JP3399018B2 - Semiconductor laser and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having low power consumption, high output and high reliability, and more particularly to a semiconductor laser suitable for application as a reproducing light source in, for example, a compact disc player.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 2-17 filed by the present applicant as a semiconductor laser having a low threshold current and a high output.
An SDH (Separated Double Hetero Junction) type semiconductor laser has been proposed in Japanese Patent Application Laid-Open No. 4287/1993 and Japanese Patent Laid-Open No. 3-225881.

This SDH type semiconductor laser is, for example, a GaAs compound having a first conductivity type, for example, n type, and one main surface having a {100} crystal plane, as shown in FIG. A stripe-shaped step portion, for example, a ridge 2r extending in the <011> crystal axis direction orthogonal to the paper surface of FIG. 7 is formed on one main surface of the semiconductor substrate 1. This ridge 2r
On the main surface of the substrate 1 having a sapphire, a normal MOCVD (chemical vapor deposition by metal organic) method, that is, a methyl-based MO
A first conductivity type clad layer 3 and a low impurity concentration or undoped active layer 4 are continuously formed by a CVD method.
A first clad layer 5 of a second conductivity type, for example p-type, and a first
Each semiconductor layer of a conductivity type, for example, n-type current blocking layer 6, a second conductivity type, for example, p-type second cladding layer 7, and a second conductivity type of cap layer 8 is formed by one-time epitaxial growth. .

The first conductivity type cladding layer 3, the second conductivity type first and second cladding layers 5 and 7, and the first conductivity type current blocking layer 6 are compared with the active layer 4. It is made of a material having a large band gap, that is, a small refractive index.

In this case, the crystal orientations of the substrate 1 and the ridge 2r, the width and height of the ridge 2r, that is, the depths of the grooves on both sides thereof, the first conductivity type cladding layer 3, the active layer 4, and the second layer. By selecting the thickness of the conductivity type first cladding layer 5 and the like, the first conductivity type cladding layer 3, the active layer 4, and the second conductivity type first cladding layer 5 are formed on the mesa groove on the ridge 2r. Slopes 9A and 9 to be separated from those in
A fault is formed by B so that the stripe-shaped triangular region 10 having a cross section divided by the slopes 9A and 9B is formed on the ridge 2r.

This is because, in the MOCVD method in which a methyl-based organic metal is used as a source gas, once the {111} B crystal plane is generated, epitaxial growth hardly occurs on this plane. . In this case, the current block layer 6 is divided into both sides by sandwiching the triangular area 10 having a stripe-shaped cross section, and both end faces generated by this division are separated from the other in the triangular area 10 having a stripe cross-section. The end surfaces of the active layer 4 are abutted with each other, that is, the end surfaces facing the slopes 9A and 9B.

In this way, the active layer 4 in the stripe-shaped triangular area 10 on the ridge 2r is formed so as to be sandwiched by the current block layers 6 having a smaller refractive index than this, and lateral confinement is performed to emit light. The second clad layer 7 of the second conductivity type and the block layer 6 are formed in the active region and on the both sides of the stripe-shaped triangular region 10 of the cross section due to the existence of the current blocking layer 6.
And the first conductivity type first cladding layer 5 and the first conductivity type cladding layer 3 form a p-n-p-n thyristor to block a current there, and thereby the ridge 2r. The current is concentrated in the upper active layer 4 so as to reduce the threshold current.

Further, in the above-mentioned Japanese Laid-Open Patent Publication No. 3-225881, a current blocking layer is entirely epitaxially grown on a substrate having a {110} crystal plane as a main surface, and then in the <001> crystal axis direction. An inverted mesa-shaped recess extending is formed, and in this recess, an active layer separated from the other part by a {110} crystal plane orthogonal to the main surface is spontaneously epitaxially grown, and the SDH having the above-mentioned ridge structure is formed. Similar to the type semiconductor laser, an SDH type semiconductor laser capable of reducing the threshold current has been proposed.

[0009]

By the way, the above-mentioned S
In a semiconductor laser having a straight stripe-shaped active layer, such as a DH type laser, in which the width of the active layer is made small to realize a low threshold value, the laser light far
Far-Field Pattern (FFP);
The far-field image) tends to be large, that is, the divergence angle of the laser light tends to be large.

Therefore, when the output light of such an SDH type semiconductor laser is used as a light source of a CD (Compact Disc) player or the like, a lens or the like is used as shown in FIG. When narrowing down the light, a lens with a large numerical aperture NA is needed,
There arises a problem that the coupling efficiency is reduced. In FIG. 8, 31 is this SDH type semiconductor laser, and the emitted light from this is a diffraction grating 32, PBS (polarizing beam splitter) 33, collimator lens 34, QW.
A P (λ / 4 plate) 35 and an object to be irradiated through an objective lens 36, in this case, a recording medium 37 such as a compact disc.
Is irradiated. Then, the reflected light from here is reflected by the polarization beam splitter 33 through the objective lens 36, the QWP 35, and the collimator lens 34 and detected by the detector 38, and the recording signal or the like is read.

As described above, the FFP of the semiconductor laser 31
If the spread of light is large and the light collection efficiency is low, it is 3 mW with a normal LD (laser diode) in a CD player, etc.
The output of about 4 mW is required when using the SDH type semiconductor laser. Further, when the SDH type semiconductor laser is arranged in the vicinity of the lens, a lens having a large curvature is required, which causes an inconvenience that the optical system becomes expensive.

In view of the above-mentioned problems, the present invention is particularly concerned with S
(EN) Provided is a semiconductor laser having a DH type configuration, which suppresses the spread of the FFP and facilitates incorporation into an optical system, and has particularly good controllability in manufacturing and high yield and productivity.

[0013]

According to the present invention, a stripe-shaped ridge extending in the <011> crystal axis direction is formed on a compound semiconductor substrate having a {100} crystal plane as a main surface, and the ridge is formed on the ridge. A compound semiconductor layer including at least a first clad layer, an active layer, a second clad layer and a current blocking layer is epitaxially grown over the entire surface to form a laser resonator, and a laser cavity is formed from a side edge portion of the ridge. A slanted surface composed of B crystal planes is formed, and at least the active layer on this ridge is separated from other portions, and this active layer is
In slopes consisting 1} B crystal plane, adapted to abut and the current blocking layer over the resonator length direction entirely, electrostatic
The current blocking layer is a semiconductor layer of the first conductivity type and a second conductivity type of the semiconductor layer.
Three layers in which a semiconductor layer and a semiconductor layer of the first conductivity type are stacked
The ridge has a structure in which the side edges of the ridge are curved in the cavity length direction of the laser cavity so that the width of the ridge is wider than the center of the cavity at both end faces that make up the laser cavity. The active layer of the laser cavity is formed according to the shape of this ridge. Further, according to the present invention, in the above-mentioned semiconductor laser, the active layer formed on the ridge is configured so that its thickness changes as the width of the ridge changes.

Further, according to the present invention, a stripe-shaped groove extending in the <011> crystal axis direction is formed in a compound semiconductor substrate having a {100} crystal plane as a main surface, and the entire surface including the inside of the groove is formed. A compound semiconductor layer comprising at least a first clad layer, an active layer and a second clad layer is epitaxially grown to form a laser resonator in at least this groove,
On the main surface of the compound semiconductor substrate, a slanted surface composed of {111} B crystal planes is formed from the side edge portion of the groove to separate the compound semiconductor layer inside the groove and the compound semiconductor layer outside the groove. As a pattern in which the side edges of the groove are curved with respect to the cavity length direction of the laser resonator so that the width of the groove is wider than the central portion of the resonator at both end faces that form the laser cavity, The active layer of the laser resonator is formed according to the shape of the groove.

Furthermore, the present invention is configured such that, in the above-mentioned semiconductor laser, the active layer formed in the groove is changed in thickness as the width of the groove is changed.

Further, according to the present invention, a stripe-shaped ridge extending in the <011> crystal axis direction is gradually formed on a compound semiconductor substrate having a {100} crystal plane as a main surface from the both sides toward the central portion. It is formed as a curved pattern having a narrow width and covers at least the first ridge layer, the active layer, the second cladding layer, and the first conductivity type over the ridge.
Semiconductor layer, second conductivity type semiconductor layer, and first conductivity type semiconductor layer
A compound semiconductor layer composed of a current blocking layer having a three-layer structure in which semiconductor layers are stacked is epitaxially grown to form a laser resonator, and a {111} B crystal plane extending from a side edge portion of the ridge is formed on the ridge. A compound semiconductor layer on the ridge and a compound semiconductor layer on both side trenches of the ridge are separated from each other to form a slope, and the width of the ridge extends from both end faces of the laser cavity toward the center. Is formed to be narrow in the cavity length direction, the thickness of the active layer of the laser cavity is changed in the cavity length direction.

Still further, according to the present invention, a stripe-shaped groove extending in the <011> crystal axis direction is gradually formed in a compound semiconductor substrate having a {110} crystal plane as a main surface from both sides toward the central portion. And forming a laser pattern in at least this groove by epitaxially growing at least the first cladding layer, the active layer and the second cladding layer over the entire surface including the inside of the groove. However, from the side edge portion of the groove, {1
11} B crystal planes are grown to divide the compound semiconductor layer inside the groove and the compound semiconductor layer outside the groove so as to divide the compound semiconductor layer from the both end faces of the laser cavity toward the center. By forming the width of the groove to be narrow in the cavity length direction, the thickness of the active layer of the laser cavity is changed in the cavity length direction.

[0018]

As described above, in the present invention, on the main surface 1S composed of the {100} crystal faces of the compound semiconductor substrate 1,
<011> A so-called ridge of a stripe-shaped step portion 2, that is, a convex step portion that extends in the crystal axis direction, or a concave step portion or groove is provided, and a laser resonator 20 is formed thereon.
Although the width of the step portion 2 is changed in the resonator direction, the width and depth of such a structure can be easily controlled by applying photolithography or the like.

By changing the width of the step portion 2 in the cavity direction, the shape of the active layer 4 on the step portion 2 can be modulated according to the shape of the step portion, and the active layer 4 is kept narrow, that is, low. The beam shape can be controlled while maintaining the threshold current, and the far field pattern can be made relatively small even when this is incorporated into an optical system such as a CD player, and the coupling efficiency can be improved. The decrease can be suppressed.

Further, by forming an SDH type semiconductor laser on the ridge 2r or in the groove 2d, it is possible to achieve a low threshold current and a high output.

Furthermore, by modulating the width of the active layer 4 to make it narrow at the center of the resonator and wide at the end face,
It can be grown relatively thick at the center of the resonator and relatively thin at the end face. Therefore, a window effect can be obtained at the end face of the resonator, and end face deterioration due to heat generation or the like in this part can be suppressed, so that the laser output can be increased and the reliability can be improved.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Each embodiment according to the present invention will be described in detail below with reference to the drawings. In each example, the case where the present invention is applied to an AlGaAs compound semiconductor laser is shown.

Example 1 In this example, as shown in FIG. 1, a compound semiconductor substrate 1 made of, for example, p-type GaAs of the first conductivity type was prepared, and its {100} crystal plane, for example, (100) crystal was prepared. A case is shown in which a stripe-shaped convex step portion, that is, a ridge 2r extending in the <001> crystal axis direction, for example, the [001] crystal axis direction, is formed on the main surface 1S composed of the planes.

The shape of the ridge 2r extends in the [001] crystal axis direction as described above, but its side edge is curved so that its width is wider at the light emitting end face than at the center of the resonator. The pattern is formed by applying photolithography, wet etching, or the like. In FIG. 1, an arrow x indicates a <011> crystal axis direction, and an arrow z indicates a <100> crystal axis direction perpendicular to the main surface 1S.

Then, the ridge 2r is covered, and the entire surface is sequentially covered with, for example, a first conductive type cladding layer 3 made of, for example, p-type AlGaAs, an active layer 4 made of undoped GaAs, and a second layer made of n-type AlGaAs. The conductivity type first cladding layer 5 is epitaxially grown.

At this time, when the epitaxial growth is performed by the MOCVD method or the like using a methyl-based material, that is, for example, trimethylaluminum, trimethylgallium, etc.,
Once the {111} B crystal plane is generated from the side edge portion of the ridge 2r extending in the [001] crystal axis direction, this {111} B crystal plane is generated.
Since epitaxial growth is unlikely to occur on the crystal plane, the slopes 9A and 9B formed by the {111} B crystal planes in which the layers 3, 4, 5 on the ridge 2r form an angle of 54.7 ° with respect to the main surface of the substrate 1 are formed. grow up.

Since the side edges of the ridge 2r are curved, the slopes 9A and 9B made of {111} B crystal planes are curved, as shown in FIG. It grows while forming the discontinuous surface 13 intermittently along the edge. That is, each layer on the ridge 2r grows by being sandwiched between the slopes 9A and 9B forming the discontinuous surface 13 to form a stripe-shaped triangular region 10 in cross section,
The laser resonator 20 is formed by dividing the active layer 4 on the ridge 2r from the other portions, that is, dividing the active layer 4 from the other portions, that is, the epitaxial layers growing in the trenches on both sides. In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and redundant description will be omitted.

At this time, since the width (length) of the bottom side of the triangular area 10 is different between the central portion and the end portion, the position of the apex where the slopes 9A and 9B intersect is the end portion and the central portion of the ridge 2r. In contrast, the end face portions 20A, 20 of the resonator 20
In B, the cross section is relatively large, and in the central part, the cross section is relatively small.

Furthermore, the film thickness of the active layer 4 on the ridge 2r is relatively thick at the central portion where the ridge 2r is formed narrow and its end face portion is large, as shown in the enlarged schematic side view of FIG. Two
It is formed relatively thin at 0A and 20B. this is,
This is because the lateral diffusion due to MOCVD migration is relatively small in the wide portion of the ridge 2r and relatively large in the narrow portion.

Further, when the upper surface of the second conductivity type first cladding layer 5 grows up to just below the end surfaces of the active layer 4 on the ridge 2r facing the slopes 9A and 9B, the material is switched to block the current. The layer 6, that is, the first conductive type semiconductor layer 6a made of p-type AlGaAs, the second conductive type semiconductor layer 6b made of n-type AlGaAs, and the p-type AlGa.
Epitaxially growing a current blocking layer 6 having a three-layer structure in which a first conductive type semiconductor layer 6c made of As or the like is laminated,
Subsequently, each layer of the second conductivity type second cladding layer 7 made of n-type AlGaAs or the like and the second conductivity type cap layer 8 made of n-type GaAs or the like is sequentially epitaxially grown. The electrode 1 is formed on the top surface of the cap layer 8 and the back surface of the base body 1.
The semiconductor lasers in which the laser resonators 20 having a triangular cross section are formed on the ridges 2r can be obtained by forming the ohmic layers 2 and 13 by sputtering or the like.

At this time, the current blocking layers 6 (6a, 6b and 6c) are epitaxially grown by being divided on both sides of the active layer 4 on the ridge 2r, and the current effectively flows only in the active layer 4 in the triangular region 10 in cross section. Further, by selecting the bandgap of the current blocking layer 6 to be larger than that of the active layer 4, light is confined in the lateral direction of the active layer 4, and the presence of the current blocking layer 6 causes a stripe-shaped cross section. On both outer sides of the triangular region 10, the second conductivity type second cladding layer 7, the block layer 6, the second conductivity type first cladding layer 5, and the first conductivity type cladding layer 3 are formed. A p-n-p-n thyristor is formed to block the current in the thyristor, so that the current is concentrated in the active layer 4 on the ridge 2r to reduce the threshold current. You can mow it.

In the above structure, for example, the length of the ridge 2r is set to 200 μm, and the end face portions 20A, 2 of the resonator 20 are arranged.
The width w _r1 at 0B is 6 μm, and the width w _r2 at the center is 4 μm.
As a result of the growth, the shape of the active layer 4 in the triangular area 10 in cross section was formed according to the shape of the ridge 2r, and the width was about 3 μm at the end face portion and about 1 μm at the center portion. In the far field pattern of the emitted light, the so-called lateral angular spread θ _H along the main surface of the substrate 1 is about 15 °, and the so-called vertical angular spread θ _V orthogonal thereto is about 30 °. Spread of SDH type semiconductor lasers (θ _H ≈30 °, θ _V ≈40 °)
It was able to be made sufficiently small compared to.

Therefore, the beam shape can be controlled while the active layer 4 of the light emitting portion is kept narrow, that is, while the low threshold current is held, and the laser beam is controlled by the CD as described with reference to FIG. Even when it is incorporated in an optical device such as a player, it is possible to suppress a decrease in coupling efficiency. Therefore, when the conventional SDH type semiconductor laser is used as a light source of a CD player, an output of about 4 mW is required, but when the semiconductor laser of the present invention is used, it is the same as an ordinary semiconductor laser of about 3 mW. Any output may be used, and the same optical system as the conventional one can be used.

Furthermore, as described above, the width of the active layer 4 is modulated by using the migration to change the film thickness, and the resonator end face portions 20A and 20B form the active layer 4 with a relatively thick film thickness. As a result, a window effect can be obtained in this portion, and deterioration of the end face due to heat generation or the like can be suppressed to achieve high output of the laser and improvement of reliability.

Embodiment 2 In the embodiment described above, the convex ridge 2 is formed on the substrate 1.
5A to 5C for facilitating the understanding of the case where a concave step portion, that is, a groove is provided in the following example. The manufacturing method will be described in detail.

Also in this case, for example, p of the first conductivity type is used.
5A, a compound semiconductor substrate 1 made of AlGaAs or the like is prepared, and as shown in FIG. 5A, first, the second conductivity is entirely formed on the major surface 1S of the {100} crystal plane, for example, the (100) crystal plane. Type n-type current blocking layer 6 is epitaxially grown by, for example, a MOCVD method using a normal methyl-based organometallic source gas or an ethyl-based organometallic source gas, and the current blocking layer 6 is traversed in the thickness direction. Stripe-shaped grooves 2d extending in the <011> crystal axis direction, for example, in the <011> crystal axis direction with a depth reaching the substrate 1.
To form.

In this case, the shape of the groove 2d is made relatively narrow in the central portion and relatively wide in the vicinity of the end portions by applying photolithography or the like, for example, crystallography using a sulfuric acid-based etching solution. Formed by dynamic etching.
In this way, a so-called inverted mesa-shaped groove 2d that widens toward the bottom is formed. In FIG. 5, the arrow x indicates the <001> crystal axis direction, and the arrow z indicates the <100> crystal axis direction orthogonal to the main surface 1S.

Then, a first conductivity type cladding layer 3 made of p-type AlGaAs or the like is epitaxially grown over the entire surface including the inside of the groove 2d by a methyl-based MOCVD method or the like. At this time, once the epitaxial growth gradually progresses along the inner surface of the groove 2d and vertical planes 19A and 19B composed of {110} crystal planes orthogonal to the main surface 1S of the substrate 1 are formed, the vertical planes 19A and 19B are formed. Since the growth rate for (1) is much slower than the growth rate for the {100} crystal plane along the main surface 1S, the flat portion 3h mainly grows along the bottom surface in the groove 2d.

On the other hand, in the step upper surface 2u on both sides of the groove 2d, if the slopes 9A and 9B made of {111} B crystal planes are generated from the side edges extending in the <011> crystal axis direction, this plane Since the epitaxial growth rate is slow, it grows while being separated from the growth layer inside the groove 2d to form a regular mesa-shaped recess.

At this time, the vertical surfaces 19A and 1 of the groove 2d are also formed.
9B has a pattern in which the side surface of the groove 2d is so-called curved so that it gradually narrows from the end portion toward the central portion, so that a vertical surface is intermittently formed along the shape, and a discontinuous surface is formed. Grow while configuring 13.

And on top of this, further undoped GaAs
An active layer 4 made of n-type AlGaAs, a second conductive type clad layer 15 made of n-type AlGaAs, and a second conductive type cap layer 8 made of n-type GaAs.
Epitaxial growth is performed by the OCVD method or the like. At this time, since the active layer 4, the clad layer 15, and the cap layer 8 hardly grow on the vertical surfaces 19A and 19B, they are separated from each other on the flat portion in the groove 2d and on the step upper surface 2u. Then, the other part is separated from the active layer 4 in the groove 2d, and the laser resonator 20 is configured such that the end faces 20A and 20B are relatively wide and the central part is narrow.

Further, a mask 17 made of photoresist or the like is applied and filled so as to cover the cap layer 8 in the recess, and a region not covered by the mask 17 (not shown) is subjected to RIE (reactive ion etching). ) Or the like anisotropically etching the cap layer 8 on the step upper surface 2u,
The second conductivity type clad layer 15 and the active layer 4 are removed by etching to flatten the entire surface.

Subsequently, as shown in FIG. 2, a p-type impurity such as Zn is diffused over the entire surface to form a second conductivity type surface layer 1.
6 is formed. With such a configuration, the groove 2
An active layer 4 is formed in d, and the active layer 4 is buried and confined in the vertical and lateral directions by the first-conductivity-type cladding layer 3 and the second-conductivity-type cladding layer 15.
It is of a (Baried Hetero) type, and outside the groove 2d, the second conductivity type surface layer 16, the first conductivity type cladding layer 3, the current blocking layer 6, and the compound semiconductor substrate 1 are pn-
A pn thyristor is formed and a current is blocked in this portion, so that a semiconductor laser having a low threshold current in which current is concentrated in the active layer 4 in the groove 2d can be obtained.

Also in this case, for example, the length of the groove 2d is set to 200 μm and the end face portions 20A, 2
The width w _d1 at 0B is 6 μm, and the width w _d2 at the center is 4 μm.
When the growth is performed to some extent, the shape of the active layer 4 in the groove 2d is formed according to the shape of the groove 2d, and the end face portion 20 is formed.
The width of A and 20B was 3 μm, and the width was about 1 μm in the central portion. Furthermore, the far field of the emitted light at this time
Pattern, lateral angular spread theta _H is 15 ° about along the main surface of the substrate 1, the vertical angular spread theta _V perpendicular thereto could be relatively small as about 30 °.

Therefore, even when an SDH type semiconductor laser is formed in the groove 2d, the active layer 4 of the light emitting portion is formed.
The beam shape can be controlled while maintaining a narrow width, that is, while maintaining a low threshold current. When this laser is incorporated in the optical device such as the CD player described in FIG. Can be suppressed. Therefore, also in this case, when it is used as a light source of a CD player, for example, the output of 3 mW, which is similar to that of a normal semiconductor laser, can be obtained, and the optical system can be incorporated into the same optical system as the conventional one.

Further, in this example as well, due to the effect of migration, the thickness of the active layer 4 can be made relatively thin near the end face portions 20A and 20B, and the thickness of the active layer 4 can be made relatively thick near the central portion. As described above, by forming the wide active layer 4 with the resonator end face portions 20A and 20B, the window effect can be obtained here, the end face deterioration due to heat generation or the like can be suppressed, and the high output of the laser and The reliability can be improved.

Comparative Example Next, a case where the emission beam shape of a normal semiconductor laser is controlled will be described with reference to the schematic enlarged perspective view of FIG. In this case, as shown in FIG. 6, n-type GaAs
On a substrate 21 made of, for example, n-type AlGaAs, a clad layer 22, an active layer 23, such as GaAs, and a p-type AlGaA.
A clad layer 24 of s or the like is sequentially epitaxially grown over the entire surface, and a current block layer 25 made of n-type GaAs or the like having a pattern widened at the end face portion and narrowed at the central portion is formed thereon. P-type AlGaAs cladding layer 26 and p-type GaAs
The cap layer 27 is formed on the entire surface by epitaxial growth, and ohmic electrodes 28 and 29 are formed on the cap layer 27 and the back surface of the substrate 21, respectively.

In such a structure, the current blocking layer 25
It is possible to increase the output and control the beam shape as described above by controlling the shape. That is, by making the width narrow at the central portion, a low threshold value and thus high output can be achieved, and by making the width wide at the end face portion, for example, the far field pattern can be made small.

However, in this case, although it is necessary to form the etching depth with high precision, it is difficult to obtain a sufficient etching selection ratio between the current block layer 25 and the cladding layer 24 thereunder, which results in a high productivity. There is a risk of lowering.

On the other hand, when the groove 2d in the second embodiment of the present invention is formed by etching, the depth may be such that it reaches the substrate 1 across the current block layer, and then once. Since the laser resonator can be formed by crystal growth of, it is extremely advantageous in productivity and reliability.

The present invention is not limited to the above-mentioned embodiments, but the active layer may be constituted by applying a quantum well structure. And the band gap becomes larger, and the window effect at the above-mentioned end face portion can be more strongly obtained. In addition, it goes without saying that various modifications can be made to the material configuration, such as the conductivity type of each layer being the opposite conductivity type.

[0052]

As described above, according to the present invention, the beam shape can be controlled with the active layer 4 kept narrow, that is, with the low threshold current and high output maintained. Even when incorporated in an optical system such as a CD player, the far field pattern can be made relatively small, the decrease in coupling efficiency can be suppressed, the output value is relatively low, and the optical system is the same as the conventional one. Can be configured with.

Furthermore, by modulating the width of the active layer 4 to make it narrow at the center of the resonator and wide at the end face,
It can be grown relatively thick at the center of the resonator and relatively thin at the end face. Therefore, a window effect can be obtained at the end face of the resonator, and end face deterioration due to heat generation or the like in this part can be suppressed, so that the laser output can be increased and the reliability can be improved.

[Brief description of drawings]

FIG. 1 is an enlarged schematic perspective view of a first embodiment of the present invention.

FIG. 2 is an enlarged schematic perspective view of a second embodiment of the present invention.

FIG. 3 is a schematic linear enlarged perspective view showing one manufacturing process of the first embodiment of the present invention.

FIG. 4 is a schematic linear enlarged side view in one manufacturing process of the first embodiment of the present invention.

FIG. 5 is a manufacturing process diagram of the second embodiment of the present invention.

FIG. 6 is a schematic enlarged perspective view of a comparative example.

FIG. 7 is a schematic linear enlarged sectional view of an example of a conventional semiconductor laser.

FIG. 8 is a configuration diagram of an example of an optical device.

[Explanation of symbols]

1 Compound semiconductor substrate 2 steps 2r ridge 2d groove 2u step top 3 First conductivity type cladding layer 4 Active layer 5 First conductivity type first cladding layer 6 Current blocking layer 7 Second clad layer of the second conductivity type 8 Second conductivity type cap layer 9A slope 9B slope 10 Triangular area 11 electrodes 12 electrodes 13 discontinuous plane 15 Second conductivity type cladding layer 16 Second conductivity type surface layer 19A vertical surface 19B vertical surface 20 resonator 20A end face 20B end face

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-1-140787 (JP, A) JP-A-4-24977 (JP, A) JP-A-5-55692 (JP, A) JP-A-63- 5587 (JP, A) JP-A 64-61084 (JP, A) JP-A 63-257287 (JP, A) JP-A 3-188692 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (6)

(57) [Claims] 1. A stripe-shaped ridge extending in the <011> crystal axis direction is formed on a compound semiconductor substrate having a {100} crystal plane as a main surface, and at least the first ridge covers the ridge and is entirely covered with the first ridge. A compound semiconductor layer composed of a clad layer, an active layer, a second clad layer and a current block layer is epitaxially grown to form a laser resonator, and a sloped surface composed of {111} B crystal planes is formed from the side edge of the ridge. When formed, at least the active layer on the ridge is separated from other portions, and the active layer is
1} B crystal plane, the current blocking layer is abutted over the entire surface in the cavity length direction, and the current blocking layer is a semiconductor layer of the first conductivity type and a second conductive type.
And a semiconductor layer of the first conductivity type and a semiconductor layer of the first conductivity type are stacked.
The ridge has a three-layer structure, and the side edges of the ridge are resonant with the laser resonator such that the width of the ridge is wider than the central portion of the resonator on both end faces of the laser resonator. A semiconductor laser having a pattern curved in the device length direction, wherein the active layer of the laser resonator is formed in accordance with the shape of the ridge. 2. The active layer formed on the ridge has a thickness that changes as the width of the ridge changes.
The semiconductor laser described in 1. 3. A compound semiconductor substrate having a {100} crystal plane as a main surface is formed with stripe-shaped grooves extending in the <011> crystal axis direction, and at least the first groove is entirely formed including the inside of the groove. A compound semiconductor layer composed of a clad layer, an active layer and a second clad layer is epitaxially grown to form a laser resonator in at least the groove, and from the side edge portion of the groove, on the main surface of the compound semiconductor substrate. In which the compound semiconductor layer inside the groove and the compound semiconductor layer outside the groove are separated from each other by forming a slant surface composed of {111} B crystal planes, and the width of the groove is the laser resonator. The side edges of the groove are curved in the cavity length direction of the laser resonator so as to be wider than the central portion of the resonator at both end surfaces constituting the groove. A semiconductor laser comprising an active layer of the laser resonator. 4. The semiconductor laser according to claim 3, wherein the thickness of the active layer formed in the groove is changed by changing the width of the groove. . 5. A stripe-shaped ridge extending in the <011> crystal axis direction is gradually narrowed from both sides toward a central portion of a compound semiconductor substrate having a {100} crystal plane as a main surface. Formed as a curved pattern, covering at least the first ridge, the active layer, the second clad layer and the first conductivity type semiconductor over the entire surface of the ridge.
Body layer, second conductivity type semiconductor layer, and first conductivity type semiconductor
A compound semiconductor layer consisting of a current blocking layer having a three-layer structure in which layers are stacked is epitaxially grown to form a laser resonator, and extended from the side edge of the ridge on the ridge {1
11} B crystal planes are grown to divide and form the compound semiconductor layer on the ridge and the compound semiconductor layers on both side trenches of the ridge, and both ends constituting the laser resonator are formed. The thickness of the active layer of the laser resonator is changed in the cavity length direction by forming the width of the ridge so as to be narrow in the cavity length direction from the surface portion to the center portion. And a method for manufacturing a semiconductor laser. 6. A compound semiconductor substrate having a {100} crystal plane as a main surface, and stripe-shaped grooves extending in the <011> crystal axis direction are gradually narrowed from both sides toward a central portion. And a laser cavity in at least the groove by epitaxially growing a compound semiconductor layer including at least the first cladding layer, the active layer and the second cladding layer over the entire surface including the inside of the groove. From the side edge portion of the groove, a slope formed of a {111} B crystal plane is grown on the main surface of the compound semiconductor substrate to form the compound semiconductor layer in the groove and the groove. By forming the external compound semiconductor layer by dividing the compound semiconductor layer, and by forming the width of the groove from the both end faces forming the laser resonator toward the central portion to be narrow in the cavity length direction. A method of manufacturing a semiconductor laser, wherein the thickness of the active layer of the laser resonator is changed in the cavity length direction.