JP2003283048A - Distribution feedback type semiconductor laser and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the yield upon manufacturing by improving a unit mode factor. <P>SOLUTION: The distribution feedback type semiconductor laser is provided with a semiconductor base board 11, a first diffraction grid layer 12a and a second diffraction grid layer 12b, which are provided on the semiconductor base board and arranged so as to be remote from each other in the emitting direction of light 23 so as to constitute a part of the diffraction grid whose phases are continuous with the same imaginary pitch, an active layer 18 arranged above the first and second diffraction grid layers, and a clad layer 19 arranged above the active layer. A region between the first and second diffraction grid layers, which are apart from each other, and below the active layer as well as a region between the first and second diffraction grid layers and the active layer are formed of a material substance the same as that of the semiconductor base board. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser that outputs light used for optical communication and optical measurement, and more particularly to a distributed feedback semiconductor laser that outputs light of a single wavelength.

[0002]

2. Description of the Related Art In a semiconductor laser that outputs light used for optical communication or optical measurement, for example, as shown in FIG. 6A, an active layer 3 and a cladding layer 3 are laminated on a semiconductor substrate 1. When voltage is applied between the lower surface of the semiconductor substrate 1 and the upper surface of the cladding layer 3, light (laser light) 4 is output from the end surface of the active layer 3. However, this light (laser light)
As a result of detailed verification, 4 can be regarded as a set of a plurality of lights each having a slightly different wavelength λ, as shown in FIG. 6B.

Therefore, light (laser light) 4 having a single wavelength λ ₀
6C, a distributed feedback type (Dist grating) in which a diffraction grating 5 is formed at a position adjacent to the active layer 2 in order to output
ributed feedback (DFB) semiconductor lasers have been proposed. In the distributed feedback semiconductor laser in which the diffraction grating 5 is incorporated in this way, when the equivalent refractive index of the waveguide is n and the grating interval is d, among the light having a large number of wavelengths λ generated in the active layer 2. , The wavelength λ should output the light 4a having the single wavelength λ ₀ (= 2nd) satisfying the condition of λ = 2nd.

However, the distributed feedback semiconductor laser is shown in FIG.
As shown in (c), when the diffraction grating 5 formed inside is of a continuous phase type that is uniform along the light emission direction, in principle, a "single mode oscillates only at a single wavelength λ _0. " Oscillation ”is not realized, and as shown in FIG. 6D, lights of different wavelengths λ ₊₁ and λ ₋₁ are output to the left-right ratio of the wavelength λ _{0 that} satisfies the condition of λ = 2nd.

In order to eliminate such inconvenience, λ
The "single mode oscillation" is realized by forming a phase shift structure called a / 4 shift structure for shifting the phase of light by λ / 4 in the middle of the diffraction grating 5.

However, the diffraction grating 5 having a phase shift structure in the middle cannot be manufactured by a batch exposure working process by a laser interference exposure method which is simple and excellent in mass productivity, and is generally long by using an electron beam drawing apparatus. The reality is that a manufacturing method that draws over time is used. On the other hand, Japanese Patent No. 1781186 (Japanese Patent Publication No. 4-67356) proposes a technique for obtaining the same effect as that of the λ / 4 shift structure even with a diffraction grating manufactured by the laser interference exposure method.

That is, in the proposed distributed feedback semiconductor laser, as shown in FIG. 7, the first and second diffraction grating waveguides 6a and 6b are provided below the active layer 2 and the first and second diffraction grating waveguides 6a and 6b, respectively. A flat coupling waveguide 7 that couples the second diffraction grating waveguides 6a and 6b is formed on the same surface as an integral structure. Then, the respective diffraction gratings of the first and second diffraction grating waveguides 6a and 6b are matched in phase so as to form a part of a virtual single diffraction grating by using the laser interference exposure method. Are formed.

The coupling waveguide 7 has a phase of transmitted light of π as compared with the case where the coupling waveguide 7 has the same structure as the first and second diffraction grating waveguides 6a and 6b. It has a transmission characteristic that shifts from an integer multiple of.

In this proposal, the phase of the light transmitted from the first diffraction grating waveguide 6a to the second diffraction grating waveguide 6b is shifted from an integral multiple of π, but the manufactured distributed feedback is used. In a type semiconductor laser, as a structure in which light with a single wavelength (laser light) is highly likely to occur, "the phase of light transmitted from the first diffraction grating waveguide 6a to the second diffraction grating waveguide 6b is π Half odd multiple of (π / 2, 3π / 2,
It is clear that this is a structure.

[0010]

However, the distributed feedback semiconductor laser having the structure shown in FIG. 7 still has the following problems to be solved.

That is, "the first and second diffraction grating waveguides 6a and 6b, and the first and second diffraction grating waveguides 6a and 6b.
To form a flat coupling waveguide 7 for coupling with the flat surface on the same surface, the first and second diffraction grating waveguides 6a and 6b existing below the active layer 2 and the flat coupling waveguide 7 and 7 need to be formed by etching a single layer made of a single material, for example, the semiconductor substrate 1 from the upper surface.

As shown in FIG. 8, the height h _{0 of} each grating forming the diffraction grating formed in the first and second diffraction grating waveguides 6a and 6b and the thickness h of the flat coupling waveguide 7 are equal to each other. ₁ is largely affected by etching conditions such as etching time, etching solution concentration, and etching solution temperature. In the manufacturing process of this distributed feedback semiconductor laser, the height h _{0 of} each grating and the coupling waveguide It is very difficult to control the thickness h ₁ of 7 with high accuracy.

Generally, in the coupling waveguide 7, the phase of the light transmitted through the coupling waveguide 7 is different from that in the case where there is a diffraction grating because of the difference in the structure of the waveguide, that is, the presence or absence of the diffraction grating. , Because the propagation constants of light are slightly different. The propagation constant of light is determined by the equivalent refractive index n that the transmitted light feels. Explaining with reference to FIG. 8, the difference between the average thickness h ₁ of the coupling waveguide 7 and the average height h _{0 of} each of the gratings forming the first and second diffraction grating waveguides 6a and 6b (h ₀ − h ₁ ).

That is, the phase shift amount of the light transmitted through the coupling waveguide 7 is exactly a half-odd multiple of π (π / 2, 3π /
2, ..., It is necessary to accurately control the difference (h ₀ −h ₁ ) described above.

However, as described above, the average thickness h ₁ of the coupling waveguide 7 and the first and second diffraction grating waveguides 6a, 6 are
The average height h ₀ of the lattice forming b depends on the etching accuracy in the manufacturing process of this distributed feedback semiconductor laser. As a result, the amount of phase shift of the light transmitted through the coupling waveguide 7 cannot be controlled with high accuracy, and the probability that a single-wavelength light (laser light) is generated in the manufactured distributed feedback semiconductor laser decreases. However, there is a problem that the production yield is reduced.

The present invention has been made in view of the above circumstances, and the region between the first and second diffraction grating layers is formed of a material different from that of the first and second diffraction grating layers. By using the etching method, the first and second
Even if the diffraction grating layer is manufactured, it is possible to maintain high shape accuracy and dimensional accuracy of the first and second diffraction grating layers and the region between the first and second diffraction grating layers, and An object of the present invention is to provide a distributed feedback semiconductor laser and a method for manufacturing a distributed feedback semiconductor laser, which can improve the probability of (laser light) generation and can significantly improve the yield during manufacturing.

[0017]

The present invention is directed to a semiconductor substrate and a light emitting direction in which light is emitted so as to form a part of a diffraction grating which is provided on the semiconductor substrate and whose phase is virtually continuous at the same pitch. First and second diffraction grating layers arranged apart from each other, an active layer arranged above the first and second diffraction grating layers, and a clad layer arranged above the active layer. It is applied to a distributed feedback semiconductor laser provided with.

In order to solve the above-mentioned problems, in the distributed feedback semiconductor laser of the present invention, the region between the first and second diffraction grating layers that are separated from each other and below the active layer and the first layer. The regions between the first and second diffraction grating layers and the active layer are formed of the same material as the semiconductor substrate.

In the distributed feedback semiconductor laser configured as described above, the coupling layer filling the region between the first and second diffraction grating layers separated from each other is the first and second diffraction grating layers. It is made of different material materials. Thus, the coupling layer between the first and second diffraction grating layers is
The fact that the second diffraction grating layer can be formed of a material different from that of the second diffraction grating layer means that when the region between the first and second diffraction grating layers for embedding the coupling layer is formed, the first and second diffraction grating layers can be formed. Even if the layer for forming the diffraction grating layer is formed by an etching method,
It is only necessary to remove this region by selective etching. Therefore, since the accuracy of the shape and size of this region can be improved, the accuracy of the shape and size of the coupling layer between the first and second diffraction grating layers is improved.

As a result, the amount of phase shift of the light transmitted through the coupling layer between the first and second diffraction grating layers is exactly a half-odd multiple of π (π / 2, 3π / 2, ...). You can control.

Another aspect of the present invention is directed to a semiconductor substrate, an active layer disposed on the semiconductor substrate, and a diffraction grating arranged above the active layer and having virtually the same pitch and continuous phase. A first diffraction grating layer and a second diffraction grating layer which are spaced apart from each other in the light emission direction so as to form a section, and a cladding layer which is disposed above the first diffraction grating layer and the second diffraction grating layer. It is applied to the distributed feedback semiconductor laser provided.

In order to solve the above-mentioned problems, in the distributed feedback semiconductor laser of the present invention, a region between the first and second diffraction grating layers which are separated from each other and above the active layer and the first layer. A region between the first and second diffraction grating layers and the active layer is formed of the same material as the semiconductor substrate.

In the distributed feedback semiconductor laser of the previous invention, the first, second, and second diffraction grating layers are arranged below the active layer, whereas the present invention is applied. In the distributed feedback semiconductor laser, the first,
Second first and second diffraction grating layers are provided. Other configurations are similar to those of the distributed feedback semiconductor laser of the previous invention.

Therefore, it is possible to obtain substantially the same operational effects as the distributed feedback semiconductor laser of the above invention.

Another aspect of the present invention is the distributed feedback semiconductor laser according to each of the above-mentioned aspects, wherein the diffraction gratings of the first and second diffraction grating layers penetrate from the upper surface to the lower surface orthogonal to the light emission direction. Has a gap of.

Further, another invention is the distributed feedback semiconductor laser according to each of the above inventions, wherein the diffraction gratings of the first and second diffraction grating layers have a plurality of mutually equal heights orthogonal to the light emission direction. Has a grid.

Generally, the diffraction grating is composed of a plurality of gratings and a plurality of grooves existing between the gratings, but in the present invention, the height of each grating is constant, and the grooves extend from the upper surface to the lower surface. It is formed with a piercing gap. By thus forming the grooves between the gratings with the heights of the respective gratings being constant, the accuracy of the shape and dimensions when the diffraction grating is manufactured by etching is improved.

Furthermore, in the distributed feedback semiconductor laser of another invention, the semiconductor substrate is made of InP, the first and second diffraction grating layers are made of InGaAsP, and the active layer is made of InGaAsP.
And a cladding layer made of InP.

Another invention is a method of manufacturing a distributed feedback semiconductor laser. Then, in the method of manufacturing the distributed feedback semiconductor laser, a step of forming a layer for forming a diffraction grating layer made of a material having a refractive index larger than that of the semiconductor substrate on the semiconductor substrate, and a diffraction grating having a uniform period. And an etching inhibitor is formed in the layer for forming the diffraction grating layer with a predetermined gap so that the first and second diffraction grating layers are formed apart from each other in the light emission direction. And a step of forming the first and second diffraction grating layers by removing the exposed portions by selective etching using an etching inhibitor as an etching mask, and the formed first and second separated grating layers. Second
Forming a buffer layer made of the same material as the semiconductor substrate between the diffraction grating layers and above the first and second diffraction grating layers; forming an active layer above the buffer layer; And a step of forming a clad layer above.

In the method of manufacturing the distributed feedback semiconductor laser having the above-described structure, the layer for forming the diffraction grating layer is etched to form a region between the first and second diffraction grating layers separated from each other. In this case, the region between the first and second diffraction grating layers to be filled with the coupling layer may be formed by etching the layer for forming the diffraction grating layer over the entire thickness. It is possible to maintain high shape accuracy and high dimensional accuracy.

Therefore, in the distributed feedback semiconductor laser manufactured by this manufacturing method, the amount of phase shift of the light propagating from the first diffraction grating layer to the second diffraction grating layer via the coupling layer is accurately π. It is multiplied by a half odd number (π / 2, 3π / 2, ...).

Further, in a method of manufacturing a distributed feedback semiconductor laser according to another invention, an active layer is formed on a semiconductor substrate,
A step of sequentially stacking a buffer layer made of the same material as the semiconductor substrate and a layer for forming a diffraction grating layer made of a material having a refractive index larger than that of the buffer layer, and a diffraction grating having a uniform period are formed. An etching inhibitor is formed in a layer for forming the diffraction grating layer with a predetermined gap so that the first and second diffraction grating layers are formed apart from each other in the light emission direction. A step of forming the first and second diffraction grating layers by removing the exposed portion by selective etching using an etching inhibitor as an etching mask, and the formed first and second diffraction grating layers separated from each other. And a step of forming a clad layer made of the same material as the buffer layer between the two diffraction grating layers and above the first and second diffraction grating layers.

In the distributed feedback semiconductor laser manufactured by the method for manufacturing a distributed feedback semiconductor laser according to the above invention, the first, second, and second diffraction grating layers are arranged below the active layer. On the other hand, in the distributed feedback semiconductor laser to which the manufacturing method of the present invention is applied, the first and second diffraction grating layers are arranged above the active layer. The other configuration is similar to the distributed feedback semiconductor laser described above.

Therefore, it is possible to obtain substantially the same operational effects as the method of manufacturing the distributed feedback semiconductor laser of the above invention.

In still another invention, in the method of manufacturing the distributed feedback semiconductor laser of the above-mentioned invention, in the step of forming the first and second diffraction grating layers, the exposed part is diffracted into the first and second diffraction grating layers. Etch to the upper surface of the layer located below the lattice layer.

In the method of manufacturing the distributed feedback semiconductor laser having the above structure, the portion other than the portion masked with the etching inhibitor is removed by etching over the entire thickness direction of the layer, and thus is removed by etching. The dimensional accuracy of the part and the part of the masked part which is not etched away is improved.

When referring to the same material, the difference in impurity concentration is ignored and they are regarded as the same material.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a schematic sectional view showing a schematic configuration of a distributed feedback semiconductor laser according to the first embodiment of the present invention.

On the upper surface of the semiconductor substrate 11 made of n-type InP, the first diffraction grating layer 12a made of n-type InGaAsP,
A bonding layer 13 made of the same material as the semiconductor substrate 11,
A second diffraction grating layer 12a made of n-type InGaAsP is formed. First and second diffraction grating layers 12a and 12b
Each of which is composed of a plurality of gratings 14 and a gap 15 existing between the gratings, and the first and second diffraction grating layers 1
All of the gratings 14 and the gaps 15 included in 2a and 12b constitute one diffraction grating 16 in which the phases are virtually continuous at the same pitch. In addition, the first and second diffraction grating layers 12
The refractive index of each grating 14 forming a and 12b is set higher than that of the semiconductor substrate 11.

Then, the first and second diffraction grating layers 12a,
The length of the coupling layer 13 that fills the region between 12b is half odd multiples of the phase π (π / 2, 3π) in the process of the light 23 having the desired single wavelength λ ₀ passing through the coupling layer 13. / 2, ...) is set to be offset.

The first and second diffraction grating layers 12a, 12b,
A buffer layer 17 made of the same material as the semiconductor substrate 11 is formed on the upper surface of the coupling layer 13. The bonding layer 1
3 and the buffer layer 17 are integrally formed. This buffer layer 1
On the upper surface of 7, each composed of InGaSaP of appropriate composition,
Active layer 1 including lower SCH layer, MQW layer, upper SCH layer
8 is formed. On the upper surface of the active layer 18, p-type
A cladding layer 19 made of InP is formed.

A p-electrode 20 is attached to the upper surface of the clad layer 19, and an n-electrode 21 is attached to the lower surface of the semiconductor substrate 11. Further, antireflection films 22a and 22b are formed on the end faces of the active layer 18 and the first and second diffraction grating layers 12a and 12b from which the single-mode light 23 is emitted.

In the distributed feedback semiconductor laser of the first embodiment having the above structure, the p electrode 20 and the n electrode 21 are provided.
When a voltage is applied between the, although the active layer 18 to oscillate light having multiple wavelengths, single wavelength lambda ₀ of the light, that the lattice spacing and the transmission refractive index of the diffraction grating 16 is determined by the having the wavelength
The light 23 having is selected and output.

In this case, the presence of the coupling layer 13 causes the phase of the light 23 to be shifted by a half-odd multiple of π (π / 2, 3π / 2, ...), so that the light 23 having the single wavelength λ ₀ is surely generated. Is output.

More specifically, the coupling layer 13 existing between the first and second diffraction grating layers 12a and 12b is
The first and second diffraction grating layers 12a and 12b are formed of the same material as the semiconductor substrate different from that of the semiconductor substrate.

Therefore, since the accuracy of the shape and dimensions of this region can be improved, the first and second diffraction grating layers 12a,
The accuracy of the shape and size of the bonding layer 13 between 12b is increased. When the accuracy of the shape and size of the coupling layer 13 is improved, the above-mentioned relationship between the size of the grating 14 and the size of the coupling layer 13 always maintains a constant value, so that the equivalent refractive index felt by the light 23 varies from element to element. Since this prevents the phase of the light 23 from being shifted by a half-odd multiple of π (π / 2, 3π / 2, ...), the light 23 having the single wavelength λ ₀ is output.

That is, the wavelength accuracy of the light 23 output from the distributed feedback semiconductor laser is significantly improved, and
The single mode rate can be improved, and the yield in manufacturing distributed feedback semiconductor lasers can be improved.

(Second Embodiment) FIG. 2 is a manufacturing process diagram showing a method of manufacturing a distributed feedback semiconductor laser according to a second embodiment of the present invention. Specifically, the manufacturing process of the distributed feedback semiconductor laser of the first embodiment shown in FIG. 1 will be described. Hereinafter, description will be given with reference to FIGS.

(A) Semiconductor substrate 11 made of n-type InP
On top of that, it is lattice-matched to InP and has a composition wavelength of 1.05 μm
The layer 12 for forming a diffraction grating made of n-type InGaAsP having a composition of 1.10 μm
Either 150 nm is formed by the crystal growth method.

(B) Layer 12 for forming a diffraction grating
A diffraction grating 16 having a uniform period of 200 nm to 300 nm is formed on the above, and the first and second diffraction grating layers 12a and 12b are separated from each other in the emission direction of the light 23 by 100 nm to 200 nm. Is formed, an etching inhibitor 24 such as a photoresist is formed in the layer 12 for forming the diffraction grating with a predetermined gap therebetween. That is, after performing the diffraction grating-like exposure over the entire upper surface of the layer 12 for forming the diffraction grating, only the portion corresponding to the coupling layer 13 is exposed over the entire surface (this corresponds to the case of a positive type resist). To). Specifically, the etching inhibitor 24 is formed only on the portions of the first and second diffraction grating layers 12a and 12b corresponding to the gratings 14 of the diffraction grating 16.

(C) Next, using the etching inhibitor 24 as an etching mask, the exposed portion of the diffraction grating layer 12 is removed by selective etching.
The first and second diffraction grating layers 12a and 12b are formed. Then, after the etching is completed, the etching inhibitor 24 is removed.

In this case, the exposed surface of the diffraction grating layer 12 made of InGaAsP is etched by immersing it in an etching solution in which sulfuric acid, hydrogen peroxide solution, and water are mixed, but it is located below the diffraction grating layer 12. Since InP of the semiconductor substrate 11 is not etched, the etching stops when it reaches the upper surface of the semiconductor substrate 11. That is, the height of each grating 14 that constitutes the diffraction grating 16 is simply determined by the thickness of the diffraction grating layer 12. Similarly, the thickness of the coupling layer 13 is also determined by the thickness of the diffraction grating layer 12.

What is important here is that a gap 15 penetrating from the upper surface to the lower surface of the diffraction grating layer 12 is formed between the adjacent gratings 14.

That is, the diffraction grating 16 can be formed accurately and with high reproducibility even if the etching time varies or the concentration or temperature of the etching solution changes.

(D) The semiconductor substrate 11 is formed on the formed region between the first and second diffraction grating layers 12a and 12b which are separated from each other and on the first and second diffraction grating layers 12a and 12b. The buffer layer 17 made of InP, which is the same material, is formed by the crystal growth method to a thickness of 50 nm to 200 nm. In this state, the coupling layer 13 made of InP, which is the same material as the semiconductor substrate 11, is formed between the first and second diffraction grating layers 12a and 12b.

(E) An active layer 18 made of a material containing InGaAsP having a photoluminescence (PL) wavelength of 1.45 μm to 1.65 μm is formed on the buffer layer 17 by a crystal growth method. The active layer 18 generally has a multiple quantum well layer structure. If necessary, it is possible to form the light separation confinement layers above and below the multiple quantum well structure.

(F) Furthermore, p is formed on the active layer 18.
A clad layer 19 made of type InP is formed by a crystal growth method to a thickness of 2 μm to 4 μm.

Finally, as shown in FIG. 1, the cladding layer 1
The p electrode 20 is attached to the upper surface of the semiconductor substrate 9 and the n electrode 21 is attached to the lower surface of the semiconductor substrate 11. In addition, single mode light 2
3 is emitted from the active layer 18, the first and second diffraction grating layers 1
The end faces of 2a and 12b are formed by cleavage, and antireflection films 22a and 22b are formed on these end faces.

The composition and film thickness of each layer constituting the distributed feedback semiconductor laser shown in the manufacturing method of the second embodiment is such that the wavelength λ = 1.
It is a value applied to a semiconductor laser that outputs light of 45 μm to 1.65 μm.

In the method of manufacturing the distributed feedback semiconductor laser of the second embodiment having the above-mentioned structure, (b)
As described in the section (c), even if the first and second diffraction grating layers 12a and 12b are formed by etching the layer 12 for forming the diffraction grating having a predetermined thickness, Accurate and highly reproducible diffraction grating 16
It is possible to form the first and second diffraction grating layers 12a and 12b having

That is, the wavelength accuracy of the light 23 output from the distributed feedback semiconductor laser manufactured by using this manufacturing method is significantly improved, and the single mode rate can be improved, so that the distributed feedback semiconductor laser can be manufactured. The yield above can be improved.

FIG. 3 shows the first and second diffraction grating layers 12a,
Experimental results showing the relationship between the distances 12b, that is, the distance L of the coupling layer 13 existing in the propagation direction of the light 23, and the single mode rate of the light 23 output in the state set at each distance L. FIG. The shapes of the diffraction gratings 16 of the first and second diffraction grating layers 12a and 12b have the same specifications.

From this experimental result, it was confirmed that the peak point of the single mode ratio exists at the specific distance L position corresponding to the wavelength of the light 23. This means that the shapes of the diffraction gratings 16 of the first and second diffraction grating layers 12a and 12b in many distributed feedback semiconductor lasers used in this experiment maintain the same value with very high accuracy, and It was proved that there was little variation between them.

In the above manufacturing method,
In (b), the etching inhibitor 24 is formed directly on the diffraction grating layer 12, but a layer (auxiliary buffer layer) made of the same material as the semiconductor substrate 11 is formed on the diffraction grating layer 12. It is also possible to form the etching inhibitor 24 on the upper surface of this layer (auxiliary buffer layer).

In this case, the first and second diffraction grating layers 12
Etching for forming a and 12b is performed twice in a divided manner. Etching to the midway position of the diffraction grating layer 12 by the first etching (100 nm to 200 nm depth)
Then, the etching inhibitor 24 is removed.

By using the auxiliary buffer remaining at the position where the etching inhibitor 24 has been removed as an etching mask, the second etching is performed to remove the exposed diffraction grating layer 12, and thereby the first and second diffraction grating layers 12 are removed. Diffraction grating layers 12a, 1
2b is formed.

(Third Embodiment) FIG. 4 is a schematic sectional view showing a schematic configuration of a distributed feedback semiconductor laser according to the third embodiment of the present invention. The same parts as those of the distributed feedback semiconductor laser of the first embodiment shown in FIG. 1 are designated by the same reference numerals, and detailed description of the overlapping parts will be omitted.

I is formed on the upper surface of the semiconductor substrate 11 made of n-type InP.
An active layer 18 made of nGaAaP is formed. A buffer layer 17 made of p-type InP is formed on the upper surface of the active layer 18. On the upper surface of the buffer layer 17, a first diffraction grating layer 12a made of p-type InGaAsP, a coupling layer 13 made of the same material as the buffer layer 17, and a second diffraction grating layer 12a made of p-type InGaAsP are provided. Has been formed.

The first and second diffraction grating layers 12a and 12b
Each of which is composed of a plurality of gratings 14 and a gap 15 existing between the gratings, and the first and second diffraction grating layers 1
All of the gratings 14 and the gaps 15 included in 2a and 12b constitute one diffraction grating 16 in which the phases are virtually continuous at the same pitch. In addition, the first and second diffraction grating layers 12
The refractive index of each grating 14 constituting a and 12b is set higher than that of the cladding layer 19.

The length of the coupling layer 13 is a half odd multiple of π (π / 2, 3π / 2, ...) In the process in which the light 23 having a desired single wavelength passes through the coupling layer 13. It is set to deviate only. The first and second diffraction grating layers 12a,
A cladding layer 19 made of the same material as that of the buffer layer 17 is formed on the upper surfaces of 12b and the coupling layer 13.

A p-electrode 20 is attached to the upper surface of the clad layer 19, and an n-electrode 21 is attached to the lower surface of the semiconductor substrate 11. Further, antireflection films 22a and 22b are formed on the end faces of the active layer 18 and the first and second diffraction grating layers 12a and 12b from which the single-mode light 23 is emitted.

Also in the distributed feedback semiconductor laser of the third embodiment having such a configuration, the coupling layer 13 existing between the first and second diffraction grating layers 12a and 12b has the first and second coupling layers.
Since the second diffraction grating layers 12a and 12b are made of a different material, the first and second diffraction grating layers 12a and 12b.
The shape, dimensional accuracy, first,
The shape and dimensional accuracy of the coupling layer 13 between the second diffraction grating layers 12a and 12b can be greatly improved.

Therefore, it is possible to obtain substantially the same operational effects as the distributed feedback semiconductor laser of the first embodiment shown in FIG.

(Fourth Embodiment) FIG. 5 is a manufacturing process diagram showing a method of manufacturing a distributed feedback semiconductor laser according to a fourth embodiment of the present invention. Specifically, the manufacturing process of the distributed feedback semiconductor laser of the third embodiment shown in FIG. 4 will be described. The same parts as those in the method of manufacturing the distributed feedback semiconductor laser according to the second embodiment shown in FIG. 2 are designated by the same reference numerals, and detailed description of the overlapping parts will be omitted. Hereinafter, description will be given with reference to FIGS.

(A) Semiconductor substrate 11 made of n-type InP
An active layer 18 made of InGaAaP, a buffer layer 17 made of p-type InP, and a layer 12 for forming a diffraction grating made of p-type InGaAsP are sequentially laminated on the above by a crystal growth method.

(B) Layer 12 for forming a diffraction grating
To form a diffraction grating 16 having a uniform period on the upper surface of the first and second diffraction grating layers 12a and 12b spaced apart from each other in the emission direction of the light 23. An etching inhibitor 24 is formed on the layer 12 with a predetermined gap. That is, after performing the diffraction grating-like exposure over the entire upper surface of the layer 12 for forming the diffraction grating, the entire surface is exposed only for the portion corresponding to the coupling layer 13. Specifically, the first and second diffraction grating layers 12a and 12
The etching inhibitor 24 is formed only on the portion corresponding to the lattice 14 in b.

(C) Next, using the etching inhibitor 24 as an etching mask, the exposed portion is removed by selective etching to form the first and second diffraction grating layers 12a and 12b. Then, after the etching is completed, the etching inhibitor 24 is removed.

In this case, the exposed surface of the diffraction grating layer 12 made of InGaAsP is etched by immersing it in an etching solution mixed with sulfuric acid, hydrogen peroxide solution, and water, but it is located below the diffraction grating layer 12. Since InP of the buffer layer 17 is not etched, the etching is stopped when the upper surface of the buffer layer 17 is reached. That is, the height of each grating 14 that constitutes the diffraction grating 16 is simply determined by the thickness of the diffraction grating layer 12.
Similarly, the thickness of the coupling layer 13 is also determined by the thickness of the diffraction grating layer 12.

That is, the diffraction grating 16 can be formed accurately and with high reproducibility even if the etching time varies or the concentration or temperature of the etching solution changes.

(D) Between the formed first and second diffraction grating layers 12a and 12b spaced apart from each other, and the first and second diffraction grating layers 12a and 12b.
A cladding layer 19 made of p-type InP is formed on the second diffraction grating layers 12a and 12b by a growth method. In this state, between the first and second diffraction grating layers 12a and 12b,
Bonding layer 1 made of InP which is the same material as the buffer layer 17
3 is formed.

Finally, as shown in FIG. 4, the cladding layer 1
The p electrode 20 is attached to the upper surface of the semiconductor substrate 9 and the n electrode 21 is attached to the lower surface of the semiconductor substrate 11. In addition, single mode light 2
3 is emitted from the active layer 18, the first and second diffraction grating layers 1
The end faces of 2a and 12b are formed by cleavage, and antireflection films 22a and 22b are formed on these end faces.

Also in the method of manufacturing the distributed feedback semiconductor laser of the fourth embodiment having the above-described structure, as in the method of manufacturing the distributed feedback semiconductor laser of the second embodiment described with reference to FIG. , (C), even if the first and second diffraction grating layers 12a and 12b are formed by etching the layer 12 for forming the diffraction grating having a predetermined thickness. First and second diffraction grating layer 1 having accurate and highly reproducible diffraction grating 16
2a, 12b can be formed.

That is, the wavelength accuracy of the light 23 output from the distributed feedback semiconductor laser manufactured by this manufacturing method is significantly improved, and the single mode rate can be improved, so that the distributed feedback semiconductor laser can be manufactured. The yield above can be improved.

[0084]

As described above, in the distributed feedback semiconductor laser and the method for manufacturing the distributed feedback semiconductor laser of the present invention, the region between the first and second diffraction grating layers is formed in the first and second regions. The second diffraction grating layer is made of a different material.

Therefore, even if the first and second diffraction gratings are manufactured by using an etching method, the first and second diffraction grating layers and the region between the first and second diffraction grating layers are formed. The shape accuracy and dimensional accuracy can be maintained high, the probability that light of a single wavelength (laser light) is generated can be improved, the wavelength accuracy of the output light can be improved, and the yield at the time of manufacturing can be greatly improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a schematic configuration of a distributed feedback semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a process diagram showing a method of manufacturing a distributed feedback semiconductor laser according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a measurement result of a single mode rate measured by using the distributed feedback semiconductor laser according to the first embodiment of the present invention.

FIG. 4 is a schematic sectional view showing a schematic configuration of a distributed feedback semiconductor laser according to a third embodiment of the present invention.

FIG. 5 is a process diagram showing a method of manufacturing a distributed feedback semiconductor laser according to a fourth embodiment of the present invention.

FIG. 6 is a diagram for explaining the operating principle of a distributed feedback semiconductor laser.

FIG. 7 is a schematic sectional view showing a schematic configuration of a conventional distributed feedback semiconductor laser.

FIG. 8 is a diagram for explaining a problem of the conventional distributed feedback semiconductor laser.

[Explanation of symbols]

11 ... Semiconductor substrate 12 ... Layer for forming diffraction grating 12a ... the first diffraction grating layer 12b ... second diffraction grating layer 13 ... Bonding layer 14 ... Lattice 15 ... Gap 16 ... Diffraction grating 17 ... Buffer layer 18 ... Active layer 19 ... Clad layer 20 ... p electrode 21 ... n electrode 22a, 22b ... Antireflection film 23 ... light 24 ... Etching inhibitor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mikiaki Fujita             5-10-10 Minamiazabu, Minato-ku, Tokyo Henri             Tsu Co., Ltd. (72) Inventor Yoshio Takahashi             5-10-10 Minamiazabu, Minato-ku, Tokyo Henri             Tsu Co., Ltd. F term (reference) 5F043 AA15 AA16 BB08 BB10 FF03                       GG10                 5F073 AA45 AA64 AA74 AA83 BA02                       CA12 CB02 DA22 EA03

Claims (8)

[Claims] 1. A semiconductor substrate (11) and an emission direction of light (23) so as to form a part of a diffraction grating (16) which is provided on the semiconductor substrate and which has virtually the same pitch and continuous phase. First and second diffraction grating layers (12a, 12b) spaced apart from each other, an active layer (18) disposed above the first and second diffraction grating layers, and A distributed feedback semiconductor laser comprising a cladding layer (19) disposed above the layer, the region between the first and second diffraction grating layers separated from each other and below the active layer; A distributed feedback semiconductor laser, wherein a region between the first and second diffraction grating layers and the active layer is formed of the same material as that of the semiconductor substrate. 2. A semiconductor substrate (11), an active layer (18) arranged on the semiconductor substrate, a diffraction grating (a phase arranged continuously above the active layer and having virtually the same pitch). 16) first and second diffraction grating layers (12a, 12b) which are arranged apart from each other in the emission direction of the light (23) so as to constitute a part of the first and second diffractions. A distributed feedback semiconductor laser comprising a cladding layer (19) disposed above a grating layer, the region being between the first and second diffraction grating layers separated from each other and above the active layer. A distributed feedback semiconductor laser, wherein a region between the first and second diffraction grating layers and the active layer is formed of the same material as that of the semiconductor substrate. 3. The first and second diffraction grating layers (12a, 12a,
The diffraction grating (16) of 12b) has a plurality of gaps (1) penetrating from the upper surface to the lower surface orthogonal to the emission direction of the light (23).
The distributed feedback semiconductor laser according to claim 1 or 2, further comprising 5). 4. The first and second diffraction grating layers (12a, 12a,
The diffraction grating (16) of 12b) comprises a plurality of gratings (14) which are orthogonal to the emission direction of the light (23) and have the same height.
The distributed feedback semiconductor laser according to claim 1 or 2, further comprising: 5. The semiconductor substrate is formed of InP, the first and second diffraction grating layers are formed of InGaAsP, the active layer is formed of a material containing InGaAsP, and the clad layer is formed of InP. The distributed feedback semiconductor laser according to any one of claims 1 to 4, wherein 6. A method of manufacturing a distributed feedback semiconductor laser, comprising a step of forming a layer for forming a diffraction grating layer made of a material having a refractive index larger than that of the semiconductor substrate on the semiconductor substrate, and a uniform period. And the first and second diffraction grating layers are formed so as to be spaced apart from each other in the light emission direction and to be etched with a predetermined gap between the layers for forming the diffraction grating layer. A step of forming an inhibitor, a step of forming the first and second diffraction grating layers by removing the exposed portion by selective etching using the etching inhibitor as an etching mask, and Forming a buffer layer made of the same material as the semiconductor substrate between the first and second diffraction grating layers separated from each other and above the first and second diffraction grating layers; Forming an active layer towards manufacturing method of a distributed feedback semiconductor laser and a step of forming a cladding layer above the active layer. 7. A method of manufacturing a distributed feedback semiconductor laser, comprising an active layer on a semiconductor substrate, a buffer layer made of the same material as the semiconductor substrate, and a material having a refractive index higher than that of the buffer layer. A step of sequentially stacking layers for forming a diffraction grating layer, and forming a diffraction grating with a uniform period and forming first and second diffraction grating layers separated from each other in the light emission direction. As described above, a step of forming an etching inhibitor with a predetermined gap in a layer for forming the diffraction grating layer, and the exposed portion is removed by selective etching using the etching inhibitor as an etching mask. The steps of forming the first and second diffraction grating layers, and between the formed first and second diffraction grating layers separated from each other and above the first and second diffraction grating layers. To the loose Method for producing a distributed feedback semiconductor laser and a step of forming a cladding layer formed of the same material substance and the layer. 8. The step of forming the first and second diffraction grating layers includes etching the exposed portion up to an upper surface of a layer located below the first and second diffraction grating layers. 8. A method of manufacturing a distributed feedback semiconductor laser according to claim 6 or 7.