JPH09260772A - Nitride semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an element continuously oscillating at a room temperature with a reduced threshold value of current by providing an active layer formed on the top of a substrate and a clad layer having a ridge-shaped stripe formed on an active layer. SOLUTION: An n-type contact layer 2, n-type light containment layer 3, n-type light guide layer 4, active layer 5, p-type guide layer 6, p-type light containment layer 7, active layer 5, p-type guide layer 6, p-type light containment layer 7 and p-type contact layer 8 are sequentially laminated on substrate 1. An insulation thin-film 10 is formed on the surface of a light guide layer 6. This insulation thin-film 10 can prevent electrodes from causing a short- circuit, when bonding a negative electrode 20 and a pad electrode 31 containing a positive electrode 30 formed on the same surface and also performs the function of concentrating the light emission of an active layer 5 below a ridge. By doing this, light in lateral direction of the active layer 5 is controlled, so that the threshold current in laser oscillation decreases. Therefore, continuous oscillation becomes possible.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a nitride semiconductor (In _X A
_{l Y Ga 1-XY N,} 0 ≦ X, 0 ≦ Y, a laser element made of X + Y ≦ 1).

[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, and the present applicant has recently used this material to generate a laser oscillation of 410 nm at room temperature under pulse current. Announced (for example, Jpn.J.
Appl. Phys. Vol 35 (1996) pp. L74-76). The disclosed laser device is a so-called electrode stripe type laser device, in which the stripe width of the nitride semiconductor layer including the active layer is set to several tens of μm, and laser oscillation is performed. However, the threshold current of the laser element is 1 to 2 A, and it is necessary to further reduce the threshold current for continuous oscillation.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. An object of the present invention is to reduce the threshold current of a laser device made of a nitride semiconductor to achieve room temperature. Is to realize an element capable of continuous oscillation.

[0004]

According to the present invention, there is provided a laser device comprising:
It is characterized by having an active layer formed on the substrate and an n-type or p-type cladding layer having a ridge-shaped stripe formed on the active layer. The cladding layer formed on the active layer is preferably p-type.

Further, an insulating thin film made of a material having a smaller refractive index than that of the clad layer is formed on the surface of the clad layer.

Further, a metal thin film which is in Schottky barrier contact with the cladding layer is formed on the surface of the cladding layer.

Further, the angle of the side surface of the ridge shape with respect to the substrate surface is 90 ° or more. 9
If it is 0 ° or more, it is easy to form an insulating thin film or a metal thin film with a uniform film thickness on the side surface of the ridge.

Further, the active layer has a multiple quantum well structure made of a nitride semiconductor containing at least indium. Preferably In _X Ga _1-X N (0 <
It is a multiple quantum well structure having a well layer of X <1).

[0009]

1 is a schematic sectional view showing the structure of a laser device according to an embodiment of the present invention, and FIG. 2 is a perspective view showing the shape of the laser device shown in FIG. FIG. 1 is FIG.
FIG. 11 is a cross-sectional view of the device shown in FIG. 1 when cut in a direction perpendicular to the resonance direction of laser light. As an element structure, an n-type contact layer 2, an n-type light confinement layer 3, an n-type light guide layer 4, an active layer 5, a p-type light guide layer 6, a p-type light confinement layer 7, and a p-type light confinement layer 7 are provided on a substrate 1. It has a basic structure in which the mold contact layers 8 are sequentially stacked. Reference numeral 20 is an ohmic negative electrode connected to the n-type contact layer 2, 30 is an ohmic positive electrode connected to the p-type contact layer 8, and a pad electrode 31 for bonding is provided on the positive electrode 30. It is provided. It should be noted that the structure of the laser device shown in the present specification is merely a basic structure, and even if any of the layers shown in these are omitted or a layer made of another nitride semiconductor is inserted, Modifications can be freely made without departing from the spirit of the claims.

The substrate 1 is made of sapphire (Al ₂ O ₃ , A surface, C
Surface, R surface), spinel (MgAl ₂ O ₄ , 111 surface), etc. are often used, but in addition, SiC, Mg
A conventionally known substrate made of a single crystal of O, Si, ZnO, GaN or the like is used.

The n-type contact layer 2 is made of In _X Al _Y Ga.
_1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1) can be used. Particularly, by using GaN, InGaN, and GaN doped with Si, an n-type layer having a high carrier concentration can be obtained. Since the obtained ohmic contact with the negative electrode 20 is obtained, the threshold current of the laser device can be reduced. The material of the negative electrode 20 is Al, T
A metal or an alloy such as i, W, Cu, Zn, Sn, or In can obtain a preferable ohmic property. Not limited to GaN, nitride semiconductors are non-doped (state in which impurities are not doped)
However, it has the property of becoming n-type due to nitrogen vacancies formed inside the crystal, but by doping a donor impurity such as Si, Ge, or Sn during crystal growth, the carrier concentration is high, and nitriding that exhibits favorable n-type characteristics A physical semiconductor can be obtained.

The n-type optical confinement layer 3 is composed of an n-type nitride semiconductor containing Al, and is preferably a binary mixed crystal or a ternary mixed crystal of Al _Y Ga _{1 -Y} N (0 <Y ≦ 1). By doing so, it is possible to obtain a crystal having good crystallinity, and it is effective in confining the longitudinal mode of laser light by increasing the difference in refractive index from the active layer. This layer is usually preferably grown to a thickness of 0.1 μm to 1 μm. If it is thinner than 0.1 μm, it is difficult to act as a light confining layer, and if it is thicker than 1 μm, cracks are likely to occur in the crystal, and it tends to be difficult to manufacture an element.

The n-type optical guide layer 4 is composed of an n-type nitride semiconductor containing In or n-type GaN, and is preferably a ternary mixed crystal or a binary mixed crystal of In _X Ga _{1 -X} N (0≤ X <
1). This layer is typically 100 Angstroms to 1
It is desirable to grow to a film thickness of μm, and especially InGa
By using N or GaN, the next active layer 5 can be easily made to have a quantum well structure.

Next, above the active layer, which is a feature of the present invention,
The configuration will be described. The active layer 5 is, as described above,
Multiple quantum wells preferably made of a nitride semiconductor containing In
Further as a door structure (MQW: Multi-quantum-well)
Preferably ternary mixed crystal In_XGa_1-XN (0 <X <1)
It is desirable to use MQW as a well layer. Ternary mixed crystal
InGaN has better crystallinity than quaternary mixed crystal
As a result, the light emission output is improved. Especially good
More preferably, the active layer is In_XGa_1-XWell layer made of N and well
Ternary mixed crystal nitride half with a larger bandgap than the To layer
A laser is assumed to be MQW in which a barrier layer made of a conductor is laminated.
Easy to oscillate. The barrier layer is ternary mixed crystal In _{X '}Ga_{1-X '}N
(0 ≦ X ′ <1, X ′ <X) is preferable, and well + barrier + well
+ ... + Barrier + Well layer, or vice versa
To form an MQW. InGaN is deposited on the active layer
If the layered MQW is used, the emission between quantum levels is about 365 nm.
It is possible to realize a high-power LD in the range of ~ 660 nm.
You. Furthermore, InGaN (however, with In composition
(The ratio is smaller than that of the well layer)
And the barrier layer is more crystalline than a crystal such as GaN or AlGaN.
Is p-type clad that grows on the active layer
The AlGaN thickness of the layer can be increased. Therefore the vertical
Optical confinement can be realized and laser oscillation can be performed. Further
In addition, the advantage of using InGaN as the barrier layer is as follows. That is, I
The crystal growth temperature differs between nGaN and GaN.
For example, in the MOVPE method, InGaN is 600 ° C to 800 ° C.
Whereas GaN grows above 800 ° C
Grow with. Therefore, a well layer made of InGaN is formed.
After growing, try to grow a barrier layer of GaN
If so, it is necessary to raise the growth temperature. Above growth temperature
Then, the InGaN well layer that was grown earlier decomposed.
Therefore, it is difficult to obtain a well layer with good crystallinity. Further
The thickness of the well layer is only several tens of angstroms,
If the well layer of
You. On the other hand, in a preferred embodiment of the present invention, the barrier layer also
Since it is InGaN, the well layer and the barrier layer are grown at the same temperature.
Can be long. Therefore, the well layer formed earlier should be decomposed.
It is possible to form MQW with good crystallinity because there is no
You. This shows the most preferred embodiment of MQW.
In addition, the well layer is InGaN, the barrier layer is GaN, Al
As in GaN, the bandgap of the barrier layer is better than that of the well layer.
Any composition may be used as long as the energy is increased.

The total thickness of the active layer 5 having a multiple quantum well structure is 1
It is preferable to adjust it to 00 angstroms or more.
If the thickness is less than 100 Å, the output is not sufficiently increased and laser oscillation tends to be difficult. If the thickness of the active layer is too thick, the output tends to decrease, and it is desirable to adjust the thickness to 1 μm or less, more preferably 0.5 μm or less. If it is thicker than 1 μm, the crystallinity of the active layer is deteriorated, or the laser beam spreads in the active layer, and the threshold current tends to increase.

Next, the p-type optical guide layer 6 is composed of a nitride semiconductor containing In or GaN, and is preferably a binary mixed crystal or a ternary mixed crystal of In _Y Ga _{1 -Y} N (0 <Y ≦ 1. ) Grow. It is desirable that the light guide layer 6 is normally grown to a film thickness of 100 angstrom to 1 μm. In particular, by using InGaN or GaN, the following p-type optical confinement layer 7 can be grown with good crystallinity. The p-type nitride semiconductor is obtained by doping acceptor impurities such as Zn, Mg, Be, Cd, and Ca during crystal growth, and Mg exhibits the most preferable p-type characteristics. When the p-type light guide layer 6 is formed in a ridge shape as shown in FIG. 1, the p-type light guide layer is made of In as described above.
Most preferably, _Y Ga _1-Y N (0 <Y ≦ 1).

The p-type optical confinement layer 7 is made of a p-type nitride semiconductor containing Al, and is preferably a binary mixed crystal or a ternary mixed crystal of Al _Y Ga _{1 -Y} N (0 <Y ≦ 1). With such a value, a crystal having good crystallinity can be obtained. This p-type optical confinement layer 7
Is preferably grown to a film thickness of 0.1 μm to 1 μm, like the n-type optical confinement layer 3. By using a p-type nitride semiconductor containing Al such as AlGaN, a difference in refractive index from the active layer can be obtained. By increasing the size, it effectively acts as an optical confinement layer for the laser light in the longitudinal mode. Further, as shown in FIG. 3, when the p-type optical confinement layer 7 is formed in a ridge shape,
As described above, the p-type optical confinement layer is formed of p-type Al _Y Ga ₁ -YN.
Most preferably, (0 <Y ≦ 1).

The p-type contact layer 8 is made of p-type In _X Al _Y Ga.
_1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1) can be used. In particular, InGaN and GaN, of which p-type GaN doped with Mg, has the highest carrier concentration p.
The mold layer is obtained, good ohmic contact with the positive electrode 30 is obtained, and the threshold current can be reduced. Positive electrode 3
The material of 0 is Ni, Pd, Ir, Rh, Pt, A
A metal or alloy having a relatively high work function such as g or Au is likely to obtain an ohmic property, and particularly a material containing at least Ni and Au, or a material containing at least Pd and Au is likely to obtain a preferable ohmic property. In the present invention, the clad layer having a ridge-shaped stripe refers to the p-type optical guide layer 6, the p-type optical confinement layer 7, the p-type contact layer 8 and the like, specifically shown in FIG. It means that at least one of these layers has a striped ridge shape. Further, if the p-type layer and the n-type layer are laminated in reverse, the n-type optical guide layer 4, the n-type optical confinement layer 3, the n-type contact layer 2, etc. are naturally formed on the active layer. It corresponds to a clad layer, and at least one of these layers has a striped ridge shape.
Even when the n-type layer is formed on the active layer,
The preferable composition of the nitride semiconductor for the ridge is p
The composition is the same as that of the mold layer, and for example, in order to form a ridge from the n-type optical guide layer 4, In _Y Ga _{1 -Y} N (0 <Y ≦ 1) is preferable.

The basic structure of the laser device of the present invention has been described above. The n-type Al _X Ga shown in the present specification has been described above.
The composition ratio X value of _1-X N, p-type Al _X Ga _1-X N, etc. is merely a general formula, and X of the n-type layer and X of the p-type layer show the same value. Not a thing. Similarly, the same general formula does not indicate the same Y value used in other general formulas.

As a next structure, the laser device of the present invention is characterized in that an insulating thin film made of a material having a refractive index smaller than that of the cladding layer is formed on the surface of the ridge-shaped cladding layer. In FIG. 1, an insulating thin film 10 is formed on the surface of the light guide layer 6. This insulating thin film 10
Is to prevent a short circuit between the electrodes when bonding the pad electrode 31 including the positive electrode 30 formed on the same surface side and the negative electrode 20 to another lead member such as a heat sink and a submount, respectively. It also has the effect of concentrating the light emission of the active layer 5 under the ridge. As a result, the light in the lateral direction of the active layer is controlled, so that the threshold current is reduced. Further, a metal thin film which is in Schottky barrier contact with the cladding layer may be formed on the surface of the ridge-shaped cladding layer. The metal thin film has an ohmic electrode on the surface in contact with the contact layer, and a Schottky barrier is formed on the surface in contact with the cladding layer. Therefore, when forming a metal thin film, it is very preferable to form the same material as the ohmic electrode of the contact layer in one step. Further, the metal thin film that makes a Schottky barrier contact with the cladding layer and the electrode that makes an ohmic contact with the contact layer may be formed separately. In this figure, the insulating thin film 10 continues from the surface of the p-type optical guide layer 6 and reaches the n-type contact layer 2. However, when forming a metal thin film, the metal thin film is the cladding on the n-layer side. It goes without saying that the layer is formed so as not to contact the layer.

In order to form the insulating thin film 10, conventional vapor phase film forming means such as plasma CVD, sputtering, molecular beam deposition, etc. can be used. As the material of the insulating thin film 10, an insulating thin film is selected smaller material than the refractive index of the p-type optical guide layer 6 in contact with the surface, for example, SiO ₂
Si oxide typified by SiN, Si nitride typified by Si ₃ N ₄ and the like can be preferably formed.
A high dielectric material such as Al ₂ O ₃ can be used. The insulating thin film has a film thickness of 100 angstroms or more and 10 μm or less, more preferably 5 μm or less, and most preferably a film thickness smaller than the total film thickness of the clad layer formed on the active layer. Similarly, a metal thin film can be formed.

FIG. 3 is a schematic sectional view showing another structure of the laser device of the present invention, and the same members as those in FIG. 1 are designated by the same reference numerals. This laser device is different from the laser device of FIG. 1 in that the p-type optical confinement layer 7 has a ridge shape. In order to make the clad layer into a ridge shape, it is preferable that the clad layer is closer to the active layer than the layer closest to the active layer.
A ridge may be used instead of the type light confinement layer 7, and can be appropriately changed depending on the thickness of the cladding layer. Needless to say, in the case where the p-type light confinement layer 7 has a ridge shape, the insulating thin film 10 has a refractive index smaller than that of the p-type light confinement layer 7.

Further, the insulating thin film 10 formed on the surface of the p-type optical confinement layer 7 is in contact with the side surface of the striped ridge. By thus forming the insulating thin film on the side surfaces of the stripes, the light leaking from the side surfaces of the stripes is also confined, so that the threshold value is lowered and the light emission output is improved.

Further, the laser element of the present invention is characterized in that the angle of the ridge-shaped side surface with respect to the substrate surface is 90 ° or more. That is, θ shown in FIG. 3 is 90 ° or more. The preferred angle is 90 ° or more and 120 ° or less, more preferably 95 ° or more, 11
At 0 ° or less, light is likely to concentrate under the stripe. By setting this angle to 90 ° or more, it becomes easy to grow the insulating thin film 10 with a uniform film thickness, so that the efficiency of light confinement increases. The preferable stripe width of the ridge-shaped cladding layer is adjusted to 0.5 μm or more and 20 μm or less, more preferably 10 μm or less, and most preferably 5 μm or less. The stripe width means the stripe width of the ridge on the side closer to the active layer. If it is larger than 20 μm, the threshold value is not lowered so much, and if it is smaller than 0.5 μm, heat is generated and the element tends to be easily broken.

In addition, the ohmic positive electrode 30 is formed on almost the entire surface of the striped p-type contact layer 8 exposed on the outermost surface of the ridge-shaped p-type layer. By thus forming the positive electrode 30 on almost the entire surface of the p layer on the outermost surface of the ridge, the contact resistance is reduced,
Vf can be reduced. Therefore, both the drive voltage and the current of the laser element can be reduced. In this case, the “substantially entire surface” means an area of 90% or more.

As a technique similar to the present invention, for example, Japanese Patent Laid-Open No. 6-152072 discloses a refractive index waveguide type laser device. However, in this publication, the etching depth exceeds the active layer and reaches the n-type layer.
In the laser device of the present invention, the etching depth does not exceed the active layer as shown in FIGS. Since the etching damage is less likely to enter the active layer by not exceeding the active layer, the life of the laser element can be extended.

[Embodiment] FIGS. 4 to 7 are schematic sectional views showing a structure of a main part of a nitride semiconductor wafer obtained in an embodiment of the present invention. Hereinafter, a method for obtaining the laser device shown in FIG. 1 will be described in detail with reference to these drawings. Although the method of the embodiment is a method of forming an LD element by the MOVPE method, the element of the present invention is not limited to the MOVPE method, and other known vapor phase epitaxy methods of nitride semiconductors such as MBE and HDVPE. Can be used to grow.

A well-cleaned spinel substrate 1 (MgAl
₂ O ₄ , 111 plane) was installed in the reaction vessel of the MOVPE apparatus, and then TMG (trimethylgallium) was added to the source gas.
Ga was applied to the surface of the substrate 1 at a temperature of 500 ° C. using ammonia.
A buffer layer (not shown) made of N is grown to a film thickness of 200 Å. The buffer layer has a function of alleviating the lattice mismatch between the substrate and the nitride semiconductor.
It is also possible to grow 1N, AlGaN, or the like. It is known that by growing this buffer layer, the crystallinity of the n-type nitride semiconductor grown on the substrate is improved, but the buffer layer may not be grown depending on the growth method, the type of the substrate and the like. Therefore, it is not particularly shown.

Subsequently, the temperature is raised to 1050 ° C., TMG and ammonia are used as a source gas, and SiH is used as a donor impurity.
_{4 An} n-type contact layer 2 made of Si-doped GaN is grown to a thickness of 4 μm using (silane) gas.

Next, the temperature is lowered to 750 ° C., TMG, TMI (trimethylindium) and ammonia are used as source gases, and silane gas is used as an impurity gas.
A crack preventing layer (not shown) made of 1Ga0.9N
It is grown to a thickness of 00 Å. The anti-crack layer is an n-type nitride semiconductor containing In, preferably In
By growing GaN, the n-type optical confinement layer 3 made of a nitride semiconductor containing Al to be grown next can be grown as a thick film. In the case of LD, it is necessary to grow the layer serving as the optical confinement layer with a film thickness of, for example, 0.1 μm or more. In the past, if a thick film of AlGaN was grown directly on the GaN or AlGaN layer, it was difficult to fabricate the device because the AlGaN grown later had cracks. It is possible to prevent the layer 3 from cracking. Moreover, even if the optical confinement layer 3 to be grown next is grown as a thick film, the film quality can be grown with good quality. The crack prevention layer is preferably grown to a film thickness of 100 angstroms or more and 0.5 μm or less. If it is thinner than 100 angstroms, it is difficult to act as a crack prevention as described above.
If it is thicker than 5 μm, the crystals themselves tend to turn black.
Although the crack prevention layer can be omitted depending on the growth method and the growth apparatus, it is not shown, but it is preferable to grow it for manufacturing the LD.

Next, the temperature is set to 1050 ° C., TEG, TMA (trimethylaluminum) and ammonia are used as source gases, and silane gas is used as an impurity gas.
An n-type optical confinement layer 3 made of Al 0.07 Ga 0.93 N is grown to a thickness of 0.6 μm.

Then, TMG, ammonia, and
Si-doped n-type GaN using silane gas as impurity gas
The n-type light guide layer 4 is grown to a film thickness of 500 angstroms.

Next, the active layer 5 is grown using TMG, TMI, and ammonia as source gases. The active layer has a temperature of 75
While maintaining the temperature at 0 ° C., first, a well layer made of non-doped In0.2Ga0.8N is grown to a thickness of 25 Å. Next, a barrier layer made of non-doped In0.01Ga0.95N was deposited at the same temperature by changing only the molar ratio of TMI.
It is grown to a film thickness of 0 angstrom. Do this operation 4
This process is repeated, and finally the well layer is grown to grow the active layer 5 having a multiple quantum well structure with a total film thickness of 325 Å.

After the growth of the active layer 5, the temperature is set to 1050 ° C. and TMG, TMA, ammonia, and Cp 2 Mg (cyclopentadienyl magnesium) as an acceptor impurity source.
Is used to grow a p-type cap layer (not shown) made of Mg-doped p-type Al0.2Ga0.8N to a film thickness of 100 angstrom. By growing the p-type cap layer to a thickness of 1 μm or less, more preferably 10 angstroms or more and 0.1 μm or less, the p-type cap layer has a function as a cap layer for preventing decomposition of the active layer made of InGaN, and is also active. By growing a p-type cap layer made of a p-type nitride semiconductor containing Al on the layer, the light emission output is remarkably improved. Conversely, the p layer in contact with the active layer is Ga
When N is set, the output of the element is reduced to about 1/3. It is presumed that this is because AlGaN is more likely to be p-type than GaN and has the effect of suppressing decomposition of InGaN during growth of the p-type cap layer, but details are unknown. When the film thickness of the p-type cap layer is thicker than 1 μm, cracks are likely to be formed in the layer itself, and it tends to be difficult to manufacture an element. Although the p-type cap layer can be omitted, it is not shown, but it is preferable to grow it for manufacturing the LD. A ridge-shaped stripe may be formed from the p-type cap layer, which is one of the cladding layers in the present invention.

Next, while maintaining the temperature at 1050 ° C., T
Mg-doped p-type G using MG, ammonia, and Cp2Mg
The p-type light guide layer 6 made of aN is grown to a film thickness of 500 angstrom. As described above, the p-type light guide layer 6 is made of InGaN or GaN, and
The p-type optical confinement layer 7 containing 1 can be grown with good crystallinity.

Then, TMG, TMA, ammonia, C
A p-type optical confinement layer 7 made of Mg-doped Al0.07Ga0.93N is grown to a thickness of 0.5 μm using p2Mg.

Furthermore, TMG, ammonia, Cp2Mg
Is used to grow the p-type contact layer 8 of Mg-doped p + -type GaN to a thickness of 0.2 μm.

The wafer in which the nitride semiconductors are laminated as described above is taken out from the reaction container, and the p-type contact layer 8 is formed.
A first mask is formed on the surface of the n-type contact layer 2 on which the negative electrode 20 is to be formed by selective etching from the uppermost p-type contact layer 8 using a reactive ion etching (RIE) device. Expose. Further, after removing the first mask, a second mask 41 is formed on the surface of the p-type contact layer 8 and the exposed surface of the n-type contact layer 2. The second mask 41 formed on the surface of the p-type contact layer has a stripe shape with a width of 2 μm. FIG. 4 is a sectional view showing the structure of the main part of the wafer after the second mask is formed.
It is.

After formation of the second mask, selective etching is similarly performed by RIE to partially etch the p-type contact layer 8, the p-type optical confinement layer 7, and the p-type optical guide layer 6 to form a ridge-shaped stripe. To do. The stripe is approximately 90 ° with respect to the plane of the substrate. After etching, the second mask 41 is removed. The structure of the main part of the wafer after the removal of the second mask 41 is shown in FIG.

Next, as shown in FIG. 7, a third mask 42 is formed at a predetermined position on the nitride semiconductor wafer, and an insulating thin film 1 made of SiO ₂ is formed by a plasma CVD apparatus.
0 indicates the surface of the p-type optical guide layer 6 and the n-type contact layer 2
Is continuously formed with a film thickness of 0.5 μm. FIG. 6 is a diagram showing the structure before the insulating thin film 10 is formed, and FIG. 7 is a diagram showing the structure after the third mask 42 is removed.

After removing the third mask 42, p
A striped positive electrode 30 made of Ni and Au is formed on almost the entire surface of the type contact layer 8, and a striped negative electrode 20 made of Ti and Al is formed on the exposed n-type contact layer 2. The negative electrode 20 serves both as an ohmic electrode and as a pad. After that, the pad electrode 31 made of Au is formed on the positive electrode 30.

The above-described wafer is first divided at a position parallel to the striped electrodes, then divided in a direction perpendicular to the electrodes, and the divided surfaces divided in the vertical direction are polished to form mirror surfaces. To do. A dielectric multilayer film is formed on the resonance surface according to a conventional method to obtain a laser chip as shown in FIG.
When this laser chip was placed on a heat sink and pulse-oscillated at room temperature, a laser oscillation of 410 nm with a threshold current of 0.1 A DC and 10 V was shown.

[Embodiment 2] FIG. 8 is a schematic sectional view showing the structure of a laser device according to this embodiment. This laser device is different from the first embodiment in that the positive electrode 30 is provided as a metal thin film in Schottky barrier contact with the cladding layer.

In Example 1, when the ridge-shaped stripe was formed, the p-type optical confinement layer 6 was formed as shown in FIG.
Mesa etch until. The angle θ of the stripe side surface after the mesa etching is about 95 °.

After the etching, in the step of forming the electrode without forming the insulating thin film 10, as shown in FIG.
A positive electrode 30 containing Ni and Au is formed over almost the entire surface of the type contact layer 8 and the surface of the p-type optical confinement layer 6. The metal containing Ni and Au is Mg-doped p-type GaN.
Is in ohmic contact with the p-type contact layer 8 made of AlGaN, but is in Schottky barrier contact with the p-type optical confinement layer made of AlGaN. In the present invention, the Schottky barrier contact in which the metal thin film is in contact with the cladding layer does not mean a perfect Schottky barrier contact but means that the contact resistance is higher than that of the p-type contact layer. After forming the metal thin film as described above, a laser element was manufactured in the same manner as in Example 1, and showed substantially the same characteristics.

[0046]

As described above, in the laser device of the present invention, the ridge-type stripe concentrates the light emission of the active layer under the ridge, and the transverse mode laser light can be controlled. The current decreases and continuous oscillation becomes possible. Nitride semiconductors have the advantage that they can oscillate at shorter wavelengths than laser devices made of II-VI group compound semiconductors that are currently being researched. Therefore, if continuous oscillation is possible with a nitride semiconductor, the demand for a writing light source and a reading light source will explosively increase, and its industrial utility value will be extremely large.

[Brief description of drawings]

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

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

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

FIG. 4 is a schematic sectional view showing a structure of a main part of a nitride semiconductor wafer obtained in an example.

FIG. 5 is a schematic cross-sectional view showing the structure of the main part of a nitride semiconductor wafer obtained in an example.

FIG. 6 is a schematic cross-sectional view showing the structure of the main part of a nitride semiconductor wafer obtained in an example.

FIG. 7 is a schematic cross-sectional view showing the structure of the main part of a nitride semiconductor wafer obtained in an example.

FIG. 8 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention.

[Explanation of symbols]

 1 ... Substrate 2 ... N-type contact layer 3 ... N-type optical confinement layer 4 ... N-type light guide layer 5 ... Active layer 6 ... P-type light Guide layer 7 ... P-type optical confinement layer 8 ... P-type contact layer 10 ... Insulating thin film 20, 30 ... Electrode

Claims (5)

[Claims] 1. A nitride semiconductor laser device comprising an active layer formed on a substrate and an n-type or p-type cladding layer having a ridge-shaped stripe formed on the active layer. 2. The nitride semiconductor laser device according to claim 1, wherein an insulating thin film made of a material having a refractive index smaller than that of the cladding layer is formed on the surface of the cladding layer. 3. The nitride semiconductor laser device according to claim 1, wherein a metal thin film that is in Schottky barrier contact with the cladding layer is formed on the surface of the cladding layer. 4. The nitride semiconductor laser device according to claim 1, wherein an angle of the side surface of the ridge shape with respect to the substrate surface is 90 ° or more. 5. The nitride semiconductor laser device according to claim 1, wherein the active layer has a multiple quantum well structure made of a nitride semiconductor containing at least indium.