JPH04229682A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To stably manufacture a buried-type semiconductor laser whose laser characteristic is good and whose reliability is high. CONSTITUTION:An n-InP buffer layer 102, an InGaAsP active layer 103, a p-InP clad layer 104 and a p-InGaAsP surface protective layer 105 are epitaxially grown sequentially on an n-InP substrate 101 whose main plane is a (100) plane. A stripe-shaped mask 106, for etching use, which is parallel to a <011> direction is formed by a photolithographic method and a dry etching method. The n-InP buffer layer 102 is etched down to the lower part of the InGaAsP active layer 103 by using a mixed solution which contains hydrochloric acid, hydrogen peroxide water and acetic acid; a mesa stripe 107 is formed. Then, the insulating film 106 is removed; the p-InGaAsP surface protective layer 105 is removed by using a mixed solution of sulfuric acid with hydrogen peroxide water; after that, InP current-blocking layers 108, 109 are grown selectively in regions other than the mesa stripe 107 by a liquid epitaxial growth operation; a laser by a buried-type heterostructure is formed.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a buried semiconductor laser, which is important as a light source for optical fiber communications. 2. Description of the Related Art A buried heterostructure in which an active layer is surrounded by a semiconductor material with a larger energy gap and a lower refractive index is widely used in the structure of a semiconductor laser. This buried heterostructure semiconductor laser has excellent characteristics such as a low oscillation threshold current value and a stable oscillation transverse mode, and is therefore attracting attention as a light source for optical fiber communication. [0003] As a conventional manufacturing method, there is one described, for example, in Technical Research Report OQE85-8, P55 of the Institute of Electronics, Information and Communication Engineers. A conventional manufacturing method is shown in FIG. As shown in FIG. 7(a), first (100)
On the n-InP substrate 101 whose main surface is the substrate, n-In
GaAsP light guide layer 501, InGaAsP active layer 1
03, p-InGaAsP buffer layer 502, thickness approximately 1
．． After epitaxially growing a 5 μm p-InP cladding layer 503, the p-InP cladding layer 50
A stripe-shaped mask pattern is formed on the substrate 3 in the <011> direction using an insulating film 504 of SiO2, Si3N4, etc. (FIG. 7(b)). Next, the p-InP cladding layer 50
After selectively etching 3 with a mixed solution of hydrochloric acid and phosphoric acid (FIG. 7(c)), a mesa stripe 505 is formed by etching with a Br-methanol solution, which is an etchant for InP and InGaAsP (FIG. 7(d)). ). lastly,
After removing the insulating film 504, liquid phase epitaxial growth
p-InP current blocking layer 108, n-InP
A current blocking layer 109 is grown so as not to be stacked on top of the cladding layer 503 of the mesa stripe 505, and a p-InP buried layer 110 and a p-InGaAsP are grown.
A contact layer 111 is grown to form a buried heterostructure (FIG. 7(e)). [Problems to be Solved by the Invention] However, a problem with the manufacturing method of the above structure is that in etching using a Br-methanol solution, Br easily evaporates and changes over time are large, resulting in large variations in etching rate. InGa
There is a problem in that it is difficult to control the stripe width of the AsP active layer 103. [0006] Furthermore, when etching with a Br-methanol solution, the shape of the stripe becomes an inverted mesa. Here p-In
Making the P cladding layer 503 thinner reduces the voltage applied to the n-InP current blocking layer 109 formed during buried epitaxial growth, suppresses thyristor operation and output saturation during high output operation, and improves temperature characteristics. It is effective from the standpoint of improving the situation. Normally, mesa stripe 505 needs to have a height sufficient to bury both sides thereof with current blocking layers 108 and 109, so etching must be performed until that height is obtained. However, when the cladding layer 503 becomes as thin as about 1 μm, In
As shown in FIG. 8, the GaAsP active layer 103 is located above the constriction, and the (111) A-plane 601, where interface states are easily created during crystal growth, is exposed on the side surface of the active layer. As a result, deterioration of laser characteristics such as an increase in threshold current value has been confirmed in our experiments. In addition to the Br-methanol solution used here for etching, a mixed solution of hydrogen peroxide and hydrochloric acid is known as an etchant for InP and InGaAsP. However, when this etching solution is used to etch a wafer on which a striped insulating film mask is formed in the <011> direction on the p-InP cladding layer 503 as in the past, it is etched with a reverse mesa similar to the Br-methanol solution. Because of the shape, good laser characteristics cannot be obtained. [0008] Therefore, there is a need for a method that prevents the mesa stripe from becoming an inverted mesa. One method of not exposing the (111)A surface 601 during etching with Br-methanol solution is to use a negative resist mask. As shown in FIG. 9, the resist has poor adhesion to the semiconductor wafer compared to an insulating film, side etching occurs under the resist mask 701, and the mesa stripe 700 becomes narrower in the width direction than the resist 701. The etched shape is generally a normal mesa, which is convenient because the (111) A plane 601 where interface states are likely to be formed is not exposed. However, the degree of adhesion between the resist mask 701 and the p-InP cladding layer 503 is not stable, and the shape of the mesa stripe 700 formed by etching changes, making control of the stripe width unstable. Furthermore, in conventional buried epitaxial growth, since the top layer of the mesa stripe is the p-InP cladding layer 503, the p-InP cladding layer 503 is directly exposed during soaking before growing the current block layer. When the p-InP cladding layer 503 is thin, the dissociation of P atoms with high vapor pressure occurs, and the resulting defects not only affect the p-InP cladding layer 503 but also the p-InP cladding layer 503.
It may reach the interface between the P cladding layer 503 and the InGaAsP active layer 103, resulting in a decrease in the luminous efficiency of the laser and an adverse effect on the reliability. As described above, when etching InP and InGaAsP using a Br-methanol solution or a mixed solution of hydrogen peroxide and hydrochloric acid, the shape of the stripe becomes an inverted mesa, making it difficult to control the stripe width.
When the P cladding layer is thinned, (111)A is formed on the sides of the active layer.
There is a problem that the laser characteristics deteriorate due to the exposed surface. [0011] Furthermore, in the conventional manufacturing method, p-I
By directly exposing the nP cladding layer, p-In
There is a problem in that the p-InP cladding layer cannot be made very thin because defects occur in the p-cladding layer, causing deterioration of laser characteristics and reliability. An object of the present invention is to improve the stripe width controllability of the mesa stripe in the etching process and to improve the stripe width controllability of the mesa stripe in the etching process, in order to stably produce a buried semiconductor laser having good laser characteristics and high reliability. To (
111) To obtain a mesa stripe in which the A-plane is not exposed and to prevent defects from occurring in the p-InP cladding layer during buried epitaxial growth. [Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides an InGaAsP active layer, a second conductivity type InP substrate having a (100) plane as a main surface, an InGaAsP active layer, a second conductivity type InP substrate, and a A step of forming a semiconductor multilayer film structure having a conductive type InP cladding layer and an InGaAsP surface protection layer as the top layer, and a step of forming a striped insulating film mask in the <011> direction on the surface protection layer. , the I adjacent to both sides of the striped mask are etched using a mixed solution containing hydrochloric acid and hydrogen peroxide using the insulating film mask as a mask.
a step of removing the nGaAsP surface protection layer, the second conductivity type InP cladding layer, and the InGaAsP active layer to form a mesa stripe; and a step of performing buried epitaxial growth on both sides of the mesa stripe to deposit a current blocking layer. A method of manufacturing a semiconductor laser having the following features is provided. [0014] Further, a step of forming a diffraction grating for defining an oscillation wavelength on a first conductivity type InP substrate having a (100) plane as a main surface, and a step of forming a first conductivity type InP substrate on the diffraction grating.
an aAsP light guide layer, an InGaAsP active layer, a second conductivity type InP cladding layer, and a second conductivity type InP layer.
A step of epitaxially growing a GaAsP surface protection layer, a step of forming a striped insulating film as an etching mask on the surface protection layer, and etching with a mixed solution containing hydrochloric acid and hydrogen peroxide using the insulating film as a mask. Next, a step of etching the semiconductor layer adjacent to both sides of the striped mask with a mixed solution containing hydrochloric acid and phosphoric acid to form a mesa stripe, and forming a current blocking layer on both sides of the mesa stripe by liquid phase epitaxial growth. The present invention provides a method for manufacturing a semiconductor laser. [Operation] As shown above, in the method of forming an etching insulating film mask on the InGaAsP surface protective layer and then etching with a mixed solution containing hydrochloric acid and hydrogen peroxide, there is no surface protective layer. Therefore, since the shape of the mesa stripe becomes a normal mesa, the (111) A plane is not exposed and the laser characteristics are not deteriorated. Furthermore, since the change over time of the etching solution is smaller than that of Br-methanol, the stripe width can be controlled better. Furthermore, in the present invention, even when the p-InP cladding layer is made thin, liquid phase epitaxial growth is performed with the p-InGaAsP surface protective layer attached.
Since the surface of the InP cladding layer is not exposed and P atoms with high vapor pressure are not dissociated, defects can be prevented from occurring in the p-InP cladding layer, and a semiconductor laser with good characteristics can be obtained. Embodiment FIG. 1 shows a first embodiment of the present invention. First, as shown in Figure 1(a), n
- On an InP substrate 101, a 5 μm thick n-InP buffer layer 102 and a 0.2 μm thick InGaAsP active layer 1
03, p-InP cladding layer 10 with a thickness of 1.0 μm or more
4. p-InGaAsP surface protective layer 1 with a thickness of 0.2 μm
05 was epitaxially grown sequentially using a liquid phase epitaxial growth method, SiO2, S
After depositing an insulating film such as i3N4, a stripe-shaped etching mask 106 with a width of 8 μm parallel to the <011> direction is formed by photolithography and dry etching.
form. Hydrochloric acid, hydrogen peroxide, and acetic acid (volume ratio: 3:
InGaAsP active layer 103 with a mixed solution containing 1:36)
The n-InP buffer layer 102 is etched to a depth of 2 μm below the surface to form a mesa stripe 107 (see FIG.
b)). This etching solution has InGaAsP as the top layer.
In an InP multilayer structure on a (100) InP substrate in which layers are laminated, if a striped insulating film mask is formed in the <011> direction and etched as in the conventional example, a mesa stripe in a forward mesa shape is formed. is obtained, so the (111)A plane 601 is not exposed on the side surface. At this time, the width of the uppermost layer of mesa stripe 107 is approximately 1.5 μm. Next, the insulating film 106 is removed using a hydrofluoric acid solution, and then the p-InGaAsP surface protection layer 105 is removed using a mixture of sulfuric acid and hydrogen peroxide, and then mesa stripes 107 are formed by liquid phase epitaxial growth. p- on both sides of
The InP current blocking layer 108 and the n-InP current blocking layer 109 are selectively grown so as not to grow on the p-InP cladding layer 104 of the mesa stripe 107. After that, further p-InP buried layer 110, p-I
An nGaAsP contact layer 111 is sequentially grown to form a buried heterostructure. Generally, in liquid phase epitaxial growth, the height of mesa stripes is approximately 2 μm.
If the stripe width is approximately 5 μm or less, n-InP
Since the current blocking layer 109 is not stacked on the mesa stripe 107, good current blocking layers are formed on both sides of the mesa stripe 107, and current is effectively injected into the active layer. In this method, since the stripe mask is an insulating film, the adhesion between the p-InGaAsP surface protection layer 105 and the insulating film mask 106 is good, and a mesa shape can be stably obtained.
) Side A 601 is not exposed. In the first embodiment, mesa stripe 1
For forming InP, a well-known mixed solution containing hydrochloric acid, hydrogen peroxide, and acetic acid (volume ratio: 3:1:36) is used as an etchant. However, it is p-InP that the mesa stripe does not become an inverted mesa like in the past.
This is because the surface protection layer 105 is used on the cladding layer 104. Because of this layer, even if etched with a mixture of hydrochloric acid, hydrogen peroxide, and acetic acid, the mesa stripe will have a regular mesa structure that is convenient for buried lasers. FIG. 2 shows a second embodiment of the invention. In FIG. 2(a), as in the first embodiment, optical C is grown on a semiconductor multilayer structure semiconductor wafer by epitaxial growth.
SiO2, Si by VD (or plasma CVD)
After depositing an insulating film such as 3N4, a striped etching mask 106 with a width of 8 μm parallel to the <011> direction is formed by photolithography and dry etching.
form. The difference from the first embodiment is that the thickness of the p-InP cladding layer 201 is reduced to approximately 0.3 μm. As mentioned earlier, thinning the cladding layer above the active layer reduces the voltage applied to the n-InP current blocking layer formed during buried epitaxial growth, which reduces thyristor operation and output saturation during high-output operation. This is because it is effective from the viewpoint of suppressing the temperature and improving temperature characteristics. Therefore, a mixture of hydrochloric acid, hydrogen peroxide, and acetic acid was used to reach a depth of about 3 μm below the InGaAsP active layer 103 so that the mesa stripe had a predetermined height.
The -InP buffer layer 102 is etched to form mesa stripes 202 (FIG. 2(b)). Insulating film mask 1
After removing 06, p-
InP current blocking layer 108, n-InP current blocking layer 109, p-InP buried layer 110, p-InGa
AsP contact layers 111 are sequentially grown to form a buried heterostructure. The difference from the first embodiment is p
-InP cladding layer 201 is thin and active layer 103 is p-
It is located immediately below the buried layer 110 via the InP cladding layer 201, and the p-InGaAsP surface protective layer 1
The point is that the buried epitaxial growth of the current blocking layer 108 is performed with 05 remaining. Here the first
In the example, there is no problem because the p-InP cladding layer 301 is thick as shown in FIG. 3(a), but if the p-InP cladding layer 302 becomes thinner than 0.5 μm as shown in FIG. 3(b), the growth p-InP cladding layer 30 during the previous soak
There is a concern that the defects L generated by the dissociation of P atoms with high vapor pressure in the InGaAsP active layer 103 may adversely affect the InGaAsP active layer 103, leading to deterioration of laser characteristics such as a decrease in luminous efficiency. However, in the second embodiment, as shown in FIG. 3(c), a p-InGaAsP surface protective layer 105 is formed and buried epitaxial growth is performed with this layer left. No defects occur in the cladding layer 303. This is to protect the p-InP cladding layer 303 with the heat-resistant p-InGaAsP layer. [0021] Furthermore, the p-InGaAsP surface protective layer 10
5 is automatically melted back into the liquid phase during the growth of the p-InP current blocking layer 108, so it does not remain in the structure after the buried epitaxial growth. This is because, as a feature of the liquid phase epitaxial growth method, since the InP layer does not grow on the narrow mesa stripe, the InGaAsP layer, which is susceptible to meltback, is selectively removed. In the structure fabricated in this way, since the p-InP cladding layer 201 is thin, the p-InP cladding layer 201
The n-InP block layer 109 has a small series resistance.
Since the voltage applied to the laser is small, thyristor operation and output saturation at high outputs can be suppressed, and temperature characteristics are also improved, resulting in good laser characteristics. FIG. 4 shows a third embodiment of the present invention. Figure 4
As shown in (a), photo CVD (or plasma CV
After depositing an insulating film (SiO2, Si3N4, etc.) in step D), a striped etching mask 401 with a width of 4 μm parallel to the <011> direction is formed by photolithography and dry etching. InGaAsP active layer 10 is formed using a mixed solution containing hydrochloric acid, hydrogen peroxide, and acetic acid.
n-InP buffer layer 102 to a depth of approximately 1 μm below 3.
The InGaAsP active layer 103 is completely removed by etching (FIG. 4(b)). Next, add an n-InP buffer layer 1 using a mixture of hydrochloric acid and phosphoric acid (volume ratio 1:2).
02 is etched approximately vertically by approximately 2 μm (Fig. 4(c)).
). Liquid phase epitaxial growth is performed in the same manner as in the second example to form a buried heterostructure (FIG. 4(d)).
. In this embodiment, mainly the InGaAsP active layer 103
A mixed solution containing hydrochloric acid and a hydrogen peroxide solution is used only for removing the n-InP buffer layer 102, and a mixed solution of hydrochloric acid and phosphoric acid that does not cause side etching is used for etching the n-InP buffer layer 102. A mixed solution of hydrochloric acid and phosphoric acid has the property of etching only the InP layer without etching the InGaAsP layer, so when thinning the p-InP cladding layer, the active layer is first treated with hydrochloric acid and hydrogen peroxide. Etching is performed with a mixed solution containing acetic acid, and then the depth required for forming the blocking layer can be adjusted using a mixed solution of hydrochloric acid and phosphoric acid. Therefore, the etching method of the third embodiment can reduce the amount of side etching with respect to the width of the insulating film mask 402, so the controllability of the stripe width is better than in the first and second embodiments, and the etching method within the wafer is The variation in the width of the active layer can be reduced by 30% compared to the conventional manufacturing method using Br-methanol, making it possible to obtain a laser element with stable characteristics. FIG. 5 shows an example of fabricating a buried structure for a DFB laser used in optical fiber communication. The present invention can also be applied to the production of DFB lasers. The manufacturing method will be described below with reference to the drawings. In FIG. 5A, a diffraction grating is formed on an n-InP substrate 101 having a (100) plane as its main surface using a well-known method. In other words, a photoresist is applied to a thickness of about 1000A on the substrate 1, a diffraction grating pattern is formed using a two-beam interference exposure method using a He-Cd laser (wavelength 345nm), and then a mixture of saturated bromine water, phosphoric acid, and water is applied. The resist on the surface of the substrate is selectively etched using a diffraction grating pattern. By removing the photoresist with an organic solvent, a diffraction grating can be formed on the substrate. In this way, period 2
After forming the 000A diffraction grating, a 0.2 μm thick n-InGaAsP optical guide layer 501 and a 0.2 μm thick n-InGaAsP optical guide layer 501 were formed.
InGaAsP active layer 103, 0.3 μm thick p-
InP cladding layer 104, p-InG with a thickness of 0.2 μm
After depositing an insulating film 106 of SiO2, Si3N4, etc. by optical CVD (or plasma CVD) on a semiconductor multilayer structure wafer on which an aAsP surface protective layer 105 has been epitaxially grown in sequence, a film of <0.11% is formed by photolithography and dry etching. ＞Width parallel to direction 4μ
Insulating film mask 10 for etching in the form of m stripes
6 (Fig. 5(b)). After that, as in the third example, hydrochloric acid, hydrogen peroxide and acetic acid (volume ratio: 3:
InGaAsP active layer 103 with a mixed solution containing 1:36)
The n-InP substrate 101 is etched to a depth of about 1 μm below, the InGaAsP active layer 103 other than the mesa stripe is completely removed, and then hydrochloric acid and phosphoric acid (volume ratio is 1) are etched.
:Additionally, the n-InP substrate 101 is coated with the mixture of 2) to a thickness of about 2μ.
m is etched almost vertically to form a mesa stripe 107 (FIG. 5(c)). After removing the insulating film 106 with a hydrofluoric acid solution, a p-InP current blocking layer 108 and an n-InP current blocking layer 109 are grown in areas other than the mesa stripe 107 by liquid phase epitaxial growth, and then p-InP Buried layer 110, p-In
GaAsP contact layers 111 are sequentially grown to form a buried heterostructure (FIG. 5(d)). The linearity in the optical output characteristics of the laser manufactured according to the present invention is determined by the threshold value I as shown in FIG.
The external differential quantum efficiency at th is η0, the threshold value Ith+1
The external differential quantum efficiency at 00 mA is η100, and (η
It was found that the linearity was 11% when expressed as 0-η100)/η0X100, and 17% for the laser manufactured by the conventional method, indicating that the linearity was significantly improved. From this, we can expect higher output and improved distortion characteristics during analog transmission. In the above embodiment, a semiconductor wafer in which an InGaAsP active layer was stacked on an n-InP buffer layer was used, but an InGaAsP active layer was stacked directly on an n-InP substrate.
Wafer with stacked AsP active layer or InGaA
The present invention can also be applied to a wafer in which an InGaAsP meltback prevention layer is laminated on an sP active layer. Furthermore, in this example, a mixed solution containing hydrochloric acid, hydrogen peroxide, and acetic acid was used as the etching solution, but the same effect can be obtained by using a weak acid such as phosphoric acid or pure water instead of acetic acid. It will be done. In addition, in this example, in order to prevent dissociation of P atoms in the p-InP cladding layer during buried epitaxial growth, the mesa stripe having the InGaAsP layer as the top layer was etched with a mixed solution containing hydrochloric acid, hydrogen peroxide, and acetic acid. formed, but Br-methano-
Similar mesa stripes may be formed using other etching solutions such as etchant. In addition, a p-InP current blocking layer and an n-InP current blocking layer were used as the current blocking layer, but
It is not limited to an InP layer, but an InGaAsP layer with a larger energy gap than the active layer, or a semi-insulating In
There is no problem even if a P layer is used. [0029] As described in detail above, the present invention provides the following effects. (1) On an InP substrate of a first conductivity type having a (100) plane as its main surface, at least an InGaAsP active layer, an InP cladding layer of a second conductivity type, and an InGaAsP surface protection layer as the top layer. After forming a stripe-shaped insulating film mask in the <011> direction on a semiconductor multilayer structure wafer with a semiconductor multilayer structure, the stripe width can be easily controlled by etching with a mixed solution containing hydrochloric acid and hydrogen peroxide. Therefore, it is possible to stably obtain mesa stripes having a regular mesa shape. Therefore, even if the p-InP cladding layer is made thinner, (111)A
Since the surface is not exposed and good current blocking layers can be formed on both sides of the mesa stripe, a laser with good characteristics can be obtained. (2) At least an InP layer of the first conductivity type, an InGaAsP active layer, an InP cladding layer of the second conductivity type, and an I layer on the top layer.
a mesa stripe having an nGaAsP surface protective layer;
By performing buried epitaxial growth on the InP substrate including the region other than the mesa stripe made of the InP layer of the first conductivity type, even if the p-InP cladding layer is thin, the InGaA layer in the uppermost layer of the mesa stripe is
Since the sP surface protective layer suppresses the generation of defects in the p-InP cladding layer during soaking before growth, it can prevent deterioration of laser characteristics such as a decrease in luminous efficiency due to the generation of defects, resulting in a laser with good characteristics. can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the manufacturing process of a semiconductor laser according to the present invention.

FIG. 2 is a cross-sectional view of the manufacturing process of the semiconductor laser of the present invention.

FIG. 3 is a cross-sectional view of the manufacturing process of the semiconductor laser of the present invention.

FIG. 4 is a cross-sectional view of the manufacturing process of the semiconductor laser of the present invention.

FIG. 5 is a perspective view of the manufacturing process of the DFB laser of the present invention.

FIG. 6 is a diagram showing optical output characteristics of a semiconductor laser according to the present invention.

FIG. 7 is a cross-sectional view of a conventional buried heterostructure manufacturing process.

FIG. 8 is a cross-sectional view of a conventional buried heterostructure manufacturing process.

FIG. 9 is a cross-sectional view of a conventional buried heterostructure manufacturing process.

[Explanation of symbols]

101 (100) n-InP substrate
102 n-InP buffer layer 103 InGaAsP active layer 104 p-InP cladding layer 201 p-InP cladding layer 301 p-InP cladding layer 302 p-InP cladding layer 303 p-InP cladding layer 401 p-InP cladding layer 503 p-InP Cladding layer 105 p-InGaAsP surface protection layer 106 Insulating film 402 Insulating film 504 Insulating film 107 Mesa stripe 202 Mesa stripe 403 Mesa stripe 505 Mesa stripe 108 p-InP current blocking layer 109 n-InP current blocking layer 110 p-InP buried layer 111 p-InGaAsP contact layer 501
n-InGaAsP light guide layer 502 p-InGa
AsP buffer layer 601 (111) A side 701 Resist mask

Claims (6)

[Claims] Claim 1: An InGaAsP active layer, a second conductivity type InP cladding layer, and an InGaAsP active layer on a first conductivity type InP substrate having a (100) plane as a main surface, and an InGaAsP active layer as a top layer.
a step of forming a semiconductor multilayer film structure having a P surface protective layer; a step of forming a striped insulating film mask in the <011> direction on the surface protective layer; forming mesa stripes by removing the InGaAsP surface protective layer, the second conductivity type InP cladding layer, and the InGaAsP active layer adjacent to both sides of the striped mask by etching with a mixed solution containing hydrogen peroxide; and a step of performing buried epitaxial growth on both sides of the mesa stripe to laminate a current blocking layer. 2. A first conductivity type I between the substrate and the active layer.
Claim 1 characterized in that an nP buffer layer is formed.
A method of manufacturing the semiconductor laser described above. 3. After etching with a mixed solution containing hydrochloric acid and hydrogen peroxide, the InP layer under the InGaAsP active layer is etched with a mixed solution containing hydrochloric acid and phosphoric acid to form a mesa stripe. 2. The method of manufacturing a semiconductor laser according to claim 1. 4. A first conductivity type InP layer and InGaA
forming a mesa stripe having an sP active layer, a second conductivity type InP cladding layer, and an InGaAsP surface protection layer as the top layer; and on a first conductivity type InP layer adjacent to the mesa stripe, A current blocking layer consisting of a second conductive type InP layer and a first conductive type InP layer is grown in this order on the first conductive type InP layer by a liquid phase epitaxial growth method, and at the same time the above-mentioned current blocking layer is grown in this order. Melting back the InGaAsP surface protective layer of the mesa stripe; and growing an InP layer of a second conductivity type and an InGaAsP layer of a second conductivity type in the first and second regions. Characteristic semiconductor laser manufacturing method. 5. Forming a diffraction grating for defining an oscillation wavelength on a first conductivity type InP substrate having a (100) plane as a main surface, and forming a first conductivity type InGaA substrate on the diffraction grating.
sP optical guide layer, InGaAsP active layer, second conductivity type InP cladding layer, second conductivity type InGaAsP
A step of epitaxially growing a surface protective layer in sequence, a step of forming a striped insulating film as an etching mask on the surface protective layer, and etching with a mixed solution containing hydrochloric acid and hydrogen peroxide using the insulating film as a mask. Next, a step of etching the semiconductor layer adjacent to both sides of the striped mask with a mixed solution containing hydrochloric acid and phosphoric acid to form a mesa stripe, and forming a current blocking layer on both sides of the mesa stripe by liquid phase epitaxial growth. A method for manufacturing a semiconductor laser, characterized in that: [Claim 6] A second layer from the substrate side as a current blocking layer.
6. The method of manufacturing a semiconductor laser according to claim 5, further comprising forming InP of a conductivity type of the second conductivity type and InP of a first conductivity type.