layer 2 on the side where the light extraction electrode is formed is
2 is 10 μm or more thicker than these. The clad layer 22 is made of GaAlAs and is thickly formed. Therefore, the clad layer 22 itself is also used as a current diffusion layer, and the current from the light extraction electrode 5 is supplied to the LED.
It can be spread evenly over the entire surface of the chip. A second light reflection layer 8 having a multilayer structure in which p-InAlP and InGaAlP having a thickness of about ½ of the emission wavelength are alternately laminated is grown and formed on the cladding layer 22. Then, p-GaA for facilitating the ohmic property of the electrode is formed thereon.
The light extraction electrode 5 made of the same material as that of the first embodiment is provided through the s contact layer 9, and the p-GaP light scattering layer 10 is provided on the exposed portion of the cladding layer 22 by utilizing the lattice mismatch. To form. An example of the size of each element formed on this chip is 0.3 mm square, and the radius of the light extraction electrode at that time is, for example, about 0.14 mm. In this embodiment, a red or infrared LED is formed.

As described above, when the light scattering layer is formed on the light extraction electrode side, the lattice mismatch between the semiconductor layers is utilized, but the surface can be roughened by using an acid such as HCl. .. In the case of HCl, the light scattering layer is preferably GaP,
Luminous efficiency is improved by about 30 to 50%. In addition, GaAlA
HNO ₃ can be used for the light scattering layer of s. According to this nitric acid method, the luminous efficiency is improved by about 10 to 20%. Although the n-type is used for the semiconductor substrate in the above-described example, a p-type substrate can be naturally used.

[0019]

The light-scattering surface of the light-scattering layer formed on the side of the light-extracting electrode (light-extracting surface) makes it easier for light to go out, and the luminous efficiency is significantly improved. Further, conventionally, the lattice constants of the respective semiconductor layers were made to match as much as possible, but the light scattering layer of the present invention, on the contrary, was designed to have a lattice constant different from that of the other semiconductor layers, so that the semiconductor substrate can be easily formed. Will be formed.

[Brief description of drawings]

FIG. 1 is a sectional view showing an element structure of an LED according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing an element structure of an LED according to a second embodiment of the present invention.

FIG. 3 is a sectional view showing an element structure of an LED according to a third embodiment of the present invention.

FIG. 4 is a sectional view showing an element structure of an LED according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view showing a device structure of a conventional LED.

[Explanation of symbols]

 1 semiconductor substrate 2 light emitting layer 3 current diffusion layer 4 substrate side electrode 5 light extraction side electrode 6 light reflecting layer 7 composition gradient layer 8 light reflecting layer 9 contact layer 10 light scattering layer

Claims (8)

[Claims] 1. A light emitting layer including an active layer, a light scattering layer formed on the light emitting layer and having a light extraction surface, and a light extraction side electrode formed on the light emitting layer or the light scattering layer. And a semiconductor light emitting device. 2. A light emitting layer including an active layer, a current spreading layer formed on the light emitting layer, a light scattering layer formed on the current spreading layer and having a light extraction surface, and the current spreading layer. And a light extraction side electrode formed on the light scattering layer. 3. The semiconductor light emitting device according to claim 1, wherein the light emitting layer has a single heterojunction, a double heterojunction, or a homojunction. 4. A semiconductor light emitting device, wherein the light emitting layer includes an InGaAlP-based mixed crystal semiconductor as an active layer,
The light scattering layer is made of GaP, ZnS, ZnSe and Zn.
The semiconductor light emitting device according to claim 1 or 2, wherein a material selected from Se-ZnS is used. 5. The thickness of the light-scattering layer is 0.5 μm or more, and the lattice constant of the semiconductor crystal of the light-scattering layer is different from the lattice constant of the semiconductor crystal in contact with the bottom surface by 0.3% or more. The semiconductor light emitting element according to claim 1 or 2, wherein 6. A semiconductor substrate is provided on the surface of the light emitting layer opposite to the surface on which the light scattering layer is formed,
3. The semiconductor light emitting device according to claim 1, wherein a substrate-side electrode is provided on the surface of the semiconductor substrate opposite to the surface on which the light emitting layer is formed. 7. The semiconductor substrate material is selected so that the band gap of the semiconductor substrate is substantially equal to or larger than the band gap of the active layer, and the substrate-side electrode has a polka dot pattern. The semiconductor light emitting device according to claim 6, which has a shape. 8. The semiconductor light emitting device according to claim 1, wherein a light reflecting layer is formed immediately below the light extraction side electrode.