JPH098401A - Semiconductor laser with precisely defined active layer region width and method for fabricating semiconductor laser - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a method of manufacturing a semiconductor laser which has a high precision and reproducibility of an oscillation region and can simultaneously form a current confinement structure, and a semiconductor laser having a structure suitable for the manufacturing method. A thin layer 5 having a polarity different from that of the underlayer 3 is introduced by using the selective growth method to realize accurate definition of the active region width of the semiconductor laser, current confinement and light confinement. A semiconductor layer 6 having the same polarity as that of the underlayer 3 is continuously formed on the thin layer 5 and the exposed underlayer 3. The active layer 7 continuously formed on the semiconductor layer 6 is laminated so that the portion 11 corresponding to the current concentration region is laterally sandwiched by the thin layers 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength-stable semiconductor laser having a good yield and a manufacturing method thereof.

[0002]

2. Description of the Related Art Semiconductor lasers have been vigorously studied as a main component of optical communication. A typical example of this structure is BH (Buried Heterostrucc).
a) type laser. The BH laser structure is
It is a highly efficient laser structure with excellent current and light confinement. This will be described with reference to FIGS. 5, 6 and 7. FIG. 5 shows a conventional example, and is a structural diagram of a BH type semiconductor laser. FIGS. 6 and 7A, 7B, and 7C are process drawings. A manufacturing method will be described with reference to FIGS.

In FIG. 5, 101 is n-GaAs which is a substrate. On this, n-AIGaAs, which is the cladding layer shown by 102, is grown to a thickness of about 1.5 μm. Then, undoped Ga which is the active layer of 103
As is grown by 0.1 μm. Further, p-AlGaAs, which is the upper cladding layer of 104, is grown to about 2 μm, the entire laser is once grown, and the first growth is completed. This growth film is etched by liquid etching or dry etching in order to limit the laser oscillation region and to constrict the current, and the growth film is processed as shown in FIG. 7A. A mask represented by 110 such as SiO ₂ is formed on the upper clad layer 104 for etching. The width left by etching is 3
It is desirable that the thickness is less than μm, and etching is performed until the clad 102 is reached. In this example, the etching depth is about 2.3 μm. Thereafter, as shown in FIG. 7B, p-AIGaAs, which is the current block layer 105, is formed. Finally, 106 shown in FIG.
The laser fabrication is completed by forming the upper cladding layer of n-AlGaAs. Finally, SiO ₂ is removed. The BH laser manufactured as described above is provided with the current blocking layer 105.
Therefore, current confinement in the active region 103 is good, and light confinement due to regrowth of the upper clad layer 106 is also good, which is a relatively good characteristic.

However, this laser structure has the following problems in manufacturing. In FIG. 7A, a convex portion that is an oscillation region is formed by etching, but the width 109 of this bottom surface greatly changes depending on etching conditions. In both wet etching and dry etching, etching proceeds not only in the vertical direction but also in the horizontal direction. As a result, the etching shape changes in proportion to the progress of the etching in the vertical direction. In this example, mask 1
The width of 5.3 μm defined by 10 was gradually narrowed, and the width 109 of the bottom was considerably narrowed to 2 μm.

Further, if a convex portion is formed by etching in a plane orientation different from the above example by 90 degrees, a trapezoid with a wide hem can be formed. Thus, when the etching method is used, the width of the mask does not always become the width near the active layer. In other words, this means that the width of the active region 103 changes depending on the manufacturing conditions, so that control of the lateral mode during laser driving, instability of the threshold current, and the like are likely to occur, leading to a decrease in yield and the like. Particularly, uniform etching over a wide area is almost impossible because of the temperature distribution in the surface and the concentration distribution of the etching liquid.

The side etching amount is proportional to the etching depth from the surface, and if the etching depth is reduced, the lateral etching amount also decreases, and it is not necessary to consider the change in the etching width. However, when the laser light is to be confined in the vertical direction, it is preferable that the clad has a thickness of at least 1.5 μm, and making the thickness too thin adversely affects the laser characteristics. Therefore, the decrease or increase in the width of the convex portion due to the side etching becomes an essential problem that cannot be avoided in order to produce the BH type laser with good reproducibility.

In addition to the above, the lateral etching rate is not limited to the substrate temperature and the in-plane concentration distribution of the composition of the etching solution described above, but the film constitution of the film to be etched (Al composition here). Further, it also varies depending on the area ratio of the mask shown at 110 and the area ratio of the exposed etching film other than that. For these reasons, it is difficult to etch the active region to a thickness of 2 μm or more with good reproducibility, and a stable fabrication method is desired.

[0008]

[Problems to be Solved by the Invention] As described above,
Since the width of the convex portion formed by etching greatly changes depending on the film thickness to be etched, the etching conditions, the composition of the base film, etc., it is difficult to form the oscillation region with good reproducibility.

Therefore, an object of the present invention is to use a growth method which is remarkably good in controllability of in-plane distribution, deposition rate and the like without using etching. The present invention provides a method for producing a semiconductor laser capable of producing a current confinement structure and a semiconductor laser having a structure suitable for the production method.

[0010]

The semiconductor laser manufacturing method of the present invention for achieving the above object is a method for manufacturing a semiconductor laser in which an active layer is scissored with a layer having a bandgap larger than that of the active layer. Selectively forming a second semiconductor layer having the second conductivity type on the first semiconductor layer having the conductivity type while avoiding the current injection region of the laser, and the second conductivity type. Continuously forming and stacking a third semiconductor layer having a first conductivity type on the second semiconductor layer having the above and the exposed first semiconductor layer, and continuously forming on the third semiconductor layer. The formation of the active layer includes a step of forming the active layer in a portion corresponding to the current concentration region so as to be laterally sandwiched by the second semiconductor layer.

Further, the semiconductor laser of the present invention for achieving the above object is a semiconductor laser in which an active layer is scissored by a layer having a band gap larger than that of the active layer, and a first semiconductor having a first conductivity type. A second semiconductor layer having a second conductivity type selectively formed on the layer, avoiding a current injection region of the laser, a second semiconductor layer having the second conductivity type, and the exposure The third semiconductor layer having the first conductivity type that is continuously formed and laminated on the first semiconductor layer and the portion that is continuously formed on the entire surface of the third semiconductor layer and corresponds to the current concentration region It is characterized in that it includes an active layer that is depressed toward the first semiconductor layer so as to be sandwiched between the second semiconductor layers.

More specifically, the film thickness of the second semiconductor layer is 0.5 μm or less. At least the semiconductor layer of the semiconductor laser contains the group V element As or P (phosphorus). The semiconductor growth method is the MBE method, or a method of forming a semiconductor layer from a partially or entirely gaseous raw material.
The step of selectively forming the second semiconductor layer is performed on the grating.

In the method of the present invention, an insulating film such as SiO 2 is used.
_A laser is manufactured by utilizing the characteristic that the semiconductor film does not easily grow on the semiconductor film ₂ and grows on the semiconductor film, that is, so-called selective growth. The growth rate of the growth method used in the present invention is 0. ln
Since it is relatively slow from m / s to 1 nm / s,
Controllability is good, and further, lateral growth can be restricted by limiting the growth film thickness, and an oscillation region having a desired width can be set. Further, the semiconductor layer that determines the width of the active layer is used to simultaneously confine the current and confine the light.

[0014]

Example 1 A first example of a method of manufacturing a semiconductor laser using the growth method of the present invention is shown in FIG. 1 is n-GaAs which is a substrate. Reference numeral 2 is Si-doped GaAs (thickness 0.5 μm) which is a buffer layer.
3 is Si-doped AIGaAs (thickness 1.0 μm) which is a clad layer. At this point, the growth is temporarily stopped (Fig. 1 (a)). On this stopped growth film, SiO ₂ which is an insulating layer shown by 4 is formed to a film thickness of 10 nm. The width of the SiO ₂ insulating layer 4 is 3 μm (see FIG. 1).
(B)). Here, an AlGaAs film is selectively grown by an organic metal growth method using triethylgallium and trimethylaluminum as the group III and arsine as the group V. The substrate temperature is 600 ° C., and the growth rate of AIGaAs is
It is 0.5 μm / h. Under this condition, the Be-doped AIGaAs which also functions as the current constriction shown in 5 is 0.3 μm.
m has grown. The reason for setting the film thickness to 0.3 μm is that when the selective growth film is made thicker, lateral growth of the growth film is observed, which gradually separates from the SiO ₂ film 4. When stacking 1 μm, the lateral retraction is about 0.7
It is about μm. Here, since the film has grown by 0.3 μm, it is recessed by 0.21 μm in the lateral direction, and the active layer width is 3.4 μm.
I was able to limit it to about m. Therefore, the layer 4 covered with SiO ₂
Growth ends while the width of the
(C)). After that, the SiO ₂ film 4 is removed by wet etching or the like. The removed shape is shown in FIG.

Thereafter, an upper layer such as a laser active layer is formed. In FIG. 2B, after the growth of the current confinement layer 5 is completed, the remaining lower clad layer 6 shown in FIG.
It grows by μm. The lower cladding layer 6 is continuously formed without interruption in order to improve the concentration of the current in the central portion. Subsequently, 0.1 μm of undoped GaAs, which is the active layer of 7, was formed. Furthermore, the Be-doped AIGaAs which is the upper clad layer of 8 is 5 μm growth, and finally B
The growth is completed by growing e-doped GaAs 9 by 0.5 μm. In the area with the current blocking layer of 5, in the vertical direction,
6 n-AlGaAs, 5 p-AIGaAs and 3 n
-Since the NPN is formed of AIGaAs, the current does not flow, but the current concentrates in the central portion and flows as indicated by reference numeral 10.

The characteristic of this growth method is that since the current block layer 5 does not grow in the region defined by the SiO ₂ layer 4, if the SiO ₂ mask 4 is formed with high precision,
A laser having an accurate width of the active layer region 11 in which a current flows can be manufactured. Current confinement is achieved by the current blocking layer 5
Since there is AlGaAs of the current blocking layer 5 on both sides of the central active layer region 11, the refractive index becomes large at the center and the light is confined in the center. In this way, the active layer 7 with high accuracy is realized, and at the same time, the confinement of current and the confinement of light are realized. Another feature of this laser is that by selecting the composition of the current blocking layer 5, the same refractive index difference can be formed in the laminating direction and the lateral direction of the active layer 7, and a near-field image with a round beam can be formed. It becomes possible to obtain. As described above, by applying the selective growth, the active layer region 11 can be accurately manufactured, and at the same time, a laser having excellent characteristics of current confinement and light confinement can be manufactured. The semiconductor laser of this embodiment operates as a Fabry-Perot type laser.

There is another method as the selective growth method. That is, this is a method in which a SiO ₂ film is provided in the peripheral portion indicated by reference numeral 5 and a current injection portion is first formed in the portion corresponding to reference numeral 4. This method is also a method for producing a BH type laser. However, when growing in a thin region with a thickness of 1 μm or more, in many cases, oblique facets are generated with respect to the substrate, and the grown cross-sectional shape is triangular or changes to a trapezoid. Therefore, it is difficult to obtain a convex portion having a vertical surface, and forming a current injection region in advance is not an appropriate growth method for stable laser production in the process. Therefore, in this method, the current injection region is formed later.

The dependence of the plane orientation of the substrate in this growth method will be described. In this method, care is taken to thin the current confinement layer of 5, as indicated above. As a result, 4
Facets are less likely to be generated at the edges of the growth layer 5 in contact with the region of No. 1, and even if they occur, the size is such that regrowth is not hindered. Also in this respect, it is important to thin the current confinement layer of 5.

[0019]

[Embodiment 2] FIG. 3 illustrates the second embodiment. The difference between this embodiment and the first embodiment is that the laser structure has a grating. Two
1 is n-InP which is a substrate. 2 on this
2, 23 Si-doped InP 0.5 μm, 1.5 μm
They are growing one by one. After that, 24 gratings are formed on the layer 23 using the interference exposure method. The cycle is 24
It is set to 0 nm. Next, SiN is used for selective growth.
Formed ₄ . In FIG. 3C, reference numeral 24 denotes a grating. SiN ₄ 25, which is a dielectric layer, was formed on this grating 24. The width of the dielectric layer 25 is 2.5 μm.

In FIG. 4A, using this dielectric layer 25, selective growth of 26 Be-doped InP is carried out. The layer thickness of the Be-doped InP layer 26 is 0.5 μm. Here, a method of growing the layer 26 on the entire surface and etching it out after the growth is conceivable. However, at this time, the underlying grating 24 is often roughened. If there is a grating, the etching method is not a suitable method. Absent. Also in this respect, the selective growth method is the dominant method.

After the layer 26 is selectively grown, the dielectric film 25 is removed (the etchant used here does not damage the grating 24), and an active layer and an upper clad layer are grown thereon. 27 is an optical confinement layer S
It is i-doped InGaAsP and is formed to match the wavelength of the 1.15 μm band. 28 is a multiple quantum well layer which is an active layer. This structure is formed by forming five cycles of a combination of an active layer of In _0.53 Ga _0.47 As (thickness: 5 nm) and a barrier of undoped InGaAsP (thickness: 200 nm) matching the wavelength band of 1.3 μm. Reference numeral 29 is Be-doped InP which is an upper clad layer and has a thickness of 1.5 μm. And finally, 30 Be-doped InGaAs
Form P and end. As for the current confinement, since the p region of the layer 26 exists in the n region, the NPN is formed and the current is concentrated in the center, as in the case of the first embodiment. Also,
Regarding light, the active layer 28 in the central portion is sandwiched by InP 26 on both sides, and the light is confined in the center because InP has a lower refractive index. Further, since there are the layers 26 on both sides and the light guide layer 27, the light also spreads to the grating portion 24 and is affected by the grating 24. The light spreads as indicated by reference numeral 31 and becomes a wavelength selective laser.

As described above, by covering the region where the current is confined with the dielectric layer and stacking the semiconductor films by the selective growth method, the growth underlayer and the regrowth layer are not damaged, and the width of the light emitting region is reduced. It is possible to fabricate a distributed feedback (DFB) semiconductor laser having good reproducibility and current confinement and light confinement effects.

Here, the height of the layer 26 is set to about 0.5 μm, but if the layer 26 is too high, facets are generated in the grown film, and it is difficult to control the active region.
Growth near the bottom does not work well and defects are likely to occur in the grown film (for example, small cavities or those having different composition contents are formed at the corners of the bottom). Therefore, although depending on the current injection width indicated by 25, the height of the layer 26 is preferably 0.5 μm or less. Incidentally, gas source MBE, CBE, MOCVD and the like are typical growth methods for realizing the present embodiment. With these growth methods, the growth rate can be monitored during the growth, and there is no variation in the etching rate as in the etching method. The growth rate can be controlled at a rate of about 1 nm / s to 10 nm / s.

[0024]

As described above, according to the present invention, for example, selective growth is used to avoid a current injection region, and a thin film having a conductivity type different from that of a base is laminated to thereby increase an oscillation region of a semiconductor laser. It is possible to precisely define the current and confine the current and confine the light. Further, compared with the formation of the current injection region using the etching method, the laser can be manufactured without damaging the underlayer, and the laser manufacturing method suitable for manufacturing the DFB laser can be realized.

[Brief description of drawings]

FIG. 1 is a process explanatory diagram of a first embodiment.

FIG. 2 is a process explanatory view of the first embodiment.

FIG. 3 is a process explanatory view of the second embodiment.

FIG. 4 is a process explanatory diagram of the second embodiment.

FIG. 5 is an explanatory view of a conventional example.

FIG. 6 is a process explanatory diagram of a conventional example.

FIG. 7 is a process explanatory view of a conventional example.

[Explanation of symbols]

1, 21 Substrate 2 Buffer layer 3 Cladding layer 4 SiO ₂ Insulating layer 5, 26 Current constriction layer 6 Remaining lower clad layer 7, 28 Active layer 8, 29 Upper clad layer 9 Be-doped GaAs 11 Central active layer region 22 , 23 Si-doped InP layer 24 Grating 25 Dielectric layer 27 Optical confinement layer 30 Be-doped InGaAsP

Claims (7)

[Claims] 1. A method of manufacturing a semiconductor laser comprising an active layer and a layer having a bandgap larger than that of the active layer, wherein a current injection region of the laser is provided on a first semiconductor layer having a first conductivity type. Avoiding the step of selectively forming a second semiconductor layer having the second conductivity type, and forming a second semiconductor layer on the second semiconductor layer having the second conductivity type and on the exposed first semiconductor layer. In the step of continuously forming and stacking the third semiconductor layer having one conductivity type and the formation of the active layer continuously formed on the third semiconductor layer, the portion of the active layer corresponding to the current concentration region is formed horizontally. And a step of manufacturing the semiconductor laser so that the semiconductor laser is sandwiched between the second semiconductor layers in the direction. 2. The method for producing a semiconductor laser according to claim 1, wherein the film thickness of the second semiconductor layer is 0.5 μm or less. 3. V in at least the semiconductor layer of the semiconductor laser
The method for producing a semiconductor laser according to claim 1, wherein the semiconductor laser contains a group element As or P (phosphorus). 4. The method for producing a semiconductor laser according to claim 3, wherein the semiconductor growth method is an MBE method. 5. The semiconductor growth method according to claim 3, wherein the semiconductor layer is formed from a feed material which is partially or wholly gaseous.
The method for producing a semiconductor laser described. 6. The method for producing a semiconductor laser according to claim 1, wherein the step of selectively forming the second semiconductor layer is performed on a grating. 7. A semiconductor laser in which an active layer is scissored with a layer having a bandgap larger than that of the active layer, and a current injection region of the laser is avoided on a first semiconductor layer having a first conductivity type. A selectively formed second semiconductor layer having the second conductivity type, a second semiconductor layer having the second conductivity type, and the exposed first semiconductor layer are continuously formed and laminated. And a third semiconductor layer having a first conductivity type, and the first semiconductor layer continuously formed on the entire surface of the third semiconductor layer such that a portion corresponding to a current concentration region is sandwiched by the second semiconductor layer. A semiconductor laser including an active layer that is depressed toward the semiconductor layer side of the.