JPH07209618A - Exciton erasure type semiconductor optical modulation device and its manufacture - Google Patents

Abstract

PURPOSE:To greatly reduce the built-in electric field of a waveguide and easily control a lateral mode by forming a macroquantum well layer and clad layers, between which the macroquantum well layer is sandwiched, in mesa stripes and forming a couple of electrodes on both sides of them across an insulating film. CONSTITUTION:This device has the 1st clad layer 2 which is formed in stripes on a substrate 1, the striped macroquantum well layer 3 formed on the clad layer 2, the 2nd clad layer 4 in a striped shape which is formed on the macroquantum well layer 3, and the 1st and 2nd electrodes 6 and 7 which are mutually separated on both flanks of the clad layer 2, macroquantum well layer 3, and clad layer 4 across the insulating film 5. Therefore, when a voltage is applied between the couple of electrodes 6 and 7, an electric field which is parallel to the surface of the substrate 1 is produced in the macroquantum well layer 3 to destroy excitons of the macroquantum well layer 3, the light absorption coefficient of exciton absorption peak wavelength decreases, and the refractive index to longer wavelength than the exciton absorption peak wavelength greatly decreases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exciton erasing type semiconductor optical modulator and a method of manufacturing the same, and more particularly, to generate and erase an electric field in a multiple quantum well (MQW) layer in a direction parallel to the plane of the layer. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exciton erasing type semiconductor light modulator that modulates light and a manufacturing method thereof. In the information processing field in recent years, there is an interest in information processing using optical computers and optical interconnections that use light, and in order to realize this, it is necessary to develop an optical arithmetic circuit. In order to configure an optical operation circuit, a minute optical operation element that can be integrated with a semiconductor light emitting element such as a semiconductor laser or a light emitting diode or a light receiving element such as a photodiode is required.

[0002]

The most widely used optical modulator is a LiNbO ₃ crystal. However, the device is larger in size than that using a semiconductor, and cannot be integrated because it cannot be planarized with a semiconductor laser. Furthermore, the optical axis alignment at the time of coupling with the semiconductor laser is impossible. Problems such as being troublesome occur.

Without such integration, it becomes impossible to construct an opto-electronics integrated circuit (OEIC), and naturally, an optical computer cannot be built. In order to realize an optical computer that can operate at high speed, an element capable of high-speed modulation operation is required. To achieve this, firstly, the capacitor of the optical modulation / operation element is required. To reduce
Secondly, it is necessary to reduce the driving voltage.

In order to solve the problem that the size of the optical modulator is increased and the problem that it is difficult to integrate the light emitting element and the light receiving element, it is possible to make an optical modulator using a semiconductor. Conceivable. As a semiconductor optical modulator, for example, there is an optical modulator having a structure in which a voltage is applied between electrodes formed above and below a semiconductor layer to change the refractive index of a waveguide.
It is inferior to the one using O ₃ crystals. Therefore, in order to sufficiently enhance the effect, the driving voltage is increased or the length of the optical operation element (optical waveguide length) is increased. However, with such a structure, high-speed optical modulation operation is achieved. However, it becomes difficult to perform the optical exchanging operation, the light loss becomes large, and it becomes difficult to compact the optical operation elements.

An exciton erasing type semiconductor optical modulator having a quantum well structure is known as a semiconductor optical modulator having a performance higher than that using LiNbO ₃ . This light modulator is
This device utilizes a phenomenon in which the excitons in the quantum well structure are erased to change the light absorption characteristics and refractive index characteristics by generating an electric field in the quantum well structure in a direction parallel to the layers. It is described in Kaihei 2-132415.

Incidentally, erasing excitons means
The decomposition of excitons into free electrons and holes.

[0007]

In the semiconductor optical modulator, an electric field parallel to the substrate surface is generated by a multiple quantum well layer (MQW layer).
In order to generate the electric field in the inside, a pin junction is formed in a direction parallel to the substrate surface, and an electric field is generated in the MQW layer of the intrinsic semiconductor region between the p-type impurity region and the n-type impurity region. Next, the structure of this device will be briefly described.

In FIG. 7, a semi-insulating semiconductor substrate 101
A first clad layer 102 is provided on the upper side, and an MQW layer 103 and a second clad layer 104 are sequentially stacked on the upper surface thereof. Intrinsic semiconductor region (i-type region) 108 serving as an optical waveguide
On both sides of the n-type impurity region 106 having a depth reaching from the surface of the second cladding layer 104 to the upper portion of the first cladding layer 102.
And a p-type impurity region 107 are formed.

Reference numeral 110 in the figure denotes an n-electrode formed on the n-type impurity region 106 through the cap layer 109,
111 denotes a p-electrode formed on the p-type impurity region 107 via the cap layer 109, and 112 denotes a light source for light modulation. When modulating light, for example, an intrinsic semiconductor region
While irradiating the MQW layer 103 of 108 with light having an exciton absorption peak wavelength λep, a reverse bias voltage is applied to the n-type impurity region 106 and the p-type impurity region 107 to generate a lateral electric field in the MQW layer 103. While the excitons in the MQW layer 103 are destroyed and the light is transmitted, the light is absorbed by the excitons when the electric field is erased.

Light intensity modulation is performed by repeatedly generating and erasing the electric field in this manner. Besides, modulation by a refractive index is also possible. By the way, the material of the quantum well layer forming the MQW layer 103 is In _1-x Ga _x As _y P _1-y (x = 0.438).
, Y = 0.940), the material of the barrier layer is InP, and
The impurity concentration of the p-type impurity region 107 is 3 × 10 ¹⁷ / cm ³ ,
The residual impurity concentration of the i-type region 108 is set to 1 × 10 ¹⁵ / cm ³ of n
P-type impurity region 107
If the distance between the n-type impurity region 106 and the n-type impurity region 106 is 2 μm, an electric field strength of 6 kV / cm is required to destroy the excitons.

However, in this structure, the i-type region of the pin junction is formed even when no voltage is applied between the electrodes 110 and 111.
Built-in electric field is applied to 108. Its size is calculated as shown in FIG. In FIG. 8, the vertical axis represents the electric field intensity, and the horizontal axis represents the p-type impurity region 107 and the i-type region.
The distance X from the boundary of 108 to the n-type impurity region 106 direction is shown.

In the region where the distance X extends from 0 μm to 0.46 μm, there is a built-in electric field exceeding 6.0 kV / cm, and therefore the excitons in this region have already been destroyed without applying a voltage. Therefore, the region where light modulation is possible is limited to the range where X is larger than 0.46 μm,
The modulatable area becomes narrow, which hinders miniaturization of the optical modulator.

Further, since the electric field strength also changes in the modulatable region, the refractive index modulation degree and the absorption modulation degree have wide dispersion, and effective optical modulation cannot be performed. In addition, in the above structure, the n-type impurity region 106 and the p-type impurity region are
Although 107 are formed by ion implantation, the MQW layer 103 in those regions is not destroyed even by ion implantation and remains as it is. As a result of this, the modulator M
From the n-type impurity region 106 of the QW layer 103 to the p-type impurity region 10
Since there is no difference in the refractive index in the lateral direction up to 7, i-type region 108
There is a tendency that the light that passes through will spread and control by the transverse mode will become difficult.

The present invention has been made in view of the above problems, and provides a semiconductor optical modulation device in which a built-in electric field in a waveguide is significantly reduced and a lateral mode can be easily controlled, and a manufacturing method thereof. The purpose is to

[0015]

The above-mentioned problems are solved by, as illustrated in FIG. 1, forming a first clad layer 2 formed in a stripe shape on a substrate 1 and a first clad layer 2 on the first clad layer 2. The striped multiple quantum well layer 3 formed, the striped second cladding layer 4 formed on the multiple quantum well layer 3, the first cladding layer 2, the multiple quantum well layer 3 And an exciton erasing type semiconductor optical modulator having first and second electrodes 6 and 7 which are separated from each other on both sides of the second cladding layer 4 by an insulating film 5. To do.

Alternatively, in the exciton erasing type semiconductor optical modulator, the first and second electrodes 6 and 7 are formed in parallel with each other. Alternatively, in the exciton erasing type semiconductor optical modulator, the first and second cladding layers 2 and 4 are made of undoped InP, and the multiple quantum well layer 3 is composed of undoped InGaAsP quantum well layers which are alternately and repeatedly stacked. It is characterized by being composed of an undoped InP barrier layer.

Alternatively, as illustrated in FIGS. 4 and 5, a first cladding layer 2 formed on a substrate 1 and a quantum well layer and a barrier layer are alternately formed on the first cladding layer 2. To form a multi-quantum well layer 3 by repeating growth, a step of forming a second clad layer 4 on the multi-quantum well layer 3, and a striped pattern on the second clad layer 4. The mask 11 is formed, and the second clad layer 4 to the second clad layer 4 in the region not covered by the mask 11 are etched, whereby the second clad layer 4 and the multiple quantum well layer 3 are formed. And a step of patterning the first cladding layer 2 into a mesa stripe shape, and the mask 11
And removing the patterned second clad layer 4, the multiple quantum well layer 3, and the first clad layer 2 to form an insulating film 5 on at least a side surface thereof, and the mesa-stripe-shaped second clad. Layer 4, multiple quantum well layer 3, and a step of forming two electrodes 6 and 7 on both side surfaces of the first cladding layer 2 with the insulating film 5 interposed therebetween. This is solved by a method of manufacturing a modulator.

[0018]

[Operation] According to the present invention, a multiple quantum well layer and a cladding layer sandwiching the quantum well layer from above and below are formed in a mesa stripe shape, and a pair of electrodes is formed on both sides of the mesa stripe layer with an insulating film interposed therebetween. Therefore, by applying a voltage to the pair of electrodes, an electric field parallel to the substrate surface is generated in the multiple quantum well layer, the excitons of the multiple quantum well layer are destroyed, and the optical absorption coefficient of the exciton absorption peak wavelength is In addition, the refractive index at wavelengths longer than the exciton absorption peak wavelength is significantly reduced.

Further, since the multiple quantum well layer serving as a waveguide is formed in a stripe shape, the difference in refractive index in the lateral direction of the waveguide becomes large, and lateral mode control becomes easy. Furthermore, since the impurity diffusion region does not exist in the multiple quantum well layer, almost no built-in electric field is generated, the modulation variable region becomes narrow, and the refractive index modulation and the optical absorption modulation do not have wide dispersion, which is effective. Light modulation is performed.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an exciton erasing type (exciton pleating type) semiconductor optical modulator showing an embodiment of the present invention. The semiconductor optical modulator shown in FIG. 1 has a first clad layer 2, an MQW layer 3 and a second clad layer 4, which are formed in a mesa stripe shape on a semi-insulating semiconductor substrate 1. An insulating film 5 is formed on both sides of the. Separated first and second electrodes 6 and 7 are formed on the insulating film 5, and a modulation power source 8 is connected between the electrodes 6 and 7.

The mesa striped MQW layer 3 serves as a waveguide, and the light to be modulated enters from one end and exits from the other end. Specific examples of materials and layer thicknesses that form the semiconductor light modulation device will be described in the manufacturing process described later. According to the semiconductor optical modulation device having such a structure, the electrodes 6 and 7 to which the signal voltage for optical modulation is applied are present on both sides of the mesa-shaped MQW layer 3 with the insulating film 5 interposed therebetween. Occurs only to a negligible extent, and does not narrow the light modulation area.

Further, M serving as a waveguide of the semiconductor optical modulator is provided.
Since the QW layer 3 has a striped shape and the insulating film 5 is present around it, the difference in refractive index between the waveguide and its surrounding becomes sufficiently large, and lateral mode control becomes easy. Further, since the semi-insulating semiconductor substrate is used, the electrodes 6 and 7 are
The parasitic capacitance due to is small.

The modulation of the semiconductor optical modulator described above is performed by applying a high frequency voltage signal between the electrodes 6 and 7 by the modulation power source 8. The optical modulation is performed by changing the light absorption coefficient and changing the refractive index. There are two ways of changing. First,
A method of performing light modulation by changing the light absorption coefficient will be described. The relationship between the wavelength and the light absorption coefficient becomes a curve as shown in FIG. 2 in each of the cases where the voltage is not applied between the electrodes 6 and 7 of the semiconductor light modulation device and the case where the voltage is applied. Applying a voltage between the electrodes 6 and 7 means generating an electric field in the QW layer 3.

The curve shown by the solid line in FIG. 2 shows the state where no electric field is generated in the MQW layer 3, and there is a peak of the light absorption coefficient at the wavelength λep. The wavelength λep at which this peak appears is called the exciton absorption peak wavelength. On the other hand, when an electric field in the direction parallel to the surface of the substrate 1 (horizontal direction in FIG. 1) is generated in the MQW layer 3, a curve like the broken line in FIG. 2 is obtained, and the curve at the exciton absorption peak wavelength λep is obtained. It can be seen that the light absorption coefficient changes and becomes significantly smaller.

The reason why the light absorption coefficient changes depending on the presence or absence of an electric field is that an exciton that absorbs light exists in the MQW layer when there is no electric field and the exciton is destroyed when an electric field is applied. Therefore, by generating and erasing a horizontal electric field in the MQW layer 3, the light of wavelength λep is intensity-modulated.

Next, a method of performing light modulation by changing the refractive index will be described. The solid line shown in FIG. 3A shows the case where no electric field is generated in the MQW layer 3, and there is a peak of the refractive index at the wavelength λop longer than the wavelength λep. On the other hand, when a horizontal electric field is generated in the MQW layer 3, the curve becomes like the broken line in FIG. 3 (a), and the peak of the refractive index at the wavelength λop disappears and becomes significantly smaller. Recognize.

The reason why the refractive index changes in this way is that excitons in the MQW layer 3 are present or destroyed by the generation and deletion of an electric field. Therefore, at that wavelength λop, the refractive index changes when voltage is applied and when voltage is not applied, and the phase of the light changes accordingly. Therefore, as shown in FIG. It will have two periods with different phases.

Therefore, the period T ₁ when no voltage is applied is a signal of "0", and the period T ₂ when a voltage is applied is a signal of "1", whereby information is transmitted. Moreover, as is apparent from FIG. 2, the light absorption coefficient of the wavelength λop hardly changes compared to when a voltage is applied and when no voltage is applied, which is convenient for use as a phase-modulation type modulator with little loss. Is good.

Since the signal voltage for operating the above-mentioned semiconductor optical modulator is applied in the lateral direction along the surface of the MQW layer 3, the number of periods of the quantum well layer and the barrier layer in the MQW layer 3 is set. Since the electric field strength in the MQW layer 3 does not decrease even if the number is increased, the period can be increased without increasing the operating voltage or deteriorating the refractive index change characteristics, whereby the light in the layer thickness direction can be increased. Better containment.

Next, the steps of the above embodiment will be described. First, as shown in FIG. 4A, a first cladding layer 2 made of undoped InP is epitaxially grown on the semi-insulating semiconductor substrate 1 made of InP to a thickness of 1000 Å. Then, undoped InP and undoped InP are deposited on the first cladding layer 2 by MOCVD or MOVPE.
In _1-x Ga _x As _y P _1-y (x = 0.438, y = 0.940) is alternately laminated every 100 Å in film thickness for 20 cycles to form an MQW layer 3. in this case,
InGaAsP serves as a quantum well layer and InP serves as a barrier layer. The exciton (exciton) peak wavelength λep of the MQW layer 3 is 1.526 μm.
It will be about.

Subsequently, undoped InP is epitaxially grown on the MQW layer 3 to a thickness of about 1000Å, and this is used as the second cladding layer 4. After the growth process of the compound semiconductor layer is completed, a photoresist is applied, and the photoresist is exposed to light and developed.
A resist pattern 11 having a width of 0 μm and a width of 2 μm in the direction perpendicular to the resist pattern 11 is formed.

Next, when the first and second cladding layers 2 and 4 and the MQW layer 3 are etched halfway through the first cladding layer 2 by using the resist pattern 11 as a mask, FIG.
As shown in (b), the plane length is 200 μm and the width is 2 μm.
A mesa-shaped semiconductor pattern of m is formed. The side surface of the mesa-shaped semiconductor pattern is preferably perpendicular to or close to the substrate surface, whereby the electrodes 6 and 7 are in a state of being parallel or nearly parallel, and an electric field component in an oblique direction with respect to the MQW layer 3. Is zero or very low. This is because when an electric field component in the oblique direction with respect to the MQW layer 3 is generated, the exciton absorption peak wavelength and the refractive index peak wavelength are shifted to the long wavelength side, and the change amount of the light absorption coefficient and the refractive index due to the modulation becomes small. This is because it is necessary to avoid this.

As a method of forming a mesa-striped semiconductor pattern, there is also a method of selectively growing the clad layers 2 and 4 and the MQW layer 3 on the substrate 1 by using an insulating film such as SiO ₂ or SiN as a mask. . Then, the resist pattern 11
Then, as shown in FIG. 4 (c), a 1500Å-thick SiO ₂ layer is grown on the upper and side surfaces of the mesa-shaped semiconductor pattern and the upper surface of the first cladding layer 2 by using a thermal CVD device or the like. Then, this is used as the insulating film 5.

Next, after coating the photoresist, the photoresist is exposed by a double exposure method or other method,
Further, development is performed to form a resist pattern 12 having a T-shaped cross section on both sides, as shown in FIG. 5 (a), on the second cladding layer 4. Next, as shown in FIG. 5B, Ti and Pt are vapor-deposited on the T-shaped resist pattern 12, both side walls of the mesa-shaped semiconductor pattern, and the upper surface of the first cladding layer 21. The metal film 13 having a two-layer structure is formed by sequentially depositing the metal film 13 by the method.

After that, when the resist pattern 12 is removed, the metal film 13 remains only on both sides of the mesa-shaped semiconductor pattern and on the first cladding layer 4, as shown in FIG. 5 (c). The metal film 13 on one side of the mesa striped MQW layer 3 is the first electrode 6, and the metal film 13 on the other side is the second electrode 7. The wiring connected to these electrodes 6 and 7 is drawn on the second cladding layer 4 on both sides of the waveguide region.

The resist pattern 12 has a T-shaped cross-section because an electric field component oblique to the MQW layer 3 is generated when the electrodes 6 and 7 are present on the second cladding layer 4. Is. As a result, the exciton erasing type semiconductor optical modulation device 10 as shown in FIG. 1 is completed.

By adopting the above layer structure and material structure, the exciton absorption peak wavelength λep is 1.52.
It becomes 6 μm. The wavelength λop at which the refractive index reaches a peak is 1.54 μm, and when excitons are erased, the change in the refractive index at that wavelength λop becomes maximum. Therefore, as described above, it becomes possible to modulate the light having the exciton absorption peak wavelength λep by absorption, or the light having the long λop by changing the refractive index.

The electric field required for exciton erasing in the MQW layer 3 is about 6 kV / cm, but a voltage of about 2.3 V can be obtained by adopting the above mesa structure, layer structure and material structure. Is applied, a lateral electric field having a magnitude exceeding 6 kV / cm is applied to the MQW layer 3. Therefore,
The semiconductor optical modulation device 10 can be operated with an extremely small voltage.

Since the semiconductor optical modulation device 10 has a structure in which the MQW layer is sandwiched between cladding layers like various light emitting devices, the semiconductor optical modulation device 10 and the light emitting device are formed on the same substrate. Alignment can be eliminated. For example, the structure can be structurally matched with the semiconductor laser 20 as shown in FIG. 5 in which the light emitting region is a quantum well layer into which a current is injected in a direction parallel to the substrate surface. The semiconductor laser 20 has the same layer structure as that of the semiconductor optical modulation device 10 described above, and the first clad layer 2, the MQW layer 23, and the second clad layer 24 are provided on the semi-insulating semiconductor substrate 1.
Are formed in a mesa shape.

The cladding layers 2, 2 of this semiconductor laser 20
4 and one side of the MQW layer 23, a p-type impurity diffusion region 25 is formed.
However, the n-type impurity diffusion region 26 is formed on the other side, and these regions 25 and 26 are provided with the semiconductor optical modulator 10 described above.
Electrodes 27 and 28 having the same structure as are connected. These points are structurally different from the semiconductor optical modulation device 10. When the semiconductor laser 20 is operated, a positive bias voltage is applied to the p-type impurity diffusion region 25 and the n-type impurity diffusion region 26 to flow a current in the lateral direction.

The film growth, mesa formation, and electrode formation of the semiconductor laser 20 are performed in parallel with those steps of the semiconductor optical modulation device 10 described above. In addition, the insulating film 5 that covers the mesa-stripe-shaped semiconductor pattern of the semiconductor light modulation device 10 is
It is removed from the semiconductor laser region by photolithography. Further, in the impurity diffusion process for forming the p-type impurity diffusion region 25 and the n-type impurity diffusion region 26 of the semiconductor laser 20, the semiconductor light modulation device 10 is covered with a photoresist (not shown) so that impurities are not introduced therein. To

The composition and layer thickness of the MQW layer 3 or the composition of the clad layers 2 and 4 are not limited to those in the above-described embodiment, and may be changed according to the wavelength band used. It is not limited to. For example,
The two clad layers are made of undoped AlGaAs, and M
The quantum well layer forming the QW layer may be made of undoped GaAs and the barrier layer may be made of undoped AlGaAs.

[0043]

As described above, according to the present invention, a multi-quantum well layer and a cladding layer sandwiching the multi-quantum well layer are formed in a mesa stripe shape, and a pair of electrodes is formed on both sides thereof with an insulating film interposed therebetween. Therefore, the refractive index difference in the lateral direction of the multiple quantum well layer that serves as a waveguide becomes large, and lateral mode control can be easily performed.

Further, since there is no impurity diffusion region in the multiple quantum well layer, almost no built-in electric field is generated, narrowing of the modulation variable region can be prevented, and wide dispersion of refractive index modulation and optical absorption modulation can be prevented. Can be prevented and effective light modulation can be performed. Furthermore, since the method of applying a voltage from the direction along the quantum well layer is adopted, by increasing the number of periods of the multiple quantum well layer without increasing the operating voltage,
The light confinement can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an exciton erasing type semiconductor optical modulator according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a wavelength and a light absorption coefficient when a voltage is applied and when no voltage is applied to the exciton erasing type semiconductor optical modulator according to the example of the present invention.

FIG. 3 (a) is a characteristic diagram showing the relationship between the wavelength and the refractive index of the exciton erasing type semiconductor optical modulator of the embodiment of the present invention when a voltage is applied and when no voltage is applied, and FIG. [Fig. 4] is a waveform diagram of light intensity showing refractive index modulation.

FIG. 4 is a cross-sectional view (1) showing a manufacturing process of an exciton erasing type semiconductor optical modulation device of an example of the present invention.

FIG. 5 is a cross-sectional view (No. 2) showing a manufacturing process of the exciton erasing type semiconductor optical modulation device of the embodiment of the present invention.

FIG. 6 is a perspective view showing a state in which a semiconductor laser is integrated with an exciton erasing type semiconductor optical modulator according to an embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a prior art exciton erasing type semiconductor optical modulator.

FIG. 8 is a diagram showing a distribution of a built-in electric field generated in the waveguide of the exciton erasing type semiconductor optical modulator according to the prior art.

[Explanation of symbols]

 1 Semi-Insulating Semiconductor Substrate 2 First Cladding Layer 3 Multiple Quantum Well Layer 4 Second Cladding Layer 5 Insulating Film 6, 7 Electrode

Claims (4)

[Claims] 1. A first clad layer (2) formed in a stripe shape on a substrate (1), and a stripe-shaped multi-quantum well layer () formed on the first clad layer (2). 3), a striped second cladding layer (4) formed on the multiple quantum well layer (3), the first cladding layer (2), the multiple quantum well layer (3) and An exciton erasing type semiconductor characterized in that it has first and second electrodes (6, 7) separated from each other through an insulating film (5) on both sides of the second cladding layer (4). Light modulator. 2. The exciton erasing type semiconductor light modulation device according to claim 1, wherein the first and second electrodes (6, 7) are formed in parallel with each other. 3. The first and second cladding layers (2, 4)
Is composed of undoped InP, and has the multi-quantum well layer (3).
2. The exciton-erasing semiconductor optical modulator according to claim 1, wherein the excitonic erase semiconductor light modulator comprises an undoped InGaAsP quantum well layer and an undoped InP barrier layer, which are alternately and repeatedly stacked. 4. A first cladding layer (2) formed on a substrate (1), and quantum well layers and barrier layers are alternately and repeatedly grown on the first cladding layer (2). Forming a multiple quantum well layer (3), forming a second cladding layer (4) on the multiple quantum well layer (3), and forming a second cladding layer (4) on the second cladding layer (4) The stripe-shaped mask (11) is formed, and the second clad layer (4) to the second clad layer (4) in the region not covered by the mask (11) are etched to obtain the first mask. Patterning the second clad layer (4), the multi-quantum well layer (3) and the first clad layer (2) into a mesa stripe shape; and after removing the mask (11), the patterned second layer Clad layer (4), multiple quantum well layer (3), first A step of forming an insulating film (5) on at least a side surface of the cladding layer (2), the mesa-stripe-shaped second cladding layer (4), the multiple quantum well layer (3), and the first cladding layer (2). And a step of forming two electrodes (6, 7) on both sides of the insulating film (5) via the insulating film (5).