JPH065979A - Semiconductor laser and forming method therefor - Google Patents

Abstract

PURPOSE:To obtain a desired function by improving a shape of a diffraction grating of a semiconductor laser and providing a sufficient depth of a groove. CONSTITUTION:An n-type InP buffer layer 21 and an InGaAs or InGaAsP mask layer 23 are formed on an n-type InP substrate 21. A pattern of a diffraction grating 34 is formed on the layer 23, and a diffraction grating 24 is formed on the layer 21 by the layer 23. An InGaAsP waveguide layer 25, an active layer 26 and an InP clad layer 27 are formed without peeling the layer 23 on the formed grating 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a distributed feedback semiconductor laser (hereinafter abbreviated as DFB laser) and a distributed reflection laser (hereinafter abbreviated as DR laser) for optical communication and optical measurement. The present invention relates to a semiconductor laser for performing epitaxial growth on an ultrafine structure and a semiconductor laser manufacturing method.

[0002]

2. Description of the Related Art Wavelengths for realizing long-distance, large-capacity optical communication 1.
Currently, a dynamic single mode laser is required as a light source in the 5 μm band. In such a laser that oscillates in a single mode, for example, a DF in which a waveguide layer having a diffraction grating is formed
There are B laser and DR laser (Japanese Patent Laid-Open No. 60-46087).
Japanese Patent Publication No. 2-30195, etc.).

The DFB laser is manufactured by first forming an n-type InP on an n-type InP substrate 1 as shown in FIG.
The buffer layer 2 is grown. Then, in FIG.
Photolithographic etching process
A diffraction grating (grating) 3 is formed on the surface of the type InP. Next, as shown in FIGS. 3C, 4D, and 4E, the InGaAsP waveguide layer 4 and the active layer 5 are formed on the formed diffraction grating 3, and further, FIG. As shown in f), the InP clad layer 6 is grown on the surface of the active layer 5. Furthermore, after forming the laser stripes, embedded growth is performed for lateral mode control and electrode processing is performed.
The B laser is completed.

Further, the DR laser is produced by first growing an n-type InP substrate 11 and a buffer layer 12 as shown in FIG. 5A, and then performing photolithographic etching as shown in FIG. 5B. , The diffraction grating 13 is formed on the surface of the n-type InP. In this case, a deep diffraction grating is formed on the passive side 13a, and a shallow diffraction grating is formed on the active side 13b. Then, as shown in FIGS. 5C, 6D, and 6E, the InGaAsP waveguide layer 14 and the active layer 15 are formed on the buffer layer 12 after the diffraction grating 13 is formed.
Then, as shown in FIG. 6F, the InP clad layer 16 is grown on the surface of the active layer 15. Further, after forming the laser stripes, embedded growth is performed for lateral mode control and electrode processing is performed to complete the DR laser.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In a semiconductor laser such as a laser or a DR laser, as described above, the I on the diffraction gratings 3 and 13 on the surface of the n-type InP.
When the nGaAsP waveguide layers 4 and 14 and the active layers 5 and 15 are grown, the diffraction gratings _{3 and} 13 are exposed to a high temperature (the growth temperature of InGaAsP) in PH ₃ or the like. Mass transfer of InP atoms (Mass Transfer; P in InP evaporates by heating,
In atoms move on the diffraction grating to move to the groove portion of the diffraction grating which is energetically stable), so that the diffraction gratings 3 and 13 (the diffraction grating 13 on the passive side in the DR laser)
The depth of the groove becomes shallow, which causes a problem that the function of the semiconductor laser is deteriorated.

On the other hand, there are various techniques for preventing the phenomenon that the depth of the grooves of the diffraction gratings 3 and 13 becomes shallow. D
In order to suppress the above-mentioned phenomenon in the FB laser or the DR laser, there is a method of adding AsH ₃ in addition to PH _3. However, if too much AsH ₃ is added, the crystal quality will deteriorate, so AsH ₃ cannot be added too much. As a result, the groove depth of the diffraction grating is limited to 20 to 30 nm. Further, in order to suppress the above phenomenon, after the diffraction grating is formed on the waveguide layer, the InP clad layer is grown at a high speed, but the depth of the groove becomes shallow when the temperature is raised. Therefore, conventionally,
Since the shape of the diffraction grating of the semiconductor laser is good and the depth of the groove cannot be sufficiently secured, there is a problem that a desired function may not be obtained.

The present invention has been made in order to solve the above-mentioned problems of the prior art, in which the diffraction grating has a good shape,
It is an object of the present invention to provide a semiconductor laser and a method for producing a semiconductor laser in which a desired function can be obtained by making the groove depth sufficient.

[0008]

The present invention is a semiconductor laser in which a buffer layer and an extremely thin layer (for example, several n) are provided on a substrate.
m) A mask layer is laminated, a diffraction grating pattern is formed on the mask layer, a diffraction grating is formed on the buffer layer according to the patterning, and all or a part of the diffraction grating is formed on the diffraction grating. The waveguide layer, the active layer, and the clad layer are laminated without peeling off the mask layer, thereby solving the above problem.

Further, according to the present invention, in a method for producing a semiconductor laser, a step of sequentially forming a buffer layer and an extremely thin mask layer on a substrate, a step of forming a diffraction grating pattern on the mask layer, and a patterning step. Forming a diffraction grating on the surface of the buffer layer using the mask layer as a mask, and forming a waveguide layer, an active layer and a clad layer on the formed diffraction grating without peeling all or part of the mask layer. The above problem is solved by including a step.

[0010]

According to the present invention, in the method for producing a semiconductor laser, an n-type InP buffer layer and an extremely thin InGaAs (or InGaAsP) mask layer are sequentially formed on an n-type InP substrate, and the mask layer is subjected to, for example, photolithography etching. The diffraction grating is patterned by the method. A diffraction grating is formed on the surface of the buffer layer using the patterning of the mask layer as a mask. InG without removing all or part of the mask layer on the formed diffraction grating
An aAsP waveguide layer, an active layer and a clad layer are formed.

By leaving an extremely thin mask layer, n-type In
Since the diffraction grating is formed in the P buffer layer, mass transfer is less likely to occur, the shape of the diffraction grating is not held and the groove does not become shallow, and the absorption of the oscillated laser light is not affected.

Further, for example, in a distributed feedback semiconductor laser,
Since the entire mask layer is not peeled off, the grooves of the diffraction grating over the substantially entire surface of the buffer layer do not become shallow, and the shape of the grating becomes good.

Further, for example, in a distributed Bragg reflector semiconductor laser,
Since the mask layer on the active side is stripped by, for example, a photolithographic etching process, mass transfer occurs in the buffer layer on the active side, the groove of the diffraction grating becomes shallow, and the mask layer on the passive side is not stripped. The grooves of the diffraction grating there are not shallow, and the diffraction grating has a good shape. Therefore, a desired function can be obtained in the semiconductor laser. The mask layer has a composition longer than the oscillation wavelength of the laser light (close to InGaAs).
Is more effective in retaining the shape of the diffraction grating, but may affect the absorption of laser light. However, if the mask layer is thinner (several nm or less) than the wavelength of light, it does not affect the absorption of the oscillated laser light.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing a manufacturing process and a structure of a DBF laser according to a first embodiment of the present invention.

In the DFB laser of the embodiment, first, as shown in FIG. 1A, an n-type InP substrate 21 is formed on an n-type InP substrate 21.
Buffer layer 22 and ultra-thin InGaAs (or
A mask layer 23 of InGaAsP) is grown in order.

Next, as shown in FIG. 1B, the mask layer 23 is patterned (formed) with a diffraction grating by a photolithography and etching process.

Then, as shown in FIG. 1C, a diffraction grating 24 is formed on the surface of the buffer layer 22 using the patterned mask layer 23 as a mask.

Then, an InGaAsP waveguide layer 25 and an active layer 26 are grown on the diffraction grating formed as shown in FIG. 3D without removing the mask layer 23. Then, as shown in FIG. 1E, an InP clad layer 27 is grown on the active layer 26.

When InP is grown with the mask layer left to form the diffraction grating 24, mass transfer of InP of the diffraction grating 24 due to a temperature rise during InP growth is less likely to occur, so that the shape of the diffraction grating 24 is changed. Retained. Further, in the mask layer 23, a composition having a longer wavelength than the oscillation wavelength of the laser light (closer to InGaAs) is more effective in maintaining the shape of the diffraction grating, but affects the absorption of the laser light. However, if the thickness of the mask layer is made extremely thin (several nm or less) than the wavelength of light, it does not affect the absorption of the oscillated laser light. Further, after forming the laser stripes, embedded growth is performed and electrode processing is performed to complete the DBF laser.

Next, a second embodiment of the present invention will be described. FIG. 2 is an explanatory diagram showing a manufacturing process and a structure of the DR laser of the second embodiment.

In the DR laser of the second embodiment, first, as shown in FIG. 2A, an n-type InP substrate 31 is formed on an n-type InP substrate 31.
Buffer layer 22 and very thin InGaAs (or I
A mask layer 33 of (nGaAsP) is grown in order.

Next, as shown in FIG. 2B, the diffraction grating 34 is patterned (formed) on the mask layer 33 by a photolithographic etching process.

Next, as shown in FIG. 2C, a diffraction grating 34 is formed on the surface of the buffer layer 32 using the patterned mask layer 33 as a mask.

Then, as shown in FIG. 2D, the active-side mask layer 33b thus formed is peeled off by a photolithographic etching process, and InGaAsP is formed thereon.
Waveguide layer 35, and further InGa as shown in FIG.
AsP active layer 36, and as shown in FIG.
The P clad layer 37 is grown.

In the above manufacturing process, the mass transfer of the diffraction grating due to the temperature rise is effectively used, and since the passive side grows while leaving the mask layer 33, the mass transfer is less likely to occur. The shape is maintained (about 80 nm), while the mask 33 is removed on the active side for growth, mass transfer occurs, and the groove of the diffraction grating 34 becomes shallow (for example, 20 to 30 nm). Further, in the mask layer 33, a composition having a longer wavelength (closer to InGaAs) than the oscillation wavelength of the laser light has a higher effect of retaining the shape of the diffraction grating, but it may affect the absorption of the laser light. However, if the mask layer is made extremely thin (≦ several nm) with respect to the wavelength of light, absorption of the oscillated laser light is not affected. Further, after forming the laser stripes, embedded growth is performed and electrode processing is performed to complete the DR laser.

[0026]

As described above, according to the present invention, the shape of the diffraction grating of the semiconductor laser can be made good and the depth of the groove can be made sufficient. Therefore, a semiconductor laser having a desired function can be obtained. Further, if the thickness of the mask layer is made shorter than the wavelength of light, an excellent effect such as no influence on absorption of the oscillated laser light can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a semiconductor laser manufacturing process and a configuration of a semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a semiconductor laser manufacturing process and a semiconductor laser configuration according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a conventional semiconductor laser manufacturing process.

FIG. 4 is a process explanatory view that is a continuation of the process description of FIG. 3;

FIG. 5 is an explanatory view of another conventional manufacturing process of a semiconductor laser.

6A and 6B are process explanatory views that are continuous with the process description of FIG.

[Explanation of symbols]

 21, 31 Substrate 22, 32 Buffer layer 23, 33 Mask layer 33b Active side mask layer 24, 34 Diffraction grating 25, 35 Waveguide layer 26, 36 Active layer 27, 37 Clad layer

Claims (2)

[Claims] 1. In a semiconductor laser, a buffer layer and an extremely thin mask layer are laminated on a substrate, a diffraction grating patterning is formed on the mask layer, and a diffraction grating corresponding to the patterning is formed on the buffer layer. And a waveguide layer, an active layer and a clad layer are laminated on the diffraction grating without peeling off all or a part of the mask layer. 2. A method for producing a semiconductor laser, comprising the steps of sequentially forming a buffer layer and an extremely thin mask layer on a substrate, forming a diffraction grating pattern on the mask layer, and forming the patterned mask layer on the substrate. A step of forming a diffraction grating on the surface of the buffer layer as a mask, a step of forming a waveguide layer, an active layer and a clad layer on the formed diffraction grating without peeling all or part of the mask layer, A method for producing a semiconductor laser, comprising: