JPH0745907A - Distributed feedback type semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a distributed feedback type laser of a gain coupling type being affected little by the distribution of a refractive index. CONSTITUTION:This laser is equipped with a first conductivity type clad layer 2 which is formed on a first conductivity type substrate 1a and of which the surface has an indented shape in which stripe-shaped projecting and recessed parts are disposed periodically in a direction of the waveguide of light and the recessed part has a flat bottom, an active layer 3 which is formed in a virtually uniform thickness on the clad layer 2 and in which an inhibited band width in a region formed on a flat bottom is larger than the inhibited band width in a region formed on a part other than the flat bottom, and a second conductivity type clad layer 4 disposed on the active layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed feedback semiconductor laser, and more particularly to the structure of a gain coupled distributed feedback semiconductor laser.

[0002]

2. Description of the Related Art FIG. 7 shows a structure of a conventional distributed feedback semiconductor laser, which is a sectional view (FIG. 7 (a)) in a direction in which light is guided (hereinafter also referred to as a waveguide direction) and a waveguide. FIG. 8 is a diagram showing the equivalent refractive index distribution in the direction (FIG. 7 (b)). In the figure, 21 is a GaAs semiconductor substrate of the first conductivity type. Reference numeral 22 denotes a first conductivity type AlG formed on the substrate 21 and having a concavo-convex structure on the surface of which concave and convex stripes are arranged at a predetermined cycle in the direction in which light is guided.
It is an aAs clad layer. Reference numeral 23 is a first conductivity type AlGaAs guide layer formed on the cladding layer 22 and having an Al composition ratio higher than that of the cladding layer 22. Reference numeral 24 is an AlGaAs active layer formed on the guide layer 23, in which the thickness of the concave portion of the concave-convex structure on the surface of the guide layer 23 is large and the thickness of the convex portion is small, and the Al composition ratio is larger than that of the guide layer 23. . Two
Reference numeral 5 is a second conductivity type AlGaAs guide layer having a smaller Al composition ratio than the active layer 24 and formed on the active layer 24 so as to have a flat surface. Reference numeral 26 is a second conductivity type AlGaAs cladding layer formed on the second conductivity type guide layer 25 and having an Al composition ratio smaller than that of the guide layer 25. Further, 11 and 12 are electrodes.

Next, the operation will be described. In this conventional example, when a current is passed between the substrate 21 and the cladding layer 26 in the forward bias direction, population inversion of carriers occurs in the active layer 23, and light is generated by recombination of the carriers. When a certain current value is exceeded, a resonance phenomenon occurs in the waveguide direction of the active layer 23 and laser oscillation occurs.

At this time, in the distributed feedback semiconductor laser of FIG. 7, since the layer thickness of the active layer 24 is periodically changed in the waveguide direction, the layer thickness of the active layer is changed in the waveguide direction. A gain distribution is formed. Therefore, this distributed feedback semiconductor laser is a gain-coupled distributed feedback laser as a guide layer 23, an active layer 24, and a guide layer 25.
Laser oscillation is performed at a wavelength (Bragg wavelength) that can be formed by the period of the diffraction grating configured by the uneven structure of. As a result, the laser oscillation has a single longitudinal mode.

[0005]

The conventional distributed feedback type semiconductor laser is constructed as described above, and the active layer 24
In addition to the gain distribution generated due to the thickness distribution of the active layer 24, the refractive index of the guide layer 23 and the active layer 24 are different from each other. Therefore, as shown in FIG. ,
A refractive index distribution also occurs in the waveguide direction. As is well known theoretically, in distributed feedback semiconductor lasers,
When a waveguide having a refractive index distribution is used, strictly speaking, oscillation modes exist at two wavelengths that are separated by an equal interval with respect to the wavelength (Bragg wavelength) determined by the period of the diffraction grating. As a result, in order to stably oscillate such a distributed feedback semiconductor laser having a refractive index distribution in the waveguide as described above, one mode with the lowest gain can be obtained by controlling the reflectance of the laser end face. It is necessary to devise the structure such as That is, in the conventional distributed feedback semiconductor laser,
There is a problem that the stability of single mode oscillation is deteriorated due to the influence of the refractive index coupling on the gain coupling type structure.

Further, in the conventional distributed feedback laser, since the oscillation wavelength of the semiconductor laser is determined by the period of the uneven structure on the cladding layer 22, the current unevenness forming technique has an oscillation wavelength of 1 μm or less. There is a problem that it is very difficult to manufacture a distributed feedback semiconductor laser.

The present invention has been made in order to solve the above problems, and obtains a distributed feedback semiconductor laser having a good single-mode oscillation characteristic, and further 1 μm.
It is an object of the present invention to obtain a distributed feedback semiconductor laser capable of obtaining an oscillation wavelength of m or less.

[0008]

DISCLOSURE OF THE INVENTION A distributed feedback semiconductor laser according to the present invention is formed on a first conductivity type semiconductor substrate, the surface of which has stripe-shaped convex portions and concave portions for guiding light. The first conductivity type clad layer having a concave and convex shape having a flat bottom surface in the recess, and a substantially uniform thickness on the first conductivity type clad layer, And, on the flat bottom surface, the forbidden band width of the region formed on the flat bottom surface is larger than the forbidden band width of the area formed on the portion other than the flat bottom surface. An active layer crystal-grown so as to be disordered to a greater extent than on the flat bottom surface on portions other than the flat bottom surface so as to be disordered to a minute degree, and a first layer disposed on the active layer. With two conductivity type clad layers That.

Further, in the distributed feedback semiconductor laser according to the present invention, the stripe-shaped convex portions and concave portions formed on the first conductivity type semiconductor substrate are periodically arranged in the light guiding direction. And a first conductivity type clad layer having an uneven shape having a flat top surface in the convex portion, and a substantially uniform thickness on the first conductivity type clad layer, and Ordered on the flat top surface such that the band gap width of the area formed on the flat top surface is larger than the band gap width of the area formed on a portion other than the flat top surface. Or to be disordered to a very small degree,
An active layer crystal-grown so as to be disordered to a greater extent than that on the flat top surface on a portion other than the flat top surface, and a second-conductivity-type cladding layer disposed on the active layer. Be prepared.

Further, in the distributed feedback semiconductor laser according to the present invention, the stripe-shaped convex portions and concave portions formed on the first conductivity type semiconductor substrate are periodically arranged in the light guiding direction. On the first conductivity type clad layer, the first conductivity type clad layer having an uneven shape having a flat bottom surface in the recess and a flat top surface in the projection,
The forbidden band width of the region formed on the flat bottom surface and the top surface has a substantially uniform thickness, and the forbidden band width of the region formed on a portion other than the flat bottom surface and the top surface. Crystal growth so that it becomes larger and disordered to a larger extent on the flat surface, and disordered to a greater extent than on the flat surface on portions other than the flat surface. And a second conductivity type clad layer disposed on the active layer.

[0011]

According to the present invention, the surface of the semiconductor substrate of the first conductivity type is provided with stripe-shaped convex portions and concave portions periodically arranged in the light guiding direction. Concavity and convexity of the first conductivity type clad layer having a flat bottom surface, and prohibition of a region formed on the first bottom surface of the first conductivity type clad layer and having a substantially uniform thickness Since an active layer having a band width larger than the forbidden band width of a region formed on a portion other than the flat bottom surface and a second-conductivity-type cladding layer arranged on the active layer are provided, the active layer has a gain. It is possible to realize a gain-coupled distributed feedback semiconductor laser that can generate a distribution and can significantly reduce the refractive index distribution, and can obtain stable single-mode oscillation that is not affected by the refractive index distribution.

Further, in the present invention, the surface formed on the first conductivity type semiconductor substrate has stripe-shaped convex portions and concave portions periodically arranged in the light guiding direction. , A first conductivity type clad layer having an uneven shape having a flat top surface on the convex portion, and formed on the flat top surface formed on the first conductivity type clad layer to a substantially uniform thickness An active layer having a forbidden band width larger than the forbidden band width of a region formed on a portion other than the flat top surface, and a second-conductivity-type cladding layer disposed on the active layer. Therefore, a gain-coupled distributed feedback semiconductor that can generate a gain distribution in the active layer and can significantly reduce the refractive index distribution and can obtain stable single-mode oscillation without being affected by the refractive index distribution. A laser can be realized.

Further, according to the present invention, the surface of the first conductivity type semiconductor substrate formed on the first conductivity type semiconductor substrate has a stripe-shaped convex portion and a concave portion for conducting light. A clad layer of the first conductivity type which is periodically arranged in a wave direction, has a flat bottom surface in the concave portion, and has a flat top surface in the convex portion, and the clad layer of the first conductivity type; A region formed on the flat bottom surface and the top top surface having a substantially uniform thickness, and a forbidden band width formed on a portion other than the flat bottom surface and the top top surface. Since the active layer having a larger forbidden band width and the second-conductivity-type cladding layer disposed on the active layer are provided, a gain-coupled distributed feedback semiconductor laser that is not affected by the refractive index distribution can be realized. Furthermore, as the period of the gain distribution, it is Can be obtained a period shorter than the shortest period of growth possible periodic structure, the oscillation wavelength can be obtained distributed feedback semiconductor laser of high performance gain coupled type is 1μm or less.

[0014]

EXAMPLES Example 1. FIG. 1 is a sectional view in the waveguide direction showing the structure of the distributed feedback semiconductor laser according to the first embodiment of the present invention. In FIG. 1, reference numeral 1a denotes a surface in which stripe-shaped concave and convex portions guide light. It is a first-conductivity-type GaAs substrate having a concavo-convex structure arranged in a waved direction at a predetermined cycle, and the first conductive type GaAs substrate is provided with (10
0) surface. 2 is formed on the substrate 1a,
It is a first conductivity type AlGaInP clad layer whose thickness is substantially uniform on the concave portion and the convex portion on the surface of the substrate 1, and its surface is flat at the bottom of the concave portion along the uneven shape of the substrate surface (100 ) It is an uneven shape having a surface. Reference numeral 3 denotes a GaInP active layer formed on the clad layer 2, the thickness of which is substantially uniform between the upper portion of the concave portion and the upper portion of the convex portion on the surface of the substrate 1, and is formed on the (100) plane of the cladding layer 2. Active layer 5 and active layer 6 formed on a plane other than the (100) plane
Including and Reference numeral 4 denotes a second conductivity type AlGaInP clad layer formed on the active layer 2, the thickness of which is uniform between the upper portion of the concave portion and the upper portion of the convex portion on the surface of the substrate 1a, and 7 is the cladding layer 4
A second conductivity type Ga formed on top of which has a flat surface
As contact layers, 11 and 12 are electrodes. Also,
The arrow 8 indicates the light guiding direction in the distributed feedback semiconductor laser according to the present embodiment.

Next, the manufacturing method will be described. First, G
Interference exposure method, EB (Electron Beam) on the aAs substrate 1a
) Photolithography is performed using an exposure method or the like, and etching is performed to form a concavo-convex structure composed of stripe-shaped concave portions and convex portions. In addition, FIB (Focused Ion Bea)
An uneven structure may be directly formed on the substrate 1a by m) or the like. At this time, a (100) plane is formed on the bottom of the recess, and a surface inclined with respect to the (100) plane is formed in a region other than the (100) plane. Then, the first conductivity type AlGaInP clad layer 2, the GaInP active layer 3, and the second conductivity type AlGa are formed on the substrate 1a having the uneven structure.
The InP clad layer 4 is continuously formed by the vapor phase epitaxy method. At this time, the width of the (100) plane of the recess of the substrate 1a is adjusted so that the (100) plane is also formed on the recess of the clad layer 2 formed on the (100) plane of the recess of the substrate 1a. I'll do it. Here, GaInP, which is a material forming the active layer of the semiconductor laser of the present embodiment, under a predetermined growth condition, in the (100) plane, the arrangement of the constituent atoms has an orderly structure with periodicity, and , Are formed in a disordered state in which the periodicity of the arrangement of the constituent atoms is disturbed on the plane inclined with respect to the (100) plane. In the vapor phase growth in the manufacturing process of the present embodiment, the active layer made of GaInP is in an ordered state in which the arrangement of the constituent atoms is periodic on the (100) plane as described above, and the (100) On a plane inclined with respect to the plane, the growth condition is such that the periodicity of the arrangement of the constituent atoms is disturbed and disordered. As a result, the ordered active layer 5 is formed at the position on the bottom surface of the recess, and the disordered active layer 6 is formed on the portion other than the bottom surface of the recess. Then, a second conductivity type GaAs contact layer 7 is grown on the second conductivity type clad layer 4, and a diffusion stripe type or a ridge type capable of confining current and light in the lateral direction with respect to the light guiding direction. After being processed into the above structure, the electrodes 11 and 12 are formed to complete the distributed feedback semiconductor laser shown in FIG.

Next, the operation will be described. When a current is passed between the substrate 1a and the contact layer 7 of the distributed feedback semiconductor laser of this embodiment shown in FIG. 1 in the forward bias direction, population inversion of carriers occurs in the active layer 3 and the carriers are recombined. Light is generated.

Here, it is known that the GaInP crystal has a band gap wider in a crystal grown in a disordered state than in a crystal grown in an ordered state. That is,
In this embodiment, the ordered active layer 5 having a narrow band gap is used.
And a disordered active layer 6 having a wide forbidden band are periodically arranged. In such a structure, most of the above-mentioned generation of light due to carrier recombination occurs. It occurs in the ordered active layer 5 having a small band gap. Therefore, in this embodiment, it is possible to obtain a gain distribution according to the period (period of the concave portion) of the concave-convex structure formed on the substrate 1a, and the gain-coupling type distributed feedback semiconductor laser operates.

As described above, the light generated in the active layer 5 on the (100) plane is guided in a direction indicated by an arrow 8 in FIG. 1 with a slight spread in the layer thickness direction and exceeds a certain current value. By the way, a resonance phenomenon occurs in the waveguide direction of the active layer 3 and laser oscillation occurs.

Further, in the semiconductor laser of this embodiment, the cladding layers 2 and 4 disposed above and below the active layer 3 are made of the same material, and the total thickness thereof is almost the same at any position in the waveguide direction. Is the same. Further, the thickness of the active layer 3 is almost the same at any position in the waveguide direction,
The disordered active layer 6 has a smaller refractive index than the disordered active layer 5, but the difference is only about 1%. Therefore,
Considering the equivalent refractive index in the vicinity of the active layer 3, there is almost no refractive index distribution in the waveguide direction, and the influence of the refractive index coupling is significantly larger than that of the conventional distributed feedback semiconductor laser shown in FIG. It can be reduced. As described above, in order to oscillate the distributed feedback type semiconductor laser having the refractive index distribution in the waveguide in the single mode, the reflectance of the laser facet is controlled so that the lowest gain mode becomes one. It is necessary to devise the structure such as doing. However, in the present embodiment, as described above, the refractive index distribution can be greatly reduced and only the gain distribution can be provided, so that the laser end face can be stabilized without any control such as controlling the reflectance. It is possible to realize simple single mode oscillation.

As described above, in the present embodiment, GaAs
A concave-convex structure having a (100) plane is formed on the surface of the substrate 1a at the bottom of the concave portion, and the surface is formed on the bottom of the concave portion along the concave-convex shape of the substrate surface on the substrate 1a. Clad layer 2 having an uneven shape having a flat (100) surface
And a forbidden band width of a region formed on the (100) plane is formed on the portion other than the (100) plane so as to have a substantially uniform thickness on the first conductivity type clad layer. The active layer 3 is crystal-grown so as to be larger than the forbidden band width of the region, ordered on the (100) plane, and disordered on a portion other than the (100) plane, and the active layer 3 on the active layer. Since it is configured to include the cladding layer 4 arranged in
Since the active layer 3 can have a gain distribution and the equivalent refractive index distribution in the vicinity of the active layer 3 in the waveguide direction can be significantly reduced, a stable single layer that is not affected by the refractive index distribution can be obtained. It is possible to realize a distributed feedback semiconductor laser that can obtain one-mode oscillation.

Example 2. FIG. 2 is a sectional view in the waveguide direction showing the structure of the distributed feedback semiconductor laser according to the second embodiment of the present invention. In the figure, 1b is a first-conductivity-type GaAs having a concavo-convex structure in which stripe-shaped concave portions and convex portions are arranged on the surface at a predetermined cycle in the direction in which light is guided.
It is a substrate, and (1
00) surface. Reference numeral 2 denotes a first conductivity type AlGaInP clad layer formed on the substrate 1b, the thickness of which is substantially uniform on the concave portion and the convex portion on the surface of the substrate 1,
The surface has an uneven shape having a flat (100) surface on the top of the convex portion along the uneven shape of the substrate surface. Reference numeral 3 denotes a GaInP active layer formed on the clad layer 2, the thickness of which is substantially uniform between the upper portion of the concave portion and the upper portion of the convex portion on the surface of the substrate 1, and is formed on the (100) plane of the cladding layer 2. And the active layer 6 formed on a surface other than the (100) surface. 4 is a second conductivity type AlGaInP clad layer formed on the active layer 2, the thickness of which is uniform between the upper part of the concave portion and the upper part of the convex portion on the surface of the substrate 1b, and 7 is formed on the clad layer 4. The second conductivity type GaAs contact layer having a flat surface, and 11 and 12 are electrodes.
Further, an arrow 9 indicates the waveguide direction of light in the distributed feedback semiconductor laser according to this embodiment.

Next, the manufacturing method will be described. In the manufacturing process of the semiconductor laser of the present embodiment, when the uneven structure is formed on the substrate, the (100) plane is formed on the top of the convex portion,
A surface inclined with respect to the (100) plane is formed in a region other than the (100) plane. The subsequent steps are exactly the same as the steps for manufacturing the semiconductor laser according to the first embodiment. That is, the first substrate is formed on the substrate 1b having the uneven structure.
The conductivity type AlGaInP clad layer 2, the GaInP active layer 3, and the second conductivity type AlGaInP clad layer 4 are continuously formed by the vapor phase growth method. Here, in the vapor phase growth, the active layer made of GaInP is formed in an ordered state on the (100) plane and in a disordered state on a plane inclined with respect to the (100) plane. Perform under growth conditions. As a result, the ordered active layer 5 is formed at a position on the top surface of the convex portion, and the disordered active layer 6 is formed on a portion other than the top surface of the convex portion. Then, a second conductivity type GaAs contact layer 7 is grown on the second conductivity type clad layer 4, and a diffusion stripe type or a ridge type capable of confining current and light in the lateral direction with respect to the light guiding direction. After processing into the above structure, the electrodes 11 and 12 are formed to complete the distributed feedback semiconductor laser shown in FIG.

Next, the operation will be described. The operation principle of this embodiment is exactly the same as that of the first embodiment. That is, when a current is passed between the substrate 1b and the contact layer 7 in FIG. 2 in the forward bias direction, population inversion of carriers occurs in the active layer 3 and light is generated by recombination of the carriers. Book second
In the second embodiment, as in the first embodiment, the active layer 5 having a narrow bandgap and disordered and the active layer 6 having a wide bandgap and disordered are periodically arranged. In such a structure, most of the above-described generation of light due to recombination of carriers occurs in the ordered active layer 5 having a small forbidden band width. Therefore, it is possible to obtain a gain distribution according to the period of the concave-convex structure formed on the substrate 1b (the period of the convex portion), and the gain-coupling type distributed feedback semiconductor laser operates. Thus (10
The light generated in the active layer 5 on the (0) plane is guided in a direction indicated by an arrow 9 in FIG. 2 with a slight spread in the layer thickness direction,
When a certain current value is exceeded, a resonance phenomenon occurs in the waveguide direction of the active layer 3 and laser oscillation occurs.

Also in the semiconductor laser of this embodiment, the cladding layers 2 and 4 disposed above and below the active layer 3 are made of the same material, and the total thickness thereof is the same as in the first embodiment. It is almost the same at any position in the waveguide direction, and the thickness of the active layer 3 is also substantially the same at any position in the waveguide direction. Therefore, similar to the first embodiment, there is almost no refractive index distribution in the waveguide direction, and the influence of refractive index coupling is greatly reduced as compared with the conventional distributed feedback semiconductor laser shown in FIG. Therefore, single mode oscillation can be realized without any ingenuity such as controlling the reflectance of the laser end face.

As described above, in this embodiment, GaAs is used.
On the surface of the substrate 1b, a concavo-convex structure having a (100) plane is formed on the top of the convex part, and the concavo-convex structure having a predetermined period is formed on the substrate 1b. A region formed on the (100) plane so as to have a substantially uniform thickness on the clad layer 2 having an uneven shape having a flat (100) plane on the top and the first conductivity type clad layer. So that the forbidden band width of is larger than the forbidden band width of the region formed on the portion other than the (100) plane, so as to be ordered on the (100) plane, and on the portion other than the (100) plane. Since the active layer 3 crystal-grown to be disordered and the cladding layer 4 arranged on the active layer are provided, the active layer 3 can have a gain distribution, and the waveguide The equivalent refractive index distribution in the vicinity of the active layer 3 can be significantly reduced. Since that, the same as the first embodiment, is not affected by the refractive index distribution can be realized a stable single-mode distributed feedback semiconductor laser oscillation is obtained.

Example 3. FIG. 3 is a sectional view in the waveguide direction showing the structure of the distributed feedback semiconductor laser according to the third embodiment of the present invention. In the figure, reference numeral 1c denotes a first-conductivity-type GaAs substrate having a concavo-convex structure in which stripe-shaped concave portions and convex portions are arranged at a predetermined period in a light guiding direction, and the concave-convex structure is formed. It has a (100) plane on the bottom of the concave portion and on the top of the convex portion. Reference numeral 2 denotes a first conductivity type AlGaInP clad layer formed on the substrate 1c, the thickness of which is substantially uniform on the concave portion and the convex portion of the surface of the substrate 1, and the surface thereof has an uneven shape on the substrate surface. Along the bottom of the concave portion and the top of the convex portion are flat and uneven (100) faces. Reference numeral 3 denotes a GaInP active layer formed on the clad layer 2, the thickness of which is substantially uniform between the upper portion of the concave portion and the upper portion of the convex portion on the surface of the substrate 1. The active layer 5 is formed on the top of the (100) plane, and the active layer 6 is formed on the top of the plane other than the (100) plane. Reference numeral 4 is a second conductivity type AlGaInP clad layer formed on the active layer 2 and having a uniform thickness in the upper part of the concave portion and the upper part of the convex portion on the surface of the substrate 1c, and 7 is formed on the clad layer 4. The second conductivity type GaAs contact layer having a flat surface, and 11 and 12 are electrodes. Further, arrows 8 and 9 indicate the waveguide directions of light in the distributed feedback semiconductor laser according to the present embodiment.

Next, the manufacturing method will be described. In the method of manufacturing a semiconductor laser according to the present embodiment, when the concave-convex structure is formed on the substrate, the (100) plane is formed on the bottom of the concave portion and on the top of the convex portion, and in the regions other than the (100) plane, (10
The surface inclined to the (0) plane is formed. The subsequent steps are exactly the same as the steps for manufacturing the semiconductor laser according to the first embodiment. That is, the first conductivity type AlGaInP cladding layers 2 and G are formed on the substrate 1c having the uneven structure.
The aInP active layer 3 and the second conductivity type AlGaInP cladding layer 4 are continuously formed by the vapor phase growth method. Here, in the vapor phase growth, the active layer made of GaInP is
In the (100) plane, it is in an ordered state, and (10
The growth conditions are such that they are formed in a disordered state on the plane inclined with respect to the (0) plane. As a result, the ordered active layer 5 is formed at a position on the top surface of the convex portion, and the disordered active layer 6 is formed on a portion other than the top surface of the convex portion.
Then, the second conductivity type GaA is formed on the second conductivity type cladding layer 4.
After the s contact layer 7 is grown and processed into a structure such as a diffusion stripe type or a ridge type capable of confining current and light in the lateral direction with respect to the light guiding direction, the electrodes 11, 1 are formed.
2 is formed to complete the distributed feedback semiconductor laser shown in FIG.

Next, the operation will be described. In the third embodiment, the active layer 5 is formed on the bottom of the recess and the (100) plane provided on the top of the projection of the concave-convex structure on the surface of the substrate 1.
Are formed in a disordered state, and the active layer 6 is formed in a disordered state on the other portion, that is, on the upper portion of the surface inclined with respect to the (100) plane. As a result, light is generated in the active layer 5 formed on the upper (100) surface of the bottom of the concave portion and the active layer 5 formed on the upper (100) surface of the convex portion, and each of them is shown in FIG. Arrow 8
And 9 are guided. Where (100) of the recess
The light generated by the active layer 5 formed on the upper surface of the surface and the light generated by the active layer 5 formed on the upper surface of the (100) surface of the convex portion are slightly near the active layer 3 in the layer thickness direction. Of the active layer 5 formed on the upper part of the (100) plane of the concave portion and (1) of the convex portion as a whole.
It can be regarded as one guided light in which a gain is generated by both the active layer 5 formed on the upper part of the (00) plane. That is, the cycle of the gained portion of the active layer 3 is half the cycle of the uneven structure on the surface of the substrate 1c. As a result, the period of the gain distribution is shorter than the shortest period of the diffraction grating that can be formed by the interference exposure method, which is currently known as a simple concavo-convex structure forming method.

In a distributed feedback semiconductor laser that oscillates at a wavelength that is as long as the period of the diffraction grating, in order to obtain a wavelength in the visible light region, the period of the diffraction grating must be 0.1 μm or less. It is very difficult to obtain such a laser by the photoengraving technique using the. Book Third
In the distributed feedback semiconductor laser according to the embodiment, since the period of the gain distribution can be made shorter than the period of the diffraction grating (concavo-convex structure) formed on the substrate as described above, at a wavelength of 1 μm or less including the visible light region. A distributed feedback semiconductor laser that oscillates can be easily realized.

Also in the semiconductor laser of this embodiment, the cladding layers 2 and 4 disposed above and below the active layer 3 are made of the same material, as in the first and second embodiments.
The total thickness is substantially the same at any position in the waveguide direction, and the thickness of the active layer 3 is also substantially the same at any position in the waveguide direction. Therefore, similar to the first and second embodiments, there is almost no refractive index distribution in the waveguide direction, and the influence of the refractive index coupling is significantly larger than that of the conventional distributed feedback semiconductor laser shown in FIG. The single mode oscillation can be realized without making any adjustments such as controlling the reflectance of the laser end face.

As described above, in this embodiment, GaAs
On the surface of the substrate 1c, on the bottom of the concave portion and on the top of the convex portion (1
00) surface is formed in a predetermined cycle, and the surface of the substrate 1c follows the uneven shape of the substrate surface.
On the bottom surface of the concave portion and on the top of the convex portion, the clad layer 2 having an uneven shape having a flat (100) surface, and on the first conductivity type clad layer, a uniform thickness is provided, and (10
The forbidden band width of the region formed on the (0) plane is larger than the forbidden band width of the region formed on the portion other than the (100) plane, so that the forbidden band is ordered on the (100) plane. 10
0) The active layer 3 which is crystal-grown so as to be disordered on a portion other than the plane, and the cladding layer 4 which is arranged on the active layer 3.
Since the active layer 3 has a gain distribution and the equivalent refractive index distribution in the vicinity of the active layer 3 in the waveguide direction can be significantly reduced,
Similar to the first embodiment, it is possible to realize a distributed feedback semiconductor laser which is not affected by the refractive index distribution and which can obtain stable single mode oscillation. Furthermore, in the present embodiment, the period of the gained portion can be set to half the period of the uneven structure on the surface of the substrate 1c, which is shorter than the shortest wavelength of the laser light obtained by the conventional distributed feedback semiconductor laser. It is possible to realize a distributed feedback semiconductor laser that can obtain laser light of a wavelength.

Example 4. FIG. 4 is a sectional view in the waveguide direction showing the structure of the distributed feedback semiconductor laser according to the fourth embodiment of the present invention. In the figure, 31 is the first conductivity type GaA.
s substrate, 32a is a first conductivity type AlGaInP formed on the substrate 31 and having a concavo-convex structure of a predetermined period on its surface.
It is a clad layer, and it is (10
0) surface. Reference numeral 33 denotes a GaInP active layer formed on the clad layer 32a so as to have a uniform thickness, and an active layer 35 formed on the (100) plane of the recess on the surface of the clad layer 32a and other than the (100) plane. And an active layer 36 formed on the surface. A second conductivity type AlGaIn 34 is formed on the active layer 33 and has a flat surface.
The P clad layer, 37 is a second conductivity type GaAs contact layer formed on the clad layer 34, and 11 and 12 are electrodes. An arrow 38 indicates the light guiding direction in the distributed feedback semiconductor laser according to this embodiment.

Next, the operation will be described. The operation principle of this embodiment is exactly the same as that of the first embodiment. That is, when a current is passed between the substrate 31 and the contact layer 37 in FIG. 2 in the forward bias direction, population inversion of carriers occurs in the active layer 33, and light is generated by recombination of the carriers. Also in the fourth embodiment, similarly to the first embodiment, the ordered active layer 35 having a narrow bandgap and the active layer 36 having a wide bandgap and disordered are periodically arranged. In such a structure, most of the above-described generation of light due to carrier recombination occurs in the ordered active layer 35 having a small forbidden band width.
Therefore, it is possible to obtain a gain distribution according to the cycle of the concave-convex structure formed in the clad layer 32a (the cycle of the concave portions),
It operates as a gain-coupled distributed feedback semiconductor laser.
Also in the semiconductor laser of this embodiment, as in the first embodiment, the cladding layers 32a and 34 disposed above and below the active layer 33 are made of the same material, and the total thickness thereof is in the waveguide direction. Is almost the same at any position of
Further, the thickness of the active layer 33 is almost the same at any position in the waveguide direction. Therefore, similar to the first embodiment, there is almost no refractive index distribution in the waveguide direction, and the influence of refractive index coupling is greatly reduced as compared with the conventional distributed feedback semiconductor laser shown in FIG. Therefore, single mode oscillation can be realized without any ingenuity such as controlling the reflectance of the laser end face. Furthermore, in the first embodiment, as shown in FIG. 1, the guided light passes through the GaAs substrate having a smaller forbidden band width than the active layer 3, so that the substrate 1 is guided while the light is guided. It is considered that the laser characteristics are deteriorated by being absorbed by the laser light and increasing the threshold current. In the fourth embodiment, the light generated in the active layer 35 on the (100) plane is As indicated by the arrow 38 inside,
Since only the layer made of a material having a forbidden band width larger than that of the active layer is guided, light is not absorbed while being guided as in the first embodiment, and the characteristics are excellent. A distributed feedback semiconductor laser can be realized.

Example 5. FIG. 5 is a sectional view in the waveguide direction showing the structure of the distributed feedback semiconductor laser according to the fifth embodiment of the present invention. In the figure, 31 is the first conductivity type GaA.
s substrate, 32b is a first conductivity type AlGaInP formed on the substrate 31 and having a concavo-convex structure of a predetermined period on its surface.
It is a clad layer, and it is (10
0) surface. Reference numeral 33 denotes a GaInP active layer formed on the clad layer 32b so as to have a uniform thickness, and an active layer 35 formed on the (100) plane of the convex portion on the surface of the clad layer 32b and a (100) plane. And an active layer 36 formed on the other surface. A second conductivity type AlGaIn 34 is formed on the active layer 33 and has a flat surface.
The P clad layer, 37 is a second conductivity type GaAs contact layer formed on the clad layer 34, and 11 and 12 are electrodes. An arrow 39 indicates the light guiding direction in the distributed feedback semiconductor laser according to this embodiment.

Next, the operation will be described. The operating principle of this embodiment is exactly the same as that of the second embodiment. That is, when a current is passed between the substrate 31 and the contact layer 37 in FIG. 5 in the forward bias direction, population inversion of carriers occurs in the active layer 33, and light is generated by recombination of the carriers. Also in the fourth embodiment, similarly to the second embodiment, the active layer 35 having a narrow bandgap and disordered and the active layer 36 having a wide bandgap and disordered are periodically arranged. In such a structure, most of the above-described generation of light due to carrier recombination occurs in the ordered active layer 35 having a small forbidden band width.
Therefore, it is possible to obtain a distribution of gain according to the cycle of the concave-convex structure formed in the clad layer 32a (the cycle of convex portions),
It operates as a gain-coupled distributed feedback semiconductor laser.
Also in the semiconductor laser of this embodiment, as in the second embodiment, the cladding layers 32b and 34 disposed above and below the active layer 33 are made of the same material, and the total thickness thereof is in the waveguide direction. Is almost the same at any position of
Further, the thickness of the active layer 33 is almost the same at any position in the waveguide direction. Therefore, similar to the second embodiment, there is almost no refractive index distribution in the waveguide direction, and the influence of the refractive index coupling is greatly reduced as compared with the conventional distributed feedback semiconductor laser shown in FIG. Therefore, single mode oscillation can be realized without any ingenuity such as controlling the reflectance of the laser end face. Further, in the second embodiment, as shown in FIG. 2, since the guided light passes through the GaAs contact layer 7 having a smaller forbidden band width than the active layer 3, the light is guided while being guided. It may be absorbed by the contact layer 7 and deteriorate the laser characteristics.
In the fifth embodiment, the light generated in the active layer 35 on the (100) plane is guided only to a layer made of a material having a forbidden band width larger than that of the active layer, as indicated by an arrow 39 in FIG. Since it is waved, it is possible to realize a distributed feedback semiconductor laser having excellent characteristics without being absorbed while the light is guided as in the second embodiment.

Example 6. FIG. 6 is a sectional view in the waveguide direction showing the structure of a distributed feedback semiconductor laser according to a sixth embodiment of the present invention. In the figure, 31 is the first conductivity type GaA.
s substrate, 32c is a first conductivity type AlGaInP formed on the substrate 31 and having an uneven structure of a predetermined period on the surface thereof.
It is a clad layer, and has a (100) plane on the bottom of the concave portion and the top of the convex portion of the uneven structure. 33 is Ga formed on the clad layer 32c so as to have a uniform thickness.
An active layer 35 which is an InP active layer and is formed on the (100) plane of the concave and convex portions on the surface of the cladding layer 32c;
0) surface and the active layer 36 formed on a surface other than the surface. Three
Reference numeral 4 is a second conductivity type AlGaInP cladding layer formed on the active layer 33 and having a flat surface, 37 is a second conductivity type GaAs contact layer formed on the cladding layer 34, and 11 and 12 are electrodes. . Further, arrows 38 and 39 indicate the waveguide directions of light in the distributed feedback semiconductor laser according to this embodiment.

Next, the operation will be described. The operation principle of this embodiment is exactly the same as that of the third embodiment. That is, when a current is passed between the substrate 31 and the contact layer 37 in FIG. 6 in the forward bias direction, population inversion of carriers occurs in the active layer 33, and light is generated by recombination of the carriers. Also in the sixth embodiment, as in the third embodiment, it is provided on the bottom of the concave portion and the top of the convex portion of the concavo-convex structure (10).
The active layer 35 is formed in an ordered state on the (0) plane, and the active layer 36 is disordered on the other portion, that is, on the plane inclined with respect to the (100) plane. It is formed in the state. This allows the (100)
Light is generated in the active layer 35 formed on the upper surface of the surface and the active layer 35 formed on the upper surface of the (100) surface on the top of the convex portion and guided in the directions of arrows 38 and 39 in FIG. 6, respectively. As a whole, as a single guided light, gain is produced by both the active layer 35 formed on the upper part of the (100) plane of the concave portion and the active layer 35 formed on the upper side of the (100) surface of the convex portion. Guided. In other words, the period of the active layer 33 having a gain is half the period of the uneven structure on the surface of the cladding layer 32c. As a result, the period of the gain distribution is shorter than the shortest period of the diffraction grating that can be formed by the interference exposure method, which is currently known as a simple concavo-convex structure forming method. Also in the semiconductor laser of this embodiment, as in the third embodiment, the cladding layers 32c and 34 disposed above and below the active layer 33 are made of the same material, and the total thickness thereof is in the waveguide direction. Is almost the same at any position, and the thickness of the active layer 33 is also substantially the same at any position in the waveguide direction. Therefore, similar to the second embodiment, there is almost no refractive index distribution in the waveguide direction, and the influence of the refractive index coupling is greatly reduced as compared with the conventional distributed feedback semiconductor laser shown in FIG. Therefore, single mode oscillation can be realized without any ingenuity such as controlling the reflectance of the laser end face. Further, in the third embodiment, as shown in FIG. 3, since the guided light passes through the GaAs substrate 1c and the GaAs contact layer 7 having a forbidden band width smaller than that of the active layer 3, the light is guided. Ga during
It may be absorbed by the As substrate 1c and the GaAs contact layer 7 to cause deterioration of laser characteristics.
In the sixth embodiment, light generated in the active layer 35 on the (100) plane is generated only in a layer made of a material having a forbidden band width larger than that of the active layer, as indicated by arrows 38 and 39 in FIG. As described in the third embodiment, a distributed feedback semiconductor laser having excellent characteristics can be realized without being absorbed while the light is guided.

In each of the above-mentioned embodiments, the bottom surface of the stripe-shaped concave portion or the top surface of the stripe-shaped convex portion provided on the surface of the substrate or the surface of the clad layer is (10)
Although the case where the (0) plane is used has been described, the present invention can be applied to the case where the bottom surface or the top surface is all the planes equivalent to the (100) plane, that is, the {100} plane. The same effect as the example can be obtained.

Further, in each of the above embodiments, the bottom surface of the stripe-shaped concave portion or the top surface of the stripe-shaped convex portion provided on the surface of the substrate or the surface of the clad layer is set to (10).
Although the case of using the (0) plane has been described, GaInP used as the material of the active layer is disordered and formed on the plane inclined with respect to the {100} plane.
It is known that the larger the inclination with respect to the 0} plane, the larger the degree of disordering and the larger the band gap. Therefore, in the present invention, the bottom face or the top face does not necessarily have to be the {100} face, and the angle formed with the {100} face is such that a face other than the bottom face or the top face is the {100} face. If the angle is equal to or less than the angle formed, the active layer formed on the upper surface of the bottom surface or the top surface is disordered to a small degree with respect to the active layer formed on the surface other than the bottom surface or the top surface. The same effects as those of the above-mentioned respective embodiments can be obtained.

[0040]

As described above, according to the present invention, the stripe-shaped convex portions and concave portions formed on the first conductivity type semiconductor substrate are periodically arranged in the light guiding direction. A first conductivity type clad layer having an uneven shape having a flat bottom surface in the recess, and the flat bottom surface formed on the first conductivity type clad layer to have a substantially uniform thickness. An active layer having a forbidden band width larger than the forbidden band width of a region formed on a portion other than the flat bottom surface, and a second-conductivity-type cladding layer disposed on the active layer. Since it is provided, the gain distribution can be generated in the active layer, the refractive index distribution can be greatly reduced, and a stable single-mode oscillation that is not affected by the refractive index distribution can be obtained. There is an effect that a semiconductor laser can be realized.

Further, according to the present invention, the surface formed on the first conductivity type semiconductor substrate has stripe-shaped convex portions and concave portions periodically arranged in the light guiding direction. And a first conductivity type clad layer having an uneven shape having a flat top surface on the convex portion, and a flat top surface formed on the first conductivity type clad layer with a substantially uniform thickness. An active layer having a forbidden band width larger than the forbidden band width of a region formed on a portion other than the flat top surface, and a second conductivity type clad layer disposed on the active layer; Since it is provided, the gain distribution can be generated in the active layer, the refractive index distribution can be greatly reduced, and a stable single-mode oscillation that is not affected by the refractive index distribution can be obtained. There is an effect that a semiconductor laser can be realized.

Further, according to the present invention, the surface of the first conductivity type semiconductor substrate formed on the first conductivity type semiconductor substrate has stripe-shaped convex portions and concave portions for guiding light. A clad layer of the first conductivity type which is periodically arranged in a wave direction, has a flat bottom surface in the concave portion, and has a flat top surface in the convex portion, and the clad layer of the first conductivity type; A region formed on the flat bottom surface and the top top surface having a substantially uniform thickness, and a forbidden band width formed on a portion other than the flat bottom surface and the top top surface. Since the active layer having a larger forbidden band width and the second-conductivity-type cladding layer disposed on the active layer are provided, a gain-coupled distributed feedback semiconductor laser that is not affected by the refractive index distribution can be realized. Furthermore, as the period of the gain distribution, it is Can be obtained a period shorter than the shortest period of growth possible periodic structure, an oscillation wavelength is effective can be obtained distributed feedback semiconductor laser of high performance gain coupled type is 1μm or less.

[Brief description of drawings]

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

FIG. 2 is a sectional view showing the structure of a distributed feedback laser according to a second embodiment of the present invention.

FIG. 3 is a sectional view showing the structure of a distributed feedback laser according to a third embodiment of the present invention.

FIG. 4 is a sectional view showing the structure of a distributed feedback laser according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view showing the structure of a distributed feedback laser according to a fifth embodiment of the present invention.

FIG. 6 is a sectional view showing the structure of a distributed feedback laser according to a sixth embodiment of the present invention.

FIG. 7 is a cross-sectional view showing the structure of a conventional distributed feedback laser diode.

[Explanation of symbols]

1a, 1b, 1c 1st conductivity type GaAs semiconductor substrate 2 1st conductivity type AlGaInP clad layer 3 GaInP active layer 4 2nd conductivity type AlGaInP clad layer 5 Ordered active layer 6 Disordered active layer 8 9 Light conduction Wave direction 11,12 Electrode 31 First conductivity type GaAs semiconductor substrate 32a, 32b, 32c First conductivity type AlGaInP clad layer 33 GaInP active layer 34 Second conductivity type AlGaInP clad layer 35 Ordered active layer 36 Disordered active layer 37 Second conductivity type GaAs contact layer 38, 39 Waveguide direction of light

Claims (6)

[Claims] 1. In a distributed feedback semiconductor laser, stripe-shaped convex portions and concave portions formed on a first conductivity type semiconductor substrate are periodically arranged in a light guiding direction. The first conductivity type clad layer having an uneven shape having a flat bottom surface in the recess, and the flat bottom surface formed on the first conductivity type clad layer with a substantially uniform thickness. An active layer having a forbidden band width larger than the forbidden band width of the region formed on a portion other than the flat bottom surface, and a second conductivity type cladding layer disposed on the active layer. A distributed feedback semiconductor laser. 2. In a distributed feedback semiconductor laser, stripe-shaped convex portions and concave portions formed on a first conductivity type semiconductor substrate are periodically arranged in a light guiding direction. The first conductivity type clad layer having an uneven shape having a flat top surface on the convex portion, and the flat top surface formed on the first conductivity type clad layer with a substantially uniform thickness. An active layer having a forbidden band width larger than the forbidden band width of a region formed on a portion other than the flat top surface, and a second-conductivity-type clad layer disposed on the active layer. A distributed feedback semiconductor laser, comprising: 3. In a distributed feedback semiconductor laser, stripe-shaped convex portions and concave portions formed on a first conductivity type semiconductor substrate are periodically arranged in a light guiding direction. And a concave-convex first conductivity type clad layer having a flat bottom surface in the concave portion and a flat top surface in the convex portion, and a substantially uniform thickness formed on the first conductivity type clad layer. And an active layer in which the forbidden band width of the region formed on the flat bottom surface and the top surface is larger than the forbidden band width of the region formed on a portion other than the flat bottom surface and the top surface. A distributed feedback semiconductor laser, comprising: a second conductivity type clad layer disposed on the active layer. 4. The distributed feedback semiconductor laser according to claim 1, wherein the active layer has a flat surface so as to be ordered or disordered to a minute degree on the flat surface. A distributed feedback semiconductor laser, which is characterized by being crystal-grown so as to be disordered to a greater extent than on the flat surface on portions other than the above. 5. The distributed feedback semiconductor laser device according to claim 1, wherein the material of the active layer is GaInP. 6. The distributed feedback semiconductor laser device according to claim 1, wherein the flat surface is the (100) surface, and the surfaces other than the flat surface are relative to the (100) surface. A distributed feedback semiconductor laser, which is characterized by having an inclined surface.