JP3278108B2 - Method for manufacturing nitride semiconductor laser element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (In _{XA).
l Y Ga 1-X-Y} N, 0 ≦ X, 0 ≦ Y, relates laser element consisting of X + Y ≦ 1), in particular the far field pattern is good, relates to a laser device which is reduced threshold.

[0002]

2. Description of the Related Art The present inventors have proposed a laser device of an effective refractive index guided type in which a ridge structure is provided between resonance surfaces in order to increase the optical waveguide efficiency. A nitride semiconductor laser device (hereinafter sometimes simply referred to as a semiconductor laser device) has a resonance surface for causing light emission of an active layer to resonate inside the semiconductor layer. The resonance surface is formed by etching (dry etching, wet etching, or the like), cleavage, or the like. The ridge structure is formed by etching or the like. And
Since the laser light is emitted from the resonance surface, if the resonance surface is smooth like a mirror, the far-field pattern of the laser light will be good.

[0003]

However, when a ridge structure and a resonance surface are formed on a nitride semiconductor by etching, two ridges are formed on the resonance surface as shown in the perspective view of FIG. 2 showing a partial structure of the nitride semiconductor. Streaks are formed and the surface is not smooth. In addition, when a resonance surface is formed by cleavage, a nitride semiconductor is often formed on a substrate such as sapphire (Al ₂ O ₃ ) having almost no cleavage, and thus the substrate is cleaved to form a resonance surface. Difficult to do. Since sapphire used as a substrate is a material as hard as diamond, it takes a long time to perform full cutting, and furthermore, there is a tendency that defects such as cracks and chips are easily generated in the nitride semiconductor layer on the cut surface.

[0004] If the resonance surface is not sufficiently smooth due to the formation of two streaks on the resonance surface or the breakage of the semiconductor, the far-field pattern of light emitted from the semiconductor laser is disturbed, resulting in a good elliptical shape or the like. Laser beam cannot be obtained.
Further, when the far-field pattern is disturbed, it becomes difficult to couple the laser beam and the lens, and it is difficult to use the laser beam as a light source. Further, when two streaks are formed on the resonance surface due to etching, light loss on the resonance surface increases due to a decrease in the feedback rate of light, and the threshold value increases. In order to enable continuous oscillation of the laser for a long time, it is necessary to lower the threshold value.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a nitride semiconductor laser device having a smooth resonance surface, a good far-field pattern shape of laser light, and a reduced threshold. .

[0006]

That is, the object of the present invention can be achieved by the following constitutions. (1) N-type nitride semiconductor layer including n-side contact layer
, P-type nitride semiconductor including active layer and p-side contact layer
And a body layer, in the manufacturing method of nitride semiconductor laser device optical waveguide mechanism is ridge structure, after forming the resonance surface by etching, when the resist film is formed exposure
The residue of the resist film generated at the time is used as a protective film on the resonance surface.
A method of manufacturing a nitride semiconductor laser device, wherein a ridge structure is formed by etching.

Further, the object of the present invention can be achieved by the following preferred embodiments. (2) The method for manufacturing a nitride semiconductor laser device according to (1), wherein the ridge structure is formed as a ridge using an upper layer including the p-side superlattice layer.

That is, according to the present invention, by forming the ridge structure after forming the resonance surface as described above, the resonance surface becomes smooth, and the far-field pattern becomes normal. Furthermore, in the present invention, since the resonance surface is smooth,
The feedback rate of light is improved, the rise of the threshold is suppressed, and the threshold can be lowered.

As a result of various studies on the roughness of the resonance surface that disturbs the far field pattern, the present inventors have found that if the resonance surface is formed after the formation of the ridge structure, two streaks are formed on the resonance surface as shown in FIG. Was found. Usually, due to the nature of photolithography, when etching a nitride semiconductor, the etching is performed from a portion having a small etching depth. this is,
When a portion having a small etching depth is formed and then an attempt is made to form a portion having a small etching depth, a difference occurs in the thickness of the resist film. It becomes difficult to photolithographically shape. Therefore, many persons skilled in the art perform photolithography from a portion having a small etching depth.

[0010] However, contrary to the above common sense when performing photolithography, the present inventors have formed a ridge structure with a small etching depth after forming a resonance surface with a large etching depth. Possible resonance surface. Then, as in part A of a perspective view showing a partial structure of the nitride semiconductor in FIG.
There is no adverse effect on the laser element due to this step. Further, the residue of the resist film which causes the step as described above has not only an adverse effect, but also prevents unnecessary erosion of the resonance surface and the other side surface when etching the ridge structure, and makes unnecessary the resonance surface. The problem of the surface angle of the resonance surface due to erosion can be prevented. That is, the present invention not only changes the conventional etching sequence, but also utilizes the remaining resist film, which is an unnecessary by-product generated by changing the etching sequence, as a protective film on the resonance surface. It forms the structure. by this,
The plane angle of the resonance plane is almost 90 ° with respect to the substrate, and the resonance plane is smooth and can maintain a mirror-like state. The far-field pattern becomes very good and the threshold value can be lowered. The present invention has solved the above-mentioned problems peculiar to a nitride semiconductor laser device formed on a substrate having no ridge and having a ridge structure.

Further, according to the present invention, since the far-field pattern of the light emitted from the semiconductor laser is improved as described above, an elliptical laser beam can be obtained. Further, if the far-field pattern is good, the laser beam and the lens are easily coupled to each other, so that it is easy to use as a light source.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A nitride semiconductor laser device of the present invention
Is a method in which a ridge structure is formed at least after forming a resonance surface. The nitride semiconductor laser device of the present invention thus formed can have a smooth resonance surface. In the resonance surface according to the present invention, unevenness on the surface of the resonance surface is 2 μm or less, preferably 1 μm or less,
More preferably, it is 0.5 μm or less. That is, the value of d in the schematic plan view of the perspective view of FIG. 2 in FIG. As shown in FIG. 1, for example, the resonance surface in the present invention has two streaks that occur on both sides of the stripe width of the ridge structure when the ridge structure has been a problem in the related art. Absent. This is obvious when compared with the conventional resonance surface shown in FIG.

[0013] In addition, it is formed by the manufacturing method of the present invention.
The nitride semiconductor laser device, as shown in FIG.
A slight step is generated at the end (portion A in FIG. 1) of the n-type nitride semiconductor layer. This step occurs because a ridge structure with a small etching depth is formed after forming a resonance surface with a large etching depth. In other words, when a resist is applied and a thin film is formed on the nitride semiconductor layer and exposed, if the step due to etching is large, the thickness of the resist thin film becomes uneven and exposure cannot be performed uniformly, so that a step as shown in FIG. 1 occurs. However, even if such a step occurs, it hardly affects the far field pattern, threshold value, and the like of the light emitted from the laser. Therefore, this step is a structure peculiar to the laser element of the present invention and a specific structure generated by the manufacturing method of the present invention.

The resonance surface is formed on the etching end face of the active layer by etching the nitride semiconductor. The resonance surface refers to a surface for resonating the laser light formed on the end surface of the active layer.

The ridge structure has a p-side layer (p
The p-side nitride semiconductor layer containing the p-type impurity is etched with a certain stripe width to form a ridge structure. Hereinafter, a portion having a ridge structure in the present invention may be referred to as a ridge portion. In the present invention, the shape of the stripe-shaped ridge structure is not particularly limited, but for example, Japanese Patent Application No. 8-676 previously proposed by the present inventors.
For example, the shape of the ridge structure described in JP-A No. 32 can be mentioned. The ridge structure is preferably formed in the p-side nitride semiconductor layer on the active layer.

As a preferred embodiment of the shape of the ridge structure, for example, as shown in FIG.
The p-side cladding layer 19 is etched to form a ridge shape as shown. Thus, it is preferable that the upper layer including the p-side superlattice layer has a ridge structure. It is preferable to form a ridge including a superlattice layer because the threshold value can be reduced. The superlattice layer is a layer in which extremely thin layers having different compositions are laminated, and since the thickness of each layer is sufficiently thin, a layer laminated without generating defects due to lattice irregularity is referred to. This is a broad concept including the quantum well structure.
The superlattice layer does not have any defects inside, but usually has a strain accompanying lattice irregularity, and thus is also referred to as a strained superlattice.

In the present invention, the resonance surface and the ridge structure are formed by etching. Methods for etching a nitride semiconductor include wet etching and dry etching, and dry etching is preferably used to form a smooth surface serving as a resonance surface.
The dry etching includes, for example, reactive ion etching (RIE) and reactive ion beam etching (RIB).
E), an electron cyclotron etching (ECR), an ion beam etching, and the like are available. In any case, by appropriately selecting an etching gas, a nitride semiconductor can be etched to form a resonance surface. For example, a specific nitride semiconductor etching means described in Japanese Patent Application Laid-Open No. H8-17803 previously filed by the present applicant can be used. According to the present invention, a ridge structure is formed after forming a resonance surface using the above-described etching method.

In the present invention, the structure of the nitride semiconductor is not particularly limited, and may have any layer structure and shape. Hereinafter, components of a preferred nitride semiconductor device that can be used in the present invention will be described.

FIG. 4 is a schematic sectional view showing a structure of a nitride semiconductor device according to an embodiment of the present invention (a cross section perpendicular to the resonance direction of laser light).
For example, an n-type nitride semiconductor layer region (an n-side contact layer 12,
It comprises a cladding prevention layer 13, an n-side cladding layer 14, and an n-side light guide layer 15. ) And a p-type nitride semiconductor region (cap layer 17, p-side light guide layer 18, p-side cladding layer 19)
And the p-side contact layer 20. ) Is a nitride semiconductor laser diode device provided with an active layer 16 made of a nitride semiconductor sandwiched between them.

Here, the nitride semiconductor device of the present embodiment has an n-side cladding layer 1 in an n-type nitride semiconductor layer region.
4 is formed of a superlattice layer, and the p-side cladding layer 19 in the p-type nitride semiconductor region is formed of a superlattice layer, so that the threshold voltage of the nitride semiconductor element as an LD element is set low. I have.

In the nitride semiconductor device of this embodiment, first, an n-side contact layer 12 is formed on a substrate 10 with a buffer layer 11 and a second buffer layer 112 interposed therebetween.
Further, a crack prevention layer 1 is formed on the n-side contact layer 12.
3. The n-side cladding layer 14 and the n-side light guide layer 15 are stacked to form an n-type nitride semiconductor layer region. In addition,
On the surface of the n-side contact layer 12 exposed on both sides of the crack prevention layer 13, an n-side electrode 23 that makes ohmic contact with the n-side contact layer 12 is formed. On the n-side electrode 23, for example, a wire An n-side pad electrode for bonding is formed. Then, an active layer 16 made of a nitride semiconductor is formed on the n-side light guide layer 15, and a cap layer 17 and a p-side light guide layer 1 are further formed on the active layer 16.
8, p-side cladding layer 19 and p-side contact layer 20 are laminated to form a p-side nitride semiconductor layer region. Further, the p-side contact layer 20 is formed on the p-side contact layer 20.
A p-side electrode 21 that is in ohmic contact with the p-side electrode 21 is formed.
A side pad electrode is formed. The p-side contact layer 2
By forming a ridge having a peak-like ridge extending long in the resonance direction by the 0 and the upper part of the p-side cladding layer 19, light is transmitted in the active layer 16 in the width direction (perpendicular to the resonance direction). Using a cleavage plane cleaved in a direction perpendicular to the ridge portion (striped electrode), a resonator that resonates in the longitudinal direction of the ridge portion is produced, and laser oscillation is performed.

(Substrate 10) In addition to sapphire having a C surface as a main surface, an R surface,
Sapphire whose main surface is A, other spinel (Mg
A1 ₂ O ₄ ) as well as an insulating substrate such as SiC (6
H, 4H, 3C), ZnS, ZnO, GaAs,
A semiconductor substrate such as GaN can be used.

(Buffer Layer 11) The buffer layer 11 is made of, for example, AlN, GaN, AlGa.
N, InGaN, etc. are grown at a temperature of 900 ° C. or less,
The film is formed to have a film thickness of several tens angstroms to several hundred angstroms. The buffer layer 11 is formed in order to reduce the lattice constant mismatch between the substrate and the nitride semiconductor. However, the buffer layer 11 may be omitted depending on the nitride semiconductor growth method, the type of the substrate, and the like. .

(Second Buffer Layer 112) The second buffer layer 112 is a layer made of a single crystal nitride semiconductor grown on the buffer layer 11 at a higher temperature than the buffer layer. It has a thicker film than the layer 11. If the second buffer layer 112 is a layer having a lower n-type impurity concentration than the n-side contact layer 12 to be grown next, or a nitride semiconductor layer not doped with an n-type impurity, preferably a GaN layer, The crystallinity of the second buffer layer 112 is improved. Most preferably, when the n-type impurity is undoped GaN, a nitride semiconductor having the best crystallinity can be obtained. If the n-side contact layer for forming the negative electrode is formed of a single nitride semiconductor layer having a thickness of several μm or more and a high carrier concentration as in the related art, n
It is necessary to grow a layer having a high type impurity concentration. A thick film layer having a high impurity concentration tends to have poor crystallinity. For this reason, even if another nitride semiconductor such as an active layer is grown on a layer having poor crystallinity, the crystal defect is inherited by another layer, so that improvement in crystallinity cannot be expected. Therefore, before growing the n-side contact layer 12 layer, the second buffer layer 112 having a low impurity concentration and good crystallinity is grown to grow the n-side contact layer 12 having a large carrier concentration and good crystallinity. Can be done. This second
The thickness of the buffer layer 112 is preferably adjusted to 0.1 μm or more, more preferably 0.5 μm or more, and most preferably 1 μm or more and 20 μm or less. If the second buffer layer 112 is thinner than 0.1 μm, the n-type contact layer 12 having a high impurity concentration must be grown thick, and the crystallinity of the n-side contact layer 12 tends to be hardly expected to be improved. . When the thickness is larger than 20 μm, the second
The buffer layer 112 itself tends to have many crystal defects. An advantage of increasing the thickness of the second buffer layer 112 is improvement in heat dissipation. That is, when a laser element is manufactured, heat easily spreads in the second buffer layer 112, and the life of the laser element is improved. Further, the leakage light of the laser light spreads in the second buffer layer 112, so that a laser light having a nearly elliptical shape is easily obtained. The second
Buffer layer 112 is made of GaN, SiC, ZnO
When a conductive substrate such as that described above is used, it may be omitted.

(N-side contact layer 12) The n-side contact layer 12 is a layer that functions as a contact layer for forming a negative electrode, and is preferably adjusted to 0.2 μm or more and 4 μm or less. If it is thinner than 0.2 μm,
When forming a negative electrode later, it is difficult to control the etching rate so as to expose this layer. On the other hand, if the thickness is 4 μm or more, the crystallinity tends to be deteriorated due to the influence of impurities. The range of the n-type impurity doped into the nitride semiconductor of the n-side contact layer 12 is 1 × 10 ¹⁷ / cm ³ to 1 × 1
0 ²¹ / cm ³ , more preferably 1 × 10
It is desirable to adjust to ¹⁸ / cm ³ to 1 × 10 ¹⁹ / cm ³ . If it is smaller than 1 × 10 ¹⁷ / cm ^3, it becomes difficult to obtain a preferable ohmic material for the n-electrode.
The threshold current and voltage of the laser element cannot be expected to decrease.
If it is larger than × 10 ²¹ / cm ³ , the leak current of the device itself increases, and the crystallinity also deteriorates, so that the life of the device tends to be shortened. The n-side contact layer 1
In (2), in order to reduce the ohmic contact resistance with the n-electrode 23, it is desirable that the impurity concentration for increasing the carrier concentration of the n-side contact layer 12 be higher than that of the n-side cladding layer 14. The n-side contact layer 1
Reference numeral 2 functions not as a contact layer but as a buffer layer when a conductive substrate such as GaN, SiC, or ZnO is used as the substrate and a negative electrode is provided on the back surface of the substrate.

In addition, at least one of the second buffer layer 112 and the n-side contact layer 12 may be a super lattice layer. When a superlattice layer is formed, the crystallinity of this layer is significantly improved, and the threshold current is reduced. Preferably, the n-side contact layer 12 having a smaller thickness than the second buffer layer 112 is used as a superlattice layer. When the n-side contact layer 12 has a superlattice structure in which a first layer and a second layer having different band gap energies are laminated, preferably, the n-electrode is formed by exposing a layer having a small band gap energy. By forming the layer 23, the contact resistance with the n-electrode 23 can be reduced and the threshold value can be reduced. In addition, as a material of the n-type electrode 23 which can obtain a preferable ohmic with an n-type nitride semiconductor, Al,
Examples include metals or alloys such as Ti, W, Si, Zn, Sn, and In.

Further, by making the n-side contact layer 12 a superlattice layer having a different impurity concentration, the lateral resistance can be reduced, and the threshold voltage and current of the LD element can be reduced. This is because the superlattice layer doped with a large amount of n-type
In the case of forming a contact layer on the layer side, the following HEMT (High-Electron-M) is used.
Obviously, the effect appears to be similar to that of the “Obility-Transistor”. a first layer (second layer) having a large band gap doped with an n-type impurity,
Undoped with small band gap
e); hereinafter, a state in which an impurity is not doped is referred to as undoped. In a superlattice layer in which a second layer (first layer) indicated by｝ is laminated, an n-type impurity-added layer and an undoped layer At the heterojunction interface, the layer side having the larger band gap energy is depleted, and electrons (two-dimensional electron gas) are accumulated at the interface (about 100 Å) on the layer side having the smaller band gap energy. Since this two-dimensional electron gas is formed on the layer side having a small band gap energy, the electrons are not scattered by impurities when traveling, so that the mobility of the electrons in the superlattice layer increases, and the resistivity is assumed to decrease. You.

(Crack Prevention Layer 13) The crack prevention layer 13 is made of, for example, 5 × 10 ¹⁸ / Si.
It is made of cm ³ -doped In _0.1 Ga _0.9 N and has a thickness of, for example, 500 Å. The crack prevention layer 13 is formed by growing an n-type nitride semiconductor containing In, preferably InGaN, to thereby prevent cracks from entering the nitride semiconductor layer containing Al formed thereon. be able to. The crack preventing layer 13 has a thickness of at least 100 Å and a thickness of 0.5 μm.
It is preferable to grow with a film thickness of not more than m. 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. The crack preventing layer 13
May be omitted when the n-type contact layer 12 is a superlattice or when the n-type clad layer 14 to be grown next is a superlattice layer.

(N-side cladding layer 14 made of n-type superlattice) The n-side cladding layer is made of, for example, n-type Al _0.2 Ga _0.8 N doped with 5 × 10 ¹⁸ / cm ^{3 of} Si, and has a thickness of 20 Å. A superlattice layer comprising a first layer having a thickness of 20 nm and undoped GaN, and a second layer having a thickness of 20 angstroms alternately laminated;
It has a thickness of, for example, 0.5 μm as a whole. The n-type cladding layer 14 functions as a carrier confinement layer and a light confinement layer. When a superlattice layer is formed, one of the layers is preferably made of a nitride semiconductor containing Al, preferably AlGaN, A good carrier confinement layer can be grown by growing at a thickness of 100 Å or more and 2 μm or less, more preferably 500 Å or more and 1 μm or less. This n-type cladding layer 1
4 can be grown with a single nitride semiconductor,
By using a superlattice layer, a carrier confinement layer having good crystallinity without cracks can be formed.

(N-side light guide layer 15) The n-side light guide layer 15 is made of undoped GaN,
It has a thickness of 0.1 μm. This n-side light guide layer 6
GaN, InGaN
Is preferably formed by growing a film having a thickness of usually 100 Å to 5 μm, more preferably 200 Å to 1 μm. Note that the light guide layer 15 can also be a superlattice layer. When the n-side light guide layer 15 and the n-side cladding layer 14 are superlattice layers, the average band gap energy of the nitride semiconductor layer forming the superlattice layer is larger than that of the active layer. When a superlattice layer is used, the first layer and the second layer
At least one of the layers may be doped with an n-type impurity or undoped.

(Active Layer 16) The active layer 16 is composed of, for example, In _0.2 Ga _0.8 N doped with Si at 8 × 10 ¹⁸ / cm ³ and has a thickness of 25 Å, 8 × 10 Si
¹⁸ / cm ³ -doped In _0.05 Ga _0.95 N and a barrier layer having a thickness of 50 Å are alternately laminated to form a multiple quantum well structure (MQW) having a predetermined thickness. Constitute. In the active layer 16, both the well layer and the barrier layer may be doped with impurities.
Either one may be doped. The threshold value tends to decrease when doped with an n-type impurity. When the active layer 16 has a multiple quantum well structure, a well layer having a small band gap energy and a barrier layer having a smaller band gap energy than the well layer are always stacked. Be distinguished. The thickness of the well layer is 1
It should be less than 00 Angstroms, preferably less than 70 Angstroms, most preferably less than 50 Angstroms. The thickness of the barrier layer is less than 150 angstroms, preferably less than 100 angstroms, and most preferably less than 70 angstroms.

(P-side Cap Layer 17) The p-side cap layer 17 has a larger band gap energy than the active layer 16, for example, Mg is 1 × 10 ²⁰ / g.
made of p-type Al _0.3 Ga _0.7 N doped with cm ³ ,
For example, it has a thickness of 200 angstroms. In the present embodiment, it is preferable to use the cap layer 17 as described above. However, since the cap layer is formed to have a small thickness, the present invention does not use i-type impurities doped with n-type impurities to compensate for carriers. It may be a type. The thickness of the p-side cap layer 17 is adjusted to 0.1 μm or less, more preferably 500 Å or less, and most preferably 300 Å or less. 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-side cap layer 17 and a nitride semiconductor layer having good crystallinity is difficult to grow. The thickness of the p-side cap layer 17 is 0.1 μm
If it is larger, carriers cannot pass through the p-type cap layer 17 serving as an energy barrier due to the tunnel effect. When the passage of the carriers due to the tunnel effect is taken into account, as described above, the thickness is 500 Å or less, and further 300 Å. It is preferable to set the following

In order to facilitate oscillation of the LD element, the p-side cap layer 17 has a large Al composition ratio.
Preferably, the AlGaN is formed using GaN.
As the thickness of the layer becomes thinner, the LD element becomes easier to oscillate. For example, if the _Al Y value is 0.2 or more _{Y Ga 1-Y} N 5
It is desirable to adjust it to not more than 00 angstroms.
Although the lower limit of the thickness of the p-type cap layer 17 is not particularly limited,
It is desirable to form the film with a thickness of 10 Å or more.

(P-side light guide layer 18) The p-side light guide layer 18 has a band gap energy of p
Smaller than the side cap layer 17, for example, undoped G
aN, and has a thickness of 0.1 μm. The p-side light guide layer 18 functions as a light guide layer of the active layer 16, and is preferably formed by growing GaN or InGaN similarly to the n-side light guide layer 15. Also, this layer is p
It also functions as a buffer layer when growing the mold cladding layer 19, and functions as a preferable light guide layer by growing it with a thickness of 100 Å to 5 μm, more preferably 200 Å to 1 μm.
The p-side light guide layer may be doped with a p-type impurity such as Mg to have a p-type conductivity. Note that the p-side light guide layer may be a superlattice layer. When a superlattice layer is formed, at least one of the first layer and the second layer may be doped with a p-type impurity or may be undoped.

(P-side cladding layer 19 = superlattice layer) The p-side cladding layer 19 is made of, for example, Mg of 1 × 10 ²⁰ /
made of p-type Al _0.2 Ga _0.8 N doped with cm ³ ,
For example, a first layer having a thickness of 20 angstroms and a p-type G doped with 1 × 10 ²⁰ / cm ^{3 of} Mg, for example.
A superlattice layer is formed by alternately stacking aN and a second layer having a thickness of 20 angstroms. This p
The side cladding layer 19 functions as a carrier confinement layer similarly to the n-side cladding layer 14, and particularly functions as a layer for lowering the resistivity of the p-type layer. Although the thickness of the p-side cladding layer 19 is not particularly limited, it is desirable that the thickness be 100 Å or more and 2 μm or less, more preferably 500 Å or more and 1 μm or less.

(P-side Contact Layer 20) The p-side contact layer 20 is formed on the p-side cladding layer 19.
For example, p-type Ga doped with Mg at 2 × 10 ²⁰ / cm ³
N and has a thickness of, for example, 150 angstroms. This p-side contact layer 20 is made of a p-type In _X Al
_Y Ga _1- XYN (0 ≦ X, 0 ≦ Y, X + Y ≦ 1) can be used. Preferably, GaN doped with Mg as described above is most preferably used as the p-electrode 21. Ohmic contact is obtained. Further, the thickness of the p-side contact layer is 500 Å or less, more preferably 30 Å.
It is desirable to adjust the thickness to 0 angstrom or less, most preferably 200 angstrom or less. Because
As described above, by adjusting the thickness of the p-type nitride semiconductor layer having a resistivity of several Ω · cm or more to 500 Å or less, the resistivity can be further reduced. , The voltage drops. Further, the amount of hydrogen removed from the p-type layer can be increased, and the resistivity can be further reduced.

In the present invention, the p-side contact layer 20
Can also be a superlattice layer. In the case of a superlattice layer, a first layer and a second layer having different band gap energies are laminated, and a first + second + first + second +...
When the layers having smaller band gap energies are finally exposed, a preferable ohmic contact with the p-electrode 21 is obtained. p electrode 21
Examples of the material include Ni, Pd, and Ni / Au.

Next, as shown in FIG.
The surface of the nitride semiconductor layer exposed between the electrode 23 and Si
An insulating film 25 made of O ₂ is formed, and a p pad electrode 22 electrically connected to the p electrode 21 and an n electrode connected to the n electrode 23 through an opening formed in the insulating film 25.
A pad electrode 24 is formed. The p pad electrode 22 enlarges the substantial surface area of the p electrode 21 so that the p electrode side can be wire-bonded and die-bonded,
On the other hand, the n-pad electrode 24 prevents the n-electrode 23 from peeling off.

In the nitride semiconductor device described above, the p-type cladding layer 19 having good crystallinity, which is a superlattice layer formed by stacking the first layer and the second layer with a thickness equal to or less than the elastic strain limit, is formed. Have. Thereby, in the nitride semiconductor device of the present embodiment, the resistance value of the p-side cladding layer 19 can be reduced by one digit or more compared to the p-side cladding layer having no superlattice structure. Voltage and current can be reduced.

Further, in the nitride semiconductor device of this embodiment in contact with the p-side cladding layer 19 comprising a p-type _{Al Y Ga 1-Y} N, the smaller nitride semiconductor band gap energy as the p-side contact layer 20, By forming the film thickness as thin as 500 angstroms or less, the carrier concentration of the p-side contact layer 20 is substantially increased, a preferable ohmic contact with the p-electrode is obtained, and the threshold current and voltage of the device are reduced. Can be. Further, since the second buffer layer 112 is provided before growing the n-side contact layer, the crystallinity of the nitride semiconductor layer grown on the second buffer layer 112 is improved, and a long-life element is formed. Can be realized. Preferably, when the n-side contact layer grown on the second buffer layer 112 is a superlattice, an element having a low lateral resistance value and a low threshold voltage / threshold current can be realized.

It should be noted that the LD element of this embodiment has InGa
In the case where a nitride semiconductor containing at least indium, such as N, is provided in the active layer 16, In _X Ga _1-X N
When _the super lattice layer in which the Al Y _{Ga 1-Y} N are alternately laminated, is preferably used as a layer for interpose the active layer 16 (n-side cladding layer 14 and the p-side cladding layer 19). Thereby, the band gap energy difference and the refractive index difference between the active layer 16 and the superlattice layer can be increased, so that the superlattice layer can be operated as a very excellent light confinement layer when realizing a laser device. it can. Further InGaN
Since In has a crystalline property that is softer than other nitride semiconductors containing Al such as AlGaN, when InGaN is used as an active layer, cracks hardly occur in the entire stacked nitride layers. Thereby, the life of the LD element can be extended.

In the case of a semiconductor device having a double heterostructure having an active layer 16 having a quantum well structure as in the present embodiment, a film thickness of 0.1 mm having a band gap energy larger than that of the active layer 16 in contact with the active layer 16. P-side cap layer 17 made of a nitride semiconductor of 1 μm or less, preferably Al
A p-side cap layer 17 made of a nitride semiconductor containing is provided, and a p-side light guide layer 18 having a smaller band gap energy than the p-side cap layer 17 is provided at a position farther from the active layer than the p-side cap layer 17. A nitride semiconductor having a larger band gap than the p-side light guide layer 18 at a position farther from the active layer than the p-side light guide layer 18;
It is very preferable to provide the p-side cladding layer 19 having a superlattice structure preferably containing a nitride semiconductor containing Al. Moreover, since the band gap energy of the p-side cap layer 17 is increased, electrons injected from the n-layer are blocked and confined by the p-side cap layer 17, and the electrons do not overflow the active layer. Leakage current is reduced.

In the above-described nitride semiconductor device of the present embodiment, a preferable structure is shown as the structure of the laser device.
In this embodiment, the n-type superlattice layer is an n-type superlattice layer below the active layer 16.
It is sufficient that at least one layer is provided in the p-type nitride semiconductor layer region (n-type layer side), and the p-type superlattice layer is also a p-type nitride semiconductor layer region above the active layer 16 (p-type layer side). It is sufficient that the device has at least one layer, and the element configuration is not particularly limited. However, when the superlattice layer is formed on the p-layer side, it is formed on the p-side clad layer 19 as a carrier confinement layer, and when formed on the n-layer side, the n-contact as an electric current injection layer to which the n-electrode 23 is in contact. Forming the layer 12 or the n-side cladding layer 14 for confining carriers tends to be the most preferable in decreasing the Vf and the threshold value of the device.

In the nitride semiconductor device of Embodiment 2 configured as described above, after each layer is formed, annealing is performed at 400 ° C. or more, for example, 700 ° C. in an atmosphere containing no hydrogen, for example, a nitrogen atmosphere. It is preferable that the threshold voltage be further reduced because the resistance of each layer in the p-type nitride semiconductor layer region can be further reduced.

In the nitride semiconductor device of the embodiment,
A p-electrode 21 made of Ni and Au is formed in a stripe shape on the surface of the p-side contact layer 12, and the n-side contact layer is exposed symmetrically with respect to the p-electrode 21 so that the n-side is exposed.
An n-electrode 23 is provided on almost the entire surface of the side contact layer. As described above, when an insulating substrate is used, a structure in which the n-electrode 23 is provided symmetrically on both sides of the p-electrode 21 is very advantageous in lowering the threshold voltage.

In this embodiment, a dielectric multilayer film composed of SiO ₂ and TiO ₂ may be formed on a cleavage plane (resonator plane) cleaved in a direction perpendicular to the ridge portion (striped electrode). .

As described above, in the present embodiment, the superlattice layer is a clad layer as a carrier confinement layer formed in the n-type region or the p-type region sandwiching the active layer, a light guide layer of the active layer, or Since it is used as a current injection layer formed in contact with an electrode, it is desirable to adjust the average band gap energy of the nitride semiconductor constituting the superlattice layer to be larger than that of the active layer.

[0048]

The present invention will be described in more detail with reference to the following examples. Example 1 Example 1 according to the present invention is an example of producing the nitride semiconductor device (LD device) shown in FIG. 4, and is produced by the following procedure. First, the substrate 10 made of sapphire (C plane) is set in a reaction vessel, and after sufficiently replacing the inside of the vessel with hydrogen, the temperature of the substrate is increased to 1050 ° C. while flowing hydrogen to clean the substrate. Subsequently, the temperature is raised to 510
C., and hydrogen was used as a carrier gas, ammonia (NH ₃ ) and TMG (trimethylgallium) were used as source gases, and a buffer layer 11 made of GaN was formed on the substrate 10 by about 2 nm.
It is grown to a thickness of 00 Å.

After the growth of the buffer layer 11, only TMG is stopped, and the temperature is increased to 1050 ° C. When the temperature reaches 1050 ° C., TMG and ammonia gas are used as source gases, and the carrier concentration is 1 × 10 ¹⁸ / cm ³ undoped GaN.
The second buffer layer 112 is grown to a thickness of 5 μm. The second buffer layer 112 is made of In _X Al _Y Ga
_1-X-Y N can be configured in (0 ≦ X, 0 ≦ Y , X + Y ≦ 1), but not its composition asks particularly preferably undoped Al (Y value) of 0.1 or less Al _Y Ga
_1-YN , most preferably undoped GaN.
Subsequently, at 1050 ° C., TMG, ammonia, and silane gas (SiH ₄ ) were used as impurity gas, and Si was added to 1 × 10 ^19.
An n-side contact layer 12 of n-type GaN doped with / cm ³ is grown to a thickness of 1 μm. More preferably, the n-side contact layer 12 is formed of a super lattice.

Next, the temperature was set to 800 ° C., and TMG, TMI (trimethyl indium) and ammonia were used as the source gas, silane gas was used as the impurity gas, and 5 × 10
^A crack preventing layer 13 made of In _0.1 Ga _0.9 N doped with ¹⁸ / cm ³ is grown to a thickness of 500 Å.

Then, the temperature was raised to 1050 ° C.
(Trimethylaluminum), TMG, ammonia, and silane gas are used to grow a first layer of n-type Al _0.2 Ga _0.8 N doped with 5 × 10 ¹⁸ / cm ^{3 of} Si to a thickness of 20 Å. Then, the TMA and the silane are stopped, and the second layer made of undoped GaN is
It is grown to a thickness of Å. This operation is repeated 100 times to grow the n-side cladding layer 14 composed of a superlattice layer having a total film thickness of 0.4 μm.

Subsequently, an n-side light guide layer 15 made of undoped GaN is grown at 1050 ° C. to a thickness of 0.1 μm. Next, the active layer 16 is grown using TMG, TMI, ammonia, and silane gas. The active layer 16 is maintained at a temperature of 800 ° C., and first, a well layer made of In _0.2 Ga _0.8 N doped with Si at 8 × 10 ¹⁸ / cm ³ is formed.
It is grown to a thickness of 5 angstroms. Next, at the same temperature only by changing the molar ratio of TMI, 8 × 10
^A barrier layer made of In _0.01 Ga _0.99 N doped with ¹⁸ / cm ³ is grown to a thickness of 50 Å. This operation was repeated twice, and finally, a multiple quantum well structure (M
The active layer 16 of QW) is grown.

Next, the temperature was raised to 1050 ° C., and TMG, TMA, ammonia was used as a source gas, and Cp ₂ M was used as an impurity gas.
g (cyclopentadienyl magnesium), the band gap energy is larger than that of the active layer, and Mg is 1
× 10 ²⁰ / cm ³ doped p-type Al _0.3 Ga _0.7
A p-side cap layer 17 made of N is grown to a thickness of 300 Å. Subsequently, at 1050 ° C., a p-side light guide layer 18 of undoped GaN having a band gap energy smaller than that of the p-side cap layer 17 is grown to a thickness of 0.1 μm.

Subsequently, TMG, TMA, ammonia, C
Using p ₂ Mg, at 1050 ° C., 1 × 10 ²⁰ / cm of Mg
First made of ^3- doped p-type Al _0.2 Ga _0.8 N
Is grown to a thickness of 20 angstroms, then only TMA is stopped, and a second layer of p-type GaN doped with Mg at 1 × 10 ²⁰ / cm ³ is grown to a thickness of 20 angstroms. This operation is performed for 100
This is repeated twice to form a p-side cladding layer 19 made of a superlattice layer having a total film thickness of 0.4 μm. Finally, at 1050 ° C., p
A p-side contact layer 20 made of p-type GaN doped with 2 × 10 ²⁰ / cm ^{3 of} Mg is formed on the side cladding layer 19.
It is grown to a thickness of 50 angstroms.

After completion of the reaction, the temperature was lowered to room temperature, and the wafer was placed in a reaction vessel in a nitrogen atmosphere.
Anneal at ℃ to further reduce the resistance of the p-type layer. After the annealing, the wafer is taken out of the reaction vessel, and as shown in FIG. 4, the n-side contact layer 12 is formed by an RIE apparatus to form a stripe consisting of a part of the uppermost p-side contact layer 20 to a part of the n-side contact layer 12.
Is exposed, and at the same time, a resonance surface is formed. p
A mask is formed on the side contact layer 20, and as shown in FIG. 4, a part of the uppermost p-side contact layer 20 and the p-side cladding layer 19 having a stripe shape is etched by an RIE apparatus to form a 4 μm stripe. It has a ridge shape having a width.

Next, a p-electrode 21 made of Ni and Au is formed on almost the entire outermost surface of the stripe ridge of the p-side contact layer 20.
To form On the other hand, an n-electrode 23 made of Ti and Al is formed on almost the entire surface of the n-side contact layer 12 in a stripe shape.

Next, as shown in FIG.
The surface of the nitride semiconductor layer exposed between the electrode 23 and Si
An insulating film 25 made of O ₂ is formed, and a p-pad electrode 22 electrically connected to the p-electrode 21 via the insulating film 25 is formed.
And an n-pad electrode 24 are formed. As described above,
The wafer on which the n-electrode and the p-electrode have been formed is transferred to a polishing apparatus, and the sapphire substrate 1 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.

After the substrate is polished, the polished surface side is scribed,
Cleavage is performed in a bar shape in a direction perpendicular to the stripe-shaped electrodes.
A dielectric multilayer film composed of SiO ₂ and TiO ₂ was formed on the resonator surface, and finally, a bar was cut in a direction parallel to the p-electrode to obtain a laser chip. Next, the chip is placed face up (with the substrate and the heat sink facing each other) and placed on the heat sink, and the respective electrodes are wire-bonded.
When laser oscillation was attempted at room temperature, the threshold current density was 2.9 kA / cm ² and the threshold voltage was 4.4 V at room temperature.
In the far field pattern, there was only one spot of the laser beam.

Example 2 In Example 1, the second buffer layer 112 was not grown, and the n-side contact layer 12 was made of Si with 1 × 10 ^19.
/ Cm ³ -doped n-type GaN single and grown 5 μm
The side-side cladding layer 14 is grown by n-type Al _0.2 Ga _0.8 N single doped with Si at 1 × 10 ¹⁹ / cm ³ by 0.4 μm, and the p-side cladding layer 19 is made of Mg at 1 × 10 ²⁰ / m 3. 0.4 μm with a single ^3- doped p-type Al _0.2 Ga _0.8 N
Grown, and the p-side contact layer 20 is made of Mg 2 × 1
0.2 μm of single p-type GaN doped with 0 ²⁰ / cm ³
A laser device was obtained in the same manner as in Example 1 except for growing. When laser oscillation was performed in the same manner as in Example 1, at room temperature, the threshold current density was 3.1 kA / cm ² , the threshold voltage was 4.6 V, and in the far field pattern, the spot of elliptical light of the laser was 1 point. Was one.

Comparative Example 1 The procedure of Example 1 was repeated, except that after forming the ridge structure, a resonance surface was formed. As a result, in the far-field pattern, the laser light was split into three in the horizontal direction. Further, since two stripes of the stripe width of the ridge structure were formed on the resonance surface, the threshold value was increased as compared with the first embodiment.

Comparative Example 2 The procedure of Example 2 was repeated, except that after forming the ridge structure, a resonance surface was formed. As a result, in the far-field pattern, the laser light was split into three in the horizontal direction. Further, since two stripes of the stripe width of the ridge structure were formed on the resonance surface, the threshold value was increased as compared with the second embodiment.

According to the present invention, it is possible to provide a method of manufacturing a nitride semiconductor laser device having a smooth resonance surface, a good far-field pattern shape of laser light, and a reduced threshold value.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a partial structure of a nitride semiconductor showing a crystal structure of an etched surface of the nitride semiconductor when a ridge is formed after forming a resonance surface according to the present invention.

FIG. 2 is a perspective view showing a partial structure of a nitride semiconductor showing a crystal structure of an etched surface of the nitride semiconductor when a resonance surface is formed after a conventional ridge is formed.

FIG. 3 is a schematic plan view when FIG. 2 is viewed from above.

FIG. 4 is a schematic sectional view of a nitride semiconductor device according to an embodiment of the present invention.

[Explanation of symbols]

 10 substrate 11 buffer layer 112 second buffer layer 12 n-side contact layer 13 crack prevention layer 14 n-side cladding layer ( ... N-side light guide layer 16... Active layer 17... Cap layer 18... P-side light guide layer 19. 20) p-side contact layer 21 p-electrode 22 p-pad electrode 23 n-electrode 24 n-pad electrode 25 insulating film

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 33/00 H01L 21/302 H01L 21/461 JICST file (JOIS)

Claims (1)

(57) [Claims] An n-type nitride semiconductor including an n-side contact layer
P-type nitride including body layer, active layer and p-side contact layer
A method of manufacturing a nitride semiconductor laser device having a semiconductor layer and an optical waveguide mechanism having a ridge structure, wherein a resist film is further formed after etching to form a resonance surface.
Remains of the resist film generated during exposure by exposure
Forming a ridge structure by etching as a protective film for the nitride semiconductor laser device.