JP2001237493A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a side mode suppression ratio for stable gain coupling. SOLUTION: There are provided a first conductivity-type semiconductor substrate, an active layer (MQW active layer) formed on the main-surface side of the semiconductor substrate, a second conductivity-type guide layer overlapping the active layer, a second conductivity-type clad layer provided on the surface side of the guide layer, a diffraction lattice formed between the guide layer and the clad layer, a high resistance region provided at a part comprising the active layer at the same cycle with the diffraction lattice, an electrode which is connected electrically to the semiconductor substrate, and an electrode electrically connected to the clad layer. A carrier generated by the electric potential applied between the pair of electrodes flows the active region except for the high resistance region. The high resistance region is implanted with proton as an impurity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a technique which is effective when applied to a technique of making a laser oscillation spectrum into a single mode and specifying an oscillation wavelength in a gain-coupled distributed feedback laser.

[0002]

2. Description of the Related Art A gain-coupled distributed feedback laser is known as one of distributed feedback lasers. As one of gain-coupled distributed feedback lasers, MQW (Multi Quantum We
ll) A structure is known in which a current blocking layer having a predetermined length is arranged at a predetermined pitch along an active layer, and only a mode on a short wavelength side of a two-mode laser oscillation spectrum is made to be a single mode. For this type of gain-coupled distributed feedback laser, see, for example, IEEE PHOTONICS TECHNOLOGY LETTERS.
L.8, NO.11, NOVEMBER 1996, PP1438-1440.

[0003]

In a public communication network using an optical fiber, in a trunk line system, a cooling device such as a Peltier element is used to control the temperature of a semiconductor laser so that desired laser oscillation is performed. A technique for performing stable communication is employed. On the other hand, a semiconductor laser without a Peltier element is used in a subscriber system for cost reduction.

FIGS. 17A to 17C are diagrams showing laser oscillation spectra of a semiconductor laser. In a conventional distributed feedback laser having a uniform diffraction grating, the laser oscillation spectrum is almost bimodal as shown in FIG.

For this reason, in a conventional semiconductor laser of this type, a coating film having different reflectivities is formed on the emission surfaces at both end surfaces of the semiconductor laser chip [AR (An
ti Reflection) film, HR (High Reflecti
on) film], and as shown in FIG. 17 (b), only one mode is set up to achieve a single mode (a semiconductor laser having a high side mode suppression ratio). At this time, which mode is set is determined by the probability.

However, when the operating temperature environment changes, a mode different from the mode according to the design is set up, the communication wavelength changes, and stable communication cannot be performed. Extremely different examples of the operating temperature environment include an extreme example, such as a desert where the temperature is remarkably higher than room temperature (25 ° C.) and an extremely cold region where the temperature is remarkably low. The difference in wavelength between the short wavelength mode and the long wavelength mode is, for example, about 2 nm.

Therefore, as shown in FIG. 17 (c), a gain-coupled distributed feedback laser has been developed in which only a mode on the short wavelength side of a two-mode laser oscillation spectrum is made to be a single mode.

FIG. 18 is a schematic diagram showing an outline of a gain-coupled distributed feedback laser. The gain-coupled distributed feedback semiconductor laser 1 has a multilayer growth layer on the main surface of a semiconductor substrate 10, and an active layer (for example, an MQW active layer) 13 is formed by a part of the layer. A guide layer 14 is formed above the MQW active layer 13. For example, when the semiconductor substrate 10 is n-type, the layer above the MQW active layer 13 is p-type. Therefore, the guide layer 14 also becomes p-type.

A diffraction grating 19 is formed on the guide layer 14. Further, a current blocking layer 18 is provided at the same cycle as the diffraction grating 19. The active layer region where the current blocking layer 18 does not overlap becomes the current injection region, and the current blocking layer 18
The active layer region on which the current overlaps becomes a non-current injection region, so that a current injection region and a non-current injection region occur alternately. Since the gain occurs only in the region where the current is injected, periodic gain modulation occurs in the direction of the resonator, and as a result, a gain-coupled distributed feedback laser is formed.

A cladding layer 21 is formed on the guide layer 14 and the current blocking layer 18. This cladding layer 2
An electrode (p-electrode) 7 that is electrically connected to the cladding layer 21 is provided above 1. In addition, the semiconductor substrate 1
0 is provided with another electrode (n-electrode) 8 on the back surface.

In such a semiconductor laser 1, when a predetermined voltage is applied between the electrodes 7 and 8, a current is injected into the current injection region of the active layer 13 as shown by a dotted arrow, and laser oscillation occurs.

However, it has been found that such a structure has the following problems. That is, since the current blocking layer 18 is located away from the active layer 13, in the current flowing between the current blocking layer 18 and the current blocking layer 18, the current at the end is below the current blocking layer 18 as indicated by the solid line arrow. Some flow around the side (diffusion in the lateral direction), so that the distinction between the current injection region and the non-current injection region in the active layer becomes unclear, and the gain coupling effect is reduced. As a result, mode stability is reduced, and stable optical communication is impeded in the optical communication system.

An object of the present invention is to provide a semiconductor laser capable of obtaining stable gain coupling.

Another object of the present invention is to provide a semiconductor laser having a high side mode suppression ratio.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0016]

The following is a brief description of an outline of typical inventions disclosed in the present application.

(1) A semiconductor substrate of a first conductivity type, an active layer formed on the main surface side of the semiconductor substrate, a guide layer of a second conductivity type overlapping the active layer, and a surface side of the guide layer A second conductivity type cladding layer, a diffraction grating formed between the guide layer and the cladding layer, and a high resistance region provided in a portion including the active layer at the same period as the diffraction grating. An electrode electrically connected to the semiconductor substrate, and an electrode electrically connected to the cladding layer, wherein carriers generated by an electric potential applied between the pair of electrodes pass through the high-resistance region. The structure is such that the active layer region except for the above flows. The high resistance region has protons implanted as impurities. The active layer is an MQW active layer. The cladding layer portion electrically connected to the electrode forms a stripe-shaped ridge, and the active layer portion corresponding to the ridge forms a resonator. A first conductivity type buffer layer formed on the semiconductor substrate and a first conductivity type guide layer formed on the buffer layer are provided between the main surface of the semiconductor substrate and the active layer; A second conductive type guide layer formed on the active layer, a second conductive type spacer layer formed on the guide layer, and formed on the spacer layer between the active layer and the clad layer. And a second conductive type diffraction grating layer forming a diffraction grating is provided, and a second conductive type cap layer is provided between the cladding layer and the electrode.

According to the means (1), in the MQW active layer, a current injection region and a non-current injection region are alternately generated by the high resistance region formed at the same period as the diffraction grating in the resonator direction. . As a result, a gain-coupled distributed feedback semiconductor laser in which the periodic gain modulation is reliably generated in the resonator direction can be obtained.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. In all the drawings for describing the embodiments of the present invention, components having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

(Embodiment 1) FIGS. 1 to 14 relate to a gain-coupled distributed feedback semiconductor laser according to an embodiment (Embodiment 1) of the present invention. FIG. 1 is a schematic view showing a characteristic portion of a semiconductor laser and a flow of carriers.

As shown in FIG. 1, the semiconductor laser 1 of the first embodiment has a multi-layer growth layer on the main surface of a semiconductor substrate 10, and a part of the layer forms an active layer (for example, An MQW active layer 13 is formed. The MQW
A guide layer 14 is formed above the active layer 13.
For example, when the semiconductor substrate 10 is n-type, the layer above the MQW active layer 13 is p-type. Therefore, the guide layer 14 also becomes p-type.

A diffraction grating 19 is formed on the guide layer 14. The region including the active layer 13 is an electrically high-resistance region (high-resistance region 9) so as to have the same period as the diffraction grating 19. That is, the high-resistance region 9 is an ion-implanted region (dotted region) into which, for example, protons (H ⁺ ) are implanted as impurities.

MQ between high-resistance regions 9
The W active layer 13 has a current injection region (MQW) where carriers flow.
(Active layer current injection region). Therefore, the current injection region and the non-current injection region occur alternately. Since the gain occurs only in the region where the current is injected, periodic gain modulation occurs in the direction of the resonator, and as a result, a gain-coupled distributed feedback laser is formed.

On the guide layer 14, a p-type cladding layer 21 is formed. An electrode (p-electrode) electrically connected to the cladding layer 21 is provided above the cladding layer 21.
7 are provided. Another electrode (n-electrode) 8 is provided on the back surface of the semiconductor substrate 10.

In such a semiconductor laser 1, when a predetermined voltage is applied between the electrodes 7 and 8, carriers are injected into the current injection region of the active layer 13 as shown by a dotted arrow, and laser oscillation occurs. Semiconductor laser 1 of the first embodiment
As a result, the region of the high resistance region 9 is made constant by proton injection, and as a result, the distinction between the current injection region (carrier injection region) and the non-current injection region (non-carrier injection region) becomes clear, and the gain coupling effect increases. Such a gain-coupled distributed feedback laser has a high side mode suppression ratio and is made single mode. In addition, the mode always has a mode on the short wavelength side.

Next, the semiconductor laser according to the first embodiment will be described with reference to FIGS. 2 is a schematic perspective view of the semiconductor laser, FIG. 3 is a sectional view taken along line AA in FIG. 2, and FIG. 4 is a sectional view taken along line BB in FIG.

The semiconductor laser 1 of the first embodiment is a gain-coupled distributed feedback laser. The semiconductor laser 1 has a flat rectangular body as shown in FIG. The semiconductor laser 1 is a ridge-type semiconductor laser having one ridge 2 at the center of the main surface (the upper surface in FIG. 2) of a semiconductor laser chip.

A resonator 3 is formed directly below the ridge 2, and a laser beam 4 is emitted from emission surfaces at both ends of the resonator 3. Coating films 5 and 6 having different reflectivities are provided on both emission surfaces. An AR film 5 is provided on the front emission surface, and an HR film 6 is provided on the rear emission surface. Thereby, the laser light 4 emitted from the front emission surface
Is higher than the light intensity of the laser light 4 emitted from the rear emission surface. The AR film 5 is formed of a SiN _x film, and the HR film 6 is formed of a film in which an SiO ₂ film and an amorphous silicon film are stacked.

An electrode 7, for example, a p-electrode 7 is provided on the main surface of the semiconductor laser 1, and an electrode 8, for example, an n-electrode 8 is provided on the back surface (the lower surface in FIG. 2) of the semiconductor laser 1. . When a predetermined voltage is applied to the pair of electrodes 7 and 8, laser light 4 is emitted from both ends of the resonator 3.

Next, the internal structure including the resonator 3 and the ridge 2 will be described. As shown in FIGS. 3 and 4, the semiconductor laser 1 is formed based on a semiconductor substrate 10, for example, an n-type (first conductivity type) -InP substrate 10. An n-type buffer layer (n-InP buffer layer) 11 and an n-type guide layer (n-InGaAsP guide layer) are provided on the main surface (upper surface in FIG. 4) of the n-type InP substrate (n-InP substrate) 10. ) 12, active layer 13, p-type guide layer (p-InG
aAsP guide layers) 14 are sequentially laminated.

A p-InP cladding layer 21 is formed on the p-InGaAsP guide layer 14, and a p-type diffraction grating layer (p-InGaAsP diffraction grating) is formed below the p-InP cladding layer 21. Layer) 16 is p-
It is formed so as to float in the InP cladding layer 21.

At the beginning of the formation of the semiconductor laser 1,
A p-type spacer layer (p-InP spacer layer) 15, a p-InGaAsP diffraction grating layer 16, and an undoped cap layer (undoped I) on the -InGaAsP guide layer 14.
An nP cap layer 17 is sequentially formed (see FIG. 6).
After that, the p-InP spacer layer 15, p-In
The GaAsP diffraction grating layer 16 and the undoped InP cap layer 17 are selectively etched, and furthermore, p-In
An epitaxial growth process for the P clad layer 21 and the like is performed.

During the epitaxial growth, p-InGa
P-InP spacer layers 1 above and below the AsP diffraction grating layer 16
5 and the undoped InP cap layer 17 are assimilated into the p-InP cladding layer 21, so that the p-InGaAsP diffraction grating layer 16 floats in the p-InP cladding layer 21.

The resonator 3 is an MQW active layer. The MQW active layer has a structure in which a well layer is sandwiched between barrier layers and a plurality of well layers are stacked. The barrier layer and the well layer are formed of InGaAsP layers having different compositions from each other.

Further, the p-InP spacer layer 15, pI
The two layers of the nGaAsP diffraction grating layer 16 have been etched away at a predetermined pitch Λ over a predetermined length. As a result, the spacer layer 15 and the diffraction grating layer 1 which sequentially overlap each other are formed.
6. The cap layer 17 remains on the p-guide layer 14 at the pitch Λ and the length a, and the diffraction grating 19 is formed.
This diffraction grating 19 has an oscillation wavelength of laser light of 1.3 μm.
In the case of the m band, the pitch Λ is about 200 nm, and the length a is 10
In the case of the 1.55 μm band, the pitch Λ is about 240 nm, and the length a is about 120 nm.

In the region from the p-guide layer 14 where the three layers have been removed to the intermediate depth of the n-guide layer 12, for example, protons (H ⁺ ) are implanted as impurities and the high resistance region 9 is formed. It has become.

As shown in FIG. 3 and FIG.
A p-type cladding layer (p-InP cladding layer) 21 is provided on the guide layer 14 and the undoped cap layer 17, and a p-type contact layer (p-InGaAs contact layer) is formed on the p-InP cladding layer 21. ) 22 are provided.

One ridge 2 is provided at the center of the main surface of the semiconductor laser 1. This ridge 2
The InGaAs contact layer 22 and the p-InP cladding layer 21 were etched over their entire depth 2
It is formed by parallel grooves 23 of a book. The main surface of the semiconductor laser 1 excluding the upper surface of the ridge 2 is covered with an insulating film 24. An electrode (p-electrode) 7 is provided so as to extend from the upper surface of the ridge 2 onto the insulating film 24.
Therefore, the ridge 2 (p-InGaAs contact layer 2)
2) has a structure electrically connected to the p-electrode 7. Further, an electrode (n-
(Electrode) 8 is provided. The p-electrode 7 is Ti / Pt /
The n-electrode 8 is formed of AuGe / Ni / Ti /
It is formed of Pt / Au.

The thickness of each semiconductor layer, the concentration of impurities and the like are not described, but they are in the 1.3 μm band or 1.55
Needless to say, a numerical value suitable for oscillating the laser light in the μm band is selected.

Next, a method of manufacturing the semiconductor laser according to the first embodiment will be described with reference to FIGS. A semiconductor laser produces a large number of semiconductor lasers (semiconductor laser chips) by sequentially processing a single semiconductor substrate and then cleaving and dividing the semiconductor laser. Here, a description will be given of a state in which a single semiconductor laser is produced.

As shown in the flowchart of FIG. 5, in the semiconductor laser of the first embodiment, after the start of step (S) 101, formation of a multilayer growth layer (S102), interference exposure (S10)
3), etching (S104), impurity diffusion (S10)
5) The operation is completed through the steps of epitaxial growth (S106), ridge formation (S107), p electrode formation (S108), n electrode formation (S109), end face coating (S110), and chipping (S111) (S112).
I do.

In the manufacture of the semiconductor laser 1, after the start of the work (S101), as shown in FIG.
0, for example, an n-InP substrate 10 is prepared. afterwards,
A multilayer growth layer is formed on the main surface (upper surface) of the n-InP substrate 10 (S102). The multilayer growth layer is formed by MBE (Molecular
Beam Epitaxy) and MOCVD (Metalorganic Chemical)
Vapor Deposition). That is, n-I
An n-InP buffer layer 1 is formed on the main surface of the nP substrate 10.
1, n-InGaAsP guide layer 12, MQW active layer 1
3, a p-InGaAsP guide layer 14, a p-InP spacer layer 15, a p-InGaAsP diffraction grating layer 16, and an undoped InP cap layer 17 are sequentially formed. The M
The QW active layer 13 has a structure in which a well layer is sandwiched between barrier layers and a plurality of well layers are stacked, and each is formed of a GaAsP layer.

Here, an example of the dimensions and impurity concentration of each layer will be described. The n-InP substrate 10 has a thickness of 450 μm and an impurity concentration of 1 to 2 × 10 ¹⁸ cm ⁻³ . The n-InP buffer layer 11 has a thickness of 300 nm and an impurity concentration of 1.0 × 10 ¹⁸ c.
m ⁻³ , n-InGaAsP guide layer 12 has a thickness of 90 nm
And the impurity concentration is 1.0 × 10 ¹⁸ cm ⁻³ and the MQW active layer 1
3 is 6 nm, and the barrier layer of the MQW active layer 13 is 5 n.
m, p-InGaAsP guide layer 14 has a thickness of 30 to 80
nm, the impurity concentration is 4-8 × 10 ¹⁷ cm ^-3 , p-InP
The spacer layer 15 has a thickness of 20 to 30 nm and an impurity concentration of 4
-8 × 10 ¹⁷ cm ^-3 , p-InGaAsP diffraction grating layer 1
6 has a thickness of 30 to 40 nm and an impurity concentration of 4 to 8 × 10 ¹⁷
cm ⁻³ , the undoped InP cap layer 17 has a thickness of 10 n
m.

Next, as shown in FIG. 7, a diffraction grating is formed by interference exposure (S103). That is, a resist film 30 is formed on the undoped InP cap layer 17, and the resist film 30 is exposed to interference light and developed. As a result, as shown in FIG. 7, the resist film 30 having a fixed length and a fixed length remains on the undoped InP cap layer 17.

Next, as shown in FIG. 8, the undoped InP cap layer 17, p-InGaAsP diffraction grating layer 16, and p-InP spacer layer 15 are etched using the remaining resist film 30 as an etching mask to form a diffraction grating. 19 are formed (S104). At this time, the dimensions of each layer are accurately etched by anisotropic etching.
This diffraction grating 19 has an oscillation wavelength of laser light of 1.3 μm.
In the case of the m band, the pitch Λ is about 200 nm, and the length a is 10
In the case of the 1.55 μm band, the pitch Λ is about 240 nm, and the length a is about 120 nm.

Next, as shown in FIG. 9, impurities, for example, protons (H.sup. ⁺ ) Are implanted using the resist film 30 as a mask for impurity implantation (S105). The impurities are removed from the p-InGaAsP guide layer 14 at the bottom of the etched portion.
Is injected into. As a result of this implantation, the impurities pass through the MQW active layer 13 and are formed to a depth in the middle of the n-InGaAsP guide layer 12, thereby forming a region (high resistance region) 9 having a high electrical resistance.

Next, as shown in FIG. 10, after removing the resist film 30, the p-InP cladding layer 2 is formed on the multilayer growth layer by epitaxial growth by MOCVD or the like.
1 and the p-InGaAs contact layer 22 are formed (S106). For example, the p-InP cladding layer 21 has a thickness of 1700 nm, an impurity concentration of 8.5 × 10 ¹⁷ cm ⁻³ ,
The p-InGaAs contact layer 22 has a thickness of 200 nm and an impurity concentration of 1.0 × 10 ¹⁹ cm ⁻³ . FIG. 11 shows p
FIG. 4 is a perspective view showing a state where an -InP cladding layer 21 and a p-InGaAs contact layer 22 are formed.

In the above epitaxial growth, pI
nP spacer layer 15 and undoped InP cap layer 1
7 is assimilated into a p-InP cladding layer 21 and p-InGa
The AsP diffraction grating layer 16 is in a state of floating in the p-InP cladding layer 21.

Next, as shown in FIG.
aAs contact layer 22 and p-InP cladding layer 21
Are formed over the entire depth thereof, and one ridge 2 is formed between the grooves 23 (S107). FIG.
FIG. 2B is an enlarged view of a portion A in FIG. Since the width of the ridge 2 is substantially equal to the width of the resonator (optical waveguide),
The width of the ridge 2 needs to be formed with high precision. The width of the ridge 2 is, for example, 2.0 μm.

Next, except for the upper surface of the ridge 2, nI
The entire area of the main surface of the nP substrate 10 is covered with the insulating film 24, and the p-electrode 7 is formed by vapor deposition or the like (S10).
8). This p-electrode 7 is formed of, for example, Ti / Pt / Au. FIG. 13A is a perspective view showing a state where the p-electrode 7 is formed. FIG. 13B is an enlarged view of a portion B in FIG.

Next, after grinding the back surface of the n-InP substrate 10 to a total thickness of about 100 μm,
The n-electrode 8 is formed on the back surface of the nP substrate 10 by vapor deposition or the like (S109). The n-electrode 8 is, for example, AuGe / N
It is formed of i / Ti / Pt / Au.

Next, although not shown, the entire semiconductor substrate is divided by cleavage of the crystal in a direction perpendicular to the resonator to form a strip, and both end faces of the strip are coated with mutually different reflectances. A film is formed (S110). One coating film is AR (Anti Reflection) film 5
(See FIG. 4), and the surface on which the AR film 5 is formed is a front emission surface. The coating film on the other surface is HR
(High Reflection) film 6 (see FIG. 4).
The surface on which the R film 6 is formed is a rear emission surface. For example, A
R film 5 is formed of SiN _X reflectance becomes 1%, HR film 6 is formed reflectivity composite membrane according to SiO ₂ and a-Si (amorphous silicon) becomes 70% or 90%.

Next, the front emission surface strip is divided at an intermediate portion between the resonators to form a chip, and the semiconductor laser 1 shown in FIG. 14 is formed (S111), and the operation is completed (S11).
2). In FIG. 14, the AR film 5 and the HR film 6 are omitted.

The semiconductor laser 1 manufactured as described above
Is incorporated in an optoelectronic device (semiconductor optical module). FIG. 15 is a schematic plan view showing an optoelectronic device (semiconductor optical module) 40. The semiconductor optical module 40 includes:
The structure is such that the optical fiber cable 43 protrudes from the tip of the guide portion 42 of the package 41.

The front emission surface package 41 includes a case 44
And a cap 45 fixed on the case 44, and a plurality of leads 46 project from both sides of the case. The lead 46 has a butterfly structure.

At the inner bottom of the case 44, a silicon platform 47 is provided. The semiconductor laser 1 and the semiconductor laser 1 are placed on the silicon platform 47.
A submount 49 to which a light receiving element 48 for receiving a laser beam emitted from the rear emission surface of the submount 49 is fixed.

The coating film covering the optical fiber 50 is removed from the inner end side of the optical fiber cable 43 guided by the guide portion 42, and the optical fiber 50 is exposed. The semiconductor laser 1 is fixed on a submount 49 near the optical fiber 50. Therefore, laser light emitted from the front emission surface of the semiconductor laser 1 is taken into the core of the optical fiber 50 from the distal end surface of the optical fiber 50. A lens 51 for condensing light is disposed between the tip of the optical fiber 50 and the semiconductor laser 1. The lens 51 plays a role of condensing laser light emitted from the front emission surface of the semiconductor laser 1 on the core of the optical fiber 50.

Although not shown, a metallized layer is formed in a predetermined pattern on the surface of the submount 49 and the silicon platform 47. In the submount 49, the metallized layer is a mounting portion for fixing the semiconductor laser 1 and the light receiving element 48,
And a relay unit for connecting a conductive wire connected to the electrode. Further, in the silicon platform 47, the metallized layer serves as a relay portion having one end fixed to the relay portion and the other end fixed to the wire. A relay portion of the silicon platform 47 and an inner end of a lead 46 (not shown) are connected by a conductive wire.

The semiconductor optical module 40 emits a laser beam from the emission surface of the semiconductor laser 1 by applying a predetermined voltage to a predetermined lead 46, and the monitor current of the light receiving element 48 is reduced by the predetermined lead 46. Output from Thus, the semiconductor laser 1 can be driven while controlling the light intensity of the emitted laser light. In addition, the incorporated semiconductor laser 1 has a high side mode suppression ratio and becomes a single mode. In addition, the mode always has a mode on the short wavelength side.

FIG. 16 is a schematic diagram showing an optical communication system in which an optoelectronic device (semiconductor optical module) 40 is incorporated. The optical communication system basically has a configuration in which a transmitter 55 and a receiver 56 are connected by an optical fiber (optical fiber cable 43), and one or a plurality of repeaters 57 are connected to the optical fiber cable 43 according to the distance between them. Is arranged in the middle of In the figure, both the transmitter 55 and the receiver 56 are schematic diagrams in which only the semiconductor optical module 40 constituting the transmission device is connected to the optical fiber, but the reception device is naturally connected to the optical fiber.

The semiconductor optical module 40 of this embodiment is
Since a semiconductor laser having a good gain coupling state is used for the transmission device, a large optical output and stable laser light emission can be performed, so that stable and highly reliable optical communication can be performed.

The built-in semiconductor laser has a high side mode suppression ratio and is in a single mode. In addition, the mode always has a mode on the short wavelength side. Therefore, stable optical communication can be achieved without wavelength fluctuation even when used in a desert or the like where the operating temperature environment is inferior or an extremely cold place where the temperature is remarkably low.

According to the first embodiment, the following effects can be obtained.

(1) In the MQW active layer 13, the high resistance region 9 formed at the same period as the diffraction grating 19 in the resonator direction
As a result, the current injection region and the non-current injection region alternately and regularly occur. As a result, the periodic gain modulation is reliably generated in the cavity direction, and the gain-coupled distributed feedback semiconductor laser 1 having a desired optical output intensity is obtained.

(2) The semiconductor optical module 40 incorporating the semiconductor laser 1 of the above (1) has a high light intensity and can perform stable laser oscillation.

(3) The semiconductor optical module 4 of the above (2)
In an optical communication system in which 0 is incorporated in the transmission device, stable optical communication can be achieved even when the operating temperature environment changes. Although the invention made by the inventor has been specifically described based on the embodiment, the present invention is not limited to the above embodiment, and various changes can be made without departing from the gist of the invention. Nor. In the above-described embodiment, an example in which the present invention is applied to a ridge-type semiconductor laser has been described.
The same effects can be obtained by applying the present invention to a semiconductor laser having a buried-hetero structure (H: H).

The present invention can be applied to a semiconductor laser having at least a diffraction grating.

[0068]

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.

(1) In the gain-coupled distributed feedback laser, a current injection region and a non-current injection region can be regularly formed along the MQW active layer, so that periodic gain modulation can be reliably generated in the resonator direction. And stable gain coupling can be obtained.

(2) A semiconductor laser having a high side mode suppression ratio can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a characteristic portion of a semiconductor laser according to an embodiment (Embodiment 1) of the present invention and a flow of carriers.

FIG. 2 is a schematic perspective view of the semiconductor laser according to the first embodiment.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a sectional view taken along line BB of FIG. 2;

FIG. 5 is a flowchart illustrating a method of manufacturing the semiconductor laser according to the first embodiment.

FIG. 6 is a schematic cross-sectional view showing a state in which a multilayer growth layer is formed on the main surface of the semiconductor substrate in the manufacture of the semiconductor laser according to the first embodiment.

FIG. 7 is a schematic cross-sectional view showing a state in which a resist formed on the multilayer growth layer has been subjected to interference exposure and development.

FIG. 8 is a schematic cross-sectional view showing a state where a part of the multilayer growth layer is etched using the resist as a mask.

FIG. 9 is a schematic cross-sectional view showing a state in which impurities are implanted using the resist and the remaining multilayer growth layer as a mask.

FIG. 10 is a schematic cross-sectional view showing a state where an epitaxial layer is formed on the multilayer growth layer from which the resist has been removed.

FIG. 11 is a schematic perspective view showing a state where an epitaxial layer is formed on the multilayer growth layer from which the resist has been removed.

FIG. 12 is a diagram showing a state where a ridge is formed by selectively etching the epitaxial layer.

FIG. 13 is a view showing a state in which a p-electrode is formed on the epitaxial layer side.

FIG. 14 is a perspective view showing a state where an n-electrode is formed on the semiconductor substrate side.

FIG. 15 is a schematic plan view showing an optoelectronic device incorporating the semiconductor laser of the first embodiment.

FIG. 16 is a schematic diagram showing an optical communication system incorporating the optoelectronic device.

FIG. 17 is a diagram showing a laser oscillation spectrum of a semiconductor laser.

FIG. 18 is a schematic diagram showing a characteristic portion and a carrier flow of a conventional gain-coupled distributed feedback laser.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Ridge, 3 ... Resonator, 4 ... Laser light, 5 ... AR film (coating film), 6 ... HR film (coating film), 7, 8 ... Electrode, 9 ... High resistance area, 10
... semiconductor substrate (n-InP substrate), 11 ... buffer layer (n-InP buffer layer), 12 ... guide layer (n-InP)
GaAsP guide layer), 13 ... active layer (MQW active layer), 14 ... guide layer (p-InGaAsP guide layer), 15 ... spacer layer (p-InP spacer layer), 1
6 ... Diffraction grating layer (p-InGaAsP diffraction grating layer), 1
7 ... cap layer (undoped InP cap layer), 18
... current blocking layer, 19 ... diffraction grating, 21 ... cladding layer (p
-InP cladding layer), 22 ... contact layer (p-In
(GaAs contact layer), 23 ... groove, 24 ... insulating film, 3
0: resist film, 40: optoelectronic device (semiconductor optical module), 41: package, 42: guide part, 43: optical fiber cable, 44: case, 45: cap, 46
... Lead, 47 ... Silicon platform, 48 ... Light receiving element, 49 ... Submount, 50 ... Optical fiber, 51 ...
Lens, 55: transmitter, 56: receiver, 57: repeater.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Atsushi Nakamura 5-2-1, Josuihonmachi, Kodaira-shi, Tokyo Within the semiconductor group of Hitachi, Ltd. (72) Inventor Yoriyuki Yamaguchi Josuihoncho, Kodaira-shi, Tokyo 5-20-1 F-term in Hitachi Semiconductor Group, Ltd. F-term (reference) 5F073 AA13 AA45 AA51 AA64 AA74 AA83 CA12 CB19 DA14 EA03

Claims (5)

[Claims] A first conductive type semiconductor substrate, an active layer formed on a main surface side of the semiconductor substrate, a second conductive type guide layer overlapping the active layer, and a surface side of the guide layer. A second conductivity type cladding layer provided, a diffraction grating formed between the guide layer and the cladding layer, a high resistance region provided in a portion including the active layer at the same period as the diffraction grating, An electrode electrically connected to the semiconductor substrate; and an electrode electrically connected to the cladding layer, wherein carriers generated by a potential applied between the pair of electrodes exclude the high-resistance region. A semiconductor laser characterized in that it flows in an active layer region. 2. The semiconductor laser according to claim 1, wherein said high-resistance region is formed by implanting impurities. 3. The semiconductor laser according to claim 2, wherein said impurities are protons. 4. The device according to claim 1, wherein the cladding layer portion electrically connected to the electrode forms a stripe-shaped ridge, and the active layer portion corresponding to the ridge forms a resonator. The semiconductor laser according to any one of claims 1 to 3. 5. A buffer layer of a first conductivity type formed on the semiconductor substrate between a main surface of the semiconductor substrate and the active layer, and a guide of a first conductivity type formed on the buffer layer. A second conductive type guide layer formed on the active layer, between the active layer and the clad layer,
A second conductivity type spacer layer formed on the guide layer,
A second conductivity type diffraction grating layer formed on the spacer layer and forming a diffraction grating is provided, and a second conductivity type cap layer is provided between the cladding layer and the electrode. The semiconductor laser according to any one of claims 1 to 4, wherein: