JP2002111133A - Nitride semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor light emitting device which is so structured as not to increase light in intensity, controls its self-oscillation, keeps FFP low, and is easily handled. SOLUTION: A nitride semiconductor light emitting device is equipped with a P-side optical guide layer, an N-side optical guide layer, and an active layer which are all interposed between a P-side clad layer and an N-side clad layer. The P-side clad layer and the N-side clad layer are formed of a super lattice equipped with nitride semiconductor layers containing at least Al or an AlxGa1-xN/GaN super lattice. The average composition of Al content contained in the clad layer is set at 0.02 to 0.04. Furthermore, all the N-side clad layers are 1 to 2 μm in thickness. The P-side optical guide layer and the N-side optical guide layer are both represented by a formula GaN and as thick as 0.1 to 0.2 μm respectively. Al contained in the optical guide layer can be increased in compositional ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (I).
_{n X Al Y Ga 1-X} -Y N, 0 ≦ X, 0 ≦ Y, X + Y
≦ 1) The present invention relates to a laser device which controls self-sustained pulsation and optimizes both the vertical FFP and the self-sustained pulsation power.

[0002]

2. Description of the Related Art Semiconductor light emitting devices are expected to be applied in various fields, and have been actively researched and developed in recent years.
In particular, various research and development have been actively conducted on nitride semiconductor laser diodes (LDs), and practical LDs have been developed.
Has also been developed.

[0003] A nitride semiconductor laser device has a layer structure in which an active layer is sandwiched between optical confinement layers (cladding layers). The light spontaneously emitted from the active layer is totally reflected between the p-side and n-side cladding layers and amplified in the waveguide layer (light guide layer) having the active layer, and the amplified light is activated as stimulated emission light. Emitted from the layer end surface (resonance surface).

The inventor of the present invention has produced a nitride semiconductor laser device including an active layer on a nitride semiconductor substrate and has achieved, for the first time in the world, continuous oscillation of 10,000 hours or more at room temperature (ICNS'97). Proceedings, October 27-31,1997, P444-446, and Jpn.J.Appl.Phys.Vol.36 (1997) pp.L1568-1571, Part
2, No. 12A, 1 December 1997).

To realize a semiconductor laser having good characteristics,
It is necessary to efficiently inject current into the active layer and confine light within the active layer. For example, as a structure of an InGaN-based laser diode, a multiple quantum well structure InGa
A separate confinement laser using a superlattice structure of GaN as a light guide layer in an N light emitting layer and AlGaN / GaN as a cladding layer has been announced (Applied Physics Vol. 68, No. 7 (19).
99) 795). In this example, a periodic ripple is observed in the FFP in the vertical direction.
It is stated that some laser beams leak to the GaN contact layer due to insufficient light confinement by the GaN / GaN cladding layer. As a countermeasure, it is necessary to increase the Al composition ratio or the thickness of the cladding layer to increase the confinement of light. In general, a semiconductor laser obtains a population inversion efficiently by obtaining a carrier confinement effect by a double heterostructure, and confine emitted light in a guide layer to cause stimulated emission to obtain light confinement. To realize this, the refractive index of light of the active layer material is designed to be higher than the refractive index of the cladding layer material.

[0006] Further, the semiconductor laser needs to reduce the threshold current density. For this reason, it is common practice to enhance the confinement of light. For example, JP-A-11-23
JP-A No. 8945 describes a method for improving the light confinement effect of a cladding layer to make the laser light of a nitride semiconductor laser device a single mode and to obtain a laser device having a reduced oscillation threshold. This method uses n
The side cladding layer is composed of a superlattice having a nitride semiconductor layer containing Al, and the total thickness of the n-side cladding layer is 0.5 μm.
m or more, and when the average Al composition contained in the n-side cladding layer is expressed in percentage (%), the product of the thickness (μm) of the entire n-side cladding layer and the average Al composition (%) is 4%. .4 or more. Light is confined in the core by adjusting the thickness of the nitride semiconductor layer including the active layer between the n-side and p-side cladding layers to a range from 200 Å to 1.0 μm. Thus, the vertical and horizontal modes of the laser beam are changed to a single mode.

[0007]

However, a structure that enhances light confinement tends to cause self-sustained pulsation because the light density of the active layer increases. Self-sustained pulsation refers to a state in which the output waveform that should be constant starts to oscillate when the value of the current applied to the laser is increased. In order to prevent this, there is a method of lowering the light density. However, realizing laser oscillation requires confinement of light. As described above, there is a trade-off relationship between confinement of light and prevention of self-excited oscillation, and there has been a problem that self-excited oscillation occurs if light confinement is strong.

The present invention is to solve such a problem. An important object of the present invention is to control the generation of self-sustained pulsation by using a structure that intentionally weakens the light confinement and leaks light based on a concept opposite to that of the related art.
An object of the present invention is to provide a nitride semiconductor light emitting device capable of reducing P.

[0009]

In order to achieve the above object, a nitride semiconductor light emitting device according to the present invention has the following arrangement. In the nitride semiconductor light emitting device according to claim 1 of the present invention, a p and n side light guide layer and an active layer are formed between an n side and a p side cladding layer, and the p and n side cladding layers are An average composition of Al comprised of a superlattice having a nitride semiconductor layer containing at least Al and contained in the p- and n-side cladding layers is set to 0.02 to 0.04;
The side light guide layer is represented by the general formula GaN, and has a thickness of 0.1 μm to 0.2 μm.

As described above, according to the present invention, the confinement of light can be reduced by reducing the ratio of Al contained in the cladding layer, and self-pulsation can be prevented without increasing the threshold current density.

The nitride semiconductor light emitting device according to a second aspect of the present invention is further characterized in that the entire thickness of the n-side cladding layer is 1 μm to 2 μm. With this structure, it is possible to prevent ripples caused by light leakage.

[0012] that further nitride semiconductor light emitting device as described in claim 3 of the present invention also, superlattice constituting the p and n-side cladding layer is a super lattice of _{Al x Ga 1-x N /} GaN Features.

Further, in the nitride semiconductor light emitting device according to a fourth aspect of the present invention, a p and n side light guide layer and an active layer are formed between the n side and the p side cladding layer.
And the n-side light guide layer has a nitride semiconductor layer containing at least Al, and sets the average composition of Al contained in the p- and n-side light guide layers to a value smaller than the Al average composition of the cladding layer. , Each having a thickness of 0.1 μm
It is characterized by 0.2 μm.

As described above, according to the present invention, the confinement of light can be reduced by increasing the ratio of Al by mixing Al into the light guide layer, and self-pulsation can be prevented without increasing the threshold current density.

In the nitride semiconductor light emitting device of the present invention, self-sustained pulsation is suppressed by weakening light confinement based on the reverse idea of the prior art and reducing the density of light in a state where light seeps out. is there. To achieve this, the present invention
The structure is such that the refractive indices of the cladding layer and the light guide layer are close to each other. For example, the mixed crystal ratio of Al in the p and n cladding layers is reduced so that the threshold current density does not increase, or the mixed crystal ratio of Al in the p and n light guide layers is increased. With this structure, the current value at which self-oscillation occurs can be increased, and the occurrence of self-oscillation can be suppressed.

Further, the NFP width in the vertical direction increases,
As a result, there is also an advantage that the FFP width in the vertical direction can be reduced. The NFP is called a near field pattern or near-field image, and refers to an intensity distribution image of a laser beam appearing on a reflection surface in both vertical and horizontal modes. On the other hand, FFP is also called a far field pattern or a far-field image, and refers to an intensity distribution image of laser light emitted sufficiently far from a reflection surface. NFP represents the light intensity distribution in the oscillation region, and FFP represents the properties of the light wave including the wavefront and phase of the light. Since the FFP indicates the spread of the emitted light, if the FFP width is small, the FFP
The angle is converged and the spread is reduced, so that the user can easily handle the laser. As described above, the nitride semiconductor light emitting device of the present invention has an advantage that, in addition to suppressing self-sustained pulsation, a laser with a small FFP and easy handling can be obtained.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. However, the embodiments described below exemplify a nitride semiconductor light emitting device for embodying the technical idea of the present invention, and the present invention does not specify a nitride semiconductor light emitting device as follows.

Further, in this specification, in order to facilitate understanding of the claims, the numbers corresponding to the members described in the embodiments will be referred to as "claims" and " In the column of "means of the above". However, the members described in the claims are not limited to the members of the embodiments.

The general formula of the n-type layer described in this specification
Al_XGa_1-XAl of N and p-type layers _XGa_1-XSuch as N
The composition ratio X value merely shows a general formula, and the n-type layer
X and the X of the p-type layer do not indicate the same value. Ma
Similarly, the same applies to the Y value used in other general formulas.
The general formulas do not indicate the same value.

In the nitride semiconductor light emitting device of the present invention,
The cladding layer has a smaller refractive index than the well layer of the active layer.
An optical confinement layer containing a nitride semiconductor. Also with superlattice
Means that the thickness of the single layer is less than 100 Å and
Multi-layer structure with nitride semiconductor layers of different compositions
, Preferably 70 Å or less, furthermore
Preferably, nitride nitride having a thickness of 40 Å or less is used.
A conductor layer is laminated. As a specific configuration, for example, Al
_XGa_1-XN (0 <X <1) layer and its Al _XGa
_1-XStack N layer and other nitride semiconductor layer with different composition
Superlattice, for example, Al_XGa_1-XN / GaN,
Al_XGa_1-XN / Al_YGa_1-YN (0 <Y <
1, Y <X), Al_XGa_1-XN / In_ZGa_1-Z
A ternary mixed crystal such as N (0 <Z <1) and a ternary mixed crystal, or 3
A superlattice can be formed by combining a binary mixed crystal and a binary mixed crystal.
it can. Among them, most preferably, Al_XGa_1-XN
And a GaN superlattice.

If the n-side cladding layer has the above-described configuration in order to confine the light emitted from the active layer, the p-side cladding layer may have the same configuration as the n-side cladding layer. However, when the p-side cladding layer is configured as in claim 1, it is desirable that the thickness of the p-side cladding layer be smaller than that of the n-side cladding layer. The reason is that the resistance value of the AlGaN layer tends to increase when the Al average composition with respect to the group III element of the p-side cladding layer is increased or the film thickness is increased, and the threshold value increases when the resistance value of AlGaN increases. This is because there is a tendency.

In the case where the p-side cladding layer is a superlattice having a nitride semiconductor containing Al (this case includes a case where the p-side cladding layer simply acts as a cladding layer for confining carriers irrespective of light leakage). It is desirable that the entire thickness of the n-side cladding layer is larger than the thickness of the entire p-side cladding layer. Similarly to the n-side cladding layer, the nitride semiconductor layer constituting the p-side cladding layer is, for example, Al _x Ga _1-x
N (0 <X <1) layer and another nitride semiconductor layer having a composition different from that of the Al _X Ga _1-X N layer are formed as a superlattice, and Al _X Ga _1-X N / GaN, Al _X Ga _1-X N
_{/ Al Y Ga 1- Y N (} 0 <Y <1, Y <X), Al X
Ga and superlattice _{1-X N / In Z Ga} 1-Z N (0 <Z <1) 3 -element mixed crystal and ternary mixed crystal such as, or in combination with ternary mixed crystal and the binary mixed crystal, Most preferably, A
a superlattice consisting of l _X Ga _1-X N and GaN.

The average composition of Al in the superlattice of the present invention is
It is determined by the following calculation method. For example, 25
200 pairs (1.0 μm) of Angstroms Al _0.5 Ga _0.5 N and 25 Å GaN
In the case of a laminated superlattice, one pair is 50 angstroms, and the Al-containing crystal ratio of the Al-containing layer to the Group 3 element is 0.1 Å.
5, 0.5 · (25 μm / 50 μm) = 0.
25, and the average Al composition of the Group 3 elements in the entire superlattice is 25%. On the other hand, when the film thickness is different,
_0.5 Ga _0.5 N to 40 Å and GaN
Are laminated at 20 angstroms, a weighted average of the film thicknesses is obtained, and 0.5 (40/60) = 0.333, and the Al average composition is 33.3%. That is, the ratio of the Al mixed crystal ratio of the single nitride semiconductor layer containing Al to the Group III element multiplied by the ratio of the nitride semiconductor layer to the film thickness of one pair of superlattices is referred to as the Al of the superlattice in the present invention. Average composition. The same applies to the case where both of Al are included, for example, Al _0.1 Ga _0.9 N 20 Å, Al
_In the case of _0.2 Ga _0.8 N30 Å,
0.1 (20/50) +0.2 (30/50) = 0.1
6, that is, 16% is defined as an Al average composition. Although the above examples have been described for AlGaN / GaN and AlGaN / AlGaN, the same calculation method is applied to AlGaN / InGaN. Therefore, when growing the n-side cladding layer, a growth method can be designed based on the above calculation method. Further, the Al average composition of the n-side cladding layer can also be detected by using an analyzer such as SIMS (secondary ion mass spectrometer) and Auger.

[0024]

FIG. 1 is a schematic sectional view showing a main part of a laser device according to one embodiment of the present invention, and shows a section taken along a direction perpendicular to a ridge stripe. Hereinafter, embodiments will be described with reference to this drawing as necessary.

[Embodiment 1] Hereinafter, a laser device manufactured as Embodiment 1 will be described in order. (Underlayer) A heterogeneous substrate made of sapphire having a 2-inch φ and C-plane as a main surface is set in a MOVPE reaction vessel, the temperature is set to 500 ° C., and trimethylgallium (TMG)
By using ammonia (NH ₃ ), a buffer layer (not shown) made of GaN is grown to a thickness of 200 Å. After growing the buffer layer, the temperature is increased to 1050 ° C.
A base layer made of GaN is also grown to a thickness of 4 μm. This underlayer functions as an underlayer for forming a protective film partially on the surface and then performing selective growth of the nitride semiconductor substrate. The underlayer is made of A having an Al mixed crystal ratio X value of 0.5 or less.
_{l X Ga 1- X N (0} ≦ X ≦ 0.5) is to be desirable grow. If it exceeds 0.5, the crystal itself tends to be cracked rather than a crystal defect, and the crystal growth itself tends to be difficult. Further, it is desirable that the film thickness be grown to be larger than the buffer layer and adjusted to a film thickness of 10 μm or less. The substrate is Sapphire and S
A substrate made of a material different from a nitride semiconductor, such as iC, ZnO, spinel, or GaAs, which is known for growing a nitride semiconductor can be used.

(Protective film) After the growth of the underlayer, the wafer is taken out of the reaction vessel, a stripe-shaped photomask is formed on the surface of the underlayer, and a stripe width of 10 μm and a stripe interval (window) of 2 μm are formed by a CVD apparatus. SiO ₂
A protective film having a thickness of 1 μm is formed. The shape of the protective film may be any shape such as a stripe shape, a dot shape, a grid shape, and the like. However, when the area of the protective film is larger than that of the window portion, the second nitride semiconductor layer having less crystal defects can be used. Easy to grow. Examples of the material of the protective film include oxides and nitrides such as silicon oxide (SiO _x ), silicon nitride (Si _x N _y ), titanium oxide (TiO _x ), and zirconium oxide (ZrO _x ), and multilayer films thereof. Alternatively, a metal or the like having a melting point of 1200 ° C. or more can be used. These protective film materials have a nitride semiconductor growth temperature of 600 ° C. to 11 ° C.
It has the property of withstanding a temperature of 00 ° C. and preventing the nitride semiconductor from growing or hardly growing on its surface.

(Nitride Semiconductor Substrate) After the formation of the protective film, the wafer is set again in the MOVPE reaction vessel, the temperature is set to 1050 ° C., and a nitride semiconductor substrate made of undoped GaN using TMG and ammonia is removed to a thickness of 20 μm. It grows with the film thickness. On the surface of the nitride semiconductor substrate after growth, almost no crystal defects are exposed at the central portion of the stripe of the protective film and the central portion of the stripe of the window. It tends to occur at the top of the window. Therefore, by preventing the ridge stripe from being related to the crystal defect at the time of forming the ridge of the laser element, the crystal defect does not dislocate in the active layer, and the reliability of the element is improved. The nitride semiconductor substrate can be grown by using the halide vapor phase epitaxy (HVPE), but can also be grown by the MOVPE method. Most preferably, the nitride semiconductor substrate is made of GaN that does not contain In or Al. The growth gas is not only TMG but also triethylgallium (TE).
Most preferably, an organic gallium compound such as G) is used, and ammonia or hydrazine is used as a nitrogen source.
Further, the GaN substrate may be doped with an n-type impurity such as Si or Ge to adjust the carrier concentration to an appropriate range.
In particular, when removing a heterogeneous substrate, an underlayer, and a protective film, the nitride semiconductor substrate serves as a contact layer. Therefore, it is desirable to dope the nitride semiconductor substrate with an n-type impurity.

(N-side contact layer 11) Next, ammonia and TMG, and silane gas
The n-side contact layer 11 made of GaN doped with 3 × 10 ¹⁸ / cm ³ of Si is formed on the nitride semiconductor layer of
It grows with the film thickness of. Further, in the case where an electrode is provided on the nitride semiconductor substrate after removing the heterogeneous substrate to the protective film, it may be omitted. The n-side contact layer 11 is a buffer layer grown at a high temperature, for example, sapphire, SiC,
On a substrate made of a material different from a nitride semiconductor such as spinel, GaN, A
It is distinguished from a buffer layer in which 1N or the like is directly grown to a thickness of 0.5 μm or less.

(Crack prevention layer 12) Next, TMG, T
Using MI (trimethylindium) and ammonia at a temperature of 800 ° C., a crack prevention layer 12 of In _0.06 Ga _0.94 N is grown to a thickness of 0.15 μm. This crack prevention layer can be omitted.

(N-side cladding layer 13 = superlattice layer) Subsequently, n is doped with Si at 1 × 10 ¹⁹ / cm ³ at 1050 ° C. using TMA, TMG, ammonia and silane gas.
The first layer made of Al _0.08 Ga _0.92 N is 25
The second layer made of undoped GaN is grown to a thickness of 25 Å by stopping growth of silane gas and TMA. Then, a superlattice layer is composed of a first layer + a second layer + a first layer + a second layer +..., And an n-side cladding layer 13 composed of a superlattice having a total film thickness of 1.2 μm is grown. The n-side cladding layer made of this superlattice has an average Al composition of 3 group elements.
0%. Note that when a superlattice in which nitride semiconductors having different band gap energies are stacked on the n-side cladding layer is produced, one of the layers is heavily doped with impurities, and so-called modulation doping tends to improve crystallinity. However, both may be doped in the same manner.

(N-side light guide layer 14) Subsequently, the silane gas is stopped, and the n-side light guide layer 14 made of undoped GaN is grown at 1050 ° C. to a thickness of 0.1 μm. This n-side light guide layer acts as a light guide layer of the active layer,
It is desirable to grow GaN or InGaN, usually 100 Å to 5 μm, more preferably 2 Å.
It is desirable to grow with a film thickness of 00 Å to 1 μm.

(Active Layer 15) Next, the active layer 14 is grown using TMG, TMI and ammonia. The temperature of the active layer is maintained at 800 ° C., and the undoped In _0.2 Ga
_A well layer of _0.8 N is grown to a thickness of 40 Å. Next, a barrier layer made of undoped In _0.01 Ga _0.95 N is grown to a thickness of 100 Å at the same temperature only by changing the molar ratio of TMI. An active layer having a multiple quantum well structure (MQW) having a total thickness of 440 angstroms is grown by stacking a well layer and a barrier layer in order, ending with the barrier layer at the end. The active layer may be undoped as in this embodiment, or may be doped with an n-type impurity and / or a p-type impurity. The impurity may be doped into both the well layer and the barrier layer, or may be doped into either one.

(P-side cap layer 16)
Raise to 50 ° C, TMG, TMA, ammonia, Cp2M
g (cyclopentadienyl magnesium), p-side
Higher band gap energy than light guide layer 17
And Mg is 1 × 10²⁰/ Cm³Doped p-type Al
_0.3Ga_0.7The p-side cap layer 16 made of N
It is grown to a thickness of 0 Å. This p-type carrier
The top layer 16 is formed to a thickness of 0.1 μm or less.
The output of the element tends to be improved. Especially the lower limit of the film thickness
Although not limited, formed with a film thickness of 10 Å or more
It is desirable to do.

(P-side light guide layer 17) Subsequently, Cp2M
g, TMA is stopped, and a p-side light guide layer 17 made of undoped GaN having a band gap energy smaller than that of the p-side cap layer 16 at 1050 ° C. is grown to a thickness of 0.1 μm. This layer acts as a light guide layer of the active layer and, like the n-type light guide layer 14, GaN, InGaN
It is desirable to grow with.

(P-side cladding layer 18 = superlattice)
Mg doped at 1 × 10 ²⁰ / cm ³ at 1050 ° C.
A third layer made of type _{Al 0.0} 8 _{Ga 0.92} N 25
A fourth layer of undoped GaN is grown to a thickness of 25 Å, and a p-side cladding layer 18 of a superlattice layer having a total thickness of 0.6 μm is grown. Grow. This p-side cladding layer also has an Al average composition of 4.0%. Note that when the p-side cladding layer is also formed of a superlattice in which at least one of the layers includes a nitride semiconductor layer containing Al and has different band gap energies, the impurity is heavily doped in one of the layers. Then, when so-called modulation doping is performed, the crystallinity tends to be improved, but both may be doped in the same manner.

Here, the thickness of the core portion (waveguide portion) sandwiched between the cladding layers will be described. The core part is n
Side light guide layer 14, active layer 15, p-side cap layer 16,
And a region in which the p-side light guide layer 17 is combined, that is, a nitride semiconductor layer including an active layer between the n-side cladding layer and the p-side cladding layer, and is a region where light emission of the active layer is guided. . In the case of the nitride semiconductor light emitting device, the reason why the FFP does not become a single beam is that, as described above, light emitted from the cladding layer is guided in the n-side contact layer and becomes a multimode. is there. In addition, there is a case where a multi-mode is caused by resonance in the core. In the present invention, first, the thickness of the n-side cladding layer is increased to increase the Al average composition, thereby providing a refractive index difference and confining light in the core by the cladding layer. However, when the multi-mode is formed in the core, the FFP is disturbed. for that reason,
In relation to the n-side cladding layer of the present invention, it is desirable to also adjust the thickness of the core portion in order to prevent multimode in the core. The preferred thickness for preventing multimode from occurring in the core portion is 200 Å or more and 1.0 μm or less, more preferably 500 Å to 0.8 μm,
Most preferably, it is desirable to adjust the thickness to a range of 0.1 μm to 0.5 μm. If the thickness is smaller than 200 angstroms, light leaks from the core and the threshold value tends to increase. On the other hand, if the thickness is more than 1.0 μm, multi-mode tends to be easily caused.

(P-side contact layer 19) Finally, 105
At 0 ° C., 2 × 10
^A p-side contact layer 18 of ²⁰ / cm ³ doped p-type GaN is grown to a thickness of 150 Å. The p-side contact layer 19 is made of a p-type In _X Al _Y Ga
_{1 -XYN} (0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and preferably Mg-doped GaN can provide the most preferable ohmic contact with the p-electrode.

The wafer on which the nitride semiconductor has been grown as described above is placed in a reaction vessel in a nitrogen atmosphere at 700.degree.
Annealing is performed at ℃ to further reduce the resistance of the layer doped with p-type impurities.

After annealing, the wafer is taken out of the reaction vessel, and the uppermost p-side contact layer 18 and the p-side cladding layer 17 are etched by the RIE apparatus to obtain a structure shown in FIG.
As shown in the figure, the ridge shape has a stripe width of 4 μm. When forming a ridge stripe, the ridge stripe is formed at a position where no crystal defect appears on the surface of the nitride semiconductor substrate. In the case of FIG. 1, a large number of crystal defects tend to appear in the center of the stripe-shaped window at the initial stage of growth. When the stripe is formed at a position where there is almost no crystal defect, the crystal defect tends not to extend to the active layer, so that the element can have a long life,
Reliability is improved.

Next, a mask is formed on the ridge surface, and RIE is performed.
To expose the surface of the n-side contact layer 11. The exposed n-side contact layer 11 has n
It also functions as a contact layer for forming the electrode 23.

Next, a p-electrode made of Ni and Au is formed in a stripe shape on the outermost surface of the ridge of the p-side contact layer 19.
On the other hand, the n-electrode made of Ti and Al was exposed earlier.
After forming a stripe on the surface of the side contact layer 11, as shown in FIG. 1, an insulating film made of SiO ₂ is formed on the surface of the nitride semiconductor layer exposed between the p-electrode and the n-electrode. P electrically connected to a p-electrode via an insulating film
A pad electrode is formed.

As described above, the sapphire substrate of the wafer on which the n-electrode and the p-electrode have been formed is polished to 70 μm, and then cleaved in a bar shape from the substrate side in a direction perpendicular to the stripe-shaped electrodes. A resonator is formed on the cleavage plane. A dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on the resonator surface, and finally, the bar is cut in a direction parallel to the p-electrode to obtain a laser device.

This laser element is placed on a heat sink,
When each electrode was wire-bonded and laser oscillation was attempted at room temperature, continuous oscillation was exhibited at room temperature, and a single laser beam had a single FFP and an elliptical shape with good shape. .

Example 2 In Example 1, when growing the n-side cladding layer 13, Si-doped n-type Al
_0.06 Ga _0.94 N25 Å and undoped GaN 25 Å are stacked to form a total film thickness of 1.
A laser device was fabricated in the same manner except that an n-side cladding layer 13 consisting of a 0 μm superlattice was grown. The n-side cladding layer has an average Al composition of 3%. This laser element also had almost the same characteristics as those of the first embodiment.

[Embodiment 3] In the first embodiment, when growing the n-side cladding layer 18, the Si-doped n-type Al
_A laser device was fabricated in the same manner except that a _0.07 Ga _0.93 N layer and a 25 Å undoped GaN layer were grown to a total thickness of 1.4 μm. The n-side cladding layer has an average Al composition of 3.5%.
It is. This laser device exhibited characteristics in which a reduction in the threshold value and an improvement in the lifetime were confirmed.

Further, in the present invention, the optical confinement effect is weakened by reducing the difference in the refractive index between the light guide layer and the cladding layer. Therefore, in addition to the method of lowering the Al mixed crystal ratio in the cladding layer, it can be realized by, for example, a method of mixing Al in the guide layer to increase the Al mixed crystal ratio.
This method can be performed using a procedure substantially similar to that of the above-described embodiment. Although the semiconductor laser device has been described in the above embodiments, the present invention is not limited to a semiconductor laser, but can be applied to other nitride semiconductor light emitting devices such as an LED device and a super luminescent diode.

[0047]

As described above, the present invention has succeeded in reducing the light density and suppressing self-sustained pulsation by adopting a structure that weakens the light confinement based on a concept reverse to that of the prior art. That is, in the prior art, the purpose was to confine light. However, in this method, the density of light was increased and self-excited oscillation was likely to occur. On the contrary, in the present invention, by controlling the Al mixed crystal ratio to intentionally weaken the confinement of light and adopt a structure in which light leaks, the generation of self-pulsation can be controlled, and the FF in the vertical direction can be controlled.
The feature of reducing P was realized.

The nitride semiconductor light emitting device of the present invention has a structure in which the difference in the refractive index between the cladding layer and the optical guide layer is reduced to suppress the light confinement effect. Optical confinement effect, the cladding layer, varies by each of the difference in refractive index n _c and n _g of the optical guide layer. For example, the confinement effect increases as the difference in n increases. Conversely, the smaller the difference in n, the smaller the confinement effect and the lower the light density. However, if the difference is too small, the laser will not oscillate. According to the present invention, by setting the Al crystal mixture ratio to an optimum value, the laser oscillation is maintained and the Al crystal mixture ratio is reduced to such an extent that the threshold current density does not increase, thereby suppressing self-pulsation and reducing FFP. And a highly reliable semiconductor laser.

In the present invention, the thickness of the n-side cladding layer is set to 1 μm or less in order to prevent the ripple due to the influence of the leakage light.
It is 2 μm. When the p-electrode and the n-electrode are formed on the same surface side, light emitted from the active layer leaks out of the n-type cladding layer, and the leaked light is guided through the n-type contact layer having a large refractive index to form n. The phenomenon of emission from the end face of the mold contact layer occurs. Although the detailed principle is not clear, if this weak light overlaps with the main laser light emitted from the resonance surface,
It is considered that the ripple is applied to the main laser beam and the FFP becomes a small multi-mode. In order for the laser beam to function well, it is desirable to suppress the ripple from riding on the FFP.

The use of the structure of the present invention has the effect of reducing the aspect ratio, and it is possible to increase the output power causing self-pulsation. For this reason, it is possible to produce a high-output stable LD, and it can be used as a laser used for DVD writing.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... n-side contact layer 12 ... crack prevention layer 13 ... n-side cladding layer 14 ... n-side light guide layer 15 ... active layer 16 ... p-side cap layer 17 ... p-side light guide layer 18 ... p-side cladding layer 19 ... p-side contact layer

Claims (4)

[Claims] 1. A p-type and n-type layer between an n-side and a p-side cladding layer.
A side light guide layer and an active layer are formed, and the p and n side cladding layers are made of a superlattice having at least a nitride semiconductor layer containing Al, and the average composition of Al contained in the p and n side cladding layers To 0.02 to 0.04, p
The nitride semiconductor light emitting device is characterized in that the n-side light guide layer is represented by the general formula GaN and the film thickness is 0.1 μm to 0.2 μm. 2. The total thickness of the n-side cladding layer is from 1 μm to
2. The nitride semiconductor light emitting device according to claim 1, wherein the thickness is 2 μm. 3. A nitride semiconductor light emitting device according to claim 2, wherein the superlattice constituting the p and n-side cladding layer is a super lattice of _{Al x Ga 1- x N / GaN} . 4. A p and n layer between an n-side and a p-side cladding layer.
A side light guide layer and an active layer are formed, and the p and n side light guide layers have a nitride semiconductor layer containing at least Al, and are formed of Al contained in the p and n side light guide layers. A nitride semiconductor light-emitting device having an average composition smaller than that of a cladding layer and a film thickness of 0.1 μm to 0.2 μm, respectively.