JPH10233550A - Semiconductor laser device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable semiconductor laser which has a plurality of light emitting parts which emit different light emission wavelengths respectively and enable stable operation for a long time. SOLUTION: A first semiconductor laser part 3 with a first active layer 19 and a second semiconductor laser part 14 with a second active layer 14 are laminated on a semiconductor board 1 one by one. A material system of the first active layer 19 and a material system of the second active layer 14 are different from each other. The first semiconductor laser part 3 has a ridge structure and the second semiconductor laser part 4 has a VSIS structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor laser device used for an optical information recording / reproducing device or the like and a method of manufacturing the same.

[0002]

2. Description of the Related Art A digital video disk (DVD), which is a next-generation optical disk, is capable of reproducing a 135-minute moving image for recording video and 4.7 for recording information.
By being able to record the capacity of GByte, it is expected that the conventional CD will be developed.

[0003] In a DVD reproducing apparatus, DVD (video recording), DVD-ROM (information recording), DVD-R
In addition to reproducing (recording information once) and reading data, CD (music recording), CD-ROM (information recording) and CD-R (recording information once) have been widely used in the past. There is also a demand for reproducing and reading data.

[0004] Here, the DVD is compared with the conventional CD,
There are major differences in the following two points. First, the first difference is that the thickness of the substrate of the optical disc is reduced from 1.2 mm to 0.6 mm.
mm. This is because when the NA of the focusing lens is increased in order to improve the recording density, the tolerance for the tilt of the optical disk is increased.

[0005] The second difference is the wavelength of the semiconductor laser used in the pickup. The wavelength of the semiconductor laser is about 780 nm for a conventional CD, and 630 nm for a DVD.
nm or 650 nm semiconductor laser is used. This is because the size of the focused spot is proportional to the wavelength.

However, it is difficult for a pickup for reading information to read two types of optical disks having different substrate thicknesses in terms of aberration. That is, for example, an optical disk having a substrate thickness of 1.2 mm cannot be read with a lens system designed with a substrate thickness of 0.6 mm as it is.

Therefore, various methods are currently being considered. For example, there are a method of switching between two types of objective lenses for CD and DVD, a method of using a bifocal lens for the objective lens, and a method of using a liquid crystal shutter. With these methods, it is possible to read two types of optical disks having different substrate thicknesses, and to use a conventional CD or C
Attempts to read data from a D-ROM are being considered.

[0008] However, it is difficult for the above method to read the currently available CD-R. This is because the write once CD-R is 780 as a recording method.
This is because a dye that responds to nm is used. For that type of CD-R, the wavelength of the semiconductor laser for reading needs to be 780 nm.

Therefore, the following configuration is conceivable as a DVD pickup capable of reading a CD-R.

First, a pickup for a CD and a DV
Two pickups for D are provided in the playback device. In this case, the pickup is independent and the DV
630 nm or 650 for the D pickup device
A semiconductor laser having a wavelength of 780 nm and an objective lens having an NA of 0.65 have a semiconductor laser having a wavelength of 780 nm and an objective lens having an NA of 0.45. However, this method leads to an increase in the size and cost of the reproducing apparatus.

Therefore, a DVD device is equipped with one pickup, and its emission wavelength is 780 nm and 63 nm.
There is a need for a method of emitting two types of light of 0 nm or 650 nm.

The following structure has been proposed as a semiconductor laser that emits two types of light.

1) Two types of chips are provided inside a semiconductor laser package.

2) As shown in FIG. 3, adjacent semiconductor laser chips 100 and 101 on the same wafer are oscillated at different wavelengths by changing the thicknesses of the coating films 102 and 103, respectively. Here, each semiconductor laser chip 100
And 101 are active layers 104 and 105, respectively.

3) As shown in FIG. 4, the widths of the grooves 204 and 205 below the active layers 202 and 203 of the adjacent semiconductor lasers 200 and 201 on the same wafer are changed to reduce the Al content of each active layer. To change the oscillation wavelength.

4) As shown in FIG. 5, a double hetero junction comprising a first active layer 300 and second and third cladding layers 301 and 302 is provided on a substrate, and a second active layer 303 is A semiconductor laser having a double hetero junction composed of fourth and fifth cladding layers 304 and 305 is provided. In FIG. 5, reference numeral 306 denotes a substrate; 307, a buffer layer;
Reference numeral 8 denotes a rib side surface, reference numeral 309 denotes a contact layer, and reference numeral 310 denotes an electrode.

FIG. 6 shows a VSIS (V-channeled Substrat).
5 shows an example of a semiconductor laser having an e Inner Stripe) structure. In FIG. 6, 311 is a substrate, 312 is a current blocking layer, and 313 is an electrode.

[0018]

However, the structure 1) has a problem of a light emitting spot. In other words, in order to use two different wavelengths of light with the same lens in the pickup, the distance between the light emitting spots must be at least one.
It is necessary to be less than 00 μm. In a package having a normal shape, the semiconductor laser chips are arranged side by side, so that the distance between the light emitting spots is 100 μm or more, and the attachment of the chips to the package includes an error of about several tens μm.

Further, the structures shown in FIGS. 3 and 4 have a problem that the wavelength difference cannot be made large. That is, in both FIGS. 3 and 4, the active layer is formed by a single growth (the active layer 1).
04 and 105, active layers 202 and 203), and the material system is the same material. Therefore, although it is possible to provide a slight difference in the Al mixed crystal ratio, if the band is in the 780 nm band, the Al
GaAs is used, and the wavelength difference is at most 10n.
m. In order for a DVD pickup to be compatible with a CD-R, it is necessary to generate emission wavelengths in the 780 nm and 630 nm or 650 nm bands, and the above structure cannot satisfy this wavelength difference.

In order to generate the above-mentioned light in the 600 nm band, GaInP, AlGa is used as an active layer and a cladding layer.
It is necessary to use InP, and the double hetero structure composed of the active layer and the cladding layer needs to be made of completely different materials.

The semiconductor laser shown in FIG.
This is a type of structure called a ridge structure. This structure is formed by vapor phase epitaxy (MOCVD (MOCVD)
Method) and molecular beam epitaxy (MBE method).

In the case of this structure, in a similar experiment conducted by the present inventors, the surface after removing the SiO ₂ after the growth of the rib side surface portion 308 is not flat but has a convex shape. After this,
When the p-GaAs contact layer 307 and the cladding layer 305, the active layer 303, and the cladding layer 304 are grown by MOCVD or MBE, the underlying p-GaAs
Since the growth is performed while maintaining the shapes of the s-contact layer 309 and the rib side surface 308 as they are, the active layer 303 has a curved structure.

With such a structure in which the active layer 303 is curved, the reliability when the semiconductor laser is operated at a high temperature is deteriorated, and the semiconductor laser cannot be incorporated in an actual pickup and used.

The semiconductor laser shown in FIG.
Although this type of laser is called a VSIS structure, this structure is usually grown by a liquid phase growth method (LPE method), and it is impossible to grow AlGaInP by this method.

[0025]

In order to achieve the above object, a semiconductor laser device according to the present invention comprises:
A first semiconductor laser unit having an active layer and a second semiconductor laser unit having a second active layer are sequentially stacked, and the material system of the first active layer and the material system of the second active layer Are different from each other.

Here, the first semiconductor laser device has a ridge structure, and the second semiconductor laser unit has a VSIS structure.
It has a structure.

Further, the active layer of the first semiconductor laser section is made of an AlGaInP-based material, and the active layer of the second semiconductor laser section is made of an AlGaAs-based material.

The method of manufacturing the semiconductor laser device is characterized in that after forming the second semiconductor laser section, the first semiconductor laser section is formed on the second semiconductor laser section.

As described above, the second structure having the VSIS structure
Since the first semiconductor laser portion having the ridge structure is formed after the semiconductor laser portion is formed, the first semiconductor laser portion is formed in a portion having a completely flat surface, and high-quality A semiconductor laser device can be realized.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
This will be described with reference to FIG. FIG. 1 is a sectional view of a semiconductor laser device according to the present embodiment and a partially enlarged view thereof.

In this embodiment, as shown in FIG. 1, a semiconductor laser chip 2 having two light emitting portions is mounted on a stem 1. This semiconductor laser chip 2 has 635
a laser unit 3 that emits a laser beam of 780 nm and a laser unit 4 that emits a laser beam of 780 nm. 5,
6 is an electrode of each part, 7 is a common electrode, and 8 is a wire for making electrical connection.

A method for manufacturing the semiconductor laser chip 2 will be described with reference to FIG.

A laser having a VSIS structure is formed as a portion 4 in the semiconductor laser chip 2. First, pG
An n layer is formed on the aAs substrate 10 by a liquid phase epitaxy (LPE) method.
A GaAs current blocking layer 11 is grown, and a striped V-shaped groove 12 reaching the substrate 10 is formed by photolithography and chemical etching.

Here, the temperature of the substrate 10 during the growth is 80
0 ° C. Next, p-Al _0.45 Ga _0.55
An As clad layer 13 is grown so as to fill the V-groove 12, and the p-Al _0.15 Ga _0.85 As active layer 14, n-Al
_{A 0.45} Ga _0.55 As clad layer 15 and an n-GaAs contact layer 16 are sequentially grown. Thereby, n-GaAs
The surface of the contact layer 16 becomes flat.

Next, the 635 nm light emitting portion 3 is formed. The n-AlGaInP cladding layer 1 is formed on the n-GaAs contact layer 16 by MBE.
7, AlGaInP light guide layer 18, multiple quantum well active layer 19, AlGaInP light guide layer 20, p-AlGa
InP cladding layer 21, p-GaInP etching stop layer 22, p-AlGaInP cladding layer 23, p-
A GaInP intermediate band gap layer 24 and a p-GaAs contact layer 25 are sequentially stacked. Here, the substrate temperature is 7
00 ° C.

Next, an Al ₂ O ₃ film is deposited thereon as a mask layer, and photolithography is performed to pattern the Al ₂ O ₃ film into a stripe pattern. Thereafter, wet etching is performed using the Al ₂ O ₃ film as a mask to form the contact layer 2.
5. Of the intermediate band gap layer 24 and the cladding layer 23,
Portions expected on both sides of the Al ₂ O ₃ film are removed. Thus, the mesa portion 26 is formed immediately below the Al ₂ O ₃ film.

The p-AlGaInP cladding layer 23
Is removed, selective etching with the p-GaInP etching stop layer 22 is performed to surely stop the etching. Thereafter, the second MBE growth is performed to grow n-GaAs 27 on both sides of the mesa portion 26 so as to have a convex cross section. Then, photolithography is performed to obtain n-GaAs.
The s polycrystal is removed by selective etching.

Next, in order to form the common electrode 7 as shown in FIG. 1, p-GaAs is formed by photolithography.
Substrate 10, n-GaAs current blocking layer 11, p-Al _0.45
Ga _0.55 As clad layer 13, p-Al _0.15 Ga _0.85 A
s active layer 14, n-Al _0.45 Ga _0.55 As clad layer 1
5 is partially removed.

Next, the surface of the contact layer 16 and the substrate 10
On the back surface and the n-GaAs contact layer 25, respectively.
The common electrode 7, the electrode 6, and the electrode 5 are formed.

Here, the threshold value at the 780 nm light emitting portion was as low as 50 mA, and the threshold value at 635 nm was as low as 40 mA. In addition, when a reliability test was performed by an energization test at a constant high temperature output, a stable operation of 5000 hours or more was assured by a test at 60 ° C. and 5 mW.

Here, for comparison, as in FIG.
An element having a ridge structure on the As substrate 10 side was also manufactured and compared.

In this experiment, the threshold value at the 780 nm light emitting portion was 52 mA, the threshold value at 635 nm was 64 mA, and almost the same value was obtained at the 780 nm light emitting portion, but the threshold value at 635 nm was higher. ing.

Also, in the reliability test, 780 nm
At the time of light emission, a stable operation could be obtained for 5000 hours or more in a test at 60 ° C. and 5 mW, but at 635 nm light emission, the operation was stopped in 500 hours under the same conditions.

This indicates that, in the semiconductor laser of this embodiment, since the surface of the n-GaAs contact layer 16 after growth is a perfect plane, the laser structure grown thereon can be grown with high quality. On the other hand, in a structure in which a ridge structure is grown on the substrate side, a non-uniform interface always occurs on the upper surface of the structure, which indicates that the laser structure grown thereon has a bad influence.

Further, according to this embodiment, the distance between the light emitting spots can be set to a distance of several tens μm or less.

In this embodiment, GaAs-based material and I
Although the example of the nGaAlP-based material has been described, other materials, for example, other system materials such as InGaAsP, ZnSSe, and GaN may be used. The growth method is not limited to MBE, but MOCVD, MOMBE, CBE, or the like can be used.

When the semiconductor laser of this embodiment is incorporated in a pickup, it is possible to generate 635 nm light and 780 nm light in a single optical path by using a double focus lens. Therefore, it is possible to read all DVD and CD-related discs including the currently distributed CD-R.

[0048]

As described above, according to the present invention,
A highly reliable semiconductor laser having a plurality of light-emitting portions each emitting a different emission wavelength and capable of stable operation for a long time can be realized.

[Brief description of the drawings]

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

FIG. 2 is a partially enlarged view for explaining a method of manufacturing the semiconductor laser device of FIG.

FIG. 3 is a longitudinal sectional view of a semiconductor laser device according to a conventional example.

FIG. 4 is a longitudinal sectional view of a semiconductor laser device according to another conventional example.

FIG. 5 is a longitudinal sectional view of a semiconductor laser device according to still another conventional example.

FIG. 6 is a longitudinal sectional view of a semiconductor laser device according to still another conventional example.

[Explanation of symbols]

 Reference Signs List 1 stem 3 first semiconductor laser unit 4 second semiconductor laser unit 14 second active layer 19 first active layer

Claims (4)

[Claims] A first active layer having a first active layer on the stem;
And a second semiconductor laser portion having a second active layer are sequentially stacked, and the material system of the first active layer and the material system of the second active layer are different. Semiconductor laser device. 2. The semiconductor laser device according to claim 1, wherein said first semiconductor laser section has a ridge structure, and said second semiconductor laser section has a VSIS structure. 3. The semiconductor device according to claim 1, wherein the active layer of the first semiconductor laser portion is A
2. The semiconductor laser device according to claim 1, wherein the active layer of the second semiconductor laser portion is made of an AlGaAs-based material. 4. The method for manufacturing a semiconductor laser device according to claim 1, wherein the first semiconductor laser unit is formed on the second semiconductor laser unit after forming the second semiconductor laser unit. Forming a semiconductor laser device, and then mounting the first semiconductor laser unit side on the stem.