JP2830813B2 - Manufacturing method of self-pulsation type semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a self-oscillation type AlG
The present invention relates to a method for manufacturing an aInP-based red semiconductor laser.

[0002]

2. Description of the Related Art AlGa oscillating at 630 to 690 nm
InP-based red semiconductor lasers have been put to practical use as light sources for barcode readers and pointers. In the future, high-density CD-ROM and digital video disk (DVD)
In order to expand applications as a light source for
A semiconductor laser having an oscillation wavelength of 0 nm and being hardly affected by return light is required. As such a semiconductor laser, there is a self-pulsation type in which a self-pulsation phenomenon occurs due to light loss in the saturable absorption layer.

The following are examples of the self-excited oscillation type semiconductor laser as described above.

[0004] 1. By increasing the number of wells (wells) in the active layer as compared with a normal laser, light loss (absorption) is increased and self-pulsation is obtained.

[0005] 2. A self-excited oscillation is obtained by using a region excluding the lower portion of the ridge forming the active layer (the active layer region where no current is injected) as a saturable absorbing layer.

FIG. 5 shows AlGa disclosed in the proceedings of the 11th Laser Diode Symposium (March 8, 1994).
FIG. 4A is a view showing the structure of an InP-based laser, and FIG.
(B) shows the AlG described in JP-A-62-97389.
FIG. 2 is a diagram illustrating a structure of an aAs-based self-pulsation type laser.

First, a method of manufacturing the AlGaInP-based laser shown in FIG. 5 will be briefly described. First, n-type GaAs was formed using a metal organic chemical vapor deposition (hereinafter referred to as MOVPE) apparatus.
An n-type GaInP buffer layer 502, n
Mold (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 503,
Ga _0.58 In _0.42 P and _{(Al 0.5 Ga 0.5) 0.5 In} 0. 5 P
(Al _0.7 Ga _0.3 ) _0.5 In in which a strained multiple quantum well active layer 504 made of and a p-type multiple quantum barrier layer 505 are inserted.
_{A 0.5} P cladding layer 506 and a p-type Ga _0.5 In _0.5 P contact layer 507 are sequentially grown.

Next, the heterostructure substrate is taken out of the MOVPE apparatus, and a silicon oxide film is deposited. Subsequently, the silicon oxide film is formed to a thickness of 5 μm by photolithography.
Process into stripes of width. Further, a ridge is formed on the heterostructure substrate using the silicon oxide film as a mask,
The n-type GaAs current blocking layer 508 is selectively grown by introducing it again into the MOVPE apparatus. Then, after taking out from the MOVPE apparatus, removing the silicon oxide mask, M
A p-type GaAs contact layer 509 is grown by an OVPE apparatus. Then, by forming the n-side electrode 510 and the p-side electrode 511, the laser structure shown in FIG. 5 is obtained. Such a manufacturing method is exactly the same as a normal ridge stripe type semiconductor laser manufacturing method.

Next, Japanese Patent Application Laid-Open No. 62-973 shown in FIG.
No. 89, an AlGaAs self-pulsation type laser will be described. In this semiconductor laser, Zn is diffused into a part of the current non-injected active layer, and the carrier lifetime in this region is reduced to be used as a saturable absorbing layer. In this laser manufacturing method, a step of depositing a silicon oxide film for diffusing Zn and opening a striped window is required.

[0010]

In the self-pulsation type laser shown in FIG. 5 in which the active layer is a saturable absorption layer, self-pulsation is obtained by increasing the number of wells in the active layer. There is a problem that a current (threshold current) for obtaining laser oscillation increases. Increasing the threshold current reduces the reliability of the laser. In fact, papers and academic conferences have not reported the reliability of the self-pulsation type laser having such a structure.

In the laser shown in FIG. 4 in which a part of the active layer in which Zn is diffused is used as a saturable absorbing layer, a step for selectively diffusing Zn is required. The problem is that the yield is reduced due to complexity.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and suppresses a rise in threshold current and provides a highly reliable self-pulsation type semiconductor laser with a high yield. An object is to realize a manufacturing method that can be easily manufactured.

[0013]

According to the present invention, there is provided a method of manufacturing a self-pulsation type semiconductor laser, comprising the steps of:
First conductivity type AlInP or AlGaInP cladding layer, active layer, second conductivity type AlInP or AlGaIn
A first step of sequentially growing a P-cladding crystal to form a double hetero structure; and depositing an insulating film on the double hetero structure manufactured by the first step, and selectively etching the stripe to form a stripe. A second step of forming a mask, a third step of selectively etching the second conductivity type cladding layer halfway using the mask to form a ridge in the second conductivity type cladding layer, A fourth step in which a semiconductor layer is further laminated on the second conductivity type clad layer having the ridge formed thereon while the mask is mounted, and a selective burying growth for embedding the ridge structure in the semiconductor layer is performed; possess a fifth step of adding an impurity with a diffusion of impurities in a portion except for the active layer in the semiconductor layers directly below the ridge, which current is injected out of the layers, the striped Ma
On the second conductivity type clad layer on which a ridge is formed using a mask
During the fourth step of further laminating the semiconductor, the ridge
By adding strain only to nearby flats,
The second conductivity type cladding layer at the time of the fifth step performed
Ridge into which current in active layer is doped
It is characterized in that it is diffused to portions other than immediately below .

[0014] Self-excited oscillation of the present invention according to another aspect of the present invention
Manufacturing method of a semiconductor laser of the first conductivity type
The first conductivity type AlInP or AlGaInP
Layer, active layer, second conductivity type AlInP or AlGa
The InP cladding layer is grown sequentially by crystal growth to form a double heterostructure.
A first step of manufacturing a structure, and a first step of manufacturing the structure.
An insulating film on the double heterostructure
To form a striped mask by etching
And the second conductivity type cladding using the mask.
The layer is selectively etched partway and the second conductivity type cladding is
A third step of forming a ridge in the pad layer;
The second conductivity type having a ridge formed in a mounted state;
A semiconductor layer is further laminated on the cladding layer, and the ridge structure is formed.
For performing selective burying growth by embedding in the semiconductor layer.
Process and the active layer directly under the ridge into which the current is injected.
Using the diffusion of impurities between semiconductor layers in the part except the conductive layer
A fifth step of adding an impurity, the striped
Second conductivity type cladding with ridge formed using mask
In a fourth step of further laminating the semiconductor on the layer,
The composition in the carrier is (Al _Y Ga _{1 -Y} ) _X In _{1 -X} P (Y = 0 to
1, X = 0.15-0.4 or 0.65-0.9)
By selectively growing certain layers,
In the fifth step performed, the second conductive type clad layer
Doped impurities are directly injected into the ridge where the current in the active layer is injected.
It is characterized by being diffused to parts other than below .

According to still another aspect of the present invention, the
The method of manufacturing the excited oscillation type semiconductor laser includes the first conductivity type GaAs.
s substrate, a first conductivity type AlInP or AlGaIn
P cladding layer, active layer, second conductivity type AlInP or A
Crystal growth of the lGaInP cladding layer is performed in
A first step of preparing a heterostructure, in the first step
Depositing an insulating film on the fabricated double heterostructure,
Selectively etch to form striped mask
That a second step, the second conductivity type click using the mask
The lad layer is selectively etched partway, and the second conductive
A third step of forming a ridge type cladding layer, said Ma
With the disk mounted, the second ridge is formed.
A semiconductor layer is further laminated on the conductive cladding layer, and the
Selective buried growth for embedding a semiconductor structure in the semiconductor layer
Fourth step, the ridge of the active layer into which the current is injected.
Impurity diffusion between semiconductor layers in the part except the lower active layer
A fifth step of adding an impurity, the using, Stra
A second conductivity type mask having a ridge formed using an
At the time of the fourth step of further laminating the semiconductor on the lad layer
Then, the second conductivity type AlGaInP is selectively buried and grown.
Thus, at the time of the subsequent fifth step,
Impurity doped into the two-conductivity-type cladding layer is applied to the current in the active layer.
Is diffused to the part other than the area just below the ridge where the
Features .

[0016]

[Operation] The operation of the method of manufacturing the self-pulsation type semiconductor laser of the present invention configured as described above will be described below.

FIG. 2 is a view showing the structure of a self-pulsation type AlGaInP laser manufactured by the manufacturing method according to the present invention. Basically, it has a ridge stripe type structure like the laser shown in FIG.
_0.25 In _0.75 P is used. In the active layer in the current non-injection region, Zn is diffused from a Zn-doped AlGaInP clad layer using general Zn as a dopant for the p-type clad layer, thereby forming a saturable absorbing layer.

FIG. 3 shows Si-doped Al _X In _{1 -X} P / Zn-doped (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P / non-doped Ga.
₄ shows a profile of Zn concentration in a multilayer structure of a _0.5 In _0.5 P / GaAs substrate.

When the composition of AlInP is lattice-matched (X = 0.5), Zn diffusion into GaInP is small. In contrast, when X = 0.25 and no lattice matching, Zn is deeply diffused in GaInP. This is because tensile strain due to lattice mismatch is caused by Zn-doped Al.
This is because it acts on GaInP to promote Zn diffusion. Therefore, as shown in FIG. 2, the diffusion of Zn can be promoted by employing an AlInP layer deviated from the lattice matching condition as the selective burying layer. And the composition in that case is also X = 0.15 to 0.4 or 0.65 to X5.
By setting the ratio to 0.9, Zn diffusion is promoted only in the active layer region where no current is injected.

The reason for the above is that the ridge side surface formed by the (111) A surface and the flat portion same as the (001) surface, which is usually used as the substrate surface, has different composition ratios of Al and In, so that the composition is different. Is different. When the distance between the ridges formed on the substrate is 100 μm or more,
When the composition on the (001) plane is shifted from the lattice matching condition by an Al composition X = 0.15 to 0.4, the composition on the (111) A plane is X = 0.45 to 0. This is because Zn diffusion hardly occurs below the ridge. When the distance between the ridges is 50 μm or less, the composition on the (001) plane deviates from the lattice matching condition.
When l composition X = 0.65 to 0.9, the composition on the (111) A plane is X = 0.45 to 0.55 close to the lattice matching condition, and similarly, Zn diffusion hardly occurs below the ridge. That's why.

In the manufacturing method according to the present invention, since a step of selectively diffusing Zn is not newly added, a self-pulsation type laser can be easily manufactured in the same step as the conventional manufacturing method of the ridge stripe type laser. .

[0023]

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

FIG. 2 is a cross-sectional view of the structure 63 manufactured by the method of the present invention.
1 is a cross-sectional view illustrating a structure of a 0 nm band AlGaInP-based self-excited oscillation semiconductor laser.

As shown in FIG. 2, the present semiconductor laser comprises a Si-doped n-type GaAs buffer layer 202 (thickness: d = 0.5 μm) on a Si-doped n-type GaAs substrate 201.
m), Si-doped n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P
Clad layer 203 (d = 0.8 μm), non-doped (A
l _0.5 Ga _0.5 ) _0.5 In _0.5 P light guide layer 204 (d = 5
0 nm) and non-doped Ga _0.58 In
_0.42 P well (d = 8 nm = 4 layers) and non-doped (Al
_0.5 Ga _0.5 ) _0.5 In _0.5 P barrier (d = 5 nm: 3 layers)
Strained multiple quantum well layer composed of non-doped (Al _0.5 Ga
_0.5 ) _0.5 In _0.5 P light guide layer 206 (d = 50n)
m), Zn-doped p-type _{(Al 0.7 Ga 0.3) 0.5 In} 0 .5 P
Cladding layer 207 (d = 0.8 μm), Zn-doped p-type Ga _0.5 In _0.5 P heterobuffer layer 208 (d = 0.1
μm), non-doped Al _0.25 In _0.75 P buried layer 20
9 (d = 0.2 μm), Si-doped n-type GaAs current blocking layer 210 (d = 0.5 μm), Zn-doped p-type G
an n-side electrode 212 and a p-type contact layer 211 on the back surface of the substrate.
It has a selective buried ridge stripe structure having a p-side electrode 213 thereon.

Next, the manufacturing method of the present invention will be described. 1A to 1D are cross-sectional views showing a manufacturing method of this embodiment in the order of steps.

The semiconductor laser of the present embodiment has three MOVs.
It is produced by PE crystal growth. The reaction tube was a water-cooled horizontal type, and an RF coil was used for heating the substrate. AlGa as raw material
For growth of InP, GaInP, and AlInP, trimethylaluminum (TMAl), triethylgallium (TE)
Ga), trimethylindium (TMIn) and phosphine (PH ₃ ) were used, and trimethyl gallium (TMGa) and arsine (AsH ₃ ) were used for GaAs growth.

As the n-type and p-type dopants, disilane (Si ₂ H ₆ ) and diethyl zinc (DEZn) were used. The growth temperature was 660 ° C., and the growth pressure was 70 torr. The growth rates are AlGaInP, AlInP, GaI
1.8 μm / hr for nP, 4.5 μm / hr for GaAs
It is.

First, the n-type GaAs substrate 101 is dissolved in a sulfuric acid-based solution.
After cleaning the surface by etching with a liquid, the MOVPE
The n-type GaAs buffer layer 102,
(Al_0.7Ga_0.3)_0.5In_0.5P cladding layer 103,
Doped (Al_0.5Ga_0.5) _0.5In_0.5P light guide layer 1
04, active layer 105, non-doped Al_0.5Ga_0.5)_{0. Five}
In_0.5P light guide layer 106, p-type (Al_0.7Ga_0.3)
_0.5In_0.5P cladding layer 107, p-type Ga_0.5In_0.5P
The hetero-buffer layer 108 is sequentially grown, and as shown in FIG.
The heterostructure shown is obtained.

After being taken out of the reaction tube, thermal CVD (40
(0 ° C.) to deposit silicon oxide to a thickness of 0.3 μm. Next, this silicon oxide is etched into a stripe shape having a width of 4 μm by a photolithography technique to form a silicon oxide mask 114, and the structure shown in FIG. 1B is obtained.

Next, using the silicon oxide mask 114 as a mask, the p-type Ga _0.5 In _0.5 P hetero buffer layer 10 is used.
8, p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 1
07 is selectively etched to form a ridge structure shown in FIG.

This substrate is placed in the reaction tube again, and a non-doped Al _0.25 In _0.75
P buried layer 109, n-type GaAs current blocking layer 11
0 is continuously and selectively grown to obtain the structure shown in FIG. Here, Al _X In _{1 -X} P grown on the side of the ridge which is the (111) A plane is lattice-matched with an Al composition x = 0.5, while X = X in a flat portion of the (001) plane. 0.2
Since it is 5, tensile strain due to lattice mismatch acts on the p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer.

After removing the silicon oxide mask 114 from the reaction tube and removing the silicon oxide mask 114, the silicon oxide mask 114 is set in the reaction tube again and p
A type GaAs contact layer is grown. During this process, the p-type (Al _0.7 G
a _0.3 ) _0.5 In _0.5 P clad layer 107 to active layer 10
5 diffuses Zn. Then, the substrate 101 is taken out from the reaction tube, and the substrate 101 is polished. After that, an n-side electrode on the back surface of the substrate and a p-side electrode on the p-type GaAs contact layer are formed to obtain a semiconductor laser having a structure shown in FIG.

The manufactured laser has a cavity length of 500 μm.
And a 30% -80% end face coating was applied. When the oscillation spectrum was measured, a multi-longitudinal mode oscillation having a wide spectrum width unique to self-excited oscillation was obtained, and the center oscillation wavelength was 637 nm. Measurement of current-light output characteristics. The threshold current at room temperature was 45 mA.
Laser oscillation was obtained at a lower threshold value as compared with the conventional laser which obtains self-pulsation by increasing the number of wells of the active layer shown in the conventional example. In addition, self-excited oscillation was obtained up to an optical output of 7 mW. Furthermore, from a 1/4 size wafer of a 2 inch substrate, 1
When 00 lasers were taken out and their characteristics were evaluated, the ratio of lasers oscillating at a threshold current of 50 mA or less was 80%.
%, Which is not different from the normal laser yield.

In the embodiment described above, AlIn
Although the case where P is used for the buried layer is shown, the same structure can be obtained when GaInP is used. The combination using Ga _X In _{1 -X} P as the buried layer is set so that the Ga composition X on the (001) plane, which is the flat portion, becomes 0.3. In this case, the composition on the (111) A plane which is the ridge side surface is X
= 0.5 and lattice matching. As a result, Zn diffuses only in the active layer region where no current is injected, and a desired structure is obtained. However, Ga _X In _1-X for P is a refractive index smaller band gap larger than that of _{Al X In 1-X P,} 650~
It can be used for a laser having an oscillation wavelength at 680 nm.

Also, when (Al _Y Ga _{1 -Y} ) _X In _{1 -X} P is used, X = 0.15 to 0.4 or 0.65 to 0.5.
Although a desired structure can be obtained by setting it to 9, the refractive index can be changed by changing the ratio (Y) of Al and Ga, so that the degree of freedom in transverse mode control can be given.

In this embodiment, the case where non-doped AlInP is used as the buried layer 109 in the step of FIG. 1D has been described. However, a desired structure can be obtained also by using Zn-doped AlInP. In particular, when Zn-doped AlInP is used, in addition to the effect of lattice distortion, the effect of extrusion diffusion is added by Zn doped into the AlInP layer, so that Zn diffusion can be promoted with a small lattice distortion.

In this embodiment, the case where the trapezoidal ridge having the (111) A surface formed by wet etching is described. However, even when the rectangular ridge is formed by dry etching such as reactive ion etching. Manufacturing methods can be applied. In this case, the ridge side surface is (11
The desired structure can be easily obtained in the same manner as in this embodiment by making the lattice mismatch on the (001) plane and the lattice mismatch on the (001) plane, which is the flat part.

Further, in this embodiment, Zn was used as a dopant for the p-type cladding layer, but magnesium (Mg),
Even if beryllium (Be) is used, a desired structure can be manufactured in a similar manufacturing process. Also, the material is AlGaInP
Although the case of the system has been described, the present invention can be applied to an AlGaAs-based laser lattice-matched to a GaAs substrate similarly to this system.

[0040]

The present invention has the following effects by being configured as described above.

In the manufacturing method according to the present invention, an impurity is doped into the active layer region into which no current is injected, thereby increasing the optical loss (absorption) in that region. Therefore, there is an effect that a highly reliable self-pulsation type semiconductor laser can be manufactured.

Further, AlInP, GaInP, A lattice-mismatched in a flat portion near the ridge as a selective burying layer.
By diffusing impurities doped into the p-type cladding layer into the active layer region except for the lower portion of the ridge by using lGaInP, a self-pulsation type semiconductor laser can be easily manufactured with good yield in the same manufacturing process as before. There is.

[Brief description of the drawings]

FIGS. 1A to 1D are cross-sectional views in a process order for explaining a manufacturing method of the present invention.

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

FIG. 3 shows Si—AlInP / Zn—AlGaInP / G
3 is a Zn profile in a multilayer structure of an aInP / GaAs substrate.

FIG. 4 is a diagram showing a configuration of an AlGaAs-based self-pulsation laser in which a part of an active layer in which Zn is diffused is used as a saturable absorption layer.

FIG. 5 is a diagram showing a configuration of a ridge stripe type AlGaInP-based self-excited oscillation laser having an active layer as a saturable absorption layer.

[Explanation of symbols]

101, 201 n-type GaAs substrate 102, 202 n-type GaAs buffer layer 103, 203 n-type AlGaInP cladding layer 104, 204 non-doped AlGaInP light guide layer 105, 205 strained multiple quantum well cleanliness layer 106, 206 non-doped AlGaInP light guide layer 107 , 207 p-type AlGaInP cladding layer 108, 208 p-type GaInP heterobuffer layer 109, 209 non-doped AlInP buried layer 110, 210 n-type GaAs current block layer 114 silicon oxide mask 211 p-type GaAs contact layer 212 n-side electrode 213 p-side electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/18

Claims (3)

(57) [Claims] A first conductive type AlInP or AlGaInP clad layer, an active layer, and a second conductive type AlInP or AlGaInP clad layer are sequentially crystal-grown on a first conductive type GaAs substrate to form a double heterostructure. A second step of depositing an insulating film on the double heterostructure manufactured in the first step and selectively etching to form a stripe-shaped mask; and A third step of selectively etching the two-conductivity-type clad layer halfway to form a ridge on the second-conductivity-type clad layer; and, with the mask mounted, the second conductive A semiconductor layer is further laminated on the mold cladding layer,
A fourth step of performing selective burying growth in which the ridge structure is buried in the semiconductor layer, and using a diffusion of impurities between semiconductor layers in a portion of the active layer other than the active layer immediately below the ridge into which current is injected. possess a fifth step of adding the second conductive forming a ridge by using a stripe-shaped mask
Fourth step of further laminating the semiconductor on the electric cladding layer
At this time, strain should be added only to the flat part near the ridge.
By the above, at the time of the subsequent fifth step, the second
The current in the active layer is
A method of manufacturing a self-pulsation type semiconductor laser, wherein the semiconductor laser is diffused into a portion other than immediately below a ridge to be injected . 2. A first conductive type GaAs substrate, comprising : a first conductive type GaAs substrate;
AlInP or AlGaInP cladding layer, active
Layer, second conductivity type AlInP or AlGaInP
Layers are sequentially grown to form a double heterostructure
A first step and a double heterostructure formed in the first step.
Deposit insulating film and selectively etch stripe
A second step of forming a mask in the shape of a circle, and using the mask to form the second conductive type cladding layer in the middle.
To selectively etch the second conductive type cladding layer.
A third step of forming a ridge, and before the ridge is formed, with the mask mounted.
Further laminating a semiconductor layer on the second conductivity type cladding layer,
Selective buried growth for embedding the ridge structure in the semiconductor layer
And removing the active layer immediately below the ridge into which the current is injected from the active layer.
Impurity by using diffusion of impurity between semiconductor layers
A fifth step of adding the second conductive forming a ridge by using a stripe-shaped mask
Fourth step of further laminating the semiconductor on the electric cladding layer
The composition in the flat part is (Al _Y Ga _1-Y ) _X In _1-X
P (Y = 0 to 1, X = 0.15 to 0.4 or 0.65
-0.9) by selectively burying the layer.
Therefore, at the time of the subsequent fifth step, the second conductivity type
The impurity doped in the cladding layer is injected by the current in the active layer.
A method of manufacturing a self-pulsation type semiconductor laser, wherein the semiconductor laser is diffused to a portion other than immediately below the ridge . 3. A first conductive type GaAs substrate having a first conductive type
AlInP or AlGaInP cladding layer, active
Layer, second conductivity type AlInP or AlGaInP
Layers are sequentially grown to form a double heterostructure
A first step and a double heterostructure formed in the first step.
Deposit insulating film and selectively etch stripe
A second step of forming a mask in the shape of a circle, and using the mask to form the second conductive type cladding layer in the middle.
To selectively etch the second conductive type cladding layer.
A third step of forming a ridge, and before the ridge is formed, with the mask mounted.
Further laminating a semiconductor layer on the second conductivity type cladding layer,
Selective buried growth for embedding the ridge structure in the semiconductor layer
And removing the active layer immediately below the ridge into which the current is injected from the active layer.
Impurity by using diffusion of impurity between semiconductor layers
A fifth step of adding the second conductive forming a ridge by using a stripe-shaped mask
Fourth step of further laminating the semiconductor on the electric cladding layer
In this case, the second conductivity type AlGaInP is selectively buried.
In the case of the fifth step to be performed subsequently,
An impurity doped in the second conductivity type cladding layer into the active layer.
Diffusion into areas other than the area under the ridge where current is injected
A method for manufacturing a self-sustained pulsation type semiconductor laser.