JP4554247B2 - Surface emitting semiconductor laser device - Google Patents

Description

  The present invention relates to a surface emitting semiconductor laser device that emits laser light from the front surface or the back surface side of a semiconductor substrate, and a manufacturing method and a manufacturing device therefor. More specifically, the present invention relates to a surface emitting semiconductor laser device that emits laser light having a stable polarization direction.

2. Description of the Related Art A surface emitting semiconductor laser device (hereinafter abbreviated as a laser device) that emits laser light from the surface side of a semiconductor substrate is known. This type of laser device has higher coupling efficiency with an optical fiber and can be easily integrated two-dimensionally than an edge-emitting laser device that emits laser light from the end surface of a semiconductor substrate. It has the advantages such as. As an example of this type of laser apparatus, a feedback distribution type laser apparatus having a diffraction grating in the optical waveguide of the laser apparatus is known, and an example thereof is described in Patent Document 1.
Japanese Patent Application Laid-Open No. 10-209554 (see FIG. 1 of that publication)

FIG. 15 is a cross-sectional view of a main part of a feedback distributed laser device. The laser device includes a lower cladding layer 224, an active layer 226 stacked on the lower cladding layer 224, and an upper cladding layer 228 stacked on the active layer 226. A laminated structure in which an active layer 226 is formed between a pair of clad layers 224 and 228 is provided.
A diffraction grating 232 is formed between the active layer 226 and the upper cladding layer 228, and the diffraction grating 232 is formed in a plane parallel to the active layer 226. This laminated structure functions as a resonator.
FIG. 16 shows a schematic configuration diagram of the diffraction grating 232 group in plan view. The solid line in the figure corresponds to the diffraction grating 232. A plurality of concentric diffraction gratings 232 are formed in common from the center toward the periphery. The distance from the center to each diffraction grating 232 is uniform with respect to the diffraction grating 232 regardless of the orientation from the center.
As shown in FIG. 15, the upper cladding layer 228 of this laser device is connected to the upper electrode 244 via the ohmic contact layer 229. The upper electrode 244 is formed to surround the ohmic contact layer 229 so as to surround the diffraction grating 232 group. The lower cladding layer 224 is in contact with the semiconductor substrate 222, and a lower electrode 242 is formed on the back surface of the semiconductor substrate 222. The lower electrode 242 is formed on the entire back surface of the semiconductor substrate 222.

When a positive voltage is applied to the lower electrode 242 to inject current into the active layer 226, light generated by electron-hole coupling propagates in the surface of the active layer 226 and gradually amplifies the gain due to stimulated emission. It will be done. At this time, a part of the light is periodically reflected by the diffraction grating 232 group periodically formed in the vicinity of the active layer 226, and the peaks and valleys of the incident light and the reflected light and the valleys and valleys overlap. Only single frequency light oscillates.
A part of the light amplified by the gain is diffracted by the diffraction grating 232 to the surface side of the semiconductor substrate 222. As indicated by the arrows in FIG. 15, the diffracted light is emitted from the surface side of the semiconductor substrate 222. With this operation, this laser device realizes that laser light is emitted from the surface side of the conductor substrate 222.
As shown in FIG. 16, the light that is fed back and repeatedly amplified by the diffraction grating 232 group repeats reciprocation along the diameter direction of the diffraction grating 232 group, and the reciprocation direction occurs with a probability equal to 360 °. Accordingly, a laser beam having the light intensity peak at the center of the diffraction grating 232 group is emitted.

Since the conventional diffraction grating 232 group described above is formed point-symmetrically with a common center, there is no gain region anisotropy in the plane on which the diffraction grating 232 is formed. Therefore, there is a problem that the polarization direction of the emitted laser light is not determined (broken line arrow in FIG. 16). That is, there arises a problem that the polarization direction varies from laser device to laser device due to manufacturing tolerances of the laser device to be manufactured, and a problem that the polarization direction is not determined depending on the operating environment (for example, temperature). If the polarization direction is not determined, for example, when used in an optical fiber or a laser processing apparatus, there arises a problem that the signal becomes unstable or cannot be processed in a desired shape.
An object of the present invention is to provide a laser device that emits laser light having a stable polarization direction.

The laser device of the present invention has a laminated structure in which an active layer is formed between a pair of clad layers. The laminated structure is provided on the upper surface of the transparent semiconductor substrate. A diffraction grating is formed in a diffraction grating layer provided above the laminated structure and extending in parallel with the active layer. The diffraction grating is formed within the distance reached by the light generated in the active layer. Furthermore, the laser device of the present invention includes an upper electrode facing the laminated structure through the diffraction grating layer, and a lower electrode formed around a region where the lower surface of the transparent semiconductor substrate is exposed. The upper electrode has a contact region in contact with the diffraction grating, and the contact region is formed within a range surrounded by the outermost diffraction grating.
The diffraction grating is formed so as to surround the center, and the distance from the center to the diffraction grating varies depending on the orientation from the center. For example, a diffraction grating having a shape such as a square, a rectangle, a triangle, or an ellipse surrounding the center is formed. In addition, when the diffraction grating is not formed in a specific direction, it can be said that the distance to the diffraction grating in the specific direction is infinite. Even if not a diffraction grating formed in a specific orientation, ing to the distance from the center to the diffraction grating varies depending on the orientation of the center.

The light generated in the active layer is reflected by the diffraction grating and reciprocates across the center. By reciprocating, a gain by stimulated emission is repeatedly obtained, the light intensity is gradually amplified, and finally laser oscillation occurs. A part of the laser-oscillated light is diffracted by the diffraction grating and emitted in the vertical direction to the laminated structure. As a result, a laser beam having a light intensity peak at the center of the diffraction grating is emitted.
If the distance from the center to the diffraction grating is uniform regardless of the orientation from the center as in the conventional structure, the generated light will be fed back uniformly in any orientation and oscillate. The polarization direction is not determined. The polarization direction is unstable.
According to the present invention, the distance from the center to the diffraction grating changes depending on the orientation from the center. Therefore, the gain obtained by the azimuth is different (has anisotropy), and as a result, the polarization direction is stabilized in a predetermined direction.
Further, in the surface emitting semiconductor laser device described above, laser light is emitted from the lower electrode side. That is, the laser light diffracted by the diffraction grating passes through the transparent semiconductor substrate and is emitted from the lower surface exposed to the outside. Laser light is emitted from the opposite direction to the conventional structure.
In the present invention, a lower electrode is formed around the laser beam exit, and current is injected using this lower electrode. Since the semiconductor substrate of the present invention is thick and current is injected into the active layer in a balanced manner even when the lower electrode is formed in the periphery, the emitted laser light is likely to be in the fundamental transverse mode.
When laser light is emitted from the upper electrode side as in the conventional structure shown in FIG. 15, the current injected into the active layer becomes stronger on the peripheral side of the diffraction grating because the thickness of the upper cladding layer is small. For this reason, there is a problem that a strong gain is given on the peripheral side and laser light of a higher order mode is emitted. When it is desired to make the light extraction port have a large diameter, the unbalance of the current injected near the center and the peripheral side becomes large, which is a particular problem. Also known is a laser device in which a small disk-shaped upper electrode is formed so as to cover the center of the diffraction grating in place of the upper electrode shown in FIG. 15 so that a current is injected in a balanced manner into the active layer. Yes. However, in this case, the disk-shaped upper electrode itself shields the laser beam, and there is a problem that the light intensity distribution of the emitted laser beam becomes a ring shape.
In the present invention, by forming the laser beam extraction port on the lower electrode side, the above problem can be avoided and the laser beam in the basic transverse mode can be emitted.
In the gain region near the center of the diffraction grating, the fundamental transverse mode is likely to stand, and higher order modes are likely to stand near the center. Therefore, it is preferable that the current is well injected into the active layer located near the center of the diffraction grating. According to the present invention, since the upper electrode is formed in the range from the center of the diffraction grating to the outermost diffraction grating, the current is often injected near the center of the diffraction grating, and the laser in the fundamental transverse mode Make it easier to emit light.

The diffraction grating preferably includes an azimuth range having a uniform distance from the center and an azimuth range having a distance different from the uniform distance. A plurality of azimuth ranges each having a uniform distance from the center and different azimuth ranges may be formed. Basically, when a concentric diffraction grating is formed and a diffraction grating is not formed in a specific orientation, the distance from the center to the diffraction grating is infinite in the specific orientation, and thus the above requirement is satisfied. The specific orientation in which the diffraction grating is not formed may be one of 360 ° or two or more orientations.
In an azimuth range where the distance from the center is uniform, the diffraction grating surrounds the center and is formed in an arc shape. Since the distance from the center to the diffraction grating is uniform, light of the same frequency resonates in this azimuth range. A single frequency laser beam can be oscillated. On the other hand, the specific orientation has a different gain characteristic. If the distance to the diffraction grating is infinite in a specific orientation, no gain characteristics are obtained. Accordingly, laser light reflecting the anisotropy of the gain characteristic is emitted, and the polarization direction of the emitted laser light is stabilized. A laser beam having a single wavelength and a stable polarization direction can be emitted.

The diffraction grating preferably has a uniform distance from the center in the first azimuth range. In the second azimuth range adjacent to the first azimuth range, it is preferable that the distance from the center to the diffraction grating is substantially infinite. Further, in the third azimuth range that is symmetrical to the first azimuth range with respect to the center, the distance from the center to the diffraction grating is preferably the same uniform distance as the first azimuth range. In the fourth azimuth range symmetrical to the second azimuth range with respect to the center, it is preferable that the distance from the center to the diffraction grating is substantially infinite.
In the first azimuth range and the third azimuth range, concentric diffraction gratings are formed at symmetrical positions across the center. Accordingly, in this azimuth range, a gain is given by repeating light reciprocating across the center, and laser oscillation can be obtained. As a result, a laser beam having a light intensity peak at the center is emitted. In addition, since an arc-shaped diffraction grating is used, the frequency of the oscillating laser is aligned with a single wavelength.
On the other hand, in the azimuth range formed by the second orientation range and the fourth azimuth range, Ru unreturned region der gain is not given. In the non-feedback region, no light of any frequency is fed back, so that the laser light oscillates only in the first azimuth range and the third azimuth range. Laser light emitted from this laser device has a single frequency.

It is preferable that a crest portion or a trough portion constituting the diffraction grating is formed in multiples around the center. That is, preferably the mountain portion or valley portion constituting the diffraction grating toward the periphery from the center are repeatedly formed.
When the above configuration is provided, the light returning while obtaining the gain across the center is periodically reflected by the diffraction grating group. Therefore, it becomes easy to oscillate at a single frequency, and so-called vertical single mode is easily realized.

It is preferable that the interval between the peak portions or the valley portions constituting the diffraction grating formed in multiple numbers around the center is narrow near the center and widely adjusted around the center.
When the interval between the peak or valley portions constituting the diffraction grating is changed from the center toward the periphery, a phase difference occurs in the laser light diffracted and emitted by each diffraction grating, and the focal point is focused at a predetermined position. It becomes like this. Laser light can be condensed without using a separate condensing optical system.

Since the surface emitting semiconductor laser device can emit laser light from the front surface or the back surface side of the semiconductor substrate, a laser array in which a plurality of surface emitting semiconductor laser devices are two-dimensionally integrated can be easily configured. It is preferable that the laser array and the condensing optical system are combined so that the laser light emitted from the laser array is focused at a predetermined position and used as a light source of the laser processing apparatus.
According to the above configuration, the polarization directions of the laser beams emitted from the laser array can be aligned by matching the polarization directions of the plurality of surface emitting semiconductor lasers. Alternatively, laser light that is not substantially polarized can be obtained by dispersing the polarization directions of a plurality of surface emitting semiconductor lasers on average. By using laser light having a stable polarization direction or laser light that is not substantially polarized, laser processing can be performed with a desired processing shape with high accuracy.

The present inventors have also created a new manufacturing method capable of easily forming concentric diffraction gratings. In this manufacturing method, the photoresist layer formed on the diffraction grating formation surface is exposed using an interference optical system that forms a Newton ring.
The interference optical system is not particularly limited. For example, a transparent member in which a concave portion and / or a convex portion are formed on both or one contact surface of a pair of transparent members and the distance between the two is changed in order from the center is used. can do.
According to the above manufacturing method, the photoresist layer is exposed along the Newton ring. For example, when a positive resist is used as the photoresist, the exposed photoresist layer is removed. When anisotropic etching is performed in this state, a groove is formed below the portion where the photoresist layer has been removed, and a concentric diffraction grating corresponding to the Newton ring is formed. By using the manufacturing method of the present invention, a concentric diffraction grating can be easily formed.
In the conventional method for forming a diffraction grating, an electron beam or the like is used. However, the exposure process takes time, and expensive equipment is used, which is a problem in terms of cost. According to the manufacturing method of the present invention, a concentric diffraction grating can be formed on the photoresist layer without using an expensive device and substantially by a single exposure. In addition to shortening the exposure process, this is effective in terms of cost.

When exposed through a transparent panel in which conical recesses or protrusions are dispersedly arranged, a large number of Newton rings can be formed at one time. When the photoresist layer is exposed using this phenomenon, a group of surface-emitting semiconductor devices having concentric diffraction gratings can be manufactured at a time.
In this case, a concentric Newton ring is formed in the photoresist layer by the angle θ formed by the conical concave or convex slope, based on the relationship of the following equation.
θ = tan ^-1 (λ / 2Λ)
λ is the wavelength of light to be irradiated, and Λ is the interval between Newton rings formed in the photoresist layer. Based on the above relational expression, the photoresist layer can be easily exposed concentrically.
According to the above manufacturing method, a plurality of Newton rings can be exposed to the photoresist layer at a time. A plurality of diffraction gratings can be manufactured simultaneously, and the manufacturing process becomes efficient.

It can be said that the inventors also created a photoresist exposure apparatus that embodies the above-described method.
That is, a photoresist exposure apparatus having a built-in interference optical system for forming a Newton ring was created.
When the interference optical system is used, a Newton ring corresponding to the diffraction grating can be formed to expose the photoresist layer. The exposure process can be simplified.

  According to the present invention, a surface emitting semiconductor laser device that emits laser light having a stable polarization direction can be provided. In addition, a manufacturing method and a manufacturing apparatus suitable for manufacturing such a semiconductor laser can be provided.

Other features of the present invention are listed.
(First embodiment)
Laser light emitted from the laser device can be emitted not only in a direction perpendicular to the laser device but also in an oblique direction. In this case, the grating interval of the diffraction grating group is determined based on the following relational expression.
Ns · k · sinθ = Neff · k + q · K
Here, Ns is the refractive index of the semiconductor substrate, k is the wavelength of the laser beam, θ is the emission angle, Neff is the effective refractive index, q is an integer, and K is the grating spacing of the diffraction grating.
(Second embodiment)
A laser array in which a plurality of laser devices are integrated and means for cooling the laser array from the upper electrode side of the integrated laser device group are provided. Typical cooling means includes water cooling means and air cooling means. By cooling from the upper electrode side, the heat generated in the active layer can be efficiently cooled. Realizes stable operation at high output.
(Third embodiment)
The laser device of the present invention can be suitably used for, for example, a laser processing device, an optical modeling device, an optical communication device, a laser radar device, a laser printer, and the like.

Embodiments will be described in detail below with reference to the drawings.
(First embodiment)
FIG. 1 shows a cross-sectional view of a main part of the laser apparatus of the first embodiment. The laser device includes a lower clad layer 24 made of, for example, n-type AlGaAs, an active layer 26 laminated thereon, and an upper clad layer 28 made of, for example, p-type AlGaAs, laminated thereon. . A laminated structure in which an active layer 26 is formed between the lower cladding layer 24 and the upper cladding layer 28 is provided. The active layer 26 has a quantum well structure and is composed of, for example, AlGaAs / GaAs / InGaAs / GaAs / AlGaAs.
A plurality of diffraction gratings 32 are formed on the upper cladding layer 28, and the surface on which the group of diffraction gratings 32 is formed is referred to as a diffraction grating layer. The diffraction grating 32 is formed as a remaining portion by forming a groove in a part of the upper cladding layer 28.
The diffraction grating 32 group is connected to an upper electrode 44 made of, for example, Ti—Pt—Au. The upper electrode 44 and the diffraction grating group 32 are in ohmic contact via a contact layer (not shown). The contact layer refers to an alloyed region formed by preparing InGaAs doped with zinc or the like at a high concentration on the diffraction grating 32 group side and welding it to the upper electrode 44 side at a high temperature. . The periphery of the diffraction grating 32 group is prohibited from being connected to the upper electrode 44 by an insulating film 45 made of silicon oxide.
The lower cladding layer 24 is in contact with the semiconductor substrate 22 made of, for example, n-type GaAs, and a lower electrode 42 is formed on the back surface of the semiconductor substrate 22. The lower electrode 42 is made of, for example, Au—Zn and is formed around the periphery of the back surface of the semiconductor substrate 22.
An antireflection plate 43 is formed on the surface where the semiconductor substrate 22 is exposed. The surface from which the semiconductor substrate 22 is exposed is a light extraction port, and the antireflection plate 43 prevents the laser light emitted from the laser device from being reflected and entering the laser device.

FIG. 2 shows a schematic configuration diagram of the diffraction grating 32 group in plan view.
The diffraction grating 32 is formed so as to surround the center. An azimuth range having a uniform distance from the center to the diffraction grating 32 is formed symmetrically in the drawing. In other words, a pair of diffraction gratings 32 is formed in a symmetrical positional relationship across the center. In this embodiment, arc-shaped diffraction gratings 32 are formed symmetrically on the left and right sides of the drawing. Further, a plurality of diffraction gratings 32 are repeatedly formed along the symmetry direction to form a multiple structure. It can also be said that similar arc-shaped diffraction gratings 32 having a common center are repeatedly formed from the center toward the periphery. A region where the arc-shaped diffraction grating 32 is formed is referred to as a gain region. The distance between the diffraction gratings 32 is about 300 nm and has the same period, and the height is about 150 nm. The diameter of the diffraction grating 32 group is about 500 μm.
On the other hand, there is an azimuth range 32a that is different from the uniform distance from the center to the diffraction grating 32 in the gain region (in this embodiment, since the diffraction grating is not formed, the distance is substantially infinite). Is formed. In other words, the azimuth range 32a can be said to be a region where the ring-opening regions of the plurality of arc-shaped diffraction gratings 32 coincide from the center to the periphery. This azimuth range 32a is referred to as a non-feedback region. The non-feedback region 32a may be formed by completely removing the upper portion of the upper clad layer 28 or may be formed without being removed at all. Alternatively, even if a part is removed, it is sufficient that the formed diffraction grating does not have a symmetrical positional relationship across the center.

Next, the operation of this laser device will be described.
First, a positive voltage is applied to the lower electrode 42 to inject current into the active layer 26. Although FIG. 1 shows a deformed shape, the film thickness of the semiconductor substrate 22 is actually large, so that the injected current is injected into the active layer 26 in a balanced manner. Photons generated by electron-hole coupling accompanying this current injection propagate along the surface of the active layer 26 and are gradually amplified by repeating the gain due to stimulated emission. At this time, some of the photons are periodically reflected by the diffraction grating 32, and only the light of a single frequency oscillates because the peaks and peaks of the incident light and the reflected light overlap with each other.
A part of this light amplified by the gain is diffracted by the diffraction grating 32 toward the back side of the semiconductor substrate 22. As shown by the arrows in the figure, the diffracted light is emitted from the exposed surface of the semiconductor substrate 22. The diameter and the shape of the exposed surface are not particularly limited. For example, when the diameter is small and the shape is circular, it is easy to inject as a basic transverse mode. A part of the light is also diffracted by the diffraction grating 32 to the surface side of the semiconductor substrate 22, but the light is absorbed by the upper electrode 44 or reflected by the upper electrode 44 or the like.

As shown in FIG. 2, in the non-feedback region 32a in which the diffraction grating 32 group is not formed, light cannot be fed back, so oscillation does not occur in this direction. Accordingly, the feedback is small in the vicinity of the non-feedback region 32a, and a strong feedback region is formed in the direction farthest from the non-feedback region 32a. In this embodiment, light oscillates upon receiving the strongest feedback along the direction orthogonal to the direction from the center to the non-feedback region 32a. Therefore, the direction of polarization of the emitted laser light is stabilized in that direction (broken arrow in FIG. 2). In this way, by forming the non-feedback region 32a, the polarization direction of the emitted laser light can be stabilized.
Further, in this embodiment, the non-feedback region 32a is formed almost linearly with the center in between, and the polarization direction can be adjusted. At the same time, since the gain region is widely formed, laser light emission centered on the light intensity peak is realized. Further, since the diffraction grating 32 group having the same period is used, a laser beam having a single frequency can be oscillated. Laser light having these characteristics can be suitably used for, for example, optical communication, laser processing apparatus, or optical modeling apparatus that is one of rapid prototyping.

FIG. 3 shows the electromagnetic field distribution of the emitted laser light when the region where the upper electrode 44 is in contact with the diffraction grating 32 group is adjusted.
If the diameter of the region where the upper electrode 44 is in contact with the diffraction grating 32 group is L, FIG. 3B shows a case where L is small, and FIG. 3C shows a case where L is large.
As shown in FIG. 3B, when the upper electrode 44 is in contact with the vicinity of the center of the diffraction grating 32 group, current is efficiently injected into the active layer 26 located near the center. The transverse mode 35 stands. In general, the higher-order mode 36 is likely to oscillate around the diffraction grating 32 group. However, in this embodiment, since the current injection is suppressed for the active layer 26 located in the periphery, the higher-order mode 36 is suppressed. The oscillation of 36 is suppressed. The upper electrode 44 is preferably formed in a range from the center of the diffraction grating 32 to the outermost diffraction grating 32.
On the other hand, as shown in FIG. 3C, when the diameter of the upper electrode 44 is increased and the upper electrode 44 is formed further to the periphery than the outermost diffraction grating 32, the active layer 26 located on the periphery is formed. However, the current is well injected, and the high-order transverse mode 36 is also oscillated.
Thus, in this embodiment, the transverse mode of the emitted laser light can be easily adjusted by adjusting the shape of the upper electrode 44.
In addition, instead of adjusting the shape of the upper electrode 44, or using the following method at the same time, higher-order mode oscillation can be suppressed. This can be realized by losing the action of the active layer 26 at a position corresponding to the periphery of the diffraction grating 32 group. Specifically, the quantum well structure of the active layer 26 may be destroyed by diffusing impurities or crystal defects into the active layer 26 from the upper clad layer 28 side. By diffusing impurities or crystal defects, there is no band gap difference, and the quantum well structure is destroyed.

Second Embodiment FIG. 4 shows a cross-sectional view of a main part of a laser apparatus according to a second embodiment. In addition, about the substantially same structure of 1st Example, the same code | symbol is attached | subjected and the description is abbreviate | omitted.
The second embodiment is different from the first embodiment in that the grating interval of the diffraction grating 34 group gradually becomes wider from the center toward the periphery.
FIG. 5 shows a schematic configuration diagram of the diffraction grating 34 group in plan view. As in the first embodiment, a non-feedback region 34a where the diffraction grating 34 group is not formed is formed from the center to the periphery. With this configuration, the polarization direction can be stabilized.

As shown in FIG. 4, the laser light emitted by this laser device can be focused at a predetermined position (A in the figure). Specifically, when the innermost grating interval is 289 nm and the outermost grating interval is 311 nm, the focal point is positioned 2.8 mm away from the diffraction grating 34 group.
When the laser apparatus of this embodiment is used, laser light can be condensed at a predetermined position without using, for example, a condensing optical system. The configuration is simplified and the device is downsized. This facilitates coupling to other optical components such as optical fibers.

Next, a modification of the diffraction grating group will be described with reference to FIG.
FIG. 6A shows an example in which an elliptical diffraction grating is formed around the center. Further, a plurality of similar elliptical diffraction gratings having a common center are repeatedly formed from the center toward the periphery. In this diffraction grating, the distance from the center to the diffraction grating changes in all directions. However, the distances of symmetrical positions across the center are equal. In this example, there is no non-feedback region where the diffraction grating is not formed, but the anisotropy of the gain distribution is generated in the gain region due to the anisotropy of the shape, and the polarization direction is stabilized. In this embodiment, the polarization direction is stabilized in the direction of the dashed arrow.
FIG. 6B shows an example in which a rectangular diffraction grating is formed around the center. Further, a plurality of similar rectangular diffraction gratings having a common center are repeatedly formed from the center toward the periphery. Also in this example, there is no non-feedback region in which the diffraction grating is not formed, but the anisotropy of the gain distribution is generated in the gain region due to the anisotropy of the shape, and the polarization direction is thereby stabilized. . In this embodiment, the polarization direction is stabilized in the direction of the dashed arrow.
FIG. 6C shows an example in which a non-feedback region in which a diffraction grating is not formed is formed in a part of a polygonal diffraction grating that is repeatedly formed. In this example, light cannot oscillate because no photon feedback occurs in the non-feedback region. Furthermore, the anisotropy of the gain distribution is generated in the gain region due to the anisotropy of the polygon. The polarization direction is stabilized under the influence of both. In this embodiment, the polarization direction is stabilized in the direction of the dashed arrow.

Third Example In the third example, an example of a manufacturing method for forming a diffraction grating group will be described. The manufacturing method of the present embodiment is a technique in which a Newton ring (interference draft) corresponding to a diffraction grating is formed on a photoresist layer by one-time irradiation of ultraviolet rays, and the photoresist layer is exposed along the Newton ring.
FIG. 7 shows the upper transparent member 52 of the interference optical mask used in this manufacturing method. For example, glass is used for the upper transparent member 52. 7A is a plan view, FIG. 7B is a front view, and FIG. 7C is a bottom view. The upper transparent member 52 has a conical cutout 54 formed from the lower surface thereof. The angle formed by the slope of the notch 54 and the lower surface of the upper transparent member 52 is θ. The upper transparent member 52 is used by attaching a flat lower transparent member made of glass to the lower surface side thereof.

In FIG. 8A, when the upper transparent member 52 and the lower transparent member 53 are attached, and when ultraviolet light is irradiated from the upper surface of the upper transparent member 52, the pair of transparent members 52 and 53 are transmitted. It shows the optical path of the ultraviolet light.
When ultraviolet light having a wavelength of λ is irradiated from the upper surface of the upper transparent member 52, the ultraviolet light transmitted through the pair of transparent members 52 and 53 appears as an interference with a period of Λ. This is due to the optical path difference of ultraviolet light. The optical path of the ultraviolet light first passes through the upper transparent member 52 and the notch 54 and is reflected by the lower transparent member 53, and then the reflected light is reflected by the upper transparent member 52 on the slope of the notch 54. Then, the lower transparent member 53 is transmitted. Therefore, it reciprocates in the notch part 54, and an optical path difference arises by this reciprocating path. Newton rings appear when this optical path difference exactly matches the wavelength of ultraviolet light. That is, a relational expression of Λ = λ / (2tanθ) is obtained. Further, it is understood from this relational expression that when a Newton ring having a predetermined interval is obtained, a notch 54 having an angle θ = tan ⁻¹ (λ / (2Λ)) may be used. Further, it is desirable that the contact surfaces of the upper transparent member 52 and the lower transparent member 53 are coated with antireflection. The ultraviolet light transmitted through the contact surface is transmitted without being reflected, and it is possible to suppress the appearance of useless Newton rings.
As shown in FIG. 8B, the upper transparent member 55 may be formed with a conical protrusion 57 instead of the notch 54. A Newton ring with an interval of Λ can be formed by a similar action.

FIG. 9 shows a Newton ring that appears on the photoresist layer 56. FIG. 58 shows a He—Cd laser device. Since the notch 54 is formed in a conical shape, an annular Newton ring having a distance of Λ appears on the photoresist layer 56 from the center toward the periphery. This interval Λ is formed at the same period from the center toward the periphery.
Next, a procedure for creating a diffraction grating using the photoresist layer 56 will be described.
The photoresist layer 56 is a positive resist, and after development, an opening is formed in the photoresist layer 56 along the bright area of the Newton ring. Next, the photoresist layer 56 corresponding to the region where the non-feedback region is desired to be formed is selectively removed. Next, anisotropic dry etching or the like is performed to remove a part of a semiconductor substrate (not shown) disposed below the opening. Then, a groove having a predetermined depth is formed on the semiconductor substrate, and the remaining portion becomes a diffraction grating. Since all the photoresist layer 56 on the non-feedback region is removed, all the semiconductor substrate in the non-feedback region is removed and a diffraction grating is not formed. A gain region where the diffraction grating group is formed and a non-feedback region where the diffraction grating group is not formed can be easily formed on the semiconductor substrate according to the above procedure.
Instead of selectively removing the photoresist layer 56 corresponding to the region where the non-feedback region is desired to be created, a mask may be selectively formed again at the above location. In this case, since the semiconductor substrate corresponding to the non-feedback region is not removed at all, a diffraction grating is not formed after all.
Alternatively, the Newton ring does not appear on the corresponding photoresist layer 56 by forming a part of the slope of the notch 54 corresponding to the region where the non-feedback region is desired to be anisotropic from the surrounding slope. You may do it. Similar effects can be obtained by adopting either method.
In addition, an anisotropic Newton ring etc. can also be created by adjusting the shape of the contact surface of this pair of transparent member suitably. A desired diffraction grating group can be easily formed.

Next, a manufacturing method in the case where a plurality of diffraction grating groups are simultaneously formed on the surface of the semiconductor substrate 157 will be described with reference to FIG. A plurality of notches 154 are distributed in the upper transparent member 152. A lower transparent member 153 is attached to the upper transparent member 152, and a photoresist 156 and a semiconductor substrate 157 are disposed below the lower transparent member 153. In the drawing, the lower transparent member 153 and the photoresist 156 are in direct contact with each other, but may be separated from each other.
The ultraviolet light emitted from the He-Cd laser device 158 enters the upper surface of the upper transparent member 152 via the pinhole 151. A hole having a diameter of about 10 μm is formed in the pinhole 151. By passing through the pinhole 151, only ultraviolet light having a single wavelength can be used. For this reason, the light and darkness of the Newton ring formed on the photoresist 156 becomes extremely large, and it is easy to reliably produce a desired Newton ring. As in this embodiment, a plurality of Newton rings can be simultaneously formed and exposed on the photoresist 156 by dispersing and arranging the plurality of notches 154 on the upper transparent member 152. Conventionally, exposure is performed while scanning on a photoresist using an electron beam apparatus, and thus the time of the exposure process tends to be extremely long particularly when a plurality of diffraction grating groups are formed in this way. It was. In the present invention, the photoresist can be exposed by substantially one irradiation of ultraviolet light regardless of the number of diffraction grating groups to be prepared. The exposure process time can be greatly shortened. In addition, since the electron beam apparatus is expensive, there is a problem in terms of manufacturing cost. In this embodiment, a pair of transparent members 152 and 153 made of inexpensive glass or the like may be prepared, which is extremely effective in terms of manufacturing cost.

(Fourth embodiment)
In the fourth embodiment, an example in which the laser apparatus of the first embodiment is applied to a laser processing apparatus will be described. FIG. 11 shows a schematic perspective view of a laser array 60 used in the laser processing apparatus.
66 is a laser device, and a total of 16 semiconductor laser devices 66 are vertically and horizontally integrated in two dimensions. The semiconductor laser device 66 is installed on the upper insulating layer 64 made of, for example, aluminum nitride. The upper insulating layer 64 has a laminated structure with a lower insulating layer 62 made of, for example, aluminum nitride, and a back metal film 61 is deposited on the back surface side of the lower electrode layer 62. Ti / Pt / Au is used for the back surface metal film 61, and the laser array 60 is bonded to another device using the back surface metal film 61. A total of 16 electrode pads 68 made of, for example, Ti / Pt / Au are formed on the peripheral side of the upper insulating film 64, and the electrode pads 68 are electrically connected to the semiconductor laser device 66 on a one-to-one basis. Is done. The wiring connecting the two is disposed in the laminated structure of the upper insulating layer 64 and the lower insulating layer 62.

FIG. 12 is a plan view of the laser array 60, and broken lines in the drawing indicate wirings connecting the electrode pads 68 and the semiconductor laser devices 66. A schematic configuration of this wiring is shown in FIG. With reference to FIG. 12 and FIG. 13, the state of wiring is well understood.
As shown in FIG. 13, an electrode-side through wiring 64 a that penetrates the upper insulating layer 64 from the electrode pad 68 toward the lower insulating layer 62 is formed. The through wiring 64a is connected to one end of the intermediate wiring 62a. The intermediate wiring 62 a extends to the laser device 66 side along the lower insulating layer 62 side in the contact surface between the upper insulating layer 64 and the lower insulating layer 62. The other end of the intermediate wiring 62 a is connected to the laser side through wiring 64 b, and the laser side through wiring 64 b penetrates the upper insulating layer 64 and is connected to the upper electrode 44 of the laser device 66. This upper electrode 44 coincides with the upper electrode of the laser device of the first embodiment. Although not shown, the lower electrode of the laser device 66 is commonly connected to a total of 16 laser devices 66.
As described above, the integrated laser devices 66 can be individually controlled by selecting a voltage to be applied to the electrode pad 68.

In FIG. 14, the schematic block diagram of a laser processing apparatus is shown.
160 is the same laser array as the laser array shown in FIG. 11, and this laser array 160 is installed on the cooling plate 174 with a thermal stress buffer substrate 172 interposed therebetween. The thermal stress buffer substrate 172 has a material or shape that is stable against heat, and the shape does not change with respect to the heat generated from the laser array 160. Therefore, it is possible to suppress a change in the emission direction of the laser light emitted from the laser array 160.
The cooling plate 174 is covered with a case 176, and the case 176 is formed so as to cover a position facing the laser array 160. By causing the cooling water to flow into the case 176, heat exchange between the heat radiation from the laser array 160 and the cooling water is performed, and the laser array 160 is prevented from generating excessive heat. Thereby, the laser array 160 operates stably. The cooling water inlet 177 is formed in the upper part of the case 176 and is formed in a positional relationship facing the laser array 160. By forming the inlet 177 at this location, the cold water flowing from the inlet 177 can efficiently exchange heat with the heat radiation from the laser array 160. Inflow water is discharged from an outlet 178 formed on the side surface of the case.

As shown in FIG. 1, the laser device integrated in the laser array 160 of the present embodiment emits laser light from the back side of the semiconductor substrate. Therefore, the surface side of the semiconductor substrate on which the active layer is formed is disposed on the side close to the cooling plate 174. Therefore, since the heat generated in the active layer can be efficiently cooled, it is easy to realize a stable operation. In particular, when it is desired to handle laser light with a large output, the number of laser devices integrated in the laser array 160 increases. In other words, it can be said that the present embodiment can easily realize a large output operation.
A condenser lens 182 is disposed between the laser array 160 and the workpiece 192, and the laser beam 184 emitted from the laser array 160 focuses on the workpiece 192 via the condenser lens 182. The energy density is concentrated on the workpiece 192, and the workpiece 192 is laser processed.
In the laser apparatus integrated in the laser array 160 of this embodiment, the polarization direction is adjusted to a constant direction. Therefore, the processing surface is always irradiated with laser light having a constant polarization direction. Therefore, the machining surface of the workpiece 192 can be laser machined with a desired shape with high accuracy.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

1 is a cross-sectional view of a main part of a semiconductor laser device according to a first embodiment. The schematic block diagram of the diffraction grating group of 1st Example is shown. (a) The principal part sectional drawing of a semiconductor laser apparatus is shown. (b) The electromagnetic field distribution of the laser beam in the fundamental transverse mode is shown. (c) The electromagnetic field distribution of the laser beam in the higher order mode. Sectional drawing of the principal part of the semiconductor device of 2nd Example is shown. The schematic block diagram of the diffraction grating group of 2nd Example is shown. (a) (b) (c) Modified examples of the diffraction grating group are shown. (a) The top view of an upper side transparent member is shown. (b) The front view of an upper side transparent member is shown. (c) A bottom view of the upper transparent member is shown. (a) (b) The optical path of the ultraviolet light which permeate | transmits an optical interference mask is shown. A manufacturing process for forming an interference manuscript on a photoresist using an optical interference mask will be described. A manufacturing process for forming a diffraction grating group on a semiconductor substrate using an optical interference mask will be described. The perspective view of the laser array of 3rd Example is shown. The top view of the laser array of 3rd Example is shown. FIG. 6 shows a schematic cross-sectional view of a laser array of a third embodiment. The schematic block diagram of a laser processing apparatus is shown. The principal part sectional drawing of the conventional surface emitting semiconductor laser apparatus is shown. The schematic block diagram of the diffraction grating group of the conventional surface emitting semiconductor laser apparatus is shown.

Explanation of symbols

22: Semiconductor substrate 24: Lower clad layer 26: Active layer 28: Upper clad layer 32: Diffraction grating 42: Lower electrode 43: Antireflection film 44: Upper electrode 45: Protective film

Claims (7)

A laminated structure in which a lower clad layer, an active layer, and an upper clad layer are laminated in order, provided on the upper surface of the transparent semiconductor substrate;
A diffraction grating provided above the laminated structure and formed in a diffraction grating layer that extends parallel to the active layer within a distance that light generated in the active layer reaches;
An upper electrode facing the laminated structure through the diffraction grating layer;
A lower electrode formed around a region where the lower surface of the transparent semiconductor substrate is exposed, and
The diffraction grating is formed around the center, and the distance from the center to the diffraction grating changes depending on the orientation from the center,
The surface emitting semiconductor laser device, wherein the upper electrode has a contact region in contact with the diffraction grating, and the contact region is formed within a range surrounded by the outermost diffraction grating.   2. The surface emitting semiconductor laser device according to claim 1, wherein the diffraction grating includes an azimuth range in which the distance is uniform and an azimuth range having a distance different from the uniform distance.   In the diffraction grating, the distance is uniform in the first azimuth range, the distance is substantially infinite in the second azimuth range adjacent to the diffraction grating, and the third azimuth symmetric to the first azimuth range with respect to the center. 3. The surface emitting semiconductor according to claim 2, wherein the distance is the uniform distance and the distance is substantially infinite in a fourth azimuth range symmetric to the second azimuth range with respect to the center. Laser device.   4. The surface emitting semiconductor laser device according to claim 3, wherein a plurality of crests or troughs constituting the diffraction grating are formed around the center.   5. The surface emitting semiconductor according to claim 4, wherein the interval between the peak portions or the valley portions constituting the diffraction grating formed in a multiple manner around the center is narrow in the vicinity of the center and widely in the periphery. Laser device. The active layer includes a region in which the quantum well structure is destroyed ,
6. The surface emitting device according to claim 1, wherein the region in which the quantum well structure is destroyed is disposed at a position corresponding to the periphery of the diffraction grating when viewed in plan. Semiconductor laser device. A laser array in which a plurality of surface-emitting semiconductor laser devices according to claim 1 are integrated;
A laser processing apparatus comprising a condensing optical system that focuses a laser beam emitted from the laser array.

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