JPH05251812A - Distributed-feedback semiconductor laser with quantum well structured optical modulator and manufacture thereof - Google Patents

Abstract

(57) [Summary] [Objective] The laser, the active layer of the optical modulator, and the optical waveguide layer are composed of a multiple quantum well (MQW) structure with different optical absorption edge wavelengths, and the refractive indices of both are connected smoothly. Integrated light source. [Structure] DFB laser device 10 with MQW optical modulator
Is a DFB laser section 12 having a substrate 20 and an MQW structure 26 provided thereon and upper and lower clad layers 30 and 24 sandwiching the MQW structure 26, an MQW structure 34 coupled to the laser section 12 and upper and lower clad layers 36 sandwiching the MQW structure 34. And the optical modulator unit 13 having 32. The MQW structures 26 and 34 are separated from each other in a plane perpendicular to the waveguide direction, and are optically coupled in the optical coupling region 16 via the lower cladding layer 32 of the modulator section. In this laser with an optical modulator, the interface 17 shares only the facing end surface 15A of the semiconductor portion 15. The cladding layer 38 on the semiconductor portions 14 and 15 has a separating portion 40 along the region sandwiching the interface 17.

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 with an external modulator, and more particularly to a distributed feedback semiconductor laser with a quantum well structure optical modulator.

The invention also relates to a method of manufacturing such a semiconductor laser.

[0003]

2. Description of the Related Art A typical prior art of a light source integrated with an optical modulator is a distributed feedback laser (hereinafter abbreviated as DFB laser) and an electric field applied absorption modulator using the Franz-Keldysh effect are monolithic. It is an integrated one. 7 shows a conventional integrated light source (H. Soda et al., Ele.
FIG. 3 is a schematic perspective view showing the structure of Tronics Letter, Vol. 26, No. 1, page 9). In this structure,
The active layer 26 of the DFB laser and the optical waveguide layer 34 of the absorption type optical modulator are connected by a butt joint (butt joint) 18. In addition, this structure has a new structure in which a DFB laser structure is manufactured to make the emission wavelength of the DFB laser longer than the optical absorption edge wavelength of the optical waveguide layer of the absorption type optical modulator, and then a part is removed by etching. It is manufactured by performing buried regrowth so that the optical waveguide layer of the modulator coincides with the active layer of the laser.

In the butt coupling, since the emission wavelength of the DFB laser is set to be longer than the optical absorption edge wavelength of the optical waveguide layer of the absorption type optical modulator, the refractive index changes at the coupling portion. as a result,
It is difficult to eliminate reflection and scattering at the joint. In the conventional technique, since the modulator portion is selectively embedded and grown, the grown film thickness becomes non-uniform due to butt coupling, and has a distribution in the waveguide direction. As a result, it is difficult to obtain high coupling efficiency and the yield is low.

If a multiple quantum well (MQW) structure is used for the active layer of the laser or the waveguide layer of the optical modulator, the oscillation threshold current of the laser can be reduced, and the quantum confined Stark effect enables a wide modulation frequency band at low voltage drive. Although high performance such as obtainability can be expected, butt coupling of MQW structure waveguides is extremely difficult. The reason is that the selective buried growth layer becomes thick near the butt joint, the effective forbidden band energy of the MQW structure waveguide becomes small, and the absorption loss of the waveguide cannot be ignored.

Therefore, there has been proposed a semiconductor light emitting device in which an active layer of a laser and a waveguiding layer of an optical modulator are optically coupled without butt coupling.

FIG. 8 is a sectional view showing the structure of a conventional semiconductor light emitting device (Japanese Patent Laid-Open No. 62-229990) in which a diffraction grating feedback laser and an electro-optical absorption modulator having a quantum well structure are formed in separate steps. is there. FIG. 9 is a cross-sectional view showing a manufacturing process of the semiconductor light emitting device of FIG.

In FIG. 8, an n-type InP substrate 20, an n-type InGaAlAs layer 22 serving as an etching stop layer,
The n-type InP layer 24 serving as the cladding layer and the In serving as the active layer
GaAlAs layer 26, InGaAlAs layer 28 serving as a guide layer on which a diffraction grating is formed, p-type In serving as a clad layer
AlAs layer 30, p-type InGaAs layer 48 serving as an electrode layer
Are stacked in this order. On the other hand, n that becomes the cladding layer
An InGaAs quantum well layer 34A and an InAlAs barrier layer 34B are alternately laminated on the In-type InAlAs layer 32, and an electrode layer is formed on the InAlAs layer 32, which is a p-type InAlAs layer 36 serving as a clad layer. P type I
An nGaAs layer 50 is arranged. A SiO ₂ film is provided on the electrode layer 48, p-type electrodes 58 and 60 are provided on the electrode layers 48 and 50, respectively, and an n-type electrode 62 is provided on the lower side of the substrate 20. .. An antireflection film 64 is provided on the light emitting end face.

To obtain this structure, as shown in FIG.
(A) First, the layers 20, 22, 24, 26, and 28 are sequentially grown on the substrate 1 by the molecular beam epitaxy method or the like, and (B) after the diffraction grating 29 is formed on the InGaAlAs layer 28, the cladding layer 30 is formed. Then, the electrode layer 48 is grown to form a laminated body, and a part of the laminated body is used as the InGaAlAs stop layer 2 with the (C) SiO ₂ film 52 or the like as a mask.
2 is selectively etched up to (D) SiO ₂ mask 5
The layers 32, 34A, 34B, 36, and 50 are sequentially grown on the InGaAlAs stop layer 22 with 2 remaining, and (E) InGaAlAs stop layer 22 is formed.
The modulator portion grown above is masked with a SiO ₂ film 52 or the like to form a laser portion (each layer 22, 24, 26, 2).
8, 30 and 32), the layer grown on the electrode layer 4 is selectively etched, and the SiO ₂ film 52 is removed.
8, 50 and 62 are vapor-deposited, and finally the antireflection film 64 is formed on the emission end face, and the structure of FIG. 9F is obtained.

As mentioned above, JP-A-62-22999.
In the semiconductor light emitting device shown in No. 0, the laser section is wet-etched up to the etching stop layer provided on the substrate, and not the butt-coupling that directly couples the active layer of the laser and the waveguide layer of the optical modulator. Optical coupling is achieved by forming the waveguiding layer of the optical modulator. In such a configuration, there is a problem in that the crystal is swelled at the bonding portion, which makes it difficult to work in subsequent manufacturing steps, particularly in the photo process. Further, there is a problem that a current flows through the clad layers of the laser section and the modulator section, a leak current is large when the laser oscillates, and an oscillation threshold current is about twice as large as that of an ordinary laser.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to make active layers and optical waveguide layers of lasers and optical modulators have different optical absorption edge wavelengths, that is, effective band gap energies. It is an object of the present invention to provide an integrated light source that has an MQW structure and has a refractive index that is smoothly connected to each other.

[0012]

As a result of intensive investigations by the present inventors, the coupling between the active layer of the DFB laser portion of the integrated light source and the waveguide layer of the optical modulator portion is not butt coupling but n-type cladding. The above object can be achieved by optically coupling through the extension of the layer and providing a separating portion straddling the optical coupling portion between the p-side electrode for laser and the p-side electrode for optical modulator. Then, the present invention was completed.

That is, a distributed feedback semiconductor laser with a quantum well structure optical modulator according to the first aspect of the present invention comprises a substrate and an optical waveguide provided on the substrate, and the optical waveguide is an active layer. A distributed feedback semiconductor laser portion including a first semiconductor portion having a first waveguide layer and first upper and lower clad layers sandwiching the first waveguide layer, and a semiconductor laser portion coupled to the semiconductor laser portion. An optical modulator section including a second semiconductor portion having two waveguide layers and second upper and lower clad layers sandwiching the second waveguide layer, wherein the semiconductor laser section and the modulator section are A third clad layer provided on the first and second semiconductor portions, the second waveguide layer having a multiple quantum well structure including a barrier layer and a well layer, and The first and second semiconductor portions correspond to the first and second semiconductor portions. In optical coupling regions in which the wave layers are separated from each other in a plane perpendicular to the waveguide direction and face each other via the first or second lower cladding layer of the semiconductor laser section or the optical modulation section. In a distributed feedback semiconductor laser with an optically coupled quantum well structure optical modulator, the first waveguide layer has a multiple quantum well structure including a barrier layer and a well layer, and the first and second The interface of the semiconductor portion shares only the opposite end faces of the first and second semiconductor portions in the waveguide direction, and the third cladding layer sandwiches the interface of the first and second semiconductor portions. It is characterized in that it has a separating portion provided along a region including the opposite end portion.

Further, in the distributed feedback semiconductor laser with a quantum well structure optical modulator of the present invention, the angle θ formed by the interface between the first and second semiconductor portions with the surface of the substrate is 6
When the thickness of the first or second lower cladding layer is 5 degrees or more and d is d, cot θ is smaller than the wavelength of the light wave propagating in the optical waveguide.

According to a second aspect of the present invention, in a method of manufacturing a distributed feedback semiconductor laser with a quantum well structure optical modulator, a distributed feedback semiconductor laser section and an optical modulator section having a quantum well structure are separately processed on a substrate. A method of manufacturing a distributed feedback semiconductor laser with an optical modulator, the method comprising the steps of: (A) a-1) a first multiple quantum consisting of a barrier layer and a well layer; A first semiconductor portion which has a well structure and first upper and lower cladding layers sandwiching the first multiple quantum well structure to form a distributed feedback semiconductor laser section; and a-2) a barrier layer and a well layer Which has a second multiple quantum well structure and second upper and lower clad layers sandwiching the second multiple quantum well structure Laminate, the other When forming the _second laminated body, a structure having the first laminated body is prepared on a substrate, and (B) an SiO ₂ film is formed on the upper clad layer of the first laminated body. A patterned resist is formed on the SiO ₂ film by photolithography and the S
Diagonal etching to the substrate using a two-layer mask consisting of an iO ₂ film and the patterned resist, then
The side surface of the portion below the SiO ₂ film existing in the remaining portion is wet-etched to form an eaves, and (C) the remaining portion of the patterned resist is removed to leave the SiO 2 of the first stacked body. Exposing the _second film, and (D) exposing the SiO ₂ film by the molecular beam epitaxy method, the obliquely etched surface of the first laminate, and the second laminate on the substrate and the first laminate. InGaA is formed on the second laminated body while contacting with the remaining portion of the portion.
s layer is formed, (E) the SiO ₂ film is wet-etched from its side surface to remove the SiO ₂ film and the second stacked body formed thereon, and (F) the first and the second layers. An interface in which a third cladding layer is formed on each of the two stacked bodies, and (G) an electrode is formed on the third cladding layer, and then the first and second stacked bodies are in contact with each other. The third clad layer is etched along a region including the opposite end portions of the first and second stacked bodies sandwiching the above-mentioned structure to form a separation portion between the electrodes.

[0016]

In order to manufacture this integrated light source, the laser portion is obliquely etched to the semiconductor substrate and the laser portion and the laser portion are not obliquely joined to each other, but the active portion of the laser and the waveguide layer of the optical modulator are directly joined. A waveguide layer of the optical modulator section is formed to achieve optical coupling. At this time, the angle θ of oblique etching of the semiconductor with respect to the substrate is set to 65 ° or more, and the thickness d of the layer located on the substrate side of the semiconductor (called a clad layer) sandwiching both sides of the MQW layer is d · cotθ (where cotθ is Tangent ta
It is preferable that the reciprocal of nθ) be smaller than the wavelength of the light wave propagating through the optical waveguide structure. A molecular beam epitaxial method can be used as a means for producing the waveguide layer of this optical modulator.

Further, in order to improve the electrical insulation between the optical modulator and the laser part, after depositing a SiO ₂ film on the laser part, the lower part is side-etched to form an eaves and a crystal is formed under the eaves. Of the SiO ₂ film is removed from the side by etching the SiO ₂ film from the side. Further, etching is added at the very end of the process to improve the electrical insulation between the optical modulator and the laser section.

In the structure of the present invention, since the active layer and the optical waveguide layer of the laser and the optical modulator have the MQW structure, high performance can be expected in the oscillation threshold current, the modulation voltage, the modulation frequency band and the like.

Hereinafter, a device structure according to one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an MQW-DF according to an embodiment of the present invention.
It is a schematic sectional drawing which shows the element structure of the integrated light source of B laser and MQW optical modulator. FIG. 2 is an enlarged view of the coupling portion of the laser section and the optical modulator section of the device structure of FIG. In FIG.
10 is an MQW-DFB laser device, 11 is an optical waveguide, 1
2 is a distributed feedback semiconductor laser section, 13 is an optical modulator section, 1
4 is the first semiconductor portion, 14A is the opposite end portion, and 15 is the second
, 15A is an opposite end, 16 is an optical coupling region,
17 is an interface, 20 is a substrate, 22 is an etching stop layer, 24 is a first lower cladding layer, 26 is an active layer (first multiple quantum well structure), 26A is a well layer, 26B is a barrier layer, and 28 is a guide. Layer, 29 is a diffraction grating (grating), 30 is a first upper clad layer, 31 is a protective layer, 32
Is a second lower cladding layer, 34 is a second multiple quantum well structure, 34A is a well layer, 34B is a barrier layer, and 36 is a second
Upper cladding layer, 38 is a third cladding layer, 38A is a thin portion, 38B and 38C are portions of the cladding layer, 40 is a separating portion, 42 is a cap layer, 44 and 46 are buried portions, 48
Is an electrode of the laser section, and 50 is an electrode of the modulator section.

The MQW-DFB laser device 10 of the present invention has an optical waveguide 11 provided on a substrate 20. The optical waveguide 11 comprises a distributed feedback semiconductor laser section 12 and an optical modulator section 13 coupled to the distributed feedback semiconductor laser section 12. The distributed feedback semiconductor laser section 12 includes a first semiconductor section 14, and the optical modulator section 13 includes a second semiconductor section 15. The first and second semiconductor portions 14 and 15 described above are provided on the substrate 20 via the etching stop layer 22. The first semiconductor portion 14 has a first lower cladding layer 24, an active layer 26, a guide layer 28, and a first upper cladding layer 30, which are laminated in this order. A diffraction grating (grating) 29 is formed on the guide layer 28. The first upper and lower clad layers 30 and 24 are doped to have different conductivity types, and sandwich the active layer 26 and the guide layer 28. The active layer 26 constitutes a first multiple quantum well structure including a barrier layer 26A and a well layer 26B. The diffraction grating 29 described above may be provided in the active layer 26.

On the other hand, the second semiconductor portion 15 included in the optical modulator portion 13 has a second lower cladding layer 32, a second multiple quantum well structure 34, and a second upper cladding layer 36, which are arranged in this order. It is laminated. Second upper and lower cladding layers 36, 32
Are doped to have different conductivity types like the first upper and lower cladding layers, and sandwich the second multiple quantum well structure. The second multiple quantum well structure 34 is composed of a well layer 34A and a barrier layer 34B, similarly to the first multiple quantum well structure. First and second semiconductor parts 14, 1
No. 5 is discontinuous because the first and second multiple quantum well structures 26 and 34 are separated from each other in a plane perpendicular to the waveguide direction. The semiconductor laser section 12 is optically coupled in the optical coupling region 16 facing each other via the lower cladding layer 32 of the optical modulation section 13. In this case, when the angle formed by the first semiconductor portion 14 of the laser section 12 and the substrate is θ, θ is preferably 65 degrees or more. When the distance between the active layer 26 and the second multiple quantum well structure 34 in the optical coupling region is d, d · cot θ is the wavelength λ / n of the guided light.
It should be smaller than _eff .

The interface 17 between the first and second semiconductor portions 14 and 15 is the end surface of the second semiconductor portion 15 in the waveguiding direction and is the end surface 15A facing the first semiconductor portion 14.
Share only. That is, in the device structure of the present invention, unlike the one described in JP-A-62-229990, the lower clad layer 32 of the modulator section 13 and the second multiple quantum well are provided on the upper clad layer 30 of the laser section 12. The structure 34 does not have a portion in the riding state (there is no portion corresponding to the portion indicated by the symbol P in FIG. 8). Further, a continuous cladding layer 38 is provided on the first and second semiconductor portions 12 and 13, and the cladding layer 38 sandwiches the interface 17 between the first and second semiconductor portions 12 and 13 and faces the opposite end portion 14A. ，
There is a separating portion 40 having a missing upper portion along a region including 15A. That is, at the thin portion 38A crossing the interface 17, D
The FB laser unit 12 and the portions 38B and 38C of the cladding 38 existing in the optical modulator unit 13 are integrally connected. A cap layer 42 is provided on the clad portions 38B and 38C. The optical waveguide 11 has a ridge structure that penetrates the DFR laser unit 12 and the optical modulator unit 13. On both sides of the DFR laser unit 12 and the optical modulator unit 13, the embedded portions 44 and 46 have the same height as the cap layer 42, respectively. It is provided in. An electrode 48 of the laser portion and an electrode 50 of the modulator portion 13 are provided on the cap layer 42 and the embedded portions 44 and 46, respectively. The isolation between the laser section 12 and the modulator section 13 is improved by the separating section 40.

In the element structure of the present invention shown in FIG. 2, the left side portion of the optical waveguide 11 in FIG. 2 is the laser portion 12,
Although the right side portion is the modulator portion 13, it is also possible to have a structure in which both are interchanged.

The MQW-DFB laser described above can be manufactured as follows. That is, molecular beam epitaxy (MBE) or metalorganic vapor phase epitaxy (MOVP)
E), the DFB laser portion (or modulator portion) formed on the substrate is selectively etched to the substrate by dry and wet etching methods, and then the modulator portion (or laser portion) is grown using the MBE method. To do. At this time, the angle of oblique etching of the laser section (modulator section) is set to 65 degrees or more, and the height of the laser emitting section measured from the substrate surface matches the height of the modulator section optical waveguide section measured from the substrate surface. And the distance (d · cot θ) between the laser active layer and the modulator waveguide layer is equal to the wavelength λ / n _eff (λ
Is a wavelength in the atmosphere of the laser, and n _eff is an equivalent refractive index). Usually M
In the BE method, the crystal grows smoothly on the stepped substrate surface, whereas in the MOVPE method, abnormal growth often occurs, so that the MBE method is more preferable.

Next, with reference to FIG. 3, the method of manufacturing the distributed feedback semiconductor laser with a quantum well structure optical modulator of the present invention will be described in detail, taking the case where the laser portion is formed first as an example. FIG. 3 is a schematic cross-sectional view showing a manufacturing process of the semiconductor laser with an optical modulator shown in FIGS. 3, the same reference numerals as those used in FIGS. 1 and 2 indicate the same members or portions, and 52 indicates SiO ₂
A film, 54 is a patterned resist, and 56 is a SiO ₂ film eaves.

As shown in FIG. 3, (A) Preparation of laser section:
First, the stop layer 22 and the well layer 26 are formed on the substrate 20.
A first multiple quantum well structure (active layer) 26 composed of A and a barrier layer 26B, first upper and lower cladding layers 30 and 24 sandwiching the first multiple quantum well structure 26, and a guide layer 28 having a diffraction grating 29 formed therein. A structure in which the first laminated body or the semiconductor portion 14 which has the distributed feedback semiconductor laser section 12 is formed is prepared. The structure described above is obtained by sequentially forming the stop layer 22, the lower cladding layer 24, the barrier layer 26A, the well layer 26B, the guide layer 28, and the upper cladding layer 30 on the substrate 20 by the molecular beam epitaxy method or the MOVPE method. ..

(B) Modulator Etching (1): Next, the upper cladding layer 30 of the first semiconductor portion 14 described above.
A SiO ₂ film 52 is formed on the SiO ₂ film 52, and a patterned resist 5 is formed on the SiO ₂ film 52 by photolithography.
4 is formed, and the SiO ₂ film 52 and the patterned resist 54 are formed.
The substrate 20 is obliquely etched using a two-layer mask consisting of. An etching stop layer 22 is provided between the substrate 20 and the second lower cladding layer 32. At this time,
Using the ECR type ion etching apparatus with the resist as a mask, after etching to almost the substrate 20, light wet etching is performed to remove the damaged layer and
The side surface of the portion below the SiO ₂ film 52 existing in the remaining portion is removed to form the eaves 56.

(C) Modulator etching (2): The remaining portion of the patterned resist 54 is removed to expose the remaining SiO ₂ film 52 of the first semiconductor portion.

(D) Re-growth of modulator part: A laminated body of the above-mentioned second semiconductor part on the exposed SiO ₂ film 52, the obliquely etched surface 17 of the first semiconductor and the substrate 20 by the molecular beam epitaxy method. Is formed to bond to the remaining portion of the first semiconductor portion and form the protective layer 31 on the stacked body of the second semiconductor portion.

(E) Laser portion etching: Next, the SiO ₂ film 52 is wet-etched from the side surface of the SiO ₂ film 52 using the protective layer 31 as a mask to remove the SiO ₂ film 52 and the laminated body of the second semiconductor portion formed thereon. Remove.

(F) Clad layer regrowth: The clad layer 3 is formed on each of the laminated bodies of the first and second semiconductor portions.
8 and the cap layer 42 are formed in this order.

(G) Etching of separation part: cap layer 4
The electrodes 48 and 50 are formed on the surface 2. Then, the cladding layers 38 are formed along the regions including the opposite ends 14A and 15A of the first and second semiconductor portions sandwiching the interface 17 where the first and second semiconductor portions are in contact with each other, using the electrodes 48 and 50 as a mask.
Is etched to form the isolation portion 40.

(H) An antireflection film 64 is formed on the emission end face.

It is also possible to prepare a structure having each layer constituting the optical modulator section on the substrate and form each layer of the laser section later.

FIG. 4 is a diagram showing (A) etching angle dependence of loss at the junction between the MQW-DFB laser of the integrated light source and the MQW optical modulator, and (B) axis shift dependence of the regrown film. .. In FIGS. 4A and 4B, D is the laser spot diameter. As shown in FIG. 4 (A), in the structure of the present invention, the etching angle θ is 65 degrees or more by the calculation using the approximation that the modulator section waveguide section Hegauss beam is emitted from the laser section oblique etching interface. If the angle, the coupling loss is 0.5 dB or less, the reflection loss at the interface is much smaller than 0.1 dB, and the axis deviation of the regrown film is also shown in FIG. 4 (B). Thus, if it is 0.15 μm or less, the coupling loss is 0.5 dB or less. In the calculation here, the thickness d of the lower clad layer of the modulator section is 0.45 μm. Furthermore, when the distance (d · cot θ) between the laser active layer and the modulator waveguide layer is smaller than the wavelength λ / n _eff of the guided light (λ is the wavelength in the atmosphere of the laser, n _eff is the equivalent refractive index). The light couples with almost no attenuation due to the tunnel effect.

Therefore, in the structure of the present invention, the guided light is coupled from the laser section to the optical modulator section without being reflected or scattered.

[0038]

Embodiments of the present invention will now be described in detail with reference to the drawings.

The device structure shown in FIGS. 1 and 2 was manufactured as follows.

That is, M is formed on the surface of the n-InP substrate 20.
An n-InGaAlAs layer is provided as an etching stop layer 22 by the OVPE method, and an n-InP clad layer 24 is formed thereon with a thickness of 0.1 μm, and then with 10 nm of InGaAs.
Is a well layer (well layer) 26A, and InGaAsP 10 nm having a wavelength of 1.3 μm is a barrier layer (barrier layer) 26B.
The InGaAsP guide layer 28 corresponding to μm was grown to 0.1 μm. After forming a grating 29 by interference exposure and etching and growing a p-InP clad layer 30 thereon, a SiO ₂ film 52 is formed by a sputtering device, and a hole is formed in a desired portion by a photolithography technique. That is, a photoresist 54 patterned is formed on the SiO ₂ film 52, perform photolithography using a two-layer mask of the SiO ₂ film 52 and the photoresist 54.

At this time, the side of the lower part of the SiO ₂ film 52 is wet-etched to form the eaves 56 (FIG. 3B).

Next, using this as a mask, the optical modulator section 13
(FIG. 2) is grown by the MBE method. In the optical modulator portion 13, the n-InAlAs cladding layer 32 is 0.3 μm thick, the InGaAs well layer 34A is 7.5 nm thick, and I is 5 nm thick.
An optical waveguide layer 34 is formed by growing 10 quantum well structure layers composed of an nAlAs barrier layer 34B, and p-InA is formed thereon.
The lAs clad layer 36 is formed. A p-InGaAs protective layer 31 is formed on the clad layer 36. The portion grown on the laser portion 11 (layers 32, 34, 36, 31)
Is removed by etching the SiO ₂ layer 52 from the side, and finally the p-InP clad layer 38, p-I
The nGaAs cap layer 42 is formed by the MOVPE method.

Next, the active layer 26 and the optical waveguide layer 34 described above are etched using a stripe having a width of 1.5 to 3.0 μm to form a ridge penetrating the laser portion and the modulator portion. After that, the laser portion is formed into an InP layer (p-InP and n-I).
nP combination or semi-insulating InP) 44,
The modulator portion is filled with polyimide 46, and finally electrodes 48 and 50 are attached to the respective portions.

Etching is performed using these electrodes 48 and 50 as a mask to form a separating portion 40 between both electrodes to strengthen the insulation between the modulator portion and the laser portion.

The lengths of the laser portion, the modulator portion and the insulating portion between them were 300 μm, 100 μm and 50 μm. A non-reflective coating (not shown) was applied to the exit end face of the modulator. Further, an n-type electrode 62 (FIG. 1) is attached to the lower surface of the substrate.

FIG. 5 shows the characteristics of the integrated light source of the MQW-DFB laser and the MQW optical modulator to which the present invention is applied. As shown in FIG. 5, the oscillation threshold current was 20 mA, the modulator-side end face light output was 6 mW, and the modulator extinction ratio of 22 dB was obtained when a voltage of −2.5 V was applied. Also 3dB of modulator
The bandwidth is 15 GHz, which is the highest performance for this type of light source.

FIG. 6 shows the MQW of the first embodiment to which the present invention is applied.
FIG. 4 is a diagram showing the extinction characteristics of all-optical output and guided light of an integrated light source of a DFB laser and an MQW optical modulator. The vertical axis represents the extinction ratio, and the horizontal axis represents the voltage applied to the modulator. As shown in FIG. 6, the driving voltage (Vmod) is low and a good characteristic of 18 dB is obtained at a voltage amplitude of 1 V _DD , and a performance index (3 dB bandwidth / extinction ratio 20 dB required for a modulator is obtained. ) 6 GHz / V is the highest. This is an effect of adopting the MQW structure in the waveguide of the optical modulator, which is an improvement of about 4 times as compared with the conventional bulk modulator. The coupling efficiency can be evaluated from the total optical output including scattered light from the modulator side and the extinction characteristic of guided light. In FIG. 6, the total light output in the state where the guided light is sufficiently extinguished corresponds to the scattered light component, and if the loss 40 cm ⁻¹ in the absorption layer obtained in another experiment is used, the coupling efficiency is as high as 90%. was gotten.

[0048]

As described above, according to the present invention, M
A light source in which a QW-DFB laser and an MQW optical modulator are integrated efficiently can be manufactured, and the performance of each can be optimized, so that a high-performance integrated light source of wide band and low voltage drive can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of an element structure of an integrated light source of an MQW-DFB laser and an MQW optical modulator according to a first embodiment of the present invention.

2 is an enlarged cross-sectional view taken along line II-II of a bonding interface between a laser and an optical modulator of the integrated light source of FIG.

FIG. 3 is a schematic cross-sectional view showing the manufacturing process of the integrated light source of the MQW-DFB laser and the MQW optical modulator of the present invention.

FIG. 4 (A) Etching angle dependence of the loss at the junction between the MQW-DFB laser of the integrated light source and the MQW optical modulator,
(B) is a diagram showing the axis deviation dependency of the regrown film.

FIG. 5 is a diagram showing the extinction characteristics of the total light output and the guided light of the integrated light source of the MQW-DFB laser and the MQW optical modulator of the first embodiment to which the present invention is applied. The vertical axis represents the extinction ratio, and the horizontal axis represents the voltage applied to the modulator.

FIG. 6 is a diagram showing characteristics of an integrated light source of the MQW-DFB laser and the MQW optical modulator of Example 1 to which the present invention is applied. The vertical axis represents the optical output on the modulator side, and the horizontal axis represents the current flowing in the laser section.

FIG. 7 is a schematic perspective view showing a structure of a conventional integrated light source.

FIG. 8 is a schematic sectional view showing a structure of a conventional integrated light source.

FIG. 9 is a schematic perspective view showing a manufacturing process of a conventional integrated light source.

[Explanation of symbols]

10 MQW-DFB Laser Element 11 Optical Waveguide 12 Distributed Feedback Semiconductor Laser Part 13 Optical Modulator Part 14 First Semiconductor Part 14A Opposing End 15 Second Semiconductor Part 15A Opposing End 16 Optical Coupling Region 17 Interface (Oblique Etching) 18) butt coupling 20 substrate 22 etching stop layer 24 first lower cladding layer 26 active layer (first multiple quantum well structure) 26A well layer 26B barrier layer 28 guide layer 29 diffraction grating (grating) 30 first Upper clad layer 31 Protective layer 32 Second lower clad layer 34 Second multiple quantum well structure 34A Well layer 34B Barrier layer 36 Second upper clad layer 38 Third clad layer 38A Thin portion 38B, 38C Clad portion 40 Separation part 42 Cap layer 44, 46 Embedded part 48 Electrode 5 of laser part 5 Modulator portion of the electrode 52 SiO ₂ film 54 patterned resist 56 eaves 58 p-type electrode 60 p-type electrode 62 n-type electrode 64 antireflection film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiromitsu Asai 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. A substrate, and an optical waveguide provided on the substrate, the optical waveguide comprising a first waveguide layer as an active layer and first upper and lower layers sandwiching the first waveguide layer. A distributed feedback semiconductor laser portion including a first semiconductor portion having a cladding layer, a second waveguide layer coupled to the semiconductor laser portion, and second upper and lower cladding layers sandwiching the second waveguide layer. And an optical modulator section including a second semiconductor section having the semiconductor laser section and the modulator section.
A third cladding layer provided on the semiconductor portion of the second waveguide layer, the second waveguide layer having a multiple quantum well structure including a barrier layer and a well layer, and the first and second waveguide layers.
The semiconductor portion of the first and second waveguide layers is separated from each other in a plane perpendicular to the waveguide direction, and the semiconductor laser portion or the light modulation portion has the first or second lower portion. In a distributed feedback semiconductor laser with a quantum well structure optical modulator optically coupled in optical coupling regions facing each other via a clad layer, the first waveguide layer is a multi-quantum layer including a barrier layer and a well layer. A well structure, the interface between the first and second semiconductor portions shares only the opposite end faces of the first and second semiconductor portions in the waveguide direction, and the third cladding layer is A distributed feedback semiconductor laser with a quantum well structure optical modulator, having a separation portion provided along a region including opposed ends of the first and second semiconductor portions sandwiching the interface. 2. The angle θ between the interface between the first and second semiconductor portions and the surface of the substrate is 65 degrees or more, and the thickness of the first or second lower cladding layer. The distributed feedback semiconductor laser with a quantum well structure optical modulator according to claim 1, wherein d · cotθ is smaller than the wavelength of the light wave propagating through the optical waveguide, where d is the d. 3. A method of manufacturing a distributed feedback type semiconductor laser with an optical modulator by forming a distributed feedback type semiconductor laser part and an optical modulator part having a quantum well structure on a substrate in separate steps. A method of manufacturing a distributed feedback semiconductor laser with a quantum well structure optical modulator, which comprises: (A) a-1) A first multiple quantum well structure including a barrier layer and a well layer, and the first multiple quantum well structure. A first semiconductor portion which has a first upper and lower cladding layers sandwiching a quantum well structure to form a distributed feedback semiconductor laser section; and a-2) a second multiple quantum well structure including a barrier layer and a well layer. And the second upper and lower clad layers sandwiching this second multiple quantum well structure, one of the second semiconductor portions that should constitute the optical modulator section is the first laminated body, and the other is the second laminated body. When making a laminated body, Providing a structure having a first laminate on, (B) Si on the upper cladding layer of said first laminate
An O ₂ film is formed, and a patterned resist is formed on the SiO ₂ film by photolithography.
Using a two-layer mask consisting of _two films and the patterned resist, diagonal etching is performed up to the substrate, and then the side surface of the lower portion of the SiO ₂ film existing in the remaining portion is wet-etched to form an eaves. , (C) the remaining portion of the patterned resist is removed to expose the remaining SiO ₂ film of the first laminate, and (D) the exposed Si by a molecular beam epitaxy method.
An O ₂ film, an obliquely etched surface of the first laminated body and the second laminated body are formed on the substrate in contact with the remaining portion of the first laminated body portion, and on the second laminated body. And (E) wet etching the SiO ₂ film from its side surface to remove the SiO ₂ film and the second laminated body formed thereon, and (F) the first and the second layers. Forming a third cladding layer on each of the second laminates, and (G) forming an electrode on the third cladding layer, and then contacting the first and second laminates. The third clad layer is etched along a region including the facing ends of the first and second stacked bodies sandwiching the interface to form a separation portion between the electrodes.