JP2003298190A - Semiconductor laser element and its fabricating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the reliability and the yield of a ridge waveguide semiconductor laser element while minimizing increase of fabrication process. <P>SOLUTION: A ridge protective layer 10 patterned into stripe is provided on the opposite sides of a ridge waveguide 11 through a space region. The ridge protective layer 10 is composed of a high resistance semiconductor material of nondoped InP or Fe doped InP. Since the upper surface of the ridge protective layer 10 is lower than the upper surface of the waveguide 11, the ridge waveguide 11 is protected against damage during fabrication process of element and chipping of crystal is reduced significantly. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device and a manufacturing technique thereof, and more particularly to a technique effectively applied to a semiconductor laser device having a ridge waveguide structure used as a light source for an optical communication data link.

[0002]

2. Description of the Related Art Generally, in a semiconductor laser, a ridge-shaped waveguide structure is formed in a second cladding layer for the purpose of improving the efficiency of current injection and controlling the transverse mode of laser light. This type of ridge waveguide type semiconductor laser has a difference in element structure. Therefore, after forming a ridge waveguide structure, a first element structure in which both sides are filled with semiconductor layers having different conductivity, and a ridge waveguide structure. After being formed, it is roughly divided into a second element structure in which both sides are not filled with a semiconductor layer.
In addition, as a technique for improving the second element structure, Kubota e
As described in T al., Jpn. J. Appl. Phys. Vol39, pp2297 (2000), there is known a structure in which both sides of the ridge waveguide part are embedded and protected by an organic material or the like.

[0003]

Among the ridge waveguide type semiconductor lasers described above, the first element structure in which both sides of the ridge waveguide structure are filled with semiconductor layers having different conductivity is the transverse mode controllability of laser light. However, at least two or more crystal growth steps are required. Furthermore, there is a drawback that the manufacturing cost increases because the number of manufacturing steps of the element increases.

On the other hand, the second element structure in which neither side of the ridge waveguide structure is filled with the semiconductor layer has an advantage that the manufacturing process is simplified because the crystal growth process is performed only once. However, in the case of this element structure, the ridge waveguide is spatially exposed during the manufacturing process and the assembling process, so that the crystal at the corner portion is likely to be chipped. As a result, there are problems that the basic characteristics and reliability of the device are deteriorated and the yield is significantly reduced. Further, as a countermeasure, the above-mentioned improved structure in which both sides of the ridge waveguide portion are filled with an organic material or the like for protection causes a problem that the number of manufacturing steps increases.

An object of the present invention is to provide a technique capable of improving the reliability and the yield of the ridge waveguide type semiconductor laser device while minimizing the increase in the number of manufacturing steps.

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

[0007]

Among the inventions disclosed in the present application, a brief description will be given to the outline of typical ones.
It is as follows.

A ridge waveguide type semiconductor laser device according to the present invention has at least a first clad layer of a first conductivity type, an active layer, and a second clad layer of a second conductivity type on a semiconductor substrate. Equipped with a waveguide structure,
The upper surface of the waveguide structure is lower than the upper surfaces of the protective layers formed on both sides of the waveguide structure with the space regions on both sides of the waveguide structure sandwiched therebetween.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. In all the drawings for explaining the embodiments, members having the same function are designated by the same reference numerals, and the repeated description thereof will be omitted.

(Embodiment 1) This embodiment is applied to a ridge waveguide type semiconductor laser device having an oscillation wavelength of 1.3 μm band, and its manufacturing method will be described below in the order of steps. .

First, as shown in FIG. 1, a semiconductor substrate 1 made of n-type InP (indium phosphide) is prepared, and a film thickness of 200 n is formed on the semiconductor substrate 1 by a well-known metal organic chemical vapor deposition method.
m n-type InP buffer layer 2, film thickness 500 nm
N-type InP clad layer 3 having a film thickness of 30 nm
Type InAlAs (indium aluminum arsenide) layer 4,
InGaAlAs (indium gallium aluminum arsenide) well layer with a thickness of 5 nm and InGaAlA with a thickness of 8 nm
InGaAlAs strained multiple quantum well structure active layer 5 composed of an s barrier layer, p-type InAlAs layer 6 having a film thickness of 30 nm,
A clad layer 7 made of p-type InP having a film thickness of 1600 nm,
Hetero barrier reduction layer 8 made of p-type InGaAsP (indium gallium arsenide phosphide) with a thickness of 30 nm, thickness 200
The contact layer 9 made of p-type InGaAs (indium gallium arsenide) and the ridge protection layer 10 made of non-doped InP having a thickness of 700 nm are sequentially grown.

Although the InGaAlAs system material is used as the strained multiple quantum well structure active layer 5 here, InG
An aAsP-based material may also be used. Although the ridge protective layer is made of non-doped InP to suppress the reactive current, it may be made of other high resistance semiconductor material such as Fe-doped InP.

Next, as shown in FIG. 2, the well-known photolithography technique (etching technique using a photoresist film as a mask) is used to form the ridge protective layer 10 in the region where the ridge waveguide is to be formed into a stripe shape having a width of 25 μm. Then, the openings 17 are formed by patterning. At this time, the opening 17
The contact layer 9 made of p-type InGaAs is formed on the bottom of the
The surface of is exposed.

Next, as shown in FIG. 3, the bottom of the opening 17 is etched by photolithography to the middle of the cladding layer 7 made of p-type InP. As a result, the waveguide 11 made of ridge-shaped p-type InP having a width of 1.3 μm is formed in the center of the opening 17.

Next, as shown in FIG. 4, a silicon oxide film 12 having a thickness of 300 nm is deposited by a CVD method, and then the waveguide 1 is formed by dry etching using a photoresist film as a mask.
A part of the silicon oxide film 12 on the upper surface of 1 is removed to expose a part of the upper surface of the waveguide 11.

Next, as shown in FIG. 5, a p-side electrode 13 electrically connected to the waveguide 11 and an n-side electrode 14 electrically connected to the semiconductor substrate 1 made of n-type InP are provided. Form. The p-side electrode 13 is formed by depositing a metal film by an electron beam evaporation method, and the n-side electrode 14 is formed on the back surface of the semiconductor substrate 1 after the p-side electrode 13 is formed and then electron beam evaporation is performed thereon. It is formed by depositing a metal film by the method.

After that, the semiconductor substrate 1 is made to have a resonator length of 250 μm.
m bar-shaped cleavage, and after forming the multilayer reflection film 15 on this resonator surface, the laser element with a width of 400 μm is formed into a chip, thereby forming a ridge waveguide with an oscillation wavelength of 1.3 μm band as shown in FIG. Type semiconductor laser device is completed.

In the device structure as described above, since the ridge protective layer 10 has a film thickness of 700 nm, the upper surface of the waveguide 11 is lower than the upper surface of the ridge protective layer 10. As a result, the ridge-shaped waveguide 11 is protected by the ridge protective layers 10 on both sides of the ridge-shaped waveguide 11, so that the waveguide 11 is not damaged in the element manufacturing process, and crystal chips and the like can be significantly reduced.

According to the above-mentioned manufacturing method, when a plurality of semiconductor layers are continuously grown on the semiconductor substrate 1, In
Since the above-mentioned device structure can be realized only by adding the ridge protective layer 10 made of P, the number of manufacturing steps can be minimized.

As a result of current injection into the above semiconductor laser device, laser oscillation occurs at a threshold current of 13 mA and a wavelength of 13
An oscillation spectrum was observed at 02 nm. In addition, the overall yield including the basic characteristics and reliability of the laser element alone was dramatically improved to 95%, compared with 30% for the laser element of the conventional structure not provided with the ridge protection layer 10, A huge effect was confirmed.

As a result of mounting the above laser device on an optical module composed of transmitting and receiving electro-optical parts and evaluating the optical transmission characteristics, a spectrum line width at the time of modulation of 2.5 nm at a relaxation oscillation frequency of 19 GHz and a modulation signal frequency of 10 GHz
Got

(Embodiment 2) This embodiment is applied to a ridge waveguide type semiconductor laser device having an oscillation wavelength of 1.3 μm band as in the case of Embodiment 1, but the material of the ridge protective layer 10 is And the shape is different. The width of the laser element was 450 μm and the cavity length was 220 μm.

In the laser device of this embodiment, the ridge protective layer 10 is made of Fe-doped InP having a film thickness of 1000 nm. Further, in the first embodiment, the ridge protective layer 10 is patterned in a stripe shape, but in the present embodiment, it is patterned in a pad shape as shown in FIG. 7.

The method of manufacturing the semiconductor laser device of the present embodiment is the same as the manufacturing method of the first embodiment,
Only the mask pattern when patterning the ridge protective layer 10 using the photolithography technique is different.

In the element structure as described above, since the ridge protective layer 10 has a thickness of 1000 nm, the upper surface of the waveguide 11 is lower than the upper surface of the ridge protective layer 10. As a result, the ridge-shaped waveguide 11 is protected by the pad-shaped ridge protective layer 10, so that the waveguide 11 is not damaged in the device manufacturing process, and crystal chips and the like can be significantly reduced.

According to the above-mentioned manufacturing method, when a plurality of semiconductor layers are continuously grown on the semiconductor substrate 1, In
Since the above-mentioned device structure can be realized only by adding the ridge protective layer 10 made of P, the number of manufacturing steps can be minimized.

As a result of current injection into the above-mentioned semiconductor laser device, laser oscillation occurs at a threshold current of 11 mA and a wavelength of 13
An oscillation spectrum was observed at 05 nm. In addition, the overall yield including the basic characteristics and reliability of the laser element itself was dramatically improved to 98%, compared with 30% for the laser element of the conventional structure not provided with the ridge protection layer 10.

As a result of evaluating the optical transmission characteristics by mounting the above laser device on an optical module composed of transmitting and receiving electro-optical system parts, the spectrum line width at the time of modulation is 2.5 nm at the relaxation oscillation frequency of 19 GHz and the modulation signal frequency of 10 GHz.
Got

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, the shape of the ridge protection layer 10 is stripe (first embodiment) or pad (second embodiment).
It is not limited to.

[0031]

The effects obtained by the typical ones of the inventions disclosed in this application will be briefly described as follows.
It is as follows.

Since the crystal breakage of the ridge waveguide portion which has occurred in the manufacturing process can be greatly reduced, the basic characteristics, reliability and yield of the ridge waveguide type semiconductor laser device are improved.

[Brief description of drawings]

FIG. 1 is a fragmentary cross-sectional view of a semiconductor substrate showing a method for manufacturing a semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a fragmentary cross-sectional view of a semiconductor substrate showing a method for manufacturing a semiconductor laser device according to an embodiment of the present invention.

FIG. 3 is a fragmentary cross-sectional view of a semiconductor substrate showing a method for manufacturing a semiconductor laser device according to an embodiment of the present invention.

FIG. 4 is a fragmentary cross-sectional view of the semiconductor substrate showing the method for manufacturing the semiconductor laser device according to the embodiment of the present invention.

FIG. 5 is a fragmentary cross-sectional view of the semiconductor substrate showing the method for manufacturing the semiconductor laser device according to the embodiment of the present invention.

FIG. 6 is a perspective view showing a semiconductor laser device according to an embodiment of the present invention.

FIG. 7 is a perspective view showing a semiconductor laser device according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Semiconductor substrate, 2 ... Buffer layer, 3 ... Clad layer, 4
InAlAs layer, 5 ... Strained multiple quantum well structure active layer, 6
... InAlAs layer, 7 ... Clad layer, 8 ... Hetero barrier reduction layer, 9 ... Contact layer, 10 ... Ridge protection layer, 11 ...
Waveguide, 12 ... Silicon oxide film, 13 ... P-side electrode, 14
... n-side electrode, 15 ... multilayer reflective film, 17 ... opening.

Continued front page    (72) Inventor Yoshiyuki Kani             216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Inside this Opnext Co., Ltd. (72) Inventor Yukio Kato             216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Inside this Opnext Co., Ltd. F-term (reference) 5F073 AA13 AA51 AA74 AA83 CA12                       CA15 EA28

Claims (8)

[Claims] 1. A semiconductor laser having at least a first conductivity type first cladding layer, an active layer, and a second conductivity type second cladding layer on a semiconductor substrate and having a ridge-shaped waveguide structure. In the device, a space region is provided on both sides of the ridge-shaped waveguide structure, and an upper surface of the waveguide structure has a protective layer formed on both sides of the waveguide structure via the space region. A semiconductor laser device characterized by being lower than the upper surface. 2. The semiconductor laser device according to claim 1, wherein the protective layer is made of a non-doped or Fe-doped high-resistance semiconductor layer. 3. The active layer comprises at least In, Al,
2. The semiconductor laser device according to claim 1, containing at least one element selected from Ga, As, and P. 4. The semiconductor laser device according to claim 1, wherein the semiconductor substrate is made of InP. 5. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is mounted on an optical module composed of a transmission / reception electro-optical system component. 6. (a) At least a first conductivity type first clad layer, an active layer, and a second conductivity type second layer on a semiconductor substrate.
A step of forming a protective layer on the semiconductor layer after forming a plurality of semiconductor layers including a clad layer; and (b) etching a part of the protective layer to expose the surface of the semiconductor layer. The method further includes at least a step of forming an opening, and (c) a step of etching the semiconductor layer exposed on the bottom surface of the opening to form a ridge-shaped waveguide structure having space regions on both sides. A method of manufacturing a semiconductor laser device, wherein an upper surface of the waveguide structure is lower than upper surfaces of protective layers formed on both sides of the waveguide structure via the space region. 7. The method of manufacturing a semiconductor laser device according to claim 6, wherein the protective layer is formed of a non-doped or Fe-doped high-resistance semiconductor layer. 8. The method of manufacturing a semiconductor laser device according to claim 7, wherein the protective layer extends in stripes along both sides of the waveguide structure.