JP2003234537A - Semiconductor laser and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve a single mode oscillation yield regardless of etching by adjusting diffraction efficiency by adjusting the height of a grating by crystal growth, particularly to a distributed feedback semiconductor laser. The realized semiconductor laser device is realized. A distributed feedback diffraction grating having a certain period is formed on an n-InP substrate. An InP buffer layer 3, InGaAsP (λ = 1.3 μm) waveguide layer 4, InGaAsP (λ = 1.4 μm) well layer 5, In
GaAsP (λ = 1.1 μm) barrier layer 6, pnp
InP buried layer 7, p-InGaAsP (λ = 1.3
μm) Cap layer 8, Au / Zn p-side electrode 9 and Au—Sn n-side electrode 10 are formed by vapor deposition. Thus, a laser structure in which the diffraction efficiency of the distributed feedback diffraction grating 2 is reduced is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] This invention is indispensable for optical fiber communication and the like.
Related high-performance semiconductor laser and manufacturing method thereof
Things. [0002] 2. Description of the Related Art In a conventional semiconductor laser, a high-speed
Dynamic single that maintains single mode operation even during tangent modulation
Mode laser (Dymanic Single Mode -Laser Diode)
Has been proposed, among which the vertical mode is controlled stably
Distributed feedback type (DFB) that can obtain stable and high optical output
Lasers (for example, Nakamura et al., IEE
Journal of Quantum Electronics IEEE J.
 Quantum Electron. QE-11, 436 (1975))
Is being promoted. FIG. 11 shows the structure of a conventional DFB laser.
You. Here, 1 is an n-InP substrate (semiconductor single crystal group)
2) Distributed feedback diffraction formed on n-InP substrate 1
The lattice 4 is In grown on the distributed feedback diffraction grating 2.
GaAsP (λ = 1.3 μm) waveguide layer, 5 is InGa
InGaAsP crystal grown on the AsP waveguide layer 4 (λ =
1.55 μm) active layer, 6 is p-InP.n-InP.
The p-InP buried layer, 7 is p-InGaAsP (λ =
1.3 μm) cap layer, 8 is Au / Zn p-side electrode,
Reference numeral 9 denotes an Au-Sn n-side electrode. As shown in FIG. 11, a distributed feedback diffraction grating is used.
2 is formed on the n-InP substrate 1 and is a distributed feedback type circuit.
InGaAsP waveguide layer 4 and InGaAs on folded grating 2
The sP active layer 5 has been crystal-grown. Recently, shown in FIG.
Such DFB laser is for low noise and low distortion analog transmission
It is attracting attention as a light source. This DFB for analog transmission
The laser has good linearity of light output current characteristics above the threshold current.
Is required. Poor linearity of optical output current characteristics
Otherwise, transmission distortion increases. This optical output current characteristic
In the cavity of the laser
Whole burnin caused by uneven presence of light
Can be considered. [0005] Hole burning is formed by DFB laser
Returned by the distributed feedback diffraction grating (grating)
The light intensity was too high
It is a phenomenon. Therefore, the diffraction efficiency of the distributed feedback grating is
Need to be smaller. To suppress this phenomenon,
Reducing the diffraction efficiency by limiting the height of the distributed feedback grating
Will be. On the other hand, by suppressing the Fabry-Perot mode,
In order for a semiconductor laser to oscillate in single mode,
The height of the distributed feedback diffraction grating is required. Therefore,
By controlling the height of the distributed feedback grating optimally,
Suppressing the occurrence of ruburning
It is necessary to achieve mode oscillation and improve the laser yield.
It is necessary. Light returned by this distributed feedback grating
Is not only the height of the distributed feedback grating but also the distribution
Since the shape of the feedback diffraction grating changes, the distributed feedback
The intensity of the light diffracted by the folded grating is calculated as the ratio of the intensity of the incident light.
A value called diffraction efficiency is defined. Conventionally, the height of a distributed feedback diffraction grating is controlled.
As shown in FIG. 12A, the InP substrate 71
Distributed feedback diffraction grating of sufficient height using resist 72
After forming the resist 75, the resist 72 is removed, and a sulfuric acid-based
Etching solution (eg, H_TwoSO_Four+ H_TwoO_Two+ H
_TwoO) Method for Reducing the Height of the Distributed Feedback Grating 75
Alternatively, as shown in FIG. 12B, the InGaAsP layer 75
A resist 76 on the InP substrate 74 on which
After the etching, the InGaAsP is left with the resist 76 attached.
The layer 75 is coated with a sulfuric acid-based etching solution (eg, H_TwoSO_Four
+ H_TwoO_Two+ H_TwoO) and etch the resist 76
Was removed to form a distributed feedback diffraction grating 77. This
This is because a distributed feedback diffraction grating 7 is formed on a heterocrystal having a uniform thickness.
7, the height of the distributed feedback diffraction grating 77 can be increased.
Method for setting thickness of heterocrystal (InGaAsP layer 75)
There is. [0008] However, FIG.
As shown in (a), the height of the distributed feedback diffraction grating 73 is
In the method of controlling by ching, distribution by etching
Because the shape of the feedback diffraction grating 73 changes,
Due to the shape of the distributed feedback diffraction grating 73 of FIG.
However, there is a problem that the time variation of the diffraction efficiency differs.
Was. For example, before etching, a semiconductor laser
The variation in diffraction efficiency within the InP substrate 71 to be formed is 1
Even if it is about 0%, after etching, the InP substrate 71
Diffraction due to uneven etching in the interior
The efficiency may vary by about 50% within the substrate.
Was. Further, the etching solution is stirred by convection.
Differing etching rate in the plane, distributed feedback grating
The height of 73 does not become the target height, and the in-plane variation of the height
The problem is that the laser characteristics are large.
The resulting yield was reduced. [0010] As shown in FIG.
(InGaAsP layer 75) etched and distributed feedback type
When forming the diffraction grating 77, a distributed feedback diffraction grating
The height of 77 is the height of the heterocrystal and
Feedback diffraction by improving in-plane uniformity of film thickness
The grating 77 can be formed at a uniform height in the plane, but distributed feedback
Control of the width of the heterocrystal forming the
Determined by etching rate to perform dry etching
And the etching rate of the heterocrystal itself is different in the plane.
And heterocrystal and resist (photoresist) 7
6 The amount of side etching is also different in the plane due to adhesion to 6.
Therefore, the width of the distributed feedback grating 77 should be sufficiently controlled.
I can't. As a result, the intensity of the returned light changes in the plane.
As a result, the desired diffraction efficiency cannot be obtained.
You. That is, the width of the distributed feedback diffraction grating 77 is within the crystal plane.
Due to the variation, the laser characteristics also varied. In the semiconductor laser shown in FIG.
The InGaAsP waveguide layer 4 is a concave portion of the distributed feedback diffraction grating 2.
A buffer for preventing the protrusion from being transmitted to the InGaAsP active layer 5.
InGaAsP waveguide layer
4 couldn't be too thin. Therefore, the intensity of the emitted light
The half-width of the degree, that is, the half-width of the spread
There is also a problem that the coupling efficiency for optical fiber etc. is low.
Was. An object of the present invention is to provide a distributed feedback diffraction grating.
Controlling the shape by crystal growth rather than etching
And the height of the distributed feedback grating is the desired height
In particular, it is possible to suppress height variations in the plane.
Realizing high yield semiconductor lasers.
You. The other purpose of this semiconductor laser is
Reduces the half-width of intensity, that is, the half-width of the spread of emitted light
Semiconductor laser with good coupling efficiency to optical fiber etc.
Is to realize the user. [0013] A semiconductor laser according to claim 1.
The laser apparatus comprises: a first crystal having a diffraction grating;
The first crystal and composition grown on a lattice by vapor phase epitaxy
And a second crystal having different
A third crystal having a smaller refractive index than the second crystal grown
Wherein the second crystal is made of InGaAsP,
The proportion of GaAs in the second crystal is large in the concave portions of the diffraction grating.
So that the composition of the second crystal is
Periodically changing the refractive index of the second crystal to the diffraction grating
The feature is that it is large in the concave part and small in the convex part
And [0014] FIG. 1 shows a first embodiment of the present invention.
The structure of the semiconductor laser in the embodiment, that is, the DFB laser
FIG. In FIG. 1, 1 is an n-InP group
The plate 2 is a first distributed feedback type having a period Λ1 = 200.0 nm.
The diffraction grating 3 adjusts the height of the distributed feedback diffraction grating 2.
Adjustment layer (InP buffer layer) for InP, 4 is InG
aAsP (λ = 1.1 μm) waveguide layer, 5 is 5 nm I
nGaAsP (λ = 1.40 μm) well layer and 10 nm
Five periods of InGaAsP (λ = 1.10 μm) barrier layer
The quantum well type InGaAsP active layer made of
InP-n-InP-p-InP buried layer, 7 is p-
InGaAsP (λ = 1.3 μm) cap layer, 8 is A
u / Zn p-side electrode, 9 is Au-Sn n-side electrode
You. In this embodiment, as shown in FIG.
Forming a distributed feedback diffraction grating 2 directly on an InP substrate 1;
An InP adjusting layer 3 for adjusting the height of the diffraction grating is grown thereon.
And the InGaAsP waveguide layer 4 and InG
aAsP active layer 5 is formed. Where this semi
Body lasers differ from conventional semiconductor lasers in that distributed feedback
The InP adjusting layer 3 is formed on the diffraction grating 2, and
The surface of the InP adjusting layer 3 is formed by the InP adjusting layer 3.
Has a low diffraction grating height reflecting the distributed feedback diffraction grating 2.
Where the distributed feedback diffraction grating 2a is formed.
You. Here, In is placed on the distributed feedback diffraction grating 2.
The effect of forming the P adjusting layer 3 is shown in FIG.
This will be described with reference to FIG. Resist by interference exposure method
A distributed feedback diffraction grating is formed on
Distributed diffraction grating on crystal by etching
Transcribe the child. Distributed feedback diffraction grating formed on crystal
The shape is, as shown in FIG. 2, two patterns (a1),
(B1). That is, this is shown in FIG.
To form a resist 82 on the InP substrate 81
When etched, (c1) depending on the degree of etching
As shown, the InP substrate 81 is only slightly etched.
And the InP substrate 81 has a kana as shown in (c2).
Etching. (C1) is (a1)
And (c2) corresponds to (b1). Crystal after etching InP substrate 81
The relationship between the growth time and the diffraction efficiency is shown in FIG. Of FIG.
a1, a2, b1, b2 are the patterns (a1) in FIG.
(B1), (a2), and (b2), respectively. Pa
In the case of turn (a1), a distributed feedback diffraction grating
When a crystal is grown on 83, the distributed feedback diffraction grating 8
In the shape of No. 3, the growth rate of the (111) plane is changed to the (100) plane.
In contrast, the height of the distributed feedback diffraction grating 83 is
Almost straight as the crystal grows, as in turn (a2)
And the diffraction efficiency also decreases almost linearly. one
On the other hand, in the case of the pattern (b1), the distributed feedback type circuit is used.
The height of the lattice 83 is the height of the crystal as shown in the pattern (b2).
As it grows, it rises once and then begins to decline, leading to diffraction effects.
The rate increases once and then grows in the same manner as pattern (a1).
Declines over time. Therefore, the shape of the distributed feedback diffraction grating 83
Reduce the amount of etching at the time of formation to obtain pattern (a1).
In this case, the control of the diffraction efficiency becomes better. that's all
In the semiconductor laser of this embodiment configured as follows:
The operation will be described below. Current is p-side of Au / Zn
P-InP.n-InP.pi supplied from the electrode 8
Well layer and barrier after being pinched by nP buried layer 6
It is implanted into the InGaAsP active layer 5 composed of layers.
The light generated in the InGaAsP active layer 5 is InGaAsP
Seepage through the waveguide layer 4 and the period of the distributed feedback diffraction grating 2
Of the light of the DFB oscillation wavelength determined on the long wavelength side
It will oscillate in long. The semiconductor laser according to this embodiment is (1) Crystal of InP adjusting layer 3 on distributed feedback diffraction grating 2
Of a distributed feedback type diffraction grating
2 as low as the distributed feedback diffraction grating 2a,
The diffraction efficiency is reduced from 3.2 to 1.0. to this
The appearance of hole burning is reduced. (2) MOCVD method excellent in film thickness controllability
The height of the distributed feedback grating can be increased by using
Is reduced, the distribution formed on the n-InP substrate 1 is reduced.
When the diffraction efficiency of the feedback type diffraction grating 2 in the n-InP substrate 1 is
Fluctuations are significantly reduced. (3) In the manufacturing process, the time between wafers and between batches
Variations in folding efficiency are reduced as compared to the conventional case. As described above, the shape of the distributed feedback diffraction grating
Is controlled not by etching but by crystal growth,
If the height of the distributed feedback grating is set to the desired height,
In addition, it is possible to suppress height variations in the plane.
To achieve a single-mode operation semiconductor laser with high yield.
Can be manifested. (Second Embodiment) FIG. 4 shows a second embodiment of the present invention.
1 is a diagram showing a structure of a semiconductor laser. Figure 4
1 is an n-InP substrate, 12 is an n-InP buffer layer
And reduce the dopant concentration in areas where the light intensity is strong.
3 μm. Carrier concentration is 1 × 10
¹⁷cm^-3It is. 2 is the distribution of the period Λ1 = 200.0 nm
Feedback diffraction grating, 13 is diffraction effect of distributed feedback diffraction grating 2
N-InGaAsP (λ = 1.05) for adjusting the rate
μm) control layer (n-InGaAsP buffer layer), 14
Denotes an n-InP flattening layer for flattening a crystal, and 4 denotes n
-InGaAsP (λ = 1.05 μm) waveguide layer, 5
5 nm InGaAsP (λ = 1.40 μm) well layer
10 nm InGaAsP (λ = 1.10 μm) barrier
Well type InGaAsP activity consisting of five periods of layers
Layer 6, embedding p-InP, n-InP, p-InP
The layer 7 is a p-InGaAsP (λ = 1.3 μm)
8 is a Au / Zn p-side electrode, 9 is Au-Sn n
It is a side electrode. In this embodiment, as shown in FIG.
-Form n-InP buffer element 12 on InP substrate 1
The n-InP buffer layer 12 has a distributed feedback diffraction grating.
Is formed, and the diffraction effect of the distributed feedback diffraction grating 2 is formed thereon.
Forming an n-InGaAsP adjusting layer 13 for adjusting the rate.
N-In for further planarizing the crystal thereon.
A P planarization layer 14 is grown, and InGaAs is further formed thereon.
The P waveguide layer 4 and the InGaAsP active layer 5 are formed.
You. The operation of the semiconductor laser of this embodiment is as follows.
This is almost the same as the embodiment. Here, as in the second embodiment.
Has a composition different from that of the crystal forming the distributed feedback diffraction grating.
By growing the crystal on a distributed feedback grating
The operation will be described with reference to FIGS. Minute
A crystal with a different composition from the crystal forming the cloth feedback diffraction grating
FIG. 5 shows the case of the growth. In FIG. 5, 101 is I
nP substrate, distribution 102 formed on InP substrate 101
It is a feedback type diffraction grating. 103 is a distributed feedback diffraction grating 1
02, which has a higher refractive index than the InP substrate 101.
Is big. The InP substrate 101 has a (111) plane growth level.
Because of the high speed, the concave portion of the distributed feedback diffraction grating 102
Increases the thickness of the grown crystal 103. High refractive index
A crystal 103 is grown on a distributed feedback diffraction grating 102.
The refractive index of the concave portion of the distributed feedback diffraction grating 102
Is larger than the refractive index of the convex portion.
Also function as the distributed feedback diffraction grating 102. Next, the product on the distributed feedback diffraction grating 102 is
Waveguide with crystal 104 having smaller refractive index than layered crystal 103
The path layer 105 and the active layer 106 are continuously grown. Refractive index
Distribution feedback by adjusting the thickness of the crystal 104
The light intensity at the position of the diffraction grating 102 can be adjusted.
Effective diffraction effect of distributed feedback grating 102 in laser
The ratio depends on the shape of the distributed feedback diffraction grating 102 and the distributed feedback diffraction.
The light intensity at the position where the grating 102 exists and the distributed feedback type
The refractive indices of crystals 101 and 103 forming
It is shown as a function of the difference and the effective diffraction efficiency is
For example. Therefore, the height is high and the diffraction efficiency is large.
A high refractive index crystal 10 in the distributed feedback diffraction grating 102
3 to create a refractive index change,
The light intensity is reduced by increasing the distance between the folded grating 102 and the active layer 105.
Effective diffraction efficiency can be reduced by reducing
Wear. FIG. 6 shows the distance d between the active layer and the distributed feedback type diffraction grating and the number of times.
The relationship of folding efficiency is shown. Diffraction efficiency of distributed feedback diffraction grating
Variation is used to reduce in-plane variation in diffraction efficiency.
It increases when performing the switching. Surface regardless of etching
Reduces diffraction efficiency using crystal growth with high uniformity inside
This improves the in-plane uniformity of diffraction efficiency and batch-to-batch uniformity.
As a result, the yield is improved. Further, the half width of the spread angle of the emitted light is reduced.
If it is attempted to reduce the thickness, it is necessary to make the waveguide layer thinner.
You. However, in the laser of FIG.
Means that the InGaAsP waveguide layer 4 is a distributed feedback diffraction grating 2
a to prevent the irregularities of a from being transmitted to the InGaAsP active layer 5.
Buffer layer, and serves as an InGaAsP active layer.
In order to keep 5 well, the thickness of the InGaAsP waveguide layer 4
There was a limit to the reduction. However, the semiconductor laser shown in FIG.
The distributed feedback type formed on the InP buffer layer 12
A heterocrystal (n-InGaAsP adjusting layer) is formed on the diffraction grating 2.
13) can be grown to cause a change in the refractive index
Therefore, as a buffer layer, for a waveguide layer with a large refractive index
Crystal with small refractive index instead of crystal (InGaAsP)
Distributed feedback diffraction grating using (InP flattening layer 14)
2 and the InGaAsP active layer 5 can be separated from each other.
You. As a result, the spread angle of the emitted light can be reduced, and the emitted light can be reduced.
Higher output due to efficient coupling to optical fiber
Becomes possible. [0027] Further, a distributed feedback diffraction grating is formed.
The composition of one crystal (InP buffer layer 12) and the diffraction efficiency
Second crystal to be changed (n-InGaAsP adjusting layer 13)
Composition and distributed feedback diffraction grating even after the growth of the second crystal
If the crystal remains, the third crystal (InP planarization layer 1)
Adjusting the composition of 4) for total diffraction efficiency
It can be a value. That is, the first crystal (InP
Buffer layer 12) and a second crystal (n-InGaAsP adjusting layer)
13) Increase diffraction efficiency by increasing the difference in refractive index
And a second crystal (n-InGaAsP).
The refractive index of the adjustment layer 13) and the third crystal (InP flattening layer 1)
4) Decreasing diffraction efficiency by increasing refractive index
be able to. As a result, the distributed feedback diffraction grating 2 and In
Diffraction without greatly changing the distance between the GaAsP active layers 5
The efficiency can be adjusted. This is the carrier injection
Of the third crystal (InP planarization layer 14) to improve the
This is effective when you want to reduce the thickness. The above n-InGaAsP (λg = 1.1
(5 μm) The adjustment layer 13 is grown to 50 nm. (11
1) Since the growth rate of the surface is higher than that of InP, 50 n
With m, the crystal interface is almost flattened. Here, InGaAs
Although the composition of sP was λg = 1.15 μm,
The diffraction efficiency can be increased by increasing the
By reducing the size, the diffraction efficiency can be reduced.
Further, the thickness of the n-InGaAsP adjusting layer 13 is set to 50 nm.
However, the film thickness was reduced to 20 nm, and n-InGa
Distribution distribution at the growth interface (surface) after growth of AsP control layer 13
Diffraction efficiency can also be achieved by leaving a return grating
Can be reduced. The n-InP flattening layer 14 has
between the n-InP planarization layer 14 and the InGaAsP active layer 5
In order to completely planarize the crystal interface,
Light intensity by increasing the distance between the conductive layer 5 and the distributed feedback diffraction grating 2
By lowering the diffraction efficiency, the diffraction efficiency of the distributed feedback diffraction grating 2 is reduced.
It is possible to reduce κL (effective diffraction efficiency) without reducing
There are two effects that can be achieved. That is, InGaAs
The distance between the P active layer 5 and the distributed feedback diffraction grating 2 is n-In
Since it is separated by the P planarization layer 14, InGaAs
The light generated in the P active layer 5 passes through the distributed feedback diffraction grating 2.
Not felt (effective diffraction efficiency is small). The thickness of the n-InP flattening layer 14 is 300 n
m, the distributed feedback diffraction grating 2 having the same diffraction efficiency
However, the n-InP flattening layer 14 is replaced with an InGaAsP active layer.
5 and the distributed feedback diffraction grating 2, the effective
Since the diffraction efficiency can be reduced to 1/5, distributed feedback diffraction
Assuming that the diffraction efficiency of the grating 2 is 5, κL (effective refractive index)
Is the same as the diffraction efficiency 1.0 in the first embodiment.
it can. The film of the n-InGaAsP adjusting layer 13
When the thickness is set to 20 nm, the InGaAsP layer 13 and the n-In
A distributed feedback diffraction grating is preserved between the P flattening layer 14
In this case, the n-InP layer 14 is replaced with n-InGaAsP
By adjusting the refractive index difference using the layer 14a, the desired diffraction
Efficiency can be obtained. That is, n-InP flattening
N-InGaAsP (λg = 1.05 μm) instead of the layer 14
m) By using the planarization 14a, n-InGaAs
P adjusting layer 13 (λg = 1.15 μm) and n-InGaAs
at the interface with the sP (λg = 1.05 μm) flattening layer 14a
Diffraction by distributed feedback grating even if it is preserved
A decrease in efficiency can be suppressed. Further, the variation in diffraction efficiency between batches is also M
Reduced compared to conventional by using crystal growth by OCVD
Is done. Performs conventional etching to reduce diffraction efficiency
If it is reduced, the diffraction efficiency of the distributed feedback grating will vary.
The sticking increases as the etching is performed. Also, the first
As shown in the example, even when a crystal is grown,
If the initial diffraction efficiency is very large,
It is necessary to increase the film thickness.
The in-plane variation in efficiency is increased. In this embodiment
In this case, the diffraction efficiency is reduced by using the distributed feedback diffraction grating 2 and InG.
Since it is realized in relation to the position with the aAsP active layer 5
Use MOVPE crystal growth method with high uniformity of film thickness
In this case, the uniformity of the diffraction efficiency becomes extremely high. this
As a result of the configuration of the embodiment, the in-plane variation of the diffraction efficiency is
It was much lower than that. By using the above structure, a semiconductor laser
Yield of single mode is improved and diffraction efficiency is reduced
By doing so, the appearance probability of hole burning is also reduced.
Further, the half width of the emitted light can be reduced, and
The coupling efficiency with respect to fiber or the like can be increased. (Third Embodiment) FIG. 7A shows a third embodiment of the present invention.
1 is a diagram showing the structure of the semiconductor laser in FIG. FIG.
In the first embodiment, the distributed feedback diffraction grating is
Although formed directly on the top, here, the InP
N-InGaAsP buffer layer 1 different in composition from substrate 1
3a is grown and the n-InGaAsP buffer layer 1
A distributed feedback diffraction grating 2 is formed on 3a to adjust the diffraction efficiency.
InP flattened with the same composition as the InP substrate 1 for adjustment
After the layer 14 is grown to adjust the diffraction efficiency, it is planarized.
To grow the n-InGaAsP waveguide layer 4 for
And n-InGaAsP buffer layer 13a and n-InG
The same is achieved by reducing the difference in the refractive index of the aAsP waveguide layer 4.
Even if a distributed feedback diffraction grating with a
Folding efficiency is obtained and reproduced by reducing the amount of InP flattening layer 14
Improved. Further, in the embodiment of FIG.
n-InGaAsP having a different composition from the substrate on the nP substrate 1
The buffer layer 13 is grown, and the n-InGaAsP
The distributed feedback diffraction grating 2 is formed on the
A crystal having a composition different from that of the InGaAsP buffer layer 13.
N-InGaAsP adjusting layer 15 is grown to form a distributed feedback type.
After slowly forming the diffraction grating and controlling the diffraction efficiency,
With a structure in which the n-InP planarization layer 14 is grown,
Diffraction efficiency of distributed feedback grating with large diffraction efficiency
Adjust to the desired value to facilitate device fabrication
it can. (Fourth Embodiment) This fourth embodiment is shown in FIG.
Shown in In FIG. 4 of the second embodiment, I
Although the nP buffer layer 12 is formed, FIG.
Instead of the nP buffer layer 12, n-
An InGaAsP buffer layer 12a is grown. Soshi
And distributed feedback on the n-InGaAsP buffer layer 12a.
-Type diffraction grating 2 and an n-InGaAsP buffer layer
N-InGaAsP-like crystal having a composition different from that of 12a
After growing the nodal layer 13b to control the diffraction efficiency, n-In
A structure in which the GaAsP planarization layer 14a is grown
Thus, the adjustment of the diffraction efficiency was further facilitated. That is,
The diffraction efficiency formed on the crystal of No. 1 is κ1, and the diffraction efficiency is
Of the distributed feedback grating remaining after growing the
Assuming that the diffraction efficiency is κ2, κ1 is the InGaAsP buffer.
Refractive Index of Layer 12a and n-InGaAsP Adjusting Layer 13b
It is proportional to the difference. Κ2 is n-InGaAsP regulation
Refractive index difference between layer 13 and n-InGaAsP planarization layer 14a
Is proportional to First, the n-InGaAsP buffer layer 12
a indicates that the refractive index is too large from the viewpoint of carrier injection.
Cannot be crystalline. Therefore, n-InGaAs
sP (λg = 1.05 μm). Next, n-In
The GaAsP control layer 13b has a diffraction effect due to a variation in composition.
In order to eliminate the fluctuation of the refractive index, use a crystal with a slightly larger refractive index.
Need to be Therefore, n-InGaAsP (λg
= 1.15 μm). In addition, better carrier injection
For this purpose, the film thickness was set to 20 nm. As a result distributed feedback type
Diffraction grating 2 cannot be sufficiently buried, and planarization layer 1
The composition of 4a is InP, and the refractive index difference from the adjustment layer 13 is large.
The diffraction efficiency sharply decreases by increasing the size.
Therefore, the composition of the planarizing layer 14a is changed to n-InGaAsP.
(Λg = 0.95 μm), ensuring carrier injection
While the value of the diffraction efficiency can be set to the target κL = 1.
Came. In this way, the film thickness with which the adjustment of the diffraction efficiency is stable
And the crystal composition, the crystal composition can be changed in three stages.
It became clear that it was necessary to adjust the diffraction efficiency
Was. (Fifth Embodiment) FIG. 9 shows a fifth embodiment of the present invention.
FIG. 3 illustrates a method for manufacturing a semiconductor laser in an example.
You. In FIG. 9, first, a hollow is formed on the entire surface of the n-InP substrate 1.
Form distributed feedback diffraction grating 2 by graphic exposure method
FIG. 9A shows a diffraction grating manufacturing process to be performed. This diffraction pattern
In the step of fabricating the wafer, the reduced pressure MOVP at the growth pressure of 60 torr
PH using method E_ThreeAnnie in an atmosphere at 600 ° C for 15 minutes
The diffraction efficiency from 2.0% to 0.3%
Lower. Unlike etching, which is supply-limited,
In the case of Neil, since the reaction is rate-limiting, the diffraction efficiency
Variation is suppressed. And reduced the diffraction efficiency
First epitaxial growth is performed on the entire surface of the distributed feedback diffraction grating 2.
Using the reduced pressure MOVPE method with a growth pressure of 60 torr as the length
n-InP buffer layer (carrier concentration n = 5 × 10¹⁷)
3 at 500 nm, n-InGaAsP waveguide layer 4 at 15
0 nm, InGaAsP (λ = 1.40 μm) well layer
10 nm InGaAsP (λ = 1.10 μm) barrier
Well type InGaAsP active layer consisting of five periods of layers
5 to grow the p-InP cladding layer 16 to 0.5 μm.
FIG. 9B shows a crystal growth step of No. 1. Next, from the crystal surface to the n-InP substrate 1
Partial over a width of 1 μm and etched in <011> direction
After the stripe 17 is formed by the
nP-n-InP-p-InP buried layer 6, p-In
A GaAsP cap layer 7 is grown by burying stripes,
Then, Au / Zn p-side electrode 8 and Au-Sn n-side electrode
9 is formed by vapor deposition to obtain the structure of FIG. The n-InP buffer layer 3 is formed on the InP substrate 1
Growth of 500 nm, the height of the distributed feedback diffraction grating is increased.
And the diffraction efficiency of the distributed feedback grating before growth
From 3.2 to 1.0. (Sixth Embodiment) FIG. 10 shows a sixth embodiment of the present invention.
1 shows a method of manufacturing a semiconductor laser according to the present invention. FIG.
First, an n-InP buffer is formed on an n-InP substrate 1.
After the crystal growth of the wafer layer 12, holographic exposure
Diffraction grating forming distributed feedback diffraction grating 2 by optical method
The manufacturing process is shown in FIG. Diffraction by annealing in MOVPE furnace
Over the entire surface of the distributed feedback diffraction grating 2 whose efficiency has been reduced uniformly
Using MOVPE method as second epitaxial growth
n-InGaAsP buffer layer (carrier concentration n = 5 ×
10¹⁷) 13 to 50 nm, n-InP planarization layer (carrier)
A concentration n = 5 × 10¹⁷) 14 at 300 nm, n-InG
aAsP waveguide layer 4 is made of InGaAs of 100 nm and 5 nm.
sP (λ = 1.40 μm) well layer and 10 nm InGa
Consists of 5 periods of AsP (λ = 1.10 μm) barrier layer
The quantum well type InGaAsP active layer 5 is formed by p-InP
A second crystal growth step for growing the lad layer 16 to 0.5 μm
It is shown in FIG. Next, from the crystal surface to the n-InP substrate 1
Partial over a width of 1 μm and etched in <011> direction
After the stripe 18 is formed by the
nP-n-InP-p-InP buried layer 6, p-In
A GaAsP cap layer 7 is grown by burying stripes,
Then, Au / Zn p-side electrode 8 and Au-Sn n-side electrode
9 is formed by vapor deposition to obtain the structure of FIG. Under the InGaAsP active layer 5, n-In
By growing the P buffer layer 14 to 300 nm, the distribution
The distance between the diffraction grating 2 and the InGaAsP active layer 5 is increased.
To reduce the light intensity at the location of the distributed feedback diffraction grating by 1 /
By reducing the number to 5, the effective
Diffraction efficiency is lower than before growth. Also, n-InG
The growth rate of the aAsP buffer layer 13 on the concave surface is high.
The surface is almost flat by stacking 40nm
Become. Further, an n-InP flattening layer 14 is laminated.
This makes the InGaAsP active layer 5 extremely flat,
The influence of the cloth feedback diffraction grating 2 is eliminated. There is no first
In the sixth embodiment, the position of the distributed feedback diffraction grating 2
On the substrate 1 or the n-InGaAsP buffer layer 12
Formed on an n-InGaAsP substrate.
Forming a distributed feedback diffraction grating 2 after growing the pha layer 12
May be. Further, in the second to fourth embodiments,
Of the distribution formed on the buffer layers 12, 13, 13a.
The diffraction efficiency of the feedback type diffraction grating 2 is
Buffer layers 12, 13, and 13a that have grown to the same
InP flattening layer 14 may be grown by adjusting
No. In the first to sixth embodiments, the distributed feedback
The position of the diffraction grating 2 is below the InGaAsP active layer 5.
However, it may be formed on the InGaAsP active layer 5.
No. That is, the buffer layers 3, 12, 13 and the active layer 5,
A diffraction grating may be formed after crystal growth of the waveguide layer 4.
No. The buffer (planarization) layer 14 is made of InP.
Crystal, but refracted from n-InGaAsP buffer layer
The composition does not matter if the crystal has a small ratio. Also,
The semiconductor crystal is InP, but other semiconductors such as GaAs
A crystal substrate may be used. The position of the distributed feedback diffraction grating is
If the layer does not have a distributed feedback grating, refraction
It suffices if they exist at crystal interfaces with different rates. Further, in the first to sixth embodiments,
Although the laser structure is a DFB laser,
Laser and distributed feedback lasers.
If the laser controls the oscillation wavelength with a distribution of the bending ratio,
Can be adapted, and the degree of change in the refractive index is changed in the cavity length direction.
By doing so, the same effect as in each embodiment can be obtained.
You. Further, whether or not there is an n-InP buffer layer is important.
However, good characteristics were confirmed. Also, buffer layer, conductive
Although the waveguide layer and the InP layer are doped,
This is not the case even when an undoped crystal is used. [0048] As described above, the semiconductor device of the present invention
The laser has a large side mode suppression ratio,
Mode oscillation is obtained, and single mode characteristics are improved and
Achieves improved laser yield and enhanced output light intensity
Laser with high coupling efficiency by reducing the half width of
It has a very large influence in practical use.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a structural view of a semiconductor laser according to a first embodiment of the present invention. FIG. 2 is a diagram showing a method of adjusting the shape of a distributed feedback diffraction grating according to the first embodiment of the present invention. FIG. 3 is a diagram showing the relationship between the crystal growth time and the diffraction efficiency in the first embodiment of the present invention. FIG. 4 is a structural diagram of a semiconductor laser in the second embodiment of the present invention. FIG. 6 is a diagram showing a method of adjusting the shape of the distributed feedback diffraction grating in the second embodiment. FIG. 6 is a diagram showing the relationship between the distance between the active layer and the distributed feedback diffraction grating and the diffraction efficiency in the second embodiment of the present invention. 7 is a structural view of a semiconductor laser according to a third embodiment of the present invention. FIG. 8 is a structural view of a semiconductor laser according to a fourth embodiment of the present invention. FIG. 9 is a structural view of a semiconductor laser according to a fifth embodiment of the present invention. FIG. 10 shows a manufacturing method. FIG. 11 is a diagram illustrating a method of manufacturing a semiconductor laser according to the sixth embodiment. FIG. 11 is a structural diagram of a conventional DFB laser. FIG. 12 is a diagram illustrating a conventional method of adjusting the shape of a distributed feedback diffraction grating. InP substrate 2 Distributed feedback diffraction grating (grating) 3 n-InP adjustment layer (buffer layer) 4 InGaAsP waveguide layer 5 InGaAsP active layer 6 p-InP n-InP p-InP buried layer 7 p-InGaAsP cap layer 8 Au / Zn p-side electrode 9 Au-Sn n-side electrode 12 n-InP buffer layer 13 n-InGaAsP adjustment layer (buffer layer) 14 InP flattening layer (buffer layer) 14a InGaAsP adjustment layer (buffer layer) 15 InGaAsP planarization layer (buffer layer) 16 p-InP cladding layer 17 stripe 18 stripe

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Masahiro Kito             Matsushita Electric, 1006 Kadoma, Kazuma, Osaka             Sangyo Co., Ltd. (72) Inventor Yasushi Matsui             Matsushita Electric, 1006 Kadoma, Kazuma, Osaka             Sangyo Co., Ltd. F term (reference) 5F073 AA22 AA44 AA55 AA64 AA74                       BA01 CA12 CB10 CB22 DA21                       EA19

Claims (1)

Claims: 1. A first crystal having a diffraction grating, a second crystal having a different composition from the first crystal grown on the diffraction grating by a vapor phase growth method, and the second crystal. A third crystal having a lower refractive index than that of the second crystal grown by a vapor phase growth method, wherein the second crystal is made of InGaAsP, and a ratio of GaAs in the second crystal is a concave portion of the diffraction grating. The composition of the second crystal changes periodically so that the number of protrusions is small and the number of protrusions is small, and the refractive index of the second crystal is large in concave portions of the diffraction grating and small in convex portions. Semiconductor laser.