JPH10173282A - Nitride semiconductor laser element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a laser element which is improved in output and composed of a nitride semiconductor by using the etched surface of the semiconductor as one resonant surface of the element and the cleavage plane of the semiconductor as the other resonant surface. SOLUTION: After a nitride semiconductor layer containing an active layer 7 is formed on a sapphire substrate 1, the resistance value of a p-type layer is further reduced by removing part of the hydrogen contained in the p-type layer by annealing the wafer in a reaction vessel maintained in a nitrogen atmosphere. Then the wafer is transferred to a polishing device and, after the surface of the substrate 1 on which the nitride semiconductor layer is not formed is lapped, the surface is finished to a specular surface with abrasives. After polishing, the polished substrate is cleaved in a bar-like state in the direction parallel to the resonant surface by scribing and a resonator is formed on the cleavage plane. One of the resonant surface of a laser element thus formed is formed of the cleavage plane on which no reflecting mirror is formed and the other resonant surface is formed of the etched surface which also forms a reflecting mirror 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (In).
_{X Al Y Ga 1-XY N} , 0 ≦ X, 0 ≦ Y, a laser element made of X + Y ≦ 1).

[0002]

2. Description of the Related Art Nitride semiconductors have only recently been put to practical use in full-color LED displays, traffic signal lights, and the like as materials for high-brightness blue LEDs and pure green LEDs. The present applicant has recently published a laser oscillation of 410 nm at room temperature under pulse current using this material (for example, Document A: Jpn. J. Appl. Phys. Vol. 35 (1996) pp. L2
17-L220, Document B: Appl. Phys. Lett. 69 (10), 2 Sep. 1996
pp.1477-1479 etc.)

The resonance surface of a laser device made of a nitride semiconductor is generally formed by using a technique such as etching or cleavage. In the document A, a resonance surface is formed by etching a nitride semiconductor, and in B, a nitride semiconductor is grown on a sapphire A surface, and the sapphire R
Cleavage at the plane forms a resonance plane. However, the outputs of these laser devices were still low and unsatisfactory.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of such circumstances, and a main object of the present invention is to provide a laser device made of a nitride semiconductor having an improved output and a method of manufacturing the same. Is to provide.

[0005]

According to the present invention, there is provided a laser device comprising:
In a nitride semiconductor laser device in which a nitride semiconductor layer including an active layer is stacked on a substrate, and the nitride semiconductor layer has an end face having a resonance face facing each other, one of the resonance faces is an etching face of the nitride semiconductor. And the other resonance surface is a cleavage surface of a nitride semiconductor.

The cleavage plane is an M plane of a nitride semiconductor.

[Outside 2] It is desirable that The M-plane is a quadrangular surface corresponding to the side surface when the nitride semiconductor is approximated by a hexagonal hexagonal system. Each of the M planes can be represented by six types of plane orientations along the side surface of the hexagonal prism.

[Outside 3] Indicates the plane orientations of all M planes.

Further, the laser light of the laser element is mainly extracted from the cleavage plane side. Although laser light is emitted from both resonance surfaces, "mainly extracted from the cleavage surface side" in the present invention means that the laser light emitted from the cleavage surface is used as various light sources such as reading and writing. Means The laser light emitted from the other etching surface is detected by a photodetector such as a photodetector, for example.
Although the laser element is controlled, the laser light emitted from the etched surface side does not mean a side "mainly extracted" in the present invention.

According to one aspect of the laser device of the present invention, a reflecting mirror for reflecting laser light into the nitride semiconductor layer (hereinafter, a reflecting mirror formed on the etched surface side in the present specification) is provided on a resonance surface formed by etching. It may be referred to as the first reflecting mirror.)
Are formed, and no reflection mirror is formed on the cleavage plane.

According to another aspect of the laser device of the present invention,
Reflecting mirrors for reflecting laser light into the nitride semiconductor layer are formed on the etching surface and the cleavage surface, respectively, and the reflectance of the reflecting mirror on the etching surface side at the emission wavelength of the active layer is higher than the cleavage surface side. Is adjusted to be higher than the reflectance of the reflecting mirror. (Hereinafter, in this specification,
The reflecting mirror formed on the cleavage plane side may be referred to as a second reflecting mirror. It is usually desirable to form a multilayer film made of a dielectric on the reflecting mirror.

According to another aspect of the laser device of the present invention, a nitride semiconductor laser including a nitride semiconductor layer including an active layer laminated on a substrate and having resonant surfaces opposed to each other at end faces of the nitride semiconductor layer is provided. In the device, at least one of the resonance surfaces is provided with a reflector for reflecting light emitted from the active layer, and the reflectance of the active layer of the reflector at the emission wavelength is adjusted so that the reflectances of the resonance surfaces are mutually different. It is different. In this case, the resonance surface may be formed by the same method such as etching and cleavage.

In the method of manufacturing a laser device according to the present invention, a step of laminating a nitride semiconductor layer including an active layer on a substrate (hereinafter referred to as a “lamination”)
This is called a laminating step. ) And etching the nitride semiconductor layer to form an etching end face of the opposing nitride semiconductor layer,
A step of forming a resonance surface (hereinafter, referred to as an etching step) and a step of cleaving a nitride semiconductor between the resonance surfaces after the formation of the resonance surface (hereinafter, referred to as a cleavage step). It is characterized by having.

In the manufacturing method of the present invention, after the etching step and before the cleavage step, a step of forming a continuous reflecting mirror (first reflecting mirror) made of a dielectric on those resonance surfaces (hereinafter referred to as a first reflecting mirror). (Reflecting mirror forming step).

Further, in the manufacturing method of the present invention, after the cleavage step,
Another reflecting mirror (second reflecting mirror) having a lower reflectance at the emission wavelength of the active layer than the reflecting mirror formed on the etched surface may be formed on the cleavage surface. (Hereinafter, this is referred to as a second reflecting mirror forming step.)

Further, in the manufacturing method of the present invention, a step of laminating a nitride semiconductor layer including an active layer on a substrate, and etching the nitride semiconductor layer to form an etching end face of the facing nitride semiconductor layer with The method is characterized by comprising a step of forming a resonance surface and a step of forming a reflection mirror made of a continuous dielectric on the surface of the nitride semiconductor layer and the resonance surface after the formation of the resonance surface.

[0015]

FIG. 1 is a perspective view showing the shape of a laser device according to the present invention, and FIG. 2 is a schematic view of the laser device shown in FIG. 1 cut at a position indicated by an alternate long and short dash line in parallel with a resonance direction. FIG. The basic structure has a double hetero structure in which an n-type layer made of a nitride semiconductor, an active layer, and a p-type layer are stacked on a substrate. Surface. The resonance surfaces have different reflectivities at the emission wavelength of the active layer. As a specific resonance surface, one is an etching surface of the nitride semiconductor and the other is a cleavage surface of the nitride semiconductor.

There are various methods for etching a nitride semiconductor such as wet etching and dry etching.
In order to form a smooth surface that becomes a resonance surface, dry etching is preferably used. Dry etching includes, for example, devices such as reactive ion etching (RIE), reactive ion beam etching (RIBE), electron cyclotron etching (ECR), and ion beam etching. The resonance surface can be formed by etching the nitride semiconductor. For example, Japanese Unexamined Patent Publication No. Hei. 8-17803 previously published by the present applicant discloses specific means for etching a nitride semiconductor.

On the other hand, in order to form a resonance surface on the end face of the nitride semiconductor by cleavage, for example, a C-plane of sapphire described in Japanese Patent Application Laid-Open No. H8-153931 previously published by the present applicant. After growing a nitride semiconductor having a C-axis orientation, there is a method of dividing a sapphire substrate by an M plane. In addition, there is a method of growing a nitride semiconductor on the sapphire A plane and cleaving the sapphire on the R plane as described in the above Document B. In the laser device of the present invention, the plane orientation of the cleavage plane of the nitride semiconductor is not particularly limited. However, when the M plane of the nitride semiconductor is used as the resonance plane, a very good yield and a resonance plane close to a mirror surface can be obtained. Can be Note that the resonance surface in the present invention refers to a resonance surface formed on an end surface of the active layer as shown by an arrow in FIG.

As described above, by setting one of the resonance surfaces of the nitride semiconductor as an etching surface and the other as an etching surface, the reflectance of the resonance surface of the laser element can be made different. In addition, it is possible to improve the output of the laser light emitted from the resonance surface having a low reflectance. In particular, as shown in FIGS. 1 and 2, when the first reflecting mirror for reflecting the emission wavelength of the active layer is formed on the resonance surface on the etching surface side, the reflectance on the cleavage surface side is further reduced. Since the light is directly emitted, a laser element having a high output can be obtained.

Further, when the resonance surface is formed by etching, as shown in FIG.
The plane of the n-layer located substantially perpendicular to the resonance surface is exposed. This plane reflects the laser light on its surface and disturbs the far-field pattern of the laser light. In other words, if there is a plane protruding from the resonance surface on the laser emission light side, the shape of the laser light is disturbed on that plane. On the other hand, in the case of a cleavage plane, since there is no protruding portion, a laser beam having a constant shape close to an ellipse can be obtained. Therefore, in the laser device of the present invention, it is desirable to mainly extract laser light emitted from the cleavage plane side and use it as various light sources.

More preferably, as shown in FIG. 1, it is most desirable to form a first reflecting mirror on the etching surface side and not to form a reflecting mirror on the cleavage surface side. When the laser light is emitted from the resonance surface, the emission is partially blocked by the reflecting mirror. Therefore, by not forming a reflecting mirror on the cleavage plane side, light extraction efficiency is improved and slope efficiency is improved, so that a high-output laser can be obtained. More preferably, if the reflecting mirror is made of a high dielectric substance such as SiO ₂ , TiO ₂ , ZrO ₂ , or polyimide, it is very convenient in the manufacturing method of the present invention. In other words, in the case of a nitride semiconductor laser device, the p-electrode and the n-electrode are often taken out of the semiconductor layer on the same surface side. Cost. However, when a reflecting mirror made of a high dielectric material is formed together with the resonance surface as in the present invention, the reflecting mirror functions as an insulating film for preventing short-circuiting of the n and p electrodes, thereby improving the reliability of the laser element. I do. The operation of the reflecting mirror made of the dielectric will be described in further detail in this embodiment.

In the laser device of the present invention, a second reflector having a lower reflectance than the first reflector formed on the etching surface may be formed on the cleavage surface. Although the formation of the second reflecting mirror has the advantage of lowering the threshold value, the output of the laser element emitted from the cleavage plane side is the second
Slightly lower than those without the reflection mirror.

[0022]

Next, the present invention will be described in detail with reference to examples. FIG. 3 is a schematic sectional view showing one structure of the laser device of the present invention, and shows a structure when the device is cut in a direction parallel to the resonance surface. FIG. 4 is a block cell diagram showing a crystal structure of the nitride semiconductor. FIGS. 5 and 6 are partial cross-sectional views showing the structure of a laser device obtained in one step of the embodiment of the present invention. FIGS. 5 and 6 are views when the device is cut in a direction parallel to the resonance direction of laser light. Is shown. Hereinafter, the laser device and the manufacturing method of the present invention will be described based on these drawings.

Embodiment 1 A method for manufacturing a laser device having the structure shown in FIG. 3 will be described below. (Lamination process) 1) On a substrate 1 made of 2 inch φ sapphire (C-plane) 2) A buffer layer 23 made of GaN 3) A contact layer 34 made of Si-doped n-type GaN 4) Si-doped n-type In0. Crack preventing layer 4 of 1Ga0.9N 4 5) n-type cladding layer 5 of Si-doped n-type Al0.2Ga0.8N 6) n-type optical guide layer 6 of Si-doped GaN 7) Si-doped In0.2Ga0.8N 25 well layers
An active layer in which a barrier layer composed of Angstroms and Si-doped In0.01Ga0.95N is laminated in pairs of 50 Angstroms and a well layer is finally laminated. 8) A p-type cap layer composed of Mg-doped p-type Al0.1Ga0.9N 8 9) p-type optical guide layer 9 made of Mg-doped p-type GaN 9 10) p-type cladding layer 10 made of Mg-doped p-type Al0.2Ga0.8N 11) p-type contact layer 11 made of Mg-doped p-type GaN Laminate.

1) In addition to the sapphire C plane, R
A sapphire having a main surface, A surface, or an insulating substrate such as spinel (MgA1 ₂ O ₄ ) can be used. Other SiC (including 6H, 4H, 3C), Z
Using a semiconductor substrate of nS, ZnO, GaAs, GaN, or the like, an element having a structure as in the present invention can be obtained.

2) The buffer layer 2 is made of AlN, GaN, A
lGaN or the like can be formed at a temperature of 900 ° C. or less with a film thickness of several tens angstroms to several hundred angstroms. This buffer layer is formed to alleviate the lattice constant mismatch between the substrate and the nitride semiconductor.
It may be omitted depending on the type of the substrate and the like.

3) The n-type contact layer 3 is made of In _x Al _Y G
a _{1 -XYN} (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and particularly, by using GaN or InGaN, among which GaN doped with Si or Ge, n A mold layer is obtained, and a favorable ohmic contact with the n-electrode is obtained.

4) By growing the crack prevention layer 4 from an n-type nitride semiconductor containing In, preferably InGaN, an n-type clad layer containing Al to be grown next can be grown as a thick film. , Very preferred.
In the case of LD, it is necessary to grow a layer to be a light confinement layer, preferably with a thickness of 0.1 μm or more. Conventionally, a thick AlGaN layer is directly formed on a GaN or AlGaN layer.
Was grown, cracks were formed in AlGaN grown later, making it difficult to fabricate the device. However, this crack prevention layer prevents cracks from entering into the n-type clad layer containing Al to be grown next. be able to. The crack preventing layer is preferably grown to a thickness of 100 Å or more and 0.5 μm or less. When the thickness is less than 100 Å, it is difficult to function as a crack prevention as described above, and when the thickness is more than 0.5 μm, the crystal itself tends to turn black. In addition, this crack prevention layer is formed by a growth method,
Depending on the conditions of the growth apparatus and the like, it can be omitted, but L
When producing D, it is desirable to grow it. This crack preventing layer may be grown in the n-type contact layer.

5) The n-type cladding layer 5 functions as a carrier confinement layer and a light confinement layer, and it is desirable to grow a nitride semiconductor containing Al, preferably AlGaN, and more than 100 Å and less than 2 μm, more preferably By growing the layer with a thickness of 500 Å or more and 1 μm or less, a carrier confinement layer having good crystallinity can be formed.

6) The n-type light guide layer 6 functions as a light guide layer of an active layer, and is preferably used for growing GaN or InGaN, and usually 100 Å to 5 μm.
m, more preferably 200 Å to 1 μm
It is desirable to grow with a film thickness of.

7) The active layer 7 includes a well layer made of a nitride semiconductor containing In and having a thickness of 70 Å or less, and a barrier layer made of a nitride semiconductor having a larger band gap energy than the well layer having a thickness of 150 Å or less. , A laser is likely to oscillate.

8) Although the cap layer 8 is of p-type, the thickness is small, so that the cap layer 8 may be of i-type in which carriers are compensated by doping with n-type impurities, and most preferably p-type. p
The thickness of the mold cap layer is 0.1 μm or less, more preferably 500 Å or less, and most preferably 300 Å or less.
Adjust to less than Angstrom. This is because if the layer is grown with a thickness greater than 0.1 μm, cracks are likely to be formed in the p-type cap layer, and it is difficult to grow a nitride semiconductor layer having good crystallinity. In addition, carriers cannot pass through the energy barrier due to the tunnel effect. When the composition ratio of Al is larger and the thickness of AlGaN is smaller, the LD element is more likely to oscillate. For example, Al _Y Ga _1-Y having a Y value of 0.2 or more
If it is N, it is desirable to adjust it to 500 angstroms or less. The lower limit of the thickness of the p-type cap layer 8 is not particularly limited, but is preferably formed to a thickness of 10 Å or more.

9) The p-type light guide layer 9 is preferably made of GaN or InGaN, like the n-type light guide layer. This layer also functions as a buffer layer when growing the p-type cladding layer, and is formed at a thickness of 100 Å to 100 Å.
5 μm, more preferably 200 Å to 1
By growing with a thickness of μm, it functions as a preferable light guide layer.

10) Like the n-type cladding layer, the p-type cladding layer 10 functions as a carrier confinement layer and a light confinement layer, and is a nitride semiconductor containing Al, preferably A
It is desirable to grow lGaN, and it is possible to form a carrier confinement layer with good crystallinity by growing it at 100 Å or more and 2 μm or less, more preferably 500 Å or more and 1 μm or less. Further, as described above, it is preferable to form this layer as a nitride semiconductor layer containing Al because a contact resistance difference between the p-type contact layer and the p-electrode can be generated.

In the case of an active layer having a quantum structure having a well layer made of InGaN as in this embodiment, a p-type cap layer having a thickness of 0.1 μm or less and containing Al is provided in contact with the active layer. A p-type light guide layer having a smaller gap energy than the p-type cap layer is provided at a position farther from the active layer than the type cap layer, and a p-type light guide layer is provided at a position further from the active layer than the p-type light guide layer P made of a nitride semiconductor containing Al having a larger band gap than the optical guide layer
It is highly preferred to provide a mold cladding layer. And p
Since the thickness of the mold cap layer is set as thin as 0.1 μm or less, it does not act as a carrier barrier,
The holes injected from the p-layer can pass through the p-type cap layer by the tunnel effect, and are efficiently recombined in the active layer, and the output of the LD is improved. That is, since the injected carriers have a large band gap energy of the p-type cap layer, the carriers do not overflow the active layer even if the temperature of the semiconductor element is increased or the injected current density is increased. Since the carrier is blocked by the cap layer, carriers are accumulated in the active layer, and light can be efficiently emitted. Therefore, even if the temperature of the semiconductor element rises, the luminous efficiency is hardly reduced, so that an LD with a low threshold current can be realized.

11) The p-type contact layer 11 is made of p-type I
n _X Al _Y Ga _{1 -XYN} (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), preferably GaN doped with Mg
Then, the most preferable ohmic contact with the p electrode 20 can be obtained. (End of lamination process)

After laminating the nitride semiconductor layer including the active layer 7 on the substrate 1 with the above configuration, the wafer is annealed in a nitrogen atmosphere in a reaction vessel to remove hydrogen contained in the p-type layer. The portion is removed to further reduce the resistance of the p-type layer.

Next, a mask having a predetermined shape is formed on the surface of the uppermost p-type contact layer, and the uppermost p-type contact layer 11 is formed by a RIE (reactive ion etching) apparatus as shown in FIG. And the p-type cladding layer 10 are mesa-etched to form a ridge shape having a stripe width of 4 μm.

After forming the ridge, a mask is formed on the exposed plane of the p-type layer, and the plane of the n-type contact layer 22 is exposed symmetrically with respect to the stripe-shaped ridge as shown in FIG. . By providing the n-type contact layer 3 on which the n-electrode 22 is to be formed symmetrically with respect to the ridge stripe, the current from the n-layer also uniformly affects the active layer, and the threshold value is reduced. .

(Etching Step) Next, a mask having a predetermined shape is formed on the surface of the n-type contact layer 3 and on the exposed surface of the p-type layer. Etching is performed so that the height is substantially the same as that described above, and a resonance surface having a resonator length of 700 μm is formed.

Next, the p-type contact layer 1 at the top of the ridge
First, an ohmic p-electrode 20 made of Ni and Au is formed on almost the entire surface. On the other hand, an ohmic n-electrode 22 made of Ti and Al is formed on almost the entire surface of the striped n-type contact layer. It should be noted that the almost entire surface refers to an area of 80% or more. As described above, the threshold value is lowered by forming the n-electrode on the entire surface and symmetrically with respect to the ridge. FIG. 5 is a partial cross-sectional view of the wafer after the formation of the p-electrode 20, and is a schematic view when the wafer is cut from directly above the ridge in a direction parallel to the laser resonance direction.

(First Reflection Mirror Forming Step) After the electrodes are formed, the wafer is transferred to a CVD apparatus, and the p-electrode 20 and the n-electrode 2 are formed.
2. A first reflecting mirror 30 made of a dielectric multilayer film of SiO ₂ and TiO ₂ is formed over all layers exposed from the substrate, such as the p-type cladding layer 10. The thickness of each layer of the first reflecting mirror 30 is λ / 4n (λ: emission wavelength of the active layer,
n: refractive index of the material). First reflector 3
FIG. 6 shows a cross-sectional view after the formation of 0. The first reflecting mirror functions as a reflecting mirror for reflecting the light emitted from the active layer on the resonance surface side, and further has an n-type contact layer 3 and a p-type cladding layer 10.
Acts as an insulating film for preventing a short circuit between the electrodes. As described above, by forming the first reflecting mirror 30 continuously between the resonance surfaces, the element can be manufactured very effectively. As a material of the reflecting mirror, for example, SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ , ZnO, M
High dielectric materials such as gO and polyimide can be used.

After forming the first reflecting mirror 30, the p-electrode 20 and
The first reflecting mirror 30 formed on the surface of the n-electrode 22 is removed. The exposed p-electrode 20 and the n-electrode 2
In order to enlarge the electrode area on the surface of the substrate 2 and spread the current uniformly, the p-pad electrode 21 and the n-pad electrode 2 are respectively provided.
2 is formed so as to have a structure as shown in FIG. Note that, as shown in FIG. 3, the p-pad electrode is formed over the surface of the p-type cladding layer 10 via a first reflecting mirror as an insulating film.

(Cleaving Step) Next, the wafer is transferred to a polishing apparatus, and the sapphire substrate on which the nitride semiconductor is not formed is wrapped using a diamond abrasive to reduce the thickness of the substrate to 50 μm. After lapping, the substrate surface is mirror-finished by polishing with a finer abrasive at 1 μm. The thickness of the substrate is 70 μm or less, more preferably 60 μm.
When the thickness is not more than μm, most preferably not more than 50 μm, the heat radiation of the element is enhanced and the life of the element is extended.

After the substrate is polished, the polished surface side is scribed,
Cleavage is performed at a position indicated by a dashed line in FIG. 6 in a bar shape in a direction parallel to the resonance plane, and a resonator is formed on the cleavage plane. Thereby, the resonator length 55 composed of the cleavage plane and the etching plane
A 0 μm resonance surface is produced. Note that the cleavage plane is the M plane of the nitride semiconductor surface grown on the sapphire substrate. Although the M-plane has been described above, specifically, as shown in FIG. 4, when the nitride semiconductor is approximated by a hexagonal system of regular hexagonal prisms, a square surface corresponding to the side surface of the hexagonal prism is used. This is the plane corresponding to. In addition, in order to cleave at the M plane, it is necessary to prepare in advance so that the resonance plane produced in the etching step becomes the M plane. Further, by cutting the wafer at a position parallel to the n-electrode, a laser device having a shape as shown in FIG. 2 is obtained.

By manufacturing a laser element as described above, an element having a structure as shown in FIG. 1 can be manufactured. One of the resonance surfaces of the laser device is formed by cleavage, and no reflection mirror is formed on the cleavage surface. The other resonance surface is formed by etching, and a reflection mirror is formed on the etching surface. This laser element was placed on a heat sink face up (in a state where the substrate and the heat sink were opposed to each other), and the respective electrodes were wire-bonded to perform laser oscillation at room temperature. At room temperature, the threshold current density was 1.5 kA / c
At m ² and a threshold voltage of 6 V, continuous oscillation with an oscillation wavelength of 405 nm was confirmed. The output of the laser beam emitted from the cleavage plane side is about twice as large as that obtained by forming both resonance surfaces by etching and further forming a reflection mirror having the same reflectance on the resonance surfaces. Improved. Further, the laser beam circulated from the cleavage plane side also had an elliptical and very clean shape with no disturbance.

Example 2 In Example 1, after completion of the cleavage step, a mask is formed on the surface of the first reflecting mirror other than the cleavage plane, and a SiO ₂ and TiO ₂ dielectric multilayer film is similarly formed on the cleavage plane. A second reflecting mirror 31 is formed. The thickness of the second reflecting mirror 31 is adjusted to 1/10 of the reflectance of the first reflecting mirror by adjusting the film thickness.

After the formation of the second reflecting mirror, the mask was removed, and the surfaces of the p-electrode 20 and the n-electrode 22 were exposed in the same manner. FIG. 7 is a schematic sectional view showing the structure of this laser element. This laser element also showed continuous oscillation at room temperature, and the output was reduced by about 20% as compared with that of Example 1.

[Embodiment 3] In the etching process of Embodiment 1, the etching is performed in the same manner except that etching is performed so that the resonator length becomes 550 µm.

Next, a p-electrode 20 is formed on the p-type contact layer 11 and an n-electrode 22 is formed on the n-type contact layer 3 in the same manner.

After the formation of the electrodes, a mask is formed on one of the etching surfaces which is to be the resonance surface, and then the wafer is transferred to a CVD apparatus. Thus, a first reflecting mirror composed of a dielectric multilayer film of SiO ₂ and TiO ₂ is formed. As described above, after the resonance surface is formed, the step of forming a reflection mirror made of a continuous dielectric on the surface of the nitride semiconductor layer and the resonance surface is provided. By acting as an insulating film formed on the surface of the semiconductor, it is possible to prevent a short circuit between the electrodes and to form a p-pad electrode 21 on the p-electrode 20 to substantially increase the electrode area. As the electrode area increases, the threshold can be reduced.

Then, after removing the mask, the wafer is cleaved between the resonance surfaces. In this manner, both resonance surfaces are formed by etching, a reflection mirror is formed on one resonance surface, and no reflection mirror is formed on the other resonance surface. Laser elements having different rates can be manufactured. In this laser element, laser light was extracted from the resonance surface on which the reflecting mirror was not formed, and continuous oscillation was confirmed at room temperature with a threshold current density of 1.5 kA / cm ² , a threshold voltage of 6 V, and an oscillation wavelength of 405 nm. Was done. The output of the laser beam emitted from the side of the resonance surface on which no reflection mirror is formed is compared with the output of a laser mirror having the same reflectance formed on both resonance surfaces by etching. And it improved 1.3 times.
However, the far-field pattern of the laser beam was disturbed because it was not a cleavage plane. However, the flat portion protruding from the resonance surface can be removed by polishing or by cleaving the substrate at a position close to the resonance surface.

[0052]

As described above, the laser device of the present invention can realize a high-power laser device by making the reflectance of the resonance surfaces different from each other. Further, when one side is a cleavage plane and the other side is an etching plane, the laser light emitted from the cleavage plane side can be obtained as a very beautiful laser light having a nearly elliptical shape.

Further, in the manufacturing method of the present invention, an insulating film can be formed in the step of manufacturing the reflecting mirror, so that a short circuit between the electrodes of the laser element on the same surface side can be prevented, and very high reliability can be obtained. An element can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a laser device according to one embodiment of the present invention.

FIG. 2 is a perspective view showing the shape of the laser device of FIG.

FIG. 3 is a sectional view showing the structure of the laser device of FIG. 2 in detail;

FIG. 4 is a unit cell diagram schematically showing a crystal structure of a nitride semiconductor.

FIG. 5 is a partial cross-sectional view showing a schematic structure of a wafer obtained in one step of the manufacturing method of the present invention.

FIG. 6 is a partial sectional view showing a schematic structure of a wafer obtained in one step of the manufacturing method of the present invention.

FIG. 7 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2 ... Buffer layer 3 ... N-type contact layer 4 ... Crack prevention layer 5 ... N-type cladding layer 6 ... N-type light guide layer 7 ... Active layer 8 ... p-type cap layer 9 ... p-type light guide layer 10 ... p-type cladding layer 11 ... p-type contact layer 20 ... p electrode 21 ... p pad electrode 22 ... n electrode 23 ... n pad electrode 30 ... first reflecting mirror 31 ... second reflecting mirror

Claims (10)

[Claims] 1. A nitride semiconductor laser device in which a nitride semiconductor layer including an active layer is laminated on a substrate and has a resonance surface facing an end surface of the nitride semiconductor layer, wherein one of the resonance surfaces is nitride. A nitride semiconductor laser device characterized in that it is a semiconductor etching surface and the other resonance surface is a nitride semiconductor cleavage surface. 2. The cleavage plane is an M-plane of a nitride semiconductor. The nitride semiconductor laser device according to claim 1, wherein 3. The nitride semiconductor laser device according to claim 1, wherein a laser beam of the laser device is mainly extracted from a cleavage plane. 4. A reflection mirror for reflecting a laser beam into the nitride semiconductor layer is formed on the etching surface, and no reflection mirror is formed on the cleavage surface. 4. The nitride semiconductor laser device according to any one of 3. 5. A reflection mirror for reflecting laser light into the nitride semiconductor layer is formed on each of the etching surface and the cleavage surface, and the reflectance of the reflection mirror on the etching surface side at the emission wavelength of the active layer. Is adjusted to be higher than the reflectance of the reflecting mirror on the cleavage plane side.
4. The nitride semiconductor laser device according to claim 1. 6. A nitride semiconductor laser device in which a nitride semiconductor layer including an active layer is stacked on a substrate and has a resonance surface facing an end surface of the nitride semiconductor layer, wherein at least one of the resonance surfaces is provided. A nitride semiconductor laser device, comprising: a reflector for reflecting light emitted from an active layer, wherein the reflectance at the emission wavelength of the active layer of the reflector is adjusted, and the reflectivities of the resonance surfaces are different from each other. . 7. A step of laminating a nitride semiconductor layer including an active layer on a substrate, and a step of etching the nitride semiconductor layer to form a resonance surface on each of the etching end faces of the facing nitride semiconductor layer. And a step of cleaving a nitride semiconductor between the resonance surfaces after the formation of the resonance surfaces. 8. The manufacturing method according to claim 7, further comprising a step of forming a continuous reflecting mirror made of a dielectric material on the resonance surface after forming the resonance surface and before cleaving the nitride semiconductor. Method. 9. The method according to claim 1, wherein after the nitride semiconductor is cleaved, another reflecting mirror having a lower reflectance at the emission wavelength of the active layer than the reflecting mirror formed on the etched surface is formed on the cleaved surface. Item 10. A method for manufacturing a nitride semiconductor laser device according to item 8. 10. A step of laminating a nitride semiconductor layer including an active layer on a substrate, and a step of etching the nitride semiconductor layer to form a resonance surface on each of the etched end faces of the facing nitride semiconductor layer. Forming a continuous reflecting mirror made of a dielectric on the surface of the nitride semiconductor layer and the resonance surface after the formation of the resonance surface.