JP3334624B2 - Nitride semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (In _a A).
_{l b Ga 1-a-b} N, 0 ≦ a, 0 ≦ b, relates to a laser device made of a + b ≦ 1).

[0002]

2. Description of the Related Art The present inventors, on a sapphire substrate,
On a nitride semiconductor substrate made of n-GaN selectively grown via a partially formed SiO ₂ film, a plurality of nitride semiconductor layers serving as a laser element structure are stacked, and the sapphire substrate is removed. A nitride semiconductor laser device capable of continuous oscillation at room temperature for 10,000 hours or more by forming a resonance surface by cleavage has been announced. For example, Jpn.J.Appl.Phy
s.Vol.37 (1998) pp.L309-L312, Part2, No.3B, 15 March
1998. FIG. 6 shows a schematic cross-sectional view similar to that shown in the above-mentioned JJAP as a conventional laser element. FIG. 6 shows that p-Al _0.14 Ga _0.86 N / Ga is formed from the p-side contact layer made of p-GaN.
It has a ridge-shaped stripe with a width of 3 μm formed by partially etching up to a p-side cladding layer having a superlattice structure of N. The n-side contact layer made of n-GaN is exposed by etching and formed on the exposed surface. An insulating film made of SiO ₂ is formed on a side surface or an exposed plane of a stripe which is exposed by etching except for each electrode, and has an n electrode formed thereon and a p electrode formed on the uppermost portion of the stripe. 1 shows a nitride semiconductor laser device. And
This nitride semiconductor laser device can obtain laser light having a single mode aspect ratio of about 4.

[0003]

However, although the above laser device has a good life characteristic and can obtain a single mode laser beam, it has a long elliptical shape with an aspect ratio of 4 and thus has a laser beam. To apply the element to various products, it becomes somewhat difficult to stop the laser beam and design the lens. When various kinds of products are manufactured using a laser element, it is desirable that the aspect ratio of the laser beam is a circle close to 1.0. Accordingly, it is an object of the present invention to provide a nitride semiconductor laser device that reduces the aspect ratio of laser light and facilitates laser beam aperture and lens design when manufacturing a product using laser light.

[0004]

That is, the present invention can achieve the object of the present invention by the following constitutions (1) to (4). (1) p-side having nitride semiconductor layer containing Al and n
Between the side of the cladding layer, having a waveguide region including the active layer having at least a InGaN, on the p-side cladding layer, in the nitride semiconductor laser device p-side contact layer are stacked, the p The side cladding layer is clad
The thickness of the entire layer is 2.0 μm or less, and the p-side
The product with the average Al composition (%) contained in the pad layer is 4.4 or less.
It is configured such that the upper, the formed by etching toward the substrate side from the interface of the p-side contact layer side and p-side cladding layer and the waveguide region width 0.5-2.0
μm has a ridge-shaped stripe, and the refractive index is 0.1 % higher than the average refractive index of the waveguide region on both sides of the stripe and the plane of the nitride semiconductor layer continuous with the side surface.
A p-electrode is provided so as to be in contact with at least the entire surface of the p-side contact layer on the uppermost layer of the stripe via the insulating film. Nitride semiconductor laser device. (2) p-side and n-side having nitride semiconductor layer containing Al
Between the side of the cladding layer, having a waveguide region including the active layer having at least a InGaN, on the p-side cladding layer, in the nitride semiconductor laser device p-side contact layer are stacked, the n At least the side cladding layer
Also comprises a superlattice having a nitride semiconductor layer containing Al,
The thickness of the entire n-side cladding layer is 0.5 μm or more,
And Al average composition (%) contained in the n-side cladding layer
And a width of 0.5 formed by etching from the p-side contact layer side to the substrate side from the interface between the p-side cladding layer and the waveguide region. Having a ridge-shaped stripe of about 2.0 μm, and having a refractive index of 0 or less than the average refractive index of the waveguide region on both side surfaces of the stripe and the plane of the nitride semiconductor layer continuous with the side surfaces thereof. Having an insulating film having a value smaller than 1 ;
A nitride semiconductor laser device further comprising a p-electrode provided so as to be in contact with at least the entire surface of the p-side contact layer on the uppermost layer of the stripe via the insulating film. (3) The (1) or (2), wherein the ridge-shaped stripe is formed such that the width of the center of the stripe is larger than the width of the end face of the stripe.
3. The nitride semiconductor laser device according to item 1. (4) The ridge-shaped stripe is formed by etching from the p-side contact layer side to the substrate side from the interface between the waveguide region and the n-side cladding layer. The nitride semiconductor laser device according to any one of 3).

[0005] Further, as another preferable configuration of the present invention, the following configuration can be cited. (5) The nitride semiconductor according to any one of (1) to (4), wherein at least one of the p-side and n-side cladding layers has a superlattice structure including a nitride semiconductor containing Al. Laser element. (6) The active layer, the cladding layer, and the contact layer,
The nitride semiconductor laser device according to any one of (1) to (5), wherein the nitride semiconductor laser device is grown on a nitride semiconductor substrate grown by utilizing lateral growth of the nitride semiconductor. (7) The aspect (1), wherein the nitride semiconductor laser device has an aspect ratio of 1.0 to 3.0.
The nitride semiconductor laser device according to any one of (1) to (6).

That is, in the nitride semiconductor laser device of the present invention, as described above, when forming a ridge-shaped stripe, the stripe is formed by specifying the width and etching amount of the stripe, and the side surface of the formed stripe is formed. The horizontal and lateral modes can be adjusted by providing an insulating film having a refractive index smaller than the refractive index of the waveguide region on the entire surface and forming a p-electrode in contact with the entire top surface of the formed stripe. Can be reduced.

Conventionally, the transverse mode becomes the fundamental mode by reducing the stripe width, and the laser element becomes the refractive index type by providing the etching amount and the different refractive index on both side surfaces of the stripe. Known in theory. However, the aspect ratio of the known nitride semiconductor laser device described in JJAP is 4, and a nitride semiconductor laser device having an aspect ratio of 1.0 to 3.0 has not been actually obtained.

On the other hand, the inventors of the present invention have proposed a method of converting the transverse mode into a fundamental mode and enhancing light confinement in the horizontal and lateral directions.
By combining the various configurations as in the present invention, the aspect ratio of the laser light of the nitride semiconductor laser device can be set to about 1.0 to 3.0.

In the present invention, it is preferable that the insulating film has a value smaller than the refractive index of the waveguide region by 0.1 or more in terms of light confinement in the horizontal and horizontal directions. In the present invention, if the ridge-shaped stripe is formed by etching so that the width of the center of the stripe is larger than the width of the end face of the stripe, and / or the waveguide region is formed from the p-side contact layer side. It is preferable that the layer be formed by etching from the interface with the n-side cladding layer toward the substrate side, because the aspect ratio can be easily adjusted.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a nitride semiconductor laser device (hereinafter sometimes simply referred to as a laser device) of the present invention will be described in more detail. The nitride semiconductor laser device of the present invention has a waveguide region including an active layer containing at least InGaN between a p-side cladding layer and a n-side cladding layer having a nitride semiconductor layer containing Al. A layer formed by laminating a p-side contact layer on the layer, and a width formed by etching from the p-side contact layer side to the substrate side from the interface between the p-side cladding layer and the waveguide region. Insulation having a ridge-shaped stripe of 0.5 to 2.0 μm and having a refractive index smaller than the refractive index of the waveguide region on both sides of the stripe and a plane of the nitride semiconductor layer continuous with the side. A p-layer at least in the uppermost layer of the stripe through the insulating film.
A p-electrode is provided so as to be in contact with the entire surface of the side contact layer.

In the present invention, the width of the stripe is the width of at least one stripe end located at the end of the element having the resonance surface for emitting laser light, and the width of the center of the stripe is larger than the above range. It may have a value.

In the present invention, the stripes are formed by laminating nitride semiconductor layers having an element structure on a substrate, stacking an uppermost p-side contact layer, and then etching from the p-side contact layer side. It is formed as a ridge-shaped stripe. The etching amount is from the p-side contact layer to the substrate side from the interface between the p-side cladding layer and the waveguide region, and preferably to the substrate side from the interface between the waveguide region and the n-side cladding layer. Adjusting the etching amount in this manner is preferable because the light confinement in the lateral direction is increased, and the threshold value of the laser element is significantly reduced. Further, the etching amount is not particularly limited, but from the viewpoint of the performance of the element, for example, up to a nitride semiconductor layer capable of forming an n-electrode, or formed on a substrate when the substrate is a nitride semiconductor substrate. N-side contact layer and n-side cladding layer.

Further, when forming a ridge-shaped stripe, etching is performed while adjusting the stripe width to 0.5 to 2.0 μm, preferably 0.5 to 1.0 μm. When the width of the stripe is within the above range, the horizontal / lateral mode is likely to be the basic mode, and the rise of the threshold is suppressed.

In the present invention, if the planar shape of the stripe (the shape when the element is viewed from directly above) is formed so as to become narrower as approaching the end of the stripe, the aspect ratio can be adjusted. It is preferable because it is easy to perform. In this case, the width of the stripe may be such that the width at the end of at least one of the stripes is within the above range, and the width of the center of the stripe may be a value larger than the above range. A specific example of the planar shape of the stripe in which the planar shape of the stripe becomes narrower as approaching the end portion is that described in Japanese Patent Application No. 9-352540 filed by the present applicant. As one example, for example, FIG. 3 shows a planar shape of a stripe in which the width of the stripe gradually decreases from the central portion as approaching the resonance surface.

Further, in the present invention, the insulating film may be any insulating film having a value smaller than the refractive index of the waveguide region, and preferably the insulating film has a refractive index of
A value smaller than the refractive index of the waveguide region by 0.1 or more, more preferably a value smaller than 0.3 or more, more preferably a value smaller than 0.7 or more. The upper limit of the refractive index is 1.0 or less. When the refractive index formed on the side surface of the stripe is smaller than 0.1, it is preferable in terms of confining light in the horizontal and horizontal directions. Since the refractive index of the waveguide region slightly depends on the layer constituting the waveguide region, an insulating film is appropriately selected and used according to the average refractive index of the waveguide region. The insulating film used in the present invention is specifically selected from the group consisting of, for example, Si, V, Zr, Nb, Hf, and Ta having a refractive index of about 1.6 to about 2.3. Oxides containing at least one element, BN, AlN, and the like. It is preferable to use these insulating films because the aspect ratio can be adjusted well. Here, the refractive index of the waveguide region described in the examples and the like as the laser device of the present invention is about 2.3 to 2.5, and the difference in the refractive index as an insulating film formed on the side surface of the stripe is small. 0.
It is preferable that one or more smaller ones be appropriately selected and used. In addition, as a preferable insulating film in a method of forming a stripe or the like having a first step to a fourth step to be described later, a material other than the above-described Si oxide is used in terms of operability in the step, and the like. More preferably, it is BN or at least one element of oxides of Zr and Hf. In the case where a silicon oxide is used as the insulating film, adjustment of processing conditions such as etching or a lift-off method, selection of a mask material at the time of etching, and the like are performed, and conditions are set such that the silicon oxide can be formed on the side surfaces of the stripe. Done.
Note that SiC is an insulator because it becomes amorphous in film formation by PVD such as sputtering or vapor deposition, and SiC containing no n-type or p-type impurities is also an insulator.

The method of forming the ridge-shaped stripe having the insulating film on both sides of the nitride semiconductor laser device of the present invention is not particularly limited as long as the stripe having the above-mentioned shape can be obtained. The method of forming a p-electrode formed on the entire surface of the uppermost p-side contact layer of the stripe via the insulating films formed on both side surfaces of the stripe is as follows. What is necessary is just to form via an insulating film so that it may contact. The electrode material to be the p-electrode is not particularly limited as long as it is an electrode material that can achieve ohmic contact with the p-side contact layer, and various kinds of materials can be used. Further, two or more layers may be formed as insulating films formed on the side surfaces of the stripe. In the present invention, the method of forming the ridge-shaped stripe and the p-electrode is not limited as described above. For example, the following method is specifically preferable.

First, p having a nitride semiconductor containing Al
After laminating the p-side contact layer on the side cladding layer,
A first step of forming a stripe-shaped first protective film on the surface of the p-side contact layer, and a nitride in a portion where the first protective film is not formed via the first protective film. A second step of etching the semiconductor to form a ridge-shaped stripe immediately below the protective film; and, after the second step, a second insulating material made of a material different from that of the first protective film.
Forming a protective film on the side surfaces of the stripe and the plane of the nitride semiconductor layer exposed by etching;
After the third step, the first protective film is removed, and an electrode electrically connected to the p-side contact layer is formed on the surface of the second protective film and the uppermost p-type nitride semiconductor layer. By performing the fourth step, a ridge-shaped stripe, an electrode, and the like can be formed.

In the above method, the second protective film is an insulating film having a value smaller than the refractive index of the waveguide region. Further, in the second step, the etching amount is applied to the substrate side from the interface between the p-side cladding layer and the waveguide region, a ridge-shaped stripe is formed in the nitride semiconductor, and the nitride semiconductor is continuous with the side surface of the stripe. Is exposed. In the present invention, the etching amount indicates how much etching is performed from the p-side contact layer toward the substrate side. For example, when the etching amount is up to the active layer, the plane of the nitride semiconductor to be the active layer is This indicates that etching is performed from the p-side contact layer to the extent that it is exposed.

In the first step, as a method of forming a first protective film of a stripe, a first protective film is formed on almost the entire uppermost layer of the p-type nitride semiconductor layer, and the first protective film is formed.
Forming a third protection film in a stripe shape on the first protection film, and then etching the first protection film in a stripe shape through the third protection film to form the first protection film. It is mentioned.

The method of forming stripes, electrodes, and the like in the first to fourth steps will be described in more detail with reference to FIGS. 1 and 2 are schematic cross-sectional views showing the partial structure of a nitride semiconductor wafer for explaining the steps of the formation method, and are perpendicular to the stripe formed by etching, that is, on the resonance surface. On the other hand, a diagram when cut in a parallel direction is shown. In the first step, as shown in FIG. 1C, a stripe-shaped first protective film 61 is formed on the uppermost p-side contact layer 13.

FIGS. 1A and 1B show the first protective film 6.
1 is a diagram showing a specific process which is an embodiment for forming 1; As shown in FIG. 1A, a first protective film 61 is formed on substantially the entire surface of the p-side contact layer 13, and then a third protective film having a stripe shape is formed on the first protective film 61. A film 63 is formed. After that, as shown in FIG. 1B, after the first protective film 61 is etched while the third protective film 63 is still attached, the third protective film 63 is removed. The first protective film 61 having a stripe shape as shown in FIG. Note that the etching can be performed from the p-side contact layer 13 side by changing the etching gas or the etching means while the third protective film 63 is attached.

In order to form the first protective film 61 in a stripe shape as shown in FIG. 1C, a lift-off method can be used. That is, a photoresist having a shape in which a striped hole is formed is formed, a first protective film 61 is formed over the entire surface of the photoresist, and then the photoresist is dissolved and removed, thereby forming the p-side contact layer 13.
This is a means for leaving only the first protective film 61 that is in contact with the first protective film 61. The first protective film 6 having a stripe shape is formed by a lift-off method.
1A and 1B, a stripe having an almost perpendicular end face and a uniform shape tends to be easily obtained, as compared with the case of forming No. 1.

The first protective film 61 is not particularly limited in insulating properties, and may be used at the time of etching performed in the next second step.
Any material having a difference from the etching rate of the nitride semiconductor may be used. Preferably, in order to provide a solubility difference with a second protective film 62 to be formed later, the second protective film 62 further has a property of being more easily dissolved in a gas or a solution used in etching than the second protective film 62. Select and use materials. For example, in the case of dry etching using an acid as described later, the first protective film 61 is made of S
i-oxide (including SiO ₂ ), photoresist and the like. The use of these is preferable because an insulating film having a small refractive index can be easily formed on the side surface of the stripe by the methods of the first to fourth steps. In this case, for example, hydrofluoric acid is used as the acid. As a material of the first protective film 61 in the case of using hydrofluoric acid, a Si oxide which is easily dissolved in hydrofluoric acid is preferably used. The stripe width (W) of the first protective film 61 is 0.5 to 2.0 μm, preferably 0.1 to 2.0 μm.
Adjust to 5 μm to 1 μm. The stripe width of the first protective film 61 approximately corresponds to the stripe width of the waveguide region. Adjusting the stripe width in this manner is preferable in adjusting the aspect ratio because the horizontal mode is likely to be in the basic mode, and is preferable because the increase in the threshold value is suppressed and the life characteristics are improved. As the third protective film, a resist used in photolithography or the like is used.

Next, in a second step, as shown in FIG. 2D, a portion of the p-side contact layer 13 where the first protective film 61 is not formed is interposed via the first protective film 61. By etching, a stripe corresponding to the shape of the protective film is formed immediately below the first protective film 61. In the second step, the amount of etching is preferably from the interface between the p-side cladding layer and the waveguide region to the substrate side, preferably between the waveguide region and n.
This is from the interface with the side cladding layer to the substrate side. In the example shown in FIG. 2D, the etching is performed partway through the n-side contact layer 5. Other element configurations between the p-side contact layer and the n-side contact layer forming the stripe of FIG. 2D include a p-side cladding layer 12 and a p-side cladding layer 12.
Side light guide layer 11, p-side cap layer 10, active layer 9, n
Side light guide layer 8, n-side cladding layer 7, crack prevention layer 6
It is. By etching as described above, a refractive index waveguide type laser device having a ridge-shaped stripe can be obtained. This laser device has good horizontal and horizontal light confinement, and further has a tendency that the threshold value is significantly lowered. preferable.

In the first and second steps, the etching means is not particularly limited, and may be wet etching,
Dry etching and the like are mentioned, and as described above, an etching means is selected and used depending on how the first protective film and the second protective film are selected and used. Preferably, dry etching is used. For example, in the case where Si oxide is used as the first protective film 61 in the first step, as a means for etching the first protective film 61, dry etching such as RIE (reactive ion etching) may be used. It is desirable to use a fluorine compound-based gas such as CF ₄ as the etching gas. Furthermore, as a method of etching the nitride semiconductor in the second step after forming the first protective film 61, for example, Cl ₂ , which is used in other III-V compound semiconductors,
This is performed using a chlorine-based gas such as CCl ₄ or SiCl ₄ . The use of such a chlorine-based gas is preferable because the difference in solubility between the nitride semiconductor and the first protective film 61 made of Si oxide due to etching increases, and the selectivity ratio can be increased.

Next, in the third step, as shown in FIG. 2E, a second protective film 62 having an insulating property is formed on the side surface of the ridge-shaped stripe and the nitride semiconductor layer exposed by etching. 2 (e), and the plane of the n-side contact layer 5 in FIG. 2 (e). As the second protective film 62,
It is an insulating film having a value smaller than the refractive index of the waveguide region and is selected from materials having different solubility by etching from the first protective film 61. Preferably, the material is selected from the material of the insulating film formed on the side surface of the ridge-shaped stripe. For example, when the first protective film 61 made of Si oxide is used as described above, the Si oxide is easily dissolved in hydrofluoric acid. An oxide of Zr (for example, ZrO ₂ ) is used. Further, among the above-mentioned materials of the insulating film, the materials other than the Si oxide are relatively difficult to dissolve in hydrofluoric acid. Therefore, if the first protective film 61 is made of Si oxide,
The second protective film 62 is preferably selected from the above-described insulating films.

As described above, when materials having different solubilities are selected and used in the etching process, only the first protective film 61 is removed and the surface of the n-side contact layer 5 is removed as shown in FIG. The second protective film 62 continuous on both the side and the side of the stripe can be formed. For example, when the first protective film 61 made of the Si oxide is used,
When the second protective film is formed on the side surface of the stripe or the like and then treated with hydrofluoric acid, only the first protective film 61 can be removed. By forming the insulating second protective film 62 having a small refractive index on the side surface of the stripe or the like in this manner,
This is preferable because the aspect ratio can be easily adjusted. In addition, when the second protective film 62 is formed continuously from the first protective film 61, the second protective film 62 can be formed with a uniform film thickness on the n-side contact layer 5, so that the film thickness is less likely to be uneven. Concentration of current due to non-uniform film thickness does not occur. In addition, since the etching amount is set in the middle of the n-side contact layer 5 in the second step, the second protective film 62 is formed on the plane of the n-side contact layer 5 in FIG. Above the n-side contact layer 5, the second protective film 62 is naturally formed on the plane of the nitride semiconductor layer exposed by etching.

In the case of using Si oxide for the second protective film 62, a material having a difference in solubility with respect to the second protective film 62 made of Si oxide, such as adjustment of an etching treatment liquid or gas, or the like. Select Si on the side of the stripe
The treatment is performed under such conditions that an oxide can be formed.

As a method of removing only the first protective film 61 and forming the second protective film 62 at a desired portion, a lift-off method can be used. For example, when using Si oxide as the first protective film 61 and using Zr oxide as the second protective film 62, the second protective film is more hydrofluoric than the first protective film made of Si oxide. As shown in FIG. 2E, the side surfaces of the ridge-shaped stripe, the plane on which the stripe is formed (the plane of the nitride semiconductor layer exposed by etching), and the first After a second protective film made of Zr oxide is continuously formed on the surface of the protective film 61, only the first protective film 61 can be removed by a lift-off method. As described above, when the lift-off method is used, FIG.
As shown in (2), the second protective film 62 having a uniform thickness with respect to the plane is easily formed.

Next, in a fourth step, as shown in FIG. 2F, after the first protective film 61 is removed, as shown in FIG. Side contact layer 13
The p-electrode 20 electrically connected to the p-side contact layer 13 is formed on the entire surface of the p-side contact layer 13, the side surface of the stripe, and the plane of the n-side contact layer 5. Here, since the second protective film 62 is formed first, it is not necessary to form only the p-side contact layer 13 having a narrow stripe width when forming the p-electrode 20, and it is formed in a large area. it can. Moreover, by selecting an electrode material that also serves as an ohmic contact, the p-electrode 20 can be formed as an electrode that also serves as an ohmic and bonding electrode. Further, it is preferable that the p-electrode is formed so as to be in contact with the entire surface of the p-side contact layer at the uppermost layer of the stripe, because light confinement in the horizontal and horizontal directions becomes favorable. If the p-electrode is formed on the side surface of the stripe via an insulating film, the aspect ratio can be easily adjusted.

Next, the structure of the nitride semiconductor laser device of the present invention will be described. The element structure constituting the element used in the present invention includes a p-side and an n-side cladding layers having a nitride semiconductor containing at least Al and a waveguide region including an active layer containing InGaN between the cladding layers. There is no particular limitation as long as the element structure is as follows. In the present invention, the waveguide region is a region formed between the p-side cladding layer and the n-side cladding layer and guiding light having at least the active layer. In the present invention, the waveguide region may have another nitride semiconductor layer other than the active layer. For example, an n-side guide layer, an active layer, a cap layer, and a p-side guide layer are sequentially stacked. Things can be mentioned. As the guide layer and the cap layer, known various kinds can be used, and for example, one embodiment shown in Examples described later is given. As described above, when the waveguide region is made of one or more nitride semiconductors, the average value of the refractive index of each layer is defined as the refractive index of the waveguide region. Further, the refractive index of the waveguide region varies depending on how many kinds of nitride semiconductor layers are formed or what composition is used. Therefore, as the insulating film formed on the side surface of the stripe or the like, a material having a refractive index smaller than the refractive index of the waveguide region by 0.1 or more is appropriately selected depending on the type of the waveguide region used as the laser element. Used.

In the present invention, the active layer in the waveguide region is not particularly limited as long as it is a nitride semiconductor that can be used as an active layer of a laser device. Specifically, In _x Ga ₁ -xN A nitride semiconductor represented by (0 <x <1) is exemplified. The active layer preferably has a multiple quantum well structure (MQW) in which a well layer having a smaller bandgap energy and a barrier layer having a larger bandgap energy than the well layer are stacked. The total thickness of the active layer is 400 to 500 angstroms, and in the case of MQW, the thickness of the well layer is 30 to 60 angstroms.
The thickness of the barrier layer is 60 to 120 angstroms.
Further, when the MQW, well layer, a _In x _{Ga 1-x} N to 0.1 greater than the x, barrier layer, and smaller than 0.1 value _{x In} x _{Ga 1-x} N is preferred. Further, it is preferable that the active layer of the MQW is formed by stacking a nitride semiconductor such as a well layer + a barrier layer +... The active layer may be undoped or doped with an n-type impurity and / or a p-type impurity. The impurity may be doped into both the well layer and the barrier layer, or may be doped into either one. Note that if only the barrier layer is doped with an n-type impurity, the threshold value tends to decrease.

The clad layer constituting the laser device of the present invention may be a nitride semiconductor containing at least Al as described above. The clad layer of a preferred embodiment will be described below. The cladding layer is composed of one or more nitride semiconductor layers having at least a nitride semiconductor layer containing Al, and is preferably a superlattice having a nitride semiconductor layer containing Al. When the cladding layer has a superlattice structure, the vertical and transverse modes are likely to be single modes, and the threshold value is further reduced, which is preferable. Further, the cladding layer having such a superlattice structure and the width 0.5,
When a ridge-shaped stripe shape of up to 2.0 is combined, it becomes easy to obtain a laser beam having a single transverse mode and a good aspect ratio. The cladding layer is a light confinement layer containing a nitride semiconductor having a lower refractive index than the well layer of the active layer.

The case where the clad layer has a super lattice structure will be further described below. The superlattice refers to a multilayer film structure in which a single layer has a thickness of 100 Å or less and nitride semiconductor layers having different compositions are stacked, preferably 70 Å or less, more preferably 40 Å or less.
A nitride semiconductor layer having a thickness of Å or less is stacked. As a specific configuration, for example, _Al X _{Ga 1-X} N
(0 <X <1) layer and a superlattice in which another nitride semiconductor layer having a composition different from that of the Al _X Ga _1-X N layer is laminated.
For example _{Al X Ga 1-X N /} GaN, Al X Ga 1-X
_{N / Al Y Ga 1-Y} N (0 <Y <1, Y <X), Al X
The superlattice in combination with _{Ga 1-X N / In Z} Ga 1-Z N (0 <Z <1) 3 -element mixed crystal and ternary mixed crystal such as, or ternary mixed crystal and the binary mixed crystal be able to. Most preferably Among them is a superlattice consisting of _{Al X Ga 1-X} N and GaN.

Further, the n-side cladding layer is made of at least Al
Consisting of a superlattice having a nitride semiconductor layer containing
The thickness of the entire side cladding layer is 0.5 μm or more, and the average Al composition contained in the n-side cladding layer is expressed as a percentage (%).
When expressed by, the thickness (μm) of the entire n-side cladding layer and A
By configuring so that the product of the 1-average composition (%) becomes 4.4 or more, the laser beam in the vertical / lateral mode can be controlled and the single mode is easily formed. The thickness of the n-side cladding layer is smaller than 0.5 μm, and the product of the thickness (μm) of the entire n-side cladding layer and the average Al composition (%) is 4.4.
If the number is smaller than that, the light confinement as the n-side cladding layer becomes insufficient, and the light is guided by the n-side contact layer, and the FFP
Are disturbed, and the threshold value also tends to increase. A preferable value of the product is 5.0 or more, more preferably 5.4 or more. The best mode is adjusted to 7 or more.

For example, the total thickness of the n-side cladding layer is 0.8 μm or more, and the average Al composition contained in the n-side cladding layer is 5.5% or more. The product in this case is 4.4 or more. Preferably, the total thickness of the n-side cladding layer is 1.0 μm or more, and the average Al composition contained in the n-side cladding layer is 5.0% or more. The product in this case is greater than or equal to 5.0. More preferably, the total thickness of the n-side cladding layer is 1.2 μm or more, and the average Al composition contained in the n-side cladding layer is 4.5% or more. The product in this case is 5.4 or more. This is because the relationship between the thickness of the n-side cladding layer and the Al
It specifically shows the relationship of the average composition.

Also, for the p-side cladding layer, when the total thickness of the p-side cladding layer is 2.0 μm or less and the average Al composition contained in the p-side cladding layer is expressed in percentage (%), p It may be configured such that the product of the thickness (μm) of the entire side cladding layer and the average Al composition (%) is 4.4 or more. With this configuration, the laser beam in the vertical / lateral mode can be controlled, and the mode is likely to be single mode. Note that p
More preferably, the n-side cladding layer has the above-mentioned structure than the side cladding layer. This is because the p-side cladding layer has a ridge-shaped stripe as in the present invention,
This is because, since an electrode is provided thereon, light is absorbed by the electrode, and therefore, even if light leaks in the vertical and horizontal modes, it can be almost ignored.

However, when the p-side cladding layer is configured as described above, it is desirable that the thickness of the p-side cladding layer be smaller than that of the n-side cladding layer. The reason is that when the Al average composition of the p-side cladding layer is increased or the film thickness is increased, the resistance value of the AlGaN layer tends to increase, and when the resistance value of AlGaN increases, the driving voltage tends to increase. Because. As a preferable film thickness,
The thickness is 1.5 μm or less, more preferably 1 μm or less.
Although the lower limit is not particularly limited, it is desirable that the film has a thickness of 50 Å or more in order to function as a cladding layer.
% Is desirable. By making the p-side cladding layer have a superlattice structure, the Al mixed crystal ratio of the entire cladding layer can be increased, so that the refractive index of the cladding layer itself decreases and the band gap energy increases, thereby lowering the threshold. It is very effective in making further,
By using the superlattice, the number of pits generated in the cladding layer itself becomes smaller than that of the non-superlattice, so that the probability of short-circuiting is reduced.

The average composition of Al in the superlattice is determined by the following calculation method. For example, in the case of a superlattice in which 200 Å (1.0 μm) of 25 Å of Al _0.5 Ga _0.5 N and 25 Å of GaN are stacked, one pair is 50 Å and an Al mixed crystal of a layer containing Al. Since the ratio is 0.5, 0.5 (25 /
50) = 0.25, and the average Al composition in the superlattice is 25%. On the other hand, when the film thickness is different, Al _0.5
Ga _0.5 N is 40 Å and GaN is 20 Å.
In the case of stacking with Angstrom, the weighted average of the film thickness is obtained, and 0.5 (40/60) = 0.33, and the Al average composition is 33.3%. That is, a value obtained by multiplying the ratio of the Al mixed crystal of the nitride semiconductor layer containing Al to the ratio of the nitride semiconductor layer to the film thickness of one pair of the superlattices is defined as the Al average composition of the superlattice.

The other device structures of the laser device of the present invention are not particularly limited, and various known device structures can be used. As the substrate on which the element structure of the laser element of the present invention is grown, a conventionally known substrate of a different kind such as sapphire or spinel, or Si on a different kind of substrate is used.
A nitride semiconductor substrate or the like obtained by forming a protective film made of a material on which a nitride semiconductor such as O ₂ does not grow or is unlikely to grow, and selectively performing lateral growth (lateral growth) thereon. No. Preferably, a nitride semiconductor substrate having few crystal defects obtained by lateral growth is preferable. When an element structure is formed on a nitride semiconductor substrate having a small number of crystal defects, the nitride semiconductor constituting the element also has a small number of crystal defects. It is preferable because a good light confinement layer can be formed. The protective film used for lateral growth has a different effect from the protective film used for forming the stripe.

The method of growing a nitride semiconductor substrate having few crystal defects obtained by using lateral growth is not particularly limited, and any method may be used. For example, JJAP Vol.
37 (1998) pp. L309-L312 and the method of forming the unevenness on the surface of the nitride semiconductor grown on a heterogeneous substrate different from the nitride semiconductor, the protective film on the plane of the protrusions and recesses Is formed, lateral growth is performed from the nitride semiconductor exposed on the side surface, and the nitride semiconductors grown laterally are connected to each other on the protective film. In addition, the nitride semiconductor substrate obtained by lateral growth may be grown with a heterogeneous substrate or with the heterogeneous substrate removed when growing the element structure.

[0042]

Embodiment 1 FIG. 4 is a schematic cross-sectional view showing the structure of a laser device according to one embodiment of the present invention, and is a view when cut in a direction perpendicular to a stripe waveguide. is there. Hereinafter, the first embodiment will be described with reference to FIG.

(Underlayer 2) A heterogeneous substrate 1 made of sapphire having 1 inch φ and a C-plane as a main surface is set in a MOVPE reaction vessel, and the temperature is set to 50.
At 0 ° C., a buffer layer made of GaN was formed using trimethylgallium (TMG) and ammonia (NH ₃ ).
It is grown to a thickness of 0 Å. After the growth of the buffer layer, the temperature is raised to 1050 ° C., and an underlayer 2 also made of GaN is grown to a thickness of 4 μm. This underlayer forms a protective film partially on the surface and then acts as an underlayer for selectively growing a nitride semiconductor substrate.

(Protective Film 3) After the growth of the underlayer 2, the wafer is taken out of the reaction vessel, a stripe-shaped photomask is formed on the surface of the underlayer 2, and a stripe width of 10 μm and a stripe interval (window portion) are formed by a PVD apparatus. ) A protective film 3 of ₂ μm SiO ₂ is formed.

(Nitride Semiconductor Substrate 4) After forming the protective film 3, the wafer is set again in the MOVPE reaction vessel, the temperature is set to 1050 ° C., and undoped GaN is grown to a thickness of 5 μm using TMG and ammonia. Let it. Thereafter, the wafer is transferred to an HVPE (hydride vapor phase epitaxy) apparatus, and a nitride semiconductor substrate 4 made of undoped GaN is grown to a thickness of 200 μm using Ga metal, HCl gas and ammonia as raw materials.
After the nitride semiconductor is grown on the protective film 3 by the MOVPE method in this manner, a G of 100 μm or more is grown by the HVPE method.
When an aN thick film is grown, the number of crystal defects is 10 ⁴ / cm ² or less, which is three orders of magnitude less than that of the underlayer 2. After growing the nitride semiconductor substrate 4, the wafer is taken out of the reaction vessel,
The sapphire substrate 1, the buffer layer 2, the protective film 3, and the undoped GaN layer are removed by polishing to obtain the nitride semiconductor substrate 4 alone.

(N-side contact layer 5) Next, using ammonia, TMG, and silane gas as an impurity gas,
An n-side contact layer 5 of GaN doped with i at 3 × 10 ¹⁸ / cm ³ is grown to a thickness of 4 μm.

(Crack Prevention Layer 6) Next, using TMG, TMI (trimethylindium) and ammonia, the temperature is set to 800 ° C., and In _0.06 Ga
_A crack prevention layer 6 of _0.94 N is grown to a thickness of 0.15 μm. The crack prevention layer can be omitted.

[0048] (n-side cladding layer 7 = superlattice layer) Subsequently, TMA at 1050 ° C., TMG, ammonia, using a silane gas, 1 × with Si ^{10 19} / cm ³ doped with n-type _Al 0.16 _{Ga 0.} 2 a first layer consisting of ₈₄ N
The second layer made of undoped GaN is grown to a thickness of 25 Å by stopping the silane gas and TMA, and growing the film to a thickness of 25 Å. Then, a superlattice layer is formed in the order of first layer + second layer + first layer + second layer +..., And an n-side cladding layer 13 composed of a superlattice having a total film thickness of 1.2 μm is grown. Since the n-side cladding layer composed of this superlattice has an Al average composition of 8.0%,
The product with the film thickness is 9.6. Note that when a superlattice in which nitride semiconductors having different band gap energies are stacked on the n-side cladding layer is manufactured, one of the layers is heavily doped, and the threshold value tends to decrease when so-called modulation doping is performed. It is in.

(N-side light guide layer 8) Subsequently, the silane gas is stopped and undoped G
An n-side light guide layer 8 of aN is grown to a thickness of 0.1 μm. The n-side light guide layer 8 may be doped with an n-type impurity.

(Active Layer 9) Next, the temperature is set to 800 ° C., and Si-doped In _0.05
A barrier layer of Ga _0.95 N is grown to a thickness of 100 Å, followed by undoped I
A well layer made of n _0.2 Ga _0.8 N is grown to a thickness of 40 Å. A barrier layer and a well layer are alternately laminated twice, and finally an active layer having a multiple quantum well structure (MQW) having a total thickness of 380 Å is grown, ending with the barrier layer.

(P-side Cap Layer 10) Next, the temperature is raised to 1050 ° C., and TMG, TMA, ammonia, Cp 2 Mg (cyclopentadienyl magnesium) is used, and the band gap energy is larger than that of the p-side light guide layer 11. Then, a p-side cap layer 7 made of p-type Al _0.3 Ga _0.7 N doped with Mg at 1 × 10 ²⁰ / cm ³ is grown to a thickness of 300 Å.

(P-side light guide layer 11) Subsequently, Cp2Mg and TMA are stopped, and the p-side light guide layer 11 made of undoped GaN having a band gap energy smaller than that of the p-side cap layer 10 at 1050 ° C. is set to 0.1 μm. It grows with the film thickness of.

(P-side Cladding Layer 12) Subsequently, a third layer made of p-type Al _0.16 Ga _0.84 N doped with Mg at 1 × 10 ²⁰ / cm ³ at 1050 ° C. was formed to a thickness of 25 Å. And then TM
A alone is stopped, and the fourth layer made of undoped GaN is
Grown to a thickness of 5 Å, with a total thickness of 0.6μ
A p-side cladding layer 18 composed of m superlattice layers is grown. Since the average composition of Al is also 8% in the p-side cladding layer, the product of the thickness and the thickness is 4.8. When the p-side cladding layer is made of a superlattice in which at least one includes a nitride semiconductor layer containing Al and has different band gap energies from each other, the impurity is doped into one of the layers in a large amount. When so-called modulation doping is performed, the crystallinity tends to be improved, but both may be doped in the same manner.

(P-side contact layer 13) Finally, at 1050 ° C., Mg
Composed of p-type GaN doped with 1 × 10 ²⁰ / cm ³
The side contact layer 13 is grown to a thickness of 150 Å. The p-side contact layer is a p-type In _X Al _Y G
a _1- XYN (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and preferably Mg-doped GaN provides the most preferable ohmic contact with the p-electrode 20.

The wafer on which the nitride semiconductor has been grown as described above is taken out of the reaction vessel, and as shown in FIG.
Si oxide (mainly SiO ₂ ) by PVD equipment
After forming a first protective film 61 of 0.5 μm in thickness, a mask of a predetermined shape is applied on the first protective film 61, and a third protective film 63 of a photoresist is It is formed with a width of 2 μm and a thickness of 1 μm.

Next, as shown in FIG. 1B, after the formation of the third protective film 63, an RIE (reactive ion etching) device is used, using CF ₄ gas and the third protective film 63 as a mask. The first protective film is etched into a stripe shape. Thereafter, by treating with an etching solution to remove only the photoresist, a first protective film 61 having a stripe width of 2 μm can be formed on the p-side contact layer 13 as shown in FIG.

Further, as shown in FIG. 2D, after the first protection film 61 in the form of a stripe is formed, S is again formed by RIE.
Etching is performed from the p-side contact layer 13 to the n-side contact layer 5 using iCl ₄ gas to form a stripe-shaped waveguide region (in this case, a ridge-shaped stripe). As described above, by performing the etching amount until the n-side contact layer 5 is exposed when forming the stripe, the light confinement in the horizontal and horizontal directions is strengthened, which is preferable for adjusting the aspect ratio.

After the formation of the ridge-shaped stripe, the wafer is transferred to a PVD apparatus, and as shown in FIG.
Second protective film 6 made of r-oxide (mainly ZrO ₂ )
2 is continuously formed with a thickness of 0.5 μm on the first protective film 61 and on the n-side contact layer 5 exposed by the etching. In this manner, the second protective film 62 is continuously formed.
Is formed, the second protective film 62 is also formed on the side surface of the stripe.

Next, the wafer was immersed in hydrofluoric acid,
As shown in (f), the first protective film 61 is removed by a lift-off method.

Next, as shown in FIG. 2 (g), the first protective film 61 on the p-side contact layer 13 is removed so that Ni is in contact with the entire surface of the exposed p-side contact layer.
A p electrode 20 of / Au is formed. However, p electrode 20
Is formed over the second protective film 62 with a stripe width of 100 μm, as shown in FIG.

After the formation of the second protective film 62, the exposed surface of the n-side contact layer 5 is made of Ti / Al as shown in FIG.
An n-electrode 21 is formed in a direction parallel to the stripe.

After the sapphire substrate of the wafer on which the n-electrode and the p-electrode are formed is polished to 70 μm as described above, the wafer is cleaved into a bar from the substrate side in a direction perpendicular to the stripe-shaped electrodes. A resonator is formed on a cleavage plane (11-00 plane, a plane corresponding to the side surface of a hexagonal columnar crystal = M plane).
A dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on the resonator surface, and finally, the bar is cut in a direction parallel to the p-electrode to obtain a laser device as shown in FIG. The resonator length is 3
It is desirable to set it to 00 to 500 μm.

This laser element is set on a heat sink,
When each electrode was wire-bonded and laser oscillation was attempted at room temperature, the oscillation wavelength was 400 to 420 n.
m and a threshold current density of 2.9 kA / cm ² showed continuous oscillation at room temperature. The aspect ratio of the laser beam showed a good value of about 2.0.

Example 2 The procedure of Example 1 was repeated except that the stripe width was 0.5 μm to form a stripe. As a result, a good laser device was obtained almost in the same manner as in Example 1.

Example 3 The procedure of Example 1 was repeated except that the stripe width was 1.0 μm to form a stripe. As a result, a laser device capable of obtaining laser light having an aspect ratio of about 1.5 was obtained.

Example 4 In Example 1, when forming a stripe, the shape was as shown in FIG. 3, that is, the stripe width on both resonance surfaces was 1 μm, and the width at the center of the stripe was 4 μm. ,
Further, the same procedure was performed except that the stripe was formed by adjusting the inclination angle from the resonance surface side of the stripe toward the center to within 5 °. As a result, a laser element having an aspect ratio of about 1.2 and capable of obtaining laser light having a shape closer to a circle than that of Example 3 was obtained.

Embodiment 5 FIG. 5 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention. Embodiment 5 will be described below with reference to FIG.

In Example 1, when manufacturing the nitride semiconductor substrate 4, a silane gas was added to the raw material in the HVPE apparatus, and the nitride semiconductor substrate 40 made of GaN doped with 1 × 10 ¹⁸ / cm ^{3 of} Si was converted to a 200 μm film. Grow in thickness. The Si concentration is 1 × 10 ¹⁷ / cm ^{3 to} 5 × 10
It is desirable to be in the range of ¹⁹ / cm ³ . After the growth of the nitride semiconductor substrate 40, the sapphire substrate 1, the buffer layer 2, the protective film 3, and the undoped GaN layer are polished and removed in the same manner as in Example 1 to obtain the nitride semiconductor substrate 40 alone.

Next, on the nitride semiconductor substrate 40, the layers from the crack prevention layer 6 to the p-side contact layer 13 are grown in the same manner as in the first embodiment. After the growth of the p-side contact layer 13, a stripe-shaped first protective film 61 is formed in the same manner as in the first embodiment. In the second step, an etching stop is performed on the surface of the n-side cladding layer 7 shown in FIG. And Thereafter, in the same manner as in Example 1, a second protective film 62 containing ZrO ₂ as a main component is formed on the side surface of the stripe waveguide and on the surface of the n-side cladding layer 7, and then the second protective film is formed. The p electrode 20 is formed through. On the other hand, an n-electrode 21 is formed on substantially the entire back surface of the nitride semiconductor substrate. After the electrodes were formed, the substrate was cleaved on the M-plane of the nitride semiconductor substrate to form a resonance surface, and a laser device having a structure as shown in FIG. 5 was obtained. Was done.

[0070]

According to the present invention, when manufacturing a product using a laser beam, a laser beam having an aspect ratio of about 1.0 to 3.0 for facilitating a laser beam aperture and lens design can be obtained. A nitride semiconductor laser device can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a partial structure of a wafer obtained in each step for explaining each step of the method of the present invention.

FIG. 2 is a schematic cross-sectional view for explaining each step of the method of the present invention and showing a partial structure of a wafer obtained in each step.

FIG. 3 is a plan view showing a planar shape of a stripe of a laser device according to an embodiment of the present invention when viewed from directly above;

FIG. 4 is a schematic sectional view showing a structure of a laser device according to an embodiment of the present invention.

FIG. 5 is a schematic sectional view showing the structure of a laser device according to one embodiment of the present invention.

FIG. 6 is a schematic sectional view showing the structure of a conventional laser device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Different substrate 2 ... Underlayer 3 ... Protective film for nitride semiconductor substrate growth 4, 40 ... Nitride semiconductor substrate 5 ... n-side contact layer 6 ... Crack prevention layer 7 n-side clad layer 8 n-side light guide layer 9 active layer 10 p-side cap layer 11 p-side light guide layer 12 p-side clad layer 13 .. p-side contact layer 61 ... first protective film 62 ... second protective film 63 ... third protective film 20 ... p electrode 21 ... n electrode

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (4)

(57) [Claims] A waveguide region including an active layer having at least InGaN is provided between a p-side cladding layer having a nitride semiconductor layer containing Al and an n-side cladding layer. In a nitride semiconductor laser device having a p-side contact layer laminated thereon, the p-side cladding layer is
The thickness of the entire lad layer is 2.0 μm or less, and its p
The product with the average Al composition (%) contained in the side cladding layer is
4.4 will be configured such that the above, the p-side contact layer side p-side cladding layer and the width of 0.5 formed by etching toward the substrate side from the interface between the waveguide region from
A ridge-shaped stripe of about 2.0 μm, and the refractive index is higher than the average refractive index of the waveguide region on both sides of the stripe and the plane of the nitride semiconductor layer continuous with the side surface.
A p-electrode is provided so as to have an insulating film having a value smaller than 0.1 or more , and further via the insulating film to contact at least the entire surface of the p-side contact layer on the uppermost layer of the stripe. Characteristic nitride semiconductor laser device. 2. A waveguide region including an active layer containing at least InGaN between a p-side cladding layer and a n-side cladding layer having a nitride semiconductor layer containing Al. In a nitride semiconductor laser device in which a p-side contact layer is laminated, the n-side cladding layer has a small thickness.
Superlattice with nitride semiconductor layer containing at least Al
And the thickness of the entire n-side cladding layer is 0.5 μm or more.
And the average composition of Al contained in the n-side cladding layer
(%) Should be 4.4 or more.
Ri has a stripe of the etched ridge of the formed width 0.5~2.0μm in toward the substrate side from the interface between the p-side cladding layer and the waveguide region from the p-side contact layer side, the stripe On both sides and the plane of the nitride semiconductor layer continuous with the side surfaces, the refractive index of the waveguide region
An insulating film having a value smaller than the average refractive index by 0.1 or more is provided, and a p-electrode is provided so as to be in contact with at least the entire surface of the p-side contact layer on the uppermost layer of the stripe via the insulating film. A nitride semiconductor laser device, comprising: 3. The ridge-shaped stripe is formed so that the width at the center of the stripe is larger than the width at the end face of the stripe.
3. The nitride semiconductor laser device according to item 1. 4. The ridge-shaped stripe is formed by etching from a p-side contact layer side to a substrate side from an interface between the waveguide region and the n-side cladding layer. 4. The nitride semiconductor laser device according to any one of 3.