JP2004103678A - Semiconductor laser and semiconductor laser module - Google Patents

Abstract

An optical system including an optical fiber and a lens, which effectively reduces the full width at half maximum of a vertical far-field image of emitted light without extremely deteriorating the main characteristics of a semiconductor laser. Achieving good coupling with the laser and improving the high-output operating characteristics of the semiconductor laser itself.
A first conductive type first clad layer, a first conductive type second clad layer, an active layer structure, a second conductive type second clad layer, and a second conductive type second clad layer are provided on a substrate showing a first conductive type. A semiconductor laser having one cladding layer in this order and having an oscillation wavelength λ (nm) in which only propagation of a fundamental mode is allowed in the longitudinal direction. In a radiation pattern of light emitted from the semiconductor laser, in the far-field pattern in the direction perpendicular (FFP _V) to the substrate, and the main peak maximum intensity is _{I Vmain,} with maximum intensity are two sub-peak is a _{+ I Vsub-} and _{I Vsub} each occurrence, 0 _{<I Vsub / I Vmain <0.5} (Vsub is _{I Vsub-} and _{I Vsub +} strength greater of) the semiconductor laser is.
[Selection diagram] None

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor laser. INDUSTRIAL APPLICABILITY The present invention can be suitably used when high coupling efficiency with an optical system is desired, such as a pump light source for an optical fiber amplifier, a light source for optical information processing, and a medical semiconductor laser.
[0002]
[Prior art]
The progress of optical information processing technology and optical communication technology in recent years has not been spared.
For example, in the telecommunications field, Er as an amplifier for signal amplification having flexibility in the transmission system, as well as a large-capacity optical fiber transmission line corresponding to the future of the information communication (IT) era.³⁺Researches on optical fiber amplifiers (EDFAs) doped with rare earths such as those described above have been actively conducted in various fields. Development of a highly efficient semiconductor laser for an excitation light source, which is an indispensable element as an EDFA component, is awaited.
[0003]
In principle, there are three types of oscillation wavelengths of the excitation light source that can be used for EDFA application: 800 nm, 980 nm, and 1480 nm. From the viewpoint of the characteristics of the amplifier, it is known that pumping at 980 nm is most desirable in consideration of gain, noise, and the like. Such a semiconductor laser (LD) having an oscillation wavelength of 980 nm is required to satisfy the contradictory characteristics of a high output and a long life as an excitation light source. Furthermore, since it is also essential that the pumping light source for the optical amplifier realizes good coupling with the optical fiber, it is generally desired to oscillate in a single transverse mode, and a far-field image of light emitted from the semiconductor laser ( In the case of FAR (field @ pattern: FFP), it is desired that the aspect ratio in the direction perpendicular to the substrate (vertical direction) and the direction parallel to the substrate (horizontal direction) is close to 1, and the absolute value of the radiation angle is also narrow.
[0004]
On the other hand, besides the application to the communication field, the semiconductor laser has an application as an SHG light source, a heat source for a laser printer, and various applications in the medical field. In these fields, the light emitted from the semiconductor laser is often various. It is often coupled to an optical system, and it is very important that the absolute value of the FFP in the vertical and horizontal directions is narrow and that the aspect ratio is close to 1.
[0005]
In a semiconductor laser having a design in which propagation of only the fundamental mode in the longitudinal direction is allowed, that is, a semiconductor laser whose normalized frequency in the longitudinal direction is π / 2 or less, the light confinement is extremely extreme in the longitudinal and lateral directions. Is different. In the lateral light confinement, the width of the current injection region is several μm to several hundred μm, and the waveguide structure has the same dimensions. Light emission pattern (near-field image: near field pattern: NFP) of the emitted light in the horizontal direction (FFP)_H) Generally has relatively little diffraction effect. On the other hand, since the vertical light confinement is realized by the active layer structure extremely thinner than the oscillation wavelength, the vertical FFP (FFP) of the emitted light is_V) Has an extreme diffraction effect, and its full width at half maximum is FFP._HIt is usually wider. Therefore, in order to improve the coupling characteristics with an external optical system, the FFP_VIt is desired to reduce the effective full width at half maximum of.
[0006]
Also, if such a semiconductor laser is realized, as a result, the vertical NFP (NFP)_VIt is thought that the light density at the end face is reduced and the high-power operation characteristics of the semiconductor laser are also improved because the size of ()) increases.
As discussed in Non-Patent Document 1, FFP_VIs known to depend on the thickness of the active layer or the light guide layer. However, by simply reducing these thicknesses, the FFP_VEven if a semiconductor laser having a small width is realized, there are problems such as deterioration of other element characteristics.
[Non-Patent Document 1] C. Casey, Jr. , {M. B. Chapter 2 of Heterostructural lasers (Academic press, 1978) by Panish
[0007]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems of the related art.
Specifically, FFP can be performed without significantly deteriorating the main characteristics of the semiconductor laser._VOf the present invention is to effectively reduce the full width at half maximum of the semiconductor laser to realize good coupling between the semiconductor laser and an optical system composed of an optical fiber and a lens, and to improve the high output operation characteristics of the semiconductor laser itself. Issues to be solved.
[0008]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, in the radiation pattern of emitted light, a far-field image (FFP) in a direction perpendicular to the substrate._VThe present inventors have found that an excellent semiconductor laser can be obtained when the above condition is satisfied, and arrived at the present invention.
[0009]
That is, the present invention, on the substrate showing the first conductivity type, at least, the first cladding layer showing the first conductivity type, the second cladding layer showing the first conductivity type, the active layer structure, the conductivity type different from the substrate A semiconductor having an oscillation wavelength λ (nm), which has a second cladding layer having the second conductivity type and a first cladding layer having the second conductivity type in this order, and in which only propagation of the fundamental mode in the longitudinal direction is allowed. A far-field image (FFP) in a direction perpendicular to the substrate in a radiation pattern of light emitted from the semiconductor laser._V), The maximum intensity is I_VmainAnd the maximum intensity is I_Vsub-And I_{Vsub +}Is provided, and the following formula is satisfied and a semiconductor laser is provided.
(Equation 7)
0 <I_Vsub/ I_Vmain<$ 0.5
(In the above equation, I_VsubIs I_Vsub-And I_{Vsub +}Represents the one with the greater strength. )
[0010]
In the semiconductor laser of the present invention, the angle at which the main peak appears is P (I_Vmain), The maximum strength is I_Vsub-And I_{Vsub +}The angles at which the two sub-peaks appear as P (I_Vsub-), P (I_{Vsub +}), It is preferable to satisfy the following expression.
(Equation 8)
| P (I_Vmain) -P (I_Vsub-) |> 40 degrees
| P (I_{Vsub +}) -P (I_Vmain) |> 40 degrees
| P (I_{Vsub +}) -P (I_Vsub-) |> 80 degrees
[0011]
According to the semiconductor laser of the present invention, in a radiation pattern of a main peak emitted from the semiconductor laser, a far-field image (FFP) in a direction parallel to the substrate is provided._HIt is preferred that there is only one local maximum in ()). In addition, a far-field image (FFP) in a direction parallel to the substrate_H) Is I_Hmain, The angle at which the peak having the maximum intensity appears is P (I_Hmain), It is preferable to satisfy the following expression.
(Equation 9)
| P (I_Vmain) -P (I_Hmain) | <5 degrees
[0012]
The semiconductor laser of the present invention preferably has an oscillation wavelength λ (nm) satisfying the following expression.
(Equation 10)
900 nm <λ <1350 nm
[0013]
Further, the semiconductor laser of the present invention preferably does not have a plurality of light emitting points in the element. Also, the average refractive index of the first conductivity type first cladding layer is set to N_xn, The average refractive index of the first conductive type second cladding layer is N_sn, The average refractive index of the active layer structure is N_a, The refractive index N of the second cladding layer of the second conductivity type_sp, The average refractive index of the second conductive type first cladding layer is N_xpIt is preferable that these refractive indexes satisfy the following expression.
[Equation 11]
N_sn<N_xn<N_a
N_sp<N_xp<N_a
[0014]
Further, the semiconductor laser of the present invention has a light guide layer on at least one side of the active layer structure, and has a refractive index of N_gIn this case, the refractive index of each layer preferably satisfies the following expression.
(Equation 12)
N_sn<N_xn<N_g<N_a
N_sp<N_xp<N_g<N_a
[0015]
In the semiconductor laser of the present invention, the substrate is made of GaAs, and the first conductive type first clad layer, the first conductive type second clad layer, the second conductive type second clad layer, and the second conductive type first clad layer are provided. It is preferable that a part contains Al, Ga and As. Further, the substrate is made of GaAs, and at least a part of the first conductive type first clad layer, the first conductive type second clad layer, the second conductive type second clad layer, and the second conductive type first clad layer are In, It preferably contains Ga and P. Further, it is preferable that the active layer structure includes a strained quantum well layer, and that the quantum well layer includes In, Ga, and As. Further, it is preferable that the first conductivity type is n-type and the second conductivity type is p-type.
[0016]
The present invention also provides a semiconductor laser module comprising the above-mentioned semiconductor laser and an optical fiber on the light emitting end side of the semiconductor laser.
The semiconductor laser module of the present invention is preferably processed so that the tip of the optical fiber has a light-collecting effect and is directly optically coupled to the front end face of the semiconductor laser.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
First, some notations used in this specification will be described.
In this specification, the expression “the B layer formed on the A layer” refers to the case where the B layer is formed such that the bottom surface of the B layer is in contact with the upper surface of the A layer, and the case where one or more layers are formed on the upper surface of the A layer. And the case where the layer B is formed on the layer. The above expression also includes the case where the upper surface of the A layer and the bottom surface of the B layer are partially in contact with each other and one or more layers exist between the A layer and the B layer in other portions. Specific aspects are apparent from the following description of each layer and specific examples of the examples.
[0018]
In addition, the definition of the position when describing the FFP follows the ordinary method in this specification. This will be described with reference to FIG. First, it is assumed that two circles are perpendicular to each other (vertical direction) and horizontal (horizontal direction) and perpendicular to each other. Further, the devices are arranged such that the center of these two circles becomes the emission center C on the element structure. Here, a point where a straight line extending in the physical vertical direction from the light emission center C on the element structure intersects with the arcs of the two circles is 0 degree when describing FFP. That is, with this as the origin, the position for describing the FFP is defined by the angle between a straight line connecting 0 degree and the light emission center on the element structure with a point on each arc. FIG. 1 shows a position where the vertical FFP is at + φ degrees and the horizontal FFP is at + θ degrees. The light intensity distribution plotted as a function of the position defined by these angles is the FFP itself. Note that the + and-directions shown in the drawings are relative, and generally the directions may be reversed.
[0019]
In this specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit and an upper limit. Also, in the drawings attached to this specification, some parts are changed in size in order to make it easier to grasp the structure of the present invention, but actual dimensions are as described in this specification.
[0020]
The semiconductor laser of the present invention has, on a substrate having a first conductivity type, at least a first cladding layer having a first conductivity type, a second cladding layer having a first conductivity type, an active layer structure, and a conductivity type different from that of the substrate. In this order, a second cladding layer having the second conductivity type and a first cladding layer having the second conductivity type are provided in this order, and only the propagation of the fundamental mode in the longitudinal direction is allowed. Hereinafter, a preferred configuration example of the semiconductor laser of the present invention and a manufacturing method thereof will be specifically described.
[0021]
First, the main features of the semiconductor laser of the present invention will be described with reference to the LD shown in FIG. The left side of FIG. 2 shows the spatial distribution of the refractive index realized by each layer structure in the vertical direction, and the lower part of FIG. 2 shows the designation of the direction used in this figure.
[0022]
FIG. 2 shows that an n-type substrate (101)_0.25Ga_0.75Thickness t made of As_xn(Nm) n-type first cladding layer (102), In_0.49Ga_0.51Thickness t composed of P_sn(Nm) n-type second cladding layer (103), thickness t of undoped GaAs_gn(Nm) first light guide layer (104), thickness t_a(Nm) active layer structure (105), thickness t of undoped GaAs_gp(Nm) second light guide layer (106), In_0.49Ga_0.51Thickness t composed of P_sp(Nm) p-type second cladding layer (107), Al_0.25Ga_0.75Thickness t made of As_xp(Nm) p-type first cladding layer (108), a contact layer (109) for lowering contact resistance with an electrode, and SiN for limiting a current injection region in the lateral direction. This shows a broad area LD composed of a layer (110), a p-side electrode (111), and an n-side electrode (112). In the present invention, the paired layers such as the n-type first cladding layer (102) and the p-type first cladding layer (108) do not necessarily have to be symmetrical, but in FIG. 2, they are made of a material having the same refractive index. The thickness also satisfies the following conditions.
(Equation 13)
t_xn= T_xp= T_x
t_sn= T_sp= T_s
t_gn= T_gp= T_g
The active layer structure (105) has a thickness of 6 nm from the substrate (101) side._0.16Ga_0.84As strained quantum well layer (121), GaAs barrier (barrier) layer (122) with a thickness of 8 nm, In with a thickness of 6 nm_0.16Ga_0.84It has a strained double quantum well structure in which an As strained quantum well layer (123) is stacked, and its oscillation wavelength is λ (nm).
[0023]
In the present invention, the vertical confinement of the active layer structure (105), which is the basis of the light confinement of the LD, is performed by two Al layers located above and below the active layer structure (105)._0.25Ga_0.75This is realized by a refractive index difference between the As first cladding layer (102, 108) and the two GaAs light guide layers (104, 106) including the active layer structure (105). When the substrate (101) is made of GaAs and the first cladding layers (102, 108) are made of AlGaAs from the viewpoint of lattice matching, the Al composition is preferably smaller than 0.4, more preferably 0.3. It is more preferably smaller, more preferably smaller than 0.2. This is because the thermal resistance of the entire device can be reduced by reducing the Al composition of the thickest cladding layers (102, 108) except for the substrate (101) and the contact layer (109) among the layers constituting the entire LD. This is because a structure suitable for high-output operation can be obtained. When the substrate (101) is made of GaAs, the first cladding layers (102, 108) are made of In._0.49Ga_0.51It is also possible to adapt P. Furthermore, the first cladding layer (102, 108) does not need to be composed of a single material, but may be composed of a plurality of layers that act on light equivalently to a single layer. . In this case, light will be controlled by the average refractive index of these layers.
[0024]
Thickness t of first cladding layer (102, 108)_x(Nm) preferably has the following relationship with the oscillation wavelength λ (nm) since it is necessary to sufficiently attenuate light in the direction away from the active layer side of the layer.
[Equation 14]
λ <t_x
In particular, when the substrate is transparent to the oscillation wavelength and has a higher refractive index than the first cladding layers (102, 108) and the second cladding layers (103, 107), such as a 980 nm band LD, It is known that the substrate mode is superimposed on the mode inherent to the LD since light leaked from the cladding layers (102, 103) to the substrate (101) propagates through the substrate. In order to suppress this, it is desirable that the thickness of the first cladding layer (102, 108) be appropriately increased with respect to the wavelength.
[0025]
In addition, in order to realize light confinement, the light guide layers (104, 106) need to be made of a material having a higher refractive index than the first cladding layers (102, 108). When the substrate (101) is GaAs and the light guide layers (104, 106) are made of an AlGaAs-based material, the light guide layers (104, 106) also have an Al composition smaller than 0.4. Is preferably smaller than 0.2, more preferably smaller than 0.1. Most preferably, GaAs containing no Al is used. Particularly, from the viewpoint of reliability, a light guide layer containing no Al is desired.
[0026]
When a normal SCH (Separated Confinement Hetero-structure) structure is made of an AlGaAs-based material, the first cladding layer (102, 108) and the light guide layer (104, 106) are in direct contact with each other. The present invention is characterized in that a second clad layer (103, 107) is provided between these layers. This layer needs to have a lower refractive index than the light guide layers (104, 106) and the first clad layers (102, 108).
[0027]
As a result, as shown on the left side of FIG. 2, the second cladding layers (103, 107) are layers having the smallest values of the refractive index. On the left side of FIG. 2, the direction of the arrow described below n means the direction in which the refractive index increases. In addition, the second cladding layers (103, 107) function as barriers for electrons in the conduction band (and also for holes in the valence band, not shown here). The direction of the arrow described above Eg on the left side of FIG. 2 means the direction in which the potential increases with respect to the electrons.
[0028]
Therefore, the second cladding layers (103, 107) have a very important function with respect to vertical light confinement as described below. This second cladding layer (103, 107) is selected so as to have a lower refractive index than the light guide layer (104, 106) and the first cladding layer (102, 108). Due to the relationship between the refractive indices, the second cladding layer (103, 107) has a light distribution on its outer side, that is, on both sides of the first cladding layer (102, 108) side and the light guide layer (104, 106) side. Exhibits the pushing function. For this reason, the NFP whose distribution is appropriately expanded to the first cladding layer (102, 108) side_VContributes to achieving a relatively narrow FFP. That is, when the anti-waveguide characteristic of the second cladding layer (103, 107) acts appropriately, the existence thereof enables a relatively narrow FFP to be realized. Furthermore, when the anti-waveguide characteristics of the second cladding layers (103, 107) are acting appropriately, a very characteristic shape appears in the FFP of the device. Generally, a semiconductor laser designed so that only the fundamental mode propagates in the vertical direction, that is, an FFP of a semiconductor laser whose normalized frequency in the vertical direction is π / 2 or less._VIs a monomodal peak as shown in FIG. 3 except for secondary cases such as superposition of noise and light interference patterns. However, in the present invention, as shown in FIG._Vmain) And two minor peaks (intensities of I_Vsub-And I_{Vsub +}And again one of the strengths is I_VsubIs also observed) and 0 <I_Vsub/ I_VmainThe feature is that <0.5 is satisfied. This sub-peak is caused by the second cladding layer (103, 107) pushing light toward the light guide layer (104, 106), so that the NFP concentrated on a portion relatively close to the active layer._VIs generated by causing large diffraction. Therefore, the presence of the second cladding layer (103, 107) not only broadens the distribution of the NFP toward the first cladding layer (102, 108), but also makes the light near the active layer indispensable for the semiconductor laser. There is also the effect of keeping the confinement. According to the present invention, it is possible to narrow the FFP without side effects such as an increase in the threshold value of the LD, a decrease in the slope efficiency, and an increase in the drive current which occur when the FFP is narrowed (the NFP is widened). . For this purpose, the degree of concentration of light in the vicinity of the active layer in the light confinement in the vertical direction, that is, the existence of two subpeaks observed in the FFP is very important. In the present invention, 0 <I_Vsub/ I_Vmain<0.5, preferably 0 <I_Vsub/ I_Vmain<0.3, more preferably 0.05 <I_Vsub/ I_Vmain<0.2. These indices include the (average) refractive index or thickness of the first cladding layers (102, 108), the second cladding layers (103, 107), the light guide layers (104, 106), and the active layer structure (105). Are defined in an absolute and relative relationship. For example, extremely lowering the refractive index or increasing the thickness of the second cladding layer (103, 107), or extremely reducing the thickness of the light guide layer (104, 106), may cause the waveguide to be excessively thick. The optical confinement in the vertical direction in the LD structure becomes too weak, resulting in an excessive increase in oscillation threshold, a decrease in slope efficiency, an increase in drive current, etc., which is not desirable. .
[0029]
The angle at which the main peak appears is P (I_Vmain), Strength is I_Vsub-And I_{Vsub +}The angles at which the two sub-peaks appear as P (I_Vsub-), P (I_{Vsub +}), It is desirable that the following relationship be satisfied in the present invention.
[Equation 15]
| P (I_Vmain) -P (I_Vsub-) |> 40 degrees
| P (I_{Vsub +}) -P (I_Vmain) |> 40 degrees
| P (I_{Vsub +}) -P (I_Vsub-) |> 80 degrees
[0030]
This is NFP_VIs an important index indicating the degree of concentration in the vicinity of the active layer among the components, and it is more desirable that the following relationship be satisfied.
(Equation 16)
| P (I_Vmain) -P (I_Vsub-) |> 50 degrees
| P (I_{Vsub +}) -P (I_Vmain) |> 50 degrees
| P (I_{Vsub +}) -P (I_Vsub-) |> 100 degrees
[0031]
More preferably, the following relationship is satisfied.
[Equation 17]
60 degrees> | P (I_Vmain) -P (I_Vsub-) |> 55 degrees
60 degrees> | P (I_{Vsub +}) -P (I_Vmain) |> 55 degrees
120 degrees> | P (I_{Vsub +}) -P (I_Vsub-) |> 110 degrees
[0032]
Another function of the second cladding layer (103, 107) is that when the LD drive is driven at a high temperature, or when the temperature of the active layer rises considerably due to self-heating of the LD during high-power operation. For example, In_0.16Ga_0.84The function is to suppress thermal leakage (overflow) of carriers from the As strained quantum well layers (121, 123) into the first cladding layers (102, 108). In this structure, as shown in FIG. 2, the carrier leaks from the active layer structure (105) side to the first clad layer (102, 108) side through the light guide layer (104, 106). Since the barrier of the second cladding layer (103, 107) is higher than the height of the barrier between the light guide layer (104, 106) and the first cladding layer (102, 108), the viewpoint of suppressing carrier overflow is also possible. desirable. However, an extremely large barrier hinders the injection of carriers injected from the first cladding layer (102, 108) side to the active layer structure (105) side, so that the first cladding layer (102, 108) is prevented. The difference between the band gap of the second cladding layer (108) and the second cladding layer (103, 107) is preferably about 0.05 eV to 0.45 eV, and more preferably about 0.1 eV to 0.3 eV.
[0033]
Next, a semiconductor laser capable of operating in a single transverse mode, which is an example of the semiconductor laser of the present invention, will be described with reference to FIG. FIG. 5 is a schematic sectional view showing a configuration of a buried stripe type semiconductor laser as an example of an epitaxial structure in the semiconductor laser of the present invention.
This semiconductor laser is formed on a semiconductor substrate (1), has a refractive index waveguide structure, and has a second conductive type first clad layer and a second conductive type upper first clad layer (10) and a second conductive type lower clad layer. The first upper cladding layer (10) of the second conductivity type and the current blocking layer (11) / cap layer (12) realize both current confinement and light confinement. The semiconductor laser further includes a contact layer (13) for lowering contact resistance with an electrode. This type of laser is used as a light source for an optical fiber amplifier used for optical communication, a pickup light source for a large-scale magneto-optical memory for information processing, and a high-power semiconductor laser for medical use. Thereby, it can be further applied to various uses.
[0034]
As the substrate (1), GaAs, InP, GaP, GaN or the like can be used for a semiconductor substrate, and AlOx or the like can be used for a dielectric substrate. As the substrate (1), not only a so-called just substrate, but also a so-called off-substrate (missoriented substrate) can be used from the viewpoint of improving crystallinity during epitaxial growth. Off-substrates have the effect of promoting good crystal growth in the step flow mode and are widely used. The off-substrate having an inclination of about 0.5 to 2 degrees is widely used, but the inclination may be about 10 degrees depending on a material system constituting a quantum well structure described later.
The substrate (1) may be previously subjected to chemical etching, heat treatment, or the like in order to manufacture a semiconductor laser using a crystal growth technique such as MBE or MOCVD. The thickness of the substrate (1) to be used is usually about 350 μm, and it is usual to secure mechanical strength during the process of manufacturing the device. In order to form the end face of the semiconductor laser, the process is performed. Normally, polishing is performed to a thickness of about 100 μm on the way.
[0035]
The buffer layer (2) is preferably provided to alleviate incompleteness of the substrate bulk crystal and facilitate the formation of an epitaxial thin film having the same crystal axis. The buffer layer (2) is preferably made of the same compound as the substrate (1). When the substrate (1) is GaAs, GaAs is usually used, and when the substrate is InP, InP is used. You. However, the use of a superlattice layer for the buffer layer (2) is also widely practiced. For example, an AlGaAs / GaAs superlattice structure may be used on a GaAs substrate instead of the same compound. . Further, the composition of the buffer layer (2) can be gradually changed in the layer. On the other hand, when a dielectric substrate is used, a material different from that of the substrate may be appropriately selected depending on the desired emission wavelength and the structure of the entire device, instead of the same material as the substrate (1).
[0036]
The first conductive type first cladding layer (3) can be made of various materials, and is appropriately selected according to the active layer structure (6) selected according to the oscillation wavelength to be realized or the substrate (1). Is done. For example, when the present invention is realized on a GaAs substrate, an AlGaAs-based material, an InGaP-based material, an AlGaInP-based material, or the like can be used. Materials and the like can be used.
[0037]
In particular, when an AlGaAs-based material is used, the Al composition of the first conductive type first cladding layer (3) is set to 0.1 in order to reduce the thermal resistance of the entire device and to obtain a structure suitable for high-output operation. It is preferably less than 40, more preferably 0.3 or less, and even more preferably 0.2 or less. Also, the thickness t of the first conductivity type first cladding layer (3)_xn(Nm) is preferably larger than the oscillation wavelength λ (nm) because it is necessary to sufficiently attenuate the light in a direction away from the active layer structure (6).
[0038]
As described above, when AlGaAs is used for the first conductivity type first cladding layer (3),_xnGa_1-xnSince the Al composition of the As layer is lower than that of an LD having a normal SCH structure or GRIN-SCH structure, an effect of increasing the dopant activation rate can be expected. In particular, when it is assumed that crystal growth is performed by the MBE method when the first conductivity type is n-type and Si is used as a dopant, N.I. {Chandet} al. , {Physical} review {B} vol. 30 (1984) P. It is known that the ionization energy of the Si donor largely depends on the Al composition as shown in 4481. In AlGaAs having a low Al composition, a layer having sufficiently small resistance can be formed even if the doping level is set relatively low. Very desirable for being able to. Therefore, the doping level of the first conductive type first cladding layer (3) is 1.0 × 10¹⁷cm^-3~ 1.0x10¹⁸cm^-33.0 × 10¹⁷cm^-3~ 7.5x10¹⁷cm^-3Is more desirable.
Furthermore, the doping does not need to be performed uniformly in the first conductivity type first cladding layer (3), but may be set higher on the substrate (1) side and lower on the side closer to the active layer structure (6). desirable. This is an effective method for suppressing absorption by free electrons in a portion having a high light density.
[0039]
The first conductive type second cladding layer (4) can be made of various materials, and is appropriately selected according to the active layer structure (6) selected according to the oscillation wavelength to be realized, the substrate, or the like. For example, when the present invention is realized on a GaAs substrate, an AlGaAs-based material, an InGaP-based material, an AlGaInP-based material, or the like can be used. Materials and the like can be used.
[0040]
Also, the first conductivity type second cladding layer (4) is made of an AlGaAs-based material,_snGa_1-snIn the case of As, the Al composition sn is preferably less than 0.5. The Al composition of the first conductive type second clad layer (4) is made larger than the Al composition of the adjacent first conductive type first clad layer (3) and the Al composition of the first optical guide layer (5). . By adopting such a configuration, the first conductive type second clad layer (4) becomes a layer having the smallest refractive index, and has a function as a barrier to electrons in the conduction band and holes in the valence band. Will be. The difference between the Al composition of the first conductive type second clad layer (4) and the Al composition of the first conductive type first clad layer (3) is preferably larger than 0.08. This allows the first conductivity type second cladding layer (4) to sufficiently suppress the carrier overflow from the active layer structure (6) to the first conductivity type first cladding layer (3). However, the difference in Al composition between these two layers should be less than 0.4 so that the carrier injection from the first conductivity type first cladding layer (3) to the active layer structure (6) is not excessively inhibited. Is preferred.
[0041]
Thickness t of first conductivity type second cladding layer (4)_sn(Nm) is the thickness t of the first light guide layer (5)._gn(Nm) is preferable. By employing such a configuration, it is possible to avoid an extreme increase in the oscillation threshold, a decrease in the slope efficiency, and an increase in the drive current. In order to obtain a moderate vertical NFP enlargement effect, t_sn/ T_gnIs preferably greater than 0.3. Further, the thickness t of the first conductive type second cladding layer (4)_snIs preferably thicker than 10 nm and thinner than 100 nm. Thickness t of first conductivity type second cladding layer (4)_snIf it is less than 10 nm, the optical effect may be weakened, while if it is more than 100 nm, the light confinement becomes extremely weak and the LD may not oscillate.
[0042]
In the first conductivity type second cladding layer (4), the second cladding layer is made of an AlGaAs-based material._snGa_1-snIn the case of As, since the Al composition sn is relatively high in the LD structure of the present invention, the doping level of the dopant may be set higher than that of the first conductive type first clad layer (3). desirable. Particularly, in the case where the first conductivity type is n-type and Si is used as a dopant, assuming that crystal growth is performed by MBE, the doping level is 3.0 × 10 3¹⁷cm^-3~ 1.0x10¹⁸cm^-3And preferably 4.0 × 10¹⁷cm^-3~ 7.5x10¹⁷cm^-3Is more desirable.
[0043]
Here, the average refractive index of the first conductive type first cladding layer (3) is N_xn, The average refractive index of the first conductive type second cladding layer (4) is N_sn, The average refractive index of the active layer structure (6) described later is N_aIf these refractive indices are N_sn<N_xn<N_aIt is desirable to satisfy This is the FFP of the completed device_VThere are essentially three maxima in which the intensity is I_VmainThe main peak having a maximum value of_Vsub-And I_{Vsub +}And two subpeaks having a maximum value of 0 <I_Vsub/ I_Vmain<0.5 is one means for realizing (I_VsubIs I_Vsub-And I_{Vsub +}With greater strength).
[0044]
Although not shown in FIG. 5, between the first cladding layer (3) of the first conductivity type and the second cladding layer (4) of the first conductivity type, viewpoints such as lattice matching with the substrate (1) are made. Or, conversely, it is made of a material such as an AlGaAs-based material or an InGaP-based material which is appropriately selected from the viewpoint of intentionally introduced strain and the like. The first conductive type second clad layer (3) is inserted near the first conductive type second clad layer (4), and a layer close to the first conductive type second clad layer (4) is inserted on the first conductive type second clad layer (4) side. It is also possible. Such a transition layer can reduce the electric resistance when carriers are injected from the first conductive type first clad layer (3) side into the active layer structure (6) through the first conductive type second clad layer (4). Very preferred.
[0045]
The first light guide layer (5) on the first conductivity type second clad layer (4) can be made of various materials, and has an active layer structure (6) selected according to an oscillation wavelength to be realized. Alternatively, it is appropriately selected according to the substrate (1) and the like. For example, when the present invention is realized on a GaAs substrate, an AlGaAs-based material, an InGaP-based material, an AlGaInP-based material, or the like can be used. Materials and the like can be used.
[0046]
When the first light guide layer (5) is made of an AlGaAs-based material, the first light guide layer (5) has a smaller Al composition than the first conductivity type first clad layer (3) in order to realize light confinement. It must be made of material. Specifically, the Al composition of the first light guide layer (5) is preferably smaller than 0.4, more preferably smaller than 0.2, and further preferably smaller than 0.1. Most preferably, GaAs containing no Al is used. Particularly, from the viewpoint of reliability, a light guide layer containing no Al is desired.
[0047]
Also, the thickness t of the first light guide layer (5)_gn(Nm) preferably satisfies the following expression in order to allow the first conductivity type second cladding layer (4) to exhibit its function sufficiently.
(Equation 18)
0.5 × [λ / (4 × N_gn)] {Nm} <t_gn<1.5 × [λ / (4 × N_gn)] Nm
In the above equation, N_gnIs the refractive index of the first light guide layer (5). Thickness t of first light guide layer (5)_gnIs less than the upper limit of the above formula, in particular, the effect of suppressing the carrier overflow of the first conductivity type second cladding layer (4) can be sufficiently exhibited, and the reduction of the kink level can be effectively avoided. Also, the thickness t of the first light guide layer (5)_gnIs set to be larger than the lower limit of the above expression, it is possible to prevent the anti-waveguiding property of the first conductive type second cladding layer (4) from becoming excessive.
[0048]
In particular, when the first optical guide layer (5) is made of an AlGaAs-based material, the thickness t of AlGaAs is used._gnThe first light guide layer (5) need not necessarily be a layer having a single Al composition, and the Al composition can be changed in the first light guide layer (5). As described above, the refractive index in the case where regions having different Al compositions exist in the first light guide layer (5) can be considered as the refractive index of the first light guide layer (5) with an average refractive index.
[0049]
The effect of the present invention does not change even if the conductivity type of the first light guide layer (5) is p-type, n-type, or undoped.
[0050]
The same applies to the second light guide layer (7) located on the active layer structure (6).
[0051]
The active layer structure (6) referred to in the present invention is a single-layer bulk active layer having a sufficient film thickness so as not to exhibit a quantum effect, or a thin film so thin that the quantum effect becomes remarkable. There may be a single quantum well active layer (Single Quantum Well: SQW) in which the light guide layer plays a role as a barrier layer. In many cases, a barrier layer having a band gap larger than that of the quantum well layer is provided on both sides of the quantum well layer. Therefore, even with the same SQW structure, the barrier layer, the quantum well layer, and the barrier layer are stacked. It could have been done. Further, as shown in FIG. 5, the active layer structure includes, from the substrate (1) side, a barrier layer (21), a quantum well layer (22), a barrier layer (23), a quantum well layer (24), and a barrier layer ( 25) and a so-called double quantum well structure (Strained Double Double Quantum Well: $ S-DQW). Further, a multiple quantum well structure using three or more quantum well layers may be used. In addition, in some cases, strain is intentionally introduced into these quantum well layers. For example, it is widely practiced to incorporate compressive stress in order to lower the threshold value. Further, a semiconductor laser having a wavelength of about 900 nm to 1350 nm which is preferably applied in the present invention is realized by including a strained quantum well layer containing In, Ga and As on a GaAs substrate and not lattice-matched to the substrate. Is desirable.
[0052]
Specific materials for the strain quantum well layer include InGaAs, GaInNAs, and the like. The strained quantum well layer can be expected to increase the optical gain and the like due to the effect of the strain. For this reason, sufficient LD characteristics can be realized even if the light between the first cladding layers (3, 9, 10) and the active layer structure (6) is moderately weak in the vertical direction. For this reason, a strained quantum well layer is desirable in the present invention.
[0053]
Even if the conductivity type of the barrier layers (21, 23, 25) is p-type, n-type, or undoped, the effect of the present invention does not change, but the barrier layers (21, 23, 25) have n-type conductivity types. It is desirable to have the parts shown. In such a situation, since the electrons are supplied from the barrier layers (21, 23, 25) to the quantum well layers (22, 24) in the active layer structure, the gain characteristic of the LD is effectively broadened. Is desirable. Such an element can effectively fix the oscillation wavelength by an external resonator such as a grating fiber as described later. At this time, the n-type dopant is preferably Si. Further, an n-type dopant such as Si is not uniformly doped in the barrier layers (21, 23, 25), but is not uniformly doped in other layers such as the strained quantum well layers (22, 24). It is most preferable that the doping is not performed in the vicinity and the doping is selectively performed in the vicinity of the center of the barrier layer (21, 23, 25).
[0054]
The second conductivity type second cladding layer (8) can be made of various materials, and is appropriately formed according to the active layer structure (6) selected according to the oscillation wavelength to be realized or the substrate (1). Selected. For example, when the present invention is realized on a GaAs substrate, an AlGaAs-based material, an InGaP-based material, an AlGaInP-based material, or the like can be used. Materials and the like can be used.
[0055]
When the second conductivity type second cladding layer (8) is formed using an AlGaAs-based material, the Al composition is preferably less than 0.5. The Al composition of the second cladding layer (8) of the second conductivity type must be larger than the Al composition of the lower first cladding layer (9) of the adjacent second conductivity type and the Al composition of the second optical guide layer (7). Must. By adopting such a configuration, the second conductivity type second cladding layer (8) becomes a layer having the smallest refractive index, and has a function as a barrier to electrons in the conduction band and holes in the valence band. Will be. The difference between the Al composition of the second cladding layer (8) of the second conductivity type and the Al composition of the lower first cladding layer (9) of the second conductivity type is preferably larger than 0.08. Thereby, the second conductive type second clad layer (8) can sufficiently suppress the carrier overflow from the active layer structure (6) to the second conductive type lower first clad layer (9). However, it is preferable that the difference in Al composition be less than 0.4 so as not to excessively hinder the carrier injection from the lower second cladding layer (9) into the active layer structure (6).
[0056]
Thickness t of the second conductivity type second cladding layer (8)_sp(Nm) is the thickness t of the second light guide layer (7)._gp(Nm) is preferable. By employing such a configuration, it is possible to avoid an extreme increase in the oscillation threshold, a decrease in the slope efficiency, and an increase in the drive current. In order to obtain a moderate vertical NFP enlargement effect, t_sp/ T_gpIs preferably greater than 0.3. Further, the thickness t of the second conductive type second cladding layer (8)_spIs preferably thicker than 10 nm and thinner than 100 nm. Thickness t of the second conductivity type second cladding layer (8)_spIf it is less than 10 nm, the optical effect may be weakened, while if it is more than 100 nm, the light confinement becomes extremely weak and the LD may not oscillate.
[0057]
The second cladding layer (8) of the second conductivity type does not necessarily have to have the same refractive index, the same thickness, and the same material as the second cladding layer (4) of the first conductivity type. In order to ensure the properties, it is desirable that the layers have the same refractive index and have the same thickness.
[0058]
Further, the average refractive index of the active layer structure (6) is N_a, The refractive index N of the second conductive type second cladding layer (8)_spThe average refractive index of the second conductive type first cladding layer (9, 10) described below is N_xpWhen these refractive indices are N_sp<N_xp<N_aIt is desirable to satisfy This is the FFP of the completed device_VThe maximum intensity existing in_VmainAnd the maximum intensity is I_Vsub-And I_{Vsub +}0 <I for two subpeaks_Vsub/ I_Vmain<0.5 is one means for realizing (I_VsubIs I_Vsub-And I_{Vsub +}Out of the two).
[0059]
In particular, in the case where the second conductivity type is p-type and Be is used as a dopant, assuming that crystal growth is performed by MBE, the doping level is 3.0 × 10 3¹⁷cm^-3~ 1.0x10¹⁸cm^-3And preferably 4.0 × 10¹⁷cm^-3~ 7.5x10¹⁷cm^-3Is more desirable.
[0060]
Although not shown in FIG. 5, between the second cladding layer (8) of the second conductivity type and the lower first cladding layer (9) of the second conductivity type, lattice matching with the substrate (1) is performed. , Or conversely, an AlGaAs-based or InGaP-based material appropriately selected from the viewpoint of intentionally introduced strain, and the band gap of the second conductive type second cladding layer (8) is It is close to the second conductive type second clad layer (8), and close to the second conductive type lower first clad layer (9) on the second conductive type lower first clad layer (9) side. It is also possible to insert such layers. Such a transition layer reduces the electrical resistance when carriers are injected from the second conductive type first clad layer (9, 10) side into the active layer structure (6) through the second conductive type second clad layer (8). Very preferred because it can.
[0061]
In the embodiment of FIG. 5, the first cladding layer of the second conductivity type is divided into two layers, a lower first cladding layer (9) of the second conductivity type and an upper first cladding layer (10) of the second conductivity type. In this case, an etching stop layer may be provided between these two layers in order to facilitate the production of the device.
[0062]
The material of the second conductive type first cladding layer (9, 10) can be selected in the same manner as the second conductive type second cladding layer (8). In particular, when an AlGaAs-based material is used as the material of the second conductive type first cladding layers (9, 10), the second conductive type first clad layer (9, 10) is formed by using the second conductive type first clad layer (9, 10) in order to reduce the thermal resistance of the entire device and to obtain a structure suitable for high-output operation. The Al composition of the mold first cladding layer (9, 10) is preferably less than 0.40, more preferably 0.3 or less, and even more preferably 0.2 or less. The total thickness of the lower first cladding layer (9) of the second conductivity type and the upper first cladding layer (10) of the second conductivity type is sufficient to attenuate light in a direction away from the active layer structure (6). Therefore, it is preferable to make the wavelength larger than the oscillation wavelength λ.
[0063]
The thickness of the lower second cladding first cladding layer (9) is about 10 nm to 200 nm so that the current injection path to the active layer does not become extremely wide due to the lateral spread of the current. It is desirable. More desirably, it is desirably about 20 nm to 70 nm.
[0064]
The doping level of the lower first cladding layer (9) of the second conductivity type and the upper first cladding layer (10) of the second conductivity type is 1.0 × 10 4¹⁷cm^-3~ 1.0x10¹⁸cm^-33.0 × 10¹⁷cm^-3~ 7.5x10¹⁷cm^-3Is more desirable.
Further, the doping does not need to be performed uniformly in the lower first cladding layer (9) of the second conductivity type or the upper first cladding layer (10) of the second conductivity type. It is desirable that the lower the side is, the lower the layer structure (6) is. This is an effective method for suppressing absorption by free electrons in a portion having a high light density.
[0065]
The upper first cladding layer (10) of the second conductivity type, together with the current blocking layer (11) formed on the side surface thereof, realizes two functions of current confinement and lateral light confinement. This is a desirable configuration when the present invention is applied to an LD operating in a single transverse mode. For this reason, from the viewpoint of confining the current in the lateral direction, the conductivity type of the current blocking layer (11) is preferably the first conductivity type or undoped. Further, in order to satisfy the viewpoint of light confinement in the lateral direction, particularly, the characteristics as a waveguide based on refractive index guiding, the current blocking layer (11) is formed of the second conductivity type first cladding layer (9, 10). ) Is formed of a material having a smaller refractive index than that of the above. In this case, the FFP in the radiation pattern of the main peak_HBasically has one maximum value, which is desirable in the present invention. In addition, it is also possible to make the lateral light confinement a so-called loss guide type. In this case, the effective band gap of the material forming the current blocking layer (11) absorbs the oscillation wavelength. The FFP in the horizontal direction in the radiation pattern of the main peak_HCan basically have one maximum value, which is desirable in the present invention.
[0066]
In the present invention, the material constituting the current blocking layer (11) can be appropriately selected depending on the substrate (1), the active layer structure (6), or what kind of lateral waveguide structure. is there. For example, the current blocking layer (11) is formed of an AlGaAs-based material together with the second cladding-type first cladding layers (9, 10)._xpGa_1-xpAs, Al_zGa_1-zAssuming As, the real refractive index waveguide structure can be realized by setting the Al composition to z> xp. In the case of fabricating a semiconductor laser that is a real refractive index guided type and operates in a single transverse mode, the difference is mainly caused by the refractive index difference between the current blocking layer (11) and the upper first cladding layer (10) of the second conductivity type. The effective refractive index difference in the lateral direction defined by^-3It is desirable that the order be Further, a portion where the second conductive type upper first clad layer (10) and the second conductive type lower first clad layer (9) are in contact with each other, which is the width of the current injection path and corresponds to the width of the waveguide. From the viewpoint of operating the LD in the single transverse mode, the width W is uniform in the range of the error in the resonator direction perpendicular to the plane of the drawing, and the width is preferably 6 μm or less, and more preferably. Is preferably 3 μm or less. However, in order to achieve high output operation and single transverse mode operation at the same time, it is not always necessary that the waveguide is uniform in the cavity direction, and the front end face side, which is the main light emission direction of the semiconductor laser, , The width of the waveguide is relatively widened to be suitable for high-power operation, while the width of the waveguide is narrowed at the rear end face so that single transverse mode operation is possible. Is desirable. In such a case, the width of the current injection path near one light emitting point is set to W._expThe width W of the narrowest current injection path in the device_stdIn this case, it is preferable to satisfy the following expression.
[Equation 19]
1.5 <W_exp/ W_std<5.0
Further, it is more preferable to satisfy the following expression.
(Equation 20)
2.5 <W_exp/ W_std<$ 3.5
[0067]
The cap layer (12) is used as a protective layer for the current blocking layer (11) in the first growth and at the same time to facilitate the growth of the second conductivity type upper first cladding layer (10), Before obtaining the device structure, some or all are removed.
[0068]
It is preferable to provide a contact layer (13) on the second conductivity type upper first cladding layer (10) for the purpose of lowering the contact resistivity with the electrode (14). The contact layer (13) is usually made of a GaAs material. This layer usually has a higher carrier concentration than the other layers in order to lower the contact resistivity with the electrode (14). The conductivity type is the second conductivity type.
[0069]
The thickness of each layer constituting the semiconductor laser is appropriately selected within a range in which the function of each layer is effectively exhibited.
[0070]
In the semiconductor laser of the present invention, the first conductivity type is desirably n-type, and the second conductivity type is desirably p-type. This is because an n-type substrate is often of better quality.
[0071]
The semiconductor laser shown in FIG. 5 is manufactured by further forming electrodes (14) and (15). For example, when the second conductivity type is p-type, the epitaxial layer side electrode (14) is formed by sequentially depositing Ti / Pt / Au on the surface of the contact layer (13) and then performing an alloying treatment. On the other hand, the substrate-side electrode (15) is formed on the surface of the substrate (1). When the first conductivity type is an n-type, for example, AuGe / Ni / Au is sequentially deposited on the substrate surface and then formed by alloying. Is done.
[0072]
On the manufactured semiconductor wafer, an end surface which is a light emission surface is formed. The end face becomes a mirror constituting the resonator. Preferably, the end face is formed by cleavage. Cleavage is a widely used method, and the end face formed by cleavage varies depending on the orientation of the substrate (1) used. For example, when an element such as an edge-emitting laser is formed using a substrate having a plane which is crystallographically equivalent to the preferably used normally (100), (110) or crystallographically The equivalent surface is the surface that forms the resonator. On the other hand, when an off-substrate is used, the end face may not be at 90 degrees to the resonator direction depending on the relationship between the inclined direction and the resonator direction. For example, when the substrate (1) whose angle is inclined by 2 degrees from the (100) substrate toward the (1-10) direction is used, the end face also inclines by 2 degrees.
[0073]
The cleavage also determines the resonator length of the element. In general, a longer resonator length is more suitable for high-output operation, but in a semiconductor laser to which the present invention is applied, it is desirable that this length is 600 μm or more. More desirably, the thickness is preferably 900 μm to 3000 μm. The reason for the upper limit of the cavity length is that a semiconductor laser having an extremely long cavity length may cause characteristic deterioration such as an increase in threshold current and a decrease in efficiency. .
[0074]
In the present invention, it is preferable to form a coating layer (16, 17) made of a dielectric or a combination of a dielectric and a semiconductor on the exposed semiconductor end face, as shown in FIG. The coating layers (16, 17) are formed mainly for the purpose of increasing the light extraction efficiency from the semiconductor laser and for the purpose of protecting the end faces. In order to efficiently extract the light output from the element from one end face, a coating layer having a low reflectance (for example, a reflectance of 10% or less) with respect to the oscillation wavelength is applied to the front end face which is the main light emission direction. Also, it is desirable to perform asymmetric coating in which a coating layer having a high reflectance (for example, 80% or more) with respect to the oscillation wavelength is applied to the other rear end face. This is not only to increase the output of the device, but also to stabilize the wavelength by actively taking in the light returning from an external resonator such as a grating fiber used for wavelength stabilization. It is also very important in promoting. For these purposes, the reflectance of the front end face is preferably 5%, more preferably 2.5% or less.
[0075]
Various materials can be used for the coating layers (16, 17). For example, it is preferable to use one or a combination of two or more selected from the group consisting of AlOx, TiOx, SiOx, SiN, Si and ZnS. AlOx, TiOx, SiOx or the like is used as the coating layer having a low reflectance, and a multilayer film of AlOx / Si or TiOx / SiOx is used as the coating layer having a high reflectance. By adjusting the thickness of each layer, a desired reflectance can be realized. However, in general, the film thickness of AlOx, TiOx, SiOx or the like as a coating layer having a low reflectance is generally adjusted so that the real part of the refractive index at the wavelength λ is near λ / 4n. is there. Also in the case of a highly reflective multilayer film, it is general to adjust each material constituting the film so as to be in the vicinity of λ / 4n.
[0076]
By cleaving the coated laser bar again, each element can be separated to obtain a semiconductor laser.
[0077]
The present invention can be applied to a device manufactured in this manner or a device further including another layer without significantly deteriorating the main characteristics of the semiconductor laser._VCan effectively reduce the full width at half maximum of the semiconductor laser, and can realize good coupling between the semiconductor laser and an optical system including an optical fiber and a lens. In other words, the refractive index, thickness, etc. of the first cladding layer (3, 9, 10), the second cladding layer (4, 8), the light guide layer (5, 7), the active layer structure (6) and the like are appropriately adjusted. In a semiconductor laser which is set and whose normalized frequency is π / 2 or less so that only the propagation of the fundamental mode in the vertical direction is permitted, the FFP is used in the radiation pattern of light emitted from the semiconductor laser._VThe maximum intensity existing in_VmainAnd the maximum intensity is I_Vsub-And I_{Vsub +}0 <I for two subpeaks_Vsub/ I_Vmain<0.5 can be realized (I_VsubIs I_Vsub-And I_{Vsub +}Out of the two). In the present invention, 0 <I_Vsub/ I_Vmain<0.5, preferably 0 <I_Vsub/ I_Vmain<0.3, more preferably 0.05 <I_Vsub/ I_Vmain<0.2. These indices are the (average) refractive index of the first cladding layer (3, 9, 10), the second cladding layer (4, 8), the light guide layer (5, 7), the active layer structure (6), or It is defined by an absolute or relative relationship such as thickness. For example, extremely lowering the refractive index or increasing the thickness of the second cladding layer (4, 8), or extremely reducing the thickness of the light guide layer (5, 7), would result in an excessively large waveguide. The optical confinement in the vertical direction in the LD structure becomes too weak, resulting in an excessive increase in oscillation threshold, a decrease in slope efficiency, an increase in drive current, etc., which is not desirable. .
[0078]
Further, according to the present invention, the refractive index, the thickness, etc. of the first clad layer (3, 9, 10), the second clad layer (4, 8), the light guide layer (5, 7), the active layer structure (6), etc. Is very appropriately set, and an angle at which one main peak appears is defined as P (I_Vmain), Strength is I_Vsub-And I_{Vsub +}The angles at which the two sub-peaks appear as P (I_Vsub-), P (I_{Vsub +}), It is preferable to satisfy the following relationship. The more preferable range is the same as the preferable range in the description of FIG.
(Equation 21)
| P (I_Vmain) -P (I_Vsub-) |> 40 degrees
| P (I_{Vsub +}) -P (I_Vmain) |> 40 degrees
| P (I_{Vsub +}) -P (I_Vsub-) |> 80 degrees
[0079]
Also in this case, the appropriate vertical design as described above is implemented, and as a result of having the real refractive index waveguide structure, the FFP_HThe maximum value of I_Hmain, The angle at which this appears is P (I_HmainIt is most desirable that the following relationship be satisfied.
(Equation 22)
| P (I_Vmain) -P (I_Hmain) | <5 degrees
[0080]
In order to stabilize the wavelength of the semiconductor laser of the present invention, it is desirable to prepare a mirror having wavelength selectivity outside the laser and to couple the external resonator to the laser of the present invention. In particular, it is desirable to form an external resonator using a fiber grating. In this case, it is also possible to form a semiconductor laser module including a fiber grating, a cooler for stabilizing the temperature, and the like in addition to the semiconductor laser. For the fiber grating, the center wavelength, the reflection or transmission band, the reflectance of the fiber grating with respect to the laser light, and the like can be appropriately selected according to the purpose. In particular, the reflectance of light to the laser side of the fiber grating is 2 to 15%, preferably 5 to 10% at the laser oscillation wavelength, and its reflection band is 0.1 to 5. It is desirably 0 nm, preferably 0.5 to 1.5 nm.
[0081]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples. The materials, concentrations, thicknesses, operating procedures, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown in the following examples.
[0082]
<Example 1>
A semiconductor laser whose sectional view from the light emission direction is shown in FIG. 5 was manufactured by the following procedure.
First, a carrier concentration of 1.0 × 10¹⁸cm^-3On the (100) plane of the n-type GaAs substrate (1), a buffer layer (2) having a thickness of 0.5 μm and a carrier concentration of 1.0 × 10 was formed by MBE.¹⁸cm^-3Si-doped n-type GaAs layer having a thickness of 2.3 μm as a first conductivity type first cladding layer (3) and a carrier concentration of 1.3 μm from the substrate side is 7.5 × 10¹⁷cm^-3And 1 μm is 3.0 × 10¹⁷cm^-3Si-doped n-type Al_0.19Ga_0.81As layer; first conductive type two clad layer (4) having a thickness of 35 nm and a carrier concentration of 8.0 × 10¹⁷cm^-3Si-doped n-type In_0.49Ga_0.51P; as the first optical guide layer (5), the thickness is 80 nm, and the doping level of Si is 2.0 × 10¹⁷cm^-3A 45 nm-thick GaAs layer; an active layer structure (6) having a thickness of 5 nm and a carrier concentration of 7.5 × 10¹⁷cm^-3Undoped Si-doped n-type GaAs barrier layer (1 nm on the quantum well layer side is undoped)_0.16Ga_0.84As strained quantum well layer, thickness 7 nm, carrier concentration 7.5 × 10¹⁷cm^-3Si-doped n-type GaAs barrier layer (1 nm on both quantum well layer sides is undoped), undoped In_0.16Ga_0.84As strained quantum well layer, thickness 5 nm, carrier concentration 7.5 × 10¹⁷cm^-3An active layer structure comprising five layers of a Si-doped n-type GaAs barrier layer (1 nm on the quantum well layer side is undoped); a second optical guide layer (7) having a thickness of 80 nm and an undoped 45 nm from the substrate side; In addition, the doping level of Be is 3.0 × 10 at 35 nm.¹⁷cm^-3A GaAs layer having a thickness of 35 nm and a carrier concentration of 7.5 × 10 2 as a second conductivity type two-cladding layer (8);¹⁷cm^-3Be-doped p-type In_0.49Ga_0.51P layer: a second conductive type lower first cladding layer (9) having a thickness of 25 nm and a carrier concentration of 5.0 × 10¹⁷cm^-3Be-doped p-type Al_0.19Ga_0.81As layer; current blocking layer (11) having a thickness of 0.3 μm and a carrier concentration of 5.0 × 10¹⁷cm^-3Si-doped n-type Al_0.23Ga_0.78As layer; a carrier layer of 7.5 × 10 with a thickness of 10 nm as a cap layer (12)¹⁷cm^-3Of Si-doped n-type GaAs layers were sequentially laminated.
[0083]
A mask of silicon nitride was provided in a portion other than the current injection region in the uppermost layer. At this time, the width of the opening of the silicon nitride mask was 1.5 μm. Using this as a mask, etching was performed at 20 ° C. for 105 seconds to remove the cap layer and the current block layer in the current injection region. As the etching agent, a mixed solution obtained by mixing phosphoric acid (85% by weight), hydrogen peroxide (30% by weight aqueous solution) and water at a volume ratio of 1: 1: 30 was used.
[0084]
Thereafter, the thickness is 2.3 μm as the second conductivity type upper first cladding layer (10) by MOCVD, and the carrier concentration is 4.0 × 10 1 μm from the substrate side.¹⁷cm^-3And 1.3 μm thereon is 7.5 × 10¹⁷cm^-3Zn-doped p-type Al_0.19Ga_0.81As layer: a contact layer (13) having a thickness of 3.0 μm and a carrier concentration of 2.7 μm from the substrate side being 1.0 × 10¹⁸cm^-3And 0.3 μm above it is 6.0 × 10¹⁸cm^-3Was re-grown.
Further, Ti / Pt / Au is deposited as an epitaxial layer side (p-side) electrode (14) by 70 nm / 70 nm / 80 nm, respectively. After polishing the substrate, the substrate-side (n-side) electrode (15) is formed. Then, AuGeNi / Au was deposited by 150 nm / 80 nm, respectively, and then alloyed at 400 ° C. for 5 minutes to complete a semiconductor laser wafer.
The width W of the current injection region of the completed semiconductor laser was 2.2 μm.
[0085]
Subsequently, the substrate is cleaved in the air into a laser bar having a cavity length of 1600 μm to expose the (110) plane, and the AlOx film is made of 165 nm so that the reflectance at the front end face becomes 2.5% at an oscillation wavelength of 980 nm. The film was formed to form a coating layer (16) (FIG. 6). Further, in order to perform the processing on the rear end face side, a coating layer (17) consisting of four layers of an AlOx layer having a thickness of 170 nm / an amorphous Si layer having a thickness of 60 nm / an AlOx layer having a thickness of 170 nm / an amorphous Si layer having a thickness of 60 nm was formed. A rear end face with a reflectivity of 92% was produced.
[0086]
With respect to the current light output characteristics at 25 ° C. of the manufactured device, the threshold current was 29.9 mA, the slope efficiency was 0.91 W / A, and the kink level was 620 mW. The maximum light output was 761 mW when 1.22 A of current was injected.
FFP at 450mW light output_VHas a full width at half maximum of 23.5 degrees and is FFP_HWas 8.5 degrees. At this time, as shown in FIG._V, Three peaks were confirmed in the order of the auxiliary peak, the main peak, and the auxiliary peak, and the positions of the respective peaks were -54.6 degrees, 0.9 degrees, and 55.3 degrees in the order of angles. When the intensity of the main peak was 1, the relative intensities were 0.07, 1, and 0.04, respectively, in the order of the angles. On the other hand, FFP_VFFP of main peak of_HShowed only one peak, and the position of the peak was -0.2 degrees. Note that the oscillation wavelength of the device at 450 mW output was 984 nm.
[0087]
Using this element, an optical fiber with a grating having a wedge-shaped fiber lens was mounted on the front end face side of the element, and a semiconductor laser module having a butterfly type package was manufactured. The reflection center of this grating fiber was 982 nm, and the reflectance was 3%. At 25 ° C., the threshold current was 25.6 mA and the slope efficiency was 0.75 mW / mA with respect to the light emitted from the fiber end. The coupling efficiency was as good as about 82.4%.
[0088]
<Example 2>
A semiconductor laser whose sectional view from the light emission direction is shown in FIG. 5 was manufactured by the following procedure.
First, a carrier concentration of 1.0 × 10¹⁸cm^-3On the (100) plane of the n-type GaAs substrate (1), a buffer layer (2) having a thickness of 0.5 μm and a carrier concentration of 1.0 × 10 was formed by MOCVD.¹⁸cm^-3Si-doped n-type GaAs layer having a thickness of 2.3 μm as a first conductivity type first cladding layer (3) and a carrier concentration of 1.3 μm from the substrate side is 7.5 × 10¹⁷cm^-3And 1 μm is 3.0 × 10¹⁷cm^-3Si-doped n-type Al_0.45Ga_0.55As layer; first conductive type two clad layer (4) having a thickness of 35 nm and a carrier concentration of 1.0 × 10¹⁸cm^-3Si-doped n-type Al_0.71Ga_0.29As: As the first light guide layer (5), the thickness is 72 nm, and the doping level of Si is 2.0 × 10 32 nm from the substrate side.¹⁷cm^-3And 40 nm is undoped Al_0.26Ga_0.74As layer; active layer structure (6) having a thickness of 5 nm and a carrier concentration of 7.5 × 10¹⁷cm^-3Undoped Si-doped n-type GaAs barrier layer (1 nm on the quantum well layer side is undoped)_0.16Ga_0.84As strained quantum well layer, thickness 7 nm, carrier concentration 7.5 × 10¹⁷cm^-3Si-doped n-type GaAs barrier layer (1 nm on both quantum well layer sides is undoped), undoped In_0.16Ga_0.84As strained quantum well layer, thickness 5 nm, carrier concentration 7.5 × 10¹⁷cm^-3An active layer structure comprising five layers of a Si-doped n-type GaAs barrier layer (1 nm on the quantum well layer side is undoped); a second optical guide layer (7) having a thickness of 72 nm and 32 nm from the substrate side being undoped; In addition, the 40 nm has a Zn doping level of 3.0 × 10¹⁷cm^-3Al_0.26Ga_0.74As layer; second conductive type clad layer (8) having a thickness of 35 nm and a carrier concentration of 7.5 × 10¹⁷cm^-3Zn-doped p-type Al_0.71Ga_0.29As: a second conductivity type lower first cladding layer (9) having a thickness of 25 nm and a carrier concentration of 5.0 × 10¹⁷cm^-3Zn-doped p-type Al_0.45Ga_0.55As layer; current blocking layer (11) having a thickness of 0.3 μm and a carrier concentration of 5.0 × 10¹⁷cm^-3Si-doped n-type Al_0.49Ga_0.51As layer; a carrier layer of 7.5 × 10 with a thickness of 10 nm as a cap layer (12)¹⁷cm^-3Of Si-doped n-type GaAs layers were sequentially laminated.
[0089]
A mask of silicon nitride was provided in a portion other than the current injection region in the uppermost layer. At this time, the width of the opening of the silicon nitride mask was 1.5 μm. Using this as a mask, etching was performed at 20 ° C. for 97 seconds to remove the cap layer and the current block layer in the current injection region. As the etching agent, a mixed solution obtained by mixing phosphoric acid (85% by weight), hydrogen peroxide (30% by weight aqueous solution) and water at a volume ratio of 1: 1: 30 was used.
[0090]
Thereafter, the second conductive type upper first cladding layer (10) was 2.3 μm thick and the carrier concentration was 4.0 × 10 μm from the substrate side by MOCVD.¹⁷cm^-3And 1.3 μm thereon is 7.5 × 10¹⁷cm^-3Zn-doped p-type Al_0.45Ga_0.55As layer: a contact layer (13) having a thickness of 3.0 μm and a carrier concentration of 2.7 μm from the substrate side being 1.0 × 10¹⁸cm^-3And 0.3 μm above it is 6.0 × 10¹⁸cm^-3Was re-grown.
Further, Ti / Pt / Au is deposited as an epitaxial layer side (p-side) electrode (14) by 70 nm / 70 nm / 80 nm, respectively. After polishing the substrate, the substrate-side (n-side) electrode (15) is formed. Then, AuGeNi / Au was deposited by 150 nm / 80 nm, respectively, and then alloyed at 400 ° C. for 5 minutes to complete a semiconductor laser wafer.
The width W of the current injection region of the completed semiconductor laser was 2.3 μm.
[0091]
Subsequently, the substrate is cleaved in the air into a laser bar having a cavity length of 1600 μm to expose the (110) plane, and the AlOx film is made of 165 nm so that the reflectance at the front end face becomes 2.5% at an oscillation wavelength of 980 nm. The film was formed to form a coating layer (16) (FIG. 6). Further, in order to perform the processing on the rear end face side, a coating layer (17) consisting of four layers of an AlOx layer having a thickness of 170 nm / an amorphous Si layer having a thickness of 60 nm / an AlOx layer having a thickness of 170 nm / an amorphous Si layer having a thickness of 60 nm was formed. A rear end face with a reflectivity of 92% was produced.
[0092]
With respect to the current light output characteristics at 25 ° C. of the manufactured device, the threshold current was 27.1 mA, the slope efficiency was 0.94 W / A, and the kink level was 580 mW. The maximum light output of the device was 682 mW.
[0093]
The full width at half maximum of the vertical FFP was 21.8 degrees, and the full width at half maximum of the horizontal FFP was 8.7 degrees. At this time, the FFP in the vertical direction is, as shown in a typical example in FIG._V, Three peaks were confirmed in the order of a sub-peak, a main peak, and a sub-peak, and the positions of the respective peaks were -53.5 degrees, -0.2 degrees, and 53.9 degrees in the order of angles. When the intensity of the main peak was 1, the relative intensities were 0.1, 1, and 0.07, respectively, in the order of the angles. On the other hand, FFP_VFFP of main peak of_HShowed only one main peak, and the position of the peak was 0.5 degree. Note that the oscillation wavelength of the device at 450 mW output was 984 nm.
[0094]
Using this element, an optical fiber with a grating having a wedge-shaped fiber lens was mounted on the front end face side of the element, and a semiconductor laser module having a butterfly type package was manufactured. The reflection center of this grating fiber was 982 nm, and the reflectance was 3%. At 25 ° C., the threshold current was 23.6 mA and the slope efficiency was 0.78 mW / mA with respect to the light emitted from the fiber end. The coupling efficiency was as good as about 82.9%.
[0095]
<Example 3>
A loss guide type semiconductor laser having an oscillation wavelength near 780 nm was manufactured by the following procedure.
First, a carrier concentration of 1.0 × 10¹⁸cm^-3On the (100) plane of the n-type GaAs substrate (1), a buffer layer (2) having a thickness of 1.0 μm and a carrier concentration of 1.0 × 10 was formed by MOCVD.¹⁸cm^-3Si-doped n-type GaAs layer: the first conductivity type first cladding layer (3) has a thickness of 1.5 μm and a carrier concentration of 1.0 × 10 μm from the substrate side.¹⁸cm^-3And 0.5 μm is 6.0 × 10¹⁷cm^-3Si-doped n-type Al_0.55Ga_0.45As layer; first conductive type two clad layer (4) having a thickness of 25 nm and a carrier concentration of 1.0 × 10¹⁸cm^-3Si-doped n-type Al_0.8Ga_0.2As layer; undoped Al having a thickness of 100 nm as active layer structure (6)_0.15Ga_0.85As single bulk active layer; second conductive type clad layer (8) having a thickness of 25 nm and a carrier concentration of 1.0 × 10¹⁸cm^-3Zn-doped p-type Al_0.8Ga_0.2As layer; second conductive type lower first cladding layer (9) having a thickness of 350 nm and a carrier concentration of 8.0 × 10¹⁷cm^-3Zn-doped p-type Al_0.55Ga_0.45As layer; current blocking layer (11) having a thickness of 0.7 μm and a carrier concentration of 3.0 × 10¹⁸cm^-3Of Si-doped n-type GaAs layers were sequentially laminated.
[0096]
A mask of silicon nitride was provided in a portion other than the current injection region in the uppermost layer. At this time, the width of the opening of the silicon nitride mask was 1.2 μm. Using this as a mask, the current block layer in the current injection region was removed. As the etching agent, a mixed solution obtained by mixing phosphoric acid (85% by weight), hydrogen peroxide (30% by weight aqueous solution) and water at a volume ratio of 1: 1: 30 was used.
[0097]
After that, the second conductive type upper first cladding layer (10) was 1.15 μm thick and had a carrier concentration of 1.4 × 10 4 by MOCVD.¹⁸cm^-3Zn-doped p-type Al_0.55Ga_0.45As layer; contact layer (13) having a thickness of 7.0 μm and a carrier concentration of 7.0 × 10¹⁸cm^-3Was re-grown.
Further, Ti / Pt / Au is deposited as an epitaxial layer-side (p-side) electrode by 70 nm / 70 nm / 80 nm, respectively, and after the substrate is polished, AuGeNi / Au is used as a substrate-side (n-side) electrode. Vapor deposition was performed at 150 nm / 80 nm, and then alloying was performed at 400 ° C. for 5 minutes to complete a semiconductor laser wafer.
The width W of the current injection region of the completed semiconductor laser was 3.2 μm.
[0098]
Subsequently, in the air, the substrate was cleaved into a laser bar having a cavity length of 250 μm to expose the (110) plane, and an AlOx film was formed at an oscillation wavelength of 780 nm so that the reflectance on both front and rear end faces was 33%.
[0099]
With respect to the current light output characteristics at 25 ° C. of the fabricated device, the threshold current was 43.5 mA, and the slope efficiency was 0.29 W / A. The full width at half maximum of the vertical direction FFP at the time of output of 3 mW of this device was 22.8 degrees, and the full width at half maximum of the horizontal direction FFP was 8.7 degrees. At this time, three peaks were confirmed in the vertical FFP in the order of the sub-peak, the main peak, and the sub-peak. When the intensity of the main peak was 1, the relative intensities were 0.21, 1, and 0.11, respectively, in the order of angles. On the other hand, FFP_VFFP of main peak of_HShowed only one peak, and the position of the peak was 0.7 degree. The oscillation wavelength of the device at the time of output of 3 mW was 775 nm.
[0100]
<Comparative Example 1>
The thickness of the first light guide layer (5) and the second light guide layer (7) is 40 nm, the undoped region therein is 10 nm, and the first conductive type second clad layer (4) and the second conductive A semiconductor laser was fabricated in the same manner as in Example 1, except that the thickness of the mold second cladding layer (8) was both 50 nm.
The threshold current was 39.5 mA, the slope efficiency was 0.70 W / A, and the kink level was 485 mW, which was lower than that of Example 1 in overall device characteristics. The maximum light output of the device was 520 mW, which was lower than that of Example 1.
Further, in the vertical FFP at the time of 450 mW light output, three peaks are confirmed in the order of the sub-peak, the main peak, and the sub-peak, and the positions of the respective peaks are -55.8 degrees and 0.3 degrees in the order of angles. , 57.6 degrees, but the relative intensities when the intensity of the main peak is 1 are 0.61, 1.0, and 0.4, respectively, in the order of the angles. It was much larger than in Example 1. The full width at half maximum of the vertical FFP as measured only at the main peak portion was 15.2 degrees, and the full width at half maximum of the horizontal FFP was 8.4 degrees. Note that the oscillation wavelength of the device at 450 mW output was 992 nm.
[0101]
Using this device, a semiconductor laser module having a butterfly-type package similar to that of Example 1 was manufactured. At 25 ° C., the threshold current was 36.1 mA and the slope efficiency was 0.48 mW / mA for the light emitted from the fiber end. The coupling efficiency was about 68.6%, which was lower than that of Example 1.
[0102]
【The invention's effect】
The semiconductor laser of the present invention effectively reduces the full width at half maximum of the vertical far-field image of the emitted light without extremely deteriorating the main characteristics of the semiconductor laser, and an optical device comprising an optical fiber and a lens. Good coupling between the system and the semiconductor laser can be realized, and the high-output operation characteristics of the semiconductor laser itself can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the definition of the position of an FFP.
FIG. 2 is a cross-sectional view of one embodiment of the semiconductor laser of the present invention as viewed from a light emitting direction.
FIG. 3 shows a conventional semiconductor laser FFP._VFIG.
FIG. 4 is an FFP of the semiconductor laser of the present invention._VFIG.
FIG. 5 is a cross-sectional view of one embodiment of the semiconductor laser of the present invention as viewed from a light emission direction.
FIG. 6 is a perspective view illustrating one embodiment of a semiconductor laser of the present invention.
[Explanation of symbols]
31 substrate
32mm element structure
101 n-type substrate
102 n-type first cladding layer
103 n-type second cladding layer
104 first light guide layer
105 active layer structure
106 ° second light guide layer
107 p-type second cladding layer
108 p-type first cladding layer
109 contact layer
110 SiN layer
111 p side electrode
112 n side electrode
121, 123 strained quantum well layer
122 barrier layer
1 1st conductivity type substrate
2 Buffer layer
3 First conductivity type first cladding layer
4} First conductivity type second cladding layer
5 First light guide layer
6 Active layer structure
7 Second light guide layer
8 Second conductive type second cladding layer
9 Lower second cladding layer of second conductivity type
10 Second conductivity type upper first cladding layer
11 Current block layer
12mm cap layer
13 Contact layer
14 Epitaxial layer side electrode
15mm substrate side electrode
16, 17 coating layer
21, 23, 25 ° barrier layer
22,24 ° strained quantum well layer

Claims (14)

On the substrate showing the first conductivity type, at least a first conductivity type first clad layer, a first conductivity type second clad layer, an active layer structure, a second conductivity type second clad layer, a second conductivity type first clad A semiconductor laser having an oscillation wavelength λ (nm) that has layers in this order and only allows propagation of a fundamental mode in the longitudinal direction.
In a radiation pattern of light emitted from the semiconductor laser, in a far-field image (FFP _V ) in a direction perpendicular to the substrate, a main peak having a maximum intensity of I _Vmain and maximum intensities of I _Vsub− and I _Vsub− , respectively. A semiconductor laser having two _{subpeaks of Vsub +} and satisfying the following expression.

(In the above formula, I _Vsub represents the larger one of I _Vsub− and I _{Vsub +} .) The semiconductor laser of claim 1 wherein the angle of the _{P (I Vmain)} the main peak appears, each maximum intensity _{I Vsub-} and _{I Vsub +} a is two sub peak appears angle _{P (I Vsub-),} A semiconductor laser characterized by satisfying the following expression when P ( _{IVsub +} ).

3. The semiconductor laser according to claim 1, wherein in a radiation pattern of a main peak emitted from the semiconductor laser, only one local maximum exists in a far-field image (FFP _H ) in a direction parallel to the substrate. A semiconductor laser characterized by not being used. _4. The semiconductor laser according to claim 3, wherein the maximum intensity of the far-field image (FFP _H ) in the direction parallel to the substrate is I _Hmain , and the angle at which the peak having the maximum intensity appears is P (I _Hmain ). And a semiconductor laser satisfying the following expression.

The semiconductor laser according to claim 1, wherein the oscillation wavelength λ (nm) satisfies the following expression.

The semiconductor laser according to claim 1, wherein the semiconductor laser does not have a plurality of light emitting points in the element. The semiconductor laser according to any one of claims 1 to 6, wherein an average refractive index of the first conductive type first cladding layer is _Nxn , and an average refractive index of the first conductive type second cladding layer is _Nsn. , an average refractive index of the active layer structure N _a, the refractive index N _sp of the second conductive type second clad _layer, when the average refractive index of the second conductive type first clad layer and N _xp, these refractive index A semiconductor laser characterized by satisfying the following expression.

The semiconductor laser according to claim 7, having at least one side to the light guide layer of the active layer structure, when the refractive index N _g, and wherein the refractive index of each layer satisfies the following formula Semiconductor laser.

The semiconductor laser according to any one of claims 1 to 8, wherein the substrate is made of GaAs, and the first conductive type first clad layer, the first conductive type second clad layer, and the second conductive type second clad. A semiconductor laser, wherein at least a part of the first cladding layer and the second conductivity type contains Al, Ga and As. The semiconductor laser according to any one of claims 1 to 9, wherein the substrate is made of GaAs, and the first conductive type first clad layer, the first conductive type second clad layer, and the second conductive type second clad. A semiconductor laser, wherein at least a part of the first cladding layer and the second conductivity type contains In, Ga and P. The semiconductor laser according to claim 1, wherein the active layer structure includes a strained quantum well layer, and the quantum well layer includes In, Ga, and As. The semiconductor laser according to any one of claims 1 to 11, wherein the first conductivity type is n-type and the second conductivity type is p-type. A semiconductor laser module, comprising: the semiconductor laser according to claim 1; and an optical fiber on a light emitting end side of the semiconductor laser. 14. The semiconductor laser module according to claim 13, wherein the tip of the optical fiber has a light-collecting effect and is processed so as to be directly optically coupled to the front end face of the semiconductor laser. Laser module.

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