JP2001015857A - Semiconductor laser - Google Patents

Abstract

(57) [Problem] To provide a semiconductor laser having a high kink level and a low drive current value. SOLUTION: On a GaAs substrate, at least a first conductivity type clad layer, an active layer containing In, Ga and As as elements, a second conductivity type first clad layer, a current blocking layer and a second conductivity type second clad layer. Wherein the current blocking layer and the second conductive type second cladding layer have a width of 1.5 to
A 2.5 μm current injection region is formed, and the effective refractive index difference Δn _eff in the lateral direction is 2.5 × 10 ⁻³ to 4.
5. A semiconductor laser having a size of 5 × 10 ⁻³ , wherein the active layer has a quantum well structure in which compressive strain is inherent, and a cavity length is 800 μm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser. The semiconductor laser of the present invention is suitably used particularly when high output and long life are required such as an excitation light source for an optical fiber amplifier.

[0002]

2. Description of the Related Art The progress of optical information processing technology and optical communication technology in recent years has been remarkable. For example, there is no shortage of high-density recording using a magneto-optical disk and two-way communication using an optical fiber network. In the telecommunications field in particular, along with a large-capacity optical fiber transmission line that is fully compatible with the future of the multimedia era, an optical fiber doped with a rare earth element such as Er ^{3+ is used} as an amplifier for signal amplification with flexibility for the transmission system. Research on amplifiers (EDFA) has been actively conducted in various fields. The development of a high-power, long-life semiconductor laser, which is an indispensable component of an EDFA, has been awaited.

The emission wavelength of a semiconductor laser that can be used for EDFA applications is 800 nm, 980 nm in principle.
m and 1480 nm. From the viewpoint of the amplifier itself, it is known that pumping at 980 nm is most desirable in consideration of gain, noise and the like. Since the laser having the transmission wavelength of 980 nm is used in combination with an optical fiber, the emitted laser light must have a stable transverse mode regardless of injection current, temperature, return light from the fiber end face, and the like. Is desired, and
Since it is an excitation light source, it is required to have high output and long life. Further, there is a demand for an SHG light source at a wavelength in the vicinity of this, and the development of a high-performance laser in various other application fields is awaited.

[0004] However, the previously reported 980
A semiconductor laser having a wavelength in the vicinity of nm, particularly an element having a refractive index waveguide structure on the premise of coupling with an optical system, has the following problems. That is, high output, for example, 1
In a light output region of about 50 to 200 mW, a non-linear behavior in current / light output characteristics called kink has been observed. This is due to instability of the transverse mode due to various causes, which hinders stable coupling with the fiber. Further, this kink is observed even in a laser having a similar layer configuration from a region having a relatively low light output, with only a slight difference in the layer composition and thickness.
When the temperature is increased, it is observed from a region having a particularly low light output.

To cope with this problem, Japanese Patent Laid-Open No.
JP200201 describes that the effective refractive index difference Δn _eff is 2.5 × 10 ^{−3 to} 5.0 × 10 ⁻³ at the emission wavelength. If the effective refractive index difference is set in such a range, the kink level is surely set to 200 to 260 mW.
Although it can be increased to a degree, next generation lasers are still required to achieve high kink levels. In particular, there is a demand for a semiconductor laser capable of achieving a high kink level while keeping the drive current value low.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to meet these needs and to solve the problems of the prior art. That is, an object of the present invention is to provide a semiconductor laser having a high kink level and a low drive current value. In particular, it has been a problem to be solved to provide a semiconductor laser having a kink level of 400 mW or more near room temperature and having an emission wavelength of around 980 nm.

[0007]

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 an InGaAs-based semiconductor laser having a refractive index waveguide mechanism, an active layer has an intrinsic compressive strain. The present inventors have found that an excellent semiconductor laser exhibiting a desired effect can be provided by forming a quantum well structure as described above and further setting the cavity length in a specific range, and have provided the present invention.

That is, according to the present invention, at least a first conductivity type cladding layer and In and Ga
And an active layer containing As, a second conductive type first clad layer,
A current blocking layer and a second conductivity type second cladding layer, wherein the current blocking layer and the second conductivity type second cladding layer form a current injection region having a width of 1.5 to 2.5 μm; A semiconductor laser having an effective refractive index difference Δn _eff of 2.5 × 10 ^{−3 to} 4.5 × 10 ⁻³ at an emission wavelength, wherein the active layer has a quantum well structure in which compressive strain is intrinsic. And a semiconductor laser having a cavity length of 800 μm or more.

As a preferred embodiment of the semiconductor laser of the present invention, an embodiment in which the cavity length is 2000 μm or less; an embodiment in which the cavity length is 1000 to 1500 μm; And A
s; the current blocking layer is formed of Al _z Ga _1-z As (0
≦ z ≦ 1), and the second cladding layer of the second conductivity type is Al
Embodiment composed of _y Ga _1-y As (0 <y ≦ 1); Embodiment having an emission wavelength of 900 to 1200 nm;
Embodiment is 1100 nm; aspect a pumping light source of the optical fiber _{amplifier; In q Ga 1-q As} (0 <q <1) layer and _{Al x Ga 1 -x As (0} ≦ x ≦ 1) and an optical guide layer Active layer having strained quantum well structure, Al _y Ga _1-y As
(0 <y ≦ 1) Second conductivity type second cladding layer and Al
_a ridge-type or groove-type current injection region composed of a zGa _1-z As (0 ≦ z ≦ 1) current block layer;
Embodiment in which the mixed crystal ratio of each layer has a relationship of x <y ≦ z; Al _a G between the first cladding layer of the second conductivity type and the current blocking layer.
a _1-a As (0 ≦ a ≦ 1) Second etching stop layer and In _b
An embodiment having a Ga _b P (0 ≦ b ≦ 1) first etching stop layer can be given. In this specification, “to” indicates a range including the numerical values described before and after that.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a semiconductor laser according to the present invention will be described in detail. In the semiconductor laser of the present invention, the effective refractive index difference Δn _eff in the lateral direction is 2.5 × 10 ^{−3 to} 4.5 × 10 ^{−3 at} the emission wavelength, and the width W of the current injection region is 1.5 to 10 × 10 ^−3. 2.5 μm, the active layer has a quantum well structure with compressive strain, and the resonator length is 8 μm.
It satisfies the condition that it is not less than 00 μm. Note that the width W of the current injection region is the width of the bottom of the current injection region, that is, the portion of the second conductive type second cladding layer closest to the substrate in the current injection region. Of these conditions, the lateral effective refractive index difference Δn _eff will first be described in detail.
FIG. 1 is a schematic sectional view of an element for explaining the effective refractive index difference Δn _eff used in the present invention. The element structure used in FIG. 1 is a structure that confine the parallel transverse mode of laser light by a refractive index difference called a refractive index waveguide structure. A stripe called a current injection region is formed, and the current blocking region (9) having a low refractive index disposed on both side surfaces of the current injection region refracts in the direction parallel to the active layer between the current injection region and the outside thereof. It has the characteristic that a rate step is created.

In this case, the effective refractive index difference Δn _eff is approximately a function of the composition and thickness of each layer and the emission wavelength, and its theory and calculation method are described in “Heterostructure Lase”.
rs; HC Casey, Jr., MB Panish; Academic Press (1
978) "Part A, p20-p109 and part B, p156-276" and "Semiconductor Laser Fundamentals and Applications" (5th print; Ryoichi Ito,
Edited by Michiharu Nakamura; Baifukan; published on March 30, 1995)
Although described in Chapters 5 and 5, etc., a specific calculation method in the layer configuration of the present invention is as follows.

[0012] To determine the effective refractive index difference [Delta] n _eff, internal current injection region first first-conductivity-type cladding layer with (in Fig. 1 AA ^* cross-section) (3), the active layer (4), the second conductivity type A multilayer film composed of one clad layer (5) and second conductive type second clad layer (8) is regarded as a slab waveguide, and a waveguide mode of a laser beam propagating through the multilayer film is calculated for a TE mode, and an emission wavelength is calculated. Find the effective refractive index of the fundamental mode at. When calculating the waveguide mode, an approximation to make the thicknesses of the first conductive type clad layer (3) and the second conductive type second clad layer (8) infinite is performed. When the active layer is composed of a strained quantum well and a light guide layer, an approximation is performed in which the refractive index of the strained quantum well used for calculation is replaced with the refractive index of the light guide layer. The effective refractive index for the fundamental mode obtained in this manner is _defined as n _eff (AA ^* ). Next, similarly, outside the current injection region (BB ^* section in FIG. 1), the first conductivity type clad layer (3), the active layer (4), the second conductivity type first clad layer (5), and the current blocking layer ( 9) and the second conductive type second cladding layer (8) is regarded as a slab waveguide, and the effective refractive index of the fundamental mode of the waveguide mode is obtained.
This is _defined as n _eff (BB ^* ). In an actual device structure, a layer such as an etching stop layer for forming the device is often inserted in addition to the layer shown in FIG. 1. In this case, the first conductivity type is used in the cross section AA ^* and the cross section BB ^* . Each of the multilayer films composed of all layers included between the cladding layer (3) and the second conductivity type second cladding layer (8) has n
_eff (AA ^* ) and n _eff (BB ^* ). In an actual device structure, the shape of the current injection region is not a rectangle as shown in FIG. 1 but an inverted trapezoidal shape in many cases. In this case, n _eff ( A
A ^* ) to determine n outside the widest part of the current injection region.
_{Find eff} (BB ^* ). N obtained in this way
_eff (AA ^*) and from n _eff (BB ^*) the effective refractive index difference is defined as ^{_{Δn eff = n eff (AA *}} ) -n eff (BB *).

According to the present invention, the effective refractive index difference Δ
n _eff satisfies the following equation (I). This makes it possible to achieve both the stability of the kink level and the stability at high temperatures. 2.5 × 10 ⁻³ ≦ Δn _eff ≦ 4.5 × 10 ⁻³ (I) The lateral direction is a direction perpendicular to both the laminating direction of each layer and the light emitting direction. That is.

Further, the optimum effective refractive index difference Δn _eff differs depending on the emission wavelength and the characteristics of the semiconductor laser required from the application field. The semiconductor laser according to the present invention has In, G
having an active layer containing a and As. The above formula (I) is characterized in that 900-1
The optimum range of the effective refractive index difference Δn _eff at an emission wavelength of about 200 nm, preferably about 900 to 1100 nm is specified.

The semiconductor laser of the present invention has a refractive index guiding mechanism, and has at least a first conductivity type cladding layer, an active layer, a second conductivity type first cladding layer, a current blocking layer and a second conductivity type cladding layer on a GaAs substrate. A layer configuration having the mold second cladding layer in this order is adopted. A planar laser can be obtained by constructing such a layer configuration entirely from a semiconductor material.
Excellent heat dissipation and high-temperature stability can be obtained.

The resonator length of the semiconductor laser of the present invention is 800
μm or more. Preferably it is 800-2000 micrometers, More preferably, it is 1000-1500 micrometers. By setting the cavity length to 800 μm or more, the current density injected into the active layer in the semiconductor laser having the effective refractive index difference Δn _eff within the range of the above formula (I) can be particularly effectively reduced. If the cavity length is less than 800 μm, the variation in the refractive index step due to the amount of injected carriers increases, which is not preferable. In particular, in the case of a semiconductor laser according to the present invention, when a high-order mode is weakly guided with a refractive index in consideration of a margin in order to completely cut off a higher-order mode, the fluctuation of the refractive index step has a larger effect than usual. It is important to control the cavity length to effect

FIG. 2 is a schematic example in which a groove type semiconductor laser is formed as an example of the epitaxial structure in the semiconductor laser of the present invention. In the semiconductor device of the present invention, a GaAs single crystal substrate is used as the substrate from the viewpoint of lattice matching. Such a GaAs single crystal substrate (1) is usually obtained by cutting out a bulk crystal.

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), and usually GaAs is used. The first conductivity type cladding layer (3) is usually made of a material having a refractive index smaller than that of the active layer (4), and when GaAs is used as the buffer layer (2), it is usually made of AlG.
An aAs-based material (Al _V Ga _{1 -V} As) is used, and its mixed crystal ratio is appropriately selected so that the refractive index satisfies the above condition.

The material and structure of the active layer (4) are appropriately selected depending on the intended emission wavelength, output, and the like, but must have a quantum well structure with intrinsic compressive strain. The active layer (4) includes at least In, Ga
And a material containing As, usually In _q Ga _1-q As (0 <q
<1), and various quantum well structures (SQW, MQW) composed of a thin film and the like can be adopted as the structure. Then, an optical guide layer is usually used in combination with the quantum well structure. As a structure of the light guide layer, a structure in which light guide layers are provided on both sides of the active layer (SCH structure), and a structure in which the refractive index is continuously changed by gradually changing the composition of the light guide layer (GRIN- (SCH structure) or the like. The composition of the light guide layer is A
l _x Ga _{1 -x} As (0 ≦ x ≦ 1) is preferable. In the semiconductor laser of the present invention, since the active layer (4) has a quantum well structure in which compressive strain is inherent, the drive current value does not increase extremely even if the resonator length is increased. This is because the active layer has a quantum well structure in which compressive strain is inherent, and therefore has a gain even at a low current density, and does not cause a large current rise as compared with a semiconductor laser having an unstrained active layer. It is.

The second conductive type first cladding layer (5) is made of a material having a smaller refractive index than the active layer (4).
And a refractive index of the second conductivity type first cladding layer (5);
The refractive index of the first conductivity type cladding layer (3) is usually the same. Therefore, as the material of the second conductive type first cladding layer (5), similarly to the first conductive type clad layer (3), an AlGaAs-based material is usually used, and the mixed crystal ratio thereof is the first conductive type. Usually the same as the cladding layer (3). In this structure, the first cladding layer (5) of the second conductivity type is made of Al _W G
This corresponds to a layer made of a _1-W As.

FIG. 2 shows two types of etching stopper layers and
And cap layers are described, but these layers
In a preferred embodiment, the current injection region
This is effective for performing the insertion precisely and easily. Second edge
The tinning prevention layer (6) is made of Al _aGa_1-aAs (0 ≦ a ≦
1) Made of material, but GaAs is usually preferred
Is done. This is the second conductivity type second crack by MOCVD or the like.
Layer, etc., especially when regrown with an AlGaAs system.
This is because the layers can be stacked with good crystallinity. 2nd etch
Usually, the thickness of the blocking layer (6) is preferably 2 nm or more.

The first etching stop layer (7) is made of In _b G
A layer represented by a _1-b P (0 ≦ b ≦ 1) is preferable, and when GaAs is used as the substrate as in the present invention, b = 0.5 is usually used in a strain-free system. . The thickness of the first etching stop layer is usually 5 nm or more, preferably 1 nm.
0 nm or more. In _0.5 Ga _0.5 P is AlGa
Since the heat dissipation is inferior to As, it is preferably 100 nm or less. If the thickness is less than 5 nm, etching may not be able to be stopped due to a disorder of the film thickness or the like. On the other hand, depending on the film thickness, a strain system can be used,
It is also possible to use b = 0, b = 1, and the like. When a strain system is used, the thickness is from one molecular layer to 15 nm, preferably 10 nm or less. If the film thickness is thin in such a manner, there is no problem even if lattice matching cannot be attained because the intrinsic strain is alleviated.

The cap layer (10) is used as a protective layer for the current blocking layer (9) in the first growth and at the same time to facilitate the growth of the second conductive type second clad layer (8). Before the device structure is obtained, some or all of them are removed. Since it is necessary for the current blocking layer (9) to literally block a current and not substantially flow, the conductivity type is preferably the same as that of the first conductivity type cladding layer or undoped. Usually, it is preferable that the refractive index is smaller than that of the second conductive type second clad layer (8) made of Al _y Ga _1-y As (0 <y ≦ 1). Normally, the current blocking layer is also made of Al _z Ga _{1 -z} As (0 ≦ z
≦ 1), and therefore it is preferable that the mixed crystal ratio satisfy z ≧ y. Further, in relation to the above-described light guide layer, it is preferable that x <y ≦ z.

The current blocking layer is made of In _0.5 Ga _0.5 P
Can also be configured. In that case, Al _a Ga _1-a As
(0 ≦ a ≦ 1) In only the second etching stopper layer (6)
The etching of the _0.5 Ga _0.5 P current blocking layer can be stopped, and the subsequent Al _y Ga _1-y As (0 <y ≦
1) it can be performed second conductive type second clad layer (8) Re-growth easily in the above _{In b Ga 1-b P (} 0 ≦ b
The first etching stop layer (7) consisting of ≦ 1) is unnecessary.

In order to realize a semiconductor laser having a longer life, the first conductive type first clad layer (3), the second conductive type first clad layer (5), and the second conductive type second clad layer (8). For example, it is preferable to use a material whose Al mixed crystal ratio is not so high. Specifically, the Al mixed crystal ratios v, w, and y of each layer
Is preferably 0.4 or less.
More preferably, from the relationship with the laser temperature characteristics, 0.3 ≦
v, w, y ≦ 0.4 are appropriate.

Here, the effective refractive index difference Δn _eff between the portion including the current blocking layer (9) and the portion not including the current blocking layer (9) satisfies the expression (I) as described above. For example, when forming the second conductivity type second cladding layer and the current blocking layer using an AlGaAs-based material, the Al mixed crystal ratio must be accurately controlled so as to satisfy the above (I).
As a result, the Al mixed crystal ratio z of the current block layer is preferably about 0.5 or less. More preferably, 0.3 ≦ z ≦ 0.
5

In order to obtain a high kink level when the effective refractive index difference Δn _eff satisfies the above formula (I), it is necessary to use a current injection layer composed of a current blocking layer and a second conductive type second cladding layer. The width W of the region must be 2.5 μm or less. However, if W is too small, the light density at the laser end face becomes high, and the laser may be broken before a sufficient light output is reached. Therefore, the lower limit of W is set to 1.5 μm or more.

The refractive index of the second-conductivity-type second cladding layer (8) is usually lower than that of the active layer (4). The second conductive type second clad layer (8) is usually the same as the first conductive type clad layer (3) and the second conductive type first clad layer (5). Further, as one of preferred embodiments of the present invention, all of the first cladding layer of the second conductivity type, the second cladding layer of the second conductivity type, and the current blocking layer are formed of the same composition material. In that case, an effective refractive index difference is formed by the first etching stop layer, and when the cap layer is not completely removed, an effective refractive index difference is formed by the cap layer in addition to the first etching layer. . By adopting such a layer configuration, it is possible to avoid various problems caused by the inconsistency of the composition at the respective interfaces of the first cladding layer of the second conductivity type, the second cladding layer of the second conductivity type, and the current blocking layer. , Very preferred.

A contact layer (11) is provided on the second conductive type second clad layer (8) for the purpose of lowering the contact resistivity of the electrode. The contact layer (11) is usually G
It is composed of aAs material. This layer usually has a higher carrier concentration than the other layers in order to lower the contact resistivity with the electrode. Usually, the thickness of the buffer layer (2) is 0.1 to 1 μm.
m, preferably 0.5 to 1 μm, and the thickness of the first conductivity type cladding layer (3) is 0.5 to 5 μm, preferably 1 to 3 μm.
m, the thickness of the active layer (4) is 0.0005 to 5 per layer.
0.02 μm, preferably 0.003 to 0.2 μm, and the thickness of the second conductivity type first cladding layer (5) is 0.05 to 0.1 μm.
3 μm, preferably 0.05 to 0.2 μm, the second conductive type second cladding layer (8) has a thickness of 0.5 to 5 μm, preferably 1 to 3 μm, and the current blocking layer (9) has a thickness of 0 μm. .3
To 2 μm, preferably 0.3 to 1 μm, for the cap layer (1
0) has a thickness of 0.005 to 0.5 μm, preferably 0.1 to 0.5 μm.
It is selected from the range of 005 to 0.3 μm.

The electrode (1) is formed on the contact layer (11).
2) is formed. At this time, the electrode (12) may be formed so as to be in contact with the entire upper surface of the contact layer (11) as shown in FIG. 2, or a part of the bottom surface of the electrode (12) may be formed on the upper surface of the contact layer (11). , And the lower portion of the electrode may form a current confinement structure together with the second current blocking layer. As an example of the latter current constriction structure, it is preferable to form a stripe-shaped current confinement structure. The second current blocking layer is preferably formed by a dielectric film. SiN is used as such a dielectric film.
x, SiOx or AlOx can be exemplified, and SiNx is particularly preferable. The thickness of such a dielectric film is 5
It is preferably not more than 00 nm, more preferably not more than 250 nm, and particularly preferably not more than 150 nm.

In the current confinement structure, the area of the contact portion between the contact layer and the electrode is preferably 1 to 20% of the area of the contact layer, more preferably 2 to 10%. It is particularly preferred that the content be 3 to 8%. The current confinement structure formed by the second current block layer is preferably formed so that current is not injected into at least one end face, preferably both end faces. The current confinement structure is preferably configured so that current is not injected into a region of preferably 10 μm or more, more preferably 20 μm or more, and still more preferably 30 μm or more from the end face. 100μ in some cases
It is also possible to configure so that current is not injected into the region of m or more.

The current confinement structure is preferably formed immediately above the current injection region formed by the current blocking layer and the second conductivity type second cladding layer. By employing such an embodiment, effective current confinement can be performed. In such a current confinement structure, for example, a second current block layer is formed on the entire surface of the contact layer (11), only the region where the current confinement structure is formed is removed by photolithography or the like, and the electrode (12) ) Can be easily formed.

The electrode (12) is made of, for example, Ti
/ Pt / Au is formed by sequentially depositing and then alloying. On the other hand, the electrode (1) is also provided on the substrate (1) side.
Construct 3). In the case of an n-type electrode, for example, AuGe / Ni / Au is sequentially vapor-deposited on the surface of the substrate (1), followed by alloying to form the electrode (13).

The wafer completed by forming electrodes thereon is first cleaved by a laser bar. The end face of the laser bar is usually asymmetrically coated with Si, Al ₂ O ₃ , SiN _x or the like so that the front end face reflectivity is about 2.5% and the rear end face reflectivity is about 93%. It is divided and used as a laser diode (LD). Although the above description has been made with respect to a groove type semiconductor laser, the present invention can be similarly applied to a ridge type semiconductor laser as long as the effective refractive index difference is within the range described in the claims.

[0035]

The present invention will be described more specifically with reference to the following examples. Materials, concentrations, thicknesses, operation 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.

(Embodiment 1) A groove type groove shown in FIG.
The device was manufactured according to the following procedure. Career concentration
Degree 1 × 10¹⁸cm^-3On an n-type GaAs substrate (1)
According to the BE method, a buffer layer (2) having a thickness of 1 μm
Rear concentration 1 × 10¹⁸cm^-3N-type GaAs layer, first conductive
2.5 μm thick carrier concentration as mold cladding layer (3)
Degree 1 × 10¹⁸cm^-3N-type Al_0.35Ga_0.65As layer, next
Two 35-nm-thick undoped GaAs light guide layers
6 nm thick undoped In sandwiched between_0.16Ga_0.84A
active layer having a single quantum well (SQW) structure
(4) Thickness as the second conductivity type first cladding layer (5)
Carrier concentration 1 × 10 at 0.1 μm¹⁸cm^-3P-type Al
_0.35Ga_0.65As layer and second etching stop layer (6)
And a carrier concentration of 1 × 10 with a thickness of 10 nm¹⁸cm^-3P-type
GaAs layer, thickness 2 as first etching stop layer (7)
Carrier concentration 5 × 10 at 0 nm¹⁷cm^-3N-type In_0.49
Ga_0.51P layer, thickness 0.5 as current block layer (9)
5 × 10 carrier concentration at μm¹⁷cm^-3N-type Al_0.39G
a_0.6110 nm thick as As layer and cap layer (10)
And carrier concentration 1 × 10¹⁸cm^-3N-type GaAs layer
They were sequentially laminated.

Next, a mask of silicon nitride was provided in a portion other than the current injection region in the uppermost layer. In this case, the width of the opening of the silicon nitride mask was 1.5 μm. First
Etching was performed using the etching stopper layer as an etching stop layer, and the cap layer (10) and the current block layer (9) in the current injection region were removed. The etching solution used at this time was sulfuric acid (98 wt%), hydrogen peroxide (30 wt%).
% Aqueous solution) and water at a volume ratio of 1: 1: 5, and etching was performed at 25 ° C. for 30 seconds.

Next, HF (49%) and NH ₄ F (40
%) In an etching solution mixed at a ratio of 1: 6 to remove the silicon nitride layer for 2 minutes and 30 seconds, and further etch the first etching stop layer in the current injection region using the second etch stop layer as an etch stop layer. Removed. The etching solution used at this time was hydrochloric acid (35 wt%) and water:
1 and etching was performed at 25 ° C. for 2 minutes.

Thereafter, a carrier concentration of 1 × 10 ¹⁸ cm ^{−3 is formed} as a second conductive type second clad layer (8) by MOCVD.
The p-type Al _0.35 Ga _0.65 As layer is grown to a thickness of 2.5 μm in the buried portion (current injection region).
Finally, as a contact layer (11) for maintaining good contact with the electrode, a thickness of 3 μm and a carrier concentration of 1 × 10 ¹⁹
A p-type GaAs layer of cm ^-3 was also grown by MOCVD to form a laser element wafer. After the electrodes were formed, the obtained laser device wafer was cleaved into laser bars having a cavity length of 1200 μm. Then, according to a conventional method, the end face was subjected to asymmetrical coating so that the front end face reflectivity was 2.5% and the rear end face reflectivity was 93%, and then divided into chips to obtain laser devices. The width W of the current injection region of this laser element, that is, the width of the second conductive type second cladding layer at the interface with the second etching stop layer was 2.2 μm. As a result of the calculation, the lateral effective refractive index difference Δn of this laser element
_eff is 3.6 × 10 ^- it was ^3.

The current light output characteristics of this laser device at 25 ° C. were examined. As a result, at 25 ° C., the threshold current was 3
It was 4.5 mA, and kink was observed at 690 mA and 475 mW. The slope efficiency was 0.76 W / A and the maximum light output was 585 mW.

Example 2 A laser device was manufactured in the same manner as in Example 1 except that the cavity length was set to 900 μm, and the current light output characteristics at 25 ° C. were examined. At 25 ° C., the threshold current is 26.
2 mA, and kink was observed at 515 mA and 405 mW. The slope efficiency was 0.87 W / A and the maximum light output was 550 mW.

Example 3 A laser device was manufactured in the same manner as in Example 1 except that the cavity length was changed to 1700 μm.
The current light output characteristics were examined. At 25 ° C, the threshold current is 4
It was 9.0 mA, and kink was observed at 987 mA and 489 mW. The slope efficiency was 0.58 W / A and the maximum light output was 630 mW.

Comparative Example 1 A laser device was manufactured in the same manner as in Example 1 except that the length of the resonator was 700 μm, and the current-light output characteristics at 25 ° C. were examined. At 25 ° C, threshold current is 21m
A, and kink was observed at 410 mA and 340 mW. The slope efficiency was 0.89 W / A and the maximum light output was 520 mW.

(Comparative Example 2) The composition of the current block layer was changed to Al
_A laser device was fabricated in the same manner as in Example 1 except that the laser length was set to _0.60 Ga _0.40 As and the cavity length was set to 1200 μm, and current light output characteristics at 25 ° C. were examined. The effective refractive index difference Δn in this case
_eff was 1.17 × 10 ^-2 . At 25 ° C., the threshold current was 28.2 mA, and kink was observed at 375 mA and 250 mW. The slope efficiency was 0.79 W / A and the maximum light output was 400 mW.

[0045]

The semiconductor laser of the present invention has a high kink level while keeping the drive current low by forming a quantum well structure having an intrinsic compressive strain in the active layer and making the cavity length 800 μm or more. And provide great industrial benefits.

[Brief description of the drawings]

FIG. 1 shows an effective refractive index difference Δn of a semiconductor laser of the present invention.
It is a figure explaining _eff .

FIG. 2 is a cross-sectional view showing one embodiment of the epitaxial structure of the semiconductor laser of the present invention.

[Explanation of symbols]

 1: GaAs substrate 2: buffer layer 3: first conductivity type cladding layer 4: active layer 5: second conductivity type first cladding layer 6: second etching stop layer 7: first etching stop layer 8: second conductivity type Second cladding layer 9: current blocking layer 10: cap layer 11: contact layer 12: epitaxial layer side electrode 13: substrate side electrode

Claims (10)

[Claims] 1. A GaAs substrate comprising at least a first conductivity type clad layer, an active layer containing In, Ga, and As as elements, a second conductivity type first clad layer, a current blocking layer, and a second conductivity type second clad. A current blocking layer and the second conductivity type second cladding layer have a width of 1.5 to
A 2.5 μm current injection region is formed, and the effective refractive index difference Δn _eff in the lateral direction is 2.5 × 10 ⁻³ to 4.
A semiconductor laser having a size of 5 × 10 ⁻³ , wherein the active layer has a quantum well structure in which compressive strain is inherent, and has a resonator length of 800 μm or more. 2. The semiconductor laser according to claim 1, wherein the cavity length is 2000 μm or less. 3. The semiconductor laser according to claim 2, wherein the cavity length is 1000 to 1500 μm. 4. The semiconductor laser according to claim 1, wherein the current blocking layer and the second conductivity type second cladding layer include Al, Ga, and As. 5. The method according to claim 1, wherein the current blocking layer is formed of Al _z Ga _{1 -z} As (0
≦ z ≦ 1), and the second cladding layer of the second conductivity type is Al
_y Ga _1-y As semiconductor laser according to claim 4, characterized in that it consists of (0 <y ≦ 1). 6. The semiconductor laser according to claim 1, wherein the emission wavelength is 900 to 1200 nm. 7. The semiconductor laser according to claim 6, wherein the emission wavelength is 900 to 1100 nm. 8. The semiconductor laser according to claim 1, which is used for an excitation light source of an optical fiber amplifier. 9. An active layer having a strained quantum well structure comprising an In _q Ga _1-q As (0 <q <1) layer and an Al _x Ga _1-x As (0 ≦ x ≦ 1) optical guide layer, _y Ga _1-y As
(0 <y ≦ 1) Second conductivity type second cladding layer and Al
_a ridge-type or groove-type current injection region composed of a zGa _1-z As (0 ≦ z ≦ 1) current block layer;
9. The semiconductor laser according to claim 1, wherein the mixed crystal ratio of each layer has a relationship of x <y ≦ z. 10. A second conductivity type between the first cladding layer and the current blocking layer _{Al a Ga 1 -a As (0} ≦ a ≦ 1) second etching stop layer and the _{In b Ga b P (0 ≦} b ≦ 1) The semiconductor laser according to any one of claims 1 to 9, further comprising a first etching stop layer.