JPH10150239A - Semiconductor laser device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor laser device, wherein the semiconductor laser device of equivalently buried type is manufactured without processing an active layer directly, and especially the device equipped with an Al-containing active layer is enhanced in reliability. SOLUTION: At least, an N-type clad layer 12, an active layer 13 of (distorted) quantum well, and a first P-type clad layer 14 are successively laminated on an N-type substrate 11 for the formation of a semiconductor laser device, wherein the first P-type clad layer 14 is possessed of a ridge stripe, a second P-type clad layer 17 which contains P-type dopant larger in diffusion coefficient than that of the first P-type clad layer 14 is laminated on the first P-type clad layer 14 on both the sides of the ridge stripe, and a region of the active layer 13 other than its region just under the ridge stripe is turned to a mixed crystal region 19 by the thermal diffusion of P-type dopant from the second P-type clad layer 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device and a method for manufacturing the same.

[0002]

2. Description of the Related Art A semiconductor laser device using an Al-containing compound semiconductor for an active layer has a red wavelength of 650 nm (active layer: Al
(Including GaInP), 780 nm wavelength (active layer: AlGaAs
), And a laser beam having a wavelength of 1300 to 1550 nm (active layer: including AlGaInAs) and a laser beam of each wavelength band. Here, a semiconductor laser device having an oscillation wavelength of 1550 nm will be described as an example. The AlGaInAs-based semiconductor laser device has a possibility of improving the temperature characteristics as compared with a GaInAsP-based semiconductor laser which is generally used. FIG. 5 is a sectional view of a conventional AlGaInAs-based semiconductor laser device. The manufacturing process of this semiconductor laser device is, for example, as follows. 1) First, an n-InP clad layer 2 was formed on an n-InP substrate 1 by MO-MBE to a thickness of 1.0 μm and GaInAs / AlGaInAs (λg = 1.15).
μm) -MQW active layer 3, p-InP cladding layer 4
A p-GaInAs contact layer 5 is sequentially stacked on the order of 0.3 μm. Here, the active layer 3 has four wells, and the well layer (GaInA
s) and the thickness of the barrier layer (AlGaInAs) are each 5 nm.
And 12 nm. The active layer 3 has a SCH made of AlGaInAs (λg = 1.15 μm) having a thickness of 150 nm on both sides of the MQW.
The structure is sandwiched between layers. 2) Next, by photolithography and etching,
A part of the p-GaInAs contact layer 5 and the p-InP cladding layer 4 is removed to form a stripe-shaped ridge having a width of about 3 μm. 3) Next, after applying polyimide 6 to the side surface of the ridge, the n-In
The P substrate 1 is polished to about 100 μm, and the p electrode 7 and n
The electrodes 8 are respectively formed. In this material system (GaInAs / AlGaInAs), ordinary GaInAsP /
Since the conduction band discontinuity is larger than that of an InP-based semiconductor laser device, carrier overflow can be suppressed, and a semiconductor laser device having good temperature characteristics can be expected.

[0003]

By the way, in a normal semiconductor laser device, in order to reduce the threshold current and stabilize the transverse mode, the width of the active layer is reduced or the effective refractive index difference in the transverse direction is reduced. Has been realized. For that, the element structure is
It is desirable to form a ridge including an active layer and bury the ridge, that is, a so-called buried structure. However, GaInAs / AlG using a material containing Al for the active layer
In the aInAs-based semiconductor laser device, there is a problem that the side surface of the active layer is oxidized at the time of forming the ridge, and crystal growth for filling cannot be performed well. Further, even if the device is fabricated by buried growth, there is a problem that the threshold current increases and the reliability of the device is lacking. Therefore, as described above, a ridge that does not include an active layer is formed to form a ridge waveguide structure. However, although the ridge waveguide type structure is relatively easy to manufacture, there is a problem that the threshold current thereof is higher than that expected from the buried type structure, and the stability of the transverse mode is lacking.

[0004]

SUMMARY OF THE INVENTION The present invention has been achieved as a result of intensive studies to solve the above problems.
The described invention is a semiconductor laser device in which at least an n-type cladding layer, an active layer made of a (strained) quantum well, and a first p-type cladding layer are sequentially laminated on an n-type substrate.
The type cladding layer has a ridge stripe portion, and a p-type dopant having a larger diffusion coefficient than the p-type dopant of the first p-type cladding layer is formed on the first p-type cladding layer on both sides of the ridge stripe portion.
A second p-type clad layer containing a type dopant is laminated, and the active layer in a region other than a region immediately below the ridge stripe portion is
The mixed crystal is formed by thermal diffusion of the p-type dopant from the second p-type cladding layer. Here, the p-type dopant of the second p-type cladding layer has a diffusion coefficient large enough to thermally diffuse and crystallize the active layer in a region other than a region immediately below the ridge stripe portion.

According to a third aspect of the present invention, an active layer including at least an n-type cladding layer and a (strained) quantum well is sequentially laminated on an n-type substrate, and a stripe-shaped interval is formed on the active layer. In this case, a first p-type clad layer containing a p-type dopant having a large diffusion coefficient is laminated, a stripe-shaped space is filled with a second p-type clad layer, and an active layer in a region immediately below the first p-type clad layer is a first p-type clad layer. The mixed crystal is formed by thermal diffusion of the p-type dopant from the cladding layer. Here, the p-type dopant of the first p-type cladding layer has a diffusion coefficient large enough to thermally diffuse and crystallize the active layer in a region immediately below the first p-type cladding layer.

Meanwhile, a technique which is unique to the superlattice structure (including the quantum well structure) and is a powerful means for producing a device includes what is called alloying or disordering. In this technology, a superlattice structure, which was originally considered to be thermally stable, is spatially separated by a hetero interface by thermally diffusing certain impurities or performing ion implantation and heat treatment. The constituent elements are mixed together to change to a new crystal form called a mixed crystal. The attraction of this technology is that the materials formed by mixed crystallization differ from the original superlattice structure in basic physical properties such as band gap energy and refractive index.
By making full use of this technology (for example, by mixing only desired regions), application to various semiconductor devices can be expected. The present invention applies this mixed crystal technique to a semiconductor laser device, and particularly improves the laser characteristics of a device having an active layer containing Al.

In other words, according to the first aspect of the present invention, the active layer in the region other than the region immediately below the ridge stripe portion has a large p-type diffusion coefficient from the second p-type cladding layer by heat treatment.
The mixed crystal is formed by thermal diffusion of the type dopant. on the other hand,
Since the region immediately below the ridge stripe portion is composed of the first p-type cladding layer containing a p-type dopant having a small diffusion coefficient, the active layer in this region is not mixed-crystallized by heat treatment. In the mixed active layer region, the band gap energy becomes larger than that of the (strained) quantum well layer of the non-mixed active layer, and the refractive index becomes smaller. Therefore,
The laser light oscillated in the active layer region immediately below the ridge stripe portion is confined within the width of the ridge stripe portion, and stable transverse mode control becomes possible, so that a structure equivalent to a buried structure can be realized. In the semiconductor laser device having the above structure, since the active layer can realize a structure equivalent to the buried structure without contacting air, when the active layer contains Al, compared with the conventional ridge waveguide type structure, Laser characteristics and reliability are improved.

According to the third aspect of the present invention, the region of the active layer below the first p-type cladding layer is made of a mixed crystal.
Since the region of the active layer below the stripe-shaped second p-type cladding layer sandwiched between the p-type cladding layers is not mixed,
The laser light oscillated in the active layer region below the second p-type cladding layer is confined within the width of the second p-type cladding layer, enabling stable transverse mode control and realizing a structure equivalent to a buried structure.

[0009] In the conventional method of forming a mixed crystal (for example, ion implantation), it is necessary to provide a separate step for forming a mixed crystal, which increases the number of steps and increases the cost of the device. According to the present invention, the mixed crystal can be formed in the vapor phase growth apparatus, so that the mixed crystal does not cause a cost increase.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Embodiment 1) FIGS. 1 (a) to 1 (d) are views showing a manufacturing process of an embodiment of a semiconductor laser device according to the present invention. This manufacturing process is as follows. That is, 1) First, an n-InP cladding layer 12 was formed on an n-InP substrate 11 to a thickness of 1.0 μm and GaInAs / AlGaInA by gas source MBE.
s (λg = 1.15 μm) · SCH-MQW active layer 13, first p-InP
1.5 μm clad layer 14, p-GaInAs contact layer 15
Are sequentially laminated to a thickness of 0.3 μm (FIG. 1A). Here, the active layer 13 has 4 wells, the thickness of the well layer (GaInAs) is 5 nm, the thickness of the barrier layer (AlGaInAs) is 12 nm, and both sides of the well layer have a thickness of 150 nm. (Λg = 1.15
μm). The doping material for the first p-InP cladding layer 14 is as follows.
It is preferable to use Be, Mg, C, Cd, and Ge having a small heat diffusion coefficient. 2) Next, using the SiO ₂ film 16 as a mask, a part of the p-GaInAs contact layer 15 and the first p-InP cladding layer 14 are removed by photolithography and etching,
A stripe-shaped ridge with a width of about 1.5 μm is formed (Fig. 1
(B)). 3) Next, the MOCVD method was used to
Using the O ₂ film 16 as a mask for selective growth, a blocking layer composed of the second p-InP clad layer 17 and the n-InP buried layer 18 is grown on both sides of the ridge (FIG. 1C). Here, the second
As a doping material for the p-InP cladding layer 17, Zn having a large thermal diffusion coefficient is used. 4) Next, the laminated substrate 1 is subjected to a heat treatment at 800 ° C. for 10 seconds in an As atmosphere in order to prevent the escape of As and P from the surface. As a result, Zn-doped p-InP
The active layer 13 immediately below the clad 17 is mixed-crystallized by the intrusion of Zn, and a mixed crystallized region 19 having the original average composition of MQW is formed (FIG. 1D). This mixed crystal region 19
Then, AlGaInAs (λg = 1.3 μm) is formed in which GaInAs of the well layer and AlGaInAs of the barrier layer are mixed. Note that the active layer immediately below the ridge is covered with the first p-InP cladding layer 14 containing a p-type dopant having a small diffusion coefficient, so that the mixed crystal does not occur there.

The setting of the above heat treatment conditions is important. Mixed crystal formation is possible if the heat treatment temperature is in the range of 600 to 900 ° C. The heat treatment time is closely related to the temperature,
The higher the heat treatment temperature, the shorter the time. As a guide, 600 ° C for about 30 minutes or more, 700 ° C for 5 minutes or more, 800 to 900
At ℃, it will be 10 seconds or more. However, it is necessary to set the heat treatment conditions so that the well layer and the barrier layer do not cause mutual diffusion or the diffusion of Zn does not extend directly below the ridge, and the heat treatment temperature and time have upper limits. For example, when heat treatment is performed at 800 ° C. for 15 minutes or more, the well layer and the barrier layer cause mutual diffusion. For the above reasons, the heat treatment is most preferably performed at a temperature of 700 to 800 ° C. for 10 to 300 seconds.

In the semiconductor laser device thus manufactured, the bandgap wavelength of the mixed crystal region 19 is shifted to the shorter wavelength side by about 250 nm, so that the semiconductor laser device is transparent to oscillation light and has a refractive index. Since it is lower than the area,
Light can be confined in the light emitting region. That is, lateral current confinement and light confinement can be performed without directly processing the active layer.

(Embodiment 2) FIGS. 2 (a) to 2 (d) are views showing a manufacturing process of a semiconductor laser device according to another embodiment of the present invention. This manufacturing process is as follows.
That is, 1) First, n-Al is formed on the n-InP substrate 21 by MO-MBE.
The InAs cladding layer 22 is 1.0 μm thick, and GaInAs / AlGaInAs (λ
g = 1.15 μm) .SCH-MQW active layer 23, p-AlInAs cladding layer 24 is 0.1 μm, and InGaAs etching stop layer 24a is 3 μm.
is laminated. Next, Zn is deposited thereon by MOCVD.
0.2 μm of the first p-InP cladding layer
The m and n-InP cladding layers 26 are sequentially laminated in a thickness of 0.5 μm (FIG. 2A). Here, the active layer 23 has four wells, the thickness of the well layer (GaInAs with 1% compressive strain) is 4 nm, and the thickness of the barrier layer (AlGaInAs of lattice matching system, λg = 1.15 μm) is
The thickness of the SCH layer is 10 nm, and both sides of the well layer are sandwiched between non-doped AlGaInAs (λg = 1.15 μm) SCH layers having a thickness of 150 nm. 2) Then, using photolithography technology,
An n-InP clad layer 26 and a first p-InP clad layer 25 in a region where the window is opened are etched by forming an m-stripe window-opened resist pattern. This etching is selectively performed up to the InGaAs etching stop layer 24a using a mixed solution of HCl: H ₃ PO ₄ = 1: 3 as an etching solution. After the etching, the resist is removed (FIG. 2B). InGaAs etching stop layer 24a functions as an etching stopper for this etching solution. 3) Next, heat treatment is performed at 800 ° C. for 10 seconds in an atmosphere of As and P to diffuse Zn and thereby form a first p-InP cladding layer 2.
Then, the lower active layer 23 is mixed-crystallized to form an AlGaInAs mixed crystallized region 23a having an original average composition of MQW. Since the mixed crystal region 23a has a smaller refractive index than that of the well layer, a lateral light confinement structure is formed.
(C)). 4) Next, a second p-InP cladding layer 27 using Zn as a p-type dopant is laminated by 1.5 μm and ap ⁺ -GaInAsP contact layer 28 is laminated by MOCVD (FIG. 2D). In this state,
An npn-type blocking layer is formed on both sides of the etched stripe-shaped portion to form a current confinement structure. 5) Finally, an electrode is formed and an end face is formed by cleavage.
In this embodiment, the n-AlInAs cladding layer 22 and the p-AlInAs layer 24 may be n-InP and p-InP, respectively. The optical confinement layer is GRIN instead of SCH.
It may be -SCH.

The semiconductor laser device of the above embodiment can be manufactured by the following method. That is, in the step 3), instead of performing the Zn diffusion heat treatment in the As atmosphere,
As shown in FIG. 3, even if an n-GaInAs surface protective layer 29 is formed as the uppermost layer on the surface and a GaAs substrate 30 is placed thereon and heat-treated, the escape of As and P from the surface can be prevented. . Further, instead of forming a stripe-shaped groove by etching, as shown in FIGS.
On the etching stop layer 24a, a striped SiO ₂ film 31 is formed using plasma CVD and photolithography techniques.
Is formed, and then the p-InP cladding layer 2 is formed by MOCVD.
5. The n-InP cladding layer 26 may be grown in a selected region.

The present invention is not limited to the above embodiment. That is, materials used for the (strained) quantum well active layer include GaInAs / AlGaInAs, AlGaInAs / AlGaInAs, and Al
GaInAs / AlInAs and GaInAs / AlInAs are preferred. Because these materials are other materials (GaInAsP, AlGaInP, etc.)
This is because mixed crystallization is more likely to occur than in the case of In addition, MBE (including gas source MBE, MO-MBE, CBE)
The device is preferred. This is because Be, which is a dopant material having a small diffusion coefficient, can be used. MBE
The growth temperature is generally lower in growth than in MOCVD growth.
By performing heat treatment, at the same time as causing mixed crystal,
The crystal in the waveguide region has an advantage that crystallinity is improved. Thereby, the threshold current and the slope efficiency are improved, and a semiconductor laser device having good characteristics can be easily manufactured. When MOCVD is used for the crystal growth apparatus, Mg is preferably used as the dopant material having a small diffusion coefficient.

[0016]

As described above, according to the present invention, a buried semiconductor laser device can be equivalently manufactured without directly processing the active layer. A semiconductor laser device having stable efficiency and transverse mode can be manufactured by a simple method, and there is an excellent effect that the reliability of a device containing Al in an active layer is improved.

[Brief description of the drawings]

FIGS. 1A to 1C are diagrams showing a manufacturing process of an embodiment of a semiconductor laser device according to the present invention.

2 (a) to 2 (d) are views showing a manufacturing process of another embodiment of the semiconductor laser device according to the present invention.

FIG. 3 is an explanatory view of another method for manufacturing the semiconductor laser device of the embodiment shown in FIG. 2;

FIGS. 4A and 4B are explanatory views of still another method of manufacturing the semiconductor laser device of the embodiment shown in FIG.

FIG. 5 is an explanatory diagram of a conventional semiconductor laser device.

[Explanation of symbols]

11, 21 n-InP substrate 12, 26 n-InP cladding layer 13, 23 active layer 14, 25 first p-InP cladding layer 15, 28 contact layer 16, 31 SiO ₂ film 17, 27 second p-InP cladding layer 18 n-InP buried layer 19, 23a mixed crystal region 22 n-AlInAs clad layer 24 p-AlInAs clad layer 24a InGaAs etching stop layer 29 surface protective layer 30 GaAs substrate

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[Procedure amendment]

[Submission date] April 8, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

[1] (a) ~ (d) are diagrams showing a manufacturing process of an embodiment of a semiconductor laser element according to the present invention.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akihiko Kasukawa 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd.

Claims (8)

[Claims] 1. A semiconductor laser device in which at least an n-type cladding layer, an active layer comprising a (strained) quantum well, and a first p-type cladding layer are sequentially laminated on an n-type substrate,
The type cladding layer has a ridge stripe portion, and a p-type dopant having a larger diffusion coefficient than the p-type dopant of the first p-type cladding layer is formed on the first p-type cladding layer on both sides of the ridge stripe portion.
A second p-type clad layer containing a type dopant is laminated, and the active layer in a region other than a region immediately below the ridge stripe portion is
A semiconductor laser device, which is mixed-crystallized by thermal diffusion of a p-type dopant from a second p-type cladding layer. 2. An n-type substrate in which at least an n-type cladding layer, an active layer comprising a (strain) quantum well, and a first p-type cladding layer are sequentially laminated, and then a ridge stripe portion is formed in the first p-type cladding layer. Then, a second p-type cladding layer is laminated on both sides of the ridge stripe portion of the first p-type cladding layer, and then heat treatment is performed to form a p-type cladding layer of the second p-type cladding layer.
2. The method of manufacturing a semiconductor laser device according to claim 1, wherein the active layer in a region other than a region immediately below the ridge stripe portion is mixed-crystallized by thermally diffusing the type dopant. 3. An active layer comprising at least an n-type cladding layer and a (strained) quantum well is sequentially laminated on an n-type substrate, and p-layers having a large diffusion coefficient are formed on the active layer at intervals of stripes. A first p-type clad layer containing a type dopant is stacked, the stripe-shaped space is filled with a second p-type clad layer, and the active layer in a region immediately below the first p-type clad layer is the first p-type clad layer.
A semiconductor laser device which is mixed-crystallized by thermal diffusion of a p-type dopant from a p-type cladding layer. 4. An active layer comprising at least an n-type cladding layer and a (strained) quantum well is sequentially laminated on an n-type substrate, and then a p-layer having a large diffusion coefficient is formed at intervals of a stripe.
A first p-type clad layer containing a type dopant is laminated to form a stripe-shaped groove, and then, by heat treatment,
4. The method according to claim 3, wherein the p-type dopant in the first p-type cladding layer is thermally diffused to mix the active layer in a region immediately below the first p-type cladding layer, and then the trench is filled with the second p-type cladding layer. A manufacturing method of the semiconductor laser device according to the above. 5. An active layer comprising a (strained) quantum well, wherein the material of the well layer / barrier layer is GaInAs / AlGaInAs or AlGaInAs / AlGaI.
4. The semiconductor laser device according to claim 1, wherein said semiconductor laser device is made of nAs, AlGaInAs / AlInAs, or GaInAs / AlInAs. 6. The p-type dopant of the first p-type cladding layer is
2. The semiconductor laser device according to claim 1, wherein one of Be, Mg, C, Cd, and Ge or a combination thereof is used, and the p-type dopant of the second p-type cladding layer is Zn. 7. The p-type dopant of the first p-type cladding layer is
4. The semiconductor laser device according to claim 3, wherein the semiconductor laser device is Zn. 8. The growth to the first p-type cladding layer is performed by MBE.
4. The method for manufacturing a semiconductor laser device according to claim 1, wherein the method is performed by a method or a gas source MBE method.