JP3405334B2 - Nitride semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light emitting diode.
(LED), laser diode (LD), etc.,
Used for light receiving elements such as solar cells and photodiodes
Nitride semiconductor (In _XAl_YGa_1-XYN, 0 ≦ X, 0 ≦
Y, X + Y ≦ 1) element, especially the structure of laser element
To do.

[0002]

2. Description of the Related Art A nitride semiconductor is known as a material for a laser device that emits light in the ultraviolet to blue region. The applicant has recently used this material to produce a laser oscillation of 410 nm at room temperature under a pulse current. Announced (for example, Jpn.J.
Appl.Phys. Vol35 (1996) pp.L74-76). The announced laser device is a so-called electrode stripe type laser device in which the nitride semiconductor layer including the active layer has a stripe width of several tens of μm and laser oscillation is performed. FIG. 5 is a schematic sectional view showing the structure of the laser device. This laser device comprises a sapphire substrate, a GaN buffer layer, n-GaN, n-In _0.1 Ga _0.9 N,
n-Al _0.15 Ga _0.95 N, n-GaN, active layer made of InGaN having a multi-quantum-well (MQW) structure, p-Al _0.2 Ga _0.8 N, p-GaN, p-A
l _0.15 Ga _0.85 N and p-GaN are stacked in this order, the n-GaN layer on the buffer layer is an n-type contact layer forming a negative electrode, and the uppermost p-GaN layer is a positive electrode. Acting as a p-type contact layer to be formed, n-Al
_{The 0.15} Ga _0.85 N layer and the p-Al _0.15 Ga _0.85 N layer act as an optical confinement layer.

[0003]

As described above, the nitride semiconductor laser developed by the present inventors realized the laser oscillation of 410 nm for the first time in the world, but it is still only the pulse oscillation and the threshold The current is 1 to 2 A. For continuous oscillation, it is necessary to further reduce the threshold current. Further, as can be seen from the figure, since it has a complicated laminated structure, complicated work is required in the nitride semiconductor growth step.

The present invention has been made in view of the above circumstances, and an object thereof is to realize a laser device made of a nitride semiconductor with a simple structure and further reduce the threshold current. , Aiming for continuous oscillation at room temperature.

[0005]

A first nitride semiconductor device according to the present invention comprises an n-type contact layer made of an n-type nitride semiconductor layer containing Al and Ga, and a nitride layer containing In, which is provided on an upper portion of a substrate. An active layer having a multiple quantum well structure made of a semiconductor
In a nitride semiconductor device sequentially provided with a p-type contact layer made of a p-type nitride semiconductor, the n-type contact layer has a substrate side so that a difference in refractive index between the n-type contact layer and the active layer becomes large on the active layer side. Is characterized by having a compositional gradient structure having a small Al mixed crystal ratio and a large Al mixed crystal ratio on the active layer side. Further, in the first nitride semiconductor device according to the present invention, the n-type contact layer is _Al y _{Ga 1-y} N
It may be made of an n-type nitride semiconductor represented by (0 <y <1). The second nitride semiconductor device according to the present invention, the substrate upper, n-type _{Al y Ga 1-y N (} 0 <y <
1) an n-type contact layer made of an n-type nitride semiconductor layer, an active layer having a multiple quantum well structure made of a well layer and a barrier layer, and a p-type contact layer made of a p-type nitride semiconductor. In the provided nitride semiconductor device, the well layer is made of InzGa1-zN (0 <z ≦ 1),
The mold contact layer is characterized by having a structure in which the Al mixed crystal ratio on the substrate side is small and the Al mixed crystal ratio on the active layer side is large.

In the first and second nitride semiconductor devices according to the present invention, Al _x is provided between the substrate and the n-type contact layer.
It is preferable to have a buffer layer made of a nitride semiconductor layer represented by Ga _1-x N (0 ≦ x <1, where x <y).

In the first and second nitride semiconductor devices according to the present invention, Al is provided between the active layer and the p-type contact layer.
It may have a first p-type layer made of a p-type nitride semiconductor containing a. In the first and second nitride semiconductor elements according to the present invention, a third p-type layer made of a p-type nitride semiconductor containing Al is provided between the active layer and the first p-type layer. Can also have

Further, the first and second nitride semiconductor devices according to the present invention are a p-type nitride semiconductor containing In between the first p-type layer and the third p-type layer, or It has a second p-type layer made of GaN and acting as an optical guide layer, and I is provided between the n-type contact layer and the active layer.
A laser oscillation element having an n-type cladding layer made of n-type nitride semiconductor containing n or n-type GaN may be used.

[0009]

1 is a schematic sectional view showing the structure of a laser device according to an embodiment of the present invention. This device is composed of GaN on a substrate 1 whose main surface is sapphire A surface.
Buffer layer 2 made of n-type Al _Y Ga _1-Y N (0 <Y <
1) n-type contact layer 3 made of In _x Ga _{1 -x} N (0
<X ≦ 1) well layer and In _{X ′} Ga _{1-X ′} N (0 ≦
An active layer 4 having a multi-quantum well structure in which a barrier layer made of X ′ <1, X ′ <X) is laminated, p-type Al _Z Ga _{1 -Z} N (0 <Z <
1) the first p-type layer 51 made of p-type GaN
It has a structure in which the mold contact layer 6 is sequentially laminated.

In the laser device of the present invention, sapphire having a plane orientation such as C plane, R plane, etc. in addition to A plane can be used for the substrate 1. In addition to sapphire, spinel 111 plane (MgA
1 ₂ O ₄ ), a known substrate made of a single crystal such as SiC, MgO, Si, ZnO or GaN is used.

The buffer layer 2 is provided to reduce the lattice mismatch between the substrate and the nitride semiconductor, and is usually GaN or A.
Although 1N, AlGaN, etc. are grown to a film thickness of 1000 angstroms or less, when a substrate having a lattice constant close to that of a nitride semiconductor or a substrate lattice-matched is used, it may not be grown depending on factors such as the growth method and growth conditions. Therefore, it can be omitted. However, when a substrate having a lattice constant different from that of the nitride semiconductor, such as sapphire and spinel, is used, the crystallinity of the nitride semiconductor layer grown next at a high temperature is dramatically improved by using the buffer layer.

In a further preferred embodiment, before the contact layer 3 containing Al is grown, the composition of this buffer layer is In _X Al _Y G having a smaller Al mixed crystal ratio than the contact layer.
a _{1- XY} N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), more preferably Al _Y Ga _1-Y N (0 ≦ Y <1),
The n-type contact layer 3 containing Al can be grown as a thick film with good crystallinity. The growth temperature of the buffer layer is lower than that of the n-type contact layer.
As described in JP-A-297023, it is desirable to grow at a temperature of 200 ° C. or higher and 900 ° C. or lower.

The n-type contact layer 3 is the most characteristic of the present invention, and is composed of an n-type nitride semiconductor containing Al and Ga, preferably n-type Al _Y Ga _{1 -Y} N (0 <Y <1). To do. Since this n-type contact layer is formed of a nitride semiconductor containing Al, the difference in refractive index between the n-type contact layer and the active layer can be increased, and the n-type contact layer acts as a clad layer as an optical confinement layer. That is, the n-type contact layer 3 acts not only as a layer for injecting a current but also as a layer for confining light in the active layer. In the conventional laser device, the contact layer is G
It was composed of aN. In the case of GaN, the ohmic characteristic with the n-electrode is very excellent, but since the refractive index is larger than that of the n-side clad layer (optical confinement layer, etc.), the light leaked from the n-side clad layer is GaN layer. It spread within the cell and inhibited the decrease in the threshold. In addition, since the contact layer made of GaN has a larger refractive index than the cladding layer made of AlGaN and the substrate, light leaking out from the active layer causes a mode in the contact layer, which causes a far field in the lateral direction of the main region. The pattern was mixed with the laser light, and it was as if it were multimode.

Therefore, since the contact layer is made of AlGaN, the light emission of the active layer can be made difficult to spread in the n-type contact layer, so that the threshold value is lowered. In addition, n-Ga
Since there is no N, all the light exuding from the active layer reaches the substrate side, and only the fundamental mode is guided in the vertical lateral direction only in the active layer. The film thickness of this n-type contact layer is 0.1.
It is desirable to adjust the thickness to 5 μm or more. 0.
When the thickness is 1 μm or less, it is difficult to act as a light confining layer, and when the electrodes are provided on the same surface side, it is disadvantageous because precise etching rate must be controlled.
On the other hand, if it is thicker than 5 μm, cracks are likely to occur in the crystal. Note that an n-type nitride semiconductor has a property of becoming n-type because of nitrogen vacancies formed inside the crystal even if it is non-doped (a state in which impurities are not doped).
By doping a donor impurity such as Ge or Sn during crystal growth, a nitride semiconductor having a high carrier concentration and exhibiting preferable n-type characteristics can be obtained. In addition, Al _Y Ga _{1 -Y} N is easy to obtain an n-type having a high carrier concentration.

Furthermore, it is desirable that the n-type contact layer 3 has a structure in which the Al mixed crystal ratio on the substrate side is small and the Al mixed crystal ratio on the active layer side is large, that is, a composition gradient structure. This is because with the above structure, an n-type contact layer with good crystallinity can be obtained, and the crystallinity of the nitride semiconductor laminated on the n-type contact layer with good crystallinity also improves, so that the crystallinity of the entire device is improved. Is improved, and the threshold value is lowered, and the reliability of the device is significantly improved. In addition, since the Al mixed crystal ratio on the active layer side is large, the difference in refractive index from the active layer also becomes large, and it effectively acts as a light confining layer.

The active layer 4 has a multiple quantum well structure in which at least the well layer contains a nitride semiconductor containing In. The multiple quantum well structure is a stack of a well layer and a barrier layer. In the present invention, if the well layer is made of a nitride semiconductor containing In, the barrier layer has a band gap larger than that of the well layer. If In is large, it is not necessary to include In. Preferably, a well layer made of In _X Ga _1-X N (0 <X ≦ 1),
And _{In X 'Ga 1-X'} N (0 ≦ X '<1, X'<X) and from the consisting barrier layer laminated structure. Since ternary mixed crystal InGaN has a better crystallinity than quaternary mixed crystal,
The luminous output is improved. The barrier layer has a bandgap energy larger than that of the well layer, and the well + barrier + well +
... + barrier layer + well layer (or vice versa) are stacked to form a multiple quantum well structure. Thus, when the active layer is an MQW in which InGaN is laminated, a high-power LD in the quantum level emission between about 365 nm and 660 nm is obtained.
Can be realized. In a particularly preferred embodiment, if both layers are InGaN, InGaN is GaN,
The crystal is softer than the AlGaN crystal. Therefore the first
Since the p-type layer of AlGaN can be thickened, laser oscillation can be realized.

The use of InGaN for the well and barrier layers has the following effects. The crystal growth temperature is different between GaN and InGaN. For example, in MOVPE method, InGaN
Is grown at 600 ° C. to 800 ° C., whereas GaN is grown.
Are grown at temperatures above 800 ° C. Therefore, InG
If a well layer made of aN is grown and then a barrier layer made of GaN is to be grown, it is necessary to raise the growth temperature. When the growth temperature is raised, the previously grown InG
Since the aN well layer is decomposed, it is difficult to obtain a well layer with good crystallinity. Further, the film thickness of the well layer is only several tens of angstroms, and it becomes difficult to fabricate the MQW when the thin film well layer is decomposed. In contrast, the barrier layer is made of InG
With aN, the well layer and the barrier layer can be grown at the same temperature. Therefore, since the well layer formed previously is not decomposed, the MQW having good crystallinity can be formed. This shows the most preferred embodiment of MQW.

The thickness of the active layer 4 is preferably 200 angstroms or more, and more preferably 300 angstroms or more in the case of a simple structure without the light guide layer as shown in FIG. This is because, in the case of the device of the present invention, when the active layer made of MQW is grown thick, the vicinity of the outermost layer of the active layer acts as a light guide layer. That is, the n-type contact layer 3 and the first p-type layer 5
1 acts as a light confining layer, and the vicinity of the outermost layer of the active layer acts as a light guide layer. The upper limit of the thickness of the active layer is not particularly limited, but it is usually desirable to adjust it to 0.5 μm or less.

Further, the film thickness of the well layer is preferably adjusted to 70 angstroms or less, more preferably 50 angstroms or less. Further, the thickness of the barrier layer is preferably adjusted to 150 angstroms or less, more preferably 100 angstroms or less. If the well layer is thicker than 70 angstroms or the barrier layer is thicker than 150 angstroms, the output of the laser device tends to be lowered.

Next, the first p-type layer 51 is made of a nitride semiconductor containing Al, and is preferably a binary mixed crystal or a ternary mixed crystal of Al _Z Ga _{1 -Z} N (0 <Z ≦ 1. ) Grow. In the case of LD, this first p-type layer 51 acts as a light confinement layer, and it is desirable to grow it to a film thickness of 0.1 μm to 1 μm. It is a p-type nitride semiconductor containing Al such as AlGaN. Therefore, it preferably acts as a light confining layer. Since this first p-type layer also uses the nitride semiconductor containing In as the active layer, it can be grown. That is, In
Since the active layer containing GaN acts as a buffer layer, it becomes easy to grow AlGaN as a thick film. Conversely, Al
It tends to be difficult to directly grow an Al-containing nitride semiconductor on a nitride-containing nitride semiconductor in a thick film that serves as an optical confinement layer. The p-type nitride semiconductor is Z
It can be obtained by doping acceptor impurities such as n, Mg, Be, Cd, and Ca during crystal growth. Among them, Mg exhibits the most preferable p-type characteristics. Further, after crystal growth, a nitride semiconductor doped with an acceptor impurity is annealed at 400 ° C. or higher in an inert gas atmosphere, whereby a p-type having a lower resistance can be obtained.

The uppermost p-type contact layer 6 is a p-type nitride semiconductor (In _X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X +.
Y ≦ 1), especially InGaN, Ga
N, and among them, p-type GaN doped with Mg,
A p-type layer having the highest carrier concentration can be obtained, good ohmic contact with the positive electrode can be obtained, and the threshold current can be reduced. The material of the positive electrode is Ni, Pd, I
A metal or alloy having a relatively high work function such as r, Rh, Pt, Ag, and Au is likely to obtain ohmic contact.

FIG. 2 is a schematic cross-sectional view showing the structure of an element according to the second aspect of the present invention, and the same symbols as those in FIG. 1 indicate the same members. This device is different from the device shown in FIG. 1 in that an In layer is formed between the active layer 4 and the first p-type layer 51.
The second p-type layer 52 is made of p-type nitride semiconductor or p-type GaN.

For the second p-type layer 52, preferably a binary mixed crystal or a ternary mixed crystal of In _Y Ga _{1 -Y} N (0 ≦ Y ≦ 1) is grown. This second p-type layer 52 acts as a light guide layer in the case of LD. In the first aspect, the active layer is 2
In the case where the thickness of the active layer is greater than or equal to 00 Å, the outermost layer of the active layer acts as a light guide layer. In the second aspect, by forming the second p-type layer 52, the film of the active layer is formed. Even if the thickness is less than 200 angstrom, this desirable laser oscillation can be obtained. The second
Since the p-type layer of InGaN, GaN, etc. is also formed, this layer acts as a buffer layer and is grown next.
The p-type layer 51 can be grown with good crystallinity without cracks. This second p-type layer 52 is typically 100 Å-
It is desirable to grow the film with a thickness of 1 μm.

FIG. 3 is a schematic sectional view showing the structure of an element according to the third aspect of the present invention. This device is different from the devices of FIGS. 1 and 2 in that an active layer 4 and a second p-type layer 5 are provided.
The third p-type layer 53 made of a nitride semiconductor containing Al and having a thickness smaller than that of the first p-type layer is provided between the first and second p-type layers. Although not particularly shown, the third p-type layer 5
3 may be provided between the active layer 4 and the first p-type layer 51. That is, in FIG. 3, the second p-type layer 52 may be omitted.

The third p-type layer 53 is composed of a p-type nitride semiconductor containing Al, and is preferably a ternary mixed crystal or a binary mixed crystal of Al _X Ga _{1 -X} N (0 <X≤1). It is desirable to grow. Further, it is desirable that this AlGaN is formed to be thinner than the first p-type cladding layer 51, and is preferably adjusted to 10 angstroms or more and 0.5 μm or less. By forming the third p-type layer 53 in contact with the active layer 4, the output of the device is remarkably improved. This is presumed to have a function of suppressing decomposition of InGaN in the active layer during the growth of the third p-type layer 53, but details thereof are unknown. As described above, the third p-type layer 53 made of the nitride semiconductor containing Al is preferably used.
By growing the film with a film thickness of 0 angstrom to 0.5 μm or less, it has a function as a cap layer for preventing the active layer made of InGaN from being decomposed, and the light emission output is improved. Further, since the third p-type layer 53 also has a small film thickness, it serves as an optical guide layer, and the film thickness of the active layer can be reduced.

FIG. 4 is a schematic sectional view showing the structure of an element according to the fourth aspect of the present invention. This device includes an n-type cladding layer 31 made of an n-type nitride semiconductor containing In between the n-type contact layer 3 and the active layer 4 or n-type GaN.
1 is different from the device shown in FIGS.

This n-type clad layer 31 is preferably a binary mixed crystal or a ternary mixed crystal of In _Y , like the second p-type layer.
Ga _1-Y N (0 ≦ Y ≦ 1) is grown. The action is the second p
When the n-th cladding layer 31 is the same as the mold layer and is an LD, it functions as a light guide layer, and thus the thickness of the active layer can be reduced. Further, as another effect, by growing the n-type cladding layer 31, an active layer of MQW having good crystallinity can be grown, so that the output of the device is improved.

The In _X Ga shown in the present invention is used.
_1-X N, Al _Y Ga _1-Y N and the like merely represent general formulas, and even when different layers are represented by the same general formula,
Those X and Y values never show the same value.

[0029]

EXAMPLES A method of manufacturing a laser device by MOVPE will be described below. The nitride semiconductor device of the present invention is MO
Not only the VPE method but also other known vapor phase epitaxy methods of nitride semiconductors such as MBE and HDVPE can be used for the growth.

[Embodiment 1] This embodiment is a method for obtaining the laser device shown in FIG. 1. Embodiment 1 will be described below with reference to FIG.
Will be explained in detail. Substrate 1 whose main surface is the A surface of sapphire is M
After installing in the reaction vessel of the OVPE device, T
Using MG (trimethylgallium) and ammonia, a buffer layer 2 made of GaN is grown to a thickness of 200 Å on the surface of the substrate 1 at a temperature of 500 ° C.

Then, the temperature is raised to 1050 ° C., TMG, TMA (trimethylaluminum), ammonia as a source gas, and SiH ₄ (silane) gas as a donor impurity are used, and an n-type contact made of Si-doped Al _0.3 Ga _0.7 N is used. Layer 3 is grown to a thickness of 4 μm. The n-type contact layer 3 also functions as a light confining layer.

Next, the temperature is set to 750 ° C. and the raw material gas is used.
TMG, TMI (trimethylindium), ammonia
To grow the active layer 4. First, the active layer 4 is
Dope In_0.2Ga_0.825 Å of well layer made of N
Grow at troth thickness. Next, change the TMI molar ratio.
Undoped In_0.01Ga
_0.95A barrier layer made of N with a thickness of 50 Å
Grow. This operation was repeated 13 times, and finally the well layer
Of a multiple quantum well structure with a total film thickness of 0.1 μm.
The active layer 4 is grown.

Next, the temperature is raised to 1050 ° C., TMG, TMA, ammonia is used as a source gas, and Cp 2 Mg (cyclopentadienyl magnesium) is used as an acceptor impurity.
Is used to grow a first p-type layer 51 of Mg-doped Al _0.3 Ga _0.7 N to a film thickness of 0.3 μm. This first
The p-type layer of 1 acts as a light confining layer.

Subsequently, TMG, ammonia, Cp2Mg
Using, the p-type contact layer 6 made of Mg-doped p-type GaN is grown to a film thickness of 0.5 μm.

The wafer in which the nitride semiconductors are laminated as described above is taken out of the reaction container, and selectively etched from the uppermost p-type contact layer 6 as shown in FIG.
After exposing the surface of the n-type contact layer 3 and forming striped electrodes on the exposed surfaces of the n-type contact layer 3 and the p-type contact layer 6, respectively, the wafer is cleaved from the R surface of the sapphire substrate. , A bar shape, and a laser resonance surface is formed in a direction orthogonal to the striped electrodes. After that, a reflecting mirror made of a dielectric multilayer film is formed on the resonance surface by a conventional method, and then the wafer is divided at positions parallel to the striped electrodes to form laser chips. When this laser chip was installed on a heat sink and pulse oscillation was attempted, it was found to be 410 at room temperature despite the simple structure.
The laser output was 10 mW and the threshold current was 10% lower than that of the conventional stripe electrode type laser device made of a nitride semiconductor.

[Second Embodiment] A second embodiment will be described with reference to FIG. In Example 1, the active layer 4 was formed by stacking 3 pairs of a well layer of 25 angstroms made of non-doped In _0.2 Ga _0.8 N and a barrier layer made of non-doped In _0.01 Ga _0.95 N with a total thickness of 25 angstroms.
Set to 0 angstrom.

Next, the temperature is set to 1050 ° C., and TMG, ammonia, and Cp 2 Mg are used as source gases, and a second p-type layer 52 made of Mg-doped p-type GaN is grown to a film thickness of 500 Å. This second p-type layer 52 acts as an optical guide layer on the p-layer side, and in addition to p-type GaN, p
Type InGaN can also be grown.

After that, a first p-type layer 51 and a p-type contact layer 6 were grown in the same manner as in Example 1 to make a laser device in the same manner.
Of the pulse oscillation, the output was 10 mW, and the threshold current was 20% lower than that of the conventional one.

[Third Embodiment] A third embodiment will be described with reference to FIG. After growing an active layer having a total film thickness of 250 Å as in Example 2, the temperature is set to 1050 ° C. and TMG, TMA, ammonia, and Cp 2 M are used as source gases.
Using g, the third p-type layer 53 of Mg-doped p-type Al _0.2 Ga _0.8 N is grown to a film thickness of 100 angstrom. The third p-type layer has a function of preventing the active layer made of InGaN from being decomposed and improving the output of the laser device.

After that, the second p-type layer 52, the first p-type layer 51, and the p-type contact layer 6 were grown in the same manner as in Examples 1 and 2, and then a laser device was similarly obtained. However, it also shows a pulse oscillation of 410 nm, the output is 10 mW,
The threshold current was 20% lower than that of the conventional one.

[Fourth Embodiment] A third embodiment will be described with reference to FIG. In Example 1, after the n-type contact layer 3 was grown, the temperature was kept at 1050 ° C. and the source gas was T 2.
Si doped n using MG, ammonia and silane gas
An n-type clad layer 31 made of n-type GaN is grown to a film thickness of 500 Å. This n-type cladding layer 31
Acts as a buffer layer when growing InGaN on the optical guide layer on the n-layer side and the active layer, and can also grow n-type InGaN in addition to n-type GaN.

Next, the active layer 4 is composed of non-doped In
25 angstrom well layer made of _0.2 Ga _0.8 N,
Two pairs of 50 angstrom barrier layers made of non-doped In _0.01 Ga _0.95 N are laminated to give a total film thickness of 175 angstroms.

After that, the third step is performed in the same manner as in the first, second and third embodiments.
P-type layer 53, second p-type layer 52, first p-type layer 51,
When a p-type cladding layer 6 was grown and similarly used as a laser device, a pulse oscillation of 410 nm was also exhibited at room temperature, the output was 15 mW, and the threshold current was reduced by 30% as compared with the conventional one.

[Embodiment 5] In the step of growing the p-type contact layer 3 of Embodiment 1, after the temperature is set to 1050 ° C., the flow rate of TMA is initially set to 0, and T is gradually increased.
Increase MA flow rate. By performing this operation,
The composition near the buffer layer is GaN, and the composition near the active layer is A
An n-type contact layer 3 of 1 _0.3 Ga _0.7 N doped with Si and having a composition gradient is grown to a film thickness of 3 μm.
In order to evaluate the crystallinity of this n-type contact layer,
When the half width of the double X-ray rocking curve was measured, the n-type contact layer of Example 1 was 5 to 6 minutes, while the one of Example 5 had a very good crystallinity of 3 to 4 minutes. Indicated. Further, when a nitride semiconductor was laminated on this n-type contact layer 3 in the same manner as in Example 1 to form a laser device, the threshold value was reduced by 20% as compared with the laser device of Example 1, The output has improved by 10%.

[0045]

According to the present invention, a laser device made of a material such as AlGaAs or InAlGaP requires a very complicated structure for laser oscillation. However, according to the present invention, the laser device has a very simple structure and a short structure. Since a laser device having a wavelength can be realized, it is very convenient in terms of production technology. In the present invention, only pulse oscillation is confirmed,
After that, the threshold current can be further reduced by improving the structure of the device to a buried hetero type or refractive index guided type device.

[Brief description of drawings]

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

FIG. 2 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention.

FIG. 3 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention.

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

FIG. 5 is a schematic cross-sectional view showing the structure of a conventional laser element.

[Explanation of symbols]

1 ... Substrate 2 ... Buffer layer 3 ... n-type contact layer 31 ... N-type clad layer 4 ... Active layer 51 ... First p-type layer 52 ... Second p-type layer 53 ... Third p-type layer 6 ... p-type contact layer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-41581 (JP, A) JP-A-6-21511 (JP, A) JP-A-6-164055 (JP, A) Jpn. J. Appl. Phys. Part 2, February 1996, Vol. 35 No. 2B, p. L217-L220 (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 33/00 JISST file (JOIS)

Claims (7)

(57) [Claims] 1. An n-type contact layer made of an n-type nitride semiconductor layer containing Al and Ga, an active layer having a multiple quantum well structure made of a nitride semiconductor containing In, and p
In a nitride semiconductor device sequentially provided with a p-type contact layer made of a type nitride semiconductor, the n-type contact layer on the substrate side is arranged so that a difference in refractive index between the n-type contact layer and the active layer becomes large on the active layer side. A nitride semiconductor device having a composition gradient structure in which the Al mixed crystal ratio is small and the Al mixed crystal ratio on the active layer side is large. 2. The n-type contact layer is Al _y Ga.
The nitride semiconductor device according to claim 1, comprising an n-type nitride semiconductor represented by _1-yN (0 <y <1). To 3. A substrate upper, n-type _Al y _{Ga 1-y} N
(0 <y <1), an n-type contact layer made of an n-type nitride semiconductor layer, an active layer having a multiple quantum well structure made of a well layer and a barrier layer, and a p-type made of a p-type nitride semiconductor in the nitride semiconductor device that includes a contact layer in this order, the well layer is made of _{in z Ga 1-z n (} 0 <z ≦ 1), the n-type contact layer, Al mixed crystal ratio of the substrate side is reduced A nitride semiconductor device having a structure in which the Al mixed crystal ratio on the active layer side is large. 4. Al _x Ga _1-x N (0 ≦ x <1, where x <y) is provided between the substrate and the n-type contact layer.
The nitride semiconductor device according to claim 1, further comprising a buffer layer made of the nitride semiconductor layer represented by. 5. The first p-type layer made of a p-type nitride semiconductor containing Al is provided between the active layer and the p-type contact layer. Nitride semiconductor device. 6. The nitride semiconductor device according to claim 5, further comprising a third p-type layer made of a p-type nitride semiconductor containing Al between the active layer and the first p-type layer. 7. A second p-type layer made of a p-type nitride semiconductor containing In or GaN between the first p-type layer and the third p-type layer and acting as an optical guide layer. And I between the n-type contact layer and the active layer.
7. A laser oscillation element having an n-type cladding layer made of n-type nitride semiconductor containing n or n-type GaN.
The nitride semiconductor device described.