JPH0685381A - Semiconductor laser element and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce the internal loss of a semiconductor laser element due to the optical absorption effect of a current stopping layer constituting the semiconductor laser element and to make an oscillation take place stably in a fundamental transverse mode at a high differential efficiency and in a low threshold current. CONSTITUTION:A first clad layer 3, an active layer 4, a second clad layer 5, a current stopping layer 6 provided with a striped groove 8 for forming a current path and a third clad layer 9 are laminated in order on a semiconductor substrate 1. The layer 6 has a first region 6a, whose thickness to come into contact to a place where the groove penetrates this layer is thin, and a second region 6b, which is linked with this region 6a and is thick in thickness, so that the striped groove 8 is formed in a two-step depth. The thickness D1 of the region 6a is set within a range of 0.05mum<D1<0.3mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device and a method for manufacturing the same, and more particularly to a semiconductor laser device that operates in a fundamental mode stably with a low threshold current and high efficiency, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A semiconductor laser device is required to have good optical characteristics in many application fields, and in order to realize this, a refractive index guiding structure is often adopted. As a refractive index waveguide structure, a self-aligned structure produced by a crystal growth method such as a molecular beam epitaxy (MBE) method or a metal organic chemical vapor deposition (MOCVD) method is known.

FIG. 12 shows a cross section of a conventional semiconductor laser device having a self-aligned structure. This semiconductor laser device includes an n-GaAs buffer layer 102 (thickness: 0.5 μm) formed on a n-GaAs substrate 101 by MOCVD.
m), n-Al _y Ga _1-y As first cladding layer 103 (y = 0.
45, thickness 1 μm), Al _x Ga _1-x As active layer 104 (x = 0.
13, a thickness of _{0.08μm), p-Al y Ga} 1-y As second cladding layer 105 (thickness 0.2 [mu] m), n-GaAs current blocking layer 1
06 (thickness 1 μm) are sequentially laminated. Subsequently, photolithography and etching are performed to perform current blocking layer 1
In 06, a stripe-shaped groove 120 having a width of 3 to 4 μm and reaching the surface of the second cladding layer 105 is formed. After that, a p-Al _y Ga _1-y As third cladding layer 108 (thickness 1 μm) and a p-GaAs cap layer 109 (thickness 1 μm) are laminated in this order by MOCVD again. . During operation, the stripe-shaped groove 1 provided in the current blocking layer 106
A current path is formed at 20, and the current blocking layer 10 is formed.
A refractive index guiding mechanism is formed by the light absorption function of 6. In this semiconductor laser device, the light absorption action causes the loss for the higher-order transverse modes to be much larger than the loss for the fundamental transverse modes, so that extremely stable fundamental transverse mode operation can be obtained.

[0004]

However, in the conventional semiconductor laser device described above, due to internal loss due to the light absorption effect of the current blocking layer 106, deterioration of characteristics such as reduction of differential efficiency and increase of oscillation threshold current. Is invited. In order to increase the differential efficiency and reduce the oscillation threshold current, the internal loss based on the light absorption effect must be minimized.

Therefore, an object of the present invention is to provide a semiconductor laser device capable of reducing the internal loss due to the light absorption effect of the current blocking layer and stably oscillating the fundamental transverse mode with a high differential efficiency and a low threshold current, and a manufacturing method thereof. To do.

[0006]

In order to achieve the above object, the semiconductor laser device of the present invention comprises a semiconductor substrate, at least a first cladding layer, an active layer, and
In a semiconductor laser device in which a second cladding layer, a current blocking layer having a stripe-shaped groove forming a current path, and a third cladding layer are sequentially stacked, the current blocking layer has the stripe shape. The first region having a small thickness, which is in contact with the portion where the groove penetrates this layer, and the second region which is continuous with the first region and has a large thickness, so that the groove has a depth of two steps. It is characterized by having.

The thickness D1 of the first region of the current blocking layer is preferably in the range of 0.05 μm <D1 <0.3 μm.

Further, the semiconductor laser device of the present invention is composed of at least a first cladding layer, an active layer, a second cladding layer, and a plurality of types of semiconductor layers on a semiconductor substrate to form a current path. In a semiconductor laser device in which a current blocking structure layer provided with a stripe-shaped groove and a third cladding layer are sequentially stacked, in the current blocking structure layer, the stripe-shaped groove has a depth of two steps. As described above, the groove has a first region having a small thickness which is in contact with a portion penetrating the layer, and a second region which is continuous with the first region and has a large thickness.

Of the semiconductor layers constituting the first region of the current blocking structure layer, the sum D5 of the thicknesses of the semiconductor layers that absorb the laser light emitted by the active layer is 0.05 μm <
It is desirable that it is within the range of D5 <0.3 μm.

Further, it is desirable that the current blocking structure layer includes, as the semiconductor layer, layers that can be selectively etched with each other.

The method for manufacturing a semiconductor laser device according to the present invention further comprises a step of laminating at least a first cladding layer, an active layer, a second cladding layer and a current blocking layer on a semiconductor substrate in this order. Photolithography and etching are performed to form a stripe-shaped groove having a predetermined width and depth on the surface side of the current blocking layer, and photolithography is performed so that currents on both sides of the stripe-shaped groove are formed. The step of providing a photoresist having a stripe-shaped window wider than the width of the groove on the surface of the blocking layer and having the stripe-shaped groove at the center; and using the photoresist as a mask, the current-blocking layer has the center of the window. Etching is performed until it penetrates at the portion, and the current blocking layer has a depth of two steps, leaving partially etched regions on both sides of the penetration portion. Forming a looped groove, on the semiconductor substrate, it is characterized by having a step of laminating at least a third cladding layer.

Further, according to the method of manufacturing a semiconductor laser device of the present invention, at least the first cladding layer, the active layer, the second cladding layer, and the first current that can be selectively etched are formed on the semiconductor substrate. A step of sequentially stacking a blocking layer, an etch stop layer, and a current blocking structure layer including a second current blocking layer, and performing photolithography to form a photo having a striped window on the surface of the current blocking structure layer. A resist is provided, and the second current blocking layer is selectively etched with respect to the etch stop layer to be removed by using the photoresist as a mask. Subsequently, the etch stop layer is formed into the first current blocking layer. By selectively etching and removing the current blocking structure layer to form a stripe-shaped groove having a predetermined width and depth, and performing photolithography. A step of providing a photoresist having a stripe-shaped window centering the stripe-shaped groove and having a stripe-shaped window wider than the width of the groove on the surface of the current blocking structure layer on both sides of the stripe-shaped groove; As a mask, the first current blocking layer is etched and removed at the center of the window, and the second current blocking layers are selectively etched and removed with respect to the etch stop layer on both sides of the center. Then, the method includes a step of forming a stripe-shaped groove having a depth of two steps in the current blocking layer, and a step of forming at least a third clad layer on the semiconductor substrate.

The present inventor has studied the characteristics of the self-aligned semiconductor laser device. As a result, the magnitude of internal loss (α) based on the light absorption effect of the current blocking layer is determined by the thickness (Db) of the current blocking layer. ) And is not simply proportional, but rather changes periodically.

For example, in the model of the self-aligned structure shown in FIG. 10 (a), the thickness (Db) of the current blocking layer is changed (the composition and thickness of each layer are shown in parentheses in the figure). ing.). In this case, according to the calculation result of the present inventor, the difference (ΔN) in the equivalent refractive index between the oscillation region A and the regions B on both sides of the oscillation region A and the magnitude of the internal loss based on the light absorption effect of the current blocking layer ( α) changes as shown in FIG. That is, when Db is increased from about 0.1 μm, the values of ΔN and α both oscillate and converge to a constant value at a sufficiently thick value. When the thickness (Db) of the current blocking layer is changed in the model of the self-aligned structure shown in FIG. 11 (a), the magnitude of the internal loss (α) based on the light absorption effect of the current blocking layer is the same. As indicated by the broken line in FIG. 6B, the model is slightly shifted with respect to α (indicated by the solid line).

These results indicate that the refractive index guiding mechanism is not simply determined by the magnitude of the light absorption of the current blocking layer, that is, the light blocking layer simply becomes thinner when the thickness (Db) of the current blocking layer is reduced. The absorption (that is, α) is decreased, and at the same time, ΔN is also decreased, indicating that the index guiding mechanism is not lost. And only when Db is 0.05 to 0.3 μm,
It shows that N is maximum and α is minimum. Therefore, if Db is set in the range of 0.05 to 0.3 μm, ΔN
Is maximized, the laser light is strongly confined in the stripe portion, and α is expected to be substantially minimized to provide a low threshold current and high efficiency characteristics (note that for higher-order transverse modes, FIG. Stable fundamental transverse mode oscillation is expected, as in the conventional example shown in.).

However, in reality, when the thickness of the current blocking layer becomes 0.3 μm or less, the original function of the current blocking layer is obtained.
(Current blocking function) becomes insufficient. Therefore, the preferable characteristics as described above cannot be obtained immediately.

Therefore, in the present invention, based on the above result, the thickness of the current blocking layer is such that the groove is in contact with the portion where the groove penetrates the layer so that the stripe groove has a depth of two steps. Has a thin first region and a second region which is continuous with the first region and has a large thickness. That is, by changing the thickness and structure of the current blocking layer outside the oscillation region (region where the stripe-shaped groove penetrates),
In the vicinity of the oscillation region (corresponding to the first region), set the condition of low loss with little light absorption, and the region outside it.
In (corresponding to the second region), the thickness of the current blocking layer is increased to provide a sufficient current blocking function. With this configuration,
The current blocking function is not sufficient in the vicinity of the oscillation region (corresponding to the first region), but if the width is set to be small, about 1 μm, there is almost no effect on the current blocking function of the entire device. Therefore, low threshold current and high efficiency characteristics are realized by the effect of reducing the internal loss (α) described above. Further, strong light confinement in the oscillation region is realized, and as a result, the spread of the far-field image in the direction parallel to the active layer becomes large and a low ellipticity is obtained.

Further, in the semiconductor laser device having a current blocking structure layer including a plurality of types of semiconductor layers instead of the current blocking layer, the stripe-shaped groove of the current blocking structure layer has a depth of two steps. As described above, a first region having a small thickness that is in contact with a portion where the groove penetrates the layer and a second region that is continuous with the first region and has a large thickness are provided. in this case,
Of the semiconductor layers forming the first region, the sum D5 of the thicknesses of the semiconductor layers that absorb the laser light emitted by the active layer.
Is set within the range of 0.05 μm <D5 <0.3 μm. As a result, in the vicinity of the oscillation region (first
(Corresponding to the region (1)), the light absorption is small and the condition is set to low loss, while the outer region (corresponding to the second region) is made thicker by increasing the thickness of the current blocking structure layer. It can have a function.

When the current blocking structure layer includes layers that can be selectively etched with each other as the semiconductor layer, the semiconductor layer underlying the layer to be etched can be used as a so-called etch stop layer to ensure etching. You can stop. Therefore, the current blocking structure layer can be accurately finished.

[0020]

The semiconductor laser device and the method for manufacturing the same according to the present invention will be described in detail below with reference to embodiments.

FIG. 1 shows a cross section of the semiconductor laser device of the first embodiment. This semiconductor laser device uses n-GaAs
On the substrate 1, an n-GaAs buffer layer 2 (thickness 1 μm) and n
-Al _y Ga _1-y As first cladding layer 3 (y = 0.55, thickness 1.5 μm) and Al _x Ga _1-x As active layer 4 (x = 0.14, thickness 0.1 μm). and _{08μm), p-Al y Ga} 1-y as second cladding layer 5 (thickness 0.20 [mu] m) and, n-GaAs current blocking layer 6 stripe-shaped grooves 8 are provided to form a current path ( Thickness 1μ
m) and p-Al _y Ga _1-y As third cladding layer 9 (thickness 1.2)
.mu.m) and the p-GaAs cap layer 10 (thickness 1 .mu.m) are provided in this order. The current blocking layer 6 has a first region 6a having a small thickness and a first region 6a which is in contact with a portion where the groove penetrates the layer so that the stripe-shaped groove 8 has a depth of two steps.
And a second region 6b which is continuous with the region and has a large thickness. In addition, 11 is a p-side electrode and 12 is an n-side electrode.

This semiconductor laser device is manufactured as follows.

First, as shown in FIG. 4 (a), n-GaAs
On the substrate 1, the n-GaAs buffer layer 2 (thickness 1 μm), the n-Al _y Ga _1-y As first cladding layer 3 (y = 0.55, thickness 1.5 μm) were formed on the substrate 1 by MOCVD. Al _x Ga _1-x As active layer 4 (x = 0.14, thickness _{0.08μm), p-Al y Ga} 1-y As second cladding layer 5 (thickness 0.20 [mu] m) and n-GaAs The current blocking layer 6 (thickness 1 μm) is continuously grown.

Next, as shown in FIG. 3B, photolithography and etching are performed to form a stripe-shaped groove 7 having a width of about 2.5 μm and a depth of 0.15 μm in the central portion of the current blocking layer 6. Form.

Next, photolithography is performed again to provide a photoresist (not shown) on the surface of the current blocking layer 6 on both sides of the stripe groove 7. At this time, the photoresist 4 has a width 4 centered on the stripe groove 7.
A stripe-shaped window of about μm is formed. (The value of W2 is 1 at maximum because the spread width of laser light is usually several μm.
Set to 0 μm). Then, as shown in FIG.
Using the photoresist as a mask, the current blocking layer 6 is formed.
Is etched by a thickness of 0.85 μm to form a current blocking layer 6
A stripe-shaped groove 8 having a depth of two steps is formed in. That is, as shown in FIG. 1, a penetrating portion is formed in the current blocking layer 6, and the thickness D1 = contact with the penetrating portion is set.
A first region 6a having a thickness of 0.15 μm and a second region 6b having a thickness D2 = 1 μm, which is continuous with the first region 6a, are formed. The width (one side) of the first region 6a corresponds to (W2-W1) / 2, which is about 0.75 μm.

Next, as shown in FIG.
The p-Al _y Ga _1-y As third cladding layer 9 (thickness: 1.2 μm) and the p-GaAs cap layer 1 were formed on the entire surface by the CVD method.
0 (thickness 1 μm) is sequentially laminated.

Finally, as shown in FIG. 3E, a p-side electrode 11 and an n-side electrode 12 are formed on both sides of the substrate. Then, the substrate is divided into chips by cleavage to complete the fabrication.

This semiconductor laser device has a structure near the oscillation region.
In the area (corresponding to the first area 6a), low light absorption is set to a low loss condition, and in the area outside the area (corresponding to the second area 6b), the current blocking layer may be thick enough. It has an excellent current blocking function. Therefore, low threshold current and high efficiency characteristics can be realized by the effect of reducing the internal loss (α) described above. Also, strong optical confinement in the oscillation region can be realized. As a result, the spread of the far-field image in the direction parallel to the active layer becomes large, and a low ellipticity can be obtained. In this configuration, the current blocking function is not sufficient in the vicinity of the oscillation region (corresponding to the first region 6a), but its width is set to a small value of 1 μm or less (about 0.75 μm). Has almost no effect on the current blocking function of.

FIG. 2 shows a cross section of the semiconductor laser device of the second embodiment. This semiconductor laser device uses n-GaAs
On the substrate 21, an n-GaAs buffer layer 22 (thickness 1 μm)
And n-Al _y Ga _1-y As first cladding layer 23 (y = 0.5
5, the thickness _{1.5μm), Al w Ga 1-} w As the first optical guiding layer 24 (w = 0.40 and a thickness of 0.15 [mu] m), a quantum well structure active layer 25, A _l WGA _1- wAs second optical guide layer 26 (thickness 0.15 μm) and p-Al _y Ga _1-y As second cladding layer 2
7 (thickness of 0.20 μm) and a plurality of types of semiconductor layers 28 to 34
From it, a current blocking structure layer 41 striped groove 36 is provided to form a current _{path, p-Al y Ga 1-} y As third cladding layer 37 (with a thickness of 1.2 [mu] m), p- A GaAs cap layer 38 (thickness 1 μm) is provided. The current blocking structure layer 41 has a first region 41a having a small thickness and a first region 41a which is in contact with a portion where the groove penetrates the layer so that the stripe groove 36 has a depth of two steps. Has a second region 41b which is continuous with the region 41a and has a large thickness. In addition, 39 is a p-side electrode and 40 is an n-side electrode.

This semiconductor laser device is manufactured as follows.

First, as shown in FIG. 6 (a), n-GaAs
On the substrate 21, by molecular beam epitaxy (MBE) method,
n-GaAs buffer layer 22 (thickness 1 μm), n-Al _y Ga _1-y
As first cladding layer 23 (y = 0.55, thickness 1.5 μm)
m), Al _w Ga _1-w As first light guide layer 24 (w = 0.40,
Thickness 0.15 μm), quantum well structure active layer 25, Al _w Ga
_1-w As second light guide layer 26 (thickness 0.15 μm), p-Al
_y Ga _1-y As The second clad layer 27 (thickness: 0.20 μm) is sequentially laminated. Then, the p-GaAs first protective layer 28 (thickness 0.03 μm) constituting the current blocking structure layer 41, p−
Al _u Ga _1-u As first etch stop layer 29 (u = 0.5)
5, thickness 0.03 μm), n-Al _v Ga _1-v As first current blocking layer 30 (v = 0.1, thickness 0.15 μm), n-GaAs second
Protective layer (thickness 0.03 μm) 31, n-Al _u Ga _1-u As second
Etch stop layer (thickness 0.03 μm) 32, n-Al _v Ga
_1-v As second current blocking layer 33 (thickness 0.6 μm) and n-Ga
A third protective layer 34 (thickness: 0.05 μm) is sequentially laminated.

Next, a photoresist (not shown) is applied to the surface of the third protective layer 34, and photolithography is performed to form a striped window having a width of about 2.5 μm in the photoresist. To do. Next, as shown in FIG. 6B, selective etching is performed using this photoresist as a mask to remove the third protective layer 34 and the second current blocking layer 33, and the second etch stop layer 32 is removed. Stop the etching with. Subsequently, the second etch stop layer 32 is selectively removed (at this time, the second protective layer 31 becomes the etch stop layer). As a result, the stripe-shaped grooves 35 are formed on the substrate.

Next, photolithography is performed again to provide a photoresist (not shown) on the surface of the third protective layer 34 on both sides of the stripe groove 35. At this time, a striped window having a width of about 4 μm centering on the striped groove 35 is formed in this photoresist. Then, as shown in FIG. 3C, selective etching is performed using this photoresist as a mask to remove the second protective layer 31 and the first current blocking layer 30 exposed at the bottom of the stripe-shaped groove 35. Then, the etching is stopped at the first etch stop layer 29. At the same time, the third protective layer 34 and the second current blocking layer 33 on both sides of the stripe-shaped groove 35 are removed,
The etching is stopped at the second etch stop layer 32. Further, after the photoresist is removed, the first etch stop layer 29 exposed at the bottom of the stripe groove is formed.
And the second etch stop layer 32 are selectively removed (at this time, the first protective layer 28 and the second protective layer 31 are respectively removed.
Becomes the etch stop layer. ). As a result, the stripe-shaped groove 3 having a depth of two steps is formed in the current blocking structure layer 41.
6 is formed. That is, in the current blocking structure layer 41, a penetrating portion is formed, and a first region 41a that is in contact with the penetrating portion and has a small thickness and a second region that is continuous with the first region 41a and has a large thickness. 41b is formed.

In this semiconductor laser device, the semiconductor layer 2 that can be selectively etched is provided as the base of the layer to be etched.
Since 8, 29, 31, 32 are provided, the etching can be surely stopped and the stripe-shaped groove 36 can be finished with high accuracy.

Next, as shown in FIG. 7 (d), the liquid phase growth method, a first protective layer 28 exposed in the bottom of the striped groove 36 was melt-back, the entire surface, p-Al _y Ga
_1-y As Third clad layer 37 (thickness: 1.2 μm), p-Ga
An As cap layer 38 (thickness 1 μm) is laminated. The first
The protective layer 28 may be melted back, and at the same time, all or part of the third protective layer 34 on both sides of the stripe groove 36 may be melted back.

At this stage, the first of the current blocking structure layer 41 is
The thicknesses D3 and D4 (shown in FIG. 2) of the region 41a and the second region 41b are about D3 = 0.26 μm and D4 = 0.97 μm. In particular, the sum D5 of the thicknesses of the semiconductor layers 28 and 30 that absorb the laser light emitted from the active layer 25 among the semiconductor layers 28 to 34 that form the first region 41a is 0.18 μm. The width (one side) of the first region 41a is (W
2-W1) / 2, which is about 0.75 μm.

Finally, as shown in FIG. 7E, a p-side electrode 39 and an n-side electrode 40 are formed on both sides of the substrate. Then, the substrate is divided into chips by cleavage to complete the fabrication.

This semiconductor laser device has the vicinity of the oscillation region.
In the region (corresponding to the first region 41a), low light absorption is set to a low loss condition, and in the region outside thereof (corresponding to the second region 41b), the thickness of the current blocking structure layer 41 is increased. And has a sufficient current blocking function. In particular,
Of the semiconductor layers 28 to 34 forming the first region 41a, the semiconductor layer 2 that absorbs the laser light emitted by the active layer 25.
The sum D5 of the thicknesses of 8,30 is 0.23 μm, which is 0.3 μm.
It is set to less than m. Therefore, low threshold current and high efficiency characteristics can be realized by the effect of reducing the internal loss (α) described above. Also, strong optical confinement in the oscillation region can be realized. As a result, the spread of the far-field image in the direction parallel to the active layer becomes large, and a low ellipticity can be obtained.

FIG. 3 shows a cross section of the semiconductor laser device of the third embodiment. This semiconductor laser device uses n-GaAs
On the substrate 21, an n-GaAs buffer layer 22 (thickness 1 μm)
And n-Al _y Ga _1-y As first cladding layer 23 (y = 0.4
5, thickness of 2.0 μm), and the multiple quantum well structure active layer 125
And p-Al _y Ga _1-y As second cladding layer 27 (thickness 0.1
And 5 [mu] m), a plurality kinds of semiconductor layers 50-56, a current blocking structure layer 71 striped grooves 59 are formed to form a current _{path, p-Al y Ga 1-} y As third cladding layer 60 (thickness 1.8 μm) and p-GaAs cap layer 61 (thickness 1 μm). The current blocking structure layer 71 is
The first region 71a, which is thin in thickness and is in contact with the penetrating portion of this layer, so that the stripe-shaped groove 59 has a depth of two steps.
And a second region 7 that is continuous with the first region and has a large thickness.
It has 1b. In addition, 39 is a p-side electrode and 40 is an n-side electrode.

This semiconductor laser device is manufactured as follows.

First, as shown in FIG. 8A, n-GaAs
On the substrate 21, by molecular beam epitaxy (MBE) method,
n-GaAs buffer layer 22 (thickness 1 μm), n-Al _y Ga _1-y
As first clad layer 23 (y = 0.45, thickness 2.0 μm)
m), a multiple quantum well structure active layer _{125, p-Al y Ga 1} -y As
The second clad layer 27 (thickness 0.15 μm) is sequentially laminated. Then, n− forming the current blocking structure layer 71
GaAs first protective layer 50 (thickness 0.03 μm), n-Al _u Ga
_1-u As first etch stop layer 51 (u = 0.55, thickness 0.03 μm), n-GaAs first current blocking layer 52 (thickness 0.5.
15 μm), n-Al _w Ga _1-w As first re-evaporation prevention layer (w =
0.1, thickness 0.03 μm) 53, n-Al _u Ga _1-u As second etch stop layer 54 (thickness 0.03 μm), n-GaAs second current blocking layer 55 (thickness 0). .6 μm), n-Al _w Ga _1-w As
The second re-evaporation prevention layer 56 (thickness: 0.05 μm) and n-Ga
A second protective layer 57 (thickness: 0.05 μm) is sequentially laminated.

Next, a photoresist (not shown) is applied to the surface of the second protective layer 57 and photolithography is performed to form a striped window having a width of about 2.5 μm in the photoresist. . Next, as shown in FIG. 6B, selective etching is performed using this photoresist as a mask to remove the second protective layer 57, the second re-evaporation preventing layer 56, the second
Of the second etch stop layer 5 by removing the current blocking layer 55 of
At 4 the etching is stopped. Subsequently, the second etch stop layer 54 is selectively removed (at this time, the first etch stop layer 54 is removed).
The re-evaporation prevention layer 53 serves as an etch stop layer. ). As a result, the stripe-shaped grooves 58 are formed on the substrate.

Next, photolithography is performed again to provide a photoresist (not shown) on the surface of the second protective layer 57 on both sides of the stripe groove 58. At this time, a striped window having a width of about 4 μm centered on the striped groove 58 is formed in the photoresist. And
As shown in FIG. 6C, selective etching is performed using this photoresist mask to remove the first re-evaporation prevention layer 53 and the first current blocking layer 52 exposed at the bottom of the stripe-shaped groove 58. Etching is stopped at the first etch stop layer 51. At the same time, the second protective layer 57, the second re-evaporation preventing layer 56, and the second current blocking layer 55 on both sides of the stripe-shaped groove 55 are removed, and the second etch stop layer 54 is removed.
Stop the etching with. Further, after removing the photoresist, the first exposed portion at the bottom of the stripe-shaped groove is exposed.
Etch stop layer 51 and second etch stop layer 54
Are selectively removed (at this time, the first protective layer 50 and the first re-evaporation preventing layer 53 serve as an etch stop layer, respectively). As a result, the stripe-shaped groove 59 having a depth of two steps is formed in the current blocking structure layer 71. That is, the current blocking structure layer 71 is formed with a penetrating portion, and the first region 71 in contact with the penetrating portion is thin.
a and a second region 71b that is continuous with the first region 71a and has a large thickness are formed.

In this semiconductor laser device, the semiconductor layer 5 that can be selectively etched is provided as the base of the layer to be etched.
Since 0, 51, 53 and 54 are provided, the etching can be surely stopped and the stripe-shaped groove 59 can be finished with high accuracy.

Next, as shown in FIG. 9D, the above substrate is introduced into an MBE apparatus to re-evaporate the first protective layer 50 exposed at the bottom of the stripe groove 59. Then MBE
By the method, a p-Al _y Ga _1-y As third cladding layer 60 (thickness: 1.8 μm) and a p-GaAs cap layer 61 (thickness: 1 μm) are laminated on the entire surface.

At this stage, the first of the current blocking structure layer 71 is formed.
The thicknesses D3 and D4 (shown in FIG. 3) of the region 71a and the second region 71b are about D3 = 0.29 μm and D4 = 0.97 μm. In particular, the sum D5 of the thicknesses of the semiconductor layers 50, 52, and 53 that absorb the laser light emitted by the active layer 125 among the semiconductor layers 50 to 56 that form the first region 71a is 0.2.
It is 1 μm. The width of the first region 41a (one side)
Corresponds to (W2-W1) / 2, which is about 0.75 μm.

Finally, as shown in FIG. 9E, a p-side electrode 39 and an n-side electrode 40 are formed on both sides of the substrate. Then, the substrate is divided into chips by cleavage to complete the fabrication.

This semiconductor laser device has the vicinity of the oscillation region.
In the region (corresponding to the first region 71a), the light absorption is small and the loss is set to be low, and in the region outside thereof (corresponding to the second region 71b), the thickness of the current blocking structure layer 71 is increased. And has a sufficient current blocking function. In particular,
Of the semiconductor layers 50 to 56 forming the first region 71a, the semiconductor layer 5 that absorbs the laser light emitted by the active layer 25.
The sum D5 of the thicknesses of 0.52, 53 is 0.26 μm,
It is set to less than 0.3 μm. Therefore, low threshold current and high efficiency characteristics can be realized by the effect of reducing the internal loss (α) described above. Also, strong optical confinement in the oscillation region can be realized. As a result, the spread of the far-field image in the direction parallel to the active layer becomes large, and a low ellipticity can be obtained.

The present inventor manufactured the semiconductor laser device of each of the above examples and evaluated its characteristics. As a result,
Compared with the conventional semiconductor laser device shown in FIG. 2, the internal loss is reduced to 1/2 to 1/3, and the oscillation threshold current is about 4
It was confirmed that the current decreased from 0 mA (conventional) to about 20 to 30 mA. Further, the external differential efficiency is improved by about 1.5 times compared with the conventional one. Such characteristics are particularly effective as a high power laser. Further, in the case where the both end surfaces of the semiconductor laser device of the third embodiment are asymmetrically coated, compared with the conventional semiconductor laser device, the oscillation threshold current can be reduced by about 25 mA, and the differential efficiency is 1.
I was able to increase it five times. Further, stable fundamental transverse mode oscillation could be obtained up to 300 mW or more. Further, the ellipticity of the emitted laser light was low, and a favorable value of about 2 could be stably obtained.

Although this embodiment has been described with reference to an AlGaAs semiconductor laser device, it is of course not limited to this material system. The present invention can be widely applied to semiconductor laser devices of other materials. Further, the structure and composition of the current blocking structure are not limited to this embodiment, but can be variously changed depending on the required characteristics and the manufacturing method.

[0051]

As is apparent from the above, the semiconductor laser device of the present invention has a stripe on which at least a first cladding layer, an active layer, a second cladding layer, and a current path are formed on a semiconductor substrate. In a semiconductor laser device in which a current blocking layer provided with a groove having a groove shape and a third clad layer are sequentially stacked, the current blocking layer is configured such that the stripe groove has a depth of two steps. Since the groove has a thin first region which is in contact with a portion penetrating this layer and a second region which is continuous with the first region and has a large thickness, the vicinity of the oscillation region (first (Corresponding to the region (1)), the light absorption is small and the condition is set to low loss. In the region outside (corresponding to the second region), the thickness of the current blocking layer is increased to provide a sufficient current blocking function. You can have it. Therefore, fundamental transverse mode oscillation can be stably performed, and low threshold current and high efficiency characteristics can be realized.
Further, strong light confinement in the oscillation region can be realized, and as a result, the spread of the far-field image in the direction parallel to the active layer can be increased.

When the thickness D1 of the first region of the current blocking layer is within the range of 0.05 μm <D1 <0.3 μm, the vicinity of the oscillation region is set to a low loss condition with little light absorption. it can. That is, it is possible to realize the low threshold current and the high efficiency characteristics by making the light absorption loss α substantially minimum.

Further, the semiconductor laser device of the present invention is composed of at least a first cladding layer, an active layer, a second cladding layer, and a plurality of types of semiconductor layers on a semiconductor substrate, and forms a current path. In a semiconductor laser device in which a current blocking structure layer provided with a stripe-shaped groove and a third cladding layer are sequentially stacked, in the current blocking structure layer, the stripe-shaped groove has a depth of two steps. As described above, since the groove has a first region having a small thickness which is in contact with a portion penetrating this layer and a second region which is continuous with the first region and has a large thickness, In the vicinity of the region (corresponding to the first region), set the condition of low loss with little light absorption, and increase the thickness of the current blocking structure layer in the region outside it (corresponding to the second region). Can have sufficient current blocking function . Therefore, fundamental transverse mode oscillation can be stably performed, and a low threshold current and high efficiency characteristics can be realized. Further, strong light confinement in the oscillation region can be realized, and as a result, the spread of the far-field image in the direction parallel to the active layer can be increased.

Of the semiconductor layers forming the first region of the current blocking structure layer, the sum D5 of the thicknesses of the semiconductor layers that absorb the laser light emitted by the active layer is 0.05 μm <
When D5 <0.3 μm, the vicinity of the oscillation region can be set to a low loss condition with little light absorption. That is, it is possible to realize the low threshold current and the high efficiency characteristics by making the light absorption loss α substantially minimum.

When the current blocking structure layer includes, as the semiconductor layer, layers that can be selectively etched with each other, the underlying semiconductor layer of the layer to be etched can be used as a so-called etch stop layer. It can be stopped without fail. Therefore, the current blocking structure layer can be accurately finished.

Further, according to the method for manufacturing a semiconductor laser device of the present invention, it is possible to manufacture a semiconductor laser device that stably oscillates in the fundamental transverse mode with high differential efficiency and low threshold current.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a cross-sectional structure of a semiconductor laser device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a sectional structure of a semiconductor laser device according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a manufacturing process of the semiconductor laser device according to the first embodiment.

FIG. 5 is a diagram showing a manufacturing process of the semiconductor laser device according to the first embodiment.

FIG. 6 is a diagram showing a manufacturing process of the semiconductor laser device according to the second embodiment.

FIG. 7 is a diagram showing a process of manufacturing the semiconductor laser device according to the second embodiment.

FIG. 8 is a diagram showing a manufacturing process of the semiconductor laser device according to the third embodiment.

FIG. 9 is a diagram showing a manufacturing process of the semiconductor laser device according to the third embodiment.

10 is a refractive index difference Δ between an oscillation region and regions on both sides thereof.
FIG. 9 is a diagram showing N and a current blocking layer thickness (Db) dependency calculated by calculating an internal loss α due to light absorption.

FIG. 11 is a refractive index difference Δ between the oscillation region and regions on both sides thereof.
FIG. 9 is a diagram showing N and a current blocking layer thickness (Db) dependency calculated by calculating an internal loss α due to light absorption.

FIG. 12 is a view showing a cross-sectional structure of a conventional self-aligned structure semiconductor laser device.

[Explanation of symbols]

1 n-GaAs substrate 2 n-GaAs buffer layer 3 n-Al _y Ga _1-y As first cladding layer 4 Al _x Ga _1-x As active layer 5 p-Al _y Ga _1-y As second cladding Layer 6 n-GaAs current blocking layer 6a First region 6b Second region 7,8 Striped groove 9 p-Al _y Ga _1-y As Third cladding layer 10 p-GaAs cap layer 11 p-side electrode 12 n-side electrode

Front page continuation (72) Inventor Masafumi Kondo 22-22 Nagachimachi, Abeno-ku, Osaka, Osaka In-house (72) Inventor Toshio Hata 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture

Claims (7)

[Claims] 1. A semiconductor substrate, at least a first cladding layer, an active layer, a second cladding layer, and a current blocking layer provided with a stripe-shaped groove forming a current path,
In a semiconductor laser device in which a third clad layer is sequentially stacked, the current blocking layer has a thickness in contact with a portion where the groove penetrates the layer so that the stripe groove has a depth of two steps. A semiconductor laser device having a thin first region and a second region continuous with the first region and having a large thickness. 2. The thickness D1 of the first region of the current blocking layer.
Is within a range of 0.05 μm <D1 <0.3 μm. 3. A stripe-shaped groove for forming a current path is formed on a semiconductor substrate, the stripe groove including at least a first cladding layer, an active layer, a second cladding layer, and a plurality of types of semiconductor layers. In a semiconductor laser device in which a current blocking structure layer and a third clad layer are sequentially stacked, in the current blocking structure layer, the groove is formed so that the stripe-shaped groove has two depths. A semiconductor laser device comprising: a first region having a small thickness which is in contact with a portion penetrating this layer; and a second region which is continuous with the first region and has a large thickness. 4. The sum D5 of the thicknesses of the semiconductor layers that absorb the laser light emitted by the active layer among the semiconductor layers that form the first region of the current blocking structure layer is 0.05 μm <D5. 4. The semiconductor laser device according to claim 3, wherein the semiconductor laser device is in the range of <0.3 μm. 5. The semiconductor laser device according to claim 3, wherein the current blocking structure layer includes, as the semiconductor layer, layers that can be selectively etched with respect to each other. 6. A step of sequentially stacking at least a first clad layer, an active layer, a second clad layer, and a current blocking layer on a semiconductor substrate, and photolithography and etching to perform the current blocking. Forming a stripe-shaped groove having a predetermined width and depth on the surface side of the layer; and performing photolithography to form the stripe-shaped groove on the surface of the current blocking layer on both sides of the stripe-shaped groove. The step of providing a photoresist having a stripe-shaped window wider than the width of this groove at the center, and etching using the photoresist as a mask until the current blocking layer penetrates at the center of the window, Forming a stripe-shaped groove having a two-step depth in the current blocking layer leaving a partially etched region on both sides of the through-hole; A method of manufacturing a semiconductor laser device characterized by comprising a step of laminating at least a third cladding layer. 7. A semiconductor substrate having at least a first clad layer, an active layer, a second clad layer, a selectively etchable first current blocking layer, an etch stop layer, and a second current. A step of sequentially stacking a current blocking structure layer including a blocking layer, and performing photolithography to provide a photoresist having a stripe-shaped window on the surface of the current blocking structure layer, and using the photoresist as a mask The second current blocking layer is selectively etched and removed with respect to the etch stop layer, and then the etch stop layer is selectively etched and removed with respect to the first current blocking layer. Forming a stripe-shaped groove having a predetermined width and depth in the current-blocking structure layer; and performing photolithography to form a current-blocking structure on both sides of the stripe-shaped groove. A step of providing a photoresist having a stripe-shaped window wider than the width of the groove on the surface of the layer and having the stripe-shaped groove as a center; and using the photoresist as a mask, a first current is applied at the center of the window. The blocking layer is etched and removed, and the second current blocking layer is selectively etched with respect to the etch stop layer on both sides of the central portion to remove the current blocking layer, so that the current blocking layer has a depth of two steps. And a step of forming at least a third clad layer on the semiconductor substrate.