JP2001274512A - Semiconductor laser and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve the manufacturing yield of semiconductor lasers,
Provided is a semiconductor laser having a novel structure and a method for manufacturing the same. SOLUTION: On a sapphire substrate 101, a buffer layer 102, a first contact layer 103, a first cladding layer 104, a first light guide layer 107, an active layer 108, a cap layer 109, a second light guide layer. A 110, a second cladding layer 111, and a second contact layer 112 are sequentially formed. Then, the first cladding layer 104 is formed in a mesa stripe shape, and the current blocking layer 106 is formed on both sides of the first cladding layer 104 so as to cover the entire side surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser and a method for manufacturing the same, and more particularly, to a semiconductor laser and a method for manufacturing the same that can be suitably used for a large-capacity optical disk device, a laser beam printer, and the like.

[0002]

2. Description of the Related Art A semiconductor laser used in an optical disk device or the like has a long life and a low threshold current operation, as well as a stable single transverse mode operation, a low astigmatic difference, a low noise and a low aspect ratio. It has been demanded. At present, a 400 nm band semiconductor laser satisfying all these characteristics has not been realized.

Conventionally, a ridge waveguide structure as shown in FIG. 3 has been used as a single transverse mode GaN semiconductor laser. This ridge waveguide structure is manufactured as follows. First, a buffer layer 202 made of a GaN semiconductor layer, a first contact layer 203 made of an n-GaN semiconductor layer, and a first cladding layer 204 made of an n-AlGaN semiconductor layer are formed on a sapphire substrate 201 by first crystal growth. , the first optical guide layer ₂₀₅ made of n-GaN semiconductor _{layer, Ga 1-X in X n} / Ga 1-Y in Y
A multiple quantum well active layer 206 composed of an N (0 <Y <X <1) semiconductor layer, a cap layer 207 composed of a p-AIGaN semiconductor layer, a second optical guide layer 208 composed of a p-GaN semiconductor layer, p-AlGaN A second cladding layer 209 made of a semiconductor layer and a second contact layer 210 made of a p-GaN semiconductor layer are sequentially formed.

Subsequently, the ridge stripe 211 is formed by partially removing the second clad layer 209 and the second contact layer 21 in the laminating direction by, for example, reactive ion etching using Cl ₂ gas. . On the surface other than the ridge stripe 211, for example, S
An insulating film 212 made of iO ₂ is formed. As a result, a refractive index difference from the ridge stripe 211 is generated, and electrical insulation can be ensured.

Then, a p-electrode 213 made of, for example, Ni / Au is formed on the ridge stripe 211, and a part of the first contact layer 203 is partially etched in the thickness direction. An n-electrode 214 made of TiAl is formed.

The ridge waveguide type GaN thus obtained
In the system semiconductor laser, when the n-electrode 214 is grounded and a voltage is applied to the p-electrode 213, holes are injected from the p-electrode 213 side and electrons are injected from the n-electrode 214 side toward the active layer 206. As a result, an optical gain occurs in the active layer 206, and laser oscillation occurs. Further, since the ridge stripe 211 has a refractive index waveguide structure having a refractive index difference in a direction perpendicular to the laminating direction, the optical mode becomes a single transverse mode and is stable. In addition, since the astigmatism is relatively small, a high-performance semiconductor laser can be realized.

[0007]

However, when actually manufacturing a ridge waveguide type GaN-based semiconductor laser as shown in FIG. 3, there are the following extremely difficult problems. In FIG. 3, ridge stripe 2
As described above, the reactive ion etching using Cl ₂ gas is used to form the ridge 11.
This is an important factor for determining the effective refractive index difference from the O ₂ insulating film 212.

FIG. 4 is a calculation result showing the dependence of the effective refractive index of the ridge stripe 211 and the difference of the effective refractive index between the ridge stripe 211 and the SiO ₂ insulating film 212 on the remaining thickness d of the p-AlGaN cladding layer. . p
As the residual thickness d of the AlGaN cladding layer increases, the effective refractive index of the ridge stripe 211 sharply increases, and the difference in effective refractive index between the ridge stripe 211 and the SiO ₂ insulating film decreases. And p-AlG
When the remaining thickness d of the aN cladding layer exceeds 200 nm, the effective refractive index difference becomes almost zero. That is, it is required to control the etching when forming the ridge stripe 211 with extremely high precision.
It is required to control the etching depth of the p-AlGaN cladding layer with a degree of accuracy.

However, in general reactive ion etching, the variation in each etching operation or on the same substrate surface is about several tens nm. Therefore, etching for forming the ridge stripe 211 cannot be performed with high accuracy, and as a result,
There is a problem that the yield of the ridge waveguide type GaN semiconductor laser is reduced.

An object of the present invention is to provide a semiconductor laser having a novel structure and a method for manufacturing the same in order to improve the manufacturing yield of the semiconductor laser.

[0011]

SUMMARY OF THE INVENTION The present invention solves the above problems by providing a first contact layer, a first cladding layer, a first light guide layer, an active layer, A cap layer, a second light guide layer, a second cladding layer,
The first cladding layer has a mesa stripe shape, and the entire side surface of the first cladding layer is formed on both sides of the first cladding layer. The present invention relates to a semiconductor laser comprising a current blocking layer so as to cover the semiconductor laser.

Further, according to a method of manufacturing a semiconductor laser of the present invention, a first contact layer, a first clad layer, a first light guide layer, A method for manufacturing a semiconductor laser, comprising: an active layer, a cap layer, a second light guide layer, a second clad layer, and a second contact layer, which are stacked in this order,
The first cladding layer is partially removed over the entire thickness direction, and the first contact layer is partially removed in a part of the thickness direction. And forming a current blocking layer on the first contact layer so as to cover the whole of the mesa stripe structure. By heating the current block layer, mass transport is generated, and a portion of the current block layer formed on the mesa stripe structure is removed.

The present inventors have conducted intensive studies in order to find a semiconductor laser having a new configuration that replaces the conventional ridge waveguide type semiconductor laser, which necessarily requires a highly accurate etching operation. As a result, based on the above-described manufacturing method of the present invention, it was possible to obtain a semiconductor laser having a novel configuration with significantly improved manufacturing yield.

That is, in a laminated structure similar to that of a conventional semiconductor laser, a first clad layer made of a predetermined semiconductor layer is formed in a mesa stripe shape instead of the second clad layer made of p-AlGaN. A current block layer made of a predetermined semiconductor layer is formed so as to cover the first clad layer having the mesa stripe shape. Thereafter, when the current block layer is heated to a predetermined temperature, mass transport occurs in the current block layer, and a portion of the current block layer formed on the upper surface of the first cladding layer in the mesa stripe shape is formed. Disappear.

As a result, the current block layer is formed only on the side surface of the mesa stripe-shaped first cladding layer.
It exists so as to cover the entire side surface. Therefore, the first cladding layer and the current blocking layer have the same configuration as the _second cladding layer and the SiO ₂ insulating layer in the conventional semiconductor laser. Then, the semiconductor laser of the present invention having such a configuration, based on the effective refractive index difference between the first cladding layer and the current block layer,
As with the conventional ridge waveguide type semiconductor laser, it exhibits a single transverse mode optical mode. That is, by manufacturing the semiconductor laser of the present invention based on the manufacturing method of the present invention, it is possible to provide a semiconductor laser having the same characteristics as the conventional semiconductor device at a high yield without requiring a highly accurate etching operation. it can.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments of the present invention with reference to the drawings. FIG. 1 is a sectional view showing an example of the semiconductor laser of the present invention. In the semiconductor laser shown in FIG. 1, a buffer layer 102 made of an AlN semiconductor layer grown at a low temperature, a first contact layer 103 made of an n-GaN semiconductor layer, and an n-AlGaN semiconductor layer are formed on a sapphire substrate 101. A first cladding layer 104, a first optical guide layer 107 made of an n-GaN semiconductor layer, and Ga _1-X In _X N /
_{Ga 1-Y In Y N (} 0 <Y <X <1) multi-quantum well made of a semiconductor layer an active layer 108, p-AlGaN cap layer 109 made of a semiconductor layer, p-GaN semiconductor layer consisting essentially of a second of Light guide layer 110, second cladding layer 111 made of p-AlGaN semiconductor layer, and p ⁺ -GaN
The 112 contact layers 112 composed of semiconductor layers are stacked in this order.

A p-electrode 113 made of, for example, Ni / Ti is formed on the second contact layer 112, and a surface of the first contact layer 103, which is exposed by etching and removing each of the above layers, For example, an n-electrode 114 made of Ti / Al is formed.

The first cladding layer 104 has a mesa stripe shape, and a current blocking layer 106 is formed on both sides of the first cladding layer 104 so as to cover the entire side surface 104B.

The current blocking layer 106 has a stepped shape, and a portion 10 of the current blocking layer 106 separated from the first cladding layer 104 in a direction perpendicular to the lamination direction.
The height of 6-2 is smaller than the height of the portion 106-1 of the current blocking layer 106 adjacent to the first cladding layer 104. Furthermore, the upper surface 10 of the portion 106-1 of the current blocking layer 106 adjacent to the first cladding layer 104 is formed.
6A and the upper surface 104A of the first cladding layer 104.
And height are almost equal. That is, the upper surface 10
4A and the upper surface 106A constitute a plane of the same level.

First Cladding Layer 10 in Mesa Stripe
By forming the current blocking layer 4 and the current blocking layer 106 as described above, it is possible to easily form an active layer bent in a step shape as described below.

First Cladding Layer 10 in Mesa Stripe
4 has a height (thickness) H of 0.2 to 5 μm, and a step h of the stepped current blocking layer 106 is 0.1 to 4 μm. Then, the first light guide layer 1 laminated on these
07 to the second light guide layer 110 is 0.05 to 0.3 μm.
m.

Therefore, the first light guide layer 107, the active layer 108, the cap layer 109, and the second light guide layer 110 laminated on the first clad layer 104 and the current block layer 106 in a mesa stripe shape are Corresponding to a plane formed by the upper surface 104A of the first cladding layer 104 and the upper surface 106A of the current block layer 106, their central portions are flat, and the current block layer 106 has a stepped shape. Correspondingly, a configuration in which the flat portion is stepped outward from the flat portion is provided. That is, the first clad layer 10 having the mesa stripe shape described above is formed.
According to the shape of the current blocking layer 106 and the current blocking layer 106, it is possible to obtain the active layer 108 which is bent in a stepwise manner.

The second cladding layer 111 has a thickness of 0.4 to 2 μm so as to fill a step formed from the first light guide layer 107 to the second light guide layer 110 formed by the stepped current blocking layer 106. Has a thickness of

First clad layer 10 in the form of a mesa stripe
4 is covered with the current blocking layer 106, even if a predetermined voltage is applied to the p-electrode 113 and the n-electrode 114, a current flows into the active layer 108 from a region other than the first cladding layer 104. Never do. For this reason,
Light is emitted only on the first clad layer having a mesa stripe shape.

Further, since the active layer 108 is bent stepwise in a direction perpendicular to the laminating direction, the active layer 108 has a refractive index change at the bent portion. That is, the active layer 108
Has a refractive index waveguide structure having a refractive index difference in the lateral direction. Therefore, the light emitted as described above is confined in a flat portion on the first cladding layer 104 having a mesa stripe shape and propagates. As a result, a single transverse mode semiconductor laser can be provided.

In the semiconductor laser shown in FIG. 1, the sapphire substrate 101 and the first contact layer 103
Is formed between the sapphire substrate 101 and the first contact layer 103 to alleviate the lattice mismatch and promote the crystal growth of the first contact layer 103. Things.

Next, a method of manufacturing a semiconductor laser according to the present invention will be described. FIG. 2 is a process chart showing an example of a method for manufacturing a semiconductor laser according to the present invention. First, as shown in FIG. 2A, a low-temperature growth buffer layer 102 made of AlN and an n-GaN
A first contact layer 103 made of a semiconductor layer;
A first cladding layer 104 made of an AlGaN semiconductor layer is sequentially stacked.

Thereafter, the assembly thus obtained is taken out of the crystal growing apparatus. Then, using photolithography and reactive ion etching, the first cladding layer 104 is partially formed over the entire thickness direction and the first contact layer 103 is partially formed over a part of the thickness direction. The first cladding layer 104 and the first contact layer 1 are removed.
03 is formed in a self-forming manner. This state is shown in FIG.

In FIG. 2B, a part of the first contact layer 103 is also removed to remove the first clad layer 1.
A mesa stripe structure composed of a part of the first contact layer 04 and the first contact layer is manufactured. The configuration of a part of the mesa stripe structure including a part of the first contact layer 103 is such that the side surface of the first cladding layer 104 is completely covered by a current blocking layer to be formed later. That's why. That is, when the mesa stripe structure is formed only of the first cladding layer, the lower portion of the first cladding layer may remain without being removed by the etching. The portion of the first cladding layer that does not constitute the mesa stripe structure cannot be completely covered by the current blocking layer. As a result, the current caused by the applied voltage leaks, and uniform light emission becomes impossible.

Next, the assembly obtained as described above is introduced again into the crystal growing apparatus, and the first contact layer 10 is formed.
3, a current blocking layer 1 made of a high-resistance GaN semiconductor layer so as to cover the mesa stripe structure 105.
06 is formed. This state is shown in FIG.

Next, for example, an NH ₃ atmosphere, NH ₃ +
An H ₂ atmosphere, or _NH 3 + _H in a reducing atmosphere such as ₂ atmosphere, the assembly obtained as mentioned above 900-1
Heat at 200 ° C, preferably 950-1150 ° C, for several minutes. Then, mass transport occurs in the current block layer 106. That is, the current blocking layer 10
The GaN semiconductor particles constituting the portion formed on the mesa stripe structure 105 of FIG.
5 moves to the portion of the current block layer existing on the side surface.
As a result, the current block layer disappears from the upper surface 105A of the mesa stripe structure 105, and the mesa stripe structure 105
Exists only on the side surface 105B side. This state is shown in FIG.

By appropriately controlling the mass transport described above, the upper surface 10 of the mesa stripe structure can be controlled.
The height of 5A and the height of the upper surface 106A of the portion 106-1 near the mesa stripe structure of the current block layer 106 can be made substantially equal.

In addition, the current block layer is formed as shown in FIG. 2 according to the thickness of the current block layer and the height of the mesa stripe structure.
As shown in (d), it can be formed stepwise. Next, the crystal growth is restarted, and as shown in FIG. 2E, the first light guide layer 107, the active layer 108, and the cap layer 10 are formed.
9, second light guide layer 110, second cladding layer 11
First and second contact layers 112 are sequentially formed.

Next, although not shown, the contact layer 112
2E, the surface of the first contact layer 103 is exposed by etching the assembly shown in FIG.
An electrode 114 is formed.

As described above, when the first cladding layer 104 is made of an AlGaN semiconductor layer and the current block layer 106 is made of a GaN semiconductor layer, the mole fraction of AlN in the AlGaN semiconductor layer Is preferably 4 to 10%, more preferably 5 to 8%.
%. This facilitates the generation of the mass transport described above, and reduces the heating temperature and the holding time.

Although the present invention has been described with reference to the embodiments of the present invention, the contents of the present invention are not limited to the above, and any modifications or changes may be made without departing from the scope of the present invention. Is possible.

For example, in the embodiment of the present invention, the current block layer 106 is formed of a GaN semiconductor layer, but may be formed of an AlGaN semiconductor layer.
At this time, Al in the AlGaN semiconductor layer
The N mole fraction is preferably smaller than the AlN mole fraction in the AlGaN semiconductor layer forming the first cladding layer 104 for the same reason as described above.

In the semiconductor laser shown in FIG. 1, the first contact layer 103, the first cladding layer 104, and the first light guide layer 107 are formed of an n-type semiconductor layer, and the cap layer 109, the second The light guide layer 110, the second cladding layer 111, and the second contact layer 112 are made of a p-type semiconductor layer. However, each of the above layers can be composed of semiconductor layers of opposite conductivity types. That is, the first contact layer 103 and the like can be formed from a p-type semiconductor layer, and the cap layer 109 and the like can be formed from an n-type semiconductor layer.

[0039]

As described above, according to the semiconductor laser and the method of manufacturing the same of the present invention, a constituent etching step is not required at the time of manufacturing the semiconductor laser. Therefore, a semiconductor laser having the same performance as that of the conventional ridge waveguide type semiconductor laser can be provided with a high production yield.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a semiconductor laser of the present invention.

FIG. 2 is a process chart in an example of a method for manufacturing a semiconductor laser of the present invention.

FIG. 3 is a cross-sectional view illustrating an example of a conventional semiconductor laser.

FIG. 4 shows the residual thickness of the second cladding layer and the effective refractive index of the ridge stripe, and the ridge stripe and SiO _2.
4 is a graph showing a relationship between an effective refractive index difference between insulating layers.

[Explanation of symbols]

 101, 201 Sapphire substrate 102, 202 Buffer layer 103, 203 First contact layer 104, 204 First cladding layer 105 Mesa stripe structure 106 Current blocking layer 107, 205 First light guide layer 108, 206 Active layer 109 207 Cap layer 110, 208 Second light guide layer 111, 209 Second cladding layer 112, 210 Second contact layer 113, 213 P electrode 114, 214 N electrode 211 Ridge stripe

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Satoshi Ueyama 4-216-203 Umedaoka, Tenpaku-ku, Nagoya-shi, Aichi F-term (reference) 5F073 AA09 AA19 AA45 AA51 AA74 CA07 CB05 CB07 CB10 CB10 DA25

Claims (12)

[Claims] A first contact layer on the substrate;
A first light guide layer, an active layer, a cap layer, a second light guide layer, a second clad layer,
A semiconductor laser comprising a second contact layer and a second contact layer laminated in this order, wherein the first cladding layer has a mesa stripe shape, and a side surface of the first cladding layer on both sides of the first cladding layer. A semiconductor laser comprising a current blocking layer so as to cover the whole. 2. The current blocking layer has a stepped shape,
In a direction perpendicular to the stacking direction of the respective layers, the height of a portion of the current blocking layer separated from the first cladding layer is higher than the height of a portion of the current blocking layer adjacent to the first cladding layer. The height of the upper surface of the first cladding layer and the height of the upper surface of a portion of the current blocking layer adjacent to the first cladding layer are substantially equal to each other. Item 2. The semiconductor laser according to item 1. 3. The active layer has a flat portion corresponding to an upper surface of the first cladding layer and an upper surface of the adjacent portion of the current blocking layer, the flat portions having substantially the same height as each other. 3. The semiconductor laser according to claim 2, wherein the semiconductor laser is bent downward from the flat portion outward in a direction perpendicular to the laminating direction of the current block layer. 4. 4. The first contact layer, the first cladding layer, and the first light guide layer are formed of an N-type semiconductor layer, and the cap layer, the second light guide layer,
4. The semiconductor laser according to claim 1, wherein the second cladding layer and the second contact layer are formed of a P-type semiconductor layer. 5. 5. The semiconductor device according to claim 1, wherein a buffer layer is provided between said substrate and said first contact layer.
5. The semiconductor laser according to any one of items 4 to 4. 6. A first contact layer, comprising: a first contact layer on a substrate;
A first light guide layer, an active layer, a cap layer, a second light guide layer, a second clad layer,
A method for manufacturing a semiconductor laser comprising a second contact layer and a second contact layer laminated in this order, wherein the first cladding layer is partially removed over the entire thickness direction and the first contact layer is removed. Is partially removed in a part of the thickness direction to form a mesa stripe structure including the first cladding layer and a part of the first contact layer in a self-forming manner. A current block layer is formed on the contact layer so as to cover the whole of the mesa stripe structure, and mass transport is generated by heating the current block layer, and the current block layer is formed on the mesa stripe structure of the current block layer. A method for manufacturing a semiconductor laser, wherein a formed portion is removed. 7. The mass transport by heating the current block layer makes the height of the upper surface of the mesa stripe structure substantially equal to the height of a portion of the current block layer close to the mesa stripe structure, In a direction perpendicular to the stacking direction, the height of a portion of the current block layer separated from the mesa stripe structure is lower than the height of a portion of the current block layer close to the mesa stripe structure, and the current block layer is 7. The method according to claim 6, wherein the semiconductor laser has a stepped shape. 8. The active layer has a flat portion corresponding to an upper surface of the mesa stripe structure and an upper surface of a portion of the current block layer close to the mesa stripe structure, and has a stepped shape of the current block layer. 8. The method of manufacturing a semiconductor laser according to claim 7, wherein the semiconductor laser is formed so as to be bent downward from the flat portion outward in a direction perpendicular to the direction in which the respective layers are stacked. 9. The heating of the current blocking layer may be 900 to 900.
The method according to claim 6, wherein the method is performed at 1200 ° C. 10. The first contact layer, the first cladding layer, and the first light guide layer are composed of an N-type semiconductor layer, and the cap layer, the second light guide layer, The method according to claim 6, wherein the second cladding layer and the second contact layer are formed of a P-type semiconductor layer. 11. The first cladding layer constituting the mesa stripe structure is made of an AlGaN semiconductor layer, and the current block layer is made of a GaN semiconductor layer;
The method according to claim 10, wherein a molar fraction of AlN in the AlGaN semiconductor layer constituting the first cladding layer is 4 to 10%. 12. The method of manufacturing a semiconductor laser according to claim 6, wherein a buffer layer is formed between said substrate and said first contact layer.