JPH10215021A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor laser device which prevents a drop in a transverse electric(TE)/transverse magnetic(TM) polarization intensity ratio due to a difference in thermal expansion coefficients. SOLUTION: An n-type clad layer 2, a light guide layer 14, a multiple quantum well active layer 15, a light guide layer 17 and a p-type clad layer 8 are formed on an n-type GaAs substrate 1. The multiple quantum well active layer 15 is constituted of two well layers 5 and of a barrier layer 16 between the respective well layers 5. The p-type clad layer 8 comprises a stripe-shaped ridge. An n-type current blocking layer 10 which has a function to block a current and whose coefficient of thermal expansion is larger than that of the p-type clad layer 8 is formed on both side faces of the ridge at the p-type clad layer 8. An optical intensity in a TE mode is larger than an optical intensity in a TM mode, and the light guide layers 14, 17 and the barrier layer 16 have a tensile strain with reference to the well layers 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device used as a light source for optical information processing, optical measurement, and the like.

[0002]

2. Description of the Related Art In recent years, I have an oscillation wavelength in a 0.6 μm band.
A red semiconductor laser device using an nGaAlP-based material has been commercialized, and is expected as a light source for high-density optical disk devices, laser beam printers, bar code readers, optical measurement devices, and the like. As a light source of a high-density optical disk device, TM (transverse magnetic)
TE (transverse electr) for light
ic) It is desired to increase the light intensity ratio, that is, the TE / TM polarization intensity ratio.

FIG. 7 shows an example of a conventional semiconductor laser device. In this example, a semiconductor laser device having an oscillation wavelength in the 680 nm band will be described.

On the n-type GaAs substrate 1, about 1.7 μm
N _0.5 (Ga _0.3 Al _0.7 )
_A cladding layer 2 composed of _0.5 P is formed.
On the cladding layer 2, a thickness of about 25 nm
An optical guide layer 3 composed of n _0.5 (Ga _0.5 Al _0.5 ) _0.5 P is formed. On the light guide layer 3, a multiple quantum well active layer 4 is formed.

The multiple quantum well active layer 4 has a size of about 6.5n.
m, two well layers 5 made of InGaP, and between the well layers 5, about 4.0 nm
And a barrier layer 6 composed of In _0.5 (Ga _0.5 Al _0.5 ) _0.5 P. Well layer 5
Is set so that the forbidden band width is smaller than that of the barrier layer 6.

On the multiple quantum well active layer 4, about 25 nm
The light guide layer 7 having a film thickness of In _0.5 (Ga _0.5 Al _0.5 ) _0.5 P is formed. On the light guide layer 7, p-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5
A cladding layer 8 composed of P is formed. The cladding layer 8 includes a ridge portion having a thickness of about 1.7 μm and portions having a thickness of about 0.25 μm on both sides of the ridge portion.

On the ridge portion of the cladding layer 8, about 50
A contact layer 9 having a thickness of nm and made of InGaP is formed. On both sides of the ridge portion of the cladding layer 8, an n-type GaAs having a thickness of about 1.0 μm is formed.
Is formed.
A contact layer 11 having a thickness of about 3.0 μm and made of p-type GaAs is formed on the contact layer 9 and the current block layer 10.

The contact layer 11 is made of, for example, AuZn.
A p-electrode 12 made of a stack of Au and Au is in contact, and an n-electrode 13 made of, for example, a stack of AuGe and Au is in contact with the GaAs substrate 1.

In the semiconductor laser device having the above structure,
One well layer 5 includes cladding layers 2 and 8 and light guide layers 3 and 7.
And the barrier layer 6 has a compressive strain of about + 0.7%. The compressive strain is a strain that is applied to a substrate such that a target layer (well layer) is compressed in a direction parallel to an interface of each layer. In other words, the lattice constant of the substrate is reduced. When a is defined as a and the lattice constant of the target layer (well layer) is defined as a ′, the distortion means that Δa / a = (a′−a) / a is positive.

The compressive strain of the well layer 5 causes the light intensity in the TE mode to be set sufficiently higher than the light intensity in the TM mode, that is, makes the TE / TM polarization intensity ratio sufficiently high. It is provided for the purpose.

FIG. 8 shows the composition ratio of Al in each layer in FIG. 7 and the degree of distortion in each layer. InG
When an aAlP-based material is used, the amount of strain is, for example,
It can be changed by changing the composition ratio of In.

[0012]

In the semiconductor laser device shown in FIG. 7, the cladding layer 8 is made of In _0.5 (Ga _0.3 A).
l _0.7 ) _0.5 P, and the current blocking layer 10
It is composed of GaAs. However, the thermal expansion coefficient of GaAs is larger than that of In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P.

Therefore, for example, GaAs is heated to 600 ° C.
When the temperature is lowered to room temperature after the formation in the above high temperature state, the GaAs shrinks and the ridge portion of the cladding layer 8 is directed toward the multiple quantum well active layer 4 as shown by an arrow in FIG. Is stressed.

This stress is applied to the multiple quantum well active layer 4.
Act in a direction parallel to the interface of this layer.
That is, when such a tensile stress acts on two well layers (compressive strain of about + 0.7%) of the multiple quantum well active layer 4,
Equivalently, the same effect as when tensile strain is generated in the two well layers occurs, the band structure is changed, and light emission in the TM mode is easily caused.

That is, as shown in FIG. 10, for example, when the optical output is 3 mW, the distribution of the TE / TM polarization intensity ratio is approximately 20%.
Concentrates on a low value that makes the peak. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and an object of the present invention is to provide a TM mode by a distortion caused by a thermal expansion coefficient of a material.
Prevents the phenomenon in which light emission of the light-emitting diode is likely to occur, so that the distribution of the TE / TM polarization intensity ratio is concentrated at a high value.
Is to provide the device.

[0016]

In order to achieve the above object, a semiconductor laser device according to the present invention comprises a substrate of a first conductivity type and a first cladding layer of the first conductivity type formed on the substrate. A first light guide layer formed on the first clad layer; n (n is a natural number of 2 or more) well layers formed on the first light guide layer; and n well layers Between (n
-1) a multiple quantum well active layer composed of a barrier layer, a second optical guide layer formed on the multiple quantum well active layer, and a stripe shape formed on the second optical guide layer. A second conductive type second cladding layer having ridges formed on both sides of the ridge of the second cladding layer, the second cladding layer having a function of blocking current, and having a larger thermal expansion coefficient than the second cladding layer. A current blocking layer of one conductivity type;
The laser light emitted from the multiple quantum well active layer is composed of a ridge of the cladding layer and a contact layer formed on the current blocking layer, and the laser light emitted from the multiple quantum well active layer has a TE mode intensity higher than the TM mode intensity. And at least one of the first light guide layer, the second light guide layer, and the (n-1) -layer barrier layer has a tensile strain with respect to the n-layer well layer. It is what you have.

In the case where the first light guide layer has a tensile strain with respect to the substrate, the first clad layer includes:
A first portion having a tensile strain with respect to the substrate, the first portion being adjacent to the first light guide layer;

When the second light guide layer has a tensile strain with respect to the substrate, the second clad layer is
A second portion having a tensile strain with respect to the substrate, wherein the second portion is adjacent to the second light guide layer;

The first light guide layer, the second light guide layer, and the barrier layer (n-1) all have tensile strain with respect to the substrate. The first light guide layer, the second light guide layer, the barrier layer of the (n-1) layer,
The first portion, and of the second part, the sum of the thickness of the third portion has a tensile strain with respect to the substrate d, the thickness of the well layer of the n-layer and L _w, When the total thickness of the n-th well layer is n × L _w , the tensile strain is set to be equal to or more than 0.0097 × n × L _w / d.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a semiconductor laser device according to the present invention will be described in detail with reference to the drawings. FIG.
Shows a semiconductor laser device according to the first embodiment of the present invention.

In the present embodiment, a semiconductor laser device having an oscillation wavelength in the 680 nm band will be described, as in the description of the prior art. On the n-type GaAs substrate 1, an n-type In _0.5 (Ga
_A cladding layer 2 composed of _0.3 Al _0.7 ) _0.5 P is formed. This on the cladding layer 2 has approximately 25nm in _{thickness, In 1-X (Ga 0.5} Al 0.5) light composed of _X P guide layer 14 is formed.

The first difference between the structure of the present embodiment and the conventional structure is that the light guide layer 14 has a tensile strain. The tensile strain in the present embodiment is a strain that is applied to the substrate 1 such that a target layer (for example, the light guide layer 14) is pulled in a direction parallel to an interface between the layers. In other words, the lattice constant of the substrate 1 is a, and the lattice constant of the target layer is a '.
In this case, Δa / a = (a′−a) / a means a distortion that becomes Maenas.

The lattice constant (amount of strain) of each layer is determined by the composition ratio of the InGaAlP-based material constituting each layer, for example, In
Can be changed by changing the composition ratio (1-x). In the present embodiment, the tensile strain of the light guide layer 14 is set to about -0.6%.

On the light guide layer 14, a multiple quantum well active layer 15 is formed. This multiple quantum well active layer 15
Has a thickness of about 6.5 nm, is disposed between the two well layers 5 made of InGaP, has a thickness of about 4.0 nm, and has a thickness of In _{1 -X.} (Ga _0.5 A
l _0.5) and a constructed barrier layer 16. From _X P. Each well layer 5 is set to have a forbidden band width smaller than that of the barrier layer 16.

Further, the two well layers 5 are formed in the same manner as in the prior art.
It has a compression strain of about + 0.7%. The compressive strain in the present embodiment is a strain that is applied to the substrate 1 such that a target layer (well layer 5) is compressed in a direction parallel to the interface between the layers. For example, let the lattice constant of the substrate 1 be a, and let the lattice constant of the target layer be a
′ Means a distortion such that Δa / a = (a′−a) / a is positive.

The lattice constant (amount of strain) of each layer is determined by the composition ratio of the InGaAlP-based material constituting each layer, for example, In
Can be changed by changing the composition ratio.
The second difference between the structure of the present embodiment and the conventional structure is that
The barrier layer 16 has a tensile strain Δa / a of about −0.6%. The amount of strain is determined, for example, by the barrier layer 1
6 can be changed by changing the composition ratio (1-x) of In.

On the multiple quantum well active layer 15, about 25 n
has a thickness of _{m, In 1-X (Ga} 0. 5 Al 0.5) light composed of _X P guide layer 17 is formed. A third difference of the structure of the present embodiment from the conventional structure is that the light guide layer 17 has a tensile strain Δa / a of about −0.6%. The amount of distortion can be changed, for example, by changing the composition ratio (1-x) of In forming the light guide layer 17.

On the light guide layer 17, a p-type In _0.5
A cladding layer 8 composed of (Ga _0.3 Al _0.7 ) _0.5 P is formed. The cladding layer 8 has a thickness of about 1.7.
The ridge portion has a thickness of about 0.25 μm on both sides of the ridge portion.

On the ridge portion of the cladding layer 8, about 50
A contact layer 9 having a thickness of nm and made of InGaP is formed. On both sides of the ridge portion of the cladding layer 8, an n-type GaAs having a thickness of about 1.0 μm is formed.
Is formed.
A contact layer 11 having a thickness of about 3.0 μm and made of p-type GaAs is formed on the contact layer 9 and the current block layer 10.

The contact layer 11 is made of, for example, AuZn.
A p-electrode 12 made of a stack of Au and Au is in contact, and an n-electrode 13 made of, for example, a stack of AuGe and Au is in contact with the GaAs substrate 1.

The semiconductor laser device having the above-described structure is characterized in that the optical guide layers 14, 17 and the barrier layer 16 which are in contact with the two well layers 5 having a compressive strain of + 0.7% each have a tensile strain (for example, about 0.7%). (−0.6%) in that the light guide layers 14 and 17 and the barrier layer 16 are formed.

That is, in view of the fact that the conventional problem is caused by the stress from the ridge portion of the cladding layer 8 and the tensile strain is equivalently generated in the two well layers 5, FIG. As shown in the drawing, the optical guide layers 14 and 17 and the barrier layer 16 that are in contact with the two well layers 5 are previously subjected to tensile strain, thereby equivalently generating a compressive strain in the two well layers 5. It was done.

Accordingly, the tensile strain of the two well layers 5 caused by the stress from the ridge portion of the cladding layer 8 is as follows.
It can be offset by the compressive strain equivalently generated in the two well layers 5 due to the tensile strain of the light guide layers 14, 17 and the barrier layer 16.

As a result, the distortion of the well layer due to the thermal expansion coefficient of the material is eliminated, and the light intensity of the TE mode is reduced to T.
In a semiconductor laser device having a light intensity higher than the light intensity in the M mode, a phenomenon in which light emission in the TM mode is easily caused can be avoided, and the distribution of the TE / TM polarization intensity ratio can be concentrated to a high value. .

It is sufficient that the layer having a tensile strain is at least one of the light guide layers 14, 17 and the barrier layer 16. When it is necessary to increase the amount of tensile strain, it is preferable to apply tensile strain to a layer separated from the substrate 1 (a layer close to the ridge portion). This is because tensile strain is more likely to be introduced in a layer separated from the substrate 1 than in a layer closer to the substrate 1. Further, it is considered that tensile strain is easier to be introduced when the layer is thinner than when the layer is thicker.

FIG. 3 shows the Al composition ratio and the degree of strain Δa / a in each layer of FIG. In the present invention, the light guide layers 14, 17 and the barrier layer 16 are each configured to have a tensile strain of about -0.6%. Also,
The two well layers 5 are each configured to have a compressive strain of about + 0.7%.

FIG. 4 shows a semiconductor laser device according to a second embodiment of the present invention. In the present embodiment, a semiconductor laser device having an oscillation wavelength in the 680 nm band will be described as in the description of the conventional technology.

The present embodiment is different from the above-described first embodiment in that the layer for providing tensile strain is further expanded. On the n-type GaAs substrate 1, about 1.
N-type In _0.5 (Ga _0.3 Al) having a thickness of 6 μm
_A cladding layer 2 composed of _0.7 ) _0.5 P is formed. On the cladding layer 2, a cladding layer 18 having a thickness of about 0.1 μm, made of n-type In _1-y (Ga _0.3 Al _0.7 ) _y P, and having a tensile strain of about −0.2% is provided. Is formed.

The lattice constant (amount of strain) of each layer is determined by the composition ratio of the InGaAlP-based material forming each layer, for example, In
Can be changed by changing the composition ratio.
On the cladding layer 18, a thickness of about 25 nm
An optical guide layer 19 composed of _1-y (Ga _0.5 Al _0.5 ) _y P and having a tensile strain of about −0.2% is formed.

On the light guide layer 19, a multiple quantum well active layer 20 is formed. This multiple quantum well active layer 20
Has a thickness of about 6.5 nm, is disposed between the two well layers 5 made of InGaP, has a thickness of about 4.0 nm, and has a thickness of In _{1 -y.} (Ga _0.5 A
l _0.5) consists _y P, tensile strain of about -0.2%
And the barrier layer 21 of FIG. Each well layer 5 is set to have a forbidden band width smaller than that of the barrier layer 21.

The two well layers 5 are formed in the same manner as in the prior art.
It has a compression strain of about +0.7. The lattice constant (amount of strain) of each layer can be changed by changing the composition ratio of the InGaAlP-based material constituting each layer, for example, the composition ratio of In.

On the multiple quantum well active layer 20, about 25 n
has a thickness of _{m, In 1-y (Ga} 0. 5 Al 0.5) consists _y P, tensile strain of about -0.2% of the light guide layer 2
2 are formed.

The light guide layer 22 has a thickness of about 0.1 μm, is made of p-type In _1-y (Ga _0.3 Al _0.7 ) _y P, and has a tensile strain of about −0.2%. Clad layer 2
3 are formed. On the cladding layer 23, a p-type I
A cladding layer 8 composed of n _0.5 (Ga _0.3 Al _0.7 ) _0.5 P is formed. The cladding layer 8 includes a ridge portion having a thickness of about 1.6 μm and portions having a thickness of about 0.15 μm on both sides of the ridge portion.

On the ridge portion of the cladding layer 8, about 50
A contact layer 9 having a thickness of nm and made of InGaP is formed. On both sides of the ridge portion of the cladding layer 8, an n-type GaAs having a thickness of about 1.0 μm is formed.
Is formed.
A contact layer 11 having a thickness of about 3.0 μm and made of p-type GaAs is formed on the contact layer 9 and the current block layer 10.

The contact layer 11 is made of, for example, AuZn.
A p-electrode 12 made of a stack of Au and Au is in contact, and an n-electrode 13 made of, for example, a stack of AuGe and Au is in contact with the GaAs substrate 1.

A feature of the semiconductor laser device having the above configuration is that a part of the cladding layers 2 and 8 adjacent to the two well layers 5 having a compressive strain of + 0.7% (that is, the cladding layers 18 and 2).
3) The cladding layers 18, 23 and the light guide layers 19, 2 so that the light guide layers 19, 22 and the barrier layer 21 have tensile strains (for example, about -0.2%).
2 and the barrier layer 21 are formed.

That is, in view of the fact that the conventional problem is caused by the stress from the ridge portion of the cladding layer 8 and the tensile strain is equivalently generated in the two well layers 5, the present invention preliminarily sets the two well layers 5 to 2. Cladding layer 18 adjacent to one well layer 5,
23, the light guide layers 19 and 22 and the barrier layer 21 are given tensile strain, so that the two well layers 5 are equivalently formed.
, So that a compression strain is generated in

Therefore, tensile strain in the two well layers 5 caused by stress from the ridge portion of the cladding layer 8 is as follows:
It can be offset by compressive strain equivalently generated in the two well layers 5 due to tensile strain of the cladding layers 18 and 23, the light guide layers 19 and 22 and the barrier layer 21.

As a result, the distortion of the well layer caused by the coefficient of thermal expansion of the material is eliminated, and the light intensity of the TE mode is reduced to T
In a semiconductor laser device set to be higher than the light intensity in the M mode, the phenomenon in which light emission in the TM mode is likely to occur is avoided, and the distribution of the TE / TM polarization intensity ratio is increased to a high value. You can concentrate on

In the case of the present embodiment, it is effective to provide the tensile strain in all of the cladding layers 18 and 23, the light guide layers 19 and 22 and the barrier layer 21. FIG.
4 shows the Al composition ratio and the degree of strain Δa / a in each layer of FIG.

In the present invention, the cladding layers 18 and 23, the light guide layers 19 and 22 and the barrier layer 21 are each configured to have a tensile strain of about -0.2%. Also, 2
The two well layers 5 are each configured to have a compressive strain of about + 0.7%.

Next, the relationship between the distortion of the well layer 5 and the distortion of the layers around the well layer 5 in the first and second embodiments will be described. First, the total thickness of the layers having tensile strain disposed around the well layer 5 is d, the tensile strain of this layer is (Δa / a) _g , the thickness of the well layer 5 is L _w , Assuming that the number of is n,
The compressive strain (Δa / a) _w generated in the well layer 5 is expressed by equation (1).

(Δa / a) _w = − (Δa / a) _g × d / (L _w × n) (1) (Δa / a) _g = (a′−a) / a (Δa / a) _w = (a ″ -a) / a where a is the lattice constant of the substrate 1 and a ′ is the lattice constant of a layer having tensile strain arranged around the well layer 5.
“″” Indicates the lattice constant of the well layer 5.

For example, in the first embodiment, the layers having tensile strain are the light guide layers 14 and 17.
In the second embodiment, the layers having tensile strain are the cladding layers 18 and 23, the light guide layers 19 and 22, and the barrier layer 21.

Light emission in the TE mode in the semiconductor laser device is light emission due to recombination of heavy holes and electrons.
Mode emission is light emission due to recombination of light holes and electrons. Here, _assuming that the mass of heavy holes is m _hh and the mass of light holes is m _lh , the TE / TM emission intensity ratio (TE / TM)
Is represented by equation (2).

TE / TM = (m _hh / m _lh ) · exp (ΔE _lh-hh / kT) (2) where ΔE _lh-hh is the energy of heavy holes and light holes in the valence band. -Shows a difference, and increases as the compression strain increases. k is Boltzmann's constant and T is the absolute temperature.

The energy difference ΔE _lh-hh has a relationship as shown in equation (3) with the strain (Δa / a) _w of the well layer 5. ΔE _lh-hh = (Δa / a) _w × 6000 [meV] (3) By the way, in general, if the TE / TM polarization intensity ratio is 50 or more, the characteristic of the semiconductor laser device of the present invention is characteristic. It is enough.

Therefore, for example, consider the case where the TE / TM polarization intensity ratio is set to 50 or more. In this case, ΔE _lh-hh needs to be about 58 [meV] or more according to the above equation (2).

From the above equation (3), to make ΔE _lh-hh about 58 [meV] or more, (Δa / a) _w
Must be set to about 0.97% or more. That is, a layer having a tensile strain may be disposed around the well layer 5 based on the above equation (1) so that the strain (compression strain) of the well layer 5 is about + 0.97% or more. Will be.

That is, if the above is expressed in an equation, the following (4)
It looks like an expression. _{- (Δa / a) g ≧} 0.0097 × L w × n / d ... (4) Therefore, the strain of the well layer 5 (compression strain) about + 0.97%
The amount of tensile strain required to achieve the above is examined.

First, the case of the first embodiment will be discussed. In the case of the first embodiment described above, the layers having tensile strain are the light guide layers 14 and 17 and the barrier layer 16.
Therefore, the total thickness d of the layer having tensile strain
Is 25 + 4.0 + 25 = 54.0 nm. Also,
The thickness L _w of the well layer 5, 6.5 nm, the number of well layers 5 n
Are two.

Therefore, from the above equation (1), the light guide layer 1
4, 17 and tensile strain of barrier layer 16 (Δa / a) _g
Should be set to about | −0.23 |% or more. However, the tensile strain (Δa / a) _g needs to be set to such an extent that the lattice relaxation of the light guide layers 14, 17 and the barrier layer 16 does not occur due to this strain. That is, the maximum tensile strain at which lattice relaxation does not occur in the light guide layers 14, 17 and the barrier layer 16 is the upper limit of the settable tensile strain.

In the case of the above-described first embodiment, for example, when the TE / TM polarization intensity ratio is set to 50 or more, as described above, the light guide layers 14 and 17 and the barrier layer 1 are used.
The tensile strain (Δa / a) _g of No. 6 is approximately | -0.23 |%
What is necessary is just to set above.

Therefore, in the above-described first embodiment, the tensile strain (Δa) of the optical guide layers 14, 17 and the barrier layer 16 is determined.
/ A) _g is set to about -0.6%. In this case, as shown in FIG. 6, when the optical output of the semiconductor laser device is 3 mW, the distribution of the TE / TM polarization intensity ratio is about 110 peaks.
It concentrates on high values that make you feel good.

That is, according to the semiconductor laser device of the present invention, the layers arranged around the well layer 5 are configured to have a tensile strain, and the amount of the tensile strain is set to an optimum value. By doing so, it is possible to prevent a phenomenon in which light emission in the TM mode is likely to occur due to distortion or the like due to the thermal expansion coefficient of the material, and it is possible to concentrate the distribution of the TE / TM polarization intensity ratio to a high value. Become.

Next, the case of the above-described second embodiment will be considered. In the case of the above-described second embodiment, the layers having tensile strain include the cladding layers 18 and 23 and the light guide layer 1.
9, 22 and the barrier layer 21, the total thickness d of the layer having tensile strain is 100 + 25 + 4.0 + 25.
+ 100 = 254.0 nm. The thickness L _w of the well layer 5 is 6.5 nm, the number n _w of the well layer 5 is two.

Therefore, according to the above equation (1), the cladding layer 1
The tensile strain (Δa / a) _g of the light guide layers 8 and 23, the light guide layers 19 and 22 and the barrier layer 21 may be set to about | −0.05 |% or more. However, tensile strain (Δa
/ A) _g needs to be set to such an extent that the lattice relaxation of the cladding layers 18 and 23, the light guide layers 19 and 22 and the barrier layer 21 does not occur due to this distortion. That is, the cladding layer 1
The maximum tensile strain in which lattice relaxation does not occur in the light guiding layers 8 and 23, the light guide layers 19 and 22 and the barrier layer 21 is the upper limit of the tensile strain that can be set.

In the case of the second embodiment described above, for example, when the TE / TM polarization intensity ratio is set to 50 or more, as described above, the cladding layers 18 and 23, the light guide layers 19 and 22, Tensile strain of barrier layer 21 (Δa / a)
_g may be set to about | -0.05 |% or more.

Therefore, in the above-described second embodiment, the cladding layers 18 and 23, the light guide layers 19 and 22, and the barrier layer 2
The tensile strain (Δa / a) _g of No. 1 is set to about −0.2%.

Also in this case, the distribution of the TE / TM polarization intensity ratio when the light output of the semiconductor laser device is 3 mW is the same as the result shown in FIG. 6 as in the first embodiment. I got it.

That is, according to the semiconductor laser device of the present invention, the layers disposed around the well layer 5 are configured to have a tensile strain, and the amount of the tensile strain is set to an optimum value. By doing so, it is possible to prevent a phenomenon in which light emission in the TM mode is likely to occur due to distortion or the like due to the thermal expansion coefficient of the material, and it is possible to concentrate the distribution of the TE / TM polarization intensity ratio to a high value. Become.

[0072]

As described above, according to the semiconductor laser device of the present invention, the following effects can be obtained. A layer arranged in contact with or adjacent to the well layer is configured to have a tensile strain, and the amount of the tensile strain is set to an optimum value. It is configured to occur. As a result, it is possible to cancel the effect of tensile strain generated in the well layer due to the stress caused by the thermal expansion coefficient of the material, to prevent a phenomenon in which light emission in the TM mode is likely to occur, and to prevent TE / TM polarization. The distribution of the intensity ratio can be concentrated on a high value.

[Brief description of the drawings]

FIG. 1 is a diagram showing a semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a view showing compressive strain equivalently generated in a well layer due to tensile strain of an optical guide layer.

FIG. 3 is a view showing the Al composition ratio and strain of each layer in FIG.

FIG. 4 is a diagram showing a semiconductor laser device according to a second embodiment of the present invention.

FIG. 5 is a view showing the Al composition ratio and strain of each layer in FIG.

FIG. 6 is a diagram showing a distribution of a TE / TM polarization intensity ratio of the semiconductor laser device of FIG. 1;

FIG. 7 is a diagram showing a conventional semiconductor laser device.

FIG. 8 is a view showing the Al composition ratio and strain of each layer in FIG. 7;

FIG. 9 is a diagram showing the direction of stress generated in an active layer during manufacturing.

FIG. 10 is a diagram showing a distribution of a TE / TM polarization intensity ratio of the semiconductor laser device of FIG. 7;

[Explanation of symbols]

1: n-type GaAs substrate 1, 2: n-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P
Cladding layer, 3,7: In _0.5 (Ga _0.5 Al _0.5 ) _0.5 P optical guide layer, 4, 15, 20: Multiple quantum well active layer, 5: InGaAs well layer (Δa / a> 0), 6: In _0.5 (Ga _0.5 Al _0.5 ) _0.5 P barrier layer, 8: p-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P
Cladding layer, 9: InGaP contact layer, 10: n-type GaAs current blocking layer, 11: p-type GaAs contact layer, 12: AuZn / Au electrode, 13: AuGe / Au electrode, 14, 17: In1 _-X (Ga _0.5 Al _{0.5) X} P optical guide layer (Δa / a <0), 16: In 1-X (Ga 0.5 Al 0.5) X P barrier layer (Δa / a <0), 18,23: In 1-y ( Ga _0.3 Al _0.7 ) _y P clad layer (Δa / a <0), 19,22: In _1-y (Ga _0.5 Al _0.5 ) _y P optical guide layer (Δa / a <0), 21: In _1-y (Ga _0.5 Al _0.5 ) _y P barrier layer (Δa / a <0).

Claims (6)

[Claims] A first conductive type substrate, a first conductive type first cladding layer formed on the substrate, a first light guide layer formed on the first cladding layer, A multiple quantum well active layer formed on one light guide layer and composed of n (n is a natural number of 2 or more) well layers and (n-1) barrier layers between the n well layers A second light guide layer formed on the multiple quantum well active layer; a second conductive type second clad layer formed on the second light guide layer and having a stripe-shaped ridge; It is formed on both sides of the ridge of the second cladding layer and has a function of blocking current,
The multiple quantum well, comprising: a first conductivity type current blocking layer having a larger thermal expansion coefficient than the second cladding layer; and a contact layer formed on the ridge of the second cladding layer and on the current blocking layer. In a semiconductor laser device in which laser light emitted from an active layer has a TE mode intensity higher than a TM mode intensity, the first light guide layer and the second light guide layer And at least one of the (n-1) -th barrier layers has a tensile strain with respect to the n-th well layer.
The equipment. 2. When the first light guide layer has a tensile strain on the substrate, the first cladding layer has a first portion having a tensile strain on the substrate. 2. The semiconductor laser device according to claim 1, wherein said first portion is adjacent to said first light guide layer. 3. When the second light guide layer has a tensile strain on the substrate, the second cladding layer has a second portion having a tensile strain on the substrate. 3. The semiconductor laser device according to claim 2, wherein said second portion is adjacent to said second light guide layer. 4. The method according to claim 1, wherein all of the first light guide layer, the second light guide layer, and the barrier layer of the (n-1) layer have a tensile strain with respect to the substrate. The semiconductor laser device according to claim 1. 5. A tensile strain on the substrate among the first light guide layer, the second light guide layer, the barrier layer of the (n-1) layer, the first portion, and the second portion. the total thickness of the third portion having a d, the thickness of the well layer of the n-layer and L _w, if the sum of the thickness of the well layer of the n-th layer and the n × L _w In addition, the tensile strain is 0.00
4. The semiconductor laser device according to claim 3, wherein the value is set so as to be not less than 97 × n × L _w / d. 6. The semiconductor laser device according to claim 5, wherein said n is 2.