JP2002084035A - Nitride semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To actualize a nitride semiconductor laser element which can continuously oscillate at a room temperature. SOLUTION: The nitride semiconductor laser element which has an n-type layer, an active layer, and a p-type layer formed on a substrate is provided with a current stricture layer on the n-type layer side, and the current stricture layer is formed of p- or i-type AlxGa1-xN (0<=x<=1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 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 emitting light in the ultraviolet to blue region. For example, the present applicant has recently published a 410 nm lasing at room temperature in pulsed current using this material (eg, Jp.
nJAppl.Phys. Vol35 (1996) pp.L74-76). This laser element is a so-called electrode stripe type laser element,
The stripe width of the nitride semiconductor layer including the active layer is several tens μm.
Then, the laser is oscillated. However,
The laser element is still oscillating at a pulse current,
In order to put a nitride semiconductor laser device into practical use, rapid continuous oscillation is desired.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to reduce the threshold current and drive voltage of a laser device made of a nitride semiconductor. An object of the present invention is to provide a laser device which can continuously oscillate at room temperature.

[0004]

According to the first aspect of the present invention, there is provided a nitride semiconductor laser device comprising an n-type semiconductor device formed on a substrate.
In a nitride semiconductor laser device having a type layer, an active layer, and a p-type layer, a current confinement layer is provided on the n-type layer side, and the current confinement layer is a p-type or i-type Al _x Ga _1-x N ( 0 ≦
x ≦ 1). Further, the nitride semiconductor laser device according to claim 2 of the present invention is characterized by claim 1.
In the nitride semiconductor laser device described above, the n-type layer includes an n-type contact layer, and the current confinement layer is formed inside the n-type contact layer.

According to a third aspect of the present invention, in the nitride semiconductor laser device according to the first aspect, the n-type layer has an n-type contact layer and an n-type optical confinement layer, The current confinement layer is formed between the n-type contact layer and the n-type optical confinement layer. According to a fourth aspect of the present invention, in the nitride semiconductor laser device according to the first aspect, the n-type layer has an n-type contact layer, an n-type optical confinement layer, and a light guide layer. The current confinement layer is formed between the n-type light confinement layer and the light guide layer.

According to a fifth aspect of the present invention, in the nitride semiconductor laser device according to the fourth aspect, the light guide layer is formed of an n-type nitride semiconductor containing In or n-type GaN. It is characterized by consisting of.
The nitride semiconductor laser device according to claim 6 of the present invention is the nitride semiconductor laser device according to claim 1,
The n-type layer has an n-type contact layer, an n-type light confinement layer, and a light guide layer, and the n-type light confinement layer is etched in a stripe shape between the n-type contact layer and the light guide layer. And the current confinement layer is n
It is formed on both sides of the light confinement layer etched in a stripe shape between the mold contact layer and the light guide layer.

[0007]

FIG. 1 is a schematic sectional view showing the structure of a laser device according to an embodiment of the present invention, showing a cross section taken along a plane perpendicular to the resonance direction of laser light. I have. As a basic 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 are formed on a substrate 1. 7 and a p-type contact layer 8 are sequentially stacked. In addition,
Reference numeral 20 denotes a striped negative electrode provided on the n-type contact layer 2 parallel to the resonance direction, and reference numeral 30 denotes a positive electrode provided on substantially the entire surface of the p-type contact layer 8. The n-type layer and the p-type layer referred to in the claims of the present invention are an n-type layer or a p-type layer directly or indirectly sandwiching an active layer. The p-type layer refers to at least one of the p-type light guide layer 6, the p-type light confinement layer 7, and the p-type contact layer 8. Point to.

The laser device of the present invention has a current confinement layer 100 on the n-type layer side. The function of the current confinement layer is as follows. The carrier concentration of the n-type layer of the nitride semiconductor is usually 1
× 10 ¹⁸ / cm ³ to 10 ²⁰ / cm ³ , with a resistivity of 10 ^-2 to 1
The resistance is as low as 0 ^-3 Ω · cm /. On the other hand, the carrier concentration of the p-type layer is usually 1 × 10 ¹⁸ / cm ³ or less, and the resistivity is 0.1 × 10 ¹⁸ / cm ³ .
1 Ω · cm or more. Therefore, if current confinement is performed on the p-type layer side, the drive voltage becomes extremely high, which hinders continuous oscillation of the laser element. However, by performing current confinement on the n-layer side having a low resistivity, the drive voltage of the laser element can be reduced, so that continuous oscillation is possible. The function of the current confinement layer of the laser device of the present invention is due to the unique properties of the nitride semiconductor.

In FIG. 1, the current confinement layer 100 is formed inside the n-type contact layer 2, but in the present invention, the current confinement layer 100 faces the n-type layer, that is, the p-type layer sandwiching the active layer. If it is on the side, the position is not particularly limited, for example, between the n-type contact layer 2 and the n-type light confinement layer 3, between the n-type light confinement layer 3 and the n-type light guide layer 4,
It can be formed in the n-type light confinement layer 3, between the n-type light guide layer 4 and the active layer 5, or even over the n-type layer multilayer,
The position is not particularly limited.

Further, it is desirable that the material of the current confinement layer 100 is a p-type or i-type (semi-insulating) nitride semiconductor. By using a p-type nitride semiconductor, a reverse bias is applied to the current confinement layer, and current confinement can be performed effectively.
Alternatively, an i-type nitride semiconductor may be used. When the current confinement layer is formed of a nitride semiconductor, the nitride semiconductor can be grown again on the current confinement layer made of the same nitride semiconductor. Therefore, the n-type layer, the active layer,
Since the p-type layer or the like can be grown, for example, the p-type layer can be formed into a stripe shape such as a ridge shape, processed into a desired shape, or selectively grown. A p-type or i-type nitride semiconductor can be obtained by doping an acceptor impurity made of a group II element such as Zn, Mg, Cd, or Ba during growth of the nitride semiconductor. p-type, i
The conductivity type such as the type can be changed by, for example, changing the amount and type of the acceptor impurity to be doped, or changing the composition and growth conditions of the nitride semiconductor. For example, a nitride semiconductor having an Al composition ratio larger than 0.4 is easily obtained as i-type, and Mg is an impurity easily obtained as p-type.
Preferably, the current confinement layer is p-type Al _x Ga ₁ -xN (0 ≦ X ≦
1), more preferably p-type GaN. Because
This is because Al _x Ga ₁ -xN makes it easier to obtain a p-type layer having the highest hole carrier concentration, and becomes more i-type as the Al composition ratio increases.

In the laser device of the present invention, the p-type layer may have a ridge-shaped stripe. When the p-type layer has a ridge shape, the light emission of the active layer is concentrated on the lower portion of the ridge, so that the transverse mode of the laser beam can be controlled and the threshold value is reduced.

[0012]

[Embodiment 1] FIGS. 2 to 5 are schematic sectional views showing the structure of the main part of a nitride semiconductor wafer obtained in one step of this embodiment. 3 shows the structure. Hereinafter, based on these figures, FIG.
A method for obtaining the laser device shown in FIG. The method described below is based on MOVPE (Metal Organic Chemical Vapor Deposition), but the laser device of the present invention is not limited to MOVPE, and other methods for obtaining a known nitride semiconductor such as MBE, HDVPE, etc. But it can be manufactured. In addition, the structure of the laser device shown below shows only a basic structure, and even if any of the layers shown in these structures is omitted or a layer made of another nitride semiconductor is inserted, the structure of the present invention is claimed. Changes can be freely made without departing from the spirit described in the section.

A well-cleaned spinel substrate 1 (MgAl
After placing the ₂ O _4, 111 plane) in a reaction vessel of the MOVPE apparatus, and TMG (trimethylgallium) as a source gas,
Using ammonia, at a temperature of 500 ° C., a Ga
A buffer layer (not shown) made of N is grown to a thickness of 200 Å. Substrate 1 has spinel,
Insulating substrates such as sapphire (Al ₂ O ₃ , A-plane, C-plane, and R-plane) are often used, but in addition, SiC, MgO, S
A conventionally known substrate made of a single crystal such as i, ZnO, or GaN is used. The buffer layer has an effect of alleviating lattice mismatch between the substrate and the nitride semiconductor.
It is also possible to grow N, AlGaN, or the like. It is known that the growth of the buffer layer improves the crystallinity of the n-type nitride semiconductor grown on the substrate, 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 was raised to 1050 ° C., and TMG, ammonia, and SiH as donor impurities were added to the source gas.
_{4 A} first n-type contact layer 2 made of Si-doped GaN is grown to a thickness of 2 μm using (silane) gas. The first n-type contact layer 2 is made of In _x Al _Y Ga _{1 -XY}
N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1),
In particular, by using GaN, InGaN, and especially GaN doped with Si, an n-type layer having a high carrier concentration can be obtained, and a favorable ohmic contact with the negative electrode can be obtained. Can be. As the material of the negative electrode, Al, Ti, W, Cu,
A preferable ohmic material is a metal or alloy such as Zn, Sn, and In.

Subsequently, TMG, ammonia,
Using Cp2Mg (cyclopentadienyl magnesium) as an impurity gas, a current confinement layer 100 made of Mg-doped p-type GaN is grown to a thickness of 0.5 μm. Since this p-type GaN layer is formed on the entire surface, it does not function as a current confinement layer yet, but is referred to as a current confinement layer as a unified term in this specification. The current confinement layer 100 may be a i-type nitride semiconductor as described above, or other in SiO _2,
An insulating material such as Al ₂ O ₃ can be formed, but preferably a nitride semiconductor allows another nitride semiconductor to grow on the current confinement layer.

After the growth of the current confinement layer 100, the wafer is taken out of the reaction vessel and the surface of the current confinement layer 100 is
Of SiO ₂ having an opening with a stripe width of
Is formed by a CVD apparatus. This stripe-shaped opening becomes a path for a current when the current confinement layer is etched later, and is 10 μm or less.
It is desirable to adjust the thickness to preferably 5 μm or less, more preferably 3 μm or less. The material of the first protective film 51, the etching means, the less likely the protective film is etched, it is necessary to nitride semiconductor to select a material such as easily etched, for example, silicon oxide such as SiO ₂ , Si ₃ N ₄ . FIG. 2 shows a partial cross-sectional view of the wafer on which the first protective film 51 is formed.

After forming the first protective film 51, the wafer is subjected to RI
The substrate is transferred to an E (reactive ion etching) apparatus, and the current confinement layer 100 in the opening is etched from above the first protective film 51 formed earlier to expose the surface of the n-type contact layer 2. FIG. 3 shows the first protective film 51 after the etching is completed.
FIG. 4 is a partial cross-sectional view showing a structure of a wafer from which is removed. As shown in this figure, the shape of the etching side surface is preferably a regular mesa shape. This is because the current confinement layer 10
When a new nitride semiconductor is to be laminated on the surface of No. 0, if the semiconductor layer has a normal mesa shape, the angles of the side surfaces are all obtuse, so that the nitride semiconductor can be easily grown even at the corners of the side surfaces. Further, the nitride semiconductor can be easily grown even in the opening where the step is generated by the etching.

After the removal of the first protective film, the wafer is transferred again into the reaction vessel, and a new structure of the laser device is formed on the current confinement layer 100 and the n-type contact layer 2 at the opening as follows. Are stacked.

The temperature was raised to 1050 ° C.
Using G, ammonia, and silane gas as a donor impurity, a second n-type contact layer 2 ′ (continuation of the n-type contact layer 2) made of Si-doped GaN is grown to a thickness of 3 μm. As described above, by growing a nitride semiconductor having the same composition with the current constriction layer 100 interposed therebetween, the nitride semiconductor is connected in a lattice-matched state in the opening.
A nitride semiconductor having good crystallinity can be grown. In addition, when the same composition is used, even when the current flows, there is no barrier due to the hetero interface, so that the current flows very easily. As in the present embodiment, the nitride semiconductor layer grown directly on the current confinement layer 100 is made thicker than the current confinement layer so that the nitride semiconductor grows in a thick film in the opening. Because you can
This is particularly preferable because the step of the opening is reduced and a flat surface is formed when the active layer and the p-type layer are laminated later. It should be noted that the same composition in the present invention does not necessarily mean that the donor impurity contained in the nitride semiconductor is the same. The donor impurity added for changing the carrier concentration can be appropriately changed. The above-described current confinement layer 10
In the case of 0, a stripe-shaped opening is formed, and another nitride semiconductor is grown thereon, thereby acting as a current confinement layer.

Next, the temperature was lowered to 750 ° C., and TMG, TMI (trimethylindium) and ammonia were used as source gases, silane gas was used as impurity gas, and Si-doped In was used.
_0.1 Ga _{0 .9} crack preventing layer consisting of N (not shown.) Are grown to a film thickness of 500 angstroms. The crack preventing layer is made of an n-type nitride semiconductor containing In, preferably
AlGaN to be grown next by growing with nGaN
It is possible to grow the n-type optical confinement layer 3 made of a nitride semiconductor containing a thick film without cracks. The crack preventing layer is preferably grown to a thickness of 100 Å or more and 0.5 μm or less. When the thickness is less than 100 Å, it is difficult to function as a crack prevention as described above, and when the thickness is more than 0.5 μm, the crystal itself tends to turn black. The crack prevention layer is not shown because it can be omitted depending on the growth method and the growth apparatus, but it is preferable to grow the LD in manufacturing an LD. The crack prevention layer is also referred to as n in the present invention.
One of the mold layers.

Next, the temperature is increased to 1050 ° C., and 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 of type Al _0.07 Ga _0.93 N is grown to a thickness of 0.6 μm. The n-type optical confinement layer 3 is made 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 ≦
By adopting 1), a material having good crystallinity can be obtained, and the difference in refractive index from the active layer is increased, which is effective for confining the longitudinal mode of laser light. This layer is usually 0.1 μm to 1 μm.
It is desirable to grow with a film thickness of μm. If the thickness is less than 0.1 μm, it does not easily function as a light confinement layer.

Subsequently, TMG, ammonia,
Using silane gas, n made of n-type GaN doped with Si
The light guide layer 4 is grown to a thickness of 500 angstroms. The n-type light 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 -xN (0 ≦ X <1). ). This layer is usually preferably grown to a thickness of 100 Å to 1 μm.
By using aN, the next active layer 5 can easily have a quantum well structure.

Next, the active layer 5 is grown by 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 In _0.2 Ga _0.8 N is grown to a thickness of 25 Å. Next, a barrier layer made of non-doped In _0.01 Ga _0.95 N was deposited at the same temperature by changing only the molar ratio of TMI.
It is grown to a thickness of 0 Å. This operation 4
This is repeated twice, and finally, a well layer is grown to grow an active layer 5 having a multiple quantum well structure with a total thickness of 325 Å. The active layer 5 preferably has a multiple quantum well structure (MQW: Mult) formed of a nitride semiconductor containing In.
As i-quantum-well), still more preferably a MQW to _{In X Ga 1-X N (} 0 <X <1) well layer of a ternary mixed crystal. Since the ternary mixed crystal InGaN has higher crystallinity than that of the quaternary mixed crystal, the light emission output is improved. Among them, particularly preferably, the active layer is made of In.
A well layer made of _X Ga _{1 -X} N, easily lasing When MQW formed by laminating a barrier layer made of nitride semiconductor of high ternary mixed crystal of a band gap than the well layer.

After the active layer 5 is grown, the temperature is raised to 1050 ° C., 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 Al _0.2 Ga _0.8 N to a thickness of 100 Å. By growing the p-type cap layer to a thickness of 1 μm or less, more preferably 10 Å or more and 0.1 μm or less, the p-type cap layer has a function as a cap layer for preventing the active layer made of InGaN from being decomposed. By growing a p-type cap layer made of a p-type nitride semiconductor containing Al on the layer, the light emission output is significantly improved. This is because AlGaN is more likely to be p-type than GaN, and when growing a p-type cap layer,
It is presumed that it has the effect of suppressing the decomposition of InGaN, but the details are unknown. If the thickness of the p-type cap layer is larger than 1 μm, cracks tend to occur in the layer itself, and it tends to be difficult to fabricate the device. Although the p-type cap layer can be omitted, it is not shown in the figure, but it is preferable to grow it in order to manufacture an LD.

Subsequently, TMG, ammonia, Cp2Mg
Is used to grow a p-type optical guide layer 6 made of Mg-doped p-type GaN to a thickness of 500 angstroms. When the p-type light guide layer 6 is also made of p-type InGaN and p-type GaN, the next p-type light confinement layer 7 containing Al can be grown with good crystallinity. When the p-type layer has a ridge shape, particularly when the p-type light guide layer 6 has a ridge shape,
Most preferably, the type light guide layer is InYGa1-YN (0 <Y≤1).

Subsequently, TMG, TMA, ammonia, C
The p-type optical confinement layer 7 made of Mg-doped Al _{0.0 7} Ga _0.93 N with p2Mg is grown to the thickness of 0.5 [mu] m. 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 ternary mixed crystal A
By setting l _Y Ga _{1 -Y} N (0 <Y ≦ 1), a crystal having good crystallinity can be obtained. Like the n-type optical confinement layer 3, the p-type optical confinement layer 7 is preferably grown to a thickness of 0.1 μm to 1 μm, and is made active by forming a p-type nitride semiconductor containing Al such as AlGaN. By increasing the refractive index difference with the layer, the layer effectively functions as a light confinement layer for longitudinal mode laser light. If the p-type light confinement layer 7 has a ridge shape, the p-type light confinement layer is
Most preferably, the type is Al _Y Ga _{1 -Y} N (0 <Y ≦ 1).

Subsequently, TMG, ammonia, Cp2Mg
Is used to grow a p-type contact layer 8 of Mg-doped p-type GaN with a thickness of 0.2 μm. The p-type contact layer 8 is made of p-type In _x Al _Y Ga _{1 -XYN} (0 ≦ X, 0 ≦ Y, X +
Y ≦ 1), especially InGaN, Ga
N, and among them, p-type GaN doped with Mg,
A p-type layer with the highest carrier concentration is obtained, good ohmic contact with the positive electrode is obtained, and the threshold current can be reduced. The materials of the positive electrode are Ni, Pd, Ir,
Metals or alloys having a relatively high work function, such as Rh, Pt, Ag, and Au, can easily obtain an ohmic, and in particular, a material containing at least Ni and Au, and a material containing at least Pd and Au can easily obtain a preferable ohmic. . FIG. 4 is a partial cross-sectional view showing the structure of the wafer on which the nitride semiconductor layers are stacked.

After completion of the reaction, the wafer is taken out of the reaction vessel, and a second protective film 52 made of SiO ₂ is formed on the surface of the p-type contact layer 8 as shown in FIG.
Is etched from above the protective film 52 to expose the surface of the n-type contact layer 2 where the negative electrode is to be formed. FIG. 5 shows a cross-sectional view after completion of the etching. In FIG. 5, the first n-type contact layer 2 and the second n-type contact layer 2 'are made of the same nitride semiconductor and function as the same contact layer. Not.

After the completion of the etching, the second mask 52 is removed, a positive electrode 30 made of Ni / Au is formed on almost the entire surface of the p-type contact layer 8, and resonance is applied to the n-type contact layer 2 exposed by the etching. A negative electrode 20 made of Ti / Al in a stripe shape parallel to the direction is formed.

The wafer as described above is first cut at a position parallel to the striped negative electrode, then cut in the direction perpendicular to the negative electrode, and the surface cut in the direction perpendicular to the negative electrode is polished. Thus, a mirror-like resonance surface is manufactured. 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 continuously oscillated at room temperature, a laser oscillation of 410 nm was exhibited at a forward voltage of 10 V and a threshold current of 100 mA. On the other hand, in the laser device according to the present invention in which the current confinement layer is not provided on the n-type layer and the current confinement layer having the 5 μm stripe groove is provided only on the surface of the uppermost p-type contact layer 8, continuous oscillation occurs. However, laser oscillation occurred only with a pulse current.

Embodiment 2 FIG. 6 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention. The basic laminated structure of the nitride semiconductor layer is the same as that of the first embodiment, but this laser device is different from that of the first embodiment in that
That is, the p-type layer is a ridge-shaped stripe. When the p-type layer has a ridge shape, the light emission of the active layer is easily concentrated below the ridge, so that the threshold current can be reduced. Positive electrode 30 formed on the surface of layer 3
, The driving voltage tends to increase. Note that this laser element also exhibits continuous oscillation as in the first embodiment, and has a forward voltage of 15 V, a threshold current of 80 mA, and a current of 410 V.
nm laser oscillation.

In FIG. 6, the side surface of the ridge has a forward mesa shape. However, the side surface of the ridge is not limited to the forward mesa shape, but may be an inverted mesa or a vertical ridge side surface. Further, although the ridge shape is formed from the p-type light confinement layer 7, the ridge shape may be formed from the p-type cap layer, the p-type light guide layer 6, and the p-type contact layer 8. Although the p-type layer has a ridge shape in order to concentrate the light of the active layer, the light is concentrated on a certain portion of the active layer even if the p-type layer is not particularly ridge-shaped, as is used in other laser devices. Any structure may be used for the p-type layer as long as it is a method for causing the p-type layer. When a p-type layer is processed and light is concentrated on a certain portion of the active layer like a ridge, as shown in FIG. 7, the lower part of the stripe of the ridge and the stripe position of the n-type layer where current is confined are set. It is desirable to make them coincide.

[Embodiment 3] FIG. 7 is a schematic sectional view showing another structure of the laser device of the present invention. 8 to 11 are schematic cross-sectional views showing the structure of the main part of the wafer obtained in the step of obtaining the laser device of FIG. Hereinafter, another method for obtaining the laser device of FIG. 7 will be described with reference to FIGS.

In the same manner as in Example 1, a buffer layer made of GaN was formed on the spinel substrate 1 to a thickness of 200 angstroms (not shown), an n-type contact layer 2 made of Si-doped GaN was set to 4 μm, and Si-doped In _0.1 Ga _0.9 N
A crack prevention layer (not shown) made of 500 Å and an n-type optical confinement layer 3 made of Si-doped n-type Al _0.07 Ga _0.93 N are continuously grown to a thickness of 0.6 μm.

After the growth of the n-type optical confinement layer 3, the wafer is taken out of the reaction vessel and a third mask 5 made of SiO ₂ is formed.
3 is formed in a stripe shape having a width of 5 μm. FIG. 8 shows the third
3 is a cross-sectional view when the mask 53 is formed on the surface of the n-type light confinement layer, and shows a view when the mask 53 is cut in a direction perpendicular to the stripe. The stripe width of the third mask 53 is desirably adjusted to 10 μm or less, preferably 5 μm or less, and more preferably 3 μm or less.

After forming the third mask 53, the wafer is transferred to an RIE apparatus, and the n-type optical confinement layer 3 is etched from above the mask. FIG. 8 is a sectional view in which the mask is removed after the etching. As described above, in FIG. 8, the etching is performed so that the etching side surface of the stripe of the n-type optical confinement layer 3 has an inverted mesa shape. However, the etching may be performed in a normal mesa shape or in a vertical direction.

[0037] After the third mask 53 is removed, in a stripe pattern etched n-type optical confinement layer 3 of the surface as shown in FIG. 10, by a CVD method, a fourth that of SiO ₂
Is formed. The fourth mask 54 has such a property that a nitride semiconductor does not easily grow on its surface. Materials having such properties include, for example, silicon oxide such as SiO ₂ and silicon nitride such as Si ₃ N ₄ . Next, the wafer on which the fourth mask 54 has been formed is transferred to the reaction vessel again, and then a nitride semiconductor serving as a current confinement layer is grown.

The wafer on which the fourth mask 54 has been formed is heated again to 1050 ° C., and is doped with Mg-doped p-type Al _0.3 Ga using TMG, TMA, ammonia and Cp 2 Mg.
_A current confinement layer 100 of _0.7 N is grown to a thickness of 0.5 μm. FIG. 10 is a sectional view showing the structure after the current confinement layer 100 is grown. Thus, the current confinement layer can be formed even inside the n-type optical confinement layer 3.

After the growth of the current confinement layer 100, the wafer is taken out of the reaction vessel, and after removing the fourth mask 54, the wafer is transferred again into the reaction vessel, whereupon the current confinement layer 100 and the striped n-type optical confinement layer are formed. A nitride semiconductor is grown on 3.

In the same manner as in Example 1, the Si-doped n-type G
The n-type optical guide layer 4 made of aN is 500 angstroms, and the active layer of the MQW structure in which a well layer 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 are stacked at 325 angstroms, A p-type cap layer (not shown) made of Al _0.2 Ga _0.8 N is 100 Å, a p-type optical guide layer 6 made of Mg-doped p-GaN is 500 Å, and a p-type light guide layer 6 made of Mg-doped Al _0.07 Ga _0.93 N is used. The light confinement layer 7 is grown to a thickness of 0.5 μm, and the p-type contact layer 8 made of Mg-doped p-type GaN is grown to a thickness of 0.2 μm. FIG. 11 shows a cross-sectional view after completion of the reaction.

Thereafter, etching is performed from the p-type contact layer 8 to expose the surface of the n-type contact layer 2 where the negative electrode is to be formed, as in the first embodiment. By forming a positive electrode 30 on the substrate and forming a striped negative electrode 20 parallel to the resonance direction on the n-type contact layer 2, a laser device of the present invention as shown in FIG. 7 is obtained. This laser element also has a forward voltage of 10 V and a threshold current of 100 mA, similarly to the laser element of the first embodiment.
A continuous oscillation of 410 nm was shown.

As described above, according to the laser device of the present invention, as shown in the first embodiment, after growing an n-type layer and a current confinement layer, a part of the current confinement layer is etched in a stripe shape. A protective method in which a nitride semiconductor is unlikely to grow on the surface of the n-type layer in a stripe shape as shown in Example 3, and then the surface of the protective film and the surface of the n-type layer And a method for selectively growing a nitride semiconductor.

[0043]

As described above, in the laser device of the present invention, since the current confinement layer is formed on the n-type layer side, the driving voltage of the laser device is reduced, and continuous oscillation is possible. This is due to the fact that the n-layer has a higher carrier concentration and a lower resistivity than the p-layer, which is unique to nitride semiconductors. As described above, according to the laser device of the present invention, a practical structure can be provided by using a nitride semiconductor. Therefore, as a laser device in a short wavelength region, a writing / reading light source for DVDs, CDs, and the like, compared with a red semiconductor laser. 4 times or more capacity can be secured and its industrial use value is very large.

[Brief description of the drawings]

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

FIG. 2 is a schematic cross-sectional view showing a structure of a main part of a wafer obtained in one step of Example 1.

FIG. 3 is a schematic cross-sectional view showing a structure of a main part of a wafer obtained in one step of Example 1.

FIG. 4 is a schematic cross-sectional view showing a structure of a main part of a wafer obtained in one step of Example 1.

FIG. 5 is a schematic cross-sectional view showing a structure of a main part of a wafer obtained in one step of Example 1.

FIG. 6 is a schematic sectional view showing another structure according to the laser device of the present invention.

FIG. 7 is a schematic sectional view showing another structure according to the laser device of the present invention.

FIG. 8 is a schematic cross-sectional view showing a structure of a main part of a wafer obtained in one step of Example 3.

FIG. 9 is a schematic cross-sectional view showing a structure of a main part of a wafer obtained in one step of Example 3.

FIG. 10 is a schematic cross-sectional view showing a structure of a main part of a wafer obtained in one step of Example 3.

FIG. 11 is a schematic cross-sectional view showing a structure of a main part of a wafer obtained in one step of Example 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... board | substrate 2 ... n-type contact layer 3 ... n-type light 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 100... Current confinement layer 20, 30.

Claims (6)

[Claims] 1. A nitride semiconductor laser device having an n-type layer, an active layer and a p-type layer formed on a substrate, wherein a current confinement layer is provided on the n-type layer side, and the current confinement layer is a p-type or i-type _{Al x Ga 1-x N (} 0 ≦ x ≦ 1) nitride semiconductor laser device, comprising the. 2. The n-type layer includes an n-type contact layer,
2. The nitride semiconductor laser device according to claim 1, wherein said current confinement layer is formed inside said n-type contact layer. 3. The n-type layer includes an n-type contact layer and an n-type optical confinement layer, and the current confinement layer is formed between the n-type contact layer and the n-type optical confinement layer. The nitride semiconductor laser device according to claim 1. 4. The n-type layer has an n-type contact layer, an n-type light confinement layer, and a light guide layer, and the current confinement layer is formed between the n-type light confinement layer and the light guide layer. The nitride semiconductor laser device according to claim 1. 5. The nitride semiconductor laser device according to claim 4, wherein the light guide layer is made of an n-type nitride semiconductor containing In or n-type GaN. 6. The n-type layer has an n-type contact layer, an n-type light confinement layer, and a light guide layer, and the n-type light confinement layer has a stripe shape between the n-type contact layer and the light guide layer. 2. The nitride semiconductor laser device according to claim 1, wherein the current confinement layer is formed on both sides of the light confinement layer etched in a stripe shape between the n-type contact layer and the light guide layer. .