JPH10135560A - Optical semiconductor device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the controllability and evenness of the width of an active layer by forming a current block layer of an optical semiconductor which constricts the current injected into the active layer into the shape of a flat crystal face by selective growth. SOLUTION: An optical guide layer 110 is formed and is grown by a first MOVPE growth and a silicon oxide film is formed on the entire surface of the optical guide layer 110 to form a stripe geometry of 3μm. Nextly, the optical guide layer 110 is grown by a second MOVPE growth with a silicon oxide film 111 as a growth blocking mask and then a current block layer 112 and a protective layer 113 are selectively formed in this order. In this selective growth, only a very narrow region of the width of 3μm is prevented from growing and the growth occurs on a (100) plane and therefore, the growth is almost the same as the entire surface growth on a flat plane. By forming the current block layer by selective growth, the width of an arpature of the current block layer on the active layer can be formed with an accuracy of patterning a silicon dioxide film and thereby can be controlled extremely precisely. By this method, the controllability and evenness of the width of the active layer can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device and a method of manufacturing the same, and more particularly, to a structure for blocking a current,
The present invention relates to a semiconductor laser, an optical modulator, a spot size conversion element, and the like formed by metal organic chemical vapor deposition, an optical semiconductor device in which these are integrated, and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a semiconductor laser, a SAS laser (Se
If-Aligned Structure Race
Lasers having a structure called r) are widely used, for example, in 1989, Applied Physics Letter,
Volume 35, H.C. Nishi, et al. , “Self
-Aligned structure InGaAs
P / InP DH lasers ", (Appl. Ph.
ys. Lett. , 35, 232 (1979), including many examples.

In this SAS laser structure, the active layer is used without being etched while being grown on the entire surface of the wafer, so that it is suitable for a laser containing Al in the active layer.

Hereinafter, a method of manufacturing the SAS laser will be described in detail with reference to the drawings in accordance with the contents of Japanese Patent Application Laid-Open No. 5-299767.

FIG. 9 is a cross-sectional view of a conventional SAS laser of this type.

In this manufacturing method, GaAs, In
The epitaxial growth of GaAlP is performed by metal organic chemical vapor deposition (hereinafter abbreviated as MOVPE). The source gases of MOVPE are trimethylindium (hereinafter, TMI), trimethylgallium (hereinafter, TMG), trimethylaluminum (hereinafter, TMAl), arsine (hereinafter, As)
H ₃ ) and phosphine (hereinafter, PH ₃ ), and the organic metal is supplied by bubbling hydrogen. Regarding impurity doping, disilane (hereinafter referred to as Si
₂ H ₆ ) and a gas obtained by diluting dimethyl zinc (hereinafter, DMZn) with hydrogen is used.

First, an n-type G having a surface orientation of (100)
An n-GaAs buffer layer 10 is formed on an aAs substrate 101.
2 was grown 1 μm, and then n-In _0.48 (Ga _0.6 Al
_0.4 ) _0.52 P cladding layer 203 of 1 μm, In _0.48 (G
a _1-x Al _x ) _0.52 Active layer 204 composed of P layer, In
_0.48 (Ga _0.6 Al _0.4 ) _0.52 P first optical guide layer 209
Is grown to 150 nm, and the p-In _0.48 Ga _0.52 P second light guide layer 210 is grown to 10 nm.

Subsequently, n-In _0.48 (Ga _0.3 Al
_0.7 ) _0.52 P current blocking layer 212 is 1 μm, p-In
_{A 0.48} Ga _0.52 P protective layer 113 is grown to a thickness of 10 nm. The p-In _0.48 Ga _0.52 P protective layer 113 is formed of n-In _0.48
(Ga _0.3 Al _0.7 ) _0.52 has a function of preventing the upper surface of the P current block layer 212 from being oxidized in the air in a later step.

Next, a silicon oxide film is formed on the entire surface, and a resist is applied thereon. The resist is patterned into stripes by photolithography, and the silicon oxide film is etched with buffered hydrofluoric acid to form openings. Using the silicon oxide film opened in a stripe shape as a mask, the p-In _0.48 Ga _0.52 P protective layer 11 is used.
3, and n-In _0.48 (Ga _0.3 Al _0.7 ) _0.52 P
The current block layer 212 is removed by etching to form a stripe-shaped groove. The etchant used was InGaP and InGaAlP with selectivity, and the p-I
The n _0.48 Ga _0.52 P second light guide layer 210 functions as an etching stopper layer.

Next, after removing the silicon dioxide film, pI
An n _0.48 (Ga _0.6 Al _0.4 ) _0.52 P clad layer 214 is buried and grown in the stripe-shaped groove, and then p ⁺ -G
The aAs contact layer 115 is grown.

Next, the surface electrode 16 is formed by a vapor deposition method or a sputtering method. Subsequently, the thickness of the wafer is set to 100 μm.
The back surface is polished to a thickness as small as possible, and then the back surface electrode 17 is formed on the entire surface.

If this wafer is cleaved to a cavity length of 300 μm, a front end face (emission face) coating film having a reflectance of 30% is applied, and a rear end face coating film having a reflectance of 90% is formed, a threshold current of 20 mA is obtained. , Slope efficiency 0.7W /
The red semiconductor laser device of A is obtained. Here, the slope efficiency is defined by the increase rate of the light output from the front end face with respect to the injection current after oscillation.

On the other hand, FIG. 10 shows the oscillation of light in the 0.98 μm band described in Nakamura et al.'S 27th p. 1 is an example of a buried semiconductor laser. In this case, after the semiconductor is wet-etched, InGaP
Since the manufacturing method of burying and growing the mixed crystal as a block layer is employed, the composition of the InGaP block layer is remarkably non-uniform, and as a result, a large mismatch of the lattice constant occurs, which causes deterioration of the device. The non-uniform composition occurs because when a groove is formed by wet etching, a specific crystal plane is not formed in the groove and all crystal orientations are mixed.

As described above, a semiconductor laser using a mixed crystal as a block layer is not used except for a case where a mixed crystal that does not cause lattice mismatch even if the composition becomes non-uniform is used for the buried layer, such as AlGaAs. It is difficult to manufacture a structure in which the block layer itself is buried and grown.

However, the current blocking capability of the block layer increases as the band gap of the semiconductor in the block layer increases, and a low leakage current can be obtained. Further, when considering confinement of light in the active region, setting the refractive index of the block layer to an appropriate value is effective for improving laser characteristics. From such a point of view, it has been eager to use various mixed crystals for the block layer.
As described above, since the SAS laser has a structure in which the block layer is formed on a flat surface, even if a mixed crystal is used as the block layer, the problem of lattice mismatch as in the case of the above-described embedded laser does not occur. Has advantages.

[0016]

However, the conventional SAS laser manufacturing method has the following problems.

The first problem is that, in the prior art, the width of the bottom of the groove exposed after the removal of the block layer, that is, the width of the active layer located below the portion where the block layer is removed, is reproducible. In addition, the uniformity is good, and it is difficult to obtain by controlling. The reason for this is that the etching width of the block layer varies depending on the variation in the thickness of the layer of the crystal-grown block layer in the wafer surface and the degree of overetching when etching the block layer. S
In AS lasers, the width of the groove bottom defines the injection current density of the semiconductor laser and the effective active layer width that is important for optical confinement. Therefore, the reproducibility, uniformity, and control of optical output characteristics such as threshold current and slope efficiency are controlled. Worse.

The second problem is that when the crystal of the block layer containing Al is wet-etched, the crystal of the block layer is exposed to the atmosphere. Degradation of laser light output characteristics,
The point is that it leads to deterioration of reliability.

The reason is that Al and oxygen are easily bonded,
This is because even if a clad layer is grown on a block layer having oxidized Al, crystal defects are generated from the oxidized Al. Therefore, it is difficult to employ a mixed crystal containing Al as a block layer, and a conventional SAS laser has a problem that a structure using a mixed crystal containing Al as a block layer cannot be mass-produced with high yield.

An object of the present invention is to improve the controllability, uniformity, and reproducibility of the width of an active layer in the manufacture of a semiconductor laser having a SAS structure using a mixed crystal as a block layer. It is to realize a threshold current and a high slope efficiency.

Another object of the present invention is to provide a semiconductor laser having a highly reliable structure in which oxidation of Al in a mixed crystal of a block layer is prevented.

[0022]

According to a method of manufacturing an optical semiconductor device of the present invention, there is provided a method of manufacturing an optical semiconductor device having a current blocking layer for narrowing a current injected into an active layer, wherein the current blocking layer is selectively grown. It is characterized by including a step of forming on a flat crystal face.

Another method for manufacturing an optical semiconductor device according to the present invention is as follows.
In a method of manufacturing an optical semiconductor device having a current blocking layer for confining a current injected into an active layer, a step of providing a growth inhibition mask on a flat crystal face, and an step of forming an organic layer on the flat crystal face on which the growth inhibition mask is formed. Forming the current block layer by performing selective growth by a metal vapor phase epitaxy method.

More specifically, a first conductive type clad layer, an active layer, and a second conductive type light having a larger forbidden band width and a smaller refractive index than the active layer are formed on a first conductive type semiconductor substrate. A step of sequentially growing a guide layer, a step of forming a growth inhibition mask extending in a stripe shape in a light guiding direction on the light guide layer, and a step of forming a growth inhibition mask on the light guide layer on which the growth inhibition mask is formed. Selectively growing a current blocking layer of one conductivity type, and growing a cladding layer of a second conductivity type on the light guide layer covered with the current blocking layer and the growth blocking mask. A method for manufacturing an optical semiconductor device characterized by the following. Here, the present invention also provides a method for manufacturing an optical semiconductor device, further comprising a step of selectively growing a second conductive type protective layer on the exposed surface of the first conductive type current blocking layer. .

Further, the current blocking layer is a compound semiconductor crystal containing aluminum, and the protective layer is a compound semiconductor crystal not containing aluminum.
Another object of the present invention is to provide a method of manufacturing an optical semiconductor device characterized by being a mixed crystal of the original or more.

According to another aspect of the present invention, there is provided a method of manufacturing an optical semiconductor device having a current blocking layer for narrowing a current injected into an active layer, wherein the width is changed along a light guiding direction on a flat crystal plane. Providing a growth-blocking mask having a striped shape, and forming the current block layer by performing selective growth on the flat crystal face on which the growth-blocking mask is formed by metal organic chemical vapor deposition. And

Here, a method of manufacturing an optical semiconductor device including a step of forming a light-emitting end face in a portion where the stripe width of the growth blocking mask is small, wherein the optical semiconductor device is II.
A method for manufacturing an optical semiconductor device, comprising a group IV-compound semiconductor or a group II-VI compound semiconductor;
The method for manufacturing an optical semiconductor device, wherein the growth prevention mask is made of a dielectric film is also provided.

Further, in the optical semiconductor device of the present invention, the first conductive type cladding layer, the active layer and the active layer, which are sequentially laminated on the first conductive type semiconductor substrate, have a larger forbidden band width and a smaller refractive index than the active layer. A light guide layer of the second conductivity type and a current blocking layer of the first conductivity type, the light guiding layer extending in the light guiding direction on the current blocking layer, and the light guide layer extending from the upper surface of the current blocking layer. There is a groove with a depth that reaches the layer,
A second conductive type protective layer may be provided on an upper surface of the current blocking layer and a side surface of the groove, and a second conductive type clad layer may be provided on a bottom surface of the groove and an entire upper surface of the protective layer.

Further, when the current blocking layer is a compound semiconductor mixed crystal containing aluminum and the protective layer is a compound semiconductor mixed crystal containing no aluminum, a more preferable optical semiconductor device is obtained. The optical semiconductor device is characterized in that the width of the groove changes along the light guiding direction. Alternatively, an optical semiconductor device is obtained in which the width of the groove is smaller at the light emitting end face than at the other end face.

When the method of forming the current block layer by selective growth is used, the opening width of the current block layer on the active layer can be formed with high precision for patterning the silicon dioxide film, so that it can be controlled very precisely. For this reason, effective production of the active layer width can be realized with excellent controllability, uniformity, and reproducibility.

Further, selective growth is performed on the (100) plane,
In addition, since the portion where growth is prevented is extremely narrow from 1 μm to 6 μm, even when the mixed crystal is used as the current blocking layer,
In-plane turbulence and variation in composition do not result in lattice irregularities. Therefore, InGa on a GaAs substrate
A mixed crystal having a relatively large band gap, such as P, AlGaInP, or AlInAs on an InP substrate, can be used as the current blocking layer, and the current blocking effect can be enhanced. Further, by freely selecting the composition ratio of the mixed crystal, the confinement of the refractive index of the guided light can be optimally designed.

Further, since the current block layer is not etched, even if the current block layer contains Al,
If the protective layer is grown at the end of the selective growth, the side surface of the block layer is also covered and Al is exposed on the crystal surface, and the crystallinity of the regrowth interface is not impaired.

As described above, a SAS laser having a reduced threshold current, improved slope efficiency, improved maximum light output, improved temperature characteristics, and improved reliability can be obtained.

[0034]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram schematically showing a semiconductor laser structure and a manufacturing method according to the present invention.

Referring to FIG. 1A, first, (10)
0) One conductivity type buffer layer 2, one conductivity type cladding layer 3, SCH
Growing the entire surface of the strained MQW layer 4 and the second light guide layer 9 of another conductivity type; Here, MQW is a multiple quantum well (Multi).
-Quantum Well), SCH is Separ
ate Definition Heterostr
This is an abbreviation for "acture." The SCH structure has a refractive index guiding function to confine light. Next, by photolithography, the dielectric film 11 is striped in a width of 1 to 6 μm.
m. Using this as a growth inhibiting mask, the current blocking layer 12 of one conductivity type is selectively grown to a thickness of 0.4 μm to 2 μm, and the protective layer 13 of another conductivity type is selectively grown to a thickness of 10 nm or more.

Next, after the dielectric film 11 is removed, the other conductive type clad burying layer 14 and the other conductive type contact layer 15 are crystal-grown to obtain the SAS laser structure shown in FIG.

Finally, a surface electrode 16 is formed.
After the back surface is polished to reduce the thickness of the wafer to 100 μm, a back electrode 17 is formed on the entire surface.

In the above-described embodiment, the semiconductor crystal includes a group III-V group composed of one or more of In, Ga, and Al and a group V composed of one or both of As and P. Applicable to compound semiconductor crystals.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a sectional view for explaining one embodiment of the optical semiconductor device of the present invention, and shows an embodiment of a SAS laser. N-type GaAs substrate 1 with (100) plane orientation
01 on the entire surface of the n-GaAs buffer layer 102
μm, n-Al _0.33 Ga _0.67 As clad layer 103
μm, SCH-strained MQW layer 4 is 67 nm, p-In _0.48
A Ga _0.52 P light guide layer 110 was formed to a thickness of 50 nm. FIG.
FIG. 4 is a band diagram of the SCH-strained MQW layer 4 and its periphery.
In this example, a 6% thick 1.7% compressive strain In _0.24 G
a _0.76 As well layer 106 having two layers,
The s barrier layer 107 is provided with a thickness of 5 nm. Also, in order to confine the light and the carrier, sandwich the strain MQW.
n-GaAs guide layer 105 and GaAs guide layer 10
8 is 5 nm each, and n-In _0.48 Ga _0.52
The P light guide layer 109 has a thickness of 40 nm. This SCH-strain M
The QW layer 4 becomes a laser active layer oscillating at a wavelength of 0.98 μm.

P-In _0.48 Ga _0.52 P light guide layer 110
Is flat, on which is spaced 3 μm, and n
-In _0.48 Ga _0.52 P current blocking layer 112 has a thickness of 1.
4 μm, p-In _0.48 Ga _0.52 P protective layer 113 having a thickness of 0.15 μm, disposed on both sides, and covering them, p-Al _0.33 Ga _0.67 As clad buried layer 114;
The p ⁺ -GaAs contact layer 115 has a thickness of 0.4
μm. Current blocking layers 1 separated by 3 μm
12 is covered with a p-InGaP protective layer 113.

Further, a surface electrode 116 covering the entire upper surface;
Under the n-type GaAs substrate 101, a back electrode 117 is provided.

Next, as an embodiment of the present invention, a manufacturing method will be described in detail with reference to FIGS. 3, 4, and 5. FIG.

Referring to FIG. 3, first, on a n-type GaAs substrate 101 having a (100) plane orientation,
By the MOVPE method, the entire surface of the n-GaAs buffer layer 102 is 0.5 μm, the n-Al _0.33 Ga _0.67 As clad layer 103 is 2 μm, and the SCH-strained MQW layer 4 is 67 n.
m, p-In _0.48 Ga _0.52 P light guide layer 110 is 50 n
m, a first MOVPE growth that grows sequentially. The SCH-strained MQW layer 4 therein has, as shown in the band diagram of FIG.
The n-In _0.48 Ga _0.52 P light guide layer 109 has a thickness of 40 nm,
An n-GaAs guide layer 105 is sandwiched between a 5 nm-thick and 5 nm-thick GaAs barrier layer 107, and is a 6-nm thick 1.7% compressive strain In _0.24 Ga _0.76 As well layer 106.
A GaAs guide layer 108 is sequentially grown to a thickness of 5 nm.

The source gas of Group III of MOVPE is TM
I and TMG, and the group V source gases are AsH ₃ and PH
₃ Regarding the impurity doping, the Si ₂
H ₆ and DMZn gas are used.

P-In _0.48 Ga _0.52 P light guide layer 110
After the first MOVPE growth is completed, a silicon oxide film is formed on the entire surface with a thickness of 150 nm, and is formed into a stripe shape with a width of 3 μm by photolithography and dry etching. A silicon nitride film may be used in place of the silicon oxide film.

Using this silicon oxide film 111 as a growth inhibiting mask, a second MOVPE growth is performed. As shown in FIG. 4, the n-In _0.48 Ga _0.52 P current blocking layer 112 is selectively grown to 1.4 μm, and the p-In _0.48 Ga _0.52 P protection layer 113 is sequentially grown to 0.2 μm. p-In _0.48 Ga _0.52 P
The protective layer 113 is inserted to avoid forming a pn junction at the regrowth interface.

In this selective growth, growth is prevented only in a very narrow region of 3 μm width, and since the growth is on the (100) plane, the growth can be performed almost in the same manner as the entire growth on the flat surface. When the direction of the stripe is the [011] direction, the side surface of this selective growth is a (111) B surface that is obliquely inclined.

After the selective growth, as shown in FIG. 5, the silicon oxide film 111 is removed with buffered hydrofluoric acid or the like, and the upper portion is buried to form a p-Al _0.33 Ga _0.67 As cladding buried layer 114 and an upper portion thereof. Then, ap ⁺ -GaAs contact layer 115 is grown to 0.4 μm.

Further, a front surface electrode 116 covering the entire upper surface is formed by vapor deposition or sputtering, and the rear surface is polished to a thickness of 100 μm to form a rear surface electrode 117 under the n-type GaAs substrate 101.

This wafer was cleaved to a cavity length of 500 μm, and a front end face coating film having a reflectance of 6% was applied.
When a rear end face coating film having a reflectance of 0% was formed and the light output characteristics were evaluated, a semiconductor laser having a threshold current of 10 mA and a slope efficiency of 1.0 W / A was obtained.

Further, the p-In _0.48 Ga _0.52 P light guide layer 110 may be made of InGaAsP quaternary mixed crystal lattice-matched to GaAs. As shown in FIG.
Since the n _0.48 Ga _0.52 P light guide layer 110 functions as a barrier for hole injection, this can be eliminated by using InGaAsP.

Further, in the above embodiment, the oscillation wavelength is set to 0.1.
In a 98 μm band semiconductor laser, In
Although the case of using the GaP system has been described, InGaAsP / I
1.3-1.6 μm band nP-based semiconductor laser, In
The present invention can be applied to a case where GaAlAs or InAlAs is used as a block layer. The advantage of using the InAlAs mixed crystal as the block layer is that InGaAsP /
Since the band discontinuity of the conduction band is larger than that of InP,
The point is that electrons having a small effective mass can be effectively blocked.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

The second embodiment is obtained by applying the first embodiment to a spot size conversion element. FIG. 7 is a perspective view showing a stage during the manufacturing process of the spot size conversion element.

In order to enhance the optical coupling efficiency between the laser beam and the optical fiber, a laser having a low radiation angle is effective. For that purpose, a spot size conversion element in which light confinement is changed in the direction of the resonator is used. Can be At this time, it is necessary to narrow the effective width of the active layer to, for example, about 0.4 μm. Moreover, it can be said that it is impossible to produce. However, if it is manufactured by selective growth, it results in the problem of patterning the growth-blocking mask, so that it is possible to manufacture without any problems.

In the second embodiment of the present invention, the first MOVPE growth method is exactly the same as in the first embodiment. That is, in the first MOVPE growth, the n-GaAs buffer layer 102 is formed to have a thickness of 0.5 μm and n-Al _0.33 Ga _0.67 A
The s-cladding layer 103 is continuously grown to 2 μm, the SCH-strained MQW layer 4 is grown to 67 nm, and the p-In _0.48 Ga _0.52 P light guide layer 110 is grown to 50 nm.

The subsequent formation of the silicon oxide film 111
Unlike the first embodiment, as shown in FIG. 7, in the pattern of the silicon oxide film 111, a portion having a width of 3 μm has a length of 300 μm, and a portion having a length of 100 μm is applied to obtain a pattern of 0.4 μm.
It is tapered to a width of μm. Using this silicon oxide film 111 as a growth inhibition mask, a second MOVPE growth is performed to form an n-In _0.48 Ga _0.52 P current blocking layer 11.
2, 1.4 μm, p-In _0.48 Ga _0.52 P protective layer 113
Is selectively grown by 0.2 μm.

After this selective growth, the silicon oxide film 111
Is removed with buffered hydrofluoric acid, and the upper portion is buried to form a p-Al _0.33 Ga _0.67 As cladding buried layer 114,
On top of this, ap ⁺ -GaAs contact layer 115
grow by μm. The subsequent electrode formation is the same as in the first embodiment.

When this wafer is cleaved to a length of 400 μm and coated with an end face to form a semiconductor laser, light confinement in the lateral direction becomes weak at the end face where the opening width of the current block layer is 0.4 μm. As a result, the spot size becomes large, so that a laser beam with a low radiation angle can be extracted.
The radiation angle is 10 ° in full width at half maximum, and the coupling efficiency with the fiber when modularized can be reduced to 1 dB.

Next, a third embodiment of the present invention will be described with reference to the drawings.

In the first embodiment described above, a semiconductor laser having an oscillation wavelength in the 0.98 μm band has been described. However, in this embodiment, the same semiconductor laser emitting red light as that described as an example of the prior art is used. Related to laser. The structure of the semiconductor laser is different from that described in the related art in the shape of the InGaP protective layer 113. Also, as a manufacturing method,
n-In _0.48 (Ga _0.3 Al _0.7 ) _0.52 There is a difference between the formation of the shape of the P current block layer 212 by etching or by selective growth.

Referring to FIG. 8, first, on an n-type GaAs substrate 101 having a (100) plane orientation,
After growing the n-GaAs buffer layer 102 to 1 μm, the n-In _0.48 (Ga _0.6 Al _0.4 ) _0.52 P cladding layer 203 is 1 μm, and the In _0.48 (Ga _1-x Al _x ) _0.52 P
Layer 204, In _0.48 (Ga _0.6 A
l _0.4 ) _0.52 P The first light guide layer 209 is 150 nm, p
-In _0.48 Ga _0.52 P The second optical guide layer 110 has a thickness of 10 nm.
grow up.

Next, a silicon oxide film (not shown) is formed on the entire surface, the resist is patterned in a stripe shape by photolithography, and the silicon oxide film is etched by dry etching. As a result, the width of 3 μm
A silicon oxide film is formed in a stripe shape. Using this as a growth inhibition mask, n-In _0.48 (Ga _0.3 Al
_0.7 ) _0.52 P current blocking layer 212 is 1 μm, and
A p-In _0.48 Ga _0.52 P protective layer 113 is formed on the
nm, selectively grown by MOVPE. This p-In
_0.48 Ga _0.52 P protective layer 113 is formed of n-In _0.48 (Ga
_0.3 Al _0.7 ) _0.52 P has a function of preventing the surface of the upper part of the P current block layer 212 from being oxidized.
Since it grows with a thickness of m, oxidation of the regrowth interface can be prevented on all surfaces.

Next, the silicon dioxide film is removed and p-
In _0.48 (Ga _0.6 Al _0.4 ) _0.52 P cladding layer 214
Buried growth, followed by p ⁺ -GaAs contact layer 1
Grow 15

Next, the surface electrode 16 is formed by a vapor deposition method or a sputtering method. Subsequently, the back surface is polished so that the thickness of the wafer is 100 μm, and the back surface electrode 17 is entirely formed.

This wafer was cleaved to a cavity length of 300 μm, and a front end face coating film having a reflectivity of 30% was applied.
When a rear end face coating film having a reflectance of 90% was formed, a semiconductor laser device having a threshold current of 15 mA and a slope efficiency of 0.8 W / A was obtained.

According to the third embodiment, even if the block layer is a mixed crystal containing Al, the surface thereof is covered with the InGaP protective layer containing no Al in a self-aligning manner during selective growth. For this reason, an effect that the block layer is protected from oxidation in a subsequent step is exhibited.

Although a dielectric film, in particular, a silicon oxide film is used as a growth inhibiting mask in the above embodiment, it may be a silicon nitride film or a silicon oxynitride film. In addition, a chemical vapor deposition method, a sputtering method, or the like may be used for forming these dielectric films, but it goes without saying that other methods may be used.

In the above embodiments, a group III-V compound semiconductor is taken as an example. However, a group II-VI compound semiconductor may be further combined with a group III-V or II-VI compound semiconductor. It may be a compound semiconductor.

[0072]

The first effect of the manufacturing method of the present invention is that the effective active layer width of the semiconductor laser can be manufactured with good uniformity, good controllability and good reproducibility, so that good optical output characteristics can be obtained. Can be obtained stably. The variation in threshold current and slope efficiency has been reduced to half of the conventional level. Since the variation is reduced as described above, the width of the active layer can be accurately controlled to the optimum design value, and the characteristics of the threshold current and the slope efficiency are improved by about 10% as an average value.

The reason for this is that the effective active layer width is determined by the patterning accuracy of the dielectric film, and is therefore ± 0.2%.
This is because the variation can be suppressed to within μm.

The second effect is that the reliability of the device is improved even when a mixed crystal containing Al is used for the current blocking layer, and a life of 100,000 hours or more can be stably obtained. .

This is because there is no step of exposing Al to the atmosphere since wet etching is not used. When a crystal containing Al is exposed to the atmosphere, the surface is oxidized, and this becomes a source of growth of crystal defects.
This is essential for ensuring reliability. According to the present invention, a SAS laser structure in which a mixed crystal containing Al is used for a current block layer has been realized.

[Brief description of the drawings]

FIG. 1 is a process chart showing one embodiment of an optical semiconductor device of the present invention.

FIG. 2 is a sectional view showing one embodiment of the optical semiconductor device of the present invention.

FIG. 3 is a process chart of one embodiment of a method for manufacturing an optical semiconductor device of the present invention.

FIG. 4 is a process drawing following FIG. 3;

FIG. 5 is a view showing a step subsequent to that of FIG. 4;

FIG. 6 is a band diagram of the optical semiconductor device of the present invention.

FIG. 7 is a perspective view illustrating a manufacturing process of a second embodiment of the method for manufacturing an optical semiconductor device of the present invention.

FIG. 8 is a sectional view showing a third embodiment of the present invention.

FIG. 9 is a sectional view showing a conventional semiconductor laser.

FIG. 10 is a cross-sectional view showing another conventional semiconductor laser.

[Explanation of symbols]

Reference Signs List 1 n-type substrate 2 n-buffer layer 3 n-cladding layer 4 SCH-strained MQW layer 10 p-light guide layer 11 dielectric film 12 n-current blocking layer 13 p-protection layer 14 p-cladding buried layer 15 p ⁺ −contact layer 16 front electrode 17 back electrode 101 n-type GaAs substrate 102 n-GaAs buffer layer 103 n-Al _0.33 Ga _0.67 As cladding layer 105 n-GaAs guide layer 106 compressive strain In _0.24 Ga _0.76 As well layer 107 GaAs barrier Layer 108 GaAs guide layer 109 n-In _0.48 Ga _0.52 P light guide layer 110 p-In _0.48 Ga _0.52 P light guide layer 111 silicon oxide film 112 n-In _0.48 Ga _0.52 P current block layer 113 p-In _0.48 Ga _0.52 P protective layer 114 p-Al _0.33 Ga _0.67 As clad buried layer 115 p ⁺ -Ga s contact layer _{203 n-In 0.48 (Ga 0.6} Al 0.4) 0.52 P cladding layer _{204 In 0.48 (Ga 1-x} Al x) 0.52 active layer 208 an In _0.48 of P layer (Ga _0.6 Al _{0.4) 0.52} P first light Guide layer 210 p-In _0.5 Ga _0.5 P second optical guide layer 212 n-In _0.48 (Ga _0.3 Al _0.7 ) _0.52 P current blocking layer 214 p-In _0.48 (Ga _0.6 Al _0.4 ) _0.52 P cladding layer

Claims (14)

[Claims] 1. A method of manufacturing an optical semiconductor device having a current blocking layer for narrowing a current injected into an active layer, comprising a step of forming the current blocking layer on a flat crystal surface by selective growth. Manufacturing method of an optical semiconductor device. 2. A method for manufacturing an optical semiconductor device having a current blocking layer for confining a current injected into an active layer, wherein a step of providing a growth inhibiting mask on a flat crystal face and a step of forming the growth inhibiting mask are performed. Forming the current blocking layer by performing selective growth on a crystal plane by metal organic chemical vapor deposition. 3. A first conductive type clad layer, an active layer, and a second conductive type light guide layer having a larger forbidden band width and a smaller refractive index than the active layer on a semiconductor substrate of the first conductive type. Sequentially growing, forming a growth blocking mask extending in a stripe shape in the light guiding direction on the light guide layer, and forming a first conductivity type on the light guide layer on which the growth blocking mask is formed. A step of selectively growing a current blocking layer, and a step of growing a second conductivity type cladding layer on the light guide layer covered with the current blocking layer and the growth blocking mask after removing the growth blocking mask. And a method for manufacturing an optical semiconductor device. 4. The method according to claim 1, further comprising: removing the growth inhibiting mask;
4. The method of manufacturing an optical semiconductor device according to claim 3, further comprising a step of selectively growing a second conductive type protective layer on the exposed surface of the conductive type current blocking layer. 5. The method according to claim 4, wherein said current blocking layer is a compound semiconductor crystal containing aluminum, and said protective layer is a compound semiconductor crystal not containing aluminum. 6. The method of manufacturing an optical semiconductor device according to claim 5, wherein the compound semiconductor crystal not containing aluminum is a mixed crystal of three or more elements. 7. A method for manufacturing an optical semiconductor device having a current blocking layer for confining a current injected into an active layer, wherein a stripe-shaped growth is performed on a flat crystal plane, the width of which is changed along a light guiding direction. An optical semiconductor device comprising: a step of providing a blocking mask; and a step of forming the current block layer by performing selective growth by metalorganic chemical vapor deposition on a flat crystal surface on which the growth blocking mask is formed. Manufacturing method. 8. The method of manufacturing an optical semiconductor device according to claim 7, further comprising the step of forming a light emitting end face in a portion of the growth blocking mask where the stripe width is small. 9. The method of manufacturing an optical semiconductor device according to claim 1, wherein said optical semiconductor device is made of a group III-V compound semiconductor or a group II-VI compound semiconductor. 10. The method of manufacturing an optical semiconductor device according to claim 1, wherein said growth blocking mask is made of a dielectric film. 11. A first conductivity type cladding layer, an active layer, and a second conductivity type light guide layer having a larger forbidden band width and a smaller refractive index than the active layer, which are sequentially stacked on a semiconductor substrate of the first conductivity type. And a current blocking layer of the first conductivity type. The groove extends in the current blocking layer in the light guiding direction, and has a depth reaching the light guide layer from the upper surface of the current blocking layer. A protection layer of a second conductivity type on an upper surface of the current blocking layer and a side surface of the groove, and a cladding layer of the second conductivity type on a bottom surface of the groove and an entire upper surface of the protection layer. Optical semiconductor device. 12. The optical semiconductor device according to claim 11, wherein said current blocking layer is a compound semiconductor mixed crystal containing aluminum, and said protective layer is a compound semiconductor mixed crystal not containing aluminum. 13. The optical semiconductor device according to claim 11, wherein a width of said groove changes along a light guiding direction. 14. The optical semiconductor device according to claim 11, wherein the width of the groove is smaller at the light emitting end face than at the other end face.