JPH06342932A - Photocoupler - Google Patents

Abstract

PURPOSE:To reduce leakage to the outside of light, and to improve the current transfer ratio of a photocoupler by forming a light-emitting device and a photodetector onto the same semi-insulating semiconductor substrate, transmitting light generated in the light-emitting device into the substrate and receiving light by the photodetector. CONSTITUTION:A P-type GaAs layer 104 for a light-emitting diode and a P-type GaAs layer 105 for a light-receiving diode are formed onto both surfaces of a semi-insulating GaAs substrate 101. An N-type GaAs layer 107 for the light- emitting diode is shaped onto the external surface of the P-type GaAs layer 104 for the light-emitting diode and an N-type GaAs layer for the light-receiving diode onto the external surface of the P-type GaAs layer 105 for the light- receiving diode respectively. An N side electrode 109 for the light-emitting diode is formed onto the external surface of the N-type GaAs layer 107 for the light-emitting diode, a P side electrode 112 for the light-emitting diode to the outer peripheral section of the layer 104, an N side electrode 110 for the light-receiving diode onto the external surface of the N-type GaAs layer 108 for the light-receiving diode and a P side electrode 113 for the light-receiving diode to the outer peripheral section of the layer 105 respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocoupler having improved current transfer efficiency and electrode formation.

[0002]

2. Description of the Related Art Photocouplers are now widely used in electronic circuits. The characteristics of this photo coupler are:
Although there are response speed, insulation characteristics, current transfer characteristics, etc., the current transfer characteristics are the most important. This is because if the current transfer characteristics are improved, power saving of the circuit can be realized and noise can be reduced.

In order to improve the current transfer characteristic, it is necessary to use a light emitting element having a high light emitting efficiency and a light receiving element having a high light receiving sensitivity, and the light from the light emitting element can be efficiently transmitted to the light receiving element. is necessary.

Therefore, as a material, GaAs, which has high luminous efficiency and light receiving sensitivity, is often used for both the light emitting element and the light receiving element. However, even if the light emitting element can efficiently convert electricity into light, if the difference between the refractive index of the light emitting element and the refractive index of the resin around it is large, the light can be efficiently extracted from the light emitting element to the outside. Therefore, it is necessary to select a material that reduces the difference in refractive index.

Further, structurally, two chips, a light emitting element and a light receiving element, are required, and a certain gap is provided between the light emitting element and the light receiving element due to mounting and insulation problems.

[0006]

However, the above-mentioned conventional photocoupler has the following drawbacks.

(1) Since two chips are required, the manufacturing cost is high and the photocoupler cannot be downsized.

(2) Further, due to the existence of the gap provided between the light emitting element and the light receiving element, only a part of the light emitted from the light emitting element can enter the light receiving element, which greatly reduces the current transfer efficiency. It is the cause.

(3) Both the light emitting element and the light receiving element are pn
It is configured by stacking epitaxial layers for bonding. When forming electrodes on the upper and lower layers stacked, a step is formed between the upper and lower layers on the surface of the substrate because the lower layer is partially etched to expose the lower layer.
Since the mask for electrode formation needs to be close to the distance of 20 μm from the surface, if the step difference between the upper and lower layers is 20 μm or less,
The electrodes are easy to form. However, in order to reduce the step to 20 μm or less, it is necessary to reduce the thickness of the upper layer to 20 μm or less, which makes it impossible to effectively prevent breakdown during energization. For this reason, priority is given to improving the breakdown characteristics, and the steps between the upper and lower layers are set to 20
If the thickness is more than μm, it becomes difficult to form the electrode, a complicated process is required for forming the electrode, and the cost is high.

(4) For stable operation of the photocoupler, it is necessary to secure a large junction area at the pn interface between the light emitting element and the light receiving element. However, if a part of the upper layer is etched to expose the lower layer, The area of the upper and lower pn interfaces cannot be made large. Therefore, the photocoupler cannot be operated stably.

In the first and second inventions, a pair of a light emitting element and a light receiving element are formed on the same substrate to improve the transmission path of light from the light emitting element. It is an object of the present invention to provide a photocoupler that solves the above problem and improves the current transmission efficiency.

The third and fourth objects of the present invention are to solve the above-mentioned problems by planarizing the surface, to achieve a high current transfer ratio, easy electrode formation, and good characteristics. To provide a simple photo coupler.

[0013]

In order to solve the above-mentioned problems, a first invention is to form a light emitting element and a light receiving element on the same semi-insulating semiconductor substrate, and to generate the light generated by the light emitting element inside the substrate. It is characterized in that it has a structure in which it is transmitted and received by a light receiving element.

According to a second aspect of the present invention, a light emitting element is formed on one surface of a semi-insulating semiconductor substrate and a light receiving element is formed on the other surface, and the light generated by the light emitting element is transmitted through the substrate to form a light receiving element on the other surface. It is characterized by having a structure for receiving light.

According to a third aspect of the present invention, a light emitting element and a light receiving element are formed on one surface of a semi-insulating semiconductor substrate, and a light reflecting portion is formed on the other surface, so that light generated by the light emitting element is transmitted through the substrate. The light-reflecting portion on the other surface reflects the light once or several times, and the light-receiving element on the one surface receives the light.

According to a fourth aspect of the invention, in the second and third aspects, one surface of the semiconductor substrate on which the light emitting element is formed and the other surface of the semiconductor substrate on which the light receiving element is formed, or the light emitting element and the light receiving element are formed. One surface of the semiconductor substrate is a flat surface. Here, the flat surface does not necessarily mean a smooth surface having no unevenness, and may be, for example, a step between the substrate and one conductive type layer formed thereon, or one conductive type layer formed on the step. It is sufficient that the step difference with the opposite conductivity type layer is an uneven surface within 20 μm.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, recesses are formed on one surface and the other surface of the semiconductor substrate, respectively, or two recesses are formed on one surface of the semiconductor substrate, and the recesses on each surface are formed. The light emitting element and the light receiving element are formed by embedding another conduction type layer in which one conduction type layer is embedded in a part of the surface.

Ga is used as the semi-insulating semiconductor substrate of each invention.
It is desirable to use As or AlGaAs, and it is particularly desirable to use a p-type or n-type GaAs substrate or GaAlAs substrate having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or less.

As the light emitting element or the light receiving element,
It is desirable to use a Si-doped GaAs or Si-doped AlGaAs epitaxial layer to form a single hetero structure or a double hetero structure.

Further, it is desirable to use a light emitting diode or a laser diode as the light emitting element and a phototransistor, a photodiode or a photothyristor as the light receiving element.

[0021]

The light generated by the light emitting element is transmitted and reflected only within the substrate without going out from the substrate, and is incident on the light receiving element on the same surface as the light emitting element or on the other surface. This allows
Light from the light emitting element is less likely to leak or be attenuated to the outside, and the current transfer ratio of the photocoupler is significantly improved.

When one conductivity type layer is embedded in the surface of another conductivity type layer, the one pn interface is left only on the lower surface because one conductivity type layer is left on the other conductivity type layer by etching. In comparison with the above, since the entire surface is the pn interface, a wide bonding area at the pn interface can be secured, and stable operation can be achieved.

Further, by deepening the embedding depth of one conductivity type layer, the layer thickness can be easily increased, and breakdown at the time of energization can be effectively prevented. Moreover, since one conductivity type layer is buried in a part of the surface and the other conductivity type layer is buried in the concave portion of the substrate surface, the one conductivity type layer, the other conductivity type layer and the exposed surfaces of the substrate are almost the same. Since it can be a flat surface, the electrodes can be easily formed.

The light emitting element and the light receiving element are formed on the same semi-insulating semiconductor substrate in order to electrically insulate both elements so as to function as a photocoupler. The semi-insulating semiconductor substrate may be GaAs-based, GaAlAs-based, or InP-based as long as it is semi-insulating.

In GaAs and GaAlAs systems, the bandgap energy of these substrates is smaller than the bandgap energy of the light emitting layer. Therefore, in order for light to pass through the substrate, the wavelength of the light emitted by the light emitting element is absorbed by the substrate. In order to prevent this, it is a manufacturing constraint that the wavelength is longer than the wavelength corresponding to the bandgap energy of the substrate.
As a light emitting device that satisfies this, Si-doped GaAs or Si-doped GaAlAs in which a high concentration of donor and acceptor exist in the light emitting layer can be used. The pn junction forming the element may have a homo structure in addition to the double hetero structure and the single hetero structure.

In the InP system, the bandgap energy of the InP substrate is generally higher than the bandgap energy of the light emitting layer, so that there is no restriction like GaAs.

[0027]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The photocouplers according to the first and second embodiments are formed of a single chip by forming light emitting elements such as light emitting diodes and laser diodes and light receiving elements such as phototransistors, photodiodes and photothyristors on the same substrate. The current transfer ratio is increased by configuring the coupler so that the light emitted from the light emitting element reaches the light receiving element without going out of the substrate.

In addition, the photocouplers according to the third and fourth embodiments further improve the characteristics in addition to the above current transfer ratio and electrode formation by making the substrate surface have a planar structure.

(First Embodiment) FIG. 1 is a side sectional view showing a photocoupler according to the first embodiment. 101 in the figure is a semi-insulating GaAs substrate, and this semi-insulating GaAs substrate 1
01 on both sides (upper and lower sides) of the light emitting diode 10
2 and the light receiving diode 103 are molded while being electrically insulated from each other.

A p-type GaAs layer 104 for light emitting diode and a p-type GaAs layer 105 for light receiving diode are formed on both surfaces of the semi-insulating GaAs substrate 101. Each p-type G
The aAs layers 104 and 105 are Si-doped. On the outer surface of the p-type GaAs layer 104 for light emitting diode, the n-type GaAs layer 107 for light emitting diode is provided.
N-type G for a light-receiving diode is formed on the outer surface of the type GaAs layer 105.
Each of the aAs layers 108 is formed. Each n-type Ga
The As layers 107 and 108 are formed in a circular shape and each p-type Ga is
It is provided in the center of the As layers 104 and 105.

An n-side electrode 109 for the light-emitting diode is formed on the outer surface of the n-type GaAs layer 107 for the light-emitting diode, and an n-side electrode 110 for the light-receiving diode is formed on the outer surface of the n-type GaAs layer 108 for the light-receiving diode. p-type G
Of the outer surface of the aAs layer 104, a p-side electrode 112 for a light emitting diode is provided on the outer peripheral edge of the n-type GaAs layer 107, and of the outer surface of the p-type GaAs layer 105, the n-type GaAs layer 108.
P-side electrodes 113 for light-receiving diodes are formed on the outer peripheral edge portions of each.

The photocoupler having the above structure is manufactured as follows. First, the semi-insulating GaAs substrate 1
On both sides of 01 by p-type GaAs by liquid phase epitaxial method
The layers 104 and 105 and the n-type GaAs layers 107 and 108 are epitaxially grown. Specifically, the slide boat method is used. Ga and GaA as raw materials in the first layer solution reservoir
Si of s and p-type dopant is added, and Ga of the second layer solution, GaAs, and Te of n-type dopant are added. By this method, after the epitaxial layer is grown on one surface of the semi-insulating GaAs substrate 101, the epitaxial layer is similarly grown on the other surface. As a result, the p-type GaAs layer 10 is formed on both surfaces of the semi-insulating GaAs substrate 101.
4 and n-type GaAs layer 107 and p-type GaAs layer 105
And n-type GaAs layer 108 are grown.

Next, the n-type GaAs layers 107 and 108 are etched so that they remain circular, and the p-type GaAs layer 1 is formed on the surface.
Make 04 and 105 appear. At this time, as shown in FIG. 2, between the p-type GaAs layer 104 and the n-type GaAs layer 107 forming the light emitting diode 102, and between the p-type GaAs layer 105 and the n-type G forming the light receiving diode 103.
A step is formed between the aAs layer 108 and the aAs layer 108.

Then, these n-type GaAs layers 107, 1
The n-side electrodes 109 and 110 and the p-side electrodes 112 and 113 are formed on the 08 and p-type GaAs layers 104 and 105, respectively. Here, if the step difference is set to 20 μm or more in order to prioritize the improvement of the breakdown characteristic, a complicated process for eliminating the influence of the step difference is required. If the step is made smaller than 20 μm in order to give priority to the ease of electrode formation, it will not be possible to effectively prevent breakdown during energization, and therefore it will be used for the purpose of operating at a lower voltage.

After separating the wafer on which the electrodes are formed by dicing, the side surface is etched by several μm to form a photocoupler chip. In this manufacturing process, since elements are formed on both sides of the wafer, a double-sided mask aligner was used.

Next, an example of specific dimensions of the photocoupler having the above construction will be shown. Here, priority was given to facilitation of electrode formation. The film thickness of each p-type GaAs layer 104, 105 is about 50 μm. Each n-type GaAs layer 107, 108 has a diameter
The thickness is about 150 μm and the film thickness is about 5 μm. By making the film thickness of the n-type layer thin in this way, the breakdown characteristics are sacrificed to facilitate the electrode formation. The size of the photocoupler chip configured by this is
It is 400 μm × 400 μm.

The wavelength of the light from the light emitting diode 102 is set to be longer than about 880 nm. This is about 88 in order for this light to efficiently pass through the GaAs substrate 101.
This is because the wavelength needs to be longer than 0 nm. Therefore, as the light emitting diode 102, a long wavelength can be obtained by a high concentration of donor and acceptor existing in the light emitting layer.
An i-doped GaAs epitaxial layer is used.

Light emitting diode 102 of this photocoupler
A current was passed through and measured from the side, the emission wavelength was 940.
It became nm, and it was confirmed that light passed through the substrate 101 from the light emitting diode 102 to the light receiving diode 103 side as shown by the arrow in FIG. When a current of 10 mA in the forward direction was passed through the light emitting diode 102 and the current transfer ratio was measured, a very high value of 45% was obtained.

As described above, since the light generated by the light emitting diode 102 is made to pass through only the semi-insulating GaAs substrate 101 and enter the light receiving diode 103 without being emitted to the outside, the light leaks to the outside. It is possible to obtain a photocoupler having a very high current transfer ratio, since it is less likely to be attenuated or attenuated.

As a result, it becomes possible to greatly reduce the current to the light emitting diode 102 for flowing the same current as in the conventional case to the light receiving diode 103. On the contrary, if the same current as the conventional one is passed through the light emitting diode 102, the current flowing through the light receiving diode 103 is increased, so that the influence of noise can be suppressed to be small.

Further, conventionally, a photocoupler which requires two chips, a light emitting diode and a light receiving diode, can be constructed by one chip, so that the manufacturing cost of the chip can be reduced and the photocoupler can be manufactured. The coupler can be miniaturized.

Although a GaAs substrate is used as the semi-insulating substrate 101 here, a material having a semi-insulating property can achieve the same effect as described above, and thus AlGa can be obtained.
It may be As or InP.

Although the Si-doped GaAs epitaxial layer is used as the light-emitting diode 102 and the light-receiving diode 103, the same action and effect as described above can be obtained by using the Si-doped AlGaAs epitaxial layer.

As the light emitting diode 102 and the light receiving diode 103, either a single hetero structure or a double hetero structure can be used, and any of them can achieve the above-mentioned effects. In this case, each element 102,
Increase the donor and acceptor concentrations in the active layer 103 to 88
Set to generate light with a wavelength longer than 0 nm. In particular, when InP is used, its bandgap energy is generally higher than the bandgap energy of the light emitting layer, so that there is no restriction like GaAs.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG.

In the photocoupler of this embodiment, the semi-insulating Ga is used.
Both the light emitting diode 202 and the light receiving diode 203 were formed adjacent to each other on the same surface of the As substrate 201.

A p-type GaAs layer 204 for light emitting diode and a p-type GaAs layer 205 for light receiving diode are formed on the upper surface of the semi-insulating GaAs substrate 201.
N-type Ga for light emitting diode on the upper surface of the type GaAs layer 204
The As layer 207 is the p-type GaAs layer 20 for the light receiving diode.
N-type GaAs layers 208 for light-receiving diodes are formed on the upper surfaces of the layers 5, respectively. Each n-type GaAs layer 207, 208 is formed so as to occupy a part of the upper surface of each p-type GaAs layer 204, 205.

An n-side electrode 209 for light-emitting diode is formed on the upper surface of the n-type GaAs layer 207 for light-emitting diode, and an n-side electrode 210 for light-receiving diode is formed on the upper surface of the n-type GaAs layer 208 for light-receiving diode. Each p-type Ga
On the upper surfaces of the As layers 204 and 205, the p-side electrodes 212 and 213 are formed, respectively, on the portions other than the portions occupied by the n-type GaAs layers 207 and 208.

On the lower surface of the semi-insulating GaAs substrate 201, a light reflecting portion 214 for reflecting the light from the light emitting diode 202 and sending it to the light receiving diode 203 is provided by the method of forward mesa etching.

The photocoupler having the above-described structure is manufactured by a method similar to that of the first embodiment described above. The size of this photocoupler chip was 400 μm × 800 μm.

With this structure, when a current is applied to the light emitting diode 202, the light from the light emitting diode 202 is once reflected by the light reflecting portion 214 on the lower surface and then reflected by the upper surface of the substrate 201 as shown by the arrow in FIG. Then, it is reflected by the light reflecting portion 214 again and then enters the light receiving diode 203.

In the same manner as in Example 1, a forward current of 10 mA was passed through the light emitting diode 22 and the current transfer ratio was measured. As a result, a value of 30% was obtained.

In the second embodiment, nothing is provided on the upper surface of the substrate between the light emitting diode 202 and the light receiving diode 203 and the reflecting surface of the light reflecting portion 214 among the upper surfaces. The current transfer ratio can be further improved by improving the flatness of the portion 214 and the like and forming the reflection film on each surface.

Further, the manner of changing the material of each member described in the first embodiment can be similarly applied to the present embodiment.

(Third Embodiment) Next, a third embodiment of the present invention for facilitating the formation of electrodes will be described with reference to FIG. FIG. 3A is a side sectional view and FIG. 3B is a plan view. The light emitting diode 302 is on one surface and the light receiving diode 303 is on the other surface.
Are formed. The conductivity type pn of the first and second embodiments described above is opposite to that of the present embodiment.

The semi-insulating GaAs substrate 301 has recesses 315 and 316 each having a depth of 50 μm and a width of 300 μm on both sides. The n-type GaAs layer 304 and the p-type GaAs layer 307 for the light emitting diode, the n-type GaAs layer 305 and the p-type GaAs for the light receiving diode are provided in the recesses 315 and 316 on both sides.
Layers 308 are each formed.

On the side of the light emitting diode 302, an n-type G
The aAs layer 304 is formed so as to fill the concave portion 315 of the substrate 301, and the central portion thereof has a shape that is largely depressed. The film thickness of the n-type GaAs layer 304 is 50 μm at a thick portion and 20 μm at a thin depressed portion. This n
A p-type GaAs layer 307 having a diameter of 200 μm and a maximum depth of 30 μm is formed in the depressed portion of the type GaAs layer 304, and the n-type layer 304 and the p-type layer 307 have the same surface height. These are flush with the substrate 301.

Also on the side of the light receiving diode 303, just like the light emitting diode 302, the n-type GaAs layer 305 is formed.
Has a p-type GaAs layer 308 formed therein.

Since the p-type layers 307 and 308 are embedded in the recessed portions of the n-type layers 304 and 305, the junction area at the pn interface can be secured wider than in the first and second embodiments, and stable operation can be achieved. It will be possible. Further, since the p-type layers 307 and 308 have a thickness of 30 μm at a thick portion, breakdown during energization can be effectively prevented.

In the central portions of the p-type layers 307 and 308, p-side electrodes 309 and 310 each having a diameter of 150 μm, and n-type electrodes are formed.
The surfaces of the mold layers 304 and 305 are 300 μm square and width, respectively.
Square-shaped n-side electrodes 312 and 313 of 50 μm are formed.

In order to manufacture this photocoupler, first, on both sides of the semi-insulating GaAs substrate 301, a width of 300 μm is formed.
Rectangular recesses 315 and 316 each having a corner and a depth of 50 μm were formed by photolithography. This semi-insulating GaAs substrate 3
In the recesses 315 and 316 of 01, the n-type GaAs layer 304 and p-type GaAs layer 307, the n-type GaAs layer 305 and p
The slide boat method was used to epitaxially grow the type GaAs layer 308. Raw materials Ga and GaAs
And a solution containing Si, which is an amphoteric dopant, is brought into contact with the substrate 301 at a high temperature to lower the temperature,
Epitaxial layers were grown in the order of p-type layers. At this time, depressions are formed on the surfaces of the n-type layers 304 and 305, and the depressions are formed by performing the epitaxial growth shown in FIG.

First, the substrate 3 on the side where the recess 315 is formed
When the n-type layer 304 is grown on the surface of 01, the n-type layer 304 grows at almost the same rate at any position on the substrate surface. Therefore, the surface of the n-type layer 304 above the recess 315 grows in a recessed shape. To do. After that, when the growth temperature drops to a certain temperature, the p-type layer 307 is continuously grown instead of the n-type layer 304. Next, similar to the method of growing the n-type layer 304 and the p-type layer 307, the n-type layer 305 and the p-type layer 308 are formed on the surface of the substrate 301 on the side where the recess 316 is formed.
Are grown (FIG. 5 (A)).

In this way, the semi-insulating GaAs substrate 30
After the epitaxial layers are grown on both sides of No. 1, the removed portion indicated by the broken line is etched or mechanically polished and then etched until the peripheral edge (convex) of the recess is exposed on both sides of the substrate 301. As a result, Fig. 5 (B)
A flat epitaxial wafer having a p-type layer and an n-type layer on both surfaces is obtained as shown in FIG.

After that, as shown in FIG. 3, on the surfaces of the p-type GaAs layers 307 and 308, a 150 μm circular p-side electrode 30 is formed.
9, 310 were formed respectively. n-type GaAs layer 30
On the surface of 4,305, square-shaped n-side electrodes 312 and 313 each having a 300 μm square and a width of 50 μm were formed. At the time of forming this electrode, since the p-type layer and the n-type layer were on the same surface, the electrode could be easily formed by a single-sided mask aligner. Also,
Since the mask for electrode formation can be brought close to the distance of 20 μm from the substrate surface as it is without a step between the p-type layer and the n-type layer, the electrode formation becomes easy.

After separating this epi-wafer by dicing, the side surface was etched by several μm to form a photo coupler chip. This chip size is 400 μm
× 400 μm. When a current was passed through the light emitting diode 302 of this photocoupler and the emission wavelength was measured from the side, the emission wavelength was 940 nm. When the current transfer ratio was measured at a forward current of 10 mA, a high value of 40% was obtained.

(Fourth Embodiment) A fourth embodiment is shown in FIG.
4A is a side sectional view and FIG. 4B is a plan view, and a light emitting diode 402 and a light receiving diode 403 are formed adjacent to each other on the same surface. Note that the conductivity type pn of the first and second embodiments described above is also reversed in the present embodiment.

In this photocoupler, semi-insulating GaAs is used.
In the same manner as the third embodiment, recesses for the light emitting diode and the light receiving diode are formed on the upper surface of the substrate 401, and a p-type GaAs layer and an n-type GaAs layer are grown in the recesses and the surface is polished. Thus, a light emitting diode 402 and a light receiving diode 403 having no steps on the surface were manufactured. Also, on the back side, utilizing the method of forward mesa etching,
A part of the back surface was scraped off to form a light reflecting portion 414.

The photocoupler obtained by forming the electrodes is
The light 416 emitted from the light emitting diode 402 is reflected by the light reflecting portion 414 as indicated by the arrow in the figure, and is incident on the adjacent light receiving diode 403. This chip size is 40
It is 0 μm × 800 μm.

The current transfer ratio of this photocoupler chip is 25
%Met. It is possible to further improve the current transfer ratio by improving the flatness of the light reflecting portion on the back surface and forming the reflecting film on the back surface.

[0070]

As described in detail above, the photocoupler of the present invention has the following effects.

(1) A light emitting element and a light receiving element are formed on the same substrate to form a chip, and the light generated by the light emitting element is
Since the light is transmitted through only the inside of the substrate and is incident on the light receiving element without being emitted from the substrate to the outside, the current transfer ratio of the photocoupler can be significantly improved.

(2) As a result, it is possible to greatly reduce the current to the light emitting element, which is necessary to pass the same current as that in the conventional case to the light receiving element.

(3) Further, when the same current as that in the conventional case is applied to the light emitting element, the current flowing to the light receiving element is increased, so that the influence of noise can be suppressed.

(4) One of the conventional photocouplers that requires two chips, a light emitting element and a light receiving element, is
Since it can be configured with one chip, the manufacturing cost of the chip can be reduced and the photocoupler can be downsized.

(5) A high current transfer ratio can be obtained, and since the surface is a flat surface, the electrodes can be formed easily, and the cost of chip fabrication can be kept low.

(6) Since the concave portion is formed in the semiconductor substrate and the light emitting element and the light receiving element are embedded therein, the surface can be made flush and the formation of the electrode becomes easier. Further, since the epitaxial layers forming the light emitting element and the light receiving element are embedded in the concave portion, a large pn junction area can be taken, and stable operation at the time of energization is possible. The breakdown voltage can be improved by increasing the embedding depth.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a photocoupler according to a first embodiment of the present invention.

FIG. 2 is a side sectional view showing a photocoupler according to a second embodiment of the present invention.

FIG. 3 is a side sectional view showing a photocoupler according to a third exemplary embodiment of the present invention.

FIG. 4 is a side sectional view showing a photocoupler according to a fourth exemplary embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a method of manufacturing the photocoupler according to the third embodiment.

[Explanation of symbols]

 101 semi-insulating GaAs substrate 102 light emitting diode 103 light receiving diode 104 p type GaAs layer for light emitting diode 105 p type GaAs layer for light receiving diode 107 n type GaAs layer for light emitting diode 108 n type GaAs layer for light receiving diode 109 n side for light emitting diode Electrode 110 Light-receiving diode n-side electrode 112 Light-emitting diode p-side electrode 113 Light-receiving diode p-side electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Takahashi 3550 Kidayomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable Ltd. Advanced Research Center

Claims (11)

[Claims] 1. A structure in which a light emitting element and a light receiving element are formed on the same semi-insulating semiconductor substrate, and light generated by the light emitting element is transmitted through the substrate and is received by the light receiving element. And a photo coupler. 2. A light emitting device on one surface of a semi-insulating semiconductor substrate,
A photocoupler having a structure in which a light receiving element is formed on the other surface, and light generated by the light emitting element is transmitted through the substrate and is received by the light receiving element on the other surface. 3. A semi-insulating semiconductor substrate having a light emitting element and a light receiving element formed on one surface, and a light reflecting portion formed on the other surface, and light generated by the light emitting element is transmitted through the substrate to the other surface. 2. A photocoupler having a structure in which the light is reflected by the light reflection part of 1 time or several times and is received by the light receiving element on one surface. 4. The photocoupler according to claim 2, wherein one surface of the semiconductor substrate on which the light emitting element is formed and the other surface of the semiconductor substrate on which the light receiving element is formed, or the light emitting element and the light receiving element. A photocoupler, wherein one surface of the formed semiconductor substrate is a flat surface. 5. The photocoupler according to claim 4,
A recess is formed on each of the one surface and the other surface of the semiconductor substrate, or two recesses are formed on one surface of the semiconductor substrate, and one conductivity type layer is embedded in a part of the surface in the recess of each surface. A photocoupler characterized in that the light emitting element and the light receiving element are formed by embedding a conductive type layer. 6. The photocoupler according to claim 1, wherein the semiconductor substrate is semi-insulating G.
A photo coupler using an aAs substrate or an AlGaAs substrate. 7. The photocoupler according to claim 6,
A photocoupler characterized in that a p-type GaAs substrate or GaAlAs substrate having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or less is used as the semiconductor substrate. 8. The photocoupler according to claim 6,
An optocoupler characterized in that an n-type GaAs substrate or GaAlAs substrate having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or less is used as the semiconductor substrate. 9. The photocoupler according to claim 1, wherein the light emitting element or the light receiving element is S
i-doped GaAs epitaxial layer or Si-doped A
A photocoupler characterized by using an lGaAs epitaxial layer. 10. The photocoupler according to claim 1, wherein a single heterostructure or a double heterostructure is used as the light emitting element or the light receiving element. 11. The photocoupler according to claim 1, wherein a light emitting diode or a laser diode is used as the light emitting element, and a photodiode, a phototransistor or a photothyristor is used as the light receiving element. And a photo coupler.