JPH09199785A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser device with a spot-size converter whose mode shape present in the vicinity of its outgoing radiation end surface is improved even when using a hard material to grow selectively. SOLUTION: A semiconductor laser device both having a spacer 3 disposed on an Al containing active layer 2 provided on a semiconductor substrate 1 whose thickness present in a spot-size converting region 4 is larger than its thickness present in a laser region 5 and becomes larger in an inversely tapered way toward the outgoing radiation end surface of the semiconductor laser device and having a ridge 6 disposed on this spacer layer 3, wherein at least one portion of the spacer layer 3 present in the spot-size converting region 4 is formed out of a no-Al containing selective growth layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device in which a tapered waveguide (spot size converter) used for optical communication is integrated.

[0002]

2. Description of the Related Art In recent years, FTTH (Fiber to th) has been attempting to provide multimedia information to general households.
e Home; an attempt to provide a large amount of information such as an image by pulling an optical fiber to a general household) is becoming practical.

In order to realize this system, it is necessary to reduce the price of the semiconductor laser module. However, in the manufacturing cost of such a semiconductor laser module, a semiconductor laser, an optical fiber, a lens or the like is required. The position of the optical element is large, and in order to reduce the cost of the position adjustment, development of a semiconductor laser device integrated with a spot size converter has been activated.

A conventionally proposed semiconductor laser device with a spot size converter will be described with reference to FIG. 5A is a plan view of the semiconductor laser device with a spot size converter, and FIG. 5B is FIG.
It is sectional drawing which followed the dashed-dotted line which connects AA 'of (a).

5 (a) and 5 (b), this semiconductor laser device with a spot size converter has an optical waveguide layer 32, an MQW core 33, an optical waveguide layer 34, and a ridge layer 35 on a cladding layer 31. After stacking, the ridge layer 35 is selectively etched to have a constant width in the gain region 37 and a spot size conversion region 38.
In this case, a ridge composed of a tapered wide portion is provided, and the entire surface is covered with an epoxy resin 36 (if necessary, the 1995 IEICE General Conference Proceedings, p.
358, C-358).

In this case, in the gain region 37, the layer thickness of the optical waveguide layer 32 to the ridge layer 35 is constant, but in the spot size conversion region 38, the thickness becomes tapered toward the emitting end face. There is.

In this way, the MQW core 3 is formed on the emission end face.
3. That is, the thickness of the active layer is reduced and the ridge width is increased to increase the spot size.
By increasing the spot size and approaching the mode shape of the optical fiber, it is expected that the coupling efficiency between the semiconductor laser and the optical fiber will be improved and the alignment accuracy of the optical axis will be relaxed.

The semiconductor laser device with a spot size converter shown in FIG. 5 is excellent in avoiding the cutoff of the guided mode at the emitting end face and reducing the radiation loss.

The utilization of such a ridge structure is
AlG in which the buried layer is difficult to grow due to the natural oxide film of
aAs system, AlGaInP system, or AlGaInA
It is inevitable for a III-V compound semiconductor laser including Al such as s series.

[0010]

However, in the semiconductor laser device using such a ridge structure, the optical waveguide layer 34 is used to increase the optical confinement ratio in the stripe width direction in the gain region 37, that is, the laser region. That is, it is necessary to reduce the thickness of the spacer layer, but when the thickness of the spacer layer is made uniform over the entire surface of the device, there is a problem that the spot size is expanded near the emission end face and the mode shape is deformed. .

In order to solve such a problem, the spacer layer in the vicinity of the emission end face may be formed thickly in a taper shape, but it is actually very difficult to form it by etching. There is no choice but to adopt a selective growth method using a selective growth mask such as SiO ₂ .

However, 1 μ with improved temperature dependence
III-containing Al used as m-band semiconductor laser
In the case of a group V compound semiconductor, selective growth is very difficult, and there is a problem that a polycrystalline semiconductor layer grows on a dielectric mask such as SiO ₂ .

That is, in the case of MOVPE method (organic metal vapor phase epitaxy method), the diffusion length of the organic metal supplied as the Al source is shorter than the diffusion length of other group III sources, and a large layer thickness ratio can be obtained. Because it is not possible.

Therefore, an object of the present invention is to provide a semiconductor laser device with a spot size converter in which the mode shape in the vicinity of the emission end face is improved even when a material which is difficult to grow selectively is used.

[0015]

FIG. 1 is an explanatory view of the principle configuration of the present invention, and means for solving the problems in the present invention will be described with reference to FIG. See FIG. 1A. (1) In the present invention, on the active layer 2 containing Al provided on the semiconductor substrate 1, the spot size conversion region 4 is thicker than the laser region 5 and is tapered toward the emission end face. In the semiconductor laser device in which the spacer layer 3 which becomes thicker is provided and the ridge 6 is provided on the spacer layer 3,
At least a part of the spacer layer 3 in the spot size conversion region 4 is made of a selective growth layer containing no Al.

As described above, even when AlGaInAs or the like containing Al, which is difficult to selectively grow, is used as the active layer 2, by forming at least a part of the spacer layer 3 with the selective growth layer containing no Al, the spot is formed. The thickness of the spacer layer 3 in the size conversion region 4 can be made thicker toward the emission end face, and the mode shape can be improved.

The spacer layer 3 in the present invention means
The layer essentially has the function of a clad layer, and means a layer provided on the side opposite to the semiconductor substrate 1 with respect to the active layer 2, and
Between the semiconductor substrate 1 and the active layer 2, a wide forbidden band clad layer containing Al is usually provided.

(2) Further, in the present invention, in the above (1), the ridge 6 is formed by the cladding layer and the contact layer, and the etching stop layer is provided between the ridge 6 and the spacer layer 3. Characterize.

In this way, the ridge 6 for controlling the transverse mode is constituted by the cladding layer and the contact layer, and
By providing the etching stop layer between the ridge 6 and the spacer layer 3, the ridge 6 can be formed without affecting the thickness of the spacer layer 3.

(3) Further, the present invention is characterized in that in the above (1) or (2), the width of the ridge 6 is tapered in the spot size conversion region 4 toward the emission end face. .

As described above, by making the width of the ridge 6 into a so-called flare type in which the width is tapered in the spot size conversion region 4 toward the emitting end face, a laser beam having a small emission angle in a direction parallel to the active layer 2 is formed. And the cutoff of the guided mode can be eliminated.

See FIG. 1B. (4) Further, in the present invention, in the above (1) or (2), the width of the ridge 6 is tapered in the spot size conversion region 4 toward the emission end face. It is characterized by being

As described above, the width of the ridge 6 is narrowed in the spot size conversion region 4 toward the emission end face in a so-called wedge shape so that the horizontal mode parallel to the active layer 2 is expanded. It is possible to obtain a laser beam having a beam shape of

See FIG. 1C. (5) Further, in the present invention, in the above (1) or (2), the width of the ridge 6 is uniform in the spot size conversion region 4 and the laser region 5. And

As described above, by making the width of the ridge 6 uniform in the spot size conversion region 4 and the laser region 5, a ridge having a stable structure can be formed.

(6) Further, according to the present invention, in any of the above (1) to (5), the active layer 2 is made of AlGaInA.
and a portion of the spacer layer 3 near the active layer 2 is made of either AlGaInAs or AlInAs, and a portion of the spacer layer 3 near the ridge 6 is made of InP. .

As described above, AlGaInAs, which is difficult to grow selectively, is used as the active layer 2, and A having a large forbidden band width is used as the clad layer to improve the carrier confinement ratio.
Even when using either 1GaInAs or AlInAs, the AlGaInAs or AlInAs should be provided in a portion of the spacer layer 3 close to the active layer 2, and the portion of the spacer layer 3 close to the ridge 6 should be made of InP not containing Al. Thereby, the thickness of the spacer layer 3 in the spot size conversion region 4 can be made thicker toward the emission end face by utilizing the InP selective growth layer.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A manufacturing process of a first embodiment of the present invention will be described with reference to FIGS. 2 (a). First, on the n-type InP substrate 11, a thickness of 10 to 500 n
m, eg 200 nm n-type AlInAs cladding layer 12, thickness 50-200 nm, eg 100 nm A
lGaInAsSCH layer (separation confinement layer) 13, MQ
W active layer 14, thickness 50-200 nm, eg 100
nm AlGaInAsSCH layer 15, thickness 10-50
0 nm, for example, 200 nm of p-type AlInAs cladding layer 16 and thickness 50-500 nm, for example, 20
The 0 nm p-type InP cladding layer 17 is sequentially deposited by the MOVPE method.

The MQW active layer 14 in this case is an example.
For example, 100Å thick Al_0.09Ga _0.59In_0.32Asba
Rear layer and 80Å thick Al_0.22Ga_0.25In_0.53Asu
5 layers of L layers are stacked alternately, and the total thickness is 1
It becomes 000Å.

Further, the energy band barrier of the p-type clad layer in this case is effectively formed by the p-type AlInAs clad layer 16, and when the upper spacer layer having a thickness distribution is formed thereon, In order to prevent the oxidation of Al on the surface of the p-type AlInAs clad layer 16, it is necessary to form the p-type InP clad layer 17 that does not contain Al, and the p-type AlInAs clad layer 16 and the p-type InP clad layer 17 form a lower part. A spacer layer is constructed.

Next, as shown in FIG. 2B, a SiO ₂ layer having a thickness of 300 nm is provided on the entire surface, and then selective etching is performed only on both sides of the region to be the spot size converter, for example, 250 μm in the cavity direction.
And the width of the area that becomes the spot size converter is 100 μm.
A rectangular SiO ₂ mask 18 is formed so that

Then, using the MOVPE method as well, p
Type InP clad layer 19, p type InGaAs etching stop layer 20, p type InP clad layer 21, and p
^{The +} type InGaAs contact layer 22 is sequentially grown.

In this case, since the p-type cladding layer 19 to the p ⁺ -type InGaAs contact layer 22 do not contain Al, selective growth is possible, and in the region between the SiO ₂ masks 18, the p-type cladding layer 19 is formed. To p ⁺ type In
The thickness of the GaAs contact layer 22 gradually increases and becomes tapered.

The maximum thickness of the p-type cladding layer 19 in the spot size conversion region is 500 to 500.
SiO ₂ mask 18 at 0 nm, for example 2500 nm
The thickness in the laser region where there is no
This p-type I becomes constant at 0 nm, for example, 500 nm.
The nP clad layer 19 constitutes an upper spacer layer.

Further, the p-type InGaAs etching stop layer 20, the p-type InP clad layer 21, and the p ⁺ -type I
The thickness of the nGaAs contact layer 22 in the laser region is, for example, 50 nm, 100 nm, and 30 nm, respectively.
The thickness is 0 nm, and the thickness of each of these layers also changes in a taper shape in the spot size conversion region.

Next, referring to FIG. 3C, a photoresist is applied on the entire surface and patterned to form, for example, a stripe-shaped photoresist pattern (not shown) having a width of 1.5 μm. as a mask, p ⁺ -type In
GaAs contact layer 22 and p-type InP clad layer 2
1 is wet-etched to form a ridge 23 having a constant width.

In this case, since the p-type InGaAs etching stop layer 20 is provided, the p-type clad layer 19 is not undesirably etched in the etching process for forming the ridge 23.

Next, referring to FIG. 3D, the photoresist pattern and the SiO ₂ mask 1 are formed.
After removing 8, the p-side electrode 24 is formed by depositing a conductive layer such as Ti / Pt / Au (Ti is on the lower side) on the entire surface and patterning the n-type InP substrate 11 (not shown). A semiconductor laser device with a spot size converter, that is, a ridge structure taper waveguide integrated Fabry-Perot semiconductor laser device (FP-LD) is completed by forming an electrode on the side and then cleaving it appropriately.

The length of the laser region in this case is 300 μm.
m, and the length of the spot size conversion region is 250 μm. When a near-field image of this ridge structure taper waveguide integrated Fabry-Perot semiconductor laser device is observed, a conventional ridge structure taper waveguide integrated Fabry-Perot semiconductor laser device is observed. The deformation of the mode shape near the ridge was smaller than that of the ridge.

This is because the ridge 23 is formed in the laser region.
This is because the position of is close to the MQW active layer 14 and thus the optical confinement ratio becomes large, while the position of the ridge 23 becomes far from the MQW active layer 14 near the emission end face, and the optical confinement ratio becomes small.

Observation of the far-field image revealed that a laser beam having a narrow emission angle with a full width at half maximum of about 10 ° was obtained in both the horizontal and vertical directions.

Furthermore, when the efficiency in direct coupling with a single mode fiber was measured, a coupling efficiency of about 2.5 dB was obtained, which is an improvement of about 1 dB over the conventional ridge structure taper waveguide integrated Fabry-Perot semiconductor laser device. It was observed.

As described above, in the first embodiment, since the coupling efficiency with the optical fiber is improved, the accuracy of the optical axis alignment with the optical fiber is not required so much, and the cost required for the optical axis alignment is reduced. It can be drastically lowered, and thereby an inexpensive semiconductor laser module can be provided.

Further, in the present invention, since the upper spacer layer is formed of the p-type InP clad layer 19 containing no Al, the active layer and the SCH layer contain Al. II
A-group compound such as AlGaInAs having a larger forbidden band width is used for the confinement of carriers by using an IV compound semiconductor.
Even when a III-V group compound semiconductor containing 1 is used, a portion where the thickness of the spacer layer gradually changes can be formed by selective growth.

Next, the second and third embodiments of the present invention will be described with reference to FIG. FIG. 4A is a perspective view of the second embodiment of the present invention, which is a so-called flare in which the shape of the ridge 23 is tapered in the spot size conversion region toward the emission end face. Except for making a mold, it is exactly the same as the first embodiment.

In the case of the second embodiment, when forming the flare type ridge 23, it is necessary to perform patterning with higher accuracy than in the first embodiment, but the cutoff of the waveguide mode is further improved. It becomes possible to reduce.

FIG. 4B is a perspective view of the third embodiment of the present invention, in which the shape of the ridge 23 is tapered toward the emission end face in the spot size conversion region. It is exactly the same as that of the first embodiment except that it is formed into a so-called wedge shape.

In the case of the third embodiment, the wedge-shaped ridge 23 can expand the horizontal mode parallel to the MQW active layer 14 to expand the shape of the output beam. The width at the exit end is 0.3
Since it is necessary to set the thickness to 0.5 μm, a higher patterning accuracy is required than in the first embodiment. Further, the cutoff of the guided mode is more likely to occur than in the first and second embodiments.

In the description of the above embodiment, the MQW active layer 14 is used as the active layer, and SC
Although the H layers 13 and 15 are used, the well layer is a single layer SQ.
A W active layer may be used, or a normal bulk active layer without an SCH layer may be used.

Further, in the above embodiment, the SiO ₂ mask is used as the selective growth mask.
The dielectric mask is not limited to the O ₂ mask, and other dielectric masks such as Si ₃ N ₄ mask may be used.

In the above embodiment, the n-type InP substrate is used as the substrate, but the p-type InP substrate may be used to invert the entire conductivity type, and the substrate is a GaAs substrate. In that case, a graded buffer layer or a stepwise composition change buffer layer may be provided, if necessary, to obtain lattice matching between the substrate and the cladding layer or the active layer.

[0052]

According to the present invention, even in a semiconductor laser device in which a part of the active layer and the clad layer are made of a III-V group compound semiconductor containing Al, which is difficult to selectively grow, a spacer that also serves as a clad layer is provided. By forming a part of the layer with a III-V group compound semiconductor containing no Al, the ridge structure taper waveguide integration in which the mode shape change in the vicinity of the emitting end face is small by the selective growth method and the coupling efficiency with the optical fiber is high. Fabry-Perot semiconductor laser device can be formed, and thereby a semiconductor laser module can be provided at low cost.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a principle configuration of the present invention.

FIG. 2 is an explanatory diagram of a manufacturing process partway through the first embodiment of the present invention.

FIG. 3 is an explanatory view of a manufacturing process of the first embodiment of the present invention after FIG. 2;

FIG. 4 is an explanatory diagram of second and third embodiments of the present invention.

FIG. 5 is an explanatory diagram of a conventional semiconductor laser device with a spot size converter.

[Explanation of symbols]

1 semiconductor substrate 2 active layer 3 spacer layer 4 spot size conversion region 5 laser region 6 ridge 11 n-type InP substrate 12 n-type AlInAs clad layer 13 AlGaInAsSCH layer 14 MQW active layer 15 AlGaInAsSCH layer 16 p-type AlInAsIn P-p layer 17 Clad layer 18 SiO ₂ mask 19 p-type InP clad layer 20 p-type InGaAs etching stop layer 21 p-type InP clad layer 22 p ⁺ type InGaAs contact layer 23 ridge 24 electrode 31 clad layer 32 optical waveguide layer 33 MQW core 34 optical waveguide layer 35 Ridge Layer 36 Epoxy Resin 37 Gain Area 38 Spot Size Conversion Area

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuru Egawa 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa, Fujitsu Limited (72) Inventor Takeyuki Yamamoto 1015 Kamedota, Nakahara-ku, Kawasaki, Kanagawa Prefecture, Fujitsu Limited

Claims (6)

[Claims] 1. A spacer layer, which is thicker than a laser region in a spot size conversion region and is tapered toward an emission end face, is provided on an active layer containing Al provided on a semiconductor substrate, and the spacer is provided. In a semiconductor laser device in which a ridge is provided on the layer, at least a part of the spacer layer in the spot size conversion region is Al.
It is characterized by comprising a selective growth layer not containing. 2. The semiconductor laser device according to claim 1, wherein the ridge is formed of a cladding layer and a contact layer, and an etching stop layer is provided between the ridge and the spacer layer. 3. The semiconductor laser device according to claim 1, wherein the width of the ridge is tapered in the spot size conversion region toward the emission end face. 4. The semiconductor laser device according to claim 1, wherein the width of the ridge is tapered toward the emitting end face in the spot size conversion region. 5. The semiconductor laser device according to claim 1, wherein the width of the ridge is uniform in the spot size conversion region and the laser region. 6. The active layer is made of AlGaInAs, and the portion of the spacer layer close to the active layer is made of AlG.
composed of either aInAs or AlInAs,
Further, the portion of the spacer layer near the ridge is In
It is comprised by P, The 1 thru | or 5 characterized by the above-mentioned.
The semiconductor laser device according to any one of 1.