JPH104208A - Surface light emission type semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface emission type semiconductor light emitting element with which the light, going toward the opposite side of the light taking-out surface, can be taken out to outside efficiently. SOLUTION: An n-GaAlAs lower clad layer 4, a p-GaAlAs active layer 3 and a p-GaAlAs layer 2 are epitaxially grown successively on an n-GaAs semiconductor substrate 5. A transparent electrode 8 consisting of ITO(indium/tin oxide) is formed on all over the lower surface of the n-GaAs semiconductor substrate 5 using a sputtering method and a sol-gel method, etc., and an n-side metal electrode 9 consisting of Au or Au/Cu is formed on the lower surface of the transparent electrode 8 by vapor deposition. When a current is allowed to flow between metal electrodes 1 and 9, a light is generated from the active layer 3, and a part of the light is directed to the n-side metal electrode 9 on the opposite side of a light taking-out surface. As the n-side metal electrode 9 has a flat surface, the light which is made incident on the n-side metal electrode 9 is efficiently reflected to a light taking-out region 6. Also, as the semiconductor substrate 5 and the n-side electrode 9 are formed by interposing with the transparent electrode 8, they are not alloyed by annealing. As a result, the reflection surface of the metal electrode 9 can be maintained flat without being roughened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a surface emitting semiconductor light emitting device.

[0002]

2. Description of the Related Art In a surface-emitting type semiconductor light-emitting device, part of light generated in an active layer is emitted from the upper surface of the light-emitting device, and the other part travels toward the lower surface. FIG. 9 shows an example of a structure for reflecting light traveling toward the lower surface toward the upper surface.

An n-GaAs semiconductor substrate 65 has n-GaAs
The GaAs lower cladding layer 64, the p-GaAlAs active layer 63 and the p-GaAlAs upper cladding layer 62 are sequentially grown by, for example, a liquid phase epitaxial (LPE) method.
On the upper surface of the p-GaAlAs upper cladding layer 62, a p-side metal electrode 61 is formed radially from the center and the center. A region other than the p-side metal electrode 61 on the upper surface of the upper cladding layer 62 is a light extraction region 68.

An n-side metal electrode 66 is formed in a mesh on the lower surface of the n-GaAs semiconductor substrate 65, and a silver (Ag) paste 67 is provided on the entire surface below the n-side metal electrode 66. The interface between the p-side metal electrode 61 and the upper cladding layer 62 and the interface between the n-side metal electrode 66 and the n-GaAs semiconductor substrate 65 are alloyed by annealing and are in ohmic contact.

When a current flows between the p-side metal electrode 61 and the n-side metal electrode 66, the active layer 63 is excited to generate light. Almost half of the emitted light exits from the light extraction region 68 to the outside. Of the generated light, the light directed to the side opposite to the light extraction region 68 passes through the lower cladding layer 64 and the semiconductor substrate 65, and is formed on the n-side metal electrode 66 formed in a mesh shape or on the silver ( Ag) Injects into the paste 67.

Since the bonding surface between the n-side metal electrode 66 and the semiconductor substrate 65 has been roughened by annealing, light incident on the mesh-shaped n-side metal electrode 66 is not reflected in the light extraction region 68.
It is not reflected efficiently toward. Further, a part of the light incident on the silver paste 67 is reflected toward the light extraction region 68. However, the silver paste 67 has large irregularities on its surface, and therefore cannot reflect light efficiently.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface-emitting type semiconductor light-emitting device having a structure for efficiently reflecting light traveling toward a side opposite to a light extraction region.

A surface emitting semiconductor light emitting device according to the present invention is a surface emitting semiconductor light emitting device in which a plurality of semiconductor layers including an active layer are laminated, wherein a transparent conductive film is formed on the lower surface of the lowermost semiconductor layer. A metal electrode is provided on a lower surface of the transparent conductive film, and a boundary surface between the transparent conductive film and the metal electrode is formed to be flat.

According to the present invention, the surface of the metal electrode located at the bottom of the light emitting element facing the active layer is flat, so that light from the active layer is efficiently reflected toward the light extraction surface of the light emitting element. be able to. Moreover, since the transparent conductive film is formed between the lowermost semiconductor layer and the metal electrode thereunder, the metal electrode and the semiconductor layer do not alloy with each other by annealing. For this reason, the surface of the metal electrode facing the active layer is not roughened, and a flat state can be maintained.

In one embodiment of the present invention, the transparent conductive film is formed on a part of the lower surface of the lowermost semiconductor layer. Since the light loss caused by the light from the active layer and the light reflected by the metal electrode passing through the transparent conductive film can be minimized, the light extraction efficiency is further improved.

In another embodiment of the present invention, the semiconductor substrate used in the crystal growth process is removed. Since the light from the active layer and the light reflected by the metal electrode are not absorbed by the semiconductor substrate, the light extraction efficiency is further improved. Preferably, an impurity of the same conductivity type as that of the lowermost semiconductor layer is doped into a junction between the lowermost semiconductor layer and the transparent conductive film. Since the contact resistance between the lowermost semiconductor layer and the transparent conductive film can be prevented from increasing, the luminous efficiency of the light emitting element can be maintained.

In still another embodiment of the present invention, a current constriction structure is provided between the active layer and the light extraction surface of the light emitting device. Since the current flows intensively just below the light extraction surface, the active layer emits light efficiently. The current constriction structure can be made by ion implantation, diffusion or other methods.

The surface-emitting type semiconductor light-emitting device of the present invention can have a small light-emitting diameter, and the light output can be increased with the improvement of the light extraction efficiency. , Various optical devices having good optical performance can be manufactured.

[0014]

【Example】

First Embodiment FIG. 1 shows a surface emitting semiconductor light emitting device according to a first embodiment. The structure of the surface-emitting type semiconductor light-emitting device shown in FIG. 1 will be clarified by describing its manufacturing process. Therefore, the manufacturing process of this surface-emitting type semiconductor light-emitting device will be described.

First, the LPE method (Liquid Phase Epitaxy:
By using liquid phase growth method) or the like, n-GaAs
On a semiconductor substrate 5, an n-GaAlAs lower cladding layer 4, a p-GaAlAs active layer 3, and a p-GaAlAs
The upper cladding layer 2 is grown and laminated in order.

Next, a mask made of an AZ resist (not shown) is formed on a portion of the upper surface of the p-GaAlAs upper cladding layer 2 where the light extraction region 6 is to be formed. A metal film to be the p-side metal electrode 1 made of, for example, Cr / Au is deposited on the entire upper surface of the mask and the upper surface of the p-GaAlAs upper cladding layer 2.

Thereafter, the AZ resist is removed together with the metal film deposited thereon. As a result, the p-side metal electrode 1 and the light extraction region 6 are formed on the upper surface of the upper cladding layer 2. The p-side metal electrode 1 is formed to extend from the center to four vertices from the center of the upper surface of the upper cladding layer 2 in order to spread and flow the current throughout the active layer 3.

Next, a transparent electrode 8 is formed on the entire lower surface of the semiconductor substrate 5 by using a sputtering method, a sol-gel method or the like.
As a material of the transparent electrode 8, a transparent conductive film such as ITO (indium tin oxide) is used. ITO is a material having a light transmittance of 90% or more and good electrical conductivity. If necessary, the lower surface of the semiconductor substrate 5 is polished, and then the transparent electrode 8 is formed. Since the thickness of the transparent electrode 8 is thin (for example, about 1000 Å to 2000 Å), if the lower surface of the semiconductor substrate 5 is flat, the bonding surface of the n-side metal electrode 9 with the transparent electrode 8 (this surface is referred to as a reflecting surface) Is flattened.

Further, an n-side electrode 9 made of Au or Au / Cu is formed on the entire lower surface of the transparent electrode 8 by vapor deposition or sputtering. Au or Au / Cu having a flat reflecting surface reflects 95% or more of incident light.

After the formation of the p-side metal electrode 1 and the n-side metal electrode 9, for example, an infrared lamp (halogen lamp, Xe
Lamp). By annealing
The side metal electrode 1 and the upper clad layer 2 are alloyed at the interface between them and make ohmic contact. On the other hand, since the semiconductor substrate 5 and the n-side electrode 9 are formed with the transparent electrode 8 interposed therebetween, they are not alloyed by annealing. For this reason, the reflection surface of the metal electrode 9 is kept flat without being roughened.

Neither the interface between the semiconductor substrate 5 and the transparent electrode 8 nor the interface between the transparent electrode 8 and the n-side electrode 9 are alloyed, but these interfaces adversely affect the operation of the surface-emitting type semiconductor light emitting device. No voltage drop occurs.

When a current flows between the p-side metal electrode 1 and the n-side metal electrode 9, the active layer 3 is excited to generate light. Part of the light generated in the active layer 3 passes through the upper cladding layer 2 and exits from the light extraction region 6 on the upper surface. Active layer 3
Another part of the light generated in step (a) passes through the lower cladding layer 4, the semiconductor substrate 5, and the transparent electrode 8 and is incident on the reflection surface of the n-side metal electrode 9, and is reflected toward the light extraction region 6 by this reflection surface. You. The transparent electrode 8 has a light transmittance of 90% or more, and n
Since the side metal electrode 9 reflects 95% or more of the incident light, the light traveling from the active layer 3 to the reflection surface is 75% or more (90% ×
95% × 90% = 76.95%) is reflected, and the light extraction area 6
Is emitted to the outside.

Second Embodiment FIG. 2 shows a surface emitting semiconductor light emitting device according to a second embodiment. This surface-emitting type semiconductor light-emitting device has exactly the same structure as the surface-emitting type semiconductor light-emitting device shown in FIG. 1 except that the shape of the light extraction region is different.

In the surface-emitting type semiconductor light-emitting device of the second embodiment, the upper surface of the p-GaAlAs upper cladding layer 2 is covered with the p-side metal electrode 1 except for its central portion. The central portion is a small circular light extraction region 6, which emits point-emitted light. The light extraction region 6 does not necessarily need to be located at the center of the upper surface of the upper cladding layer 2 and may be other than circular.

Of the light generated in the active layer 3, the light traveling toward the side opposite to the light extraction region 6 is efficiently reflected by the n-side metal electrode 9 having a flat surface, so that it is the same as that of the first embodiment. The light extraction efficiency has been improved. Further, by making the light extraction region 6 small, the emission diameter of light emitted from the light extraction region to the outside can be reduced. In the surface emitting type semiconductor light emitting devices of the following third to fifth embodiments, point emission type light extraction regions can be used.

Third Embodiment FIG. 3 shows a third embodiment of the surface-emitting type semiconductor device. The shapes of the transparent electrode and the n-side metal electrode are different from those of the surface emitting semiconductor light emitting device shown in FIG. Other structures are the same as those shown in FIG.

After a transparent electrode is formed on the entire lower surface of the n-GaAs semiconductor substrate 5, the transparent electrode is formed in a mesh by a photolithography process or etching using hydrofluoric acid or the like (a mesh-shaped transparent electrode). Is denoted by reference numeral 8A).

P-side metal electrode 1 and mesh-shaped transparent electrode 8
After the formation of A, annealing is performed to bring the p-side metal electrode 1 and the upper cladding layer 2 into ohmic contact. After that, from the lower surface of the transparent electrode 8A, n made of Au or Au / Cu
The side metal electrode 9 is deposited. The n-side metal electrode 9 is a transparent electrode 8
A and the lower surface of the n-GaAs semiconductor substrate 5 where the transparent electrode 8A is not formed. After forming the n-side metal electrode 9, annealing is not performed.

Light traveling from the light emitting layer 3 to the side opposite to the light extraction region 6 passes directly through the lower cladding layer 4 and the n-GaAs semiconductor substrate 5 or thereafter passes through the mesh-shaped transparent electrode 8A. Incident on the reflection surface of the n-side metal electrode 9. By forming the transparent electrodes in a mesh,
Since light loss caused by light passing through the transparent electrode can be minimized, the light extraction efficiency of light emitted from the light extraction region 6 can be further increased. Since the excitation current flows through the transparent electrode 8A, a current necessary for light emission can be secured.

Fourth Embodiment FIG. 4 is a sectional view schematically showing a surface emitting semiconductor light emitting device according to a fourth embodiment.

The semiconductor layer of this surface-emitting type semiconductor light-emitting device is made of n-GaAs by using the LPE method or the like.
On a semiconductor substrate, an n-GaAlAs lower cladding layer 4, a p-GaAlAs active layer 3, and a p-GaAlAs
The upper cladding layer 2 is formed by sequentially epitaxially growing the substrate and then removing the n-GaAs semiconductor substrate by etching or the like.

A semiconductor substrate used in the crystal growth process, for example, the above-mentioned n-GaAs semiconductor substrate has a property of slightly absorbing short-wavelength light. The light radiated from the active layer 3 to the side opposite to the light extraction region 6 passes through the semiconductor substrate twice before being reflected from the metal electrode and then emitted to the outside through the light extraction window 6. By removing the semiconductor substrate from the light emitting element, light loss caused by light absorption of the semiconductor substrate can be eliminated, and the light extraction efficiency can be further increased.

A p-side metal electrode 1 having the same shape as that shown in FIG. 1 is formed on the upper surface of the upper cladding layer 2, and the periphery thereof is a light extraction region 6. On the lower surface of the lower cladding layer 4, a transparent electrode 8 and an n-side metal electrode 9 are formed. Further, an impurity having the same conductivity type as that of the lower clad layer 4 is doped into a portion (indicated by reference numeral 10) of the upper clad layer 4 which is joined to the transparent electrode 8 by an ion implantation method or a diffusion method. In this embodiment, since the conductivity type of the lower cladding layer 4 is n-type, the impurity is n-type,
For example, Zn or the like is used.

A transparent electrode 8, for example, ITO and n-Ga
The contact resistance with the AlAs lower cladding layer 4 at these interfaces is high. This makes it difficult for the current to flow through the semiconductor layer. Therefore, by doping the junction 10 of the lower cladding layer 4 with the transparent electrode 8 with an impurity having the same conductivity type as that of the lower cladding layer 4, the contact resistance of the junction 10 is reduced, thereby providing a sufficient excitation current. Can flow.

Fifth Embodiment FIG. 5 is a sectional view schematically showing a surface emitting semiconductor light emitting device according to a fifth embodiment. The same components as those shown in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.

The portion 11 of the upper cladding layer 2 located below the p-side metal electrode 1 is doped with an impurity by ion implantation or diffusion. As the impurity to be doped, an impurity having a conductivity type different from the conductivity type of the upper cladding layer 2 or a light H ⁺ ion is used. Since a reverse-biased pn junction is formed between the lower surface of the impurity-doped portion 11 and the upper cladding layer 4, no current flows in this portion.

When a current flows between the p-side metal electrode 1 and the n-side metal electrode 9, the current is applied to the active layer located below the light extraction region 6 so as to avoid impurities doped in the upper cladding layer 2. Concentrate on part 3 and flow. Due to this current confinement structure, light is emitted only in the portion of the active layer 3 corresponding to the light extraction region 6, and high-output light is emitted to the outside.

APPLICATION EXAMPLES The surface-emitting type semiconductor light-emitting devices having the various structures described above are:
Light extraction efficiency is high, and high-output light can be emitted. Furthermore, since the light emission diameter can be reduced by adopting a point emission type light extraction region, it can be applied to many optical devices, light detection devices, optical information processing devices and the like.

FIG. 6 shows a projector using a surface-emitting type semiconductor light emitting device.

The surface-emitting type semiconductor light-emitting device 20 is fixed to a mounting piece of the lead frame 22. The n-side metal electrode of the light emitting element 20 is electrically connected to the lead frame 22. The p-side metal electrode of the light emitting element 20 is electrically connected to another lead frame 23 by a wire. Semiconductor light-emitting element 2
0, the mounting piece of the lead frame 22, the upper part of the lead frame 23 and the wires are sealed in the mold resin 24.
A Fresnel lens 21 is formed on the front surface of the mold resin 24. The Fresnel lens 21 allows the semiconductor light emitting element 20 to be formed.
Outgoing light is collected or collimated.

On both sides of the front surface of the mold resin 24 where the Fresnel lens 21 is formed, projections 24a are provided. The protrusion 24a is for protecting the Fresnel lens 21 and is formed to have the same height as the annular protrusion of the Fresnel lens 21 or to protrude slightly therefrom.

Since the surface-emitting type semiconductor light-emitting device has a high light extraction efficiency, it can emit a high output light. For this reason, a projector using a semiconductor light emitting element similarly emits high output light.

FIG. 7 is a schematic view of an optical distance sensor provided with a surface-emitting type semiconductor light emitting device.

This optical distance sensor is composed of a light projecting section comprising a surface emitting semiconductor light emitting element 30 and a collimating lens 31, and a light receiving section comprising a light receiving lens 32 and a position detecting element 33. The light emitting unit and the light receiving unit are housed in a case 35. The projection light from the light projecting unit is projected from the exit window 36 opened in the case 35 toward the object b.
The reflected light from the object b is received by the light receiving window opened in the case 35.
From 37, the light enters the position detection element 33 of the light receiving section.

The distance from the case 35 to the measured object or the displacement of the measured object b is measured using the principle of triangulation. That is, the reflected light from the object b is
Since the position of incidence on the target 33 changes according to the position of the object b, the distance or the amount of displacement is calculated based on the output signal of the position detection element 33.

The surface-emitting type semiconductor light-emitting device emits high-output light having a small emission diameter. Since the diameter of the beam spot projected on the object to be measured b is reduced, the resolution is improved, and accurate distance detection can be performed. In addition, since high output light is emitted, detection over a long distance can be performed.

FIG. 8 shows a photocoupler having a surface emitting semiconductor light emitting device. (A) is a perspective view showing the case with a part of the case removed, and (B) is a horizontal sectional view of the case.

The surface-emitting type semiconductor light-emitting device 40 is die-bonded to a mounting piece of a lead frame 42. Light emitting element
Forty n-side metal electrodes are electrically connected to the lead frame 42. The p-side metal electrode of the light emitting element 40 is electrically connected to another lead frame 41 by a wire. The photodiode 48 is die-bonded to the mounting piece of the lead frame 43. The lower surface electrode of the photodiode 48 is electrically connected to the lead frame 43. The upper electrode of the photodiode 48 is electrically connected to another lead frame 44 by a wire. Surface emitting semiconductor light emitting device 40, photodiode 48, lead frame
The mounting pieces 42 and 43, the upper parts of the lead frames 41 and 44, and the wires are sealed in a case 45. The lower ends of the lead frames 41, 42, 43 and 44 are out of the case 45.

The case 45 is formed in an elliptical spherical shape, and a reflection film 46 is formed on the inner surface thereof. Preferably, case 45
A transparent epoxy resin is used as a material for the above. The surface-emitting type semiconductor light-emitting device 40 and the photo diode 48 are
Are arranged at the focal position of the ellipse formed by the above.

The surface-emitting type semiconductor light-emitting device 40 is driven by electric signals applied to the lead frames 41 and 42,
The surface-emitting type semiconductor light emitting element 40 emits light. Light emitted from the surface-emitting type semiconductor light-emitting element 40 is reflected by the reflective film 46 on the inner surface of the case 45. The reflected light enters the light receiving surface of the photodiode 48. The photodiode 48
The optical signal is converted into an electric signal again and output to the outside through the lead frames 43 and 44.

The electric signal input to the surface-emitting type semiconductor light-emitting device 40 is converted into an optical signal, converted into an electric signal again, and output to the outside, so that the input signal and the output signal are electrically connected. Insulated. Such a photocoupler is used for controlling a high-voltage circuit and the like.

In the photocoupler, the light coupling efficiency between the light emitting element and the photodiode is strongly dependent on the light emitting diameter and light intensity of the light emitting element. As described above, the surface-emitting type semiconductor light-emitting element can reduce the emission diameter and emit high-output light, so that high coupling efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a structure of a surface emitting semiconductor light emitting device according to a first embodiment.

FIG. 2 is a perspective view schematically showing a structure of a surface-emitting type semiconductor light-emitting device according to a second embodiment.

FIG. 3 is a partial cross-sectional perspective view schematically illustrating a structure of a surface-emitting type semiconductor light emitting device according to a third embodiment.

FIG. 4 is a cross-sectional view schematically illustrating a structure of a surface-emitting type semiconductor light emitting device according to a fourth embodiment.

FIG. 5 is a cross-sectional view schematically illustrating a structure of a surface-emitting type semiconductor light emitting device according to a fifth embodiment.

FIG. 6 is a perspective view showing an application example and showing a configuration of a light projector.

FIG. 7 shows an application example and shows a configuration of an optical distance sensor.

8A and 8B show an application example and a configuration of a photocoupler, wherein FIG. 8A is a partially cutaway perspective view, and FIG. 8B is a horizontal sectional view.

FIG. 9 is a partially sectional perspective view schematically showing the structure of a conventional surface-emitting type semiconductor light-emitting device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 p-side metal electrode 2 p-GaAlAs upper cladding layer 3 p-GaAlAs active layer 4 n-GaAlAs lower cladding layer 5 n-GaAs semiconductor substrate 6 light extraction region 8 transparent electrode 9 n-side metal electrode 20, 30, 40 surface emission Type semiconductor light emitting device

Claims (6)

[Claims] In a surface-emitting type semiconductor light emitting device comprising a plurality of semiconductor layers including an active layer, a transparent conductive film is formed on a lower surface of a lowermost semiconductor layer, and a metal electrode is formed on a lower surface of the transparent conductive film. And a boundary surface between the transparent conductive film and the metal electrode is formed to be flat. 2. The surface emitting semiconductor light emitting device according to claim 1, wherein said transparent conductive film is formed on a part of the lower surface of said lowermost semiconductor layer. 3. The surface-emitting type semiconductor light-emitting device according to claim 1, wherein the lowermost semiconductor layer is a lowermost layer by removing a semiconductor substrate used in a crystal growth process. 4. The semiconductor device according to claim 1, wherein at least a junction of the lowermost semiconductor layer with the transparent conductive film is doped with an impurity having the same conductivity type as that of the lowermost semiconductor layer. 4. The surface-emitting type semiconductor light-emitting device according to item 1. 5. A current constriction structure is provided between the active layer and a light extraction surface of a light emitting device.
The surface-emitting type semiconductor light-emitting device according to any one of the above. 6. An optical apparatus using the surface-emitting type semiconductor light-emitting device according to claim 1 in a light projecting unit.