JP2000049410A - Nitride semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser device of a long service life provided with high reliability. SOLUTION: In this device 100, protective layers 20a and 20b provided on the laser end face of a nitride semiconductor laser diode 10 are composed of Al1-x-y-zGaxInyBzN (0<=x,y,z<=1 and 0<=x+y+z<=1) transparent to light oscillated by the nitride laser diode 10. Also, at the time of defining the refractive index of the protective layers 20a and 20b as (n) and the wavelength of the light oscillated by the nitride laser diode 10 as λ, it is desirable that the thickness of the protective layers 20a and 20b is the integral multiple of λ/2n.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor laser device.

[0002]

2. Description of the Related Art A semiconductor laser device using a nitride semiconductor such as GaN, InN, or AlN can emit light from green to blue, and is expected as a light source for a high-density optical disk device. Here, the prior art will be described using a blue nitride semiconductor laser device as an example.

FIG. 11 shows a conventional nitride semiconductor laser device 6.
00 is shown. In the nitride semiconductor laser device 600,
An electrode forming layer 62 (including a lower portion 62a and an upper portion 62b) made of n-type GaN on a sapphire substrate 61;
aAlN cladding layer 63, InGaN / GaN
, A multiple quantum well active layer (hereinafter, referred to as MQW active layer) 64 composed of p-type GaAlN,
An electrode forming layer 66 made of type GaN is sequentially provided. On the lower electrode forming layer 62a, an n-type electrode (hereinafter referred to as an n-type electrode) 67 made of a laminate of Ti / Al is provided.
On the electrode formation layer 66, a p / p layer made of a Ni / Au laminate is used.
A mold-side electrode (hereinafter, referred to as a p-type electrode) 68 is formed, and a laser diode (also referred to as a laser element or a cavity) 60 is obtained. A protection layer 69 made of SiO ₂ or SiN is provided on both end faces (hereinafter, referred to as laser end faces) of the laser diode 60 that emits or reflects laser light. By providing this protective layer 69, deterioration of the laser end faces on both sides is prevented. Here, SiO ₂ or SiN does not need to be a compound having exactly this stoichiometric ratio, and it is sufficient that SiO ₂ or SiN has substantially the same specific resistance (insulating property) and refractive index as SiO ₂ or SiN.

The conventional nitride semiconductor laser device 600 is manufactured by the following manufacturing method. First, an electrode forming layer 62, a cladding layer 63, an MQW active layer 64, a cladding layer 65, and an electrode forming layer 66 are sequentially grown on a sapphire substrate 61 by crystal growth. Then, the lower electrode forming layer 62 is etched by etching a part of the electrode forming layer 66 to the middle of the electrode forming layer 62.
Expose a. An n-type electrode 67 is formed on the exposed electrode forming layer 62a, and a p-type electrode 68 is formed on the electrode forming layer 66 by vapor deposition. Then, on both sides of the laser,
The protective layer 69 is formed by a sputtering method or an electron beam (EB) evaporation method.

Another conventional nitride semiconductor laser device 700
Are shown in FIGS. 12A and 12B. Semiconductor laser device 7
00, as shown in FIGS. 12A and 12B, a sapphire substrate 72 was used as a substrate, and an n-type GaAl
N cladding layer 73, InGaN / GaN MQW active layer 74, p-type GaAlN cladding layer 75, p-type GaN
Of the electrode forming layer 76 is sequentially crystal-grown. A Ni / Au electrode 77 is formed on the front surface, and a Ti / Al electrode 71 is formed on the back surface, whereby a laser diode 70 is obtained.
To reduce the operating current of the laser diode 70,
On the rear end face (rear face) of the laser diode 70, Si
A reflection layer 90 is provided in which four pairs of O ₂ layers 91 and TiO ₂ layers 92 are formed alternately with a thickness of λ / 4n (n is the refractive index of each layer). Is provided with a protective layer 80 of SiO _{2 with} a thickness of λ / 2n (n is the refractive index of the protective layer), and oscillated light is extracted from the front surface. Here, λ is the oscillation wavelength of the laser diode 70. The front protective layer 80 and the rear reflective layer 90 are deposited by a sputtering method or an electron beam evaporation method.

By providing the reflective layer 90 on the rear surface, the reflectivity of the rear surface becomes about 98%, and most of the oscillated light can be taken out from the front surface.
The operating current can be reduced to about 70% as compared with the case where only the O ₂ protective layer is formed.

[0007]

However, the conventional nitride semiconductor laser devices 600 and 700 described above
There is a problem that the service life, especially at high output, is short.
The inventor of the present application has found that the cause of the short life of the nitride semiconductor laser device is as follows.

(1) While the laser diodes 60 and 70 are composed of a plurality of crystal layers, the protective layers 69 formed on the end faces of the laser diodes 60 and 70
Since the reflection layer 80 and the reflection layer 90 are formed of SiO ₂ or TiO ₂ , the laser diode is an amorphous layer, and the length of a bond (for example, Si—O) of a material constituting the amorphous layer is included in the laser diode. Since the crystal layer and the lattice constant are different, lattice mismatch occurs at these interfaces, and lattice defects occur in the crystal layer (especially in the MQW active layer). If the protective layers 69 and 80 and the reflective layer 90 are formed on the laser end face by sputtering or electron beam evaporation, material particles scattered from the target collide with the laser end face with relatively high energy. It is considered that the laser end face is damaged by this, and as a result, a phenomenon that lattice defects occur in the crystal layers constituting the laser diodes 60 and 70 is occurring.

(2) Thermal expansion coefficients of a plurality of crystal layers constituting laser diodes 60 and 70, protective layers 69 and 80
Since the thermal expansion coefficients of the reflective layer 90 and the protective layer 69 and 80 and the reflective layer 90 are different, the crystal layer (particularly the MQW active layer) ), And crystal defects occur or increase. For example, the coefficient of thermal expansion (3.15 × 10 ⁻⁶ K ⁻¹ ) of the MQW active layer 64 and the coefficient of thermal expansion (1.6 × 10 ⁻⁷ K ⁻¹ ) of the protective layer 69 are significantly different.

The present invention has been made in view of the above problems, and has as its object to provide a highly reliable nitride semiconductor laser device having a longer life than conventional ones.

[0011]

The nitride semiconductor laser of the present invention is provided.
The laser device includes a nitride semiconductor laser diode and the nitride semiconductor laser diode.
Provided on the laser end face of the nitride semiconductor laser diode
A protective layer, wherein the protective layer is formed of the nitride laser die.
Al that is transparent to the light that oscillates_{1- xyz}G
a_xIn_yB_zN (0 ≦ x, y, z ≦ 1, and 0 ≦ x +
y + z ≦ 1), which achieves the above purpose.
Is done.

When the refractive index of the protective layer is n and the wavelength of light emitted by the nitride laser diode is λ, the thickness of the protective layer may be an integral multiple of λ / 2n.

[0013] The nitride semiconductor laser diode may have an I
It is preferable to have a configuration having a multiple quantum well active layer composed of n _u Ga _1-u N / In _v Ga _1-v N (0 ≦ u, v ≦ 1).

The protective layer is formed by MO-CVD or MB.
It is preferably formed by the E method.

[0015] The semiconductor device may further include a reflective layer in contact with the protective layer, the reflective layer reflecting light emitted by the nitride laser diode.

The reflection layer has a first refractive index different from each other.
And a second layer may be alternately stacked.

Assuming that the refractive index of the first layer is n ₁ , the refractive index of the second layer is n ₂ , and the wavelength of light oscillated by the nitride laser diode is λ, the first layer and the second layer The thickness may satisfy the relationship of λ / 4n ₁ and λ / 4n ₂ , respectively.

The thickness of the protective layer may be an integral multiple of λ / 2n, where n is the refractive index of the protective layer and λ is the wavelength of light emitted by the nitride laser diode. Good.

The thickness of the protective layer may be λ / 4n, where n is the refractive index of the protective layer and λ is the wavelength of light oscillated by the nitride laser diode.

The protective layer is made of GaN, and the first and second layers are transparent to light emitted from SiO ₂ and TiO ₂ or the nitride laser diode, respectively, and have a refractive index. Two different types of Al
_{1-abc Ga a In b B} c N (0 ≦ a, b, c ≦ 1, and,
0 ≦ a + b + c ≦ 1).

A third layer is further provided between the first and second layers, wherein the first, second and third layers are crystal layers, and the first and third layers are It is preferable that a difference in lattice constant between the first layer and the second layer is smaller than a difference in lattice constant between the first layer and the second layer.

The protective layer is a GaN layer, and the reflective layer comprising the first layer / third layer / second layer is GaN / AlG
A configuration having an aN / AlN laminated structure may be adopted.

The protective layer and the reflective layer are made of MO-C
It is preferably formed by the VD method or the MBE method.

The protective layer provided on the laser end face of the nitride semiconductor laser diode of the nitride semiconductor laser device of the present invention is made of Al _1-xyz Ga _x In _y which is transparent to light emitted by the nitride laser diode. since consist B _z N, it is possible to take a sufficient lattice matched with a nitride semiconductor laser diode. Therefore, it is possible to suppress the occurrence of defects in the nitride semiconductor laser diode, particularly in the active layer, and to extend the life of the nitride semiconductor laser device. Furthermore, since the thermal expansion coefficients of the protective layer and the nitride semiconductor laser diode can be matched, the occurrence of defects due to thermal stress can be suppressed. Further, when the protective layer is deposited on the end face of the nitride semiconductor laser diode by using the MO-CVD method or the MBE method, it is possible to prevent the end face of the laser diode from being damaged in the step of depositing the protective layer. By providing a reflective layer on the protective layer, the reflectance can be increased.

[0025]

(Embodiment 1) FIG. 1 shows a blue nitride semiconductor laser device 100 according to an embodiment of the present invention.
It is a perspective view of.

The nitride semiconductor laser device 100 has a nitride semiconductor laser diode 10 and protective layers 20a and 20b made of GaN formed on both end faces of the laser. GaN protective layers 20a and 20b
Is transparent to the light oscillated by the nitride semiconductor laser diode 10. That is, the protective layers 20a and 20a
GaN forming b has a band gap larger than the light energy of light oscillated by the nitride semiconductor laser diode 10. The semiconductor material forming the protective layers 20a and 20b is not limited to GaN, and may be any material as long as it is transparent to the light oscillated by the nitride semiconductor laser diode 10.

The nitride semiconductor laser diode 10 has the following structure. An n-type electrode 11 made of a Ti / Al laminate is provided under a substrate 12 made of n-type GaN. On the substrate 12, Si-doped n-type Ga
Cladding layer 13 made of _0.9 Al _0.1 N, undoped I
MQW active layer 14 made of a laminate of n _0.02 Ga _0.98 N / In _0.15 Ga _0.85 N, Mg-doped p-type Ga _0.9 Al _0.1
A cladding layer 15 made of N, an electrode forming layer 16 made of Mg-doped p-type GaN, and a p-type electrode 17 made of a Ni / Au laminate are sequentially provided. Further, protective layers 20a and 20b made of GaN are provided on both end faces of the nitride semiconductor laser diode 10.

Next, a method of manufacturing the blue nitride semiconductor laser device will be described with reference to FIGS. 2A, 2B, 2C and 2D.

As shown in FIG. 2A, a metal organic chemical vapor deposition (hereinafter referred to as MO) is formed on a substrate 12 made of n-type GaN.
Each semiconductor layer is crystal-grown by -CVD method).

First, at a growth temperature of about 1050 ° C., a cladding layer 13 made of Si-doped n-type Ga _0.9 Al _0.1 N is deposited to a thickness of about 0.5 μm. Next, the growth temperature is lowered to about 800 ° C., and undoped In _0.02 Ga _0.98 N / In _0.15 Ga
_The MQW active layer 14 composed of a _0.85 N stacked body is
m (the thickness of each layer is about 5 nm). The growth temperature is again increased to about 1050 ° C., and Mg-doped p-type Ga _0.9
After depositing the cladding layer 15 of Al _0.1 N to a thickness of about 0.5 μm, an electrode forming layer 16 of Mg-doped p-type GaN is deposited to a thickness of about 1 μm at a growth temperature of about 1050 ° C.

Next, as shown in FIG. 2B, the substrate 12 is polished so that the entire thickness from the substrate 12 to the electrode forming layer 16 becomes about 150 μm. Thereafter, a p-type electrode 17 made of a Ni / Au laminate is placed on the electrode forming layer 16 by the substrate 1.
An n-type electrode 11 made of a laminate of Ti / Al is formed underneath 2 by an evaporation method. By cleaving or dry-etching the obtained laminate, about 500 μm
nitride semiconductor laser diode 1 having a width of m
0 'is obtained.

Next, as shown in FIG. 2C, GaN is provided on the laser end faces on both sides of the nitride semiconductor laser diode 10 '.
Protective layers 20a and 20b having a thickness of about 0.16
It is formed to have a thickness of μm. Protective layers 20a and 20b
Is formed at a temperature of about 1000 ° C. using the MO-CVD method. Since the protective layers 20a and 20b are formed by the MO-CVD method, the material particles having high kinetic energy do not collide with the laser end face, so that the laser end face is not damaged. Therefore, in the step of depositing the protective layers 20a and 20b, no lattice defect occurs in the crystal grown on the substrate 12. Protective layer 2
The same effect can be obtained when molecular beam epitaxial growth (hereinafter referred to as MBE) is used for 0a and 20b instead of MO-CVD.

The coefficient of thermal expansion of GaN forming the protective layers 20a and 20b is 3.17 × 10 ⁻⁶ K ⁻¹ ,
The thermal expansion coefficient of the MQW active layer 14 (3.15 × 10
^-6 K ^-1 ), so that distortion due to thermal stress hardly occurs between the MQW active layer 14 and the protective layers 20 a and 20 b when cooled to room temperature or during operation.

The thicknesses of the protective layers 20a and 20b are such that the refractive index n of GaN is 2.6 and the laser oscillation wavelength λ is 4
Although 20 nm is set to twice λ / 2n = 0.08 μm, that is, 0.16 μm, it may be set to an integral multiple of λ / 2n. By setting the thickness of the protective layers 20a and 20b to an integral multiple of λ / 2n,
As in the case where a and 20b are not formed, the laser oscillation characteristics can be kept unchanged. From the viewpoint of productivity, the thickness of the protective layers 20a and 20b is λ
/ 2n or λ / n.

Finally, as shown in FIG. 2D, the nitride semiconductor laser device 100 is completed by cutting at a predetermined pitch (for example, about 400 μm) to obtain a predetermined size of the nitride semiconductor laser diode 10.

In the above embodiment, the forbidden band width of the protective layers 20a and 20b made of GaN provided on the laser end face is 3.45 eV, and the energy of the laser light (oscillation wavelength 420 nm) emitted from the MQW active layer 14 (2.95 eV), so that the laser light is not absorbed by the protective layers 20a and 20b but is entirely transmitted. In addition, since the protective layers 20a and 20b are grown undoped, the specific resistance of the protective layers 20a and 20b is 10 ⁹ Ω · cm or more, and almost no leak current flows through the protective layers 20a and 20b.

FIG. 3 shows a blue nitride semiconductor laser device 100 according to the present embodiment and the conventional SiO ₂ semiconductor device shown in FIG.
Semiconductor laser device 600 using protective layer made of
Is the result of a life test, and the rate of change of operating current (△ IOP)
Shows the change with time. The straight line E1 is the result of the nitride semiconductor laser device 100 according to the first embodiment, and the curve C
1 shows the result of the conventional nitride semiconductor laser device 600. In the life test, the ambient temperature was 50 ° C and the oscillation wavelength was 420 n
m and the operating current was controlled so that the laser output was constant at 50 mW.

FIG. 3 shows that the change rate of the operating current of the nitride semiconductor laser device 100 according to the first embodiment does not change even after 10,000 hours, and it is not deteriorated.
On the other hand, in the conventional nitride semiconductor laser device 600, when the operation time exceeds 500 hours, the rate of change of the operation current sharply increases and deteriorates. It can be seen that the life of the nitride semiconductor laser device 100 of the first embodiment is about 20 times or more as long as the life of the conventional nitride semiconductor laser device 600. From this result, it can be seen that the protective layer 20a made of GaN was used.
It is considered that the deterioration of the laser end surface is suppressed by the laser beams 20b and 20b, and a long lifetime is obtained because the lattice defects are hardly generated in the MQW active layer 14 when the protective layers 20a and 20b are deposited.

In the first embodiment, the protective layer 20a and the protective layer 20a
GaN was used as the material for
The material of 20a and 20b is Al_1-xyzGa_x
In _yB_zN (0 ≦ x, y, z ≦ 1, and 0 ≦ x + y +
z ≦ 1) can be suitably used, and these layers are
X, y, and z so that they are transparent to laser oscillation light
You can choose The material of the protective layers 20a and 20b
Using a nitride semiconductor material containing Al, In, and B
Of materials that provide good lattice matching
Matching spreads.

As described above, the protective layers 20a and 20a
As the material of b, it is preferable to use a nitride semiconductor material in order to achieve lattice matching with the crystal layer of the nitride semiconductor constituting the semiconductor laser diode. However,
Other materials may be used as long as they can be lattice-matched with the crystal layer of the nitride semiconductor constituting the semiconductor laser diode and have transparency to light emitted by the laser. Of course, as described above, it is preferable to use a material having matching thermal expansion coefficient and high electric resistance. Further, the protective layers 20a and 20b are preferably formed by MO-CVD or MBE.

As the MQW active layer 14, for example, In _u Ga _1-u N / In _v Ga _1-v N (0 ≦ u ≦ 1,0
≦ v ≦ 1) can be suitably used.
Known structures and manufacturing methods of the nitride semiconductor laser diode 10 can be widely used. Japanese Patent Application Laid-Open No. 9-219556 is incorporated herein by reference for reference.

The composition of protective layers 20a and 20b and M
As described above, the composition of the QW active layer 14 is selected so as to be transparent to the laser oscillation light, and the difference between the lattice constants of the protective layers 20a and 20b and the MQW active layer 14 is as follows. The lattice constant of the MQW active layer 14 is about 3
% Is preferably selected. When the difference between the lattice constants exceeds about 3%, the protective layers 20a and 20a
Lattice mismatch occurs at the interface between Ob and the MQW active layer 14,
Lattice defects may occur in the MQW active layer 14, and the life of the nitride semiconductor laser device may be shortened. In addition, the protective layer 2
If the thicknesses of Oa and 20b are sufficiently large, the protective layers 20a and 20b can absorb the stress, so that even if there is a lattice mismatch exceeding about 3%, the life may not be shortened.

It is preferable that the difference between the coefficient of thermal expansion of the protective layers 20a and 20b and the coefficient of thermal expansion of the MQW active layer 14 is selected to be about 20% or less of the coefficient of thermal expansion of the MQW active layer 14. .

In the above-described example, in order to increase the resistance of the protective layers 20a and 20b, MO-CVD or M
Although an undoped semiconductor layer is grown by the BE method, in order to further increase the resistance, a group V atom (for example, about 10 ¹⁵ cm ⁻³⁾ that only compensates for the vacancies of nitrogen existing in the semiconductor layer.
Arsenic or phosphorus atoms). By increasing the resistance of the protective layers 20a and 20b, it is possible to prevent a current from leaking through the protective layers 20a and 20b. The specific resistance of the protective layers 20a and 20b is preferably 10 ⁵ Ω · cm or more, and more preferably 10 ⁹ Ω · cm or more. In the first embodiment, the example in which the cladding layer and the active layer are provided on the substrate made of n-type GaN has been described. However, a substrate made of p-type GaN of opposite conductivity type is used, and the cladding made of p-type GaAlN is formed thereon. Active layer comprising an undoped InGaN / InGaN laminate, a cladding layer comprising n-type GaAlN, an electrode forming layer comprising n-type GaN, and n comprising a Ti / Al laminate
Type electrode sequentially provided, nitrides p-type electrode made of a stack of Ni / Au is provided on the lower substrate made of p-type GaN semiconductor laser _{diode, Al 1-xyz Ga x In} y
B _z N (0 ≦ x, y, z ≦ 1, and 0 ≦ x + y + z ≦
Even when the thin layer of 1) is provided, the same effect as in the first embodiment can be obtained.

In the above embodiment, the laser diode 1
Although the protective layers 20a and 20b are provided on both sides of 0, they may be provided on only one side. Further, the protective layers 20a and 20b
Is not limited to an integral multiple of λ / 2n, and the reflection layer may serve as an odd multiple of λ / 4n so as to reflect on the protective layers 20a and 20b.

The above-described variations of the material of the protective layer and the configuration of the semiconductor laser diode can be similarly applied to the following embodiments.

Embodiment 2 A nitride semiconductor laser device 200 according to Embodiment 2 of the present invention will be described with reference to FIGS. 4A and 4B. FIG. 4A is a perspective view of a nitride semiconductor laser device 200 according to the second embodiment, and FIG.
It is sectional drawing along the B-4B 'line.

Second Embodiment Nitride Semiconductor Laser Device 20
0 is outside the protective layer 20b formed on the rear surface of the semiconductor laser diode 10 of the first embodiment,
a and the semiconductor laser diode 1
0 has a thickness of about 0.08 μm provided on the front (output surface) side, and the protective layer 20b provided on the rear surface
Is different from the nitride semiconductor laser 100 of the first embodiment in that the thickness is about 0.16 μm. Other configurations of the nitride semiconductor laser device 200
Since the configuration is substantially the same as that of 00, components having substantially the same function are denoted by the same reference numerals, and detailed description thereof will be omitted.

Reflective layer 3 of nitride semiconductor laser device 200
0a is the AlN layer 31 (thickness:
About 0.05 μm) / GaN layer 32 (thickness: about 0.04 μm)
m) has a structure in which eight pairs of two types of nitride semiconductor layers having different refractive indexes are alternately stacked. The thickness of each of these nitride semiconductor layers 31 and 32 is λ / 4n with respect to laser oscillation light (eg, λ = 420 nm).
(N: refractive index of each layer), whereby the reflectance of the rear surface is about 93%. Also,
Since these nitride semiconductor layers 31 and 32 are undoped semiconductor layers, their specific resistance is 10 ⁹ Ω · cm or more,
There is no fear that a leak current flows through these nitride semiconductor layers 31 and 32.

The nitride semiconductor laser device 200 is manufactured as follows.

As in Embodiment 1, a semiconductor laser diode 10 'is formed as shown in FIG. 2B.

On the rear surface of the obtained semiconductor laser diode 10 ′, a protective layer 20 b made of GaN is formed to a thickness of about 0.16 μm as in the first embodiment. The formation of the protective layer 20b is performed at 1000 ° C., which is slightly lower than the growth temperature of the semiconductor laser diode (double hetero structure), using the MO-CVD method. This thickness is the refractive index n of GaN.
= 2.6, and a thickness twice as large as λ / 2n = 0.08 μm obtained as a laser oscillation wavelength λ = 420 nm. The thickness of the protective layer 20b may not be so strict. This is because the interface between the AlN layer 31 grown on the protective layer 20b and the protective layer 20b is the cavity surface, so that the cavity length is only increased by the thickness of the protective layer 20b, and the laser oscillation characteristics such as operating current and the like are increased. Is hardly affected.

Next, an AlN layer 31 (thickness: about 0.05 μm) / GaN layer 32 (thickness: about 0.0 μm) is formed on the protective layer 20b.
Eight pairs of two types of nitride semiconductor layers (4 μm) are alternately deposited to form the reflective layer 30a. AlN layer 31 and Ga
The thickness of the N layer 32 is λ / 4n with respect to the oscillation wavelength λ = 420 nm, where n is the refractive index of each (AlN has a refractive index of 2.0 and GaN has a refractive index of 2.6). ing. By providing the reflective layer 30a, the reflectivity on the rear surface of the semiconductor laser diode 10 'becomes about 93%. Also, since the AlN layer 31 and the GaN layer 32 are grown in an undoped state, their specific resistances are 10
⁹ Ω · cm or more, AlN layer 31 and GaN layer 32
There is no worry about leakage current flowing through the layer.

Subsequently, on the front surface of the semiconductor laser diode 10 ′, a protective layer 20 made of GaN is formed as in the first embodiment.
a is formed. Here, the thickness of the protective layer 20a is λ
/ 2n, that is, 0.08 μm. The order of depositing the protective layer 20b and the reflective layer 30a on the rear surface of the semiconductor laser diode 10 'and the order of depositing the protective layer 20a on the front surface of the semiconductor laser diode 10' may be reversed.

The nitride semiconductor laser device 200 of the second embodiment is completed by cleaving the obtained laminated body at a pitch of, for example, about 400 μm in the same manner as in the first embodiment to obtain a predetermined size of the semiconductor laser diode 10. I do.

In the second embodiment, the effect of extending the life of the semiconductor laser device can be obtained as in the first embodiment.
Further, a high reflectance is obtained.

When a nitride semiconductor material is used as the material of the reflective layer 30a, the protective layer 20 of the first embodiment is used.
As with the materials a and 20b, various nitride semiconductor materials can be used. In particular, Al _1-xyz Ga _x In
_y B _z N (0 ≦ x, y, z ≦ 1, and 0 ≦ x + y + z ≦
1) can be suitably used, and x, y and z may be selected so that this layer is transparent to laser oscillation light. This is the same for the following embodiments.

(Embodiment 3) FIG. 5 is a sectional view of a nitride semiconductor laser device 300 according to Embodiment 3 of the present invention.
The configuration of the reflection layer 30b of the nitride semiconductor laser device 300 is different from that of the nitride semiconductor laser device 200 of the second embodiment. Other configurations of the nitride semiconductor laser device 300 include:
Since the nitride semiconductor laser device is the same as the nitride semiconductor laser device 200, components having substantially the same functions are denoted by the same reference numerals, and detailed description thereof will be omitted.

The nitride semiconductor laser device 300 includes a protective layer (Ga) provided on the rear surface of the semiconductor laser diode 10.
N) On the 20b, the thickness is λ / 4n (n: refractive index of each layer,
[lambda]: laser oscillation wavelength), two types of insulating layers of SiO ₂ layer 33 and TiO ₂ layer 34 are alternately laminated in five pairs to form a reflective layer 3.
0b is formed. On the front surface of the semiconductor laser diode 10, a protective layer 20a having a thickness of λ / 2n is formed.

A method for manufacturing the nitride semiconductor laser device 300 will be described. As shown in FIG. 2C, a protective layer 20b is provided on the rear surface of the semiconductor laser diode 10 'by 0.16.
The process is the same as that of the second embodiment up to the formation of a thickness of μm.

Next, the SiO ₂ layer 33 is formed on the protective layer 20b.
(Thickness: 0.07 μm) / TiO ₂ layer 34 (thickness: 0.07 μm)
Four pairs of insulating layers having different refractive indexes are formed alternately. Each of these layer thicknesses has an oscillation wavelength λ = 4
The thickness is λ / 4n with respect to 20 nm, so that the reflectance of the back surface is about 98%. These SiO ₂
Since the layer 33 / TiO ₂ layer 34 is formed on the protective layer 20b, the semiconductor laser diode 1
Since it does not directly affect the end face of the active layer 14 of 0 ′,
It may be formed using a sputtering method or an electron beam evaporation method.
However, in order to minimize damage to the crystal layer of the semiconductor laser diode 10 ′, it is preferable to grow by the MBE method.

Thereafter, a protective layer (Ga
N) 20a (thickness: 0.08 μm) is formed on the front surface of the semiconductor laser diode 10 ′. Hereinafter, a nitride semiconductor laser device 300 is obtained in the same manner as in the previous embodiment.

In the third embodiment, the effect of extending the life of the semiconductor laser device is obtained as in the first embodiment.
Even higher reflectivity is obtained.

(Embodiment 4) FIG. 6 is a sectional view of a nitride semiconductor laser device 400 according to Embodiment 4 of the present invention.
The nitride semiconductor laser device 400 differs from the nitride semiconductor laser device 200 of the second embodiment in the configuration of the protective layer 20c formed on the rear surface of the semiconductor laser diode 10.
The other configuration of the nitride semiconductor laser device 400 is the same as that of the nitride semiconductor laser device 200. Therefore, components having substantially the same functions are denoted by the same reference numerals, and detailed description thereof will be omitted.

The protective layer (GaN) 20c formed on the rear surface of the semiconductor laser diode 10 has a thickness of λ / 4n (n: refractive index of the protective layer, λ: laser oscillation wavelength). AlN layer 31 having a thickness of λ / 4n on protective layer 20c
The reflective layer 30a is formed by alternately depositing eight pairs of two types of nitride semiconductor layers, namely, a nitride semiconductor layer and a GaN layer 32. On the front surface of the semiconductor laser diode 10, a protective layer (GaN) 20a having a thickness of λ / 2n is formed.

Protective layer 2 of nitride semiconductor laser device 400
Since 0c functions as a reflective layer, the reflectance of the rear surface is higher than that of the nitride semiconductor laser device 200 of the second embodiment, and a reflectance of about 95% can be obtained. The thickness of the protective layer 20c is not limited to λ / 4n, and may be an odd multiple of λ / 4n. From the viewpoint of productivity, the thickness of the protective layer 20c is λ / 4n
It is preferred that

FIG. 7 shows nitride semiconductor laser devices 200 and 400 (E2 in FIG. 7) and 300 of the second to fourth embodiments.
(E3 in FIG. 7) and the change rate ΔI of the operating current of the conventional nitride semiconductor laser device 700 (C2 in FIG. 7) shown in FIGS. 12A and 12B at 50 ° C. and 50 mW output at 50 ° C.
The result of the time change of op (life test) is shown.

FIG. 7 shows that the nitride semiconductor laser devices 200, 400 and 300 according to the present invention are not deteriorated even after the high-power operation for 1000 hours, and the end face deterioration is suppressed by the protective layer, and at the same time, the active layer It can be seen that a long life was obtained because the introduction of defects was extremely small.

As described above, in the second to fourth embodiments, the effect of extending the life of the semiconductor laser device can be obtained as in the first embodiment, and a higher reflectance can be obtained.

(Embodiment 5) FIG. 8 is a sectional view of a nitride semiconductor laser device 500 according to Embodiment 5 of the present invention.
The nitride semiconductor laser device 500 differs from the nitride semiconductor laser device 200 of the second embodiment in the configuration of the reflection layer 40 formed on the rear surface of the semiconductor laser diode 10. The other configuration of the nitride semiconductor laser device 500 is the same as that of the nitride semiconductor laser device 200. Therefore, components having substantially the same functions are denoted by the same reference numerals, and detailed description thereof will be omitted.

The nitride semiconductor laser device 500 includes a protective layer (Ga
N) 20b on the Al _0.5 Ga _0.5 N layer 41 (0.01 μm).
m) / AlN layer 42 (0.03 μm) / Al _0.5 Ga _0.5
N layer 41 (0.01 μm) / GaN layer 43 (0.04 μm)
m) 16 pairs of the four-layer laminate are deposited. On the front surface of the semiconductor laser diode 10, a protective layer (GaN) 20a having a thickness of λ / 2n is formed.

A method for manufacturing the nitride semiconductor laser device 500 will be described. As shown in FIG. 2C, a protective layer 20b is formed on the rear surface of the semiconductor laser diode 10 ′ by 0.16 μm.
The process is the same as that of the second embodiment until it is formed to have a thickness of m.

On the protective layer 20b, an Al _0.5 Ga _0.5 N layer 41 (0.01 μm) / AlN layer 42 (0.03 μm)
A 16 layer stack of / Al _0.5 Ga _0.5 N layer 41 (0.01 μm) / GaN layer 43 (0.04 μm) is deposited by MO-CVD or MBE. These nitride semiconductor _{layers, Al 1-xyz GaxIn y B} z N (0 ≦ x,
Among y, z ≦ 1, and 0 ≦ x + y + z ≦ 1), those in which x, y, and z are selected so as to be transparent to laser oscillation light are used. In addition, it is preferable to have matching of lattice constant and thermal expansion coefficient and high electric resistance.

Al _0.5 Ga _0.5 N layer 41 / AlN layer 42 /
The thickness of each layer of the Al _0.5 Ga _0.5 N layer 41 / GaN layer 43 is λ / 20n, 3λ / 20n, λ / 20n, and λ with respect to the refractive index n of each layer and the oscillation wavelength (λ = 420 nm). / 4n. Al _0.5 Ga _0.5 N layer 41 /
May be set so that the total thickness of the AlN layer 42 / Al _0.5 Ga _0.5 N layer 41 is λ / 4n, Al _0.5 Ga _0.5
The thickness of the N layer 41 is not limited to λ / 20n. With this configuration, the reflectance on the rear surface of the laser cavity can be made 99%. In addition, since each nitride semiconductor layer constituting the reflection layer 40 is grown in an undoped state, the specific resistance of each nitride semiconductor layer is 10 ⁹ Ω · cm or more.
There is no need to worry about leakage current flowing through.

Thereafter, a protective layer (Ga
N) 20a (thickness: 0.08 μm) is formed on the front surface of the semiconductor laser diode 10 ′. Hereinafter, a nitride semiconductor laser device 500 is obtained in the same manner as in the previous embodiment.

FIG. 9 shows the calculated values of the end face reflectivity for each wavelength of the reflective layer 40. As can be seen from FIG.
It can be seen that the reflectance at the wavelength of nm is about 99%. The configuration (the number of layers) of the laminate constituting the reflective layer 40 may be appropriately set so that a necessary reflectance is obtained.

Instead of the above-described reflection layer 40, an AlN layer 42 (0.05 μm) / GaN, which is a laminate of an AlN layer 42 and a GaN layer 43 each having a thickness of λ / 4n, is used.
Even if two or more layers of the layer 43 (0.04 μm) are periodically formed, substantially the same reflectance can be obtained. However, in the case of this two-layered layer, the difference in lattice constant is slightly less than 2% at room temperature, and under the influence, a tensile stress is particularly applied to the AlN layer 42 to cause distortion. The Al _0.5 Ga _0.5 N layer 41 having an intermediate lattice constant between the AlN layer 42 and the GaN layer 43
By inserting between the N layer 42 and the GaN layer 43,
Since the distortion caused by the lattice mismatch can be reduced, the life of the semiconductor laser device can be further extended.

In order to further reduce the distortion due to the lattice mismatch, the AN layer 42 and the GaN layer 43
Instead of the l _0.5 Ga _0.5 N layer 41, an Al _q Ga _1-q As layer (0 ≦ q ≦ 1) may be inserted as a multilayer, or a layer in which the value of q continuously changes from 1 to 0. May be used.

(Embodiment 6) In Embodiment 6 of the present invention, in the nitride semiconductor laser device 500 of Embodiment 5, the protective layer (GaN) 20b provided on the rear surface of the semiconductor laser diode 10 is omitted, and Diode 1
0 on the rear surface of Al _0.5 Ga _0.5 N layer 41 (0.01 μm) /
AlN layer 42 (0.03 μm) / Al _0.5 Ga _0.5 N layer 4
Sixteen pairs of four-layer stacks of 1 (0.01 μm) / GaN layer 43 (0.04 μm) are deposited. With this configuration also, a reflective layer having a high reflectance can be obtained.

Incidentally, an In _0.02 Ga _0.98 N layer may be used as a protective layer formed directly on the rear surface of the semiconductor laser diode 10. Further, the thickness of the protective layer may be set to an odd multiple of λ / 4n to function as a reflective layer.

FIG. 10 shows the nitride semiconductor laser devices of the fifth and sixth embodiments (E4 and E5 in FIG. 10 respectively) and the conventional nitride semiconductor laser device 700 (FIG. 10) shown in FIGS. 12A and 12B. 50 ° C of C3) in
5 shows the results of the time change (life test) of the change rate ΔIop of the operating current at the 50 mW output in FIG.

FIG. 10 shows that the nitride semiconductor laser devices of Embodiments 5 and 6 were not degraded even after 1000 hours of high-power operation, and the end face degradation was suppressed by the protective layer, and at the same time the defects in the active layer were reduced. It can be seen that a long life was obtained because the introduction was extremely small.

As described above, in the fifth and sixth embodiments, similar to the first embodiment, the effect of extending the life of the semiconductor laser device can be obtained, and further higher reflectance can be obtained.

In order to sufficiently increase the electric resistance of each of the nitride semiconductor layers constituting the reflection layer 40 in the fifth and sixth embodiments, the MO-CVD method or the MBE method is used.
An undoped layer may be grown by a method. In order to further increase the resistance, as described above, a group V atom (for example, about 10 ¹⁵ cm ^{−3 of} arsenic or phosphorus atoms) may be implanted to compensate for the nitrogen vacancy present in each semiconductor layer. .

In a stacked structure of two or more types of insulating layers or high-resistance semiconductor layers, if the difference between the lattice constants of two adjacent layers at room temperature is large, the adjacent two
By adopting a structure in which the third layer is inserted so that the difference in lattice constant between the layers at room temperature is reduced, the reflective layer can be formed with almost no distortion in the active layer. Further, by depositing these layers by MO-CVD or MBE, damage to the laser end face in the deposition step can be suppressed, and by using a material whose thermal expansion coefficient is very close to that of the active layer, the material can be formed at room temperature. Can be reduced.

In the above-described embodiment, an example in which the reflection layer is provided on the rear end face of the semiconductor laser diode has been described. A reflective layer may be provided on the side. The reflectance of each reflective layer may be set as appropriate depending on the application.

[0087]

According to the present invention, a nitride semiconductor laser device having high reliability and a long life can be obtained not only at the time of low output but also at the time of high output oscillation which is greatly affected by distortion and defects. INDUSTRIAL APPLICABILITY The nitride semiconductor laser device of the present invention is suitably used for a light source of a high-density optical disk device or the like.

[Brief description of the drawings]

FIG. 1 is a perspective view of a nitride semiconductor laser device according to a first embodiment of the present invention.

FIG. 2A is a diagram showing a manufacturing step of the nitride semiconductor laser device of the first embodiment.

FIG. 2B is a diagram showing another manufacturing step of the nitride semiconductor laser device of the first embodiment.

FIG. 2C is a diagram showing another manufacturing step of the nitride semiconductor laser device of the first embodiment.

FIG. 2D is a diagram showing another manufacturing step of the nitride semiconductor laser device of the first embodiment.

FIG. 3 is a graph showing life test results of the nitride semiconductor laser device of Embodiment 1 and a conventional nitride semiconductor laser device.

FIG. 4A is a perspective view of a nitride semiconductor laser device according to a second embodiment of the present invention.

FIG. 4B is a sectional view taken along line 4B-4B ′ of FIG. 4A.

FIG. 5 is a sectional view of a nitride semiconductor laser device according to a third embodiment of the present invention.

FIG. 6 is a sectional view of a nitride semiconductor laser device according to a fourth embodiment of the present invention.

FIG. 7 is a graph showing life test results of the nitride semiconductor laser devices of Embodiments 2 to 4 and a conventional nitride semiconductor laser device.

FIG. 8 is a sectional view of a nitride semiconductor laser device according to a fifth embodiment of the present invention.

FIG. 9 is a graph showing a calculated value of an end face reflectance with respect to each wavelength of a reflection layer in the nitride semiconductor laser device of the fifth embodiment.

FIG. 10 is a graph showing life test results of the nitride semiconductor laser devices of Embodiments 5 and 6 and a conventional nitride semiconductor laser device.

FIG. 11 is a perspective view showing a conventional nitride semiconductor laser device.

FIG. 12A is a perspective view showing another conventional nitride semiconductor laser device.

FIG. 12B is a sectional view of another conventional nitride semiconductor laser device shown in FIG. 12A.

[Explanation of symbols]

10, 10 'nitride semiconductor laser diode (laser element) 11 n-type electrode 12 substrate 13, 15 clad layer 14 MQW active layer 16 electrode forming layer 17 p-type electrode 20a, 20b, 20c protective layer 30a, 30b, 40 reflective layer Reference Signs List 31 AlN layer 32 GaN layer 33 SiO ₂ layer 34 TiO ₂ layer 41 Al _0.5 Ga _0.5 N layer 42 AlN layer 43 GaN layer 60, 70 Laser diode 61, 72 Sapphire substrate 62 Electrode forming layer 62a Lower electrode forming layer 62b Upper electrode forming layers 63,65,73,75 cladding layer 64, 74 MQW active layer 66 electrode forming layer 67 n-type electrode 68 p-type electrode 69 protective layer 76 n electrode forming layer 77 Ni / Au electrode 90 reflective layer 91 SiO ₂ layer 92 TiO _Two- layer 100, 200, 300, 400, 500 nitride semiconductor laser device 600, 700 nitride semiconductor laser device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahiro Ishida 1-1, Yukicho, Takatsuki-shi, Osaka Matsushita Electronics Industrial Co., Ltd. (72) Inventor Tadahiro Hashimoto 1-1, Yukicho, Takatsuki-shi, Osaka Matsushita Electronics Industrial Co., Ltd.

Claims (13)

[Claims] 1. A semiconductor device comprising: a nitride semiconductor laser diode; and a protection layer provided on a laser end face of the nitride semiconductor laser diode, wherein the protection layer is transparent to light emitted by the nitride laser diode. Al _1-xyz Ga _x In _y B _z N (0
≦ x, y, z ≦ 1, and 0 ≦ x + y + z ≦ 1). 2. The thickness of the protective layer is an integral multiple of λ / 2n, where n is the refractive index of the protective layer and λ is the wavelength of light emitted by the nitride laser diode. The nitride semiconductor laser device according to any one of the preceding claims. 3. The nitride semiconductor laser diode according to claim 1,
_{In u Ga 1-u N /} In v Ga 1-v N (0 ≦ u, v ≦ 1) nitride semiconductor laser device according to claim 1 having a multiple quantum well active layer made of. 4. The protective layer is formed by MO-CVD or M-CVD.
2. The nitride semiconductor laser device according to claim 1, formed by a BE method. 5. The nitride semiconductor laser device according to claim 1, further comprising a reflecting layer in contact with said protective layer, for reflecting light oscillated by said nitride laser diode. 6. The nitride semiconductor laser device according to claim 5, wherein the reflection layer has a stacked structure in which first and second layers having different refractive indexes are alternately stacked. 7. When the refractive index of the first layer is n ₁ , the refractive index of the second layer is n ₂ , and the wavelength of light emitted by the nitride laser diode is λ, the first layer and the second layer 7. The nitride semiconductor laser device according to claim 6, wherein the thicknesses of the layers satisfy the relations of λ / 4n ₁ and λ / 4n ₂ , respectively. 8. The thickness of the protective layer is an integral multiple of λ / 2n, where n is the refractive index of the protective layer and λ is the wavelength of light emitted by the nitride laser diode. A nitride semiconductor laser device according to claim 5. 9. The thickness of the protective layer is λ / 4n, where n is the refractive index of the protective layer and λ is the wavelength of light oscillated by the nitride laser diode. 3. The nitride semiconductor laser device according to item 1. 10. The method according to claim 1, wherein the protective layer is GaN,
The layer and the second layer are SiO ₂ and TiO ₂ , respectively,
Alternatively, two types of Al that are transparent to light emitted by the nitride laser diode and have different refractive indices from each other.
_{1-abc Ga a In b B} c N (0 ≦ a, b, c ≦ 1, and,
7. The nitride semiconductor laser device according to claim 6, wherein 0 ≦ a + b + c ≦ 1). 11. A semiconductor device further comprising a third layer between the first layer and the second layer, wherein the first, second, and third layers are crystalline layers, and the first layer and the third layer are 7. The nitride semiconductor laser device according to claim 6, wherein a difference in lattice constant between the third layer and the third layer is smaller than a difference in lattice constant between the first layer and the second layer. 12. The protection layer is a GaN layer, and the reflection layer including the first layer / third layer / second layer is GaN / A
The nitride semiconductor laser device according to claim 11, having a 1GaN / AlN stacked structure. 13. The protective layer and the reflective layer may be made of MO
-Formed by a CVD method or an MBE method.
3. The nitride semiconductor laser device according to item 1.