JPH10200201A - Semiconductor laser - Google Patents

Abstract

(57) [Summary] An object of the present invention is to achieve both high kink level and temperature characteristics.
An object of the present invention is to provide a laser having a kink level of about 980 nm and a lasing wavelength. 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 conductivity type second cladding layer form a current injection region, wherein the effective refractive index difference Δ in the lateral direction is
n _eff is not less than 2.5 × 10 ^{−3 and} 5.0 × at the emission wavelength.
10 ⁻³ or less, and the width W of the current injection region is
It is not less than 1.5 μm and not more than 2.5 μm.

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 laser of the present invention is suitably used particularly for applications requiring high output and long life, 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, high-density recording using a magneto-optical disk and two-way communication using an optical fiber network have no spare time. 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.

[0003] In principle, there are three types of emission wavelengths of a semiconductor laser that can be used for EDFA applications.
m, 980 nm and 1480 nm. From the viewpoint of the amplifier itself, the excitation at 980 nm is the gain,
It is known that noise and the like are most desirable. Since the laser having the transmission wavelength of 980 nm is used by being coupled to an optical fiber, the emitted laser light must have a stable transverse mode irrespective of injection current, temperature, return light from the fiber end face, and the like. Nozomi,
Furthermore, since it is an excitation light source, it is expected that it has high output and long life.

At wavelengths near this range, there is also a demand for an SHG light source, and the development of high-performance lasers in various other applications is also awaited.

[0005]

However, a semiconductor laser having a wavelength of around 980 nm, which has been conventionally reported, and particularly an element having a refractive index waveguide structure on the premise of coupling with an optical system, are as follows. There was a problem. That is, in a light output region of high output, for example, about 150 to 200 mW, a non-linear phenomenon in current / light output characteristics called kink is 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, and is particularly low when the temperature is increased. It is observed from the area of light output.

An object of the present invention is to achieve both high kink level and temperature characteristics.
An object of the present invention is to provide a laser having a kink level of about W and an oscillation wavelength of around 980 nm.

[0007]

The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have found that in an InGaAs-based semiconductor laser having a refractive index waveguide mechanism, the effective refractive index difference and laser oscillation in the lateral direction are reduced. We found that the width of the current injection region for the required current constriction was closely related to the kink level and its temperature characteristics, and by optimizing these ranges and their combinations, it was possible to obtain high kink levels and temperature characteristics. It has achieved both. That is, the gist of the present invention is that at least a first conductivity type cladding layer, In, Ga and As as elements are formed on a GaAs substrate.
An active layer, a second conductivity type first cladding 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. _Wherein the effective refractive index difference Δn _eff in the lateral direction is not less than 2.5 × 10 ^{−3 and not} more than 5.0 × 10 ⁻³ at the emission wavelength, and the width W of the current injection region is Is not less than 1.5 μm and not more than 2.5 μm.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
First, the effective refractive index that constitutes the main feature of the present invention will 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 Lasers;
HC Casey, Jr., MB Panish; Academic Press (197
8) ", Part A, p20-p109 and part B, p156-276 and" Semiconductor Laser Fundamentals and Applications "(5th ed .; Ryoichi Ito, Michiharu Nakamura, edited by Baifukan; published on March 30, 1995) Although described in Chapters 3 and 5, etc., a specific calculation method in the layer configuration of the present invention is as follows.

In order to determine the effective refractive index difference Δn _eff , first, inside the current injection region (AA ^* cross section in FIG. 1), the first conductivity type clad layer (3), the active layer (4), and the second conductivity type A multilayer film composed of one clad layer (5) and a second conductive type second clad layer (8) is regarded as a slab waveguide, and a waveguide mode of laser light propagating through the multilayer film is calculated for a TE mode,
Find the effective refractive index of the fundamental mode at the oscillation wavelength. 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 way is _defined as n _eff (AA ^* ). Next, similarly, outside the current injection region (BB ^* cross section in FIG. 1), the first conductivity type cladding layer (3),
A multilayer film composed of the active layer (4), the second conductive type first clad layer (5), the current blocking layer (9) and the second conductive type second clad layer (8) is regarded as a slab waveguide,
The effective refractive index of the fundamental mode of the guided mode is calculated, and
_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 ^* . N _eff (AA ^* ) and n _eff (BB ^* ) are obtained for a multilayer film composed of all layers included between the cladding layer (3) and the second conductivity type second cladding layer (8). Also, in the actual device structure, the shape of the current injection region is often not a rectangle as shown in FIG. 1 but an inverted trapezoidal shape. In this case, n _eff ( AA ^* ), and n _eff (BB ^* ) outside the widest part of the current injection region. From the thus obtained n _eff (AA ^* ) and n _eff (BB ^* ), the effective refractive index difference is _defined as Δn _eff = n _eff (AA ^* ) − n _eff (BB ^* ).

The present invention is characterized in that the effective refractive index difference Δn _{eff in the} lateral direction satisfies the following formula (I), whereby both the kink level stability and the high-temperature stability can be achieved. Becomes 2.5 × 10 ⁻³ ≦ Δn _eff ≦ 5.0 × 10 ⁻³ (I) Note that the lateral direction is a direction perpendicular to both the lamination direction of each layer and the light emission 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 of the present invention has an active layer containing In, Ga and As,
Formula (I) above shows that 900 to 120 from such an active layer
The optimum range of the effective refractive index difference Δn _eff at an emission wavelength of about 0 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.

FIG. 2 is a schematic example of a groove-type semiconductor laser 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 the incompleteness of the substrate bulk crystal and facilitate the formation of an epitaxial thin film having the same crystallographic 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 desired emission wavelength and output. Active layer (4) is made of a material containing at least In, Ga, and As, is constituted by a conventional _{In q Ga 1-q As (} 0 <q <1), various of the quantum well structure (SQW As the structure comprising a thin film , MQW) or the like. 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 Al _x Ga _{1 -x} As
(0 ≦ x ≦ 1) is preferable.

The first cladding layer (5) of the second conductivity type is an active layer.
It is composed of a material having a lower refractive index than the layer (4).
And a refractive index of the second conductivity type first cladding layer (5);
It is usually the same as that of the first conductivity type cladding layer (3).
You. Therefore, the material of the second conductivity type first cladding layer (5)
Then, like the first conductivity type cladding layer (3), usually,
AlGaAs-based material is used, and its mixed crystal ratio is
Usually the same as the electric cladding layer (3). With this structure
Means that the first cladding layer (5) of the second conductivity type is Al _WGa
_1-WThis corresponds to a layer made of As.

FIG. 2 illustrates two types of etch stop layers and cap layers, which are employed in a preferred embodiment of the present invention to accurately and easily create a current injection region. It is effective for The second etching stop layer (6) is made of Al _a Ga _1-a As (0 ≦ a ≦
1) Although it is composed of a material, usually GaAs is preferably used. This is because the second conductivity type second cladding layer and the like can be stacked with good crystallinity when regrowth is performed by the MOCVD method or the like, particularly, by using an AlGaAs-based material. The thickness of the second etching stop layer (6) is usually preferably 2 nm or more.

The first etching stopper 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 radiation 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 prevented due to 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, even if lattice matching cannot be achieved, there is no problem 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) Since the re-growth of the second conductive type second clad layer (8) it can be easily conducted, the above-mentioned _{In b Ga 1-b P (} 0 ≦
The first etching stop layer (7) consisting of b ≦ 1) is unnecessary.

In order to realize a semiconductor laser having a longer life, a first conductive type first clad layer (3), a second conductive type first clad layer (5), and a 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 system, the Al mixed crystal ratio must be accurately controlled 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.

The effective refractive index difference Δn _eff is given by the above formula (I)
To obtain a high kink level when the range is satisfied,
The width W of the current injection region composed of the current blocking layer and the second conductivity type second cladding layer must be 3.5 μm or less, more preferably 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 destroyed before reaching a sufficient light output. Therefore, the lower limit of W is 1.0 μm or more, more preferably 1.5 μm or more. The width W of the current injection region
Is the width of the bottom of the current injection region, that is, the width of the portion of the second conductivity type second clad layer closest to the substrate in the current injection region.

The refractive index of the second conductive type second cladding layer (8) is usually equal to or lower than the refractive index 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.

It is preferable to provide a contact layer (11) on the second conductive type second clad layer (8) for the purpose of lowering the contact resistivity of the electrode. Contact layer (11)
Is usually made of a GaAs material. In this layer, the carrier concentration is usually made higher than the other layers in order to lower the contact resistivity with the electrode. The buffer layer (2) usually has a thickness of 0.1 to 1 μm, preferably 0.5 to 1 μm.
１1 μm, the thickness of the first conductivity type cladding layer (3) is 0.5
And the thickness of the active layer (4) is 0.0005 to 5 μm per layer in the case of a quantum well structure.
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 3 μm, preferably 1 to 2.5 μm, and the thickness of the cap layer (10) is 0. .0
05 to 0.5 μm, preferably 0.005 to 0.3 μm
m, the thickness of the current blocking layer (9) is selected from the range of 0.3 to 2 μm, preferably 0.3 to 1 μm.

The semiconductor light emitting device shown in FIG. 2 is constituted by further forming electrodes (12) and (13). Electrode (1
In the case of p-type, 2) is formed by sequentially depositing, for example, Ti / Pt / Au on the surface of the contact layer (11), followed by alloying. On the other hand, the electrode (13) is formed on the surface of the substrate (1). In the case of an n-type electrode, for example, AuGe / Ni / Au is sequentially deposited on the surface of the substrate (1) and then formed by alloying. You.

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 3.5% and the rear end face reflectivity is about 93%. It is divided and used as a laser diode (LD). Although the above description relates 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.

[0029]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. Example 1 A groove type laser device shown in FIG. 2 was manufactured as follows.

Carrier concentration 1 × 10¹⁸cm^-3N-type Ga
Buffer layer (2) on As substrate (1) by MBE method
1 × 10 μm thick carrier concentration 1 × 10¹⁸cm^-3of
n-type GaAs layer, first conductivity type cladding layer (3)
1.5 μm thick carrier concentration of 1 × 10¹⁸cm^-3N
Type Al_0.35Ga_0.65As layer, then two layers 30 nm thick
6nm thick sandwiched between undoped GaAs optical guide layers
Undoped In_0.2Ga_0.8As single quantum well (S
An active layer (4) having a QW) structure,
0.1 μm thick, carrier concentration 1 × as a pad layer (5)
10¹⁸cm^-3P-type Al_0.35Ga_0.65As layer, second edge
10 nm thick, carrier concentration
1 × 10¹⁸cm^-3P-type GaAs layer, first etching stopper
Stopping layer (7) having a thickness of 20 nm and a carrier concentration of 5 × 10
¹⁷cm^-3N-type In_0.49Ga_0.51P layer, current block layer
(9) thickness 0.5 μm, carrier concentration 5 × 10¹⁷
cm ^-3N-type Al_0.39Ga_0.61As layer, cap layer (1
0) as thickness 10 nm, carrier concentration 1 × 10¹⁸cm
^-3N-type GaAs layers were sequentially laminated.

Next, a mask made of silicon nitride was provided in a portion other than the uppermost current injection region. 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 etchant 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 performed at 25 ° C. for 30 seconds.

Then, 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 etchant used at this time was hydrochloric acid (35 wt%) and water:
1, and the temperature was 25 ° C. and the time was 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 1.5 μm at 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. The obtained laser device wafer is cleaved into laser bars after forming the electrodes, and subjected to asymmetrical coating on the end faces so that the front end face reflectivity is 3.5% and the rear end face reflectivity is 93% according to a conventional method. The laser element was divided into chips. The width W of the current injection region of the laser device, that is, the width of the second conductivity type second cladding layer at the interface with the second etching stop layer is 2.2.
μm.

As a result of the calculation, the actual value of the laser device in the lateral direction is obtained.
Effective refractive index difference Δn_effIs 3.71 × 10 ^-3Met. This
Relationship between current and optical output at 25 ° C and 70 ° C of laser element
Is shown in FIG. At 25 ° C., the threshold current is 22 mA,
Kink was observed at 350 mA and 250 mW. 70 ° C
The threshold current is 35 mA, 340 mA, 240 m
Kink was observed at W.

The results are shown in Table 1 together with the results of Examples 2 and 3 and Comparative Examples 1 to 5. In Table 1, z represents the Al mixed crystal ratio of the Al _z Ga _{1 -z} As current blocking layer, I _th represents the threshold current, and * in the “kink level” column.
The figures with the mark are COD (Catastrophic Optical Dam)
age) level, that is, a numerical value indicating that the laser element was destroyed there.

(Example 2) The composition of the current block layer was changed to Al
FIG. 4 and Table 1 show the results obtained in the same manner as in Example 1 except that _0.382 Ga _0.618 As was used. In this case, the effective refractive index difference Δn _eff was 3.0 × 10 ⁻³ . At 25 ° C., the threshold current is 23 mA, and at 360 mA and 260 mW, kink is first observed, and at 70 ° C., the threshold current is 37 m
A, and kink was first observed at 330 mA and 200 mW.

Example 3 The composition of the current block layer was changed to Al
FIG. 5 and Table 1 show the results obtained in exactly the same manner as in Example 1 except that _0.40 Ga _0.60 As was used. The effective refractive index difference Δn _{eff in} this case was 4.5 × 10 ⁻³ . At 25 ° C., the threshold current was 21 mA, kink was first observed at 340 mA and 240 mW, and at 70 ° C., the threshold current was 34.5.
The first kink was observed at 330 mA and 220 mW.

Comparative Example 1 The composition of the current block layer was changed to Al
FIG. 6 and Table 1 show the results obtained in the same manner as in Example 1 except that _0.36 Ga _0.64 As was used. In this case, the effective refractive index difference Δn _eff was 5.40 × 10 ⁻⁴ . At 25 ° C., the threshold current was 24 mA, and kink was first observed at 375 mA and 275 mW.
The first kink was observed at 220 mA and 105 mW.

Comparative Example 2 The composition of the current block layer was changed to Al
FIG. 7 and Table 1 show the same results as in Example 1 except that _0.413 Ga _0.587 As was used. In this case, the effective refractive index difference Δn _eff was 5.5 × 10 ⁻³ . At 25 ° C., the threshold current was 18 mA, and kink was first observed at 265 mA and 210 mW, but at 70 ° C., the threshold current was 3 mA.
It was 3.5 mA, and the first kink was observed at 290 mA and 180 mW.

Comparative Example 3 The composition of the current blocking layer was changed to Al
FIG. 8 and Table 1 show the results obtained in the same manner as in Example 1 except that _0.60 Ga _0.40 As was used. In this case, the effective refractive index difference Δn _eff was 1.17 × 10 ⁻² . At 25 ° C., the threshold current was 17 mA, kink was first observed at 250 mA and 200 mW, and the laser element was destroyed at 410 mA and 300 mW. At 70 ° C., the threshold current was 33 mA, kink was first observed at 260 mA and 160 mW, and the laser element was destroyed at 390 mA and 200 mW.

Comparative Example 4 A laser device was manufactured in exactly the same manner as in Example 1 except that the width of the opening of the silicon nitride mask was changed to 0.7 μm, and the result of measuring the relationship between current and light output at 25 ° C. Is shown in FIG. 9 and Table 1. In this case, the width of the current injection region of the laser device was 1.2 μm.

The threshold current was 16 mA, and the laser element was broken at 210 mA and 150 mW without any kink observed.

Comparative Example 5 A laser device was manufactured in exactly the same manner as in Example 1 except that the width of the opening of the silicon nitride mask was 3.0 μm, and the result of measuring the relationship between current and optical output at 25 ° C. Is shown in FIG. 10 and Table 1. In this case, the width of the current injection region of the laser device was 4.0 μm.

The threshold current is 30 mA, 170 mA,
356m after the first kink was observed at 100mW
A, kink was observed over several stages such as 150 mW.

[0045]

[Table 1]

Example 4 n-type GaAs was formed by MBE.
s substrate (dopant: Si, carrier concentration: 1 × 10¹⁸
cm^-3A) a buffer layer made of n-type GaAs on the surface of
(Dopant: Si, carrier concentration: 1 × 10¹⁸c
m^-3, Layer thickness 1 μm), n-type Al_0.4Ga_0.6Consists of As
First conductivity type first cladding layer (dopant: Si, carrier
A concentration: 1 × 10 ¹⁸cm^-3, A layer thickness of 1.5 μm)
An optical guide layer made of undoped GaAs (having a layer thickness of 0.
Undoped type In sandwiched between_0.2Ga_0.8
As active layer (layer thickness 0.06 μm, SQW), p-type Al
_0.4Ga_0.6As-type second cladding layer made of As
-Punt: Be, 1 × 10¹⁸cm^-3, Layer thickness 0.1μ
m), an etching stopper layer made of p-type GaAs (DOPA
Port: Be, carrier concentration: 1 × 10¹⁸cm^-3, Layer thickness
0.01 μm), n-type In_0.5Ga_0.5Current block consisting of P
Lock layer (dopant: Si, carrier concentration: 1 × 10
¹⁸cm^-3, Layer thickness 0.5 μm), a key made of n-type GaAs.
Cap layer (dopant: Si, carrier concentration: 1 × 10
¹⁸cm^-3, A layer thickness of 0.1 μm)
A wafer was obtained.

Next, as a protective layer on the cap layer,
An iN _x film is formed, and S
Stripe-shaped holes having a width of 3.0 μm were formed in the iN _x film. Then, sulfuric acid (98% by weight): hydrogen peroxide solution (30
Wt.%): Water is used to selectively etch the cap layer at a temperature of 25 ° C. using a mixed etching aqueous solution having a volume ratio of 3: 1: 1. The current blocking layer was selectively etched at a temperature of 25 ° C. using a 4: 1 mixed etching aqueous solution to form a groove. The width of W became 2.2 μm.

Next, p-type Al _0.4
A second conductivity type second cladding layer (dopant: Zn, carrier concentration: 1 × 10 ¹⁸ cm ⁻³ , layer thickness: 1.5 μm) made of Ga _0.6 As is formed, a groove is embedded, and a second conductivity type second cladding layer is formed. A contact layer made of p-type GaAs (dopant: Zn, carrier concentration: 1 × 1) is formed on the surface of the cladding layer.
0 ¹⁹ cm ^-3 and a layer thickness of 3.0 μm). The second conductive type second clad layer and the contact layer are formed by MOCV
Formed by Method D.

After forming the electrodes, the obtained laser device wafer is cleaved into laser bars, and an asymmetric coating is applied to the end faces according to a conventional method so that the front end face reflectivity is 3.5% and the rear end face reflectivity is 93%. After that, it was divided into chips to obtain laser devices. The width W of the current injection region of this laser device, ie,
The width of the second conductive type second cladding layer at the interface with the etching stop layer was 2.2 μm.

As a result of the calculation, the effective refractive index difference Δn _{eff in} the lateral direction of this laser device was 3.7 × 10 ⁻³ . At 25 ° C., the threshold current is 18 mA, 340 mA, 250 mW
A kink was observed at. At 70 ° C, threshold current is 34mA
And kink was observed at 320 mA and 220 mW.

Table 2 shows the results together with the results of Comparative Examples 6 to 9. In Table 2, y is Al _y Ga _1-y
The Al mixed crystal ratio of the second cladding layer of the As second conductivity type, I _th represents a threshold current, and the numerical value marked with * in the column of “kink level” indicates the COD (Catastrophic Optical Damage) level,
That is, it is a numerical value indicating that the laser element was destroyed there.

Comparative Example 6 Example 4 was _repeated except that the composition of the second conductive type second cladding layer was changed to Al _0.415 Ga _0.585 As.
Table 2 shows the results obtained in exactly the same manner as described above. The effective refractive index difference Δn _{eff in} this case was 1.0 × 10 ⁻³ . At 25 ° C., the threshold current was 20 mA, and kink was first observed at 365 mA and 270 mW, but at 70 ° C., the threshold current was 38 mA.
The first kink was observed at 270 mA and 150 mW.

Comparative Example 7 Table 2 shows the results obtained in the same manner as in Example 4 except that the composition of the second conductive type second cladding layer was changed to Al _0.37 Ga _0.63 As. In this case, the effective refractive index difference Δn _eff was 6.0 × 10 ⁻³ . At 25 ° C., the threshold current was 17 mA, and kink was first observed at 240 mA and 190 mW. At 70 ° C., the threshold current was 30 mA, and kink was first observed at 280 mA and 170 mW.

Comparative Example 8 A laser device was manufactured in exactly the same manner as in Example 4 except that the width of the opening of the silicon nitride mask was 1.8 μm, and the result of measuring the relationship between current and optical output at 25 ° C. Are shown in Table 2. In this case, the width of the current injection region of the laser element was 1.0 μm. The threshold current is 1
6 mA, 200 km without kink observed
A, The laser element was broken at 155 mW.

Comparative Example 9 A laser device was manufactured in exactly the same manner as in Example 4 except that the width of the opening of the silicon nitride mask was changed to 4.8 μm, and the result of measuring the relationship between current and optical output at 25 ° C. Are shown in Table 2. In this case, the width of the current injection region of the laser device was 4.0 μm. The threshold current is 2
It was 4 mA, and the first kink was observed at 160 mA and 100 mW.

[0056]

[Table 2]

[0057]

The semiconductor laser of the present invention realizes both high kink level and temperature characteristics by setting the lateral effective refractive index difference Δn _eff and the width W of the current injection region to specific ranges. Yes, providing significant industrial benefits.

[Brief description of the drawings]

FIG. 1 is a drawing for explaining an effective refractive index difference Δn _eff of a semiconductor laser of the present invention.

FIG. 2 is an explanatory sectional view showing an example of a groove type epitaxial structure of the semiconductor laser of the present invention.

FIG. 3 is a graph showing the relationship between current and light output at 25 ° C. and 70 ° C. of the semiconductor laser device of Example 1 of the present invention.

FIG. 4 is a graph showing the relationship between current and light output at 25 ° C. and 70 ° C. of the semiconductor laser device of Example 2 of the present invention.

FIG. 5 is a graph showing the relationship between current and light output at 25 ° C. and 70 ° C. of the semiconductor laser device of Example 3 of the present invention.

FIG. 6 shows the semiconductor laser device of Comparative Example 1 at 25 ° C. and 70 ° C.
3 is a graph showing the relationship between the current and the light output in FIG.

FIG. 7 shows the semiconductor laser device of Comparative Example 2 at 25 ° C. and 70 ° C.
3 is a graph showing the relationship between the current and the light output in FIG.

FIG. 8 shows a semiconductor laser device of Comparative Example 3 at 25 ° C. and 70 ° C.
3 is a graph showing the relationship between the current and the light output in FIG.

FIG. 9 is a graph showing the relationship between current and optical output at 25 ° C. of the semiconductor laser device of Comparative Example 4.

FIG. 10 is a graph showing the relationship between current and light output at 25 ° C. of the semiconductor laser device of Comparative Example 5.

[Explanation of symbols]

1: GaAs single crystal 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 Conductive type second cladding layer 9: Current blocking layer 10: Cap layer 11: Contact layer 12: Electrode 13: Electrode 14: Kink

Continued on the front page (72) Inventor Hideki Goto 1000 Higashikiana-cho, Ushiku-shi, Ibaraki Mitsubishi Tsukuba Works

Claims (8)

[Claims] At least a first conductive material is formed on a GaAs substrate.
Mold cladding layer, containing In, Ga and As as elements
Active layer, second conductivity type first cladding layer, current blocking layer and
The current block having a second cladding layer and a second conductivity type.
Layer and the second conductive type second cladding layer form a current injection region.
The semiconductor laser to be formed, the effective refractive index difference in the lateral direction
Δn_effIs 2.5 × 10^-35.0
× 10 ^-3And the width W of the current injection region
Is not less than 1.5 μm and not more than 2.5 μm.
Semiconductor laser. 2. The semiconductor laser according to claim 1, wherein the current blocking layer and the second conductivity type second cladding layer contain Al, Ga, and As. 3. 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 2, characterized in that it consists of (0 <y ≦ 1). 4. The semiconductor laser according to claim 1, wherein an emission wavelength is from 900 to 1200 nm. 5. The semiconductor laser according to claim 4, wherein the emission wavelength is 900 to 1100 nm. 6. The semiconductor laser according to claim 1, which is used for an excitation light source of an optical fiber amplifier. 7. An active layer having a strained quantum well structure comprising an In _q Ga _1-q As (0 <q <1) thin film and an Al _x Ga _1-x As (0 ≦ x ≦ 1) optical guide layer, and Al _y Ga
Ridge-type or groove-type current injection region composed of _1-y As (0 <y ≦ 1) second conductivity type second cladding layer and Al _z Ga _1-z As (0 ≦ z ≦ 1) current block layer 7. The semiconductor laser according to claim 1, wherein a mixed crystal ratio of each layer has a relation of x <y ≦ z. 8. 8. An Al _a Ga _{1 -a} As (0 ≦ a ≦ 1) second etching stop layer and an In _b Ga _b P (0 ≦ b ≦) between the second conductivity type first cladding layer and the current blocking layer. 1) The semiconductor laser according to any one of claims 1 to 7, further comprising a first etching stop layer.