JP3502527B2 - Nitride semiconductor laser device - Google Patents

Description

Detailed Description of the Invention

[0001]

This invention relates to nitride semiconductors (eg,
In _X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1).

[0002]

2. Description of the Related Art Nitride semiconductors have recently been put into practical use by the present applicant as materials for high-brightness blue LEDs and pure green high-brightness LEDs. Further, the present applicant succeeded in continuous oscillation at room temperature of 406 nm for the first time in the world in a blue laser device using this material. (Nikkei Electronics, 19
This laser device has a multiple quantum well structure of In _X Ga _{1 -X} N in the active layer, and the resonance surface at both ends of the active layer is formed by etching.
At 0 ° C., a threshold current density of 3.6 kA / cm ² , a threshold voltage of 5.5 V, and an output of 1.5 mW show continuous oscillation for 27 hours.

[0003]

A laser light source having a short wavelength has been earnestly desired as a light source for DVD, communication and the like. Although the feasibility has been shown by the nitride semiconductor, it is only continuous oscillation for several tens of hours, and continuous oscillation for further longer time is required for practical use. Therefore, an object of the present invention is to improve the life of a laser light source using a nitride semiconductor.

[0004]

In order to continuously oscillate a nitride semiconductor for a long time, it is necessary to study not only the crystallinity but also the mechanism for obtaining a gain. As a result of a detailed study of the gain, we have newly found that the gain becomes extremely large by setting the length of the nitride semiconductor for obtaining the gain to a specific range or less, and thus achieved the present invention. That is, the nitride semiconductor laser device of the present invention is characterized in that the distance of the medium for obtaining the gain of the laser device is 100 μm or less. The preferred distance is 80 μm or less.

It is characterized in that the medium is an active layer made of a nitride semiconductor containing at least indium. A preferred active layer is an active layer having a multiple quantum well structure in which a well layer made of a nitride semiconductor containing indium and a barrier layer made of a nitride semiconductor having a bandgap energy larger than that of the well layer are stacked.

Further, the laser device of the present invention is characterized in that it has a structure in which the end face of the nitride semiconductor is used as a resonator, and the distance for obtaining the gain corresponds to the resonator length of the active layer. This structure in which the end face of the nitride semiconductor is used as a resonator is generally called a Fabry-Perot type laser and has a thickness of several μm to several tens of μm.
The active layer having the stripe width of is the waveguide region.

Further, the laser element of the present invention is characterized in that the laser element has a surface emitting type structure, and the distance corresponds to the film thickness of the active layer. The surface emitting type is a laser device in which reflective mirrors are formed in parallel with the stacking direction of the nitride semiconductor layers with an active layer that emits light interposed therebetween, and is a nitride semiconductor layer in which Fabry-Perot type laser devices are stacked. While the laser light is emitted in parallel with, the surface emitting laser emits the laser light vertically.

Further, in the case of a surface emitting laser, a medium for obtaining a gain is composed of a well layer made of a nitride semiconductor containing indium and a barrier layer made of a nitride semiconductor having a bandgap energy larger than that of the well layer. It is an active layer of a multiple quantum well structure, and is characterized in that the distance of the medium corresponds to the total film thickness of the well layer.

Further, the laser device of the present invention is characterized in that the peak position where the gain becomes maximum is on the high energy side of the peak position of the emission spectrum in the spontaneous emission light state.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION First, on a sapphire substrate, 30
0 angstrom undoped GaN buffer layer, 3 μm Si-doped GaN layer, 0.18 μm S
i-doped In0.06Ga0.94N layer (crack prevention layer),
0.4 μm Si-doped Al0.07Ga0.93N layer (n-side cladding layer), Si-doped GaN layer (n-side guide layer), 3
An active layer having a multiple quantum well structure formed by alternately stacking four well layers of 0 angstrom undoped In0.18Ga0.82N and three barrier layers of 60 angstrom undoped In0.06Ga0.94N, 100 angstrom Mg-doped Al0.15Ga0.85N layer (p-side cap layer), 0.1 μm Mg-doped GaN layer (p-side guide layer), 0.4 μm Mg-doped Al0.07Ga0.93N layer (p-side cladding layer), 0.15 μm Mg-doped GaN
A wafer was prepared by sequentially laminating layers (p-side contact layer). This wafer has a sapphire substrate on which a nitride semiconductor layer to be a laser device structure is laminated,
The action of each layer will be described in detail later. After breaking this wafer into a rectangular chip shape, a YAG: Nd laser was irradiated from the nitride semiconductor layer side of the chip, and spontaneous emission from the active layer was observed by excitation (pumping). FIG. 1 schematically shows a state in which a chip is irradiated with YAG: Nd laser light. As shown in this figure,
Exciting the edge part of the sample with a striped area,
The spontaneous emission emitted upon excitation was measured and the emission was analyzed from various angles as a function of stripe length (L). It should be noted that one end face is not vertical so that stimulated emission light is not generated.

FIG. 2 is a diagram showing the relationship between the stripe length (L) and the emission intensity at 402 nm of the spontaneous emission spectrum. In FIG. 2, (a) is a linear scale, (b)
[Fig. 3] is an enlarged view showing a part of (a). In addition, the solid line shown in FIGS. (A) and (b) shows the measured value, and the wavy line shows the theoretical value. The following formula is used for the theoretical formula. In the equation, g ₀ is a modal gain, I ₀ is a spontaneous emission light intensity, and L is a stripe length.

[0012]

[Equation 1]

As shown in this figure, the stripe length is 80
The laser light intensity tends to be saturated when the thickness exceeds μm. This means that a large gain is obtained up to 80 μm, but the gain becomes smaller at 80 μm or more. Therefore, the preferable stripe length for obtaining a large gain is adjusted to 100 μm or less, more preferably 80 μm or less. The lower limit is not particularly limited, but in the case of a Fabry-Perot type laser device, it is 5
It is desirable to adjust to μm or more.

FIG. 3 is a diagram showing a comparison between the gain spectrum (a) and the spontaneous emission light spectrum (b). Figure 3
(A) shows a gain spectrum extracted from a theoretical value when the upper limit of the stripe length is set to 30 μm. That is, FIG. 3A shows the modal gain g ₀ obtained from the equation (1). As shown in this figure, the maximum value of the gain is about 140 in the nitride semiconductor laser device.
There is also 0 cm ^-1 . Conventional semiconductor laser, eg infrared G
In the aAlAs laser, this gain value is approximately 50 to 1
There is only 00 / cm ^-1 . Similarly, with a red laser made of InAlGaP, it is only 50 to 100 / cm ^-1 .
Comparing the conventional semiconductor laser and the nitride semiconductor laser, in the nitride semiconductor laser, the length of the medium for obtaining this gain is set to 100 μm or less, so that it is 10 times or more larger than that of the conventional semiconductor laser. Gain can be obtained. Therefore, the present invention shows the possibility of realizing a high-power, low-threshold laser.

The "blackened squares" in FIG. 3 (b) show the emission spectrum of the spontaneous emission light (LED state) actually measured. The stripe length at this time is 5 μm. On the other hand, the “hollow square” is the spontaneous emission spectrum of I ₀ derived from the equation (1). Thus, the fact that the spectra of both are substantially the same indicates that the gain derivation method shown in FIG. 3A is correct.

Further, comparing FIGS. 3 (a) and 3 (b), the gain spectrum position at which the gain in FIG. 3 (a) becomes the maximum, compared with the spontaneous emission (LED state) spectrum in FIG. 3 (b) ( Laser oscillation state) is located on the high energy side. This indicates that the gain of the nitride semiconductor laser including the active layer containing In is likely to be generated by electron-hole plasma. That is, by increasing the gain of the nitride semiconductor as in the present invention, the stimulated emission light (laser light) is generated on the higher energy side than the peak energy of the LED state in the laser element.
Is obtained.

[0017]

【Example】

[Embodiment 1] FIG. 4 is a perspective view showing a structure of a laser device according to an embodiment of the present invention, and shows a structure of a nitride semiconductor on a resonance surface side. Embodiment 1 will be described below with reference to this drawing.

Approximately 1 inch in diameter, film thickness 20 with C plane as main surface
0 μm, GaN substrate 40 containing Si 1 × 10 ¹⁸ / cm ³
Is transferred into a reaction vessel of a MOVPE (metal organic chemical vapor deposition) apparatus, and S is deposited on the GaN substrate 40 at 1050 ° C.
A second buffer layer 41 made of GaN doped with 1 × 10 ¹⁸ / cm ^{3 of} i is grown to 2 μm. The second buffer layer 41 is a nitride semiconductor single crystal layer grown at a high temperature of 900 ° C. or higher, and is a buffer layer grown at a low temperature for relaxing lattice mismatch between the conventionally grown substrate and the nitride semiconductor. Is distinguished from. In addition, the second buffer layer 4
1 is preferably a strained superlattice layer formed by stacking nitride semiconductors having different film thicknesses of 100 angstroms or less, more preferably 70 angstroms or less, and most preferably 50 angstroms or less. When the strained superlattice layer is used, the crystallinity of the single nitride semiconductor layer is improved, so that a high-power laser device can be realized.

(Crack prevention layer 42) Next, Si was added at 5 × 1.
A crack prevention layer 42 of In 0.1 Ga 0.9 N doped with 0 ¹⁸ / cm ³ is grown to a thickness of 500 Å. The crack prevention layer 42 can prevent cracks from entering the Al-containing nitride semiconductor layer by growing an n-type nitride semiconductor containing In, preferably InGaN. The crack prevention layer is preferably grown to a film thickness of 100 angstroms or more and 0.5 μm or less. If the thickness is less than 100 Å, it is difficult to prevent cracks as described above, and 0.5 μ
If it is thicker than m, the crystal itself tends to turn black. The crack prevention layer 42 may be omitted.

(N-side clad layer 43) Next, Si is added to 5 ×
A first layer of 10 ¹⁸ / cm ³ doped n-type Al0.2Ga0.8N, 20 Å, undoped
The strained superlattice structure having a total film thickness of 0.4 μm is formed by alternately stacking 100 layers of the second layer of GaN of pe) and 20 angstroms. The n-side cladding layer 43 acts as a carrier confinement layer and an optical confinement layer, and it is desirable to use a nitride semiconductor containing Al, preferably a superlattice layer containing AlGaN. The total thickness of the superlattice layer is 100 angstroms or more. 2 μm or less, more preferably 500
It is desirable to grow at a thickness of angstrom or more and 1 μm or less. When the strained superlattice layer is used, a carrier confinement layer having good crystallinity without cracks can be formed. By using at least one of the n-side clad layer and / or the p-side clad layer as the strained superlattice layer, the crystallinity of the nitride semiconductor is improved and the output is further improved.

(N-side light guide layer 44) Subsequently, Si is added to 5
An n-type light guide layer 44 made of n-type GaN doped with × 10 ¹⁸ / cm ³ is grown to a film thickness of 0.1 μm. The n-side light guide layer 44 acts as a light guide layer of the active layer,
It is desirable to grow GaN or InGaN, usually 100 angstrom to 5 μm, and more preferably 2
It is desirable to grow the film with a film thickness of 00 angstrom to 1 μm. This n-side light guide layer 44 is usually Si, G
Although an n-type impurity such as e is doped to obtain an n-type conductivity type,
In particular, it can be undoped. When forming a superlattice, at least one of the first layer and the second layer may be doped with an n-type impurity or may be undoped.

(Active layer 45) Next, undoped In0.
Well layer made of 2 Ga 0.8 N, 25 angstrom,
A barrier layer made of undoped In0.01Ga0.95N and an active layer 4 of multiple quantum well structure (MQW) having a total film thickness of 175 Å, which is formed by alternately stacking 50 Å.
Grow 5

(P-side cap layer 46) Next, 1 × 10 ²⁰ / cm ^{3 of} Mg-doped p-type Al 0. having a bandgap energy larger than that of the p-side optical guide layer 47 and larger than that of the active layer 45. A p-side cap layer 46 made of 3 Ga 0.9 N is grown to a film thickness of 300 Å. Although the p-side cap layer 46 is p-type, it has a small film thickness, so that it is doped with an n-type impurity to compensate the carrier.
It may be of a type or undoped, and most preferably a p-type impurity-doped layer. p-side cap layer 17
Is adjusted to 0.1 μm or less, more preferably 500 angstroms or less, and most preferably 300 angstroms or less. This is because if the film is grown to have a film thickness greater than 0.1 μm, cracks are likely to occur in the p-type cap layer 46 and a nitride semiconductor layer having good crystallinity is difficult to grow. If the AlGaN having a higher Al composition ratio is formed thinner, the LD element is likely to oscillate. For example, if the Y value is 0.
For Al _Y Ga _{1 -Y} N of 2 or more, it is desirable to adjust the thickness to 500 angstroms or less. p-side cap layer 46
The lower limit of the film thickness is not particularly limited, but it is desirable to form the film with a film thickness of 10 angstroms or more.

(P-side optical guide layer 47) Next, if the bandgap energy is smaller than that of the p-side cap layer 46, Mg
A p-side light guide layer 47 made of p-type GaN doped with 1 × 10 ²⁰ / cm ³ is grown to a film thickness of 0.1 μm. This layer acts as an optical guide layer of the active layer, and it is desirable to grow GaN or InGaN as with the n-side optical guide layer 44. Further, this layer also acts as a buffer layer when growing the p-side cladding layer 48, and acts as a preferable light guide layer by growing it to a film thickness of 100 angstrom to 5 μm, more preferably 200 angstrom to 1 μm. . This p-side light guide layer is usually doped with p-type impurities such as Mg to have a p-type conductivity type, but it is not necessary to dope impurities. In addition, this p
The mold light guide layer can also be a superlattice layer. When forming a superlattice layer, at least one of the first layer and the second layer may be doped with p-type impurities or may be undoped.

(P-side clad layer 48) Next, 1 × Mg is added.
10 ²⁰ / cm ³ doped p-type Al0.2 Ga0.8 N first layer, 20 Å, Mg 1 × 10 ²⁰
/ Cm ³ -doped p-type GaN second layer, 20 angstroms alternately laminated total thickness 0.4μ
A p-side clad layer 48 made of a superlattice layer of m is formed.
Like the n-side cladding layer 43, this layer acts as a carrier confinement layer, and when it has a superlattice structure, it acts as a layer for lowering the resistivity on the p-type layer side. This p
The thickness of the side clad layer 48 is not particularly limited, either, but it is 100 angstroms or more and 2 μm or less, and more preferably 5
It is desirable to grow it to a thickness of at least 00 Å and at most 1 μm.

In the case of a double hetero structure nitride semiconductor device having an active layer 45 having a quantum structure well layer, a film thickness of 0.1 μm or less which is in contact with the active layer 45 and has a band gap energy larger than that of the active layer 45. Of the Al-containing nitride semiconductor is provided, and a p-side optical guide layer 47 having a smaller bad gap energy than the cap layer 46 is provided at a position farther from the active layer than the cap layer 46. It is extremely difficult to provide the p-side clad layer 48 made of a superlattice layer containing a nitride semiconductor containing Al having a band gap larger than that of the p-side light guide layer 47 at a position farther from the active layer than the side light guide layer 47. Is preferred. In addition, electrons injected from the n-layer, which have a large bandgap energy in the p-side cap layer 46, are blocked by the cap layer 46, so that electrons do not overflow the active layer, so that the leak current of the element is small. Become.

(P-side contact layer 49) Finally, a p-side contact layer 49 made of p-type GaN doped with Mg at 2 × 10 ²⁰ / cm ³ is grown to a film thickness of 150 Å. The p-side contact layer has a thickness of 500 Å or less, more preferably 400 Å or less, 2
Adjust the film thickness to 0 angstrom or more. When a nitride semiconductor layer having an element structure was grown as described above, the plane orientation of the nitride semiconductor element portion was found to be GaN substrate 4
It coincided with the plane orientation of 0.

After completion of the reaction, the wafer is annealed at 700 ° C. in a nitrogen atmosphere in a reaction vessel, and p
The resistance of the mold layer is further reduced. After the annealing, the wafer is taken out from the reaction container and, as shown in FIG. 4, the uppermost p-side contact layer 49 and the p-side cladding layer 48 are etched by a RIE device to form a ridge shape having a stripe width of 4 μm. , Ni / Au on the entire surface of the ridge
The p-electrode 51 is formed. The ridge formation position is Ga
When forming the N substrate, a striped ridge parallel to the striped protective film is formed at a position just above the striped protective film formed on the sapphire substrate. The stripe width is adjusted to 20 μm or less, more preferably 15 μm or less, and most preferably 10 μm or less.

Next, as shown in FIG. 4, SiO 2 is formed on the surfaces of the p-side cladding layer 48 and the contact layer 49 excluding the p-electrode 51.
_An insulating film 50 made of ₂ is formed, and a p pad electrode 52 electrically connected to the p electrode 51 through the insulating film 50 is formed.

Next, the sapphire substrate, the buffer layer and the protective film of the wafer are polished and removed to expose the surface of the Si-doped GaN substrate layer 40, and the n-electrode made of Ti / Al is formed on the entire surface of the GaN substrate 40. 53 is formed with a film thickness of 0.5 μm, and a thin film of Au / Sn is formed thereon for metallization with a heat sink.

Next, the substrate is cleaved from the n-electrode side 53 at a position perpendicular to the stripe ridge, that is, at the M plane of the GaN substrate 40, and a resonance plane is formed on the M plane of the end face of the active layer. It is important that the resonator length during cleavage is 80 μm and does not exceed 100 μm.

Finally, a dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on the resonance surface, and the bar is cut in the direction parallel to the p electrode to form a laser chip. FIG. 4 shows the structure of the laser chip. Since the resonator length is short, the reflectance of the dielectric multilayer film needs to be designed close to 100% in order to reduce reflection loss. As described above, the medium for obtaining the gain of the laser element has an active layer made of a nitride semiconductor containing In, preferably an active layer having a multi-quantum well structure, and a structure having an end face of the active layer as a resonator, A laser chip with a cavity length of 80 μm was obtained. When this laser chip was placed face up (the GaN substrate and the heat sink faced each other) on the heat sink, the p-pad electrode 52 was wire-bonded, and laser oscillation was attempted at room temperature. In the first LED state, emission of 413 nm was emitted. Indicates
As the current was further increased, continuous oscillation with an oscillation wavelength of 405 nm was confirmed at room temperature with a threshold current density of 2.0 kA / cm ² and a threshold voltage of 4.0 V, and a life of 2000 hours or more was shown. On the other hand, when the resonator length was 200 μm, the threshold current density was also high, and the life was only 500 hours or longer.

[Embodiment 2] FIG. 5 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention, and specifically shows the structure of a surface emitting laser device. The case of the surface emitting laser element will be described below with reference to FIG.

On the surface of the same GaN substrate 40 as in Example 1, 4
A mask with a predetermined shape made of SiO ₂ having μmφ dots is formed, and the GaN substrate is etched by RIE to a position of 5 μm except the mask.

After the etching is completed, a dot-shaped mask is formed.
Transfer the wafer as it is into the MOVPE reaction vessel
Then, 1 × Mg is deposited on the GaN substrate 40 at 1050 ° C.
10 ²⁰/cm³N-side current narrowing made of doped p-type GaN
The confinement layer 54 is grown to a film thickness of 5 μm.

Next, the wafer is taken out from the reaction container,
After removing the dot-shaped mask, MOV the wafer again.
The n-side current constriction layer 54 is transferred to the reaction vessel of the PE device,
On the GaN substrate 40, In _X Ga _1-X N (0 ≦ X ≦
1), the n-side reflective layer 55 made of Al _Y Ga _1-Y N (0 <Y ≦ 1) is formed. The thickness of each layer of the n-side reflective layer 55 is designed to be λ / 4n (λ: emission wavelength of spontaneous emission light, n: refractive index of nitride semiconductor), and the emission of the active layer is in-plane. Resonate with. This reflecting mirror is called a Bragg reflecting mirror, and in the case of the laser element of the present invention, it is necessary to design the film thickness so as to have a reflectance of about 100% with respect to the spontaneous emission light of the active layer.

Then, in the same manner as in Example 1, the n-side cladding layer 43 'and the n-side light guide layer 44' made of the nitride semiconductor having the same composition as that of the example are formed on the n-side reflecting mirror 55. Layer 45 ', p-side cap layer 46', p-side light guide layer 4
7 ′ and the p-side cladding layer 48 ′ are sequentially stacked.

Further, on the p-side cladding layer 48 ', a p-side reflection layer 56 having the same nitride semiconductor laminated structure as the above-mentioned n-side reflection layer 55 is grown, and finally as in Example 1. A p-side contact layer 49 'made of Mg-doped p-type GaN is grown.

After completion of the reaction, annealing is performed in the same manner as in Example 1 to further reduce the resistance of the p-type layer. After the annealing, the wafer is taken out from the reaction container, and Ni / Au is almost entirely formed on the p-side contact layer 49 'as shown in FIG.
To form a p-electrode 51 '. In the case of a nitride semiconductor, the resistance of the p-type layer is higher than that of the n-type layer. Therefore, by forming the electrode on almost the entire surface of the p-type layer on the outermost surface, the heat generation amount is small and the life is long. It is possible to realize various laser devices.

Next, the sapphire substrate, the buffer layer, and the protective film of the wafer are polished and removed to expose the surface of the Si-doped GaN substrate layer 40, and the G corresponding to the position of the current confinement layer.
On the surface of the aN substrate 40, an n electrode 5 made of Ti / Al
3'is formed with a film thickness of 0.5 μm. That is, n electrode 5
3'is formed on almost the entire surface of the GaN substrate 40 'corresponding to the position excluding the dot-shaped mask formed previously.

In the surface emitting laser device of the present invention, the medium in which the gain is obtained is the active layer 45 'having a multiple quantum well structure.
InGaN well layer in the case of a surface emitting laser,
The total thickness of the well layer is preferably adjusted to 2000 angstroms or less, more preferably 1000 angstroms or less, and most preferably 500 angstroms or less.

Next, the GaN substrate 40 is separated into chips to form laser chips. FIG. 5 shows the structure of the laser chip. This laser chip was placed on the heat sink with the p-electrode 51 'and the heat sink facing each other, and the n-electrode 53' was wire-bonded, and laser oscillation was attempted at room temperature. It emits light of 413 nm, and as the current is further increased, the threshold current density is 10.0 kA / c at room temperature.
At m ² and a threshold voltage of 4.0 V, continuous oscillation with an oscillation wavelength of 405 nm was confirmed, and a life of 2000 hours or more was exhibited as in Example 1.

[0043]

As described above, since the distance of the nitride semiconductor that can obtain a large gain is clarified for the first time in the laser device of the present invention, a laser device having a low threshold current density and a long lifetime, which could not be realized conventionally, is obtained. Can be realized. It was discovered that a large gain can be obtained in such a short distance, and the first long-life laser device was realized.
Its industrial utility is extremely high in realizing various devices using short-wavelength light sources.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a state in which a nitride semiconductor laser chip is irradiated with YAG: Nd laser light to be excited.

FIG. 2 is a diagram showing the relationship between the stripe length (L) and the emission intensity at 402 nm of the spontaneous emission spectrum.

FIG. 3 is a spectrum diagram with respect to bandgap energy of laser light.

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

FIG. 5 is a schematic cross-sectional view showing the structure of a surface emitting laser device according to another embodiment of the present invention.

[Explanation of symbols]

40 ... Nitride semiconductor substrate 41 ... Second buffer layer 42 ... ・ Crack prevention layer 43 ... N-side cladding layer 44 ... N-side light guide layer 45 ... Active layer 46 ... Cap layer 47 ... P-side light guide layer 48 ... P-side cladding layer 49 ... P-side contact layer

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-7-235724 (JP, A) JP-A-1-194377 (JP, A) JP-A-8-139414 (JP, A) JP-A-7- 297476 (JP, A) JP-A-8-264891 (JP, A) Actual development 5-13079 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 5/00-5 / 50

Claims (3)

(57) [Claims] 1. A laser device having a structure in which a nitride semiconductor is used and an end face of the nitride semiconductor is used as a resonator, wherein a distance of a medium for obtaining a gain of the laser device is 80 μm or less, and the medium is at least A nitride semiconductor laser device, which is an active layer made of a nitride semiconductor containing indium, and the distance corresponds to a cavity length of the active layer. 2. The active layer having a multiple quantum well structure in which a well layer made of a nitride semiconductor containing indium and a barrier layer made of a nitride semiconductor having a bandgap energy larger than that of the well layer are stacked. The nitride semiconductor laser device according to claim 1, wherein: 3. The nitriding according to claim 1, wherein the peak position where the gain is maximum is on the high energy side with respect to the peak position of the emission spectrum in the spontaneous emission light state. Thing semiconductor laser device.