JPH08130342A - Semiconductor laser - Google Patents

Abstract

PURPOSE: To provide a semiconductor laser generating no COD even when it is operated at large output. CONSTITUTION: An n-AlGaAs first clad layer 20, an active layer 30, a p-AlGaAs etched second clad layer 40a, and a p-GaAs etched contact layer 50a are formed successively from the substrate side on an n-GaAs substrate 10. The edge face side on both sides of a stripe-like ridge 70 is embedded by an n-GaAs edge-face side block layer 110 and the remaining part is embedded by an n-AlGaAs center- part lower-side block layer 80a and an n-GaAs center-part upper-side block layer 90a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high power semiconductor laser, and more particularly, to the optical damage at the end face of a resonator which is a drawback of a semiconductor laser having a GaAs substrate.
The present invention relates to a structure of a semiconductor laser which suppresses a high optical damage (abbreviated as COD)).

[0002]

2. Description of the Related Art Conventionally, a semiconductor laser of this type is disclosed, for example, in Document 1: "1991 Autumn Meeting of the Institute of Electronics, Information and Communication Engineers C-118 FIG. 1".

The structure of the semiconductor laser disclosed in this document will be briefly described below.

On the n-GaAs substrate, in order from the substrate side,
n-AlGaAs clad layer, active layer, p-AlGaA
An s clad layer and a p-GaAs contact layer are formed. The active layer is a quantum well layer made of InGaAs and A
InGa in which barrier layers made of 1GaAs are alternately laminated
It is composed of a semiconductor layer having an As / AlGaAs multiple quantum well structure. A ridge is formed by the p-AlGaAs cladding layer and the p-GaAs contact layer. Both sides of the ridge are filled with the n-InGaP block layer and the n-GaAs block layer.

Further, an n-type electrode is formed on the lower surface of the substrate and a p-type electrode is formed on the upper surface of the contact layer.

[0006]

However, in the conventional semiconductor laser, both sides of the ridge are filled with the same current blocking layer over the entire area between the emitting end face and the high-reflecting end face, so that the same optical confinement structure is obtained. ing. Therefore, when operating at high output, the light density becomes high at both end faces of the semiconductor laser, particularly at the emitting end face, and the end face portion generates heat due to the absorption of light based on the surface level. As a result of this heat generation, the band gap energy at the end face portion is reduced. Therefore, the laser light is further absorbed and heat is generated. As a result of repetition of this, there is a possibility that a phenomenon in which crystals melt and break at the end face portion, that is, optical damage (hereinafter sometimes referred to as COD) occurs.

Therefore, there has been a demand for the appearance of a semiconductor laser that does not cause COD breakdown even when operating at high output.

[0008]

As described above, in order to obtain a semiconductor laser which does not cause COD even when operating at a high output, in the present invention, the structure of the semiconductor laser is as follows. First, this semiconductor laser is
The substrate includes at least an s substrate, a first clad layer above the GaAs substrate, an active layer above the first clad layer, a second clad layer above the active layer, and a current blocking layer. Then, a stripe-shaped ridge is formed between the emitting end face and the high-reflecting end face, and both sides of the ridge are filled with a current block layer, which is a light confinement type.

When the current blocking layer is formed by the first block layer provided on the high reflection end face side and the second block layer provided on the emission end face side, both sides of the ridge are formed. The equivalent refractive index of the second region located from the substrate to the surface of the second block layer is equal to that of the first region located adjacent to the second region on both sides of the ridge from the substrate to the surface of the first block layer. Greater than rate. Further, the equivalent refractive index of the ridge region located at the ridge portion from the substrate to the surface of the second cladding layer is larger than the equivalent refractive index of the first region.

In the preferred embodiment of the invention, the equivalent refractive index of the second region is greater than the equivalent refractive index of the ridge region.

Further, in the preferred embodiment of the present invention, the second
The equivalent refractive index of the region is smaller than the equivalent refractive index of the ridge region.

The current blocking layer is formed between the second block layer provided on the emission end face side, the third block layer provided on the high reflection end face side, and between the second block layer and the third block layer. And a first block layer that is located on both sides of the ridge, and an equivalent refractive index of a second region located on both sides of the ridge from the substrate to the surface of the second block layer, and on both sides of the ridge. To the surface of the third block layer, the equivalent refractive index of the third region is located on both sides of the ridge adjacent to the second region and the third region, and is equal to that of the first region from the substrate to the surface of the first block layer. It is larger than the equivalent refractive index. Further, the equivalent refractive index of the ridge region located at the ridge portion from the substrate to the surface of the second cladding layer is larger than the equivalent refractive index of the first region.

In a preferred embodiment of the present invention, the second region and the third region have an equivalent refractive index higher than that of the ridge region.

Further, in the preferred embodiment of the present invention, the second
The equivalent refractive index of the region and the third region is smaller than the equivalent refractive index of the ridge region.

Further, in the preferred embodiment of the present invention, the second
The equivalent refractive index of the area is larger than the equivalent refractive index of the third area.

[0016]

According to the semiconductor laser of the present invention described above, the current blocking layer is formed of two layers or three layers. When the current blocking layer is formed of two layers, the current blocking layer is formed of a first block layer provided on the high reflection end face side and a second block layer provided on the emission end face side. Then, the equivalent refractive index of the region (second region) located on both sides of the ridge from the substrate to the surface of the second block layer is located adjacent to the second region on both sides of the ridge, and is from the substrate to the first block layer. The structure is larger than the equivalent refractive index of the region up to the surface (first region).

When the current blocking layer is formed of three layers, the current blocking layer is a second block layer provided on the emitting end face side, a third block layer provided on the high reflection end face side, and a third block layer. The first block layer is formed between the second block layer and the third block layer. And
Equivalent refractive index of the region located on both sides of the ridge from the substrate to the surface of the second block layer (second region) and the equivalent refractive index of regions located on both sides of the ridge from the substrate to the surface of the third block layer (third region) The refractive index is larger than the equivalent refractive index of a region located adjacent to the second region and the third region on both sides of the ridge and extending from the substrate to the surface of the first block layer.

By the way, the effect of confining laser light is weak in a region having a large equivalent refractive index. Therefore, when the current blocking layer is formed of two layers,
Alternatively, when the current blocking layer is formed of three layers, light confinement becomes weak at both end faces of the emitting end face and the reflecting end face. Therefore, the laser light propagating in the resonator constituted by the emitting end face and the high-reflecting end face spreads at that portion, and the light density is reduced. Therefore, heat generation is suppressed at the emission end face portion. And COD becomes difficult to occur.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. In these drawings, each component merely shows the shape, size, and positional relationship of each component to the extent that the present invention can be understood. In addition,
In the following description, in order to facilitate understanding of the element that constitutes the semiconductor laser of the present invention, a method of manufacturing this element will be briefly described, and then the elements that constitute the semiconductor laser of the present invention will be described.

FIG. 1 and FIG. 4 are perspective views schematically showing the structure of elements constituting a semiconductor laser which is an embodiment of the present invention. 2 (A) to (C), FIG. 3 (A), (B)
FIG. 6 is a perspective view schematically showing a step of manufacturing an element that constitutes the semiconductor laser according to the embodiment of the present invention.

First, on the n-GaAs substrate 10, is the substrate side
In order, n-Al_x Ga_1-x As first clad layer (for example,
For example, x = 0.2, carrier concentration 5 × 10¹⁷cm^-3Less than,
Thickness 1.5-2 μm) 20, active layer 30, p-Al_x G
a_1-x As second cladding layer (eg, x = 0.2,
Rear concentration 2 × 10¹⁸cm^-3Below, thickness 1.5-2 μm)
40, p-GaAs contact layer (for example, carrier concentration
Degree 1.5 × 10¹⁹cm ^-3Below, thickness 0.3-0.5μ
m) 50 is formed (FIG. 2 (A)). The active layer is
-Put In_x Ga_1-x Quantum well layer made of As (eg,
For example, 0.15 ≦ x ≦ 0.2, and a thickness of 8 to 10 nm),
A barrier layer of undoped GaAs (eg, a thickness of 4
0 to 80 nm) and And-In_x 
Ga_1-x In the semiconductor layer of As / GaAs multiple quantum well structure
It is composed of And each layer by MOVPE
Formed and lattice matched to the substrate 10.

Next, a SiO ₂ stripe 60 having a width of 4 to 6 μm is formed into p-Ga by a photolithography process.
It is formed on the As contact layer 50. Then, for example,
By chemical etching using a mixed solution of hydrogen bromide, p
The stripe-shaped ridge 7 is formed by etching the -GaAs contact layer 50 and the p-AlGaAs cladding layer 40.
0 is formed (FIG. 2 (B)). In this case, the thickness of the remaining p-AlGaAs cladding layer 40 after etching is about 0.5 μm, and the width of the ridge 70 is 3 to 5 μm.
The etching time is controlled so that The width of the ridge 70 is set in order to obtain a good optical output in the optical oscillation transverse mode.
It is controlled to 3 to 5 μm. In the figure, 40a indicates an etched second clad layer, and 50a indicates an etched contact layer.

Next, the n-Al _x Ga _1-x As lower block layer (for example, x = 0.6, carrier concentration 5 × 10 ¹⁷ c
m ⁻³ or less, thickness 0.5 to 1 μm) 80, n-GaAs
Upper block layer (for example, carrier concentration 2 × 10 ¹⁸ cm
^-3) embedding both sides of the stripe-shaped ridge 70 by 90. Each layer is formed by MOVPE. After that, the SiO ₂ stripe 60 is removed by, for example, chemical etching using hydrofluoric acid (FIG. 2C).

Next, a SiO ₂ etching mask 100 having a predetermined shape is formed on the surface formed by the p-GaAs etched contact layer 50a, the n-AlGaAs lower block layer 80 and the n-GaAs upper block layer 90. . After that, for example, by chemical etching using a hydrogen bromide-based mixed solution, the SiO ₂ etching mask 10 is formed.
N-GaAs upper block layer 90 and n-AlGa formed in the part exposed from 0 and the lower part
The As lower block layer 80 is etched (FIG. 3).
(A)). In the figure, 80a indicates the lower block layer of the central part of n-AlGaAs, and 90a indicates the upper block layer of the central part of n-GaAs.

Next, in the portion where the n-GaAs upper block layer 90 and the n-AlGaAs lower block layer 80 are removed by etching, the n-GaAs end face side block layer (for example, carrier concentration is 2 × 10 ¹⁸ cm ^-3 or less). ) 110
Embed The n-GaAs end face side block layer 110 is M
It is formed by OVPE. After that, the SiO ₂ etching mask 100 is removed by, for example, chemical etching using hydrogen fluoride (FIG. 3 (B), FIG. 1).

Next, on the back side of the substrate 10, an n-type electrode and p-G are formed.
A p-type electrode is formed on the aAs-etched contact layer 50a. Then, the n-GaAs end face side block layer 1
The length of 10 in the stripe direction is 10 to 20 μm, respectively.
Cleave so that m. At this time, the length of the central block layers 80a and 90a in the stripe direction is, for example, 500 to 1000 μm. After that, one cleaved surface is AR coated to provide a low reflection film, and the other cleaved surface is HR coated to provide a high reflection film. Then, the cleaved surface provided with the low-reflection film becomes the emission end surface.

When the device is formed in this manner, the current blocking layer includes the second blocking layer provided on the emission end face side, the third blocking layer provided on the high reflection end face side, and the second blocking layer.
The first block layer is formed between the block layer and the third block layer. In this embodiment, the second
The block layer and the third block layer are composed of the n-GaAs end face side block layer 110, and the first block layer is n-Al.
It is composed of a GaAs central lower block layer 80a and an n-GaAs central upper block layer 90a.

Here, the second region 130 located on both sides of the ridge from the substrate to the surface of the second block layer, that is, the substrate 10, the n-AlGaAs first cladding layer 20, the active layer 3 is formed.
0, p-AlGaAs etched second cladding layer 4
0a and the refractive index of the average value which weighted the light intensity in each layer of the second region 130 including the n-GaAs end face side blocking layer 110, that is, the equivalent refractive index is n ₂ .

Further, it is located on both sides of the ridge and is located at a third position from the substrate.
The third region 140 up to the surface of the block layer, that is, the substrate 10, the n-AlGaAs first cladding layer 20, the active layer 3
0, p-AlGaAs etched second cladding layer 4
0a, and the equivalent refractive index of the third region 140 composed of the n-GaAs end face side blocking layer 110 is n ₃ .

Further, it is located adjacent to the second region 130 and the third region 140 on both sides of the ridge, and is located first from the surface of the substrate.
The first region 120 to the surface of the block layer, that is, the substrate 1
0, n-AlGaAs first cladding layer 20, active layer 3
0, p-AlGaAs etched second cladding layer 4
0a, the equivalent refractive index of the first region 120 including the n-AlGaAs central lower block layer 80a and the n-GaAs central upper block layer 90a is n ₁ .

Further, it is located at the ridge portion and is second from the substrate.
The ridge region 150 to the surface of the clad layer, that is, the substrate 10, the n-AlGaAs first clad layer 20, the active layer 3
0, p-AlGaAs etched second cladding layer 4
The equivalent refractive index of the ridge region 150 made of ₀ is n ₀ .

In this embodiment, the equivalent refractive index n ₀ of the ridge region 150 is larger than the equivalent refractive index n _{1 of} the first region 130. Therefore, a refractive index guiding structure is formed, and light is strongly confined in the active layer in the ridge region 155. And
The light density required for laser oscillation can be obtained.

Further, in this embodiment, the second block layer and the third block layer are the same, so that the second region 130 is formed.
Equal the equivalent refractive index n ₂ of the equivalent refractive index n ₃ of the third region 140. Then, an equivalent refractive index n ₂ of the second region 130 and the equivalent refractive index n ₃ of the third region 140, the first region 120
Is larger than the equivalent refractive index n ₁ .

Further, in this embodiment, the second area 130
Greater than the equivalent refractive index n ₂ of the equivalent refractive index n ₃ of the third region 140, the effective refractive index n ₀ of the ridge region 150.

That is, there is a relationship of n ₂ = n ₃ > n ₀ > n ₁ .

For this reason, light confinement is weak at the emission end face or the high reflection end face. Therefore, the laser light propagating in the resonator constituted by the emitting end face and the high-reflecting end face spreads at that portion, and the light density is reduced. Then, heat generation is suppressed at the emission end face portion or the high reflection end face portion. Then, COD destruction becomes significantly less likely to occur.

In this embodiment, the length of the end face side blocking layer 110 in the stripe direction is set to 10 to 20 μm, but if this length is too long, it causes an increase in loss and disturbance of the oscillation mode. If it is too short, the effect of lowering the level of COD destruction cannot be obtained.

Up to now, the case where the current blocking layer is formed of three layers has been described, but as shown in FIG. 4, the current blocking layer is two layers, that is, the first blocking layer provided on the high reflection end face side. And the second block layer provided on the emission end face side, the equivalent refractive index of the second regions 130 located on both sides of the ridge from the substrate to the surface of the second block layer is n ₂ , First region 1 located on both sides adjacent to the second region from the substrate to the surface of the first block layer 1
If the equivalent refractive index n ₁ is 20, the effect of lowering the level of COD breakdown is obtained when the relationship of n ₂ > n ₀ > n ₁ is satisfied.

Further, n ₀ > n ₂ = n ₃ > n ₁ (when the current block layer is formed of three layers) or n ₀ > n ₂
> N ₁ (when the current blocking layer is formed of two layers)
If the relationship is satisfied, the level of COD destruction can be lowered and the disturbance of the optical oscillation transverse mode can be suppressed. In this case, the end surface side blocking layer 110, that is,
The second block layer and the third block layer (when the current block layer is formed of three layers) or the second block layer (when the current block layer is formed of two layers) are
-Al _x Ga _1-x As lower block layer (for example, 0.3
≦ x ≦ 0.5, carrier concentration 5 × 10 ¹⁷ cm ⁻³ or less, thickness 0.5 to 1 μm) and n-GaAs upper block layer (for example, carrier concentration 2 × 10 ¹⁸ cm ⁻³ or less). Just configure it.

Although the case where the relationship of n ₂ = n ₃ (where the current blocking layer is formed of three layers) is satisfied has been shown so far, the same effect can be obtained even if n ₂ > n _3. Obtainable. For example, n ₂ > n ₀ > n ₃ > n
_When the relationship of ₁ (when the current blocking layer is formed of three layers) is satisfied, the level of COD breakdown can be significantly reduced and the disturbance of the optical oscillation transverse mode can be suppressed. In this case, the second block layer is composed of an n-GaAs block layer (for example, carrier concentration is 2 × 10 ¹⁸ cm ⁻³ or less), and the third block layer is composed of n-Al _x Ga _1-x A.
s lower block layer (for example, 0.3 ≦ x ≦ 0.5, carrier concentration 5 × 10 ¹⁷ cm ⁻³ or less, thickness 0.5 to 1 μm)
And an n-GaAs upper block layer (for example, a carrier concentration of 2 × 10 ¹⁸ cm ⁻³ or less), and the first block layer is an n-Al _x Ga _1-x As lower block layer (for example, x =
0.6, carrier concentration 5 × 10 ¹⁷ cm ⁻³ or less, thickness 0.
5-1 μm) and n-GaAs upper blocking layer (eg,
Carrier concentration is 2 × 10 ¹⁸ cm ⁻³ or less).

Obviously, the invention is not limited to the embodiments described above. Similar effects can be obtained when the ridge is formed by the n-AlGaAs clad layer, the active layer, the p-AlGaAs clad layer and the p-GaAs contact layer. In this case, it is necessary to fill both sides of the ridge up to the upper side of the active layer with a p-type block layer and the upper side thereof with an n-type block layer.

In this embodiment, the n-type substrate is used for description, but a p-type substrate can be used by switching the conductivity type between n and p.

A bulk layer may be used as the active layer.

[0044]

As is apparent from the above description, according to the semiconductor laser of the present invention, the current blocking layer is formed of two layers or three layers. Therefore, when the current block layer is formed of two layers, only the equivalent refractive index of the region on the emission end face side is formed, or when the current block layer is formed of three layers, both the emission end face side and the high reflection end face side are formed. The equivalent refractive index of the region is larger than that of the remaining region.

As a result, when the current blocking layer is formed of two layers, it is at the emission end face portion, or when the current blocking layer is formed of two layers, at both the emission end face portion and the reflection end face portion. , Light confinement is weak. Therefore,
The laser light propagating in the resonator formed by the emitting end face and the high-reflecting end face spreads at that portion, and the light density decreases. Therefore, heat generation is suppressed at the emission end face portion. Then, COD destruction is less likely to occur.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an essential part of an element constituting a semiconductor laser used in an example.

2A to 2C are perspective views schematically showing a process of manufacturing an element that constitutes a semiconductor laser.

3A and 3B are perspective views schematically showing a process of manufacturing an element that constitutes the semiconductor laser, following FIG.

FIG. 4 is a schematic perspective view showing an essential part of an element constituting a semiconductor laser used in an example.

[Explanation of symbols]

10: Substrate 20: First Cladding Layer 30: Active Layer 40: Second Cladding Layer 40a: Etched Second Cladding Layer 50: Contact Layer 50a: Etched Contact Layer 60: SiO ₂ Stripe 70: Ridge 80: Lower Block Layer 80a: Central lower block layer 90: Upper block layer 90a: Central upper block layer 100: SiO ₂ etching mask 110: End face block layer 120: First region 130: Second region 140: Third region 150: Ridge region

Claims (7)

[Claims] 1. A GaAs substrate, a first cladding layer above the GaAs substrate, an active layer above the first cladding layer, a second cladding layer above the active layer, and a current blocking layer. An optical confinement type semiconductor laser having at least a stripe-shaped ridge formed between an emitting end face and a high-reflecting end face, the both sides of which are filled with the current blocking layer, wherein the current blocking layer is the high-reflecting end face. A first block layer provided on one side of the ridge, and a second block layer provided on the side of the emission end face, and located on both sides of the ridge from the substrate to the surface of the second block layer. Is larger than the equivalent refractive index of the first region located on both sides of the ridge adjacent to the second region and extending from the substrate to the surface of the first block layer. The ridge section Located from the surface of the substrate to the second
A semiconductor laser, wherein the equivalent refractive index of the ridge region up to the surface of the cladding layer is larger than the equivalent refractive index of the first region. 2. The semiconductor laser according to claim 1, wherein the second region has an equivalent refractive index higher than that of the ridge region. 3. The semiconductor laser according to claim 1, wherein the second region has an equivalent refractive index smaller than that of the ridge region. 4. A GaAs substrate, a first cladding layer above the GaAs substrate, an active layer above the first cladding layer, a second cladding layer above the active layer, and a current blocking layer. In at least an optical confinement type semiconductor laser in which a stripe-shaped ridge is formed between an emitting end face and a highly reflective end face, and both sides thereof are filled with the current blocking layer, the current blocking layer is provided on the emitting end face side. A second block layer provided on the first reflective layer, a third block layer provided on the highly reflective end face side, and a first block layer formed between the second block layer and the third block layer. And an equivalent refractive index of a second region located on both sides of the ridge from the substrate to the surface of the second block layer and a second region located on both sides of the ridge from the substrate to the third block layer. The surface of And the equivalent refractive index of the third region of the first region is equal to that of the second region on both sides of the ridge and adjacent to the second region and from the surface of the substrate to the surface of the first block layer. The equivalent refractive index of the ridge region located at the ridge portion from the substrate to the surface of the second cladding layer is higher than the refractive index,
A semiconductor laser characterized by being larger than an equivalent refractive index of a region. 5. The semiconductor laser according to claim 4, wherein an equivalent refractive index of the second region and the third region is
A semiconductor laser having a larger refractive index than the ridge region. 6. The semiconductor laser according to claim 4, wherein an equivalent refractive index of the second region and the third region is
A semiconductor laser having a smaller refractive index than that of the ridge region. 7. The semiconductor laser according to claim 4, wherein the second region has an equivalent refractive index higher than that of the third region. .