JP2003037337A - Semiconductor laser diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser diode emitting laser light in a single peak intensity pattern at a narrow emission angle. SOLUTION: The semiconductor laser diode comprises a substrate 1, and a multilayer film including an active layer 3 formed on the substrate 1. The multilayer film has a stripe structure 6 of tapered width extending in the longitudinal direction of a resonator, and first and second side faces 30a and 30b holding the stripe structure 6 between. At least one of the first and second side faces 30a and 30b is inclining to the major surface 1a of the substrate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser suitable as a light source for optical communication.

[0002]

2. Description of the Related Art In recent years, in the field of optical communication, optical communication technology for transmitting signal light emitted from a semiconductor laser through an optical fiber has been developed, and signal light of a semiconductor laser serving as a light source on the transmission side is received. In order to receive efficiently with the light receiving element, it is required to reduce the loss of signal light. In order to reduce the loss of signal light, high coupling efficiency between the emitted light of the semiconductor laser and the optical fiber is required.

In general, the emission angle of laser light of a semiconductor laser is as wide as 20 ° to about 30 °, so if laser light is directly coupled to an optical fiber without using optical components such as a lens, it is very low, such as several percent. Only coupling efficiency can be realized.

On the other hand, if an optical component such as a lens is inserted between the semiconductor laser and the optical fiber to focus the laser light, high coupling efficiency can be obtained. However, the alignment accuracy of the semiconductor laser, the optical component and the optical fiber is high. Of about 1 μm is required, and it is necessary to perform alignment with extremely high accuracy, and therefore the high cost of equipment for precision processing becomes a problem.

In order to solve this problem, a method has been considered in which the emission angle of the laser light of the semiconductor laser is set to about 10 degrees to narrow the spread of the laser light and the laser light is directly coupled to the optical fiber. A semiconductor laser that realizes such a narrow emission angle is disclosed in Japanese Patent Laid-Open No. 2000-36638.

This conventional semiconductor laser will be described with reference to FIG. 8A is a perspective view of a conventional semiconductor laser, and FIG. 8B is a perspective view of the conventional semiconductor laser as seen from above. Each stripe region of the active region is seen through. ing. Further, FIG. 8C is a diagram showing a light intensity pattern of a far-field image of laser light emitted from a conventional semiconductor laser.

As shown in FIG. 8A, the conventional semiconductor laser has an active layer 102 on a substrate 101 made of InP.
In such a manner that the stripe structure 103 including
The buried layer 104 made of P is formed.
Further, the buried layer 104 and a part of the substrate 101 are removed, and isolation trenches 105 a and 105 b are formed in parallel with the center line of the stripe structure 103 over the entire resonator.
The stripe structure 103 includes a tapered region 106 and a parallel region 107. Further, the laser light 108
The light is emitted from the end surface of the tapered region 106 of the stripe structure 103.

Light propagating from the parallel region 107 of the stripe structure 103 to the taper region 106 is tapered region 106.
The light confinement in the active layer 102 is continuously reduced during the propagation. Therefore, from the active layer 102 to the buried layer 1
The light leaking out to 04 becomes large, and the spot size of the laser beam 108 at the emission end is made larger than the spot size in the parallel region 107. Such an increase in the spot size of the laser beam 108 means that the emission angle is narrowed.

The separation grooves 105a and 105b are formed in order to increase the response speed when the semiconductor laser is directly modulated. This is because, in the buried layer 104 as the current blocking layer, the region to which the voltage is applied is limited to the region sandwiched by the separation trench 105a and the separation trench 105b, so that the electric capacity is reduced. The response speed when there is a groove can be made higher than the response speed when there is no separation groove.
The semiconductor laser having 05a and 105b is effective when modulating the semiconductor laser.

[0010]

However, in the laser having the tapered stripe structure having the active layer 102, the light (hereinafter referred to as “radiation light”) 109 exuding from the tapered region 106 is As shown in FIG. 8B, the light propagates in the buried layer 104 next to the active layer 102 in parallel with the substrate 101 and is reflected by the sidewalls of the isolation trenches 105a and 105b. The reflected radiated light 110 travels in the buried layer 104 as it is, and is emitted from the end face of the semiconductor laser to the outside together with the laser light 108 guided in the active layer 102.

In this case, as shown in FIG. 8 (c), the emitted light 109 and the emitted laser light 108 interfere with each other at the emitting end face of the laser light, and a single-peaked light in the far-field image parallel to the substrate 101. There is a problem that the intensity pattern cannot be obtained and the utilization efficiency of the laser light for the optical fiber is significantly reduced.

The present invention has been made in view of the above points, and a main object thereof is to provide a semiconductor laser which improves the utilization efficiency of laser light.

[0013]

A semiconductor laser according to the present invention comprises a substrate and a multilayer film formed on the substrate and including an active layer, the multilayer film having stripes extending in a cavity length direction. A stripe structure having a tapered portion in which the width of the stripe changes in a taper shape, and a first side surface and a second side surface sandwiching the stripe structure,
At least one of the first side surface and the second side surface is inclined with respect to the main surface of the substrate.

It is preferable that both the first side surface and the second side surface are inclined with respect to the main surface of the substrate.

It is preferable that a separation groove is formed on the substrate, and a side surface of the separation groove is the first side surface of the multilayer film.

In a preferred embodiment, a width W1 at a front end face of the stripe structure and a width W2 at a rear end face of the stripe structure satisfy a relationship of W1 <W2, and the taper portion of the stripe structure. Is a portion of the tapered region in which the width of the stripe structure continuously changes between the front end face and the rear end face.

In a preferred embodiment, the multilayer film further has a buried layer that fills the stripe structure, and a contact layer formed on the buried layer.

In a preferred embodiment, the angle formed by the first side surface or the second side surface of the multilayer film and the surface of the contact layer is 105 degrees or more and 165 degrees or less.

In a preferred embodiment, a radiation absorption layer having a bandgap energy smaller than the bandgap energy corresponding to the wavelength of the laser light emitted from the semiconductor laser is provided between the buried layer and the substrate. Further prepared.

In a preferred embodiment, the radiation absorption layer is made of an InGaAs-based material.

In a preferred embodiment, the angle formed between the first side surface or the second side surface of the multilayer film and the surface portion of the contact layer is 15 degrees or more and 75 degrees or less.

In a preferred embodiment, the contact layer is made of a material having a bandgap energy smaller than the bandgap energy corresponding to the wavelength of laser light emitted from the semiconductor laser.

In a preferred embodiment, the contact layer is made of an InGaAs-based material.

In a preferred embodiment, the substrate and the buried layer are made of InP, and the active layer is In.
It consists of GaAsP.

Another semiconductor laser according to the present invention comprises a substrate and a multilayer film formed on the substrate and including an active layer, wherein the multilayer film has a stripe structure extending in the cavity length direction. A first side surface and a second side surface sandwiching the stripe structure, and a buried layer for burying the stripe structure; The angle formed between the side surface of or the second side surface and the main surface of the buried layer is an obtuse angle or an acute angle.

In a preferred embodiment, a contact layer made of an InGaAs-based material is further formed on the buried layer, the substrate and the buried layer are made of InP, and the active layer is made of InGaAsP.
Consists of.

In a preferred embodiment, a radiation absorption layer made of an InGaAs-based material is further formed between the buried layer and the substrate, and the substrate and the buried layer are made of InP. The active layer is In
It consists of GaAsP.

The angle formed is preferably 105 degrees or more and 165 degrees or less.

Alternatively, the angle formed is 15 degrees or more and 75
It is preferably not more than a degree.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present application have earnestly studied a semiconductor laser capable of emitting a laser beam having a narrow emission angle and a unimodal light intensity pattern, and have developed such a semiconductor laser. I came up with the idea and completed the present invention. According to the semiconductor laser of the present invention, it is possible to improve the utilization efficiency of laser light for an optical waveguide (for example, an optical fiber). Further, even when the separation groove is formed in order to improve the response speed by direct modulation, the semiconductor laser of the present invention can be realized, so that the advantage of not reducing the modulation speed can be enjoyed.

Before explaining the embodiment of the present invention, FIG.
A technical example for avoiding the influence of the radiated light 109 in the configuration shown in FIG. 8 will be described with reference to (a) to (c). 9B and 9C are cross-sectional views taken along the line AA 'and the line BB' in FIG. 9A, respectively.

The structure shown in FIG. 9A is the same as the structure shown in FIG. 8B except that the recess 205 is provided.
More specifically, the recess 205 is provided in a part of the mesa groove 204 to prevent the emitted light from propagating in the resonator. In FIG. 9A, the concave portion 205 is arranged at the position on the right side of the paper (the right side of the taper portion). However, if it is possible to prevent the emitted light from propagating in the resonator, the central portion (taper portion) of It may be provided at the position or on the left side (the left side of the taper portion). Here, reference numeral 201 is an active layer, 202 is a spot size converter, and 20
3 is a mesa structure, 204 is a mesa groove, 2
Reference numeral 05 is a concave portion, 206 is a rear end surface, and 207
Is the exit end face, and 208 is the light intensity distribution.

Providing the concave portion 205 can prevent the radiation light from propagating in the resonator, so it seems that the influence of the radiation light can be avoided, but in reality, the following problems occur. That is, in the case of the configuration shown in FIG. 9A, as shown in FIG. 9C, the light intensity distribution 208 may extend outside the mesa structure 203 in the portion where the recess 205 is formed. . In particular, in order to realize a modulation band of 10 GHz or more, the width of the mesa structure 203 is about 5 μm, and the mesa structure 2 in the region where the concave portion 205 is formed is formed.
The width of 03 is about 2 to 3 μm. In that case, FIG.
As shown in (c), the width of the mesa structure 203 is smaller than the width of the light intensity distribution 208, and therefore the light intensity distribution 208 extends outside the mesa structure 203. As a result, the light intensity distribution 208 is disturbed, and the emission pattern from the emission end face loses the monomodality.

Therefore, with the configuration shown in FIG. 9A, it is difficult to emit laser light having a monomodal light intensity pattern, even if the influence of the emitted light 109 can be avoided.

According to the present invention, the side surface of the mesa structure is not made vertical so that the influence of the radiated light can be avoided and the laser light having a monomodal light intensity pattern can be emitted. Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In the following drawings, for simplification of description, components having substantially the same function are designated by the same reference numeral. The present invention is not limited to the embodiments below.

(First Embodiment) A semiconductor laser according to the first embodiment of the present invention will be described below with reference to FIG. Note that FIG. 1A is a diagram showing a laser light emitting end face of the semiconductor laser according to the first embodiment of the present invention. Further, FIG. 1 (b) shows X- in FIG. 1 (a).
It is sectional drawing which follows an X-ray.

The semiconductor laser of this embodiment comprises a substrate 1 and
Multilayer film (2, 3, 4, 5, 7,
8, 9, 10) and the multilayer film has
At least the active layer 3 is included. Here, the multilayer film is
The multilayer structure includes a stripe structure 6 (2 to 4) having a taper portion (a portion of a region B in FIG. 1B) that extends in the cavity length direction and in which the width of the stripe changes in a taper shape. The first and second side faces 3 sandwiching the stripe structure 6 therebetween.
There are 0a and b. Then, at least one of the first side surface 30a and the second side surface 30b is inclined with respect to the main surface 1a of the substrate 1.

In the configuration shown in FIG. 1, the first side surface 30a
Both the second side surface 30b and the second side surface 30b are inclined with respect to the main surface 1a of the substrate 1. Further, on the substrate 1, the separation groove (11
a, 11b) are formed, and the side surface (or side wall) of the separation groove 11a is the first side surface 30a of the multilayer film. Similarly, the side surface (or side wall) of the separation groove 11b is
It is the second side surface 30b of the multilayer film. Further, in this structure, as shown in FIG. 1B, the width W1 at the front end face and the width W at the rear end face of the stripe structure 6 are
2 satisfies the relationship of W1 <W2, and
The stripe structure 6 is a region (tapered region) in which the width of the stripe structure 6 continuously changes between the front end face and the rear end face.
have.

Next, the configuration of this embodiment will be described in more detail. As shown in FIG. 1A, a stripe-shaped mesa portion is formed on a substrate 1 made of n-type InP, and n-type In _1-x Ga _x As _y P _1-y ( Where x =
0.11, y = 0.24), and the thickness is about 60n.
m, λg is about 1.05 μm, the optical confinement layer 2, the multiple quantum well active layer 3, the p-type In _1-x Ga _x As _y P _1-y (where x = 0.11, y = 0. 24), the optical confinement layer 4 having a thickness of about 60 nm and λg of about 1.05 μm is formed in a mesa shape, and extends in a stripe shape in the cavity length direction. On the optical confinement layer 4, p-type In
A cladding layer 5 made of P and having a thickness of about 400 nm is formed. The shaded area in FIG. 1B represents a stripe structure 6, which includes the optical confinement layer 2, the multiple quantum well active layer 3, and the optical confinement layer 4.
It is composed of.

On both sides of the stripe structure 6, a current block layer 7 made of p-type InP and a current block layer 8 made of n-type InP are formed. Further, p-type In is formed on the current blocking layer 8 and the cladding layer 5.
A buried layer 9 made of P and a contact layer 10 made of p-type In _1-x Ga _x As (here, x = 0.47) are sequentially formed.

Then, the current blocking layers 7 and 8, the buried layer 9, the contact layer 10 and a part of the substrate 1 are removed,
Two stripe-shaped separation grooves 11a and 11b having a V-shaped cross section are formed on both sides of the stripe structure 6.

The separation grooves 11a and 11b are formed in parallel with the center line of the stripe structure 6 in the cavity length direction,
The opening width of each of the separation grooves 11a and 11b is about 30 μm.
Is. In the V-shaped separation groove 11a, the separation groove 11a
Of the side surface (the first side surface 30) close to the stripe structure 6 of
The separation groove angle 12, which is the angle between a) and the surface of the contact layer 10, is 135 degrees. The separation groove angle is 12
Need only be formed so as to fall within the range of 105 degrees to 165 degrees. Similarly, in the separation groove 11b,
The side surface of the separation groove 11b on the side close to the stripe structure 6 (second
The separation groove angle 12 which is an angle formed by the side surface 30b) of the above and the surface of the contact layer 10 is 135 degrees, and may be formed so as to be an angle in the range of 105 degrees to 165 degrees. The separation groove angles 12 of the separation grooves 11a and 11b do not have to be the same. Also, the first side surface 3
0a and the second side surface 30b are also inclined with respect to the main surface 1a of the substrate 1.

The separation grooves 11a and 11b can be formed by an etching technique so that the separation groove angle 12 is in the range of 105 to 165 degrees.
When the substrate 1 has a plane orientation of (100) and the stripe structure 6 is formed in the <110> direction, it can be easily formed by using an isotropic etchant such as an acetic acid-based etchant. You can

An insulating film 13 made of SiO ₂ is formed over the isolation trenches 11a and 11b to a part of the upper portion of the contact layer 10, and a striped window is formed on the contact layer 10. Furthermore, the insulating film 13
Ti / Pt / Au so as to cover the striped window of
The p-side electrode 14 made of the alloy is formed and is in contact with the contact layer 10 through the window. The p-side electrode 14 is
It may also be composed of a Pt / Ti / Pt / Ti / Au multilayer film or an alloy. On the back surface 1b of the substrate 1, Au /
An n-side electrode 15 made of an Sn alloy is formed. n
The side electrode 15 can also be made of a Au / Sn / Au multilayer film or an alloy.

The multiple quantum well active layer 3 is composed of 7 pairs of well layers and barrier layers. The well layer is an InGaAsP well layer introduced with compressive strain in the range of about 0.7%, and the thickness thereof is about 6 nm. The InGaAsP well layer is formed of, for example, In _1-x Ga _x As _y P _1-y (where x is
= 0.21, y = 0.68). The barrier layer is an InGaAsP barrier layer having a thickness of about 10 nm and a λg of about 1.05 μm in which no strain is intentionally introduced. The InGaAsP barrier layer is made of, for example, In _1-x Ga _x A
S _y P _1-y (where x = 0.11 and y = 0.24). The length of the resonator of the semiconductor laser is about 400 μm, and the width of the stripe structure 6 including the multiple quantum well active layer 3 changes in the resonator length direction. Specifically, the stripe width W1 is about 0.6 μm in the region A having a length of about 25 μm from the front end face from which the laser light of the semiconductor laser is emitted, while the length from the rear end face of the semiconductor laser is about 0.6 μm. The stripe width W2 in the region C of 25 μm is set to about 1.6 μm. In a region B between the regions A and C of the stripe structure 6 (hereinafter, also referred to as “tapered region”), the stripe width changes linearly so as to connect the regions A and C. The oscillation wavelength of the semiconductor laser is around 1.3 μm.

Next, the trajectory of the emitted light of the semiconductor laser according to this embodiment will be described with reference to FIG. It should be noted that, with reference to FIG. 8 as well, a comparison is made with the trajectory of the emitted light of the conventional semiconductor laser.

FIGS. 2A, 2B and 2C are views of the semiconductor laser according to the present embodiment as seen through from above, respectively, showing the stripe structure, a view showing the laser light emitting end face, and FIG. It is a figure which shows the light intensity pattern of the far-field image of the parallel direction of the emitted laser beam.

As shown in FIGS. 2 (a) and 8 (b),
When the semiconductor laser is viewed from above, the locus of the emitted light 16 of the semiconductor laser according to the present embodiment and the locus of the emitted light 109 of the conventional semiconductor laser are the same. That is, the emitted light 16 of FIG. 2A is reflected by the side walls of the separation grooves 11a and 11b, and the emitted light 109 of FIG.
Reflected at 5a and 105b.

Here, in the case of the present embodiment, as shown in FIG. 2B, since the separation groove angle is set to 135 degrees instead of 90 degrees, the emitted light 17 reflected by the side walls of the separation groove 11a is striped. The structure 6 does not move in the lateral direction parallel to the substrate 1 but in the direction of the substrate 1. Therefore, the emission light 16 when viewed from the end face side of the semiconductor laser according to the present embodiment does not overlap the light distribution range 19 of the laser light 18 at the emission end face. Therefore, the separation groove 11a
The radiated light 17 and the laser light 18 reflected on the side wall of the laser do not interfere with each other, and as shown in FIG. 2C, the light intensity pattern in the far-field image in the direction parallel to the substrate 1 has a unimodal peak. .

On the other hand, as described above, in the case of FIG. 8B, the radiated light 110, which is the radiated light 109 reflected by the side wall of the separation groove 11a, interferes with the emitted laser light 108, and as a result, However, it becomes impossible to obtain a monomodal light intensity pattern. In order to avoid the influence of the radiated light 110, as shown in FIG. 9, if a recess 205 is provided to prevent the radiated light from propagating in the resonator, this time the light intensity distribution will be outside the mesa structure. This may cause the light intensity distribution to be disturbed and the emission pattern from the emission end face to lose the monomodality.

In the semiconductor laser according to this embodiment, the emitted light 16 emitted from the stripe structure 6 is the first
When reflected by the side surface 30a or the second side surface 30b, the side surfaces 30a and 30b are not formed perpendicularly to the substrate 1, so that the reflected radiated light 17 does not travel parallel to the substrate 1. Therefore, the reflected radiated light 17 does not overlap the light distribution range of the laser light 18 emitted from the stripe structure 6 on the emission end face of the laser light, and the laser light 18 and the emitted light do not interfere with each other.

First side surface 30a or second side surface 30
If the radiated light 17 reflected by b can be prevented from interfering with the laser light 18, the light intensity pattern in the far-field image in the direction parallel to the substrate 1 will have a single-peaked peak, so The coupling efficiency can be increased, and as a result, the utilization efficiency of the laser light with respect to the optical fiber can be improved. In addition, since no optical component such as a lens is used in coupling the optical fiber and the semiconductor laser, a small optical module can be constructed. The semiconductor laser of this embodiment may be optically coupled not only with the optical fiber but also with the waveguide of the planar optical waveguide (PLC).

When the separation groove angle 12 approaches 90 degrees, the reflected radiated light 17 may overlap the light distribution range 19 of the laser light 18 on the emission end face. On the other hand, when the separation groove angle 12 becomes large and approaches 180 degrees, the region to which a voltage is applied expands and the electric capacity increases. That is, in order to avoid the influence of the radiated light 17, an angle (obtuse angle) exceeding 90 degrees may be used, and in an extreme example, 1
It may be 80 degrees, but the separation groove angle 12 is 18
When it gets close to 0 degree, the influence of the parasitic capacitance begins to appear, and
When the influence of the parasitic capacitance increases, there is a problem in that the modulation speed decreases. Considering these points, the separation groove angle is preferably within a predetermined range (for example, a range of 105 degrees to 165 degrees).

FIG. 3 is a graph showing the relationship between the separation groove angle 12 on the horizontal axis and the capacity and the radiation angle with respect to the separation groove angle 12. In FIG. 3, a standardized value is shown when the separation groove angle 12 is 90 degrees, and the vertical axis of the capacitance is an arbitrary unit (a.
u. ). As shown in FIG. 3, set the separation groove angle 12 to 1
If the range is from 05 degrees to 165 degrees, the capacity increase is 50
% Or less, and the emission angle can be 15 degrees or less. Within this range, it can be used practically without any problems.

In this embodiment, the separation groove angle 12 is the first
Alternatively, the angle is defined by the angle between the second side surfaces 30a and 30b and the surface of the contact layer 10, but of course is determined by the angle between the side surface 30a or 30b and the main surface (upper surface) 9a of the buried layer 9. Good. In any case, it is possible to define the configuration in which the side surface 30a or 30b is inclined with respect to the main surface (upper surface) 1a of the substrate 1. If the buried layer 9 is made of n-type InP, the contact layer 10 may not be provided depending on the contact resistance. Therefore, in this case, the main surface 9a of the buried layer 9 is not formed. Separation groove angle 1 depending on the angle formed by
It is very convenient to specify 2. Here, the “main surface” of the main surface of the burying layer 9 and the main surface of the substrate 1 typically means the upper surface, for example, a surface having a wide area, or FIG. It is a surface extending in the horizontal direction in the configuration shown in FIG.

In the above description, the separation groove 11a has been mainly described, but the same applies to the separation groove 11b, and at least one of the separation groove 11a and the separation groove 11b has a side wall inclined with respect to the substrate. All you have to do is do it.

In the structure of this embodiment, the isolation trenches 11a and 11b are formed in the substrate 1 in order to reduce the influence of the electrical capacitance (parasitic capacitance) that reduces the modulation speed. To reduce the effect of parasitic capacitance,
Not only the form in which the groove is formed in a part of the substrate, but the form other than the multilayer film (mesa part) sandwiched between the side surfaces 30a and 30b, which corresponds to the form in which the groove is made larger, may be removed. That is, in the configuration shown in FIG.
The left side portion 40a or the right side portion 40b arranged on the substrate 1 may be removed.

(Second Embodiment) Next, a semiconductor laser according to a second embodiment of the present invention will be described with reference to FIG. Note that FIG. 4A is a diagram showing a laser light emitting end face of the semiconductor laser according to the second embodiment of the present invention. Further, FIG. 4B shows X- in FIG.
It is sectional drawing which follows an X-ray.

The semiconductor laser according to the second embodiment of the present invention is structurally different from the semiconductor laser according to the above-mentioned first embodiment in that the substrate 1 does not have a stripe-shaped mesa portion, N-type In _1-x lattice-matched to InP on ₁
A radiant light absorption layer 20 made of Ga _x As (where x = 0.47) and having a thickness of 0.1 μm is formed, and a buffer layer 21 made of n-type InP is formed on the radiated light absorption layer 20. That is, the buffer layer 21 is formed in a stripe-shaped mesa portion, and the stripe structure 6 is formed on the mesa portion. Further, the separation grooves 11a and 11b are formed on the substrate 1
The buffer layer 21 is formed so as to be partially removed instead of being removed up to this point, but the effect remains the same even when the substrate 1 is removed here. The same components as those of the semiconductor laser according to the first embodiment are designated by the same reference numerals, and the description thereof will be omitted here.

The semiconductor laser according to the second embodiment has a structure in which the emitted light reflected by the side walls of the separation grooves 11a and 11b is absorbed by the emitted light absorbing layer 20. In order to absorb the emitted light, the bandgap energy of the emitted light absorption layer 20 may be made smaller than the bandgap energy of the oscillation wavelength of the laser light.

In the semiconductor laser according to the second embodiment,
The emitted light that is reflected by the sidewalls of the separation grooves 11a and 11b and travels to the substrate 1 can be absorbed by the emitted light absorption layer 20.
Therefore, it is possible to doubly prevent the radiation light reflected by the side walls of the separation grooves 11a and 11b from further reflecting on the substrate 1 and interfering with the laser light on the emission end face, and the far-field image in the direction parallel to the substrate 1 can be prevented. The light intensity pattern at is a more monomodal peak.

(Third Embodiment) Next, a semiconductor laser according to a third embodiment of the present invention will be described with reference to FIG. Note that FIG. 5A is a diagram showing a laser light emitting surface of the semiconductor laser according to the third embodiment of the present invention. Further, FIG. 5B shows XX in FIG.
It is sectional drawing which follows the line.

The semiconductor laser according to the third embodiment of the present invention is the same as the semiconductor laser according to the first embodiment, except that the separation groove angle 12 is formed within the range of 15 degrees to 75 degrees. is there. In FIG. 5, the separation groove angle 1
2 is 60 degrees.

Forming the separation grooves 11a and 11b so that the separation groove angle 12 is in the range of 15 degrees to 75 degrees is as follows.
This can be done by etching technology. The plane orientation of the substrate 1 is the (001) plane, and the stripe structure 6 is <110>.
When it is formed in the direction, it can be easily formed by using an anisotropic etchant such as a hydrochloric acid-based etchant.

The same components as those of the semiconductor laser according to the first embodiment are designated by the same reference numerals, and the description thereof will be omitted here.

Next, the locus of emitted light of the semiconductor laser according to the third embodiment of the present invention will be described with reference to FIG. 6 (a), 6 (b) and 6 (c) show the third embodiment of the present invention.
Of the semiconductor laser according to the embodiment of the present invention in which the separation groove angle is 60 degrees, each is a view seen from above through the stripe structure, a view showing the emitting end face of the laser light, and a view of the emitted laser light. It is a figure which shows the light intensity pattern of the far-field image in a parallel direction. Note that the reference numerals given in FIG. 6 and the reference numerals given in FIG.

First, as shown in FIGS. 6 (a) and 6 (b),
In the semiconductor laser according to the third embodiment of the present invention,
The radiated light 22 generated from the tapered region of the stripe structure 6 and traveling parallel to the substrate 1 travels in the current block layers 7 and 8 on the sides of the stripe structure 6 and is reflected by the side wall of the isolation trench 11a. At this time, since the separation groove angle 12 is 60 degrees, the reflected radiated light 23 does not proceed in the lateral direction of the stripe structure 6 in parallel with the substrate 1 but proceeds away from the substrate 1, so that at the emission end face. , Does not overlap the light distribution range 19 of the laser light 18. Therefore, similarly to the semiconductor laser according to the first embodiment, the radiated light 23 reflected by the side wall of the separation groove 11a and the laser light 18 do not interfere with each other, and FIG.
As shown in, the light intensity pattern in the far-field image parallel to the substrate 1 has a monomodal peak.

Furthermore, in the semiconductor laser according to the present embodiment, In _1-x Ga _x As (where x = x) having a bandgap energy smaller than the bandgap energy corresponding to the wavelength of laser light of 1.3 μm. 0.4
Since the radiated light 23 reflected by the side wall of the separation groove 11a is absorbed by the contact layer 10 composed of 7), the reflected radiated light 23 may be scattered in the semiconductor laser and overlap the light distribution range 19 of the laser light 18. Absent.

When the separation groove angle 12 approaches 90 degrees, the reflected radiated light 23 may overlap the light distribution range 19 of the laser light 18 on the emission end face. Conversely, if the separation groove angle 12 becomes too small, the multilayer structure including the stripe structure 6 between the separation grooves 11a and 11b becomes
It is separated from the substrate 1 and does not function as a semiconductor laser. Further, in order to avoid the influence of the radiated light, an angle (acute angle) of less than 90 degrees may be set, and in an extreme example, it may be close to 0 degrees, but the separation groove angle 12 is set to 0 degrees. When it gets closer, the effect of parasitic capacitance begins to appear,
This causes a decrease in modulation speed. Therefore, considering these points, the separation groove angle is preferably within a predetermined range (for example, a range of 15 degrees to 75 degrees).

FIG. 7 is a graph showing the relationship between the separation groove angle 12 on the horizontal axis and the capacitance and the radiation angle with respect to the separation groove angle 12. In FIG. 7, the standardized value is shown when the separation groove angle 12 is 90 degrees, and the vertical axis of the capacitance is an arbitrary unit (a.
u. ). As shown in FIG. 7, set the separation groove angle 12 to 1
In the range of 5 degrees to 75 degrees, the increase in capacity can be suppressed to 50% or less, and the radiation angle can be set to 15 degrees or less. Within this range, it can be used practically without any problems.

Although the separation groove 11a has been described, the same applies to the separation groove 11b, as long as at least one of the separation groove 11a and the separation groove 11b has a side wall inclined with respect to the substrate.

The bandgap energy of the contact layer 10 does not have to be smaller than the energy of the laser light 18, and for example, In having a composition wavelength of 1.2 μm can be used.
_1-x Ga _x As _y P _1-y (where x = 0.22, y = 0.
48). That is, even if the contact layer 10 does not absorb the emitted light, the effect of avoiding the influence of the emitted light can be obtained by not making the side surface of the mesa structure vertical. InGa having a composition wavelength of 1.2 μm
Even AsP can fulfill the original role of the contact resistance of the contact layer 10 (especially when the buried layer 9 is made of n-type InP).

As described above, the oscillation wavelength of the semiconductor laser devices according to the first to third embodiments is 1.3 μm band.
It may be in the 1.55 μm band, or may be another oscillation wavelength. Further, the semiconductor laser devices according to the first to third embodiments have a Fabry-Perot type semiconductor laser configuration, but a diffraction grating is formed near the active layer (for example, the substrate near the active layer). It may have a distributed feedback laser (DFB laser) configuration.

[0074]

According to the semiconductor laser of the present invention, since at least one of the first side surface and the second side surface is inclined with respect to the main surface of the substrate, the light is emitted from the stripe structure. When the emitted light is reflected by the first side surface or the second side surface, the reflected emitted light can be prevented from traveling parallel to the substrate. Therefore, the reflected radiated light can be prevented from overlapping the light distribution range of the laser light emitted from the stripe structure on the emission end face of the laser light, so that the utilization efficiency of the laser light can be improved.

[Brief description of drawings]

FIG. 1A is a cross-sectional view taken along line XX in FIG. 1B showing a laser light emitting end face of a semiconductor laser according to a first embodiment.

FIG. 2A is a top view of the semiconductor laser according to the first embodiment seen through the stripe structure. FIG. 2B is a view showing a laser light emitting end face of the semiconductor laser according to the first embodiment. c) A diagram showing a light intensity pattern of a far-field image in a parallel direction of laser light emitted from the semiconductor laser according to the first embodiment.

FIG. 3 is a graph showing the relationship between the capacity and the radiation angle with respect to the separation groove angle.

FIG. 4A is a sectional view taken along line XX in FIG. 4B showing a laser light emitting end face of the semiconductor laser according to the second embodiment.

FIG. 5A is a cross-sectional view taken along line XX in FIG. 5B showing the emission end face of the laser light of the semiconductor laser according to the third embodiment.

6A is a top view of the semiconductor laser according to the third embodiment as seen through the stripe structure. FIG. 6B is a view showing the laser light emitting end face of the semiconductor laser according to the third embodiment. c) A diagram showing a light intensity pattern of a far-field image in a parallel direction of laser light emitted from the semiconductor laser according to the third embodiment.

FIG. 7 is a graph showing the relationship between the capacity and the radiation angle with respect to the separation groove angle.

FIG. 8A is a perspective view of a conventional semiconductor laser seen through a stripe structure. FIG. 8B is a perspective view of a conventional semiconductor laser seen from above through a stripe structure. FIG. 8C is a laser emitted from a conventional semiconductor laser. The figure which shows the light intensity pattern of the far-field image of light.

9A is a cross-sectional view taken along the line BB ′ in FIG. 9B and FIG. 9A showing a laser light emitting end face of the semiconductor laser in which the influence of radiated light is avoided. Sectional view along line C '

[Explanation of symbols]

1, 101 substrate 2, 4 Optical confinement layer 3 Multiple quantum well active layer 5 Clad layer 6,103 stripe structure 7, 8 Current blocking layer 9,104 Embedded layer 10 Contact layer 11a, 11b, 105a, 105b Separation groove 12 Separation groove angle 13 Insulating film 14 p-side electrode 15 n-side electrode 16, 17, 22, 23, 109, 110 Synchrotron radiation 18, 108 Laser light 19 Light distribution range 20 Radiation absorption layer 21 buffer layer 102 active layer 106 taper region 107 Parallel area 201 Active layer 202 spot size converter 203 Mesa structure 204 Mesa groove 205 recess 206 rear end face 207 Exit end face 208 Light intensity distribution

Claims (17)

[Claims] 1. A substrate, and a multilayer film formed on the substrate and including an active layer, wherein the multilayer film has a stripe structure extending in a cavity length direction, and a stripe width is tapered. A stripe structure having a changing tapered portion; and a first side surface and a second side surface sandwiching the stripe structure, wherein at least one side surface of the first side surface and the second side surface is A semiconductor laser tilted with respect to the main surface of a substrate. 2. The first side surface and the second side surface are both inclined with respect to the main surface of the substrate.
The semiconductor laser described in 1. 3. The semiconductor laser according to claim 1, wherein a separation groove is formed on the substrate, and a side surface of the separation groove is the first side surface of the multilayer film. 4. A width W1 at a front end surface of the stripe structure and a width W2 at a rear end surface of the stripe structure satisfy a relationship of W1 <W2, and the tapered portion of the stripe structure has the stripe structure. 2. The semiconductor laser according to claim 1, wherein the width of the taper region is a portion of a taper region that continuously changes between the front end face and the rear end face. 5. The multilayer film according to claim 1, further comprising a buried layer filling the stripe structure and a contact layer formed on the buried layer. The semiconductor laser described. 6. The angle formed between the first side surface or the second side surface of the multilayer film and the surface of the contact layer is 1.
The semiconductor laser according to claim 5, wherein the semiconductor laser has an angle of not less than 05 degrees and not more than 165 degrees. 7. A radiation absorption layer having a bandgap energy smaller than the bandgap energy corresponding to the wavelength of the laser light emitted from the semiconductor laser is further provided between the buried layer and the substrate.
The semiconductor laser according to claim 5. 8. The semiconductor laser according to claim 7, wherein the radiation absorption layer is made of an InGaAs-based material. 9. The angle formed between the first side surface or the second side surface of the multilayer film and the surface portion of the contact layer is:
6. The angle is 15 degrees or more and 75 degrees or less.
The semiconductor laser described in 1. 10. The semiconductor laser according to claim 9, wherein the contact layer is made of a material having a bandgap energy smaller than a bandgap energy corresponding to a wavelength of laser light emitted from the semiconductor laser. . 11. The semiconductor laser according to claim 10, wherein the contact layer is made of an InGaAs-based material. 12. The substrate and the buried layer are made of InP.
12. The semiconductor laser according to claim 4, wherein the active layer is made of InGaAsP. 13. A substrate, and a multilayer film formed on the substrate and including an active layer, wherein the multilayer film has a stripe structure extending in a cavity length direction, and the stripe width is tapered. A stripe structure having a changing taper portion, a first side surface and a second side surface sandwiching the stripe structure, and a buried layer for burying the stripe structure, the first side surface or the second side surface And the main surface of the buried layer forms an obtuse angle or an acute angle. 14. An I layer is further formed on the buried layer.
The semiconductor laser according to claim 13, wherein a contact layer made of an nGaAs-based material is formed, the substrate and the buried layer are made of InP, and the active layer is made of InGaAsP. 15. A radiation absorption layer made of an InGaAs-based material is further formed between the buried layer and the substrate, the substrate and the buried layer are made of InP, and the active layer is made of InGaAsP. The semiconductor laser according to claim 13, which comprises: 16. The semiconductor laser according to claim 13, wherein the angle formed is 105 degrees or more and 165 degrees or less. 17. The semiconductor laser according to claim 13, wherein the angle formed is 15 degrees or more and 75 degrees or less.