JP3379619B2 - Nitride semiconductor laser device - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a nitride semiconductor (In
_X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, 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. The applicant has recently used this material to produce a laser oscillation of 410 nm at room temperature under a pulse current. Announced (for example, Jpn.J.
Appl.Phys. Vol35 (1996) pp.L74-76). The announced laser device is a so-called electrode stripe type laser device in which the nitride semiconductor layer including the active layer has a stripe width of several tens of μm and laser oscillation is performed. However, the threshold current of the laser element is 1 to 2 A,
It is necessary to further reduce the threshold current for continuous oscillation.

For example, Japanese Patent Laid-Open No. 6-152072 discloses some structures of laser devices made of nitride semiconductor. This publication discloses a buried hetero-type laser element in which both sides of a striped active layer sandwiched by cladding layers are sandwiched by i-type nitride semiconductors. However, it is difficult to reduce the threshold current with this laser device structure.

[0004]

At present, when pulse oscillation of a short wavelength laser of 410 nm has been confirmed, continuous oscillation at room temperature is urgently desired. Therefore, the present invention has been made in view of such circumstances, and an object thereof is to reduce the threshold current of a laser element made of a nitride semiconductor and aim at continuous oscillation at room temperature. It is in.

[0005]

The laser device of the present invention comprises:
Between the n-type clad layer and the p-type clad layer, an active layer having a stripe-shaped oscillation region having a width narrower than those of the clad layers is provided, and on both side surfaces of the stripe of the active layer,
At least AlyGa1- whose refractive index is smaller than that of the active layer
A current blocking layer having a nitride semiconductor layer containing yN (0 ≦ y ≦ 1) is provided, and the current blocking layer includes a first current blocking layer on a side closer to the n-type cladding layer, and p A plurality of laminated films having at least a two-layer structure composed of a second current blocking layer on the side close to the mold clad layer, wherein the plurality of laminated films are composed of layers having different compositions And

Between the first current blocking layer and the second current blocking layer, there is provided a third current blocking layer having a film thickness substantially equal to or larger than that of the active layer. Characterize.

The active layer has a multi-quantum well structure and is characterized by having a nitride semiconductor layer made of at least In _X Ga _1-X N (0 <X <1).

The current blocking layer is characterized by including an i-type layer at least in a state of being doped with p-type impurities or in a non-doped state.

The first current blocking layer is p-type or i-type, and the second current blocking layer is n-type or i-type.

[0010]

[0011]

FIG. 1 is a schematic cross-sectional view showing one structure of the laser device of the present invention. As a basic structure, an n-type contact layer 2, an n-type cladding layer 3, an active layer 4 and a p-layer are formed on a substrate 1. The n-type contact layer 2 is provided with a negative electrode 11, and the p-type contact layer 6 is provided with a positive electrode 10 on substantially the entire surface thereof. ing. The active layer 4 has a stripe-shaped oscillation region. In the laser device of the present invention, the cladding layers 3, 5 are
Since it has the stripe-shaped active layer 4 having a narrower width, the area of the positive electrode 10 can be increased. For this reason, the current density of the p-type contact layer 6 is reduced, and the contact resistance between the positive electrode and the p-type contact layer 6 is lowered, so that the threshold current of the laser element is lowered. JP-A-6-15207 mentioned above.
The width of the p-type clad layer 5 is different between the publication No. 2 and the present invention. That is, while the width of the active layer and the stripe width of the p-type clad layer are the same in the past, the width of the p-type clad layer 5 is wider than the stripe width of the active layer 4 in the present invention. Therefore, the area of the positive electrode can be increased, and the contact resistance between the positive electrode and the p contact layer can be reduced. Further, in the present invention, the current blocking layer 20 made of a nitride semiconductor having a smaller refractive index than the active layer is provided on both side surfaces of the stripe of the active layer 4. This current blocking layer 20
By setting the refractive index of 1 to be low, the laser light in the lateral direction is confined, and a so-called refractive index guided type laser element can be formed, so that the threshold current can be made smaller than that of the conventional electrode stripe type. The current blocking layer refers to a layer that has a function of making current difficult to flow only in the current blocking layer and concentrating the current in the active layer 4. Further, since the current blocking layer is made of a nitride semiconductor, there is also an advantage that the p-type contact layer 5 easily grows on the current blocking layer 20.

FIG. 2 is a schematic cross-sectional view showing another structure of the laser device of the present invention. This laser device differs from the structure of the laser device of FIG. 1 in that the current blocking layer is an n-type cladding layer. The first current blocking layer 31 on the side closer to
Second current blocking layer 32 on the side closer to the mold cladding layer
It has at least a two-layer structure consisting of If the current blocking layer 20 has a single layer structure as shown in FIG.
The current blocking layer needs to be at least i-type (insulator), but if it has at least a two-layer structure as shown in FIG.
For example, nitride semiconductors having different conductivity types may be laminated so that 31 layers are p-type and 32 layers are n-type, and reverse bias is applied to act as a current blocking layer. Further, the nitride semiconductor has a property that it is difficult to grow a thick film having a single composition and good crystallinity. (In particular, for a nitride semiconductor containing Al, when a thick film is grown in a state where the Al composition ratio is high, cracks are likely to occur in the crystal.) For example, when the active layer has a multiple quantum well structure In the active layer, a plurality of well layers and barrier layers having a film thickness of 100 Å or less are grown.
In this case, in order to confine light in the lateral direction of the active layer,
It is possible to form a current blocking layer with good crystallinity by growing a nitride semiconductor of a single composition in a plurality of thin films, rather than by growing a nitride semiconductor of a single composition all at once. That is,
When the current blocking layer is AlGaN, if a layer having a high Al composition ratio is grown as a thick film all at once, cracks easily occur in the crystal. In order to grow a current blocking layer as a thick film that only confines the laser light in the lateral direction, it is more difficult to crack the current blocking layer as a whole when growing a stack of thin films rather than growing them all at once. . If the current blocking layer is cracked, the p-type cladding layer 5 grown on the current blocking layer cannot grow with good crystallinity, and the laser output tends to decrease. The composition of the nitride semiconductor in each current blocking layer may be the same or different. It is preferable to stack a layer having a high Al composition ratio and a layer having a low Al composition ratio.

FIG. 3 is also a schematic sectional view showing another structure of the laser device of the present invention. In this laser device, the current blocking layer is the first current blocking layer 41 on the n-type cladding layer side.
And a second current blocking layer 42 on the p-type clad layer side, a third current blocking layer 43 having a film thickness substantially equal to or larger than that of the active layer 4 is provided. ing. The function of this laser device is that the third current blocking layer 43 in contact with the stripe side surface of the active layer 4 is formed of a single nitride semiconductor. For example, when there are two or more types of current blocking layers having different refractive indexes on the side surface of the active layer, light tends to easily pass through the current blocking layer having a large refractive index. By forming a small single composition nitride semiconductor on the side of the stripe, lateral light is most effectively trapped. 1 to 3 show the basic structure of the laser device, and the laser device of the present invention is not limited to this structure. For example, in the laser device having the structure shown in FIG. 1, the current blocking layer 20 may be formed in contact with the n-type contact layer 2 and the p-type contact layer 6. In this case, the stripe widths of the n-type clad layer 3 and the p-type clad layer 5 are the same as that of the active layer 4, and the n-type contact layer 2 and the p-type contact layer 6 act as a clad layer and a contact layer.

In the laser device of the present invention, the active layer has a nitride semiconductor layer containing at least In _X Ga _1-X N (0 <X <1), and the current blocking layer has at least Al _Y Ga _1-Y N. (0
It is characterized by having a nitride semiconductor layer containing ≦ Y ≦ 1). Since InGaN has a softer crystal property than Al _Y Ga ₁ -YN, it is easy to form a multiple quantum well structure for laser oscillation. In addition, since the band gap energy is 1.95 eV to 3.4 eV, 365 nm
It is possible to realize a high-power LD in the range of 660 nm. Further, since it is a material having a relatively large refractive index among the nitride semiconductors, the cladding layer and the current blocking layer can be easily designed by using the active layer. Meanwhile, the current blocking layer is made of Al _Y G
With a _1-Y N, the difference in refractive index from the active layer can be increased, so that lateral light confinement can be effectively performed. More preferably, Al _Y Ga _{1 -Y} N has the property that the resistivity increases as the Y value increases, that is, as the Al mixed crystal ratio increases. Therefore, it is optimal for use as an i-type current blocking layer. This property is a very useful action of Al _Y Ga ₁ -YN.

The current blocking layer is preferably i-type at least in the state of being doped with p-type impurities or in the state of being undoped. When the current blocking layer is composed of only one layer as shown in FIG. 1, the current blocking layer needs to be i-type.
The same applies to the current blocking layer made of a plurality of nitride semiconductors as shown in FIG. It is known that a nitride semiconductor tends to be n-type in a non-doped state due to nitrogen vacancies inside the crystal. However, it is difficult to control the carrier concentration in the n-type with nitrogen vacancies. So M
By doping an acceptor impurity made of a Group II element such as g and Zn, the n-type conductivity is compensated and the i-type or p-type conductivity is easily obtained.

When the current blocking layer is made of a plurality of nitride semiconductors as shown in FIGS. 2 and 3, the current blocking layer may be reverse-biased, so that the conductivity type is not particularly limited. That is, the first current blocking layers 31 and 41 approaching the n-type cladding layer 4 are p-type or i-type, and the second current blocking layers 32 and 42 approaching the p-type cladding layer 5 are n-type. Or, if it is i-type, the direction of the current is opposite,
Acts as a current blocking layer. As shown in FIG. 3, when the current blocking layer is composed of three or more layers, the conductivity type of the third current blocking layer 43 is not particularly limited. In the most preferable embodiment of the current blocking layer, the first current blocking layer is made of i-type or p-type Al.
_{Y1Ga1 -Y2N} (0≤Y1 <1), and the second current blocking layer is an i-type or n-type Al _{Y2Ga1 -Y2N} (0≤Y2 <1)
And the third current blocking layer is made of Al _Y3 Ga regardless of conductivity type.
_1-Y3 N (0 <Y3 ≦ 1, where Y1 <Y3, Y2 <Y3), and it is desirable that the third current blocking layer is substantially the same as or thicker than the film thickness of the active layer.

[0017]

DETAILED DESCRIPTION OF THE INVENTION

[Embodiment] FIGS. 4 to 7 are schematic sectional views showing the structures of wafers obtained in the embodiments, and a method for producing a laser device of the present invention by the MOVPE method will be described below in detail with reference to these drawings. .

(Step of growing clad layer and active layer) After the substrate 100 having the spinel (MgAl2O4) 111 plane as the main surface is placed in the reaction vessel of the MOVPE apparatus,
TMG (trimethylgallium) and ammonia were used as source gases, and GaN was formed on the surface of the substrate 100 at a temperature of 500 ° C.
A buffer layer of 100 Å is grown to a film thickness of 200 Å. In addition to spinel for the substrate 100, the A side, R
It is also possible to use sapphire having a plane or C plane as a main surface, and a conventionally known substrate made of a single crystal of SiC, MgO, GaN, Si, ZnO, or the like is used. Since the buffer layer can be deleted depending on the type of substrate, the growth method, etc., it is not shown in the figure.

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.
_An n-type contact layer 101 made of Si-doped GaN is grown to a thickness of 4 μm using ₄ (silane) gas.
The n-type contact layer 101 is made of In _X Al _Y Ga _1-XY N (0
≦ X, 0 ≦ Y, X + Y ≦ 1), especially G
aN, InGaN, GaN doped with Si among them
With such a constitution, an n-type layer having a high carrier concentration can be obtained and preferable ohmic contact with the negative electrode can be obtained, so that the threshold current of the laser element can be reduced. The material of the negative electrode is Al, Ti, W, Cu, Z
A metal or an alloy such as n, Sn, or In provides a preferable ohmic contact.

Next, the temperature is set to 750 ° C., TMG, TMI (trimethylindium) and ammonia are used as source gases, and silane gas is used as an impurity gas.
A crack prevention layer of 1 Ga 0.9 N is grown to a thickness of 500 Å. The crack prevention layer is grown from an n-type nitride semiconductor containing In, preferably InGaN, so that the n-type optical confinement layer 102 made from a nitride semiconductor containing Al to be grown next can be grown as a thick film. Therefore, it is very preferable. In the case of LD, the layer serving as the optical confinement layer and the optical guide layer is,
It is necessary to grow with the above film thickness. Traditionally GaN,
When a thick film of AlGaN is grown directly on the AlGaN layer, it is difficult to fabricate the device because cracks are likely to occur in the AlGaN grown later, but this crack prevention layer is the optical confinement layer to be grown next. It is possible to prevent cracks from entering. This crack prevention layer is 10
It is preferable to grow the film with a thickness of 0 angstrom or more and 0.5 μm or less. If the thickness is less than 100 Å, it is difficult to prevent cracks as described above,
If it is thicker than 0.5 μm, the crystal itself tends to turn black. The crack prevention layer is also not shown because it can be omitted depending on the growth method, the growth apparatus, etc.

Next, using TEG, TMA (trimethylaluminum), ammonia as a raw material gas, and silane gas as an impurity gas, an n-type optical confinement layer 102 made of Si-doped n-type Al0.3Ga0.7N having a thickness of 0.5 μm is formed. Grow thick. The n-type optical confinement layer 102 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). ,
It is possible to obtain a crystal having good crystallinity, and it is effective for confining the laser light in the vertical direction by increasing the refractive index difference from the active layer.
It is usually desirable to grow this layer to a film thickness of 0.1 μm to 1 μm. If it is thinner than 0.1 μm, it is difficult to act as an optical confinement layer. If it is thicker than 1 μm, even AlGaN grown on the crack prevention layer tends to have cracks in the crystal, which makes it difficult to form an element. is there.

Then, TMG, ammonia, and
Si-doped n-type GaN using silane gas as an impurity gas
The n-type light guide layer 103 is made to grow to a film thickness of 500 angstroms. The n-type light guide layer 103 is In
N-type nitride semiconductor containing n or n-type GaN, preferably ternary mixed crystal or binary mixed crystal of In _X Ga _1-X N (0 ≦
X ≦ 1). It is usually desirable to grow this layer to a film thickness of 100 Å to 1 μm.
By using GaN or GaN, the next active layer 104 can be easily formed into a quantum structure. In the present invention, the n-type contact layer 101, the crack prevention layer, the n-type optical confinement layer 102, and the n-type optical guide layer 103 are all included in the n-type cladding layer in the claims.

Next, TMG, TMI, and ammonium are used as source gases.
The active layer 104 was grown by using. Active layer
Hold at 750 ℃, first undoped In0.2Ga0.8N
A well layer consisting of 25 angstroms
Let Next, change the TMI molar ratio to the same temperature.
A barrier layer made of non-doped In0.01Ga0.95N.
It is grown to a film thickness of 0 angstrom. This operation 1
Repeat 3 times, and finally grow the well layer to a total film thickness of 0.1μ
an active layer 1104 having a multi-quantum well structure with a thickness of m
I grew it. The active layer 104 is a nitride semiconductor containing In.
Composed of, preferably, ternary mixed crystal In _XGa_1-XN (0 <X
<1) is desirable. Ternary mixed crystal InGaN
It is possible to obtain a crystal with better crystallinity than the quaternary mixed crystal.
Thus, the light emission output is improved. Among them, especially preferred is
In layer_XGa_1-XWell layer made of N and more than well layer
A barrier layer made of a nitride semiconductor with a large band gap
Multi-quantum well structure (MQW: Multi-quantum-)
well). Similarly, for the barrier layer, ternary mixed crystal In_{X '}Ga
_{1-X '}N (0 ≦ X ′ <1, X ′ <X) is preferable, for example, well
+ Barrier + well + ... + barrier + well layer (or vice versa)
To form a multiple quantum well structure. This
If the active layer is MQW in which InGaN is laminated,
High output power between about 365 nm and 660 nm due to emission between child levels
LD can be realized. Furthermore, on the well layer
When InGaN barrier layers are stacked, InGaN
The barrier layer has a crystal structure that is higher than that of GaN and AlGaN crystals.
soft. Therefore, increase the AlGaN thickness of the cladding layer.
Therefore, laser oscillation can be realized. Furthermore, InG
The crystal growth temperature is different between aN and GaN. For example, M
InGaN grows at 600 ° C to 800 ° C by OVPE method
In contrast, GaN is grown at temperatures above 800 ° C.
Make it longer. Therefore, a well layer made of InGaN is grown.
And then try to grow a barrier layer of GaN.
For example, it is necessary to raise the growth temperature. Raise the growth temperature
Then, the InGaN well layer grown earlier decomposes.
Therefore, it is difficult to obtain a well layer with good crystallinity. further
The thickness of the well layer is only tens of angstroms,
When the well layer is decomposed, it becomes difficult to produce the MQW.
On the other hand, in the present invention, the barrier layer is also InGaN.
Therefore, the well layer and the barrier layer can be grown at the same temperature. Therefore,
Since the well layer formed earlier does not decompose,
A good MQW can be formed. This is the best of MQW
Although the preferred embodiment is also shown, in addition to the well layer,
nGaN, well layer such as GaN and AlGaN for barrier layer
The bandgap energy of the barrier layer
Any composition may be used. In addition, this active layer 104 is simply
A single quantum well structure composed of only one well layer is acceptable.
Yes.

After the growth of the active layer 104, the temperature is set to 1050 ° C., TMG, TMA, ammonia, and Cp 2 Mg (cyclopentadienyl magnesium) as an acceptor impurity source are used, and a p-type cap made of Mg-doped p-type Al 0.2 Ga 0.8 N is used. The layer was grown to a thickness of 100 Å. 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 acts as a cap layer for preventing decomposition of the active layer made of InGaN. By growing a p-type nitride layer containing Al, preferably a p-type cap layer made of Al _Y Ga _{1 -Y} N (0 <Y <1) on the active layer, the light emission output is significantly improved. If the film thickness of this p-type cap layer is thicker than 1 μm, the layer itself tends to be cracked, and it tends to be difficult to manufacture an element. Since this p-type cap layer can be omitted depending on the growing method, the growing apparatus, etc., it is not particularly shown.

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 105 made of aN is grown to a film thickness of 500 angstrom. The p-type light guide layer 105 is also
A p-type nitride semiconductor containing In or p-type GaN, preferably a binary mixed crystal or a ternary mixed crystal of In _X Ga _{1 -X} N (0
≦ X ≦ 1) is grown. It is desirable that the optical guide layer is usually grown to a film thickness of 100 angstrom to 1 μm. In particular, when it is made of InGaN or GaN, the next p-type optical confinement layer 106 can be grown with good crystallinity.

Subsequently, TMG, TMA, ammonia and C
A p-type optical confinement layer 106 made of Mg-doped Al0.3Ga0.7N is grown to a thickness of 100 angstroms using p2Mg. p-type optical confinement layer 106
Is then regrown after the current blocking layer is grown. FIG. 4 shows a cross-sectional structure of a wafer grown up to the p-type optical confinement layer 106. The p-type optical confinement layer 106 is composed 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). By doing so, a material having good crystallinity can be obtained. The p-type light confinement layer has a thickness of 0.1 μm to 1 μm, like the n-type light confinement layer.
It is desirable to grow the AlN-containing film such that the p-type nitride semiconductor contains Al such as AlGaN to increase the difference in the refractive index from the active layer, which is effective as an optical confinement layer in the vertical direction of laser light. Act on.

(Step of Producing Active Layer Having Striped Oscillation Region) After the growth of the p-type optical confinement layer 106, the wafer is taken out of the reaction container, and the surface of the optical confinement layer 106 is striped by photolithography. A first protective film 300 made of SiO _{2 and having a} width of 5 μm is formed. After forming the first protective film 300, as shown in FIG. 5, etching is performed from the p-type light confinement layer 106 to the n-type light confinement layer 102 using a RIE (reactive ion etching) device to form a stripe shape. An active layer having an oscillation region is manufactured. The etching depth is stopped when the n-type optical confinement layer 102 is etched to a depth of 200 angstroms after passing through the n-type optical guide layer 103. Note that FIG. 5 is a cross-sectional view when the wafer is cut in a direction perpendicular to the stripe.

After the etching is completed, the first protective film 300 is removed, a second protective film 301 made of SiO 2 is newly formed on the surface of the uppermost p-type optical confinement layer 106, and then the wafer is reacted again. A current blocking layer is formed on the exposed surface of the n-type optical confinement layer 102 after being transferred into the container.

(Step of Forming Current Blocking Layer) After the wafer is placed in the reaction vessel again, TMG and TM are added to the source gas.
A, Ammonia, Cp2Mg as impurity gas, 10
A first current blocking layer 201 made of Mg-doped p-type Al0.01Ga0.95N is grown at 50 ° C. to a film thickness of 600 Å. The first current blocking layer 201 may also be i-type Al _Y Ga _{1 -Y} N. Z for i-type
If p-type impurities such as n and Cd are doped to the extent that n conductivity is compensated, or if the Al mixed crystal ratio is set to 0.4 or more, for example, i-type is likely to occur.

Then, while maintaining the temperature at 1050 ° C., the flow rate of TMA was increased and DEZ (diethyl zinc) was used as the source gas instead of Cp 2 Mg, and Zn-doped i
A third current blocking layer 203 of type Al0.3Ga0.7N is grown to a film thickness of 0.15 μm.

Then, using TMG, TMA, ammonia as a source gas and silane gas as an impurity gas, Si-doped n
A second current blocking layer 202 of type Al0.3Ga0.7N is grown to a thickness of 600 Å. FIG. 6 shows a cross-sectional view of a wafer on which the current blocking layers 201, 203 and 202 are grown so as to have a p-i-n laminated structure as described above. In this way, the current blocking layer is selectively grown on the surface of the n-type optical confinement layer 102. The current blocking layer made of a nitride semiconductor hardly grows on the second protective film 301 made of SiO ₂ . As the protective film having such a property of selective growth, for example, silicon nitride (Si _X N _Y ) can be used.

In this embodiment, the current blocking layer is formed on the surface of the n-type optical confinement layer 102. However, the current blocking layer can be formed on the surface of the n-type contact layer 101 or n by adjusting the etching depth. It may be formed from the surface of the mold light guide layer 103, and the type of the clad layer is not particularly limited. Furthermore, the current blocking layer is made of the same material as in the present embodiment.
The structure does not have to be a layer structure, and may be a one-layer structure or a two-layer structure as long as both side surfaces of the stripe-shaped active layer can be sandwiched.
Also, a structure having three or more layers may be used.

(Step of re-growing clad layer) After the growth of the current blocking layer, the wafer is taken out from the reaction vessel, the second protective film 301 is removed, and then the wafer is transferred to the reaction vessel again. Next, at 1050 ° C, TMG, TMA, ammonia, Cp2M
g, and the p-type optical confinement layer 106 that was stopped halfway
Growth of Mg-doped p-type Al0.3Ga0.7N
The total thickness of the light confinement layer 106 made of 0.1
Grow with a film thickness of μm. By this growth, the p-type light confinement layer 106 is continuously formed on both surfaces of the stripe-shaped p-type light confinement layer that has been grown halfway and the n-type current blocking layer 202. Further particularly advantageous in this step is to grow a light confinement layer having the same composition as the p-type light confinement layer grown halfway.
When a layer having the same composition is grown, the crystal can be grown without distortion between crystals, so that a crystal with a very good film quality can be grown.

Next, a p-type contact layer 107 made of Mg-doped p-type GaN is grown to a film thickness of 0.5 μm. p
The type contact layer 107 is a p-type In _X Al _Y Ga _1-XY N
(0 ≦ X, 0 ≦ Y, X + Y ≦ 1), particularly InGaN, GaN, and Mg-doped p
When the type GaN is used, a p-type layer having the highest carrier concentration can be obtained, good ohmic contact with the positive electrode can be obtained, and the threshold current can be reduced. As a material for the positive electrode, a metal or alloy having a relatively high work function such as Ni, Pd, Ir, Rh, Pt, Ag, and Au is likely to be ohmic.

After taking out the wafer in which the nitride semiconductors are laminated as described above from the reaction container, selective etching is performed from the uppermost p-type contact layer 107 by a reactive ion etching (RIE) apparatus to form a negative electrode. N should form
The plane of the mold contact layer 101 is exposed. Next, the positive electrode 10 is formed on substantially the entire surface of the uppermost p-type contact layer 107, and the striped negative electrode 11 parallel to the oscillation region of the active layer is formed on the exposed n-type contact layer 101. In the present invention, the p-type cap layer and the p-type light guide layer 1 are used.
05, the p-type optical confinement layer 106, and the p-type contact layer 107 are all included in the p-type cladding layer of the claims.

After forming the electrodes, the wafer is transferred to a polishing apparatus, the substrate is polished to a thickness of 80 μm to be thin, and then the wafer is cleaved in a direction perpendicular to the stripe electrodes to form a resonance surface. A resonator is formed by forming a reflecting mirror made of a dielectric multilayer film on the cleaved surface using a sputtering device. Further, the wafer is diced in a direction parallel to the striped negative electrode 11 to form a laser chip having a cavity length of 500 μm. FIG. 8 is a sectional view showing the structure of this laser chip. When the chip obtained as described above was placed on a heat sink to form a laser device, the threshold current was 0.1 A DC, and continuous oscillation of 410 nm was exhibited.

[0037]

As described above, in the present invention, both sides of the stripe of the active layer having the stripe-shaped oscillation region are
Since it is sandwiched between current blocking layers made of a nitride semiconductor whose refractive index is smaller than that of the active layer whose refractive index is small, light in the lateral direction of the laser is confined and the laser becomes a single mode, and the oscillation threshold value decreases. . Further, since the clad layers sandwiching the active layer are larger than the stripe width of the active layer, the positive electrode can be formed especially on almost the entire surface of the p-type contact layer. For this reason, the current density of the contact layer can also be reduced, so that the threshold value can be lowered, and continuous oscillation at room temperature will be possible in the near future. As described above, according to the present invention, it is possible to realize a practical index guided laser device for the first time in a nitride semiconductor, and in order to realize a short wavelength semiconductor laser, its industrial utility value is very large.

[Brief description of drawings]

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

FIG. 2 is a schematic cross-sectional view showing the structure of one laser element according to the present invention.

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

FIG. 4 is a schematic cross-sectional view showing the structure of a wafer for explaining one step of an example.

FIG. 5 is a schematic cross-sectional view showing the structure of a wafer for explaining one step of an example.

FIG. 6 is a schematic cross-sectional view showing the structure of a wafer for explaining one step of an example.

FIG. 7 is a schematic cross-sectional view showing the structure of a wafer for explaining one step of an example.

FIG. 8 is a schematic cross-sectional view showing the structure of one laser device according to the present invention.

[Explanation of symbols] 1 ... Substrate 2 ... n-type contact layer 3 ... n-type clad layer 4 ... Active layer 5 ... p-type cladding layer 6 ... p-type contact layer 10 ... Positive electrode 11 ... Negative electrode 20, 31, 32, 41, 42, 43 ... Current blocking layer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-2-219090 (JP, A) JP-A-6-152072 (JP, A) JP-A-2-283085 (JP, A) JP-A-7- 162090 (JP, A) JP 61-164287 (JP, A) JP 3-276688 (JP, A) JP 6-268259 (JP, A) JP 6-334259 (JP, A) JP-A-5-267780 (JP, A) JP-A-4-213878 (JP, A) JP-A-5-327126 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (5)

(57) [Claims] 1. An active layer having a striped oscillation region having a width narrower than those of the clad layers is provided between the n-type clad layer and the p-type clad layer, and both side surfaces of the stripe of the active layer are provided. Has a smaller refractive index than the active layer ,
Also includes AlyGa1-yN (0≤y≤1)
A current blocking layer having a layer , the current blocking layer having a first current blocking layer on the side closer to the n-type cladding layer and a second current blocking layer on the side closer to the p-type cladding layer. A plurality of laminated films having at least a two-layer structure including a blocking layer
And the plurality of laminated films are composed of layers having different compositions.
The nitride semiconductor laser device characterized in that is. 2. A third current blocking layer having a film thickness between the first current blocking layer and the second current blocking layer which is substantially equal to or larger than that of the active layer. The nitride semiconductor laser device according to claim 1, further comprising: 3. The active layer has a multiple quantum well structure and has a nitride semiconductor layer made of at least InxGa1-xN (0 <x <1). Nitride semiconductor laser device. 4. The current blocking layer includes an i-type layer at least in a state of being doped with p-type impurities or in a non-doped state, according to claim 1. Nitride semiconductor laser device. 5. The first current blocking layer is p-type or i-type.
5. The nitride semiconductor laser element according to claim 1, wherein the second current blocking layer is an n-type or an i-type.