JPH10290043A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a leakage current flowing into a zinc diffusion region constituting a window structure part by a method wherein the window structure part in which. the band gap energy of the part of an active layer is larger than that of other parts of the active layer in an optical waveguide is provided and a high-resistance region is formed between the upper part of the window structure part in a current blocking layer and a laminated structure. SOLUTION: Window structure parts (zinc diffusion regions) 31 are formed in both end parts of an optical waveguide, and a high-resistance region 32 is formed between parts which are situated on the window structure parts 31 in a current blocking layer 23 and a laminated structure 22. The window structure parts 31 are formed by diffusing impurities such as zinc or the like. Thereby, the band gap energy of the part of an active layer 25 in the window structure parts 31 is made larger than the band gap energy of other parts (parts in which zinc is not diffused) of the active layer 25 in the optical waveguide. As a result, it is possible to effectively suppress a leakage current flowing into the window structure parts 31 via the current blocking layer 23.

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 semiconductor laser having a so-called edge window structure, which reduces leakage current caused by the edge window structure.

[0002]

2. Description of the Related Art In recent years, in optical disk devices and the like, both reading and storage of signals are performed by using a semiconductor laser, so that a demand for higher output of the semiconductor laser is increasing. Therefore, in a conventional semiconductor laser, a so-called “end face window structure” is adopted as one of approaches for increasing the output.

[0003] This end face window structure is such that an impurity such as zinc (Zn) is diffused into the end face of an optical waveguide constituting a semiconductor laser and the band gap energy of the end face is increased, so that the end face of the optical waveguide is formed. Is to suppress the light absorption. With this end face window structure, it is possible to increase the output of the semiconductor laser while effectively suppressing the deterioration of the light emitting end face of the semiconductor laser.

FIG. 12A is a perspective view showing the structure of a conventional semiconductor laser having an end face window structure. FIG.
FIG. 12B is a sectional view taken along the line AA in FIG.
FIG. 13 is a sectional view taken along the line BB in FIG.

Referring to these drawings, the structure of a conventional semiconductor laser LD will be described.
Is provided on the n-GaAs substrate 1 and is a so-called MQW
Has a laminated structure 200 in which an active layer 3 is sandwiched between an n-AlGaInP lower cladding layer (first lower cladding layer) 2 and a p-AlGaInP upper cladding layer (second upper cladding layer) 4. doing.

Here, the upper cladding layer 4 is formed on the entire surface of the active layer 3 by p-Al having a thickness of about 0.2 μm.
GaInP first upper cladding layer 4a and a thickness of about 1.25 formed on a predetermined band-shaped region of the first upper cladding layer 4a.
a second p-AlGaInP second upper cladding layer 4b having a thickness of about 0.1 μm, and a p-GaInP band discontinuous relaxation layer 7 having a thickness of about 0.1 μm is formed on the upper surface of the second upper cladding layer 4b. ing. The thickness of the lower cladding layer 2 is about 1.5 μm. The surface of the first upper cladding layer 4a has a thickness of 60 .ANG.
A -GaInP etching stopper layer 5 is formed.

On both sides of the second upper cladding layer 4b on the etching stopper layer 5, the driving current is blocked so that the driving current concentrates on a predetermined band-shaped region constituting the optical waveguide in the laminated structure 200. An n-GaAs current blocking layer 8 is formed, and the second upper cladding layer 4b in the laminated structure 200 and the cladding 4b of the first upper cladding layer 4a, the active layer 3 and the lower cladding layer 2 thereunder are formed. The optical waveguide is constituted by the portions corresponding to the above.

In the laminated structure 200, the bandgap energy of the active layer portion formed by diffusing Zn at both ends of the optical waveguide is larger than the bandgap energy of the other active layer portion of the optical waveguide. The current blocking layer 8 has a structure in which a part thereof is located on the diffusion region 10 at both ends of the optical waveguide.

A p-GaAs contact layer 9 is formed on the entire surface of the band discontinuity relaxation layer 7 and the current block layer 8.
A p-electrode (front electrode) 9 a is formed on the contact layer 9, and an n-electrode (back electrode) 1 a is formed on the back side of the substrate 1.

The Zn diffusion region 10 is a so-called window region, and the semiconductor laser having such a window region is generally called a semiconductor laser having an end face window structure.

In the semiconductor laser LD having such a configuration,
When a drive voltage is applied to each of the electrodes 9a and 1a, a main current Im flows in the laminated structure 200, whereby laser light L is generated in the active layer 3 and emitted from the light emitting end face of the optical waveguide.

At this time, a Zn diffusion region 10 is formed at the end face portion of the optical waveguide, and the band gap energy of the active layer at this portion is larger than at other portions. Laser light is hardly absorbed, and laser oscillation at high output can be performed satisfactorily.

Next, a method of manufacturing the semiconductor laser LD will be described. FIGS. 13A to 13E are diagrams showing a method of manufacturing a semiconductor laser LD in the order of main steps. The semiconductor laser LD can be manufactured as follows.

First, on an n-GaAs substrate 1, n-A
1GaInP lower cladding layer 2, active layer 3, p-AlGa
The InP first upper cladding layer 4a, the p-GaInP etching stopper layer 5, the p-AlGaInP second upper cladding layer 4b, and the p-GaInP band discontinuous relaxation layer 7 are sequentially crystal-grown (see FIG. 13A). At this time, the above n
-The AlGaInP lower cladding layer 2 is about 1.5 μm thick,
The p-AlGaInP first upper cladding layer 4a has a thickness of about 0.2 μm.
The p-AlGaInP second upper cladding layer 4b is formed to have a thickness of about 1.25 μm, and the p-GaInP band discontinuous relaxation layer 7 is formed to have a thickness of about 0.1 μm. Note that this crystal growth includes metal organic chemical vapor deposition (MOCV).
D) or molecular beam epitaxy (MBE).

Subsequently, after a SiN film 11 having a thickness of about 500 Å is formed on the entire surface, the portions of the SiN film 11 that are to be both ends of the optical waveguide are formed with a width W1 of several tens μm.
m by patterning so that the opening 11
a is formed (see FIG. 13B). Then, a ZnO film serving as a diffusion source and a SiO ₂ film (not shown) serving as a cap layer are each formed to a thickness of 1000 Å by the S
By forming a film on the iN film 11 and then performing a heat treatment, zinc (Zn) is selectively diffused into a portion of the SiN film 11 exposed in the opening 11a. Thus, a Zn diffusion region 10 is formed (see FIG. 13C). afterwards,
The ZnO film and the SiO ₂ film are removed.

Further, by patterning the SiN film 11, a portion 11b having a stripe pattern with a width of about 3 μm is formed along a direction connecting both Zn diffusion regions 10. At this time, since there is no SiN film on the Zn diffusion region 10, the portion to be the optical waveguide in this portion is covered with the resist 12 (see FIG. 13D).

Then, the band discontinuous relaxation layer 7 and the second upper cladding layer 4b are selectively etched by the wet etching method using the resist 12 and the SiN film 11b as a mask, thereby forming an optical waveguide in the laminated structure 200. Is formed. The etching depth at the time of this selective etching is controlled by stopping the etching by the etching stopper layer 5.

Next, after removing the resist 12, Si
The n-GaAs current block layer 8 is buried and grown using the N film 11b as a selective growth mask (see FIG. 13E).

Next, the SiN film 11b is removed and p-Ga
Crystal growth is performed on the entire surface of the As contact layer 9 (FIG. 12A).
Finally, p-GaAs contact layer 9 has p-
An ohmic electrode 9a is formed, and an n-ohmic electrode 1a is formed on the back surface of the n-GaAs substrate 1, thereby completing the semiconductor laser LD.

[0020]

By the way, in the semiconductor laser LD having such an end face window structure, the semiconductor laser L
The zinc diffusion region 10 as a window structure of the light emission end face of D
Since it is a high-concentration p-type region having a carrier concentration of about 10 ¹⁸ to 10 ¹⁹ cm ⁻³ , the resistance is lower than that of other regions where diffusion is not performed. Therefore, there is a problem that a leak current easily flows in the zinc diffusion region 10.

In addition, the zinc diffusion region 10 is made of n-GaAs
When reaching the substrate 1, the pn junction is formed in the GaInP or AlGaInP region in the region where Zn is not diffused, whereas the zinc diffusion region 1
At 0, a pn junction is formed in the GaAs region. Ga
The pn junction in the As region is made of GaInP or AlGaI.
Since the band gap energy is smaller than that of the pn junction in the nP region, the leak current flows more easily in the zinc diffusion region (window structure) 10.

Here, the leakage current is shown in FIG.
As shown in (1), the following three are mainly considered.

The first leak current is generated when the current blocking effect of the current blocking layer 8 is not sufficient.
Is the leak current Ir1 flowing into the zinc diffusion region 10 via

The second leak current is a leak current Ir2 flowing directly from the p-GaAs contact layer 9 to the zinc diffusion region 10.

The third leak current flows from the p-GaAs contact layer 9 to the p-AlGaInP second upper cladding layer 4b.
Leakage current Ir3 flowing into the zinc diffusion region 10 through

When these leakage currents occur, various problems occur, such as an increase in the threshold value of the semiconductor laser LD and an increase in power consumption for generating a desired optical output.

The present invention has been made under such a background, and has as its object to provide a semiconductor laser capable of suppressing a leak current flowing into a zinc diffusion region constituting a window structure.

[0028]

A semiconductor laser according to the present invention (Claim 1) has a semiconductor substrate of a first conductivity type, and an active layer provided on the semiconductor substrate and having an active layer of a first conductivity type and a lower cladding layer. A laminated structure sandwiched between a two-conductivity-type upper cladding layer, a front electrode disposed on the front surface side of the laminated structure, a back electrode disposed on the back surface side of the semiconductor substrate, A first conductivity type current blocking layer formed between the first electrode and the surface electrode to block the driving current so that the driving current is concentrated on a predetermined band-shaped region constituting the optical waveguide in the laminated structure. A window structure formed at both ends of the optical waveguide by diffusion of impurities, wherein the bandgap energy of the active layer portion is larger than the bandgap energies of the other active layer portions of the optical waveguide; Layer, a portion located on the window structure, between the above lamination structure, and is characterized in that the high-resistance region is provided.

According to a second aspect of the present invention, there is provided a semiconductor laser comprising: a first conductivity type semiconductor substrate; and a first conductivity type lower cladding layer and a second conductivity type upper cladding layer provided on the semiconductor substrate. Between the laminated structure and the surface electrode disposed on the front side of the laminated structure, the back electrode disposed on the back side of the semiconductor substrate, and between the laminated structure and the surface electrode A first conductivity type current blocking layer formed to block the driving current so that the driving current is concentrated on a predetermined band-shaped region constituting the optical waveguide in the laminated structure; and the laminated structure has both ends of the optical waveguide. A window structure portion formed by diffusion of an impurity in the portion, the band gap energy of the active layer portion being larger than the band gap energy of the other active layer portion of the optical waveguide; The portion located on the portion, the lower region made of a semiconductor material that does not absorb the laser light oscillated in the active layer, and an upper region having a smaller band gap energy than the lower region disposed on the lower region Characterized by a two-layer structure consisting of:

The semiconductor laser according to the present invention (claim 3) is the semiconductor laser according to claim 2, wherein the portion of the current blocking layer located on the window structure completely covers the upper surface of the window structure. The planar shape is made larger than the planar shape of the upper surface of the window structure so as to cover the window structure.

According to a fourth aspect of the present invention, there is provided a semiconductor laser comprising: a first conductivity type semiconductor substrate; and a first conductivity type lower cladding layer and a second conductivity type upper cladding layer provided on the semiconductor substrate. , A second conductivity type contact layer formed on the laminated structure, a surface electrode disposed on the contact layer, and a rear surface side of the semiconductor substrate. A first conductivity type current blocking layer formed between the back electrode and the laminated structure and the front surface electrode, and blocking the driving current such that the driving current is concentrated on a predetermined band-shaped region constituting the optical waveguide in the laminated structure; Wherein the laminated structure is formed by diffusing impurities at both ends of the optical waveguide, and the band gap energy of the active layer portion is larger than the band gap energy of the other active layer portions of the optical waveguide. It has a window structure, the contact layer, the planar shape, is characterized in that is obtained by a shape that is not in contact with the window structure which is positioned on the optical waveguide ends.

According to a fifth aspect of the present invention, there is provided a semiconductor laser comprising: a first conductivity type semiconductor substrate; and an active layer provided on the first conductivity type semiconductor substrate, the first conductivity type lower cladding layer and the second conductivity type upper cladding layer. Between the laminated structure and the surface electrode disposed on the front side of the laminated structure, the back electrode disposed on the back side of the semiconductor substrate, and between the laminated structure and the surface electrode A first conductivity type current blocking layer formed to block the driving current so that the driving current is concentrated on a predetermined band-shaped region constituting the optical waveguide in the laminated structure; and the laminated structure has both ends of the optical waveguide. A window structure portion formed by diffusion of impurities in the portion, the band gap energy of the active layer portion being larger than the band gap energy of the other active layer portion of the optical waveguide, and the window structure of the optical waveguide; Located adjacent to the inside,
A current limiting layer comprising a first conductivity type region or a high resistance region, wherein the current blocking layer partially covers the surface of the window structure or the surface of the window structure and the current limiting region; It is characterized by having become.

[0033]

Embodiments of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a view for explaining a semiconductor laser according to a first embodiment of the present invention. FIG. 1A is a perspective view showing the structure of the semiconductor laser, and FIGS. 1B and 1C.
1A is a sectional view taken along the line AA in FIG. 1A, and FIG. FIG. 2 is a diagram showing a method of manufacturing the semiconductor laser LD in the order of its main steps (FIGS. 1A to 1F).

In the figure, LD1 is the semiconductor laser of the first embodiment, and its n-GaAs substrate 21 has
A so-called MQW active layer 25 is formed of an n-AlGaInP lower clad layer (first conductive type lower clad layer) 28 and a p-Al
GaInP upper cladding layer (second conductivity type upper cladding layer) 2
7a is provided.

Here, the upper cladding layer 27a has a thickness of about 0.2 μm and is formed on the entire surface of the active layer 25.
An AlGaInP first upper cladding layer 26 and a p-AlGaInP second upper cladding layer 2 having a thickness of about 1.25 μm formed on a predetermined band-shaped region of the first upper cladding layer 26;
The p-GaInP band discontinuous relaxation layer 30 having a thickness of about 0.1 μm is formed on the surface of the second upper cladding layer 27. The thickness of the lower cladding layer 28 is about 1.5 μm. On the surface of the first upper cladding layer 26, a p-GaInP etching stopper layer 29 having a thickness of 60 Å is formed.

On the etching stopper layer 29, on both sides of the second upper cladding layer 27, the driving current is blocked so that the driving current is concentrated on a predetermined band-like region constituting the optical waveguide in the laminated structure 22. An n-GaAs current blocking layer 23 is formed, and the second upper cladding layer 27 in the laminated structure 22 and the etching stopper layer 29, the first upper cladding layer 26, and the active layer 25 thereunder are formed.
The lower waveguide 28 and the portion corresponding to the second upper cladding layer 27 constitute the optical waveguide.

In the laminated structure 22, the band gap energy of the active layer portion formed by the diffusion of Zn at both ends of the optical waveguide is larger than the band gap energy of the other active layer portion of the optical waveguide. The current blocking layer 23 has a structure in which a part thereof is located on the diffusion regions 31 at both ends of the optical waveguide.

A p-GaAs contact layer 24 is formed on the entire surface of the band discontinuous relaxation layer 30 and the current blocking layer 23, and a p-electrode (surface electrode) 24a is formed on the contact layer 24. On the back side of the substrate 21, an n-electrode (back side electrode) 21a is formed.

The first embodiment is characterized in that a window structure (Zn diffusion region) 31 is formed at both ends of the optical waveguide as shown in FIG. A high-resistance region 32 is provided between a portion of the block layer 23 located on the window structure 31 and the laminated structure 22. The window structure 31 is formed by diffusion of an impurity such as zinc (Zn), so that the band gap energy of the active layer 25 in the window structure 31 is reduced by the other active layer 25 of the optical waveguide. It is larger than the band gap energy of the portion (the portion where zinc is not diffused).

Next, referring to FIG.
A method of manufacturing the device will be described. First, the process flows shown in FIGS. 2A to 2C are exactly the same as those of the conventional semiconductor laser. That is, first, n-Ga
About 1.5 μm thick n-AlGaInP on As substrate 21
Lower cladding layer (carrier concentration: 4 × 10 ¹⁷ cm ⁻³ ) 28,
Active layer 25, p-AlGaInP first about 0.2 μm thick
Upper cladding layer (carrier concentration: 4 × 10 ¹⁷ cm ⁻³ ) 26;
A 60 Å thick p-GaInP etching stopper layer (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) 29, a p-AlGaInP second upper cladding layer (carrier concentration 7 × 10 ¹⁷ cm ⁻³ ) about 1.25 μm thick 27 About 0.1μm
Crystal growth of a thick p-GaInP band discontinuous relaxation layer (carrier concentration: 1 × 10 ¹⁸ cm ⁻³ ) 30 is sequentially performed (FIG. 2).
(a)). For this crystal growth, metal organic chemical vapor deposition (MOC)
VD) or molecular beam epitaxy (MBE).

Subsequently, S having a thickness of about 500 Å
After the iN film 33 is formed, a portion 34 (hereinafter, referred to as an “end face portion 34”) corresponding to the end face of the semiconductor laser LD 1 is formed.
Notch 3 is formed by patterning with width W1 of about several tens of μm.
5 is formed (FIG. 2 (b)).

Next, a ZnO film serving as a diffusion source and a SiO ₂ film serving as a cap layer are formed on the SiN film 33 to a thickness of about 1000 angstroms, respectively. selectively diffusing zinc (Zn) in a portion which is exposed to, then, ZnO film, SiO ₂
The film is removed (FIG. 2 (c)). Thus, the window structure 31 is formed as a zinc diffusion region.

In this embodiment, after the zinc diffusion region 31 is formed, the notch 35 of the SiN film 33 is widened so that the diffusion front of the zinc diffusion region 31 can be seen from the front side (FIG. 2D). . Subsequently, ions of protons (H) and the like are implanted using the SiN film 33 as a mask,
The high resistance region 32 is formed. The ion species used for this ion implantation is proton (H) as long as it has high resistance.
However, the invention is not limited thereto, and silicon (Si) or the like may be used. Note that the depth of the high resistance region formed by ion implantation is usually 0.5
It is about μm. In FIG. 2D, the high resistance region 32
To the zinc diffusion region 31 and its vicinity, that is, the end face portion 34
The high resistance region 32 may be formed over the entire region of the end face portion 34.

Next, as in the conventional semiconductor laser, a mask having a band-like pattern having a width of about 3 μm is formed in order to form an optical waveguide. At this time, the high resistance region 3 by ion implantation
Since there is no SiN film 33 on 2, a resist 36 is formed on this portion, and this is used as an etching mask (FIG. 2E). Then, after forming an optical waveguide by wet etching using the resist 36 and the SiN film 33 as a mask, the resist 36 is removed, and the SiN film 33 is removed.
Is used as a selective growth mask to bury and grow the n-GaAs current block layer 23 (FIG. 2 (f)). The control of the etching depth at the time of the formation of the optical waveguide is performed by stopping the etching process by the etching stopper layer 29 as in the related art.

Thereafter, the SiN film 33 is removed and p-Ga
The As contact layer 24 is crystal-grown (FIG. 1A), and finally, the surface of the n-GaAs substrate 21 and the p-GaAs
The ohmic electrodes 21a and 2a are formed on the surface of the contact layer 24.
4a is formed to complete the semiconductor laser LD1.

Next, the operation and effect of this embodiment will be described with reference to FIG. In the first embodiment, since the high resistance region 32 by ion implantation is inserted between the zinc diffusion region 31 of the end face portion 34 and the current block layer 23, zinc (Zn) diffusion is performed through the current block layer 23. Leakage current Ir1 (see FIG. 12 (c)) flowing into region 31 can be effectively suppressed.

In this embodiment, the high resistance region 32
Are formed in a size larger than that of the zinc diffusion region 31, so that the high-concentration p-type zinc diffusion region 31 does not come into direct contact with the p-GaAs contact layer 24, and the p-Ga
Leakage current Ir2 (see FIG. 12 (c)) flowing directly from the As contact layer 24 to the zinc (Zn) diffusion region 31 can be effectively suppressed.

Further, in this embodiment, the p-GaInP band discontinuous relaxation layer 30 and the p-A
Since a part of the lGaInP second upper cladding layer 27 has a higher resistance, the p-GaAs contact layer 24
The width of the leak current path reaching the zinc diffusion region 31 through the GaInP second upper cladding layer 27 is reduced, and the leak current Ir3 flowing through this current path can be reduced.

Embodiment 2 Next, a second embodiment of the present invention will be described. FIG. 3 is a diagram for explaining a semiconductor laser according to a second embodiment of the present invention.
3A is a perspective view showing the structure of the semiconductor laser LD2, and FIGS. 3B and 3C are AA sectional view and BB sectional view in FIG. 3A, respectively. FIG. 4 shows this semiconductor laser L
It is a figure for explaining a manufacturing method of D2 in order of a main process (Drawing (a)-(f)).

In the figure, LD2 is the semiconductor laser of the second embodiment, and the same reference numerals as those of FIG. 1 indicate the same as those of the semiconductor laser LD1 of the first embodiment. In the second embodiment, as shown in FIG. 3C, window structure portions 31 are formed at both ends of the optical waveguide, and the current block layer 23 is located on the window structure portion 31. Are a lower region 40 made of a semiconductor material that does not absorb the laser light oscillated by the active layer 25;
The second embodiment is different from the first embodiment in that it has a two-layer structure including an upper region 41 which is disposed above the lower region 0 and has a lower band gap energy than the lower region 40.

Specifically, the current blocking layer 23 is formed of n-
A lower layer region 40 made of AlGaInP and n-GaAs
And an upper layer region 41 composed of The window structure portion 31 is formed by diffusion of zinc, whereby the band gap energy of the active layer 25 portion in the window structure portion 31 is changed to the other active layer 25 portion of the optical waveguide (zinc is diffused). Is larger than the bandgap energy of the portion (not present).

Next, referring to FIG.
2 will be described. First, FIGS. 4 (a) to 4 (c)
Is exactly the same as the process flow shown in the first embodiment. That is, first, n
-Lower cladding layer 28 and active layer 2 on GaAs substrate 21
5, first upper cladding layer 26, etching stopper layer 2
9, second upper cladding layer 27, and band discontinuous relaxation layer 3
0 is sequentially grown (FIG. 4 (a)), and then a SiN film 33 having a notch 35 at the end face 34 is formed (FIG. 4 (b)).
). Thereafter, zinc (Zn) is selectively diffused into the semiconductor region exposed in the notch 35 using a ZnO film serving as a diffusion source and a SiO ₂ film serving as a cap layer formed on the SiN film 33. . Thereby, the window structure 31 is formed as a zinc diffusion region.

The semiconductor laser L according to the present embodiment
In the manufacturing method of D2, after forming the zinc diffusion region 31,
The SiN film 33 on the end face 34 is removed by etching. At this time, the region to be removed by etching is sufficiently large so that the diffusion front of the zinc diffusion region 31 can be seen from the crystal surface side.

Next, using this SiN film 33 as a mask,
p-GaInP band discontinuous relaxation layer 30, p-AlGa
After the InP second upper cladding layer 27 is removed by etching,
n-AlGaInP current blocking layer 40, n-GaAs
The current block layer 41 is buried and grown (FIG. 4D).

The Al composition ratio of the n-AlGaInP current block layer 40 is determined as follows:
For example, the Al composition ratio of the cladding layers 26, 27, and 28 is set to be substantially equal. The control of the etching depth is performed by stopping the etching with the etching stopper layer 29.

Next, similarly to the conventional semiconductor laser, in order to form an optical waveguide, a resist film 36 having a band-like pattern of about 3 μm width is formed on the SiN film 33 by n-AlGaI.
4 is formed so as to extend over the region in which the nP current block layer 40 and the n-GaAs current block layer 41 are embedded.
(e)). Next, an optical waveguide is formed by wet etching using the resist film 36 as a mask, the resist 36 is removed thereafter, and the n-GaAs current block layer 41 is buried and grown using the SiN film 33 as a selective growth mask ( FIG. 4 (f)).

Then, the SiN film 33 is removed and p-Ga
The As contact layer 24 is crystal-grown (FIG. 3A). Finally, the back surface of the n-GaAs substrate 21 and the p-GaAs
An ohmic electrode is formed on the surface of the contact layer 24 to complete the semiconductor laser LD2.

Next, the operation and effect of this embodiment will be described with reference to FIG. In the second embodiment, the current blocking layer 23 in the end face portion 34 is formed of n-AlGaI
It has a structure in which an nP current block layer 40 and an n-GaAs current block layer 41 are laminated, and the thickness thereof is 2 μm.
Since it is formed thicker before and after, the leak current Ir1 (see FIG. 12C) flowing into the zinc diffusion region 31 via the current blocking layer 23 can be effectively suppressed.

Here, the current block layer 23 on the end face 34 is
Is made up of AlGaInP / Ga without using only GaAs.
The reason for adopting the two-layer structure of As will be described. Assuming that the end face 3
In the case where the current block layer 23 of No. 4 is composed of only GaAs, GaAs is buried to a position of about 0.2 μm from the active layer, so that the effect of reducing the leak current is great. Therefore, the loss (loss) increases near the end face, and the laser characteristics deteriorate. On the other hand, the GaAs current blocking layer and the active layer 25
If the distance is increased, the increase in loss can be suppressed, but the effect of reducing the leak current is reduced.

In the second embodiment, the portion of the current blocking layer 23 located on the window structure 31 and adjacent to the active layer 25 is made of AlGaInP having an Al composition ratio that does not absorb light having an oscillation wavelength. The current blocking layer 2
Even if 3 is closer to a distance of about 0.2 μm from the active layer, absorption of light having an oscillation wavelength does not occur, and laser characteristics do not deteriorate.

In this embodiment, since the planar shapes of the current blocking layers 40 and 41 are larger than the planar shape of the zinc diffusion region 31, the high-concentration Zn diffusion region 31
The leak current Ir2 flowing directly from the p-GaAs contact layer 24 into the zinc (Zn) diffusion region 31 (FIG. 12 (c)).
Reference) can be effectively suppressed.

Further, in the present embodiment, p-GaAs
Since the minimum width of the current path from the contact layer 24 to the zinc diffusion region 31 through the p-AlGaInP upper cladding layer 27 is extremely narrow, about 0.2 μm, which is the layer thickness of the p-AlGaInP first upper cladding layer 26. The leakage current Ir3 flowing through this path can be extremely reduced.

Embodiment 3 FIG. 5 is a diagram for explaining a semiconductor laser LD3 according to Embodiment 3 of the present invention, and FIG. 5A is a perspective view showing the structure of the semiconductor laser LD, and FIGS. (c) is an AA sectional view and BB sectional view in FIG. 5 (a), respectively. FIG. 6 is a view for explaining this semiconductor laser manufacturing method in the order of main steps (FIGS. (A) to (f)).

In the figure, LD3 is the semiconductor laser of the third embodiment, and the same reference numerals as those of FIG. 1 denote the same components as those of the semiconductor laser LD1 of the first embodiment.

The feature of the third embodiment is that, as shown in FIG. 5C, window structures 31 are formed at both ends of the optical waveguide, and the contact layer 24c is
The planar shape is formed so as not to come into contact with the window structures 31 located at both ends of the optical waveguide. In the third embodiment, the current blocking layers 23 are not formed on both ends of the optical waveguide.

Next, a method of manufacturing a semiconductor laser will be described with reference to FIG. As shown in FIGS. 6A to 6C, after performing the same processes as those shown in FIGS. 2A to 2C in the method of manufacturing the semiconductor laser according to the first embodiment,
As shown in FIG. 6D, the SiN film 33 is patterned to form a strip-shaped mask having a width of about 3 μm. Also in this case, since there is no SiN film on the zinc diffusion region 31, a resist 36 is formed in this portion, and this is used as a mask.

Thereafter, FIG. 2 (f) of the first embodiment is used.
And a process similar to the process shown in FIG.
The formation of the aAs current blocking layer 23 (FIG. 6 (e)) and the formation of the contact layer 24 (FIG. 6 (f)) are performed.

In the third embodiment, p-GaAs
After the crystal growth of the contact layer 24, the contact layer 24
Is patterned so that it does not overlap with the zinc diffusion region 31, and the p-GaAs current block layer 23 on the end face 34 is removed by etching (see FIG. 5A). At this time, the area to be removed by etching is sufficiently large so that the diffusion front of the zinc diffusion region 31 can be seen from the crystal surface side, and the etching depth is set until the p-GaInP band discontinuous relaxation layer 30 is completely exposed. . Finally, p-Ga
The p-side ohmic electrode 50 is
-An n-side ohmic electrode 21a is formed on the GaAs substrate 21 to complete the semiconductor laser LD3.

Next, the operation and effect of this embodiment will be described with reference to FIG. In the third embodiment, the p-GaAs contact layer 24c and the n-Ga
The As current blocking layer 23 is completely removed, and the n-GaAs current blocking layer 23 is also p-type on the zinc diffusion region 31.
Since there is no GaAs contact layer 24c, p-G
The leak current Ir1 flowing from the aAs contact layer 24c to the zinc diffusion region 31 via the current block layer 23 can be eliminated.

Since the p-GaAs contact layer 24c is not in direct contact with the zinc diffusion region 31, the p-GaAs contact layer 24c is not directly in contact with the p-GaAs contact layer 24c.
The leak current Ir2 flowing directly from the s-contact layer 24c to the zinc diffusion region 31 can be eliminated.

Further, the p-GaAs contact layer 24c
Is formed only as far as possible from the zinc diffusion region 31 inside the chip, so that the p-GaAs contact layer 24 is formed.
Since the leak path from c to the zinc diffusion region 31 through the p-AlGaInP upper cladding layer 27 becomes longer, the leak current Ir3 flowing through this leak path can be reduced.

Embodiment 4 FIG. 7 is a diagram for explaining a semiconductor laser according to a fourth embodiment of the present invention. FIG. 7 (a) is a perspective view showing the structure of a semiconductor laser LD4, and FIG. It is AA sectional drawing in 7 (a). 8 (a) to 8 (c), FIGS. 9 (a) to 9 (c), FIG.
(a), (b) is a figure for demonstrating this semiconductor laser manufacturing method in a main process order.

In the figure, LD4 is the semiconductor laser of the fourth embodiment, and the same reference numerals as those of FIG. 1 indicate the same as those of the semiconductor laser LD1 of the first embodiment. In the fourth embodiment, as shown in FIG. 7B, the laminated structure 22 has window structures 31 formed at both ends of the optical waveguide. ,
An n-GaAs current limiting region 60 is formed adjacent to this, and the current blocking layer 23 has a structure in which a part thereof covers the upper surface of the window structure 31. In the fourth embodiment, the n-GaAs buffer layer 61 is formed between the lower cladding layer 28 and the substrate 21. Other configurations are the same as those of the first embodiment.

Next, a method of manufacturing the semiconductor laser LD4 will be described with reference to FIGS. First, n-G
a- (n) having a thickness of about 0.5 μm
GaAs buffer layer (carrier concentration 1 × 10 ¹⁸ cm ⁻³ )
61, an n-AlGaInP lower cladding layer (carrier concentration: 4 × 10 ¹⁷ cm ⁻³ ) 28 of about 1.5 μm thickness, so-called M
QW active layer 25, about 0.2 μm thick p-AlGaIn
P first upper cladding layer (carrier concentration 4 × 10 ¹⁷ cm ⁻³ )
26, a p-GaInP etching stopper layer (ESL) having a thickness of about 60 angstroms (carrier concentration 1 × 10 ¹⁸
cm ^-3 ) 29, about 1.25 μm thick p-AlGaInP
Second upper cladding layer (carrier concentration: 7 × 10 ¹⁷ cm ⁻³ ) 2
7, p-GaInP band discontinuous relaxation layer (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) of about 0.1 μm thickness 30, about 0.4 μm
m-thick p-GaAs layer (carrier concentration 5 × 10 ¹⁸ c
m ⁻³ ) 62 are sequentially grown by MOCVD (FIG. 8A).

Next, after forming the SiN film 33 by thermal CVD, the SiN film 3 is formed by photolithography as shown in FIG.
Drill a hole 63 in 3. FIG. 8 (c) is a sectional view taken along the line AA in FIG. 8 (b). As shown in FIG.
After removing the p-GaAs layer 62 exposed in 3, Si is diffused into the region of the hole 63 by ion implantation (or diffusion) to form an n-type current limiting region 60. At this time, the diffusion of the impurity is caused by the fact that the current limiting region 60 is
9 is performed so as to reach the vicinity.

Next, using the photomechanical technique once again, as shown in FIG.
A hole 64 is made in the SiN film 33 along the / 110> direction. That is, after removing the SiN film 33 shown in FIG. 8B and forming the SiN film 33a again by thermal CVD, a hole 64 is made in the SiN film 33a. This time, Zn is diffused in the region where the hole 64 is formed (FIG. 9B). In the figure, the Zn diffusion front is the n-GaAs buffer layer 6.
1, but may reach the n-AlGaInP lower cladding 28 or the n-GaAs substrate 21.

FIG. 9C is a sectional view taken along the line AA in FIG. 9B. The portion of the active layer 25 where Zn is diffused is disordered, and becomes a region that does not absorb the light having a wavelength of 650 nm emitted from the portion of the active layer 25 where Zn is not diffused. The Zn diffusion layer (window structure) 31 and the above-described current limiting region 60
Are arranged adjacent to each other as shown in FIG.

Next, using photolithography technology, FIG.
The patterning of the resist film is performed as shown in FIG.
A strip-shaped resist 65 having a width of 3 μm along the 0> direction is formed. Then, using the resist film 65 as a mask, the S
The iN film 33a is selectively etched using HF (hydrofluoric acid). As a result, a region not covered with the resist 65 is removed. Further, using the resist 65 as an etching mask, the p-GaAs layer 62, the p-GaInP band discontinuous relaxation layer 30, and the p-AlGaInP second upper cladding layer 27 are removed. This etching process stops at the etching stopper layer 29.

After removing the resist film 65,
This time, the n-GaAs current blocking layer (carrier concentration of 4) is formed using the stripe-shaped SiN film 33a as a selective growth mask.
(× 10 ¹⁸ cm ⁻³ , layer thickness 1 μm) 23 is grown (FIG. 1).
0 (b)). This n-GaAs current blocking layer 23
It is grown so as to cover the upper part of the n-diffusion layer 31 and then S
The iN film 33a is removed (FIG. 10B). And p-
GaAs contact layer (carrier concentration 1 × 10 ¹⁹ c
(m ⁻³ , layer thickness 1 μm) 24 (see FIG. 7A), and ohmic electrodes 24 a, 21 a are formed on the front side of the contact layer 24 and the back side of the substrate 21.
D4 is completed (see FIG. 7B).

Next, the operation principle of the semiconductor laser LD4 manufactured by the above process will be described. The flow of current when a forward bias is applied to the semiconductor laser LD4 will be described with reference to FIG. The above semiconductor laser LD4
In this case, the semiconductor region forming the current path 66 has a pnpn thyristor structure, and the amount of current flowing through the path 66 is small. For the same reason, the current amounts of the current paths 67 and 68 are small. Further, since the semiconductor region forming the current path 69 has a pn junction structure, it is considered that the current amount is large in the current path 69. However, the sheet resistance of the p-AlGaInP first upper cladding layer 26 is Since it is about two to three orders of magnitude higher than those in other regions, the current amount is suppressed as in other current paths. Thus, the leakage current flowing through the window structure 31 for Zn diffusion is suppressed.

In the fourth embodiment, the current limiting region is constituted by the n-type semiconductor layer. However, the current limiting region 60 may be constituted by the i-type high resistance region. In order to substantially reduce the leakage current, the current limiting region 60 is completely covered by the current blocking layer 23, and the current limiting region 60
The width in the 0> direction must be equal to or larger than a predetermined dimension.

In brief, if the current limiting region 60 is formed of an i-type high resistance region, the amount of current in the current paths 66 and 69 is reduced as described above, but the current paths 67 and 68 are formed. The semiconductor region to be formed has a pipn structure. In the current paths 67 and 68 of this structure, the amount of current is determined by the substantial thickness of the i-layer, that is, the thickness (L) of the current limiting region 60. In addition, an ohmic current flows at a low bias, and a space at a high bias. The limiting current will flow. Here, the amount of ohmic current is smaller than the amount of space-limited current, and the critical voltage V at which the mode of generation of leakage current switches from the mode of ohmic current to the mode of space-limited current is expressed by the following equation. It depends strongly on the thickness L of the current limiting region 60.

[0083]

(Equation 1)

In this embodiment, the operating voltage of the semiconductor laser LD4 is close to 3V. Therefore, in this case, at least the thickness of the current limiting region 60 needs to be about 5 μm in order to maintain the mode based on the ohmic current as the leak current generation mode. However, the thickness of the substantial current limiting region 60 in the current path 68 is 1
μm (thickness of p-AlGaInP second cladding layer 27)
Therefore, there is a possibility that the current amount of the current path 68 is increased as compared with the case where the current limiting region 60 is made of an n-type semiconductor.

As a countermeasure to avoid an increase in the amount of current in the current path 68, a structure in which the n-GaAs current block layer 23 covers the entire surface of the current limiting region 60 as shown in FIG. . That is, in this structure, the current path 70 is formed instead of the current path 68 as a path for the leakage current. Therefore, if the width of the current limiting region 60 in the </ 110> direction is set to 5 μm, the generation mode of the leakage current is changed. The mode can be maintained by the ohmic current, and the current path 7
0 current amount can be suppressed.

[0086]

According to the semiconductor laser of the present invention (claim 1), the portion of the current block layer located in the window structure portion and the laminated structure in which the active layer is sandwiched between the upper and lower cladding layers. In addition, since the high resistance region is provided, it is possible to effectively suppress the leak current flowing into the window structure portion via the current blocking layer, and as a result, the threshold value and the power consumption of the semiconductor laser can be reduced while being reduced. There is an effect that output can be achieved.

According to the semiconductor laser of the present invention (claim 2), the portion of the current block layer located on the window structure is made of a semiconductor material which does not absorb the laser light oscillated by the active layer. A lower layer region formed on the lower layer region and an upper layer region having a lower bandgap energy than the lower layer region, so that the impurity diffusion region serving as a window region is provided via the current blocking layer. The leakage current flowing into the semiconductor device can be extremely effectively suppressed, the distance between the current blocking layer and the active layer can be reduced, and the laser characteristics can be improved.

According to the present invention (claim 3), in the semiconductor laser according to claim 2, the portion of the current block layer located on the window structure completely covers the upper surface of the window structure. Therefore, the window structure does not come into direct contact with the contact layer, and the leakage current flowing directly from the contact layer into the window structure can be more effectively suppressed. As a result, the output of the semiconductor laser can be further increased. There is an effect that can be.

According to the semiconductor laser of the present invention (claim 4), since the contact layer has a planar shape such that the contact layer does not overlap with the window structure, the contact layer is directly connected to the window structure. It is possible to effectively suppress the leak current flowing in, and as a result, there is an effect that it is possible to increase the output while suppressing the threshold value and the power consumption of the semiconductor laser.

According to the semiconductor laser of the present invention (claim 5), a current limiting region comprising a first conductivity type region or a high resistance region is provided inside the window structure of the optical waveguide, and the first conductivity type current blocking layer is provided. Has a structure in which a part thereof covers the surface of the window structure, or the surface of the window structure and the current limiting region, so that the leakage current flowing into the window structure is suppressed by the current blocking layer and the current limiting region. As a result, there is an effect that it is possible to increase the output while suppressing the threshold value and the power consumption of the semiconductor laser.

[Brief description of the drawings]

FIGS. 1A and 1B are views showing a structure of a semiconductor laser according to a first embodiment of the present invention, wherein FIG. 1A is a perspective view, FIG. 1B is a cross-sectional view along AA, and FIG. is there.

FIG. 2 is a view for explaining a method of manufacturing the semiconductor laser according to the first embodiment of the present invention in the order of main steps (FIGS. 1A to 1F).

3 (a) is a perspective view, FIG. 3 (b) is a sectional view taken along line AA, and FIG. 3 (c) is a sectional view taken along line BB. is there.

FIG. 4 is a view for explaining a method of manufacturing a semiconductor laser according to the second embodiment of the present invention in the order of main steps (FIGS. (A) to (f)).

5 (a) is a perspective view, FIG. 5 (b) is a sectional view taken along line AA, and FIG. 5 (c) is a sectional view taken along line BB. is there.

FIG. 6 is a view for explaining a method of manufacturing a semiconductor laser according to the third embodiment of the present invention in the order of main steps (FIGS. (A) to (f)).

FIGS. 7A and 7B are views showing a structure of a semiconductor laser according to a fourth embodiment of the present invention, wherein FIG. 7A is a perspective view and FIG.

FIG. 8 is a view for explaining a method for manufacturing a semiconductor laser according to the fourth embodiment of the present invention in the order of main steps (FIGS. (A) to (c)).

FIG. 9 is a view for explaining a method of manufacturing a semiconductor laser according to a fourth embodiment of the present invention in the order of main steps (FIGS. (A) to (c)).

FIG. 10 is a view for explaining a method of manufacturing a semiconductor laser according to the fourth embodiment of the present invention in the order of main steps (FIGS. (A) and (b)).

FIG. 11 is a diagram showing a flow of a leak current of a semiconductor laser according to a fourth embodiment of the present invention.

12 (a) is a perspective view, FIG. 12 (b) is a sectional view taken along line AA, and FIG. 12 (c) is a sectional view taken along line BB.
It is sectional drawing.

FIG. 13 is a view for explaining a conventional method of manufacturing a semiconductor laser in the order of main steps (FIGS. (A) to (e)).

[Explanation of symbols]

Reference Signs List 21 semiconductor substrate, 22 semiconductor laminated structure, 23 current block layer, 24 contact layer, 25 active layer, 26
First upper cladding layer, 27 Second upper cladding layer, 28
Lower cladding layer, 31 Window structure, 32 High resistance region, Ir
1, Ir2, Ir3 leak current, 40 lower layer region, 41
Upper layer region, 60 current limiting region, 66 to 70 current path, LD1, LD2, LD3, LD4 semiconductor laser.

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Masatoshi Fujiwara 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation

Claims (5)

[Claims] A first conductive type semiconductor substrate, and a laminated structure provided on the semiconductor substrate and having an active layer sandwiched between a first conductive type lower clad layer and a second conductive type upper clad layer. A front electrode disposed on the front side of the laminated structure; a rear electrode disposed on the back side of the semiconductor substrate; and an optical waveguide formed between the laminated structure and the front electrode, forming an optical waveguide in the laminated structure. A first conductivity type current blocking layer that blocks the drive current so that the drive current is concentrated on the predetermined band-shaped region. The laminated structure is formed by diffusion of impurities at both end portions of the optical waveguide. A portion of the current blocking layer located on the window structure portion, wherein the active layer portion has a window structure in which the band gap energy is larger than the band gap energy of the other active layer portion of the optical waveguide; A high resistance region is provided between the semiconductor laser and the semiconductor laser. A first conductive type semiconductor substrate; and a laminated structure provided on the semiconductor substrate and having an active layer sandwiched between the first conductive type lower clad layer and the second conductive type upper clad layer. A front electrode disposed on the front side of the laminated structure; a rear electrode disposed on the back side of the semiconductor substrate; and an optical waveguide formed between the laminated structure and the front electrode, forming an optical waveguide in the laminated structure. A first conductivity type current blocking layer that blocks the drive current so that the drive current is concentrated on the predetermined band-shaped region. The laminated structure is formed by diffusion of impurities at both end portions of the optical waveguide. The active layer portion has a window structure in which the bandgap energy is larger than the bandgap energy of the other active layer portion of the optical waveguide. The portion of the current blocking layer located on the window structure portion has Departure It has a two-layer structure including a lower layer region made of a semiconductor material that does not absorb the vibrated laser light and an upper layer region disposed on the lower layer region and having a lower bandgap energy than the lower layer region. Semiconductor laser. 3. The semiconductor laser according to claim 2, wherein a portion of the current blocking layer located on the window structure has a planar shape such that the upper surface of the window structure is completely covered. A semiconductor laser which is larger than the planar shape of the upper surface of the part. 4. A first conductivity type semiconductor substrate, and a laminated structure provided on the semiconductor substrate and having an active layer sandwiched between a first conductivity type lower cladding layer and a second conductivity type upper cladding layer. A second conductivity type contact layer formed on the laminated structure, a front electrode disposed on the contact layer, a back electrode disposed on the back side of the semiconductor substrate, the laminated structure and the front electrode; And a first conductivity type current blocking layer that blocks the drive current so that the drive current concentrates on a predetermined band-shaped region forming the optical waveguide in the laminated structure. A window structure formed at both ends of the waveguide by diffusion of impurities, wherein the bandgap energy of the active layer portion is larger than the bandgap energy of the other active layer portion of the optical waveguide; A semiconductor laser, characterized in that the planar shape is obtained by a shape that is not in contact with the window structure which is positioned on the optical waveguide ends. 5. A first conductive type semiconductor substrate, and a laminated structure provided on the semiconductor substrate and having an active layer sandwiched between a first conductive type lower clad layer and a second conductive type upper clad layer. A front electrode disposed on the front side of the laminated structure; a rear electrode disposed on the back side of the semiconductor substrate; and an optical waveguide formed between the laminated structure and the front electrode, forming an optical waveguide in the laminated structure. A first conductivity type current blocking layer that blocks the drive current so that the drive current is concentrated on the predetermined band-shaped region. The laminated structure is formed by diffusion of impurities at both end portions of the optical waveguide. A window structure in which the band gap energy of the active layer portion is larger than the band gap energy of the other active layer portion of the optical waveguide;
A current-conducting region that is located adjacent to the inside of the window structure portion of the optical waveguide and that is formed of a first conductivity type region or a high-resistance region; A semiconductor laser having a structure that covers the surface of the substrate or the window structure and the surface of the current limiting region.