JP2000058969A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress instantaneous optical damage and to obtain a high-output semiconductor laser element that has not been achieved until now by providing window structure that does not absorb a laser beam near at least one end face of a resonator. SOLUTION: A buffer layer 2, an n-type clad layer 3, an n-type optical waveguide layer 4, an n-type carrier block layer 5, an active layer 6, a p-type carrier block layer 7, p-type optical waveguide layers 8 and 9, a p-type clad layer 10, and a contact layer 11 are successively subjected to epitaxial crystal growth on an n-GaAs substrate 1. Further, a current block layer 12 with a stripe-shaped window is buried between the optical waveguide layers 8 and 9. Window structure 13 is a disordered region by ion implantation. An active layer being located at this portion becomes the window structure that does not absorb any laser beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device which is suitably used in communications, laser medicine, laser processing, printing, etc., and which can operate at high output.

[0002]

2. Description of the Related Art For the purpose of increasing the output of a semiconductor laser device, a carrier block layer having a large forbidden band width and a small thickness is provided on both sides of an active layer so that an optical waveguide layer formed outside the carrier block layer can be formed. Semiconductor laser devices with increased design flexibility have been proposed. In such a structure, the carrier block layer has a function of efficiently confining injected carriers in the active layer, and light generated in the active layer passes through the carrier block layer because the carrier block layer is formed thin. Can easily leak to the outer optical waveguide layer. Therefore, instantaneous optical damage caused by local concentration of laser light at the emission end face of the semiconductor laser element can be prevented, the end face breakdown level can be increased, and high output operation can be realized.

FIG. 10A shows an example of a cross section of a laser structure of such a semiconductor laser device.
(B) is a distribution diagram of the forbidden band width corresponding to each layer. Carrier block layers 62 and 63 are formed on both sides of the active layer 61, waveguide layers 64 and 65 are formed on both sides thereof, and cladding layers 66 and 67 are formed on the outside thereof. The structure having such a configuration is a known isolated confinement heterostructure (SCH)
Separate Confinement Heterostructure)
DCH Decoupled Confineme
nt Heterostructure). FIG. 11A is a distribution diagram of the forbidden band width of the separated confinement structure.
(B) It is a distribution diagram of the forbidden band width of the completely separated confinement structure. When designed to have the same oscillation wavelength and radiation angle,
The respective film thicknesses L1 and L2 of the entire laser structure of the SCH structure and the DCH structure satisfy L1> L2.

[0004]

In a completely separated confinement type semiconductor laser device, an output in which instantaneous optical damage (COD) occurs at an emission end face by expanding an optical waveguide layer and reducing a laser beam density in an active layer. The level could be increased, and the output of the semiconductor laser was dramatically improved. However, studies by the inventors have revealed that in order to further increase the output of a semiconductor laser in the future, it is necessary to make the emitting end face resistant to instantaneous optical damage.

It is considered that instantaneous optical damage occurs by the following mechanism. That is, a high-density surface level exists at the laser end face, and a non-radiative recombination current flows through this level. For this reason, it is considered that the injected carrier density near the end face is lower than that inside the laser and has not reached the population inversion state. Therefore, net absorption of light occurs near the end face. Due to this light absorption, heat is generated near the end face,
The band gap becomes narrower, and the light absorption further increases. Due to this positive feedback loop, the end face temperature rises, and eventually the end face melts and the laser stops oscillating.

An object of the present invention is to suppress instantaneous optical damage,
An object of the present invention is to produce a semiconductor laser device having a very high output which has not been realized until now.

[0007]

According to the present invention, n-type and p-type optical waveguide layers having a bandgap greater than or equal to the bandgap of the active layer are provided on both sides of the active layer, respectively. And n-type and p-type cladding layers each having a bandgap greater than or equal to the bandgap of the optical waveguide layer so as to sandwich the optical waveguide layer, and the active layer and the optical waveguide layer are provided between the active layer and the optical waveguide layer. In a semiconductor laser device provided with a carrier block layer having a forbidden bandwidth equal to or greater than each of the forbidden bandwidths of the optical waveguide layer and the optical waveguide layer, a window structure that does not absorb laser light is provided near at least one end face of the resonator. It is a semiconductor laser device characterized by the following.

According to the present invention, the window structure, that is, the forbidden band width is sufficiently larger than the oscillation wavelength, and a region transparent to the oscillated laser light is provided near the end face, thereby generating heat due to light absorption and forbidden band. Optical damage at the end face can be suppressed without falling into a positive feedback loop of a reduction in width and an increase in absorption. By combining with a completely separate confinement structure, it is possible to obtain a very high output that could not be realized until now.

In the present invention, it is preferable that the window structure is formed by disordering of the active layer due to diffusion of impurities or defects. As a result, the atoms forming the active layer and the carrier block layer are mixed due to the diffusion of impurities or defects. Since the band gap of the carrier block layer is wide, the window has a sufficiently large band gap with respect to the laser oscillation wavelength. At the same time, the refractive index difference between the waveguide layer and the cladding layer is small in the completely separated confinement structure, so that the change in the refractive index distribution due to disorder is small. Therefore, the waveguide mode determined by the refractive index distribution has a small difference between the end face window structure portion and the central portion, and the coupling efficiency when the waveguide mode propagates is high. Therefore, an increase in threshold current and a decrease in efficiency can be prevented. With such a completely separated confinement structure having a window structure, a semiconductor laser device having a high output and a low threshold can be obtained.

In the present invention, the impurities and defects are preferably introduced by ion implantation. According to the present invention, difficulties involved in manufacturing a window structure can be reduced. That is, impurities and defects can be easily introduced by ion implantation, but the following effects are obtained in the case of a completely separated confinement structure. In other words, when the window structure is manufactured by ion implantation after the entire laser structure is manufactured, ions are implanted from the outermost surface of the laser structure toward the active layer, but in the completely separated confinement structure, compared with the conventional separated confinement structure, The distance from the outermost surface to the active layer is short. Therefore, the acceleration energy of the ions can be kept low, and the damage to the laser structure can be reduced accordingly, and the ion implantation device can be small. Further, when ion implantation is performed at a stage where the laser structure has been grown halfway, and then regrown to produce a laser structure having a window structure, the complete separation confinement structure can reduce the overall Al composition ratio, so the regrowth interface Oxidation degradation of the steel does not matter. This is because the lower the Al composition ratio, the lower the oxygen concentration accumulated at the regrowth interface.

In the present invention, it is preferable that the window structure is formed by etching the vicinity of the end face and embedding the window structure with a material having a band gap larger than that of the active layer. By using such a method, a stable window structure can be formed for a long period of time. However, in the case of a completely separated confinement structure, the entire structure can be reduced in Al. And good regrowth with a small value.

In the present invention, the semiconductor material forming the optical waveguide layer is GaAs, and the Al composition ratio is 0.3 or less.
X ≦ 0 when GaAs (Al _x Ga _1-x As)
3), it is preferable to use either InGaP or InGaAsP. This is because these materials are hardly oxidatively deteriorated, so that oxidative deterioration does not occur during the process of forming a window structure that does not absorb light, and particularly good regrowth becomes possible.

The window structure is preferably provided in the vicinity of the emission end face. In order to further increase the output, it is preferable to provide them near both end faces forming the resonator.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a perspective view showing a first embodiment of the present invention, and FIG. 2A is a sectional view of a semiconductor laser taken along the line 1b-1b 'in FIG. FIG. 2B is a cross-sectional view of a window structure region taken along line 1c-1c ′ in FIG. 1, and FIG. 2C is a cross-sectional view taken along line 1d-1d ′ in FIG. It is. In this semiconductor laser device, n-type GaAs
Buffer layer 2 made of GaAs (thickness t = 0.5 micron), n-AlGaAs (Al composition ratio x = 0.24,
t = 1.9 microns) cladding layer 3, n-A
an optical waveguide layer 4 made of lGaAs (Al composition ratio x = 0.1, t = 0.31 micron), n-AlGaAs (Al
Carrier block layer 5 having composition ratio x = 0.4, t = 0.03 microns), non-doped InGaAs well layer (In composition ratio y = 0.2, t = 0.008 microns) /
Non-doped AlGaAs barrier layer (Al composition ratio x = 0.
1, a double quantum well active layer 6 composed of t = 0.006 μm, p-AlGaAs (Al composition ratio x = 0.4,
carrier block layer 7 composed of t = 0.03 microns, p-AlGaAs (Al composition ratio x = 0.1, t =
0.3,1 micron), optical waveguide layers 8, 9, p-Al
A cladding layer 10 made of GaAs (Al composition ratio x = 0.24, t = 1.9 microns) and a contact layer 11 made of p-GaAs are formed by MOCVD (metal organic chemical vapor deposition) or the like. Further, n-AlGaAs (Al) having a striped window between the optical waveguide layers 8 and 9
A current blocking layer 12 having a composition ratio x = 0.20, t = 0.15 microns) is embedded. Electrodes (not shown) are formed on the lower surface of the substrate 1 and the upper surface of the contact layer 11, respectively. The window structure 13 is a region disordered by ion implantation. The active layer in this portion has a window structure that does not absorb laser light.

FIG. 3 is a process chart showing a method for manufacturing the semiconductor laser according to the first embodiment, and shows a cross section taken along line 1b-1b 'in FIG. On an n-GaAs substrate 1, a buffer layer 2, n
Clad layer 3, n-type optical waveguide layer 4, n-type carrier block layer 5, active layer 6, p-type carrier block layer 7, p-type optical waveguide layers 8, 9, p-type clad layer 10, contact layer 11.
Are sequentially epitaxially grown. p-type optical waveguide layer 8
A current confinement layer 12 having a striped window is formed between the layers 9 and 9. A resist film 14 is formed on the entire surface of the wafer. As shown in FIG. 3B, the resist film 14 is patterned at an interval of about 20 μm from the cavity facet of the semiconductor laser. Thereafter, as shown in FIG. 3B, silicon ions are implanted into the wafer using the resist 14 as a mask. In order to promote disordering of the active layer, silicon atoms may be diffused in the crystal by heat treatment. After the ion implantation, the resist 14 is removed and the wafer is annealed to diffuse silicon atoms to form a disordered active layer, that is, a region functioning as a window structure. Finally, the shape is as shown in FIG.

As shown in FIGS. 11 (a) and 11 (b), in the complete isolation / confinement structure, the film thickness L2 of the entire laser structure is adjusted to the thickness of the isolation / confinement structure conventionally used in a high-power semiconductor laser device. It can be made thinner than the entire film thickness L1.
This is because in the completely separated confinement structure, the waveguide mode is close to a Gaussian type and the seepage into the cladding layer is small, so that the cladding layer can be thinned. As a result, ions can be implanted into the active layer with low acceleration energy. As the acceleration energy of the ion implantation apparatus increases, the size of the apparatus increases, the damage to the laser element increases, and the life is shortened. Therefore, the ion acceleration energy is desirably small. As described above, according to the present embodiment, it is possible to obtain a semiconductor laser that can be easily ion-implanted, has a long life, and can perform a high-power operation that has not been achieved conventionally.

(Second Embodiment) FIG. 4 shows a second embodiment of the present invention.
FIG. 5A is a perspective view showing the embodiment, and FIG.
FIG. 5B is a cross-sectional view of the semiconductor laser taken along line b-3b ′ in the resonator direction, FIG. 5B is a cross-sectional view of the window structure region taken along 3c-3c ′ in FIG. 4, and FIG. 3d-
It is sectional drawing in 3d '. In this semiconductor laser device, n-G is sequentially formed on a substrate 21 made of n-GaAs.
buffer layer 22 made of aAs (thickness t = 0.5 micron), n-AlGaAs (Al composition ratio x = 0.24,
(t = 1.9 microns), n-
An optical waveguide layer 24 made of AlGaAs (Al composition ratio x = 0.1, t = 0.31 micron), n-AlGaAs
(Al composition ratio x = 0.4, t = 0.03 μm) carrier block layer 25, non-doped InGaAs
Double quantum well active layer composed of s well layer (In composition ratio y = 0.2, t = 0.008 micron) / non-doped AlGaAs barrier layer (Al composition ratio x = 0.1, t = 0.006 micron) 26, p-AlGaAs (Al composition ratio x
= 0.4, t = 0.03 microns), a carrier block layer 27, p-AlGaAs (Al composition ratio x =
0.1, t = 0.31 micron)
8, 29, p-AlGaAs (Al composition ratio x = 0.2
4, a cladding layer 30 consisting of t = 1.9 microns);
The contact layer 31 made of p-GaAs is formed by MOCVD.
(Metalorganic chemical vapor deposition) or the like, and furthermore, n-AlGaAs having a striped window between the optical waveguide layers 28 and 29 (Al composition ratio x = 0.2, t =
A current blocking layer 32 of 0.15 microns) is embedded. Lower surface of substrate 21 and contact layer 31
An electrode (not shown) is formed on the upper surface. The window structure 33 is a region disordered by ion implantation. This portion of the active layer has a window structure that does not absorb laser light.

FIG. 6 is a process chart showing a method of manufacturing the semiconductor laser according to the second embodiment, and shows a cross section taken along line 3b-3b 'in FIG. On the n-GaAs substrate 21, a buffer layer 22, a cladding layer 23, an optical waveguide layer 24, a carrier block layer 25, an active layer 26, a carrier block layer 27, and an optical waveguide layer 28 are sequentially epitaxially grown. A resist film 34 is formed on the entire surface of the wafer. As shown in FIG. 6B, the resist film 34 is patterned at an interval of about 20 μm from the cavity facet of the semiconductor laser. As shown in FIG. 6B, silicon ions are implanted into the wafer using the resist 34 as a mask. In order to promote disordering of the active layer, silicon atoms may be diffused in the crystal by some heat treatment. After ion implantation, the wafer is annealed, or by utilizing the heat of crystal growth after this step, silicon atoms are diffused and disordered active layer, which functions as a window transparent to the oscillation wavelength. An area is formed. After removing the resist film 34, the current constriction layer 32 having a window in the form of a stripe, the waveguide layer 29, the cladding layer 30, and the contact layer 31 are regrown. Finally, the result is as shown in FIG.

In the separated confinement structure, since the cladding layer also plays a role of confining carriers, a high Al composition ratio is required so as to have a sufficient band gap for confining carriers. On the other hand, in the completely separated confinement structure, the carrier composition is confined by the carrier block layer, so that the Al composition ratio of the cladding layer can be reduced. In addition, in the completely separated confinement structure, since the optical waveguide layer can be widened,
Without damaging the active layer, it is also possible to interrupt the growth of the optical waveguide layer having a low Al composition ratio and perform processing such as ion implantation. The lower the Al composition ratio, the lower the oxygen concentration accumulated at the regrowth interface. Therefore, in the completely separated confinement structure,
Formation of a potential barrier due to oxidation deterioration accompanying regrowth and non-radiative recombination of carriers are suppressed.

As described above, according to the present embodiment, the first
In addition to the effects of the above-described embodiment, non-radiative recombination is suppressed as compared with the case of the separated confinement structure, whereby operation at a low driving voltage is possible.

(Third Embodiment) FIG. 7 shows a third embodiment of the present invention.
FIG. 8A is a perspective view showing the embodiment, and FIG.
FIG. 8B is a cross-sectional view of the semiconductor laser taken along line b-5b ′, FIG. 8B is a cross-sectional view of the window structure region taken along line 5c-5c ′ in FIG. 7, and FIG. 5d-
It is sectional drawing in 5d '. In this semiconductor laser device, n-GaAs is sequentially formed on a substrate 41 made of n-GaAs.
a buffer layer 42 made of aAs (thickness t = 0.5 micron); n-AlGaAs (Al composition ratio x = 0.24;
t = 1.9 microns) cladding layer 43, n-
An optical waveguide layer 44 made of AlGaAs (Al composition ratio x = 0.1, t = 0.31 micron), n-AlGaAs
(Al composition ratio x = 0.4, t = 0.03 μm) carrier block layer 45, non-doped InGaAs
Double quantum well active layer composed of s well layer (In composition ratio y = 0.2, t = 0.008 micron) / non-doped AlGaAs barrier layer (Al composition ratio x = 0.1, t = 0.006 micron) 46, p-AlGaAs (Al composition ratio x
= 0.4, t = 0.03 microns), a carrier block layer 47, p-AlGaAs (Al composition ratio x =
0.1, t = 0.31 micron)
8,49, p-AlGaAs (Al composition ratio x = 0.2
4, t = 1.9 microns) cladding layer 50,
The contact layer 51 made of p-GaAs is formed by MOCVD.
N-AlGaAs (Al composition ratio x = 0.20, t = t = 0) formed by using (organic metal-organic chemical vapor deposition) or the like, and further having a striped window between the optical waveguide layers 48 and 49.
A current blocking layer 52 of 0.15 microns) is embedded. Lower surface of substrate 41 and contact layer 51
An electrode (not shown) is formed on the upper surface.

The window structure 53 is a region buried with a material having a larger band gap than the active layer. This portion has a window structure that does not absorb laser light. FIG. 9 is a process chart showing a method for manufacturing a semiconductor laser according to the third embodiment, which is 5b-5b 'in FIG.
Of FIG. On an n-GaAs substrate 41, an n-type buffer layer 42, an n-type cladding layer 43, an n-type optical waveguide layer 44, an n-type carrier block layer 45, an active layer 46, a p-type carrier block layer 47, and a p-type optical waveguide layer 48 are sequentially epitaxially grown. Si on the entire surface of this wafer
An O ₂ film 54 is formed. As shown in FIG. 9B, this SiO ₂ film is patterned at an interval of about 20 μm from the cavity facet of the semiconductor laser. This SiO ₂ film 54
Is etched off to the middle of the n-type optical waveguide layer 44 by using as a mask, and buried with non-doped GaAs. Thus, a region 53 functioning as a window structure is formed. SiO
After removing the _second film 54, the current confinement layer 52 having a striped window, the p-type optical waveguide layer 49, the p-type cladding layer 50, the p-type
The mold contact layer 51 is regrown.

As described above, in the completely separated confinement structure,
Because the carrier block layer traps the carrier,
The Al composition ratio of the cladding layer can be reduced. In addition, in the completely separated confinement structure, since the optical waveguide layer is wide,
Without damaging the active layer, it is also possible to interrupt the growth of the optical waveguide layer having a low Al composition ratio and perform processing such as ion implantation. The lower the Al composition ratio, the lower the oxygen concentration accumulated at the regrowth interface. Therefore, in the completely separated confinement structure,
Formation of a potential barrier due to oxidation deterioration accompanying regrowth and non-radiative recombination of carriers are suppressed.

As described above, in the completely separated confinement type semiconductor laser device having the window structure of the present embodiment, in addition to the effect of the first embodiment, high efficiency operation is possible by suppressing the formation of the potential barrier. In addition, since non-radiative recombination of carriers is suppressed, a semiconductor laser operable at a low driving voltage can be obtained.

(Fourth Embodiment) A fourth embodiment will be described with reference to FIG. 4 which is a perspective view and FIG. 5 which shows a cross section.
This semiconductor laser device includes a substrate 2 made of n-GaAs.
1, a buffer layer 22 made of n-GaAs (thickness t = 0.5 micron) and n-AlGaAs (Al
A cladding layer 23 composed of a composition ratio x = 0.14, t = 1.9 microns, an optical waveguide layer 24 composed of n-GaAs (t = 0.31 microns), n-AlGaAs (Al
Carrier block layer 25 having composition ratio x = 0.4, t = 0.03 microns, non-doped InGaAs well layer (In composition ratio y = 0.2, t = 0.008 microns)
/ Non-doped AlGaAs barrier layer (Al composition ratio x =
0.1, t = 0.006 micron) double quantum well active layer 26, p-AlGaAs (Al composition ratio x =
0.4, t = 0.03 micron) carrier blocking layer 27, p-GaAs (t = 0.31 micron) optical waveguide layers 28, 29, p-AlGaAs
A cladding layer 30 composed of (Al composition ratio x = 0.14, t = 1.9 microns) and a contact layer 31 composed of p-GaAs are formed by MOCVD (metal organic chemical vapor deposition) or the like. A current blocking layer 32 of n-AlGaAs (Al composition ratio x = 0.10, t = 0.15 micron) having a striped window is embedded between the optical waveguide layers 28 and 29. Electrodes (not shown) are provided on the lower surface of the substrate 21 and the upper surface of the contact layer 31.
Are formed respectively.

The window structure 33 is a region disordered by ion implantation. This portion has a window structure that does not absorb laser light. This semiconductor laser device is manufactured in exactly the same manner as in the second embodiment, and a description thereof will be omitted.
In the semiconductor laser device according to the embodiment of the present invention, the optical waveguide layer is formed of GaAs containing no Al.
Oxidation degradation does not occur during the process of forming a window structure that does not absorb light, and particularly good regrowth becomes possible. As described above, it is particularly preferable that the optical waveguide layer is formed of GaAs.

In the embodiment of the present invention described above, silicon is used as the ion species, but other ion species such as zinc and gallium may be used as long as they cause disorder.

[0028]

As described above, according to the present invention, instantaneous optical damage at the end face can be suppressed, so that a higher laser light output than before can be obtained. In addition, a semiconductor laser device capable of high efficiency with low threshold current and low voltage driving can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing the structure of the semiconductor laser according to the first embodiment of the present invention.

FIG. 3 is a process chart showing a method for manufacturing a semiconductor laser according to a second embodiment of the present invention.

FIG. 4 is a perspective view showing a structure of a semiconductor laser according to second and fourth embodiments of the present invention.

FIG. 5 is a sectional view showing a structure of a semiconductor laser according to second and fourth embodiments of the present invention.

FIG. 6 is a process chart showing a method of manufacturing a semiconductor laser according to the second and fourth embodiments of the present invention.

FIG. 7 is a perspective view showing a structure of a semiconductor laser according to a third embodiment of the present invention.

FIG. 8 is a sectional view showing a structure of a semiconductor laser according to a third embodiment of the present invention.

FIG. 9 is a process chart showing a method of manufacturing a semiconductor laser according to a third embodiment of the present invention.

10A is a cross-sectional view illustrating an example of a completely separated confinement semiconductor laser, and FIG. 10B is a distribution diagram of a forbidden band width corresponding to each layer.

11A is a distribution diagram of a forbidden band width of a separated confinement semiconductor laser, and FIG. 11B is a distribution diagram of a forbidden band width of a completely separated confinement semiconductor laser.

[Explanation of symbols]

1,1,41 ... substrate 3,10,23,30,43,50,66,67 ...
Cladding layer 4, 8, 9, 24, 28, 29, 44, 48, 49, 6
4, 65... Optical waveguide layer 5, 7, 25, 27, 45, 47, 62, 63... Carrier blocking layer 6, 26, 46, 61... Active layer 13, 33, 53. ..Window structures

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F041 AA44 CA04 CA05 CA34 CA35 CA36 CA39 CA65 CA71 CB03 5F073 AA09 AA20 AA45 AA51 AA74 AA86 AA88 CA07 DA14 DA15 EA28

Claims (5)

[Claims] An n-type and a p-type optical waveguide layer having a forbidden band width equal to or larger than the forbidden band width of the active layer are provided on both sides of the active layer, respectively, so as to sandwich the active layer and the optical waveguide layer. N-type and p-type cladding layers each having a forbidden band width equal to or larger than the forbidden band width of the optical waveguide layer are provided, and each of the active layer and the optical waveguide layer is provided between the active layer and the optical waveguide layer. A semiconductor laser device provided with a carrier block layer having a forbidden band width equal to or larger than a forbidden band width, characterized in that the semiconductor laser device has a window structure that does not absorb laser light near at least one end face in a resonance direction. 2. The semiconductor laser device according to claim 1, wherein said window structure is formed by disordering of an active layer due to diffusion of impurities or defects. 3. The semiconductor laser device according to claim 2, wherein said impurities and defects are introduced by ion implantation. 4. The semiconductor laser device according to claim 1, wherein said window structure is manufactured by etching a portion near an end face and filling it with a material having a band gap larger than that of an active layer. 5. The semiconductor device according to claim 1, wherein the semiconductor material forming the optical waveguide layer is GaAs.
s, AlGaAs and InGa having an Al composition ratio of 0.3 or less
5. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is one of P and InGaAsP.