JP2924714B2 - Distributed feedback semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed feedback semiconductor laser device, and more particularly to a distributed feedback semiconductor laser device provided with a diffraction grating for realizing a linear relationship between current and light output.

[0002]

2. Description of the Related Art Distributed feedback (hereinafter referred to as "DFB") semiconductor lasers can oscillate at a single wavelength due to the wavelength selectivity of a diffraction grating provided therein, and have recently been used as a light source for long-distance high-speed optical communication. Is coming.

FIG. 5 shows an example of a method of manufacturing a conventional DFB semiconductor laser device.

First, a diffraction grating 15 is formed on an n-type InP substrate 1 by using interference exposure and etching techniques, and the n-InGaAsP guide layer 3 and the InGa
An AsP active layer 4 and a p-InGaAsP guide layer 5 are sequentially grown. Etching, p-InP, n-InP
After the light confinement / current block structure is formed by crystal growth of p, the p-InP layer 6 and the p ⁺ -InGaAsP layer 7 are crystal-grown to form the p-side electrode 8 and the n-type electrode 9. Cleavage, reflection coating, non-reflection coating, and the like are performed to form a resonator, thereby forming a DFB semiconductor laser device.

[0005] Also, another conventional (EL in Figure 6 (a) ~ (c)
ECTRONICS LETTERS 25, 220-221 (1989)).

[0006] First, figure6As shown in FIG.
P-InP guide layer 17 in contact with P substrate 16;
AsP active layer 18, n-InP barrier layer 19, n-In
After crystal growth of the GaAsP guide layer 20, FIG.6
The n-InGaAsP gas is etched by etching as shown in FIG.
The id layer 20 is processed into a diffraction grating 21. Next figure6(C)
The n-InP cladding layer 22 is grown as shown in FIG.
The mesa structure is formed by
A DFB semiconductor laser device was manufactured by forming a structure.

When a DFB semiconductor laser is used in analog modulation such as optical CATV, it is very important that the relationship between the applied current value and the optical output value is a linear relationship, and satisfies predetermined conditions. Must be manufactured as follows. As a main factor that determines the current and optical output characteristics (IL characteristics) of a DFB semiconductor laser, a product κL of a cavity length L and an optical coupling coefficient κ with respect to a diffraction grating is known. The Matahikari coupling coefficient kappa, in substance, or 5 in contact with the diffraction grating and the diffraction grating, n-type InP substrate 1 and the n-InGaAs
proportional to the difference Δn in equivalent refractive index between the sP guide layer 3 and
κ = π · Δn / λ _B Where π is the pi,
λ _B is the Bragg wavelength. Further, the equivalent refractive index difference Δn and the coupling coefficient κ have a relationship with the height a of the diffraction grating. When the height of the diffraction grating is approximately 400 ° or less, the coupling coefficient κ and the height a of the diffraction grating are proportional. Is known to have

[0008]

In order to manufacture a DFB semiconductor laser device having good light output characteristics (IL characteristics), it is conventionally optimal to control the value of κL to 0.8 to 1. Have been. For example, light C having a cavity length L of 300 μm
In the case of a 1.3 μm band analog DFB semiconductor laser for ATV, it is desired that the optical coupling efficiency κ is 27 to 33 cm ⁻¹ , and the equivalent refraction between the n-InP substrate 1 sandwiching the diffraction grating and InGaAsP having a composition of 1.15 μm. The rate difference Δn is 1.1 × 1
It was necessary to keep the range of 0 ^{-3 to} 1.5 × 10 ^-3 . In this case, the height a of the diffraction grating is about 200 °, and the accuracy at that time needs to be ± 25 °. However, when the n-InGaAsP guide layer 3 is grown in crystal contact with the diffraction grating 15, the actual control accuracy of the height of the diffraction grating 15 is ± 5 because the shape of the diffraction grating 15 is changed.
The limit is about 0 °, and it is extremely difficult to form the height with an accuracy of 200 ± 25 °. Good IL characteristics were not obtained, and the product yield was 40%.

When the cavity length L is increased from 300 μm to 600 μm in order to increase the output of the laser, for example, to maintain κL at 0.8 to 1, κ should be 27 to 3
It is necessary to reduce the 3 cm ^-1 to 14~17cm ^-1. As means for setting the value of κ low, n-InGa
Although a method of reducing the wavelength composition of the AsP guide layer 3 to be lower than that of 1.15 μm is conceivable, when the n-InGaAsP guide layer 3 having a low wavelength composition is used, the element ratio of As and As + P varies during crystal growth. As a result, the change in the wavelength becomes sharp and the controllability of the wavelength deteriorates.

Here, in order to secure a product yield of 80%, the n-InP substrate 1 and the n-InGa
The equivalent refractive index difference Δn from the AsP guide layer 3 is 0.58 × 1
0 ^-3 ~0.7 × 1 0 ^-3 must be controlled to, the actual difference Δn of the effective refractive index in the 0.4 × 10 ^-3 ~0.9 × 10
^The limit is to control to about ^-3 , and the manufacturing efficiency of the DFB semiconductor laser having the linear IL characteristic is poor, and the yield is very low.

Further, as shown in FIG. 7, the actual measured value of κL is considerably different from the value obtained by calculation, and it cannot be said that κ can be controlled as calculated.

The present invention solves the above-mentioned problems by focusing on changing the effective refractive index of the diffraction grating, increases the probability of manufacturing a DFB semiconductor laser device having good light output characteristics, and increases the product yield. It is an object of the present invention to provide a DFB semiconductor laser device having a high density.

[0013]

According to the semiconductor laser device of the present invention, in order to solve the above problems, a diffraction grating is formed along an active layer.
In distributed feedback semiconductor laser devices with different orientations
The semiconductor materials sandwiching the diffraction grating are different from each other.
Semiconductor materials having different refractive indices, and alternately sandwiching the diffraction grating.
Two types of semiconductor materials with different refractive indexes are alternately stacked
A distributed feedback semiconductor laser device was constructed as a multilayered structure .

The semiconductor material constituting the diffraction grating has distributed feedback
Forming a guide layer of a semiconductor laser device,
Distributed distribution of body substances as substances with different wavelength compositions
A semiconductor laser device was constructed. Also, distributed feedback laser
The area near the top of the diffraction grating located on the guide layer side of the device is
The same kind of semiconductor element and constituent elements
As a semiconductor material whose composition ratio is similar, distributed feedback type
A semiconductor laser device was constructed.

One of the semiconductor materials sandwiching the diffraction grating.
The semiconductor on the active layer side of the distributed feedback semiconductor laser device.
Distributed feedback semiconductor laser element using InGaAsP as material
Composed child. Also, one of the semiconductor materials sandwiching the diffraction grating
On the side opposite to the active layer of the distributed feedback semiconductor laser device
Feedback semiconductor laser element using InP as semiconductor material
Composed child.

[0016]

Since the diffraction grating has a multilayer structure of semiconductor materials having different refractive indices, the effective refractive index of the formed diffraction grating is an average value of the materials constituting the diffraction grating, and is substantially equal to that of the diffraction grating. has the same effect as a diffraction grating by a low refractive index material is formed. Therefore, the diffraction grating in the present semiconductor laser device has the same properties as the low-height diffraction grating, and the height of the diffraction grating can be reduced substantially without reducing the height in manufacturing, and Therefore, the accuracy of the DFB semiconductor laser device can be substantially improved by reducing the error of the DFB semiconductor laser device, the probability of manufacturing a DFB semiconductor laser device having good optical output characteristics can be increased, and a DFB semiconductor laser device having a high product yield can be provided.

Further, since the diffraction grating is formed by laminating substances having an arbitrary wavelength composition, the average refractive index can be formed to a desired value, the required κL can be obtained, and the light output characteristics can be improved. .

The material near the top of the formed diffraction grating is
Since the material has a wavelength composition similar to the material grown on the diffraction grating, even if the material grows on the diffraction grating and the shape changes, the characteristics of the diffraction grating do not change significantly and are stable. Performance can be provided.

[0019]

FIG. 1 shows an embodiment of a distributed feedback semiconductor laser device according to the present invention.

The distributed feedback semiconductor laser device shown in FIG. 1 has a diffraction grating 2 between an n-InP substrate 1 and an n-InGaAsP guide layer 3 as shown in FIG.
In between the guide layer 3 and the p-InGaAsP guide layer 5, In
A GaAsP active layer 3 is provided, p-InP6 and p ⁺ -InGaAsP7 are formed on a p-InGaAsP guide layer 5, and a p-side electrode 8 is provided on the upper surface thereof.
An n-side electrode 9 is provided on the substrate 1 side, and is configured after processing such as cleavage, reflection, and non-reflection.

FIG. 2 shows the diffraction grating 2. The diffraction grating 2
N-InGaAsP11 having a wavelength composition of 1.15 μm;
-InP10 has a multilayer structure in which three layers are alternately laminated by about 66 ° each, and the height is about 400 °, and the shape, accuracy, and the like are the same as those in the related art.

The manufacture of the diffraction grating 2 is performed as follows. That is, the wavelength composition 1.1 is applied to the layer of the n-InP substrate 1.
5 μm n-InGaAsP is grown at about 66 °, and n-InP is grown thereon at about 66 °. This operation is performed three times, and three layers of n-InGaAsP and n-InP are alternately laminated. Next, a diffraction grating 2 is formed on the multilayer film composed of n-InGaAsP11 and n-InP10 by performing exposure interference work and etching. Then, as described above, n-InGaAsP is grown in contact with the diffraction grating 2 to form the n-InGaAsP guide layer 3. In this way, the diffraction grating 2 having a height of about 400
It is formed between the substrate 1 and the n-InGaAsP guide layer 3.

As described above, the diffraction grating 2 is made of n-InGaAs.
Since it is formed from a multilayer film of sP11 and n-InP10, the effective refractive index is n-type having a composition of 1.15 μm.
The average refractive index of InGaAsP and n-InP is about 3.28. From this value, the equivalent refractive index difference Δn is 0.
The calculated value is 5 × 10 ^{−3 to} 1.2 × 10 ⁻³ , which is about one-half of 1.1 × 10 ^{−3 to} 1.5 × 10 ⁻³ of the conventional similar semiconductor laser device.

Accordingly, the height a of the diffraction grating 2 of the semiconductor laser device of the present embodiment is substantially about 1/2, and the height of the diffraction grating 2 for setting κ at 25 to 35 cm ^-1 which is the same as the conventional one. Is about 400 ± 5, which is about twice the height conventionally required.
0 ° can be satisfied. Thereby, the diffraction grating 2 becomes equivalent to that formed with an accuracy of ± 25 °, κ is set to 25 to 35 cm ⁻¹ , and the resonator length L is set to 300 μm.
In the case of m, κL can be reliably controlled to 0.8 to 1, and the product yield can be improved to about 80%.

(Embodiment 2) FIG. 3 shows an embodiment in which the cavity length L of the semiconductor laser device of Embodiment 1 is set to 600 μm. The n-InGaAsP of Embodiment 1 (composition 1.15 μm) is used.
m) is replaced with n-InGaAsP (composition: 1.35 μm). That is, the diffraction grating 2 shown in FIG.
Represents n-InGaAsP and n-InP having a composition of 1.35 μm.
And a laminated structure. Therefore, the average refractive index of the diffraction grating 2 is about 3.3. On the other hand, the resonator length L
When is set to 600 μm, κ must be controlled to 14 to 17 cm ⁻¹ to control κL to 0.8 to 1.0. In the case of this embodiment, since the average refractive index of the diffraction grating 2 is about 3.3, when the height of the diffraction grating is 400 ± 50 °, Δn is 0.58 × 10 ^{−3 to} 0.7 × 10 ^{−. 3} , κ
Is 14 to 17 cm ^-1 , the κL can be controlled to 0.8 to 1.0 even when the resonator length L is 600 μm, the IL characteristic is improved, the occurrence of defective products is small, and the distributed feedback type with high yield is achieved. A semiconductor laser device can be provided.

Embodiment 3 FIG. 4 is a view showing a third embodiment of the semiconductor laser device. As shown in FIG. 4, a diffraction grating 2 of this semiconductor laser device is in contact with an n-InP substrate 1 and is made of n-InGaAs.
P14 (1.05 μm composition), on which n-InP1
0, n-InGaAsP13 (1.15 μm composition), n-InP10, n-InGaAsP12 (1.
(Composition of 25 μm) each having a thickness of 66 °. The diffraction grating 2 is formed by subjecting the multilayer film to exposure interference technology and etching as in the conventional case. Then, in the same manner as in the above embodiment, the n-InGaAsP guide layer 3, the InGaAsP active layer 4, the p-InGaAsP guide layer 5, the p-InP layer 6, and the p ⁺ -InGaAsP layer 7 were grown in contact with the diffraction grating 2. Thereafter, a p-side electrode 8 and an n-side electrode 9 were formed to form a distributed feedback semiconductor laser device.

The average refractive index of the diffraction grating 2 having a multilayer structure is about 3.24, which is almost the same as that of the first embodiment. From the result of the first embodiment, κ can be controlled to 25 to 35 cm ⁻¹ . Furthermore, n-
The composition of the tip (diffraction grating peak) of the diffraction grating 2 on the side of the InGaAsP guide layer 3 is close to the composition of the n-InGaAsP guide layer 3 and the composition is 1.25 μm n-InGaAsP.
12 so that it is in contact with the diffraction grating 2 and n-I
When the nGaAsP guide layer 3 is crystal-grown, even if the peaks of the diffraction grating 2, that is, the n-InGaAsP12 are scraped off, the amount of change in κ can be reduced, and the distributed feedback semiconductor with stable performance and high yield can be obtained. A laser element can be provided.

[0028]

According to the distributed feedback semiconductor laser device of the present invention, since the diffraction grating is formed from a multilayer film of semiconductor materials having different refractive indexes, the effective refractive index of the diffraction grating can be reduced. As a result, a diffraction grating can be manufactured with high accuracy by substantially reducing the height of the diffraction grating, and a distributed feedback semiconductor laser device having a high yield can be provided. Also, the difference in equivalent refractive index between the substance in contact with the diffraction grating can be reduced, and the same effect can be obtained as when the wavelength composition of the guide layer is substantially reduced. Even when the length is increased, it is possible to provide a distributed feedback semiconductor laser device with high accuracy and good strain yield.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a distributed feedback semiconductor laser device according to one embodiment of the present invention.

FIG. 2 is a sectional view showing a diffraction grating of the distributed feedback semiconductor laser device according to the present invention.

FIG. 3 is a sectional view showing another diffraction grating of the distributed feedback semiconductor laser device according to the present invention.

FIG. 4 is a sectional view showing another diffraction grating of the distributed feedback semiconductor laser device according to the present invention.

FIG. 5 is a cross-sectional view showing a conventional distributed feedback semiconductor laser device.

FIGS. 6A, 6B and 6C are cross-sectional views showing a conventional distributed feedback semiconductor laser device.

FIG. 7 is a graph showing calculated and measured values of κL.

[Explanation of symbols]

Reference Signs List 1 n-InP substrate 2, 15, 21 diffraction grating 3 n-InGaAsP guide layer 4 InGaAsP active layer 5 p-InGaAsP guide layer 6 p-InP 7 p ⁺ InGaAsP 8 p-side electrode 9 n-side electrode 10 n-InP 11, 13 n-InGaAsP (composition 1.15 μm) 12 n-InGaAsP (composition 1.25 μm) 14 n-InGaAsP (composition 1.05 μm) 23 n-InGaAsP (composition 1.35 μm)

Claims (5)

(57) [Claims] 1. A distributed feedback semiconductor laser device having a diffraction grating in a direction along an active layer, wherein two kinds of semiconductor materials sandwiching the diffraction grating are semiconductor materials having different refractive indexes from each other, and the diffraction grating is used as a semiconductor material. A distributed feedback semiconductor laser device having a multilayer structure in which two kinds of semiconductor materials having different refractive indexes are alternately stacked with the diffraction grating interposed therebetween. 2. The semiconductor device according to claim 1, wherein one of the two semiconductor materials constituting the diffraction grating is one of the two semiconductor materials.
2. The distributed feedback semiconductor laser device according to claim 1, wherein the semiconductor element has the same kind of constituent element as that of the other semiconductor substance and has different wavelength compositions. 3. A semiconductor having the same kind of constituent element as the semiconductor substance forming the guide layer and having a similar composition ratio near the top of the diffraction grating located on the guide layer side of the distributed feedback laser element. 3. The distributed feedback semiconductor laser device according to claim 1, wherein the distributed feedback semiconductor laser device is made of a substance. 4. The distributed feedback semiconductor laser device according to claim 1, wherein one of the two kinds of semiconductor materials sandwiching the diffraction grating, the semiconductor material on the active layer side of the distributed feedback semiconductor laser device is InGaAsP. The distributed feedback semiconductor laser device according to any one of the above items. 5. The semiconductor device according to claim 1, wherein one of the two semiconductor materials sandwiching the diffraction grating, the semiconductor material on the side opposite to the active layer of the distributed feedback semiconductor laser device is InP. 4. The distributed feedback semiconductor laser device according to any one of items 3 to 3.