JPH04269885A - Optically coupled device and its manufacture - Google Patents

Abstract

PURPOSE:To perform a high-grade transmission operation at an optically coupled device in which a semiconductor laser and a photodetector have been combined. CONSTITUTION:A groove 30 is formed in advance on the side of a light- absorbing part A at a semiconductor substrate 20. A current constriction layer 30 is grown on the whole face of the semiconductor substrate 20 so as to fill the groove 30; a stripe-shaped groove 22 is formed. After that, an active layer 24 and clad layers 23, 25 are laminated sequentially. Since the stripe-shaped groove does not reach the surface of the semiconductor substrate at the light- absorbing part having the groove, an electric-current route is not formed. Since the stripe-shaped groove reaches the surface of the semiconductor substrate at an excitation part, the electric-current route is formed. As a result, a semiconductor laser is provided with a switching characteristic.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical coupling device combining a semiconductor laser and a light receiving element, and a method of manufacturing the same.

0002

[Prior Art] An optical coupling device (photocoupler) is composed of a combination of a light emitting element and a light receiving element so as to be optically coupled.The input and output are electrically isolated and have the characteristic of transmitting signals by light. ing.

FIG. 4 shows a diagram of the basic principle of an optical coupling device.

In the figure, reference numeral 1 denotes a light emitting element, in which a GaAs infrared light emitting diode with high luminous efficiency is used.
Reference numeral 2 denotes a light receiving element, and a Si phototransistor, photodiode, photothyristor, or the like is used. Furthermore, recently, OPIC light-receiving elements in which a photodiode and a signal processing circuit are integrated into one chip have also been used. In the figure, 3 is a lead frame, 4 is a bonding wire, 5 is a transparent or translucent resin, and 6 is a black epoxy resin.

As mentioned above, optical coupling devices have electrical isolation between input and output, are capable of transmitting a wide range of signals from direct current to high frequencies, and are unidirectional in signal transmission, allowing noise to be input on the output side. Does not affect the side, easy to connect with logic elements,
It has characteristics such as small size and light weight.

[0006]

[Problems to be Solved by the Invention] The response characteristics (signal transmission characteristics) of an optical coupling device are usually determined mainly by the phototransistor on the output side, but it is also possible to use a phototransistor with high-speed response, such as a silicon PIN photodiode. When using , the responsiveness of the light emitting diode will have an effect.

FIG. 5 shows an example of pulse response of a light emitting diode.

As shown in the figure, since the rise and fall times are each about 10 nsec, it can be seen that the modulation characteristic has a limit of about 50 MHz. For this reason, there is a limit to high-speed signal transmission in optical coupling devices that use light-emitting diodes as light-emitting elements.

Therefore, in order to solve the above-mentioned problems, the present applicant has proposed an optical coupling device having high-speed signal transmission characteristics as shown in FIG.

The prior art shown in FIG. 6 is characterized in that a semiconductor laser is used as a light emitting element to improve signal transmission characteristics. That is, in the prior art, the semiconductor laser 10
, and a light receiving element 2 are installed to face each other, and transmit signals using laser light emitted from a semiconductor laser.

FIG. 8 shows an example of pulse response characteristics of a semiconductor laser.

As shown in the figure, the rise and fall times are each 0.3 nsec, and modulation of 1 GHz or higher is possible.

FIG. 7 shows a method of manufacturing the optical coupling device shown in FIG. 6.

First, the semiconductor laser 1 is mounted on the lead frame 3.
0 and the silicon photodiode 2 are die-bonded so as to face each other. Subsequently, lead wiring is provided to the semiconductor laser 10 and the silicon photodiode chip 2 using the bonding wire 4. Thereafter, an optical path is formed between the semiconductor laser 10 and the photodiode 2 using a transparent resin or semi-transparent resin 5 for the oscillated laser beam, and the periphery thereof is molded with a flame-retardant black epoxy resin 6.

As a result, the optical coupling device uses a semiconductor laser with high-speed response as a light-emitting element, thereby enabling high-speed signal transmission.

Here, the current-light output characteristic of the semiconductor laser is shown in FIG. 10-A, the input signal to the optical coupling device is shown in FIG. 10-B,
The output signal from the optical coupler is shown in FIG. 10-C.

As shown in the figure, for the input signal shown in FIG. 10-B, the current-optical output characteristic of the semiconductor laser is determined as shown in FIG. 10-C.
The output signal from the light receiving element shown in is obtained.

The structure of the above semiconductor laser is VSIS (V-
Channeled Substrate Inn
FIG. 9 shows a schematic diagram of the structure in the case of an er Stripe structure.

An n-type GaAs current blocking layer 21 is grown to a thickness of 0.8 μm on a p-type GaAs substrate 20 by the LPE method (liquid phase epitaxial growth method), and then the width is 3 μm and the depth is 1.0 μm. Striped grooves 22 are formed by chemical etching. After this, in the second LPE growth, p-type G
The a0.55Al0.45As cladding layer 23 is 0.2 μm thick in the area where the stripe groove 22 does not exist, and the p-type Ga0.
The thickness of the 86Al0.14As active layer 24 is 0.06 μm, and the thickness of the n-type Ga0.55Al0.45As cladding layer 25 is 1 μm.
, an n-type GaAs contact layer 26 is continuously grown to a thickness of 2 μm to form an electrode 27.

Since the striped grooves 22 penetrate the n-type GaAs current blocking layer 21 and reach the semiconductor substrate 20, a current path is formed only in the striped grooves 22, reducing reactive current. .

However, in the current-optical output characteristic of a normal semiconductor laser, the optical output rises nonlinearly with respect to the injected current near the oscillation threshold Ith. Therefore, depending on the bias current value, even in the extinction state, a certain amount of light enters the light receiving element and a current flows, resulting in a problem that the extinction ratio becomes small.

For example, under the conditions shown in FIG. 10, a relatively large extinction ratio can be obtained if the bias is set below the oscillation threshold Ith, but as shown in FIG. However, if this value is exceeded, laser oscillation begins and the extinction ratio drops significantly.

In order to increase the extinction ratio, it is possible to reduce the bias current and increase the current amplitude, but it is not easy to maintain high speed, for example, due to electrical circuit problems.

In view of the above, the present invention makes it possible to obtain a large extinction ratio by suppressing the optical output from the semiconductor laser in the extinction state and increasing the optical output from the semiconductor laser in the emission state. The purpose of this invention is to provide an optical coupling device that enables high-quality transmission and a method for manufacturing the same.

[0025]

Means for Solving the Problems The means for solving the problems according to claim 1 of the present invention is provided in an optical coupling device in which a semiconductor laser 10 and a light receiving element 2 are optically coupled so as to be electrically separated, as shown in FIG. , the semiconductor laser 10 has a light absorption section A
and an excitation part B. In the light absorption part A and the excitation part B, a current sandwiching layer 21, an active layer 24, and cladding layers 23 and 25 are sequentially laminated on a semiconductor substrate 20. A striped groove 22 contributing to laser oscillation is provided on the light absorption portion A side of the semiconductor substrate 20.
A groove 30 is formed to prevent the semiconductor substrate 20 from reaching the surface of the semiconductor substrate 20.

Further, the problem solving means according to claim 2 is as shown in FIG. A layer 21 is grown, and after the growth of the current confinement layer 21, a striped groove 22 is formed, and then an active layer 24 and cladding layers 23 and 25 are sequentially laminated to obtain a semiconductor laser 10.
The semiconductor laser 10 and the light receiving element 2 are optically coupled so as to be electrically separated.

[0027]

[Operation] In the above problem solving means, in the light absorption section A where the groove 30 is provided, the striped groove 22 does not reach the semiconductor substrate 20, and no current path is formed. On the other hand, in the excitation part B without the groove 30, the striped groove 22 reaches the semiconductor substrate 20 and a current path is formed.

When a current is applied to the semiconductor laser 10, carriers are injected into the active layer 24 in the light absorbing portion A where the current path exists, and spontaneous emission light is excited. However, since no carriers are injected in the excitation part B, which has no current path, the active layer 2
The spontaneous emission light that has propagated through the laser is absorbed and the gain that leads to laser oscillation is suppressed compared to a normal laser.

Furthermore, when the current is increased, the spontaneous emission increases and a laser oscillation condition is reached, so that laser light starts to be emitted. When oscillation starts, the groove 3
The thin current pinching layer 21 at the 0 portion is turned on, and the optical output increases rapidly.

That is, the semiconductor laser 10 has a switching characteristic in which the output current increases rapidly when the input current value exceeds a certain value. Therefore, a large change in optical output is obtained in the semiconductor laser 10 when transitioning from the extinction state to the emission state, and as a result, a large extinction ratio is obtained. This means that a large extinction ratio can be obtained even with a small input current amplitude, resulting in the advantage that the load on the semiconductor laser drive circuit system is reduced.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 is a perspective view showing the structure of a semiconductor laser in an optical coupling device according to an embodiment of the present invention, FIG. 2 is a diagram showing a method for manufacturing the semiconductor laser, and FIG. FIG. 3-B is a diagram showing the output characteristics, and FIG. 3-B is a diagram showing an input signal to the optical coupling device, and FIG. 3-C is a diagram showing the output signal from the optical coupling device. In addition, the same reference numerals are attached to the same functional parts as those of the prior art shown in FIGS. 6 and 9.

The optical coupling device of this embodiment includes a semiconductor laser having switching characteristics and a normal light receiving element, and is characterized in that the output current from the light receiving element is suppressed in the extinction state.

Note that the configuration other than the semiconductor laser is the same as the prior art, so the configuration of the semiconductor laser will mainly be explained here.

The semiconductor laser 10 is a striped semiconductor laser, as shown in FIG. 1, and consists of a light absorption section A and an excitation section B. A p-type semiconductor substrate 2 is provided in the light absorption section A and the excitation section B.
0, an n-type current blocking layer 21, a p-type cladding layer 23, a p-type active layer 24, an n-type cladding layer 25, an n-type contact layer 2
6 are sequentially laminated, and the current blocking layer 21 is provided with a striped groove 22 that contributes to laser oscillation.

The light absorbing portion A formed on the light emitting end face side is
It provides an absorption loss to the spontaneously emitted light generated in the excitation part B, works to suppress laser oscillation until the spontaneously emitted light exceeds a certain level, and also works to prevent the spontaneously emitted light from being output to the outside.

[0037] Then, the light absorption part A of the semiconductor substrate 20
Grooves are formed on the sides to prevent the striped grooves 22 from reaching the semiconductor substrate 20 when forming the striped grooves. As a result, the striped grooves 22 do not reach the surface of the semiconductor substrate 20 in the vicinity of the light emitting surface (light absorption section A), but reach the surface of the semiconductor substrate 20 in other parts (excitation section B).

Next, a method for manufacturing the above-mentioned optical coupling device will be explained.

First, a semiconductor laser 10 is manufactured as shown in FIG. That is, on the light absorption part A side of the p-type GaAs semiconductor substrate 20, a width of 10 μm, a length of 50 μm, and a depth of 0.5 μm is formed.
A groove 30 is formed. After this, n-type GaAs was formed using the LPE method.
The current pinching layer 21 is grown to have a thickness of 0.8 μm in the portion without the groove 30 and to have a flat growth surface.

Next, the striped grooves 22 are formed with a width of 3 μm.
It is formed in a shape with a depth of 1 μm using photolithography and etching techniques after the growth of the current confinement layer 21. As a result, in the portion where the groove 30 is present, the striped groove 22 does not reach the semiconductor substrate 20, and no current path is formed. On the other hand, in other parts, the striped grooves 22 reach the semiconductor substrate 20 and a current path is formed.

Next, p-type Ga0.55Al0.45As is deposited on the semiconductor substrate 20 in which the striped grooves 22 are formed.
The cladding layer 23 is 0.1 μm in the part where the striped groove 22 does not exist, the p-type Ga0.86Al0.14As active layer 24 is 0.08 μm, and the n-type Ga0.55Al0.45
A double heterostructure is successively grown by LPE using an As cladding layer 25 of 1.2 μm and an n-type GaAs contact layer 26 of 1.5 μm, and then an electrode 27 is formed to complete the semiconductor laser 10.

Then, the semiconductor laser 10 and the light receiving element are optically coupled so as to be electrically separated, as in the prior art.

When a current is passed through the semiconductor laser 10, carriers are injected into the active layer 24 in a certain part of the current path (light absorption section A), and spontaneous emission light is excited. However, since no carrier is injected in the part where there is no current path (excitation part B), the spontaneously emitted light propagating within the active layer 24 is absorbed, and the gain leading to laser oscillation is reduced to that of a normal laser. It is suppressed in comparison.

Furthermore, when the current is increased, the spontaneous emission increases and a laser oscillation condition is reached, so that emission of laser light begins. When oscillation starts, the groove 3
The thin current pinching layer 21 at the 0 portion is turned on, and the optical output increases rapidly. This state is shown in the current-light output characteristics shown in FIG. 3-A.

When the input signal from t0 to t3 shown in FIG.
By setting the current to be equal to or higher than the current ISW from 0 to t1 and from t2 to t3, the light emitted from the semiconductor laser 10 transitions from almost 0 to a large laser light output state,
As a result, a large extinction ratio can be obtained. The state of the output current at this time is shown in FIG. 3-C.

As described above, by providing the semiconductor laser 10 with switching characteristics, the amplitude of the current output from the light receiving element can be increased, and high quality transmission becomes possible.

Furthermore, if this switching characteristic is utilized in a Schmitt Trigger manner, it is easy to construct a circuit in which signals below a certain level of input current are not transmitted, which simplifies the design of electronic circuits later. It becomes possible.

[0048] This makes it possible to cut out noise components below a certain current value that are riding on the input current.
From this point of view as well, high-quality transmission is possible.

It should be noted that the present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

[0050]

As is clear from the above explanation, according to the present invention, by providing grooves on the light absorption portion side of a semiconductor substrate to prevent the striped grooves from reaching the surface of the semiconductor substrate, light absorption can be improved. In some parts, the striped grooves do not reach the surface of the semiconductor substrate, so no current path is formed.
On the other hand, in the excitation section, the striped grooves reach the surface of the semiconductor substrate, so that a current path is formed. Therefore, the semiconductor laser can be provided with switching characteristics.

Therefore, a large change is obtained in the optical output of the semiconductor laser upon transition from the extinction state to the emission state, and as a result, a large change is given to the output current of the light receiving element. Moreover, this large change in output current can be provided by a smaller change in input current than in the past. Furthermore, since signals below a certain input current value are difficult to be transmitted, it is also possible to cut noise.

From these points, it is possible to obtain an optical coupling device that enables higher quality signal transmission and has a wider range of applications, which is an excellent effect.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the structure of a semiconductor laser of an optical coupling device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a method for manufacturing a semiconductor laser.

[Figure 3] Figure 3-A is a diagram showing the current-optical output characteristics of a semiconductor laser, Figure 3-B is a diagram showing the input signal to the optical coupling device, and Figure 3-C is the same diagram showing the output from the optical coupling device. It is a figure which shows a signal.

FIG. 4 is a diagram of the basic principle of an optical coupling device.

FIG. 5 is a diagram showing an example of pulse response characteristics of a light emitting diode.

FIG. 6 is a diagram showing the overall structure of an optical coupling device using a semiconductor laser according to the prior art.

7 is a diagram showing a method of manufacturing the optical coupling device of FIG. 6. FIG.

FIG. 8 is a diagram showing an example of pulse response characteristics of a semiconductor laser used in the optical coupling device of FIG. 6;

9 is a perspective view showing the structure of a semiconductor laser of the optical coupling device of FIG. 6. FIG.

[Figure 10-A] Figure 10-A shows the current when the bias is set below the oscillation threshold in the semiconductor laser shown in Figure 9.
FIG. 10-B is a diagram showing the optical output characteristics, and FIG. 10-C is a diagram showing the input signal to the optical coupling device, and FIG. 10-C is a diagram showing the output signal from the optical coupling device.

11] FIG. 11-A is a diagram showing the current-optical output characteristics when the bias exceeds the oscillation threshold in the semiconductor laser shown in FIG. 9, and FIG. 11-B is a diagram showing the input signal to the optical coupling device. The figure shown in FIG. 11-C is a diagram similarly showing an output signal from the optical coupling device.

[Explanation of symbols]

2 Photo receiving element 10 Semiconductor laser 20 Semiconductor substrate 21 Current pinching layer 22 Striped groove 23,25 Clad layer 24 Active layer 30 groove

Claims (2)

[Claims] 1. An optical coupling device in which a semiconductor laser and a light receiving element are optically coupled so as to be electrically separated,
The semiconductor laser is composed of a light absorption part and an excitation part. In the light absorption part and the excitation part, a current sandwiching layer, an active layer, and a cladding layer are sequentially laminated on a semiconductor substrate. An optical coupling device characterized in that a striped groove that contributes to oscillation is provided, and a groove is formed on the light absorption portion side of the semiconductor substrate to prevent the striped groove from reaching the surface of the semiconductor substrate. . 2. Forming a groove on the light absorbing portion side of the semiconductor substrate, growing a current pinching layer over the entire surface of the semiconductor substrate to fill the groove, and forming a striped groove after growing the current pinching layer, 1. A method of manufacturing an optical coupling device, characterized in that an active layer and a cladding layer are then sequentially laminated to obtain a semiconductor laser, and the semiconductor laser and a light-receiving element are optically coupled so as to be electrically isolated.