JP2830108B2 - Manufacturing method of semiconductor laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a single-axis mode / narrow spectral linewidth semiconductor laser required as a light source for coherent optical communication capable of high-speed and large-capacity transmission.

2. Description of the Related Art In recent years, coherent optical communication has attracted attention as a next-generation high-speed, large-capacity communication. In this coherent optical communication, a semiconductor laser that oscillates at a single wavelength, has a very narrow spectral line width, and has a variable oscillation wavelength is required as a light source. As a semiconductor laser satisfying such requirements, a semiconductor laser having a structure in which an active light emitting region, an inactive optical waveguide, and a distributed reflection (DBR) region are integrated is promising. (For example, Patent Application No. 59-127008). 4th
The figure shows a cross-sectional structure in the optical axis direction as an outline of this structure. This device is composed of an active region A, an optical waveguide region B, and a distributed reflection (DBR region C) on an n-type InP substrate 1.
Here, in the active region A, an InGaAsP optical waveguide layer 2 having a bandgap wavelength λg = 1.05 μm,
1.30 μm InGaAsP active layer 3, p-InP cladding layer 4, λ
The InGaAsP contact layer 5 and the Au / Zn electrode 8 of g = 1.30 μm, and in the optical waveguide region B and the DBR region C, the InGaAsP optical waveguide layer 2 and the p−
It is composed of an InP cladding layer 4. Further, in the DBR region C, a pitch of 2000
The diffraction grating 7 of Å is formed. An Au / Sn electrode 6 is formed on the back surface of the InP substrate 1 over the entire region.
In the semiconductor laser having such a configuration, light generated in the active region A passes through the transparent optical waveguide region B, is reflected by the diffraction grating 7 in the DBR region C, returns to the active region A, and reaches laser oscillation. Further, in the structure shown in FIG. 4, since the respective regions are connected by the common optical waveguide layer 2, a high light wave coupling efficiency can be obtained between the respective regions, and a low threshold value operation can be achieved due to a high optical feedback effect to the active region. It is possible. The obtained laser light can have a good single longitudinal mode characteristic due to the wavelength selectivity of the diffraction grating 7 and a narrow spectral linewidth characteristic with a small spectral fluctuation due to the presence of the optical waveguide region B having a large light transmittance. . Further, by forming the Au / Zn electrodes 9 and 10 in the DBR region C and the optical waveguide region, it is possible to change the oscillation wavelength by changing the refractive index of the optical waveguide layer 2 by, for example, current injection. FIGS. 5A to 5C show an example of actually manufacturing an element having such a structure. First, n-In
N-InGaAsP optical waveguide layer 2, undoped InGaAs on P substrate 1
A P active layer 3, a p-InP clad layer 4a and a p-InGaAsP contact layer 5 are sequentially formed by epitaxial growth (a). Next, the p-InGaAsP contact layer 5, the p-InP cladding layer 4, and the InGaAsP active layer 3 in regions other than the active region A are sequentially removed by a selective etching solution, and then the active region A is removed.
The diffraction grating 7 is selectively formed on the optical waveguide layer 2 in the DBR region C by masking the optical waveguide region B with the SiO ₂ film 10 (b). Next, the active region A is masked with the SiO ₂ film 11 and p-In
The P clad layer 4b is formed by, for example, epitaxial growth by a liquid phase growth method (c). Further, by forming electrodes in necessary regions on the front and back surfaces, the structure shown in FIG. 4 can be obtained. The problem here is that in the step of selectively forming a diffraction grating in the region C, when a commonly used wet etching solution of saturated bromine water is used, the solute concentrates near the boundary between the mask region and the opening region. Is etched abnormally. This not only does not form a uniform diffraction grating, but also causes scattering of light between the regions B and C, which impairs effective optical feedback in the DBR region. In addition, when reactive ion etching (RIE) using CCl ₄ etc. is used to form the diffraction grating, abnormal etching at the boundary is hindered, but not only the depth of the diffraction grating can not be reduced but also it regrown on the diffraction grating. In this case, the crystallinity of the epitaxial layer is a problem. In order to prevent abnormal etching at the mask boundary in the wet etching for forming the diffraction grating, the insulating film mask 10 is formed in the step shown in FIG.
There is a method in which the diffraction grating 7 is formed on the entire surface without using the method, and then the diffraction grating in the region excluding the region C is removed by etching. This leads to an increase in waveguide loss and a decrease in the optical feedback effect, which impairs the characteristics of the semiconductor laser such as an increase in the oscillation threshold. Further, FIG. 5 (c)
In forming the second InP layer 4b by the liquid phase epitaxy method by masking the active region A with the insulating film 11 in the step (b), the diffraction grating 7 is deformed due to thermal damage or tort back, or the boundary between A and B is formed. Abnormal growth occurs, which leads to a decrease in the coupling efficiency and diffraction efficiency of light waves and an increase in waveguide loss, which also causes deterioration of characteristics of the semiconductor laser.

As described above, in the conventional method of manufacturing a semiconductor laser, an active region and an optical waveguide region are masked with an insulating film to selectively form a diffraction grating in a light feedback region. Since only the semiconductor layer exposed in the light feedback region was etched to form the diffraction grating, a diffraction grating having a uniform and sufficient diffraction effect in the light feedback region was formed by abnormal etching at the boundary region with the mask. Could not be formed. Further, a second liquid phase growth method is used for the optical waveguide region and the optical feedback region.
However, since the InP cladding layer was formed, there was a problem that an optical waveguide that caused strong light wave feedback in the active region could not be formed due to abnormal growth at the interface between the active region and the optical waveguide region.

Means for Solving the Problems In order to solve the problems described above, the present invention provides an InP substrate on an InP substrate.
sP optical waveguide layer, InGaAsP active layer, InP cladding layer, InGaAsP
After removing the contact layer, the cladding layer, and the active layer in the second and third regions excluding the first region of the multilayer epitaxial substrate including the contact layer, a second InP layer is deposited on at least the surface of the second region. Forming a diffraction grating on the surface of the first, second, and third regions; and forming a third InP layer on at least the diffraction grating in the third region by a vapor deposition method.
A method for manufacturing a semiconductor laser, comprising a step of depositing a layer.

Also, the present invention provides a method for manufacturing a multilayer epitaxial substrate comprising:
Removing the contact layers in the second and third regions excluding the region, forming a diffraction grating on the entire surface after removing the cladding layer and the active layer in the third region, A method of manufacturing a semiconductor laser, comprising a step of removing a clad layer and then depositing a second InP layer on at least the second and third regions of the semiconductor layer surface by vapor phase epitaxy.

Further, the present invention provides a step of removing the contact layer and the cladding layer in the second and third regions excluding the first region of the multilayer epitaxial substrate, and removing the entire surface after removing the active layer in the third region. A step of forming a diffraction grating, and a step of removing an active layer in a second region and then depositing a second InP layer on at least a surface of the semiconductor layer in the second and third regions. This is a laser manufacturing method.

According to the above-mentioned means, a diffraction grating having a uniform and high diffraction efficiency in the optical feedback region is provided, and the optical waveguide region
A semiconductor laser having a structure including a low-loss optical waveguide having a high light-wave coupling efficiency without abnormal etching or abnormal growth between the active region and the optical feedback region can be easily obtained, and has a high threshold operation at a low threshold. A single longitudinal mode characteristic and a narrow spectral line width characteristic can be realized.

Embodiment Hereinafter, a first embodiment of the present invention will be described. FIGS. 1A to 1F show the flow of a method for manufacturing a semiconductor laser according to the present invention. FIG. 1 (a) shows a multi-layer epitaxial substrate as an original. Here, the layer structure is a conventional example (fifth example).
N-InP substrate 1 (carrier concentration n to
N × InGaAsP optical waveguide layer 2 (carrier concentration n〜5 × 10 ¹⁷ cm ⁻³ , thickness d = 0.5 μm, bandgap wavelength λg = 1.05 μm) on 1 × 10 ¹⁸ cm ⁻³ ) and undoped InGaAsP
Active layer 3 (d = 0.12 μm, λg = 1.3 μm), p-InP cladding layer 4a (p〜5 × 10 ¹⁷ cm ⁻³ , d = 1.5 μm), p-I
nGaAsP contact layer 5 (p to 2 × 10 ¹⁸ cm ⁻³ , d = 0.5 μm)
m, λg = 1.3 μm). Using this multilayer epitaxial substrate, three regions of an active region A, an optical waveguide region B, and a DBR region C in the following procedure are formed. First, area A
The regions B and C p-InGaAsP contact layer 5 of masked using conventional photolithography, p-InP cladding layer 4a, and the InGaAsP active layer 2 to each InGaAsP layer _{H 2 SO 4 + H 2 O} 2 + H HC in ₂ O (1: 1: 5) solution and InP layer
Remove sequentially using l + H ₃ PO ₄ (1: 2) solution. Here, since the λg of the InGaAsP optical waveguide layer is 1.05 μm, the etching rate with respect to the sulfuric acid-based etching solution is low.
The GaAsP active layer 2 can be selectively removed with a sulfuric acid-based etchant (FIG. 1B). Next, metal organic chemical vapor deposition (MOVP
A second p-InP cladding layer 4b (carrier concentration p〜5 × 10 ¹⁷ cm ^-3 , d〜0.3 μm) is grown on the entire surface by using E) (FIG. 1 (c)). Next, the p-InP cladding layer 4 in the region C
Only b is removed with Hcl-based etchant and then pitched over the entire surface
A diffraction grating having a depth of 2000 ° and a depth of 1500 ° is formed using holographic exposure and a saturated aqueous bromine solution (FIG. 1 (d)). Next, the p-InP cladding layer 4b in the regions A and B is removed, and a third p-InP cladding layer 4c (carrier concentration: 5 × 10 ¹⁷ cm ⁻³ , d to 0.5 μm) is grown on the entire surface by MOVPE. And (first
(FIG. 9E) Finally, the third InP layer 4c in the region A is removed to expose the contact layer 5. Thus, a semiconductor laser including the active region A, the optical waveguide region B, and the DBR region C can be obtained. In the conventional example shown in FIG. 5, since the regions A and B are masked with an insulating film and a diffraction grating is selectively formed only in the region C, abnormal etching or control of the etching at the boundary between the regions B and C is performed. DBR for difficulties such as sex
Although a good diffraction grating could not be formed in the region, in the manufacturing method of the present invention, in the regions A and B, the IV by the MOVPE method was used.
Since a diffraction grating is formed on the entire surface via the nP film, it is necessary to obtain a diffraction grating DBR region that is uniform and has no abnormal shape at the boundary, similar to forming a diffraction grating on the entire surface on a flat substrate. Can be done. In this manufacturing method, the second and third InP layers on the regions B and C are formed by MOVPE which is a vapor phase growth.
Since it is formed by the method, there is no problem such as thermal damage during growth, deformation of the diffraction grating due to melt back, and abnormal growth between regions. Further, in the present manufacturing process, since a selective etching solution having a sufficient selectivity is used, there is no abnormal etching in the boundary region where the layers are required to be removed when each layer is removed. By such a method, the coupling efficiency of light waves,
The waveguide loss and the diffraction efficiency are improved, high light feedback to the active region is obtained, and a semiconductor laser having a low threshold value, a single longitudinal mode and a narrow spectral line width can be easily obtained. Next, a second embodiment of the present invention will be described. Fig. 2 (a)
(D) show this manufacturing process. Here, the underlying multilayer epitaxial substrate is the same as that of the first embodiment (FIG. 1A). In the second embodiment, first, the region A is masked to remove the InGaAsP contact layer 5, and then the regions AB are masked to remove the p-InP cladding layer 4 in the region C.
(A), the InGaAsP active layer 3 is removed (FIG. 2 (a)). Next, a diffraction grating is formed on the entire surface by the above-described method (FIG. 2B), and the p-InP cladding layer 4a and the InGaAsP active layer 3 in the region B are removed (FIG. 2C). Further, a second p-InP cladding layer 4c is grown on the entire surface by MOVPE, and then the second p-InP cladding layer in the region A is removed to obtain a structure similar to that of the first embodiment. it can. The features of this manufacturing method are that the MOVPE regrown film used for the selective formation of the diffraction grating is not used in the first embodiment, and the process of FIG. 2B does not require a mask and is etched in a self-aligned manner. Is that the process can be simplified. According to this method, a diffraction grating is also formed on the InGaAsP contact layer in the region A, which is the active region. However, since the cladding layer 4a is thick, there is no effect on laser light, and no particular adverse effect is exerted when forming electrodes. When the active layer is etched in the region B, the contact layer 5 in the region A is also slightly etched. However, since the contact layer 5 is sufficiently thicker than the active layer 3, this does not cause any problem. When a diffraction grating is formed by holographic exposure, areas B and C
There is a step of about 1.5 μm between the regions, and a region where a diffraction grating is not formed near the boundary region of the region C due to the swelling of the resist. However, this region is smaller than the whole region C and does not pose a serious problem. Thus, also in the second embodiment, a high-performance semiconductor laser can be realized by a simpler method. Next, a third embodiment of the present invention is shown in FIGS. In this case, the underlying multilayer epitaxial structure is the same as that shown in FIG. First, the InGaAsP contact layer 5 and the InP cladding layer 4a in the regions B and C are removed by masking the region A, and the InGaAsP active layer 3 in the region C is removed by masking the regions A and B (FIG. 3 (a) )). Next, after forming a diffraction grating on the entire surface (FIG. 3 (b)), the InGaAsP active layer 3 in the region B is removed by a jar line (FIG. 3 (c)). In addition, MO
By forming the second InP layer 4c by the VPE method,
Each region of optical waveguide and DBR can be obtained. This method is a simpler method as in the second embodiment, but the area B
In the point that the InP cladding layer 4a was removed before the formation of the diffraction grating, the step between the regions B and C, which was a problem in forming the diffraction grating, was removed. There is no disappearance region of the diffraction grating, and a uniform diffraction grating can be formed over the entire region c. Although the depth of the diffraction grating is determined by the thickness of the active layer 3, there is no particular problem in producing a relatively shallow diffraction grating such as a primary diffraction grating. 1st, 2nd,
Although the current narrowing structure and the process of fabricating the three-dimensional waveguide are omitted in the third embodiment, there is no problem if the process is performed immediately after fabricating the multilayer structure or after the process of the present invention.

As described above, in the present invention, the active region, the photoconductive region, and the DB
To fabricate a semiconductor laser consisting of the R region, an InGaAsP optical waveguide layer, InGaAsP active layer, InP cladding layer, I
Using a multilayer epitaxial substrate consisting of an nGaAsP contact layer, the first method is to use InG in the optical waveguide region / DBR region.
removing the AsP contact layer, the InP cladding layer and the InGaAsP active layer, forming a second InP layer on the optical waveguide region and the active region;
Process of forming a cladding layer and forming a diffraction grating on the entire surface, DB
A method of manufacturing a semiconductor laser including a step of forming a third InP cladding layer on the R region by a vapor phase growth method, and a second method is an InGaAsP contact layer in the optical waveguide region / DBR region of the multilayer epitaxial substrate. Process to remove the DB
Step of forming a diffraction grating on the entire surface after removing the InP cladding layer and InGaAsP active layer in the R region.
A method of manufacturing a semiconductor laser including a step of forming a second InP cladding layer by vapor-phase growth on an optical waveguide region / DBR region after removing a P cladding layer / InGaAsP active layer. A step of removing the InGaAsP contact layer and the InP cladding layer in the optical waveguide region and the DBR region of the multilayer epitaxial substrate, a step of removing the InGaAsP active layer in the DBR region, and then forming a diffraction grating on the entire surface; This is a method of manufacturing a semiconductor laser including a step of forming a second InP cladding layer on the optical waveguide region / DBR region by a vapor deposition method after removing an active layer, and selectively homogenizing and high diffraction in the DBR region. A high-efficiency diffraction grating can be formed, and a low-loss optical waveguide with high light-wave coupling efficiency without abnormal etching and abnormal growth between the regions can be formed, and high light from the DBR region to the active region can be formed. Its practical value of semiconductor laser having a high single longitudinal mode characteristic and a narrow spectral linewidth characteristics of low threshold operation by the feedback effect which can be easily provided there is greater.

[Brief description of the drawings]

FIGS. 1A to 1F show a first embodiment of the present invention, FIGS. 2A to 2D show a second embodiment of the present invention, and FIGS.
FIGS. 4A to 4D are sectional structural views showing a flow of a semiconductor laser manufacturing process according to a third embodiment of the present invention, and FIG. 4 is a sectional structural view of a semiconductor laser in which an active region, an optical waveguide region, and a DBR region are integrated. 5 (a) to 5 (c) show a manufacturing method in a conventional example. 1 .... n-InP substrate, 2 .... n-InGaAsP optical waveguide layer, 3 ....
... InGaAsP active layer, 4 ... InP cladding layer, 5 ... P-In
GaAsP contact layer, 7: diffraction grating, A: active region, B: optical waveguide region, C: DBR region.

Claims (3)

(57) [Claims] 1. A first InGaAsP layer of a first conductivity type, a second InGaAsP layer having a smaller bandgap energy than the first InGaAsP layer, and a second conductivity type on an InP substrate of a first conductivity type. A first InP layer of a second conductivity type and a third InG of a second conductivity type.
masking a first region of the multilayer epitaxial substrate made of an aAsP layer, forming a third region adjacent to the first region and a third region adjacent to the second region by masking the first region;
InGaAsP layer, the first InP layer and the second InGaAs
After removing the P layer, a second layer is formed in the first, second, and third regions.
Depositing an InP layer of the third region and the second region of the third region.
Forming a diffraction grating on the exposed semiconductor surface in the first, second, and third regions after removing the InP layer, and forming a third region on the diffraction grating in the third region by a vapor phase growth method. of
A method for manufacturing a semiconductor laser, comprising a step of depositing an InP layer. 2. A first InGaAsP layer of a first conductivity type, a second InGaAsP layer having a smaller bandgap energy than the first InGaAsP layer, and a second conductivity type on an InP substrate of the first conductivity type. A first InP layer of a second conductivity type and a third InG of a second conductivity type.
masking a first region of the multilayer epitaxial substrate made of an aAsP layer, forming a third region adjacent to the first region and a third region adjacent to the second region by masking the first region;
Removing the first InP layer and the second InGaAsP layer in the third region, and removing the diffraction grating on the exposed semiconductor surface in the first, second, and third regions. Forming the first InP in the second region.
After removing the layer and the second InGaAsP layer, the second InP layer is formed on the exposed semiconductor surface in the second and third regions by vapor phase growth.
A method for manufacturing a semiconductor laser, comprising a step of depositing a layer. 3. A first InGaAsP layer of a first conductivity type, a second InGaAsP layer having a lower band gap energy than the first InGaAsP layer, and a second InGaAsP layer of a first conductivity type on an InP substrate of the first conductivity type.
A first InP layer of a conductivity type, and a third InG of a second conductivity type
masking a first region of the multilayer epitaxial substrate composed of an aAsP layer, forming a second region adjacent to the first region and a third region of the third InGaAsP adjacent to the second region;
Removing the layer and the first InP layer; and removing the second InGaAsP layer in the third region, and then removing the diffraction grating over the entire exposed semiconductor surface in the first, second, and third regions. Forming the second InGaAsP in the second region.
A method for manufacturing a semiconductor laser, comprising removing a layer and depositing a second InP layer on the surfaces of the second and third regions by vapor phase growth.