JP2002280670A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable laser with good yield in the laser where a semiconductor which includes Al such as AlInP or AlGaInP and in which a lattice constant changes by a composition is used for a current block layer. SOLUTION: The semiconductor laser has a first conductive clad layer 103, an active layer 105, a second conductive clad layer 107 having a ridge shape, and the current block layer 109 constituted of a first conductive semiconductor whose refractive index is smaller than the second conductive clad layer 107. The current block layer 109 is constituted of two types of semiconductors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a buried ridge type semiconductor laser used for a light source of an optical disk system.

[0002]

2. Description of the Related Art AlGaInP red semiconductor lasers (λ
= 660 nm) for DVD-ROM, DVD-RAM,
It is used as an optical pickup light source for DVD players. Generally, this laser uses a ridge-type stripe structure. In this case, the lateral mode is controlled by utilizing the light absorption of the n-type GaAs used for the current blocking layer.

[0003] The n-type GaAs current blocking layer absorbs light, and waveguide loss occurs in this laser structure. As a result, the threshold current increases, and the external differential quantum efficiency decreases, so that the operating current increases. As a result, the reliability of the laser decreases. Therefore, in order to manufacture a highly reliable laser, it is necessary to eliminate the waveguide loss and reduce the operating current. In order to eliminate the waveguide loss, a real refractive index waveguide laser using AlInP, AlGaInP, or AlGaAs having a larger band gap than the active layer and a smaller refractive index than the cladding layer instead of GaAs for the current blocking layer is manufactured. It is effective to do.

FIG. 8 shows a structure diagram of a general real refractive index guided laser. The laser shown in FIG. 8 uses a double hetero structure in which a heavy quantum well active layer 805 is sandwiched between an n-type AlGaInP cladding layer 803 and a p-type AlGaInP cladding layer 807. An n-type AlInP current blocking layer 80 is provided on both sides of the p-type AlGaInP cladding layer 807.
9 are provided. In FIG. 8, reference numeral 801 denotes an n-type G
aAs substrate, 802 is an n-type GaAs buffer layer, 804
Is a non-doped AlGaInP light guide layer, 806 is a non-doped AlGaInP light guide layer, and 808 is p-type GaI
An nP hetero buffer layer, 810 is a p-type GaAs contact layer, 811 is an n-side electrode, and 812 is a p-side electrode.

[0005] However, AlInP, AlGaIn
P has a large dependence of the lattice constant on the Al composition. When P is used in the current block layer of the ridge stripe laser, (11
1) A ridge slope portion A (FIG. 9) composed of a surface;
1) Al, Ga, I at flat portion B (FIG. 9)
The composition of the growth layer is different because the rate of n is different.

Normally, since the crystal grows under the condition that the lattice constant of the current blocking layer coincides with the flat portion (001) plane having the same plane orientation as the substrate, lattice irregularity occurs in the growth from the ridge slope (111) surface. Then, distortion occurs at the interface. The Al composition of the ridge slope portion is about 10% higher than that of AlInP grown from the flat portion, and the lattice misalignment is as large as -0.7%.
Here, the lattice irregularity is ((lattice constant of AlInP−GaAs).
(lattice constant of s substrate) / lattice constant of GaAs substrate × 10
0). Dislocations due to this strain affect the active layer and reduce the reliability of the laser. Therefore, in order to manufacture a highly reliable laser, it is essential to reduce the dislocation in the ridge slope. Heretofore, the following has been known in the related art.

[0007] As a first conventional example, Japanese Patent Laid-Open No. 8-32165 is disclosed.
No. 6 discloses that a real refractive index guided semiconductor laser using AlInP for a current blocking layer suppresses the generation of dislocations by setting the AlInP film thickness to 0.5 μm or less. It is described that the estimated lifetime reached 10,000 hours when driven under the conditions of an ambient temperature of 50 ° C. and an optical output of 5 mW.

A second conventional example is disclosed in Japanese Patent Application Laid-Open No. 9-14867.
In Japanese Patent Application Laid-Open No. 4 (1999) -1995, crystal growth is performed under the condition that the lattice constant of AlInP, which is the current blocking layer, matches the ridge slope (111) plane, thereby suppressing the generation of AlInP dislocations on the ridge slope and improving reliability. There is a statement that it has improved.

[0009]

However, a high-power laser having an optical output of 50 mW class has a higher operating current than a low-power laser, and therefore the ridge slope near the laser oscillation part has a high temperature. In this high-temperature atmosphere, dislocations are likely to occur, and the dislocation of AlInP on the slope of the ridge extends to the active layer, causing a problem that the reliability of the laser is reduced.

In the first conventional example, generation of dislocations is suppressed by setting the AlInP film thickness to 0.5 μm or less. The deterioration of sex occurs. In the second conventional example, the crystallinity of the ridge slope is improved, but on the other hand,
AlInP grown from the flat (001) plane is displaced from the lattice matching conditions, causing dislocations and reducing reliability.

In order to solve the above-mentioned conventional problems, the present invention provides a highly reliable laser in a current block layer using a semiconductor containing Al such as AlInP or AlGaInP and having a lattice constant which varies depending on the composition. The purpose is to provide well.

[0012]

In order to achieve the above object, a semiconductor laser according to the present invention comprises a first conductive type clad layer, an active layer, a ridge-shaped second conductive type clad layer, and a second conductive type clad layer. A current blocking layer made of a semiconductor of the first conductivity type having a smaller refractive index than the conductivity type cladding layer, wherein the current blocking layer is made of two kinds of semiconductors.

Further, the semiconductor laser of the present invention comprises a first conductivity type cladding layer, an active layer, a second conductivity type cladding layer having a ridge shape, and a first conductivity type cladding layer having a lower refractive index than the second conductivity type cladding layer. A semiconductor laser having a current block layer made of a semiconductor containing conductive Al, wherein the current block layer is made of AlInP and AlGaAs.

Further, in the semiconductor laser according to the present invention, it is preferable that the current block layer is formed by alternately stacking AlInP and AlGaAs.

In the semiconductor laser of the present invention, the thickness of each layer constituting the current blocking layer is preferably 15 nm or less, more preferably 10 nm or less. However, it is necessary to be 2 nm or more for the reason of the steepness of the interface.

Further, the semiconductor laser of the present invention has a first conductivity type cladding layer, an active layer, a second conductivity type cladding layer having a ridge shape, and a first conductivity type cladding layer having a lower refractive index than the second conductivity type cladding layer. A current block layer made of a semiconductor containing conductive Al, wherein the current block layer is made of a plurality of AlInPs having different Al compositions.

Further, in the semiconductor laser according to the present invention, the current blocking layer is preferably made of AlInP which is lattice-matched to the ridge slope.
And a stacked structure of AlInP lattice-matched to the flat portion.

Further, in the semiconductor laser of the present invention, the thickness of each layer constituting the current blocking layer is preferably 15 nm or less, more preferably 10 nm or less. However, it is necessary to be 2 nm or more for the reason of the steepness of the interface.

Further, the semiconductor laser of the present invention comprises a first conductivity type cladding layer, an active layer, a second conductivity type cladding layer having a ridge shape, and a first conductivity type cladding layer having a lower refractive index than the second conductivity type cladding layer. A current blocking layer made of a semiconductor containing conductive Al, wherein the current blocking layer is made of AlInP in which the composition of Al changes continuously and periodically.

Further, the semiconductor laser of the present invention is characterized in that
Is the composition of Al lattice-matched to the ridge slope,
It preferably changes continuously and periodically between the Al composition that lattice-matches the flat portion.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows an embodiment of the present invention.
1 is a cross-sectional view of the AlGaInP-based laser shown in FIG. Same figure
As shown in FIG.
On a doped n-type GaAs substrate 101, a Si-doped n-type
Type GaAs buffer layer 102 (Si concentration: n = 2 × 10
¹⁸cm^-3, Thickness: t = 0.5 μm), first conductivity type crack
Si-doped n-type (Al_0.7Ga_0.3)_0.5I
n_0.5P cladding layer 103 (n = 1 × 10¹⁸cm^-3, T
= 1.5 μm), undoped (Al_0.5Ga_0.5)_0.5
In_0.5P light guide layer 104 (t = 20 nm), active layer
105, non-doped (Al_{0. Five}Ga_0.5)_0.5In
_0.5P well (t = 5 nm: 2 layers) and non-doped Ga
_0.5In_0.5Multiplex consisting of P wells (t = 5 nm: 3 layers)
Quantum well layer, undoped (Al_0.5Ga_0.5)_0.5In
_0.5P light guide layer 106 (t = 20 nm), second conductivity type
Zn-doped p-type (Al_0.7Ga_0.3)
_0.5In_0.5P cladding layer 107 (Zn concentration: p = 5 × 1
0¹⁷cm^-3, T = 0.2 μm), Zn-doped p-type Ga
_0.5In_0.5P hetero buffer layer 108 (p = 1 × 10¹⁸
cm^-3, T = 50 nm), Si-doped Al_0.5In_0.5
P and Al_0.6Ga_0.4As n-type current blocking layer 109
(N = 1 × 10¹⁸cm^-3, T = 0.3 μm), Si dopant
N-type GaAs cap layer 110, Zn-doped p-type
It has a GaAs contact layer 111, and further has
On the n-side electrode 112 and the p-type GaAs contact layer 111
an embedded double hetero structure having a p-side electrode 113;
Has become.

Next, a method of manufacturing the semiconductor laser of this embodiment shown in FIG. 1 will be described. FIG. 2 (a), (b)
FIG. 4 is a process cross-sectional view for explaining the method for manufacturing the semiconductor laser of the present embodiment. A vertical MOCVD apparatus was used for crystal growth. AlGaInP, AlIn as source gas
When growing P, GaInP, and GaAs crystals, trimethylgallium (TMGa), trimethylaluminum (TMAl), trimethylindium (TMIn),
Phosphine (PH ₃ ) and arsine (AsH ₃ ) were used.
When performing p and n-type doping, diethyl zinc (DEZn) and silane (SiH ₄ ) were used, respectively. As a heat source of the substrate, a resistance heater was used. The growth temperature was 660 ° C., and the pressure in the growth atmosphere was 4.7 kPa. The growth rate is 2 μm / h.

First, the n-type GaAs substrate 101 is
D reactor, n-type GaAs buffer layer 102, n
Mold (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 103,
Non-doped (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P light guide layer 104, multiple quantum well active layer 105, non-doped (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P light guide layer 106, p
Mold (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 107,
p-type Ga _0.5 In _0.5 P hetero buffer layer 108, p-type G
The heterostructure substrate shown in FIG. 2A is manufactured by sequentially growing the aAs cap layer 114.

After taking out from the MOCVD reactor, a silicon oxide film is deposited to a thickness of 0.3 μm by using an atmospheric pressure thermal CVD method (370 ° C.). Next, this silicon oxide film is subjected to photolithography and dry etching techniques to form a striped silicon oxide mask 115 having a width of 1.5 μm.
To form Using the silicon oxide as a mask, a p-type GaAs cap layer 114 is formed using a sulfuric acid-based etchant.
2B by selectively etching the p-type GaInP heterobuffer layer 108 using a hydrochloric acid-based etchant and the p-type AlGaInP cladding layer 107 using a sulfuric acid-based or hydrochloric acid-based etchant. Thus, a mesa structure is formed on the heterostructure substrate.

The substrate is placed in the MOCVD reactor again, and the n-type current blocking layer 109 (0.3 μm) and the n-type GaAs cap layer 110 (0.1 μm) are selectively grown using the silicon oxide mask 115. The detailed structure of the n-type current block layer 109 will be described later.

Thereafter, the silicon oxide mask 115 is taken out of the MOCVD reactor, the silicon oxide mask 115 is removed using buffered hydrofluoric acid, and the silicon oxide mask 115 is placed again in the MOCVD reactor to form p-type GaAs.
A contact layer 111 was grown. Finally, an n-side electrode 112 made of Au, Ge, and Ni was formed on the back surface of the substrate, and a p-side electrode 113 made of Cr / Au / Pt was formed on the surface of the substrate, to obtain a semiconductor laser having the structure shown in FIG.

Next, the features of the semiconductor laser of the present invention will be described. FIG. 3 is a sectional view of a main part of the current block layer of FIG. In FIG. 3, reference numeral 307 denotes p-type AlGaIn
A P clad layer, 309 is an n-type current block layer, and 310 is an n-type GaAs cap layer.

The n-type current block layer 309 is made of Al _0.5 In
By growing _0.5 P and Al _0.6 Ga _0.4 As alternately, the strain of Al _0.5 In _0.5 P on the slope of the ridge is relaxed by Al _0.6 Ga _0.4 As which is a lattice matching system. AlIn
As described above, P has a composition of 1 at the flat portion and the ridge slope portion.
Since there is a difference of 0%, the lattice irregularity is -0.7%, and there is an environment in which distortion is likely to occur on the slope of the ridge and dislocation is likely to occur. Al
_{Since 0.6} Ga _0.4 As is a lattice-matched system, even if the Al composition of the flat part and the ridge slope part differ by 10%, the lattice irregularity is −
0.014% is 1/50 as compared with AlInP, and the generation of dislocation can be suppressed because the strain is small.

FIG. 4 shows the dependence of the stress applied to the ridge slope due to strain and the proportion of the AlGaAs layer occupying the current blocking layer. The stress applied to the ridge slope when the current block layers are all AlInP is set to 1. From this FIG.
It can be seen that the greater the proportion of the AlGaAs layer, the smaller the stress applied to the ridge slope. In order to sufficiently reduce the stress applied to the ridge slope, the proportion of the AlGaAs layer needs to be 30% or more. However, if the ratio of the AlGaAs layer is large, the effective refractive index difference between the inside and the outside of the ridge becomes small, and it becomes difficult to control the horizontal spread angle. Therefore, the ratio of the AlGaAs layer is desirably 70% or less. Considering these two points, the ratio of the AlGaAs layer is suitably 30% to 70%.

The thickness of the entire current blocking layer is constant, and the thickness of one layer of AlInP and AlGaAs is reduced to increase the total number of layers, thereby further suppressing the occurrence of dislocations. . However, AlInP / A
In consideration of the steepness of the interface of lGaAs, the film thickness per layer is suitably 2 to 15 nm. In the laser fabricated this time, the ratio of the AlGaAs layer was set to 50%. Specifically, 10 nm was set as one set, and 15 sets were grown, and the current blocking layer thickness was set to 300 nm. Finally, the film thickness and film thickness ratio of AlInP and AlGaAs may be designed to be optimal values that can control the horizontal spread angle and suppress dislocations.

The life test of the semiconductor laser manufactured as described above was performed. The service life is as follows: ambient temperature 70 ° C, constant light output 80
Drive was performed under the condition of mW, and the estimated time until the operating current changed by ± 20% of the initial value was set. The lifetime of the manufactured laser reached 10,000 hours, and a highly reliable semiconductor laser was manufactured.

According to this embodiment, the ridge slope A
By alleviating the strain applied to the lInP, the dislocation at the slope of the ridge is suppressed, and the reliability of the laser is improved.

(Embodiment 2) FIG. 5 is a sectional view of a main part of a current blocking layer of a semiconductor laser according to Embodiment 2 of the present invention. In FIG. 5, 507 is a p-type AlGaInP cladding layer, 509 is an n-type current blocking layer, 510 is an n-type GaAs cap layer, α is an AlInP layer lattice-matched to the ridge slope, and β is an AlInP layer lattice-matched to the flat part. It is. Since only the configuration of the current block layer is different from that of the first embodiment, detailed description of other configurations is omitted. A feature of the present invention is that the n-type current block layer 509 is composed of AlInP lattice-matched to the (111) plane and AlInP layer lattice-matched to the (001) plane. Specifically, the flow rate of TMAl is set to (11
1) In the case of lattice matching with the plane, it is reduced by 10% as compared with the case of lattice matching with the (001) plane. Embodiment 1
Here, AlGaAs and Al used for the current block layer
Since InP has a large difference in the refractive index, it affects the characteristics of the device, particularly the horizontal divergence angle, and lowers the yield. On the other hand, in the second embodiment, since the same AlInP is used for the current blocking layer, the refractive index is almost the same, and the control of the horizontal divergence angle is easy, so that a red laser can be manufactured with a high yield. AlInP lattice-matched to the (111) plane and AIn lattice-matched to the (001) plane
By controlling the film thickness of the lInP layer, the strain applied to only the ridge slope portion can be distributed to the ridge slope portion and the flat portion at a desired ratio.

FIG. 6 shows AlInP lattice-matched to the (111) plane of the stress applied to the ridge slope portion and the flat portion, and (00)
1) The ratio dependency of the AlInP layer lattice-matched to the plane is shown. The horizontal axis represents the ratio of the AlInP layer lattice-matched to the (111) plane occupying the current block layer. The semiconductor laser fabricated this time employs a structure in which stress is evenly applied to the ridge slope and the flat portion, which are considered to suppress dislocations most.
Specifically, each film thickness is set to 10 nm as one set, 15 sets are grown, and the current block layer thickness is set to 300 n.
m.

The life test of the semiconductor laser manufactured as described above was performed. The service life is as follows: ambient temperature 70 ° C, constant light output 80
Drive was performed under the condition of mW, and the estimated time until the operating current changed by ± 20% of the initial value was set. The lifetime of the manufactured laser reached 10,000 hours, and a highly reliable semiconductor laser was manufactured.

According to this embodiment, the ridge slope A
By alleviating the strain applied to the lInP, the dislocation at the slope of the ridge is suppressed, and the reliability of the laser is improved.

(Embodiment 3) FIG. 7 is a cross-sectional view of a main part of a current block layer of a semiconductor laser according to Embodiment 3 of the present invention, and shows the AlInP film thickness and Al _x In of the current block layer.
It is a figure which shows the relationship with Al composition of _1-xP . 7, reference numeral 707 denotes a p-type AlGaInP cladding layer;
Is an n-type current blocking layer, 710 is an n-type GaAs cap layer, and α is a layer for one period in which Al composition changes with AlInP. Since only the configuration of the current block layer is different from that of the first embodiment, detailed description of other configurations is omitted. A feature of the present invention is that the Al composition of the AlInP current block layer is continuously and periodically changed between the respective Al compositions when lattice-matched to the (111) plane and the (001) plane.
By controlling the average value of the Al composition of the AlInP current block layer in this manner, the strain applied to only the ridge slope portion can be distributed to the ridge slope portion and the flat portion at a desired ratio. In the second embodiment, dislocations are likely to occur because stress is concentrated at the interface between AlInPs having different compositions. In the third embodiment, generation of dislocations can be suppressed by continuously changing the composition of AlInP so that there is no interface of the composition.

Specifically, AlInP is formed at a rate of 10 nm per cycle.
For 30 cycles, and the thickness of the current block layer is set to 300 n.
m. Further, by continuously changing the composition of Al, an interface where stress tends to concentrate is not formed.

The life test of the semiconductor laser fabricated as described above was performed. The life is as follows: ambient temperature 80 ° C, constant light output 80
Drive was performed under the condition of mW, and the estimated time until the operating current changed by ± 20% of the initial value was set. The lifetime of the manufactured laser reached 10,000 hours, and a highly reliable semiconductor laser was manufactured.

According to this embodiment, the ridge slope A
By alleviating the strain applied to the lInP, the dislocation at the slope of the ridge is suppressed, and the reliability of the laser is improved.

[0042]

As described above, in the first embodiment, the crystallinity of AlInP can be improved by relaxing the strain applied to AlInP on the slope of the ridge.

In the second embodiment, the strain applied to the ridge slope portion and the flat portion is distributed at a desired ratio, so that the strain applied to the ridge slope portion can be reduced and the crystallinity of AlInP can be improved.

In the third embodiment, the strain is distributed to the ridge slope portion and the flat portion at a desired ratio, and an interface where stress tends to be concentrated is not formed, so that the strain applied to the ridge slope portion is reduced, and the crystallinity of AlInP is reduced. Can be improved.

As described above, according to the semiconductor laser of the present invention, the dislocation generated from the ridge is suppressed, and there is a remarkable effect that a highly reliable real refractive index waveguide semiconductor laser can be manufactured at a high yield.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of a semiconductor laser according to a first embodiment.

FIG. 2 is a process sectional view illustrating the method for manufacturing the semiconductor laser according to the first embodiment.

FIG. 3 is a cross-sectional view of a main part of the current block layer according to the first embodiment.

FIG. 4 is a diagram showing the relationship between the stress applied to the ridge slope and the ratio of the AlGaAs layer occupying the current block layer.

FIG. 5 is a sectional view of a main part of a current block layer according to a second embodiment.

FIG. 6 shows the stress applied to the ridge slope portion and the flat portion and (11)
It is a figure which shows the relationship of the ratio of AlInP lattice-matched to the 1) plane and the AlInP layer lattice-matched to the (001) plane.

FIG. 7 is a sectional view of a main part of a current blocking layer of a semiconductor laser according to a third embodiment, and FIG.
FIG. 6 is a diagram showing a relationship between a film thickness and the Al composition of Al _x In _1-x P in a flat portion.

FIG. 8 is a cross-sectional view showing a structure of a conventional semiconductor laser.

FIG. 9 is a sectional view near a ridge.

[Explanation of symbols]

101, 801 n-type GaAs substrate 102, 802 n-type GaAs buffer layer 103, 803 n-type AlGaInP cladding layer 104, 804 non-doped AlGaInP light guide layer 105, 805 multi-quantum well active layer 106, 806 non-doped AlGaInP light guide layer 107, 307 , 507,707,807 p-type AlG
aInP cladding layer 108, 808 p-type GaInP hetero buffer layer 109, 309, 509, 709, 809 n-type current blocking layer 110, 310, 510, 710 n-type GaAs cap layer 111, 810 p-type GaAs contact layer 112, 811n Side electrode 113, 812 P-side electrode 114 P-type GaAs cap layer 115 Silicon oxide mask

Claims (9)

[Claims] 1. A current comprising a first conductivity type cladding layer, an active layer, a second conductivity type cladding layer having a ridge shape, and a first conductivity type semiconductor having a lower refractive index than the second conductivity type cladding layer. A semiconductor laser having a blocking layer, wherein the current blocking layer is made of two kinds of semiconductors. 2. A semiconductor comprising: a first conductivity type clad layer; an active layer; a second conductivity type clad layer having a ridge shape; and a first conductivity type Al having a lower refractive index than the second conductivity type clad layer. A current blocking layer comprising: AlInP and Al
A semiconductor laser comprising GaAs. 3. The method according to claim 1, wherein the current blocking layer comprises AlInP and A
3. The semiconductor laser according to claim 2, wherein lGaAs is alternately stacked. 4. The semiconductor laser according to claim 3, wherein each of the layers constituting the current blocking layer has a thickness of 15 nm or less. 5. A semiconductor comprising a first conductivity type clad layer, an active layer, a second conductivity type clad layer having a ridge shape, and a first conductivity type Al having a lower refractive index than the second conductivity type clad layer. And a current block layer comprising: a plurality of AlInPs having different Al compositions. 6. An AlInP lattice-matched to a ridge slope portion and an Al lattice-matched to a flat portion, wherein the current blocking layer is
6. The semiconductor laser according to claim 5, comprising a stacked structure of InP. 7. The semiconductor laser according to claim 5, wherein each of the layers constituting the current blocking layer has a thickness of 15 nm or less. 8. A semiconductor including a first conductivity type clad layer, an active layer, a second conductivity type clad layer having a ridge shape, and a first conductivity type Al having a lower refractive index than the second conductivity type clad layer. And a current blocking layer made of AlInP in which the composition of Al changes continuously and periodically. 9. The composition according to claim 8, wherein the Al composition changes continuously and periodically between an Al composition lattice-matched to the ridge slope portion and an Al composition lattice-matched to the flat portion. Semiconductor laser.