JPH10256647A - Semiconductor laser element and fabrication thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser element excellent in current-optical output characteristics and voltage-current characteristics and having low coherence, and a high yield fabrication method thereof. SOLUTION: A first conductivity type buffer layer 2 having composition of Alx Ga1-x As, a first conductivity type clad layer 3 having composition of Alx Ga1-x As, an active layer 4 having composition of Aly Ga1-y As, a second conductivity type second clad layer 5 having composition of Alx Ga1-x As, a second conductivity type GaAs cap layer 6, a first conductivity type current constriction layer 7 divided into two regions, a second conductivity type third clad layer 3 having composition of Alx Ga1-x As, and a second conductivity type GaAs contact layer 9 are formed sequentially on a first conductivity type GaAS substrate 1 thus constituting an AlGaAs based semiconductor laser element. The p-conductivity type clad layer 5 out of first and second clad layers comprises a plurality of inner layers 5a, 5b, 5c doped with different dopant and the diffusion coefficient of dopant in respective inner layers increases sequentially as receding from the active layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an Al _y Ga _1-y As
The present invention relates to an Al _x Ga _1-x As (0 ≦ x ≦ 1) semiconductor laser device having an active layer made of (0 ≦ y ≦ 1) and emitting near-infrared light.

[0002]

Al _x Ga _1-x As system (0 ≦ x ≦ 1) (hereinafter abbreviated as LD elements) semiconductor laser device of the conventional example will be described based on the drawings which oscillates BACKGROUND ART In a single transverse mode. In this example, the conductivity type of the GaAs substrate is n-type, but in the case of p-type, all the following conductivity types may be reversed. FIG. 17 is a cross-sectional view of a conventional LD element parallel to a cleavage plane. The normal to the cleavage plane of the LD element is also the optical axis of the laser radiation. On a plane perpendicular to the cleavage plane of the n-type GaAs substrate 1 (hereinafter referred to as an element plane),
n-type buffer layer 2, n-type first cladding layer 3, active layer 4, p-type second cladding layer 5, p-type GaAs cap layer 6, n-type current confinement layer 8, p-type third Clad layer 9, p
The mold contact layers 10 are stacked in this order. However, the current confinement layer 8 is divided into two portions with a stripe-shaped portion having a width of several μm (hereinafter referred to as a stripe) vertically penetrating between both cleavage surfaces at the center of the element surface.
The stripe is filled with the third cladding layer 9, and the GaAs cap layer 6 and the third cladding layer 9 are adjacent to each other.

A p-side electrode 11 and an n-side electrode 12 for passing a current are respectively laminated on both element surfaces of the LD element. p
When a forward current flows from the n-side to the n-side, the pn junction formed at the interface between the current confinement layer 8 and the GaAs cap layer 6 or the second cladding layer 5 is in the reverse direction, and no current flows. Forward current concentrates only on the stripes. Therefore, the current traversing the active layer 4 close to the stripe concentrates substantially on the stripe width. Further, the current confinement layer 8 has a role of an absorbing layer for the light emitted from the active layer 4, and by appropriately selecting the stripe size, enables stable transverse mode oscillation of the device. Can be reduced.

[0004] Such an LD is usually manufactured as follows. FIG. 18 is a cleaved sectional view showing one device of a wafer after a main manufacturing process of a conventional LD device. FIG. 18A shows a process after patterning a silicon oxide layer, and FIG. 18B shows a selective epitaxial growth of a current confinement layer. Later, (c) is after the formation of the electrode metal film. First, on an n-type GaAs substrate 1 (Si-doped, carrier concentration 2 × 10 ¹⁸ cm ⁻³ , thickness 300 μm), a buffer layer 2 (n-type, thickness: 300 μm) is formed by metal organic chemical vapor deposition (hereinafter referred to as MOCVD). 0.2 μm), first cladding layer 3
(N-type Al _0.5 Ga _0.5 As, dopant is Se, carrier concentration 5 × 10 ¹⁷ cm ⁻³ , thickness 1 μm), active layer 4 (non-doped Al _0.1 Ga _0.9 As, thickness 0.1 μm), second cladding layer 5 (p-type Al _0.5 Ga _0.5 As, dopant is Zn, carrier concentration 5 × 10 ¹⁷ cm ⁻³ , thickness 0.3 μm), GaAs cap layer 6 (p-type GaAs, carrier concentration 1 × 10 ¹⁸ cm ⁻³ , Thickness 0
_{. 01μm)} and are successively grown.

The GaAs cap layer 6 has a high resistance Al oxide film if a subsequent oxide film forming step and its patterning step are directly applied to the GaAlAs layer. Provided. Next, a silicon oxide layer is formed on the wafer by sputtering, a photoresist is applied and patterned, and a width of 5 μm is formed on the cap layer 6.
m is formed (FIG. 18)
(A)).

Next, the current confinement layer 8 is again formed by MOCVD.
(N-type GaAs, carrier concentration 1 × 10 ¹⁹cm^-3, Thickness 0.3
μm) to grow. At this time, selective growth occurs and oxidation
The GaAs film does not grow on the i-layer (mask 7) (FIG. 18).
(B)). Then, the mask is taken out from the MOCVD apparatus.
7 is removed, the third cladding layer 9 (p-type Al_0.5Ga
_0.5As, carrier concentration 5 × 10¹⁷cm^-30.8μm thick
 ) And contact layer 10 (p-type GaAs, carrier concentration)
1 × 10¹⁹cm^-3, A thickness of 5.0 μm). last
Then, the p-side electrode 11 and the n-side electrode 12 on the upper and lower sides of the wafer are formed.
You. This state is shown in FIG.

After the above manufacturing process, the wafer is cleaved (parallel to the plane of FIG. 18) into bars, and the bars are scribed to obtain individual laser elements.

[0008]

However, the LD device manufactured as described above has the following problems. During these epitaxial growths, Se, which is a dopant, diffuses from the first cladding layer, and Zn diffuses from the second cladding layer 5, and mixes in the active layer. That is, the dopant piles up in the active layer 4. Therefore, the pn junction in the active layer is defective or the junction position is shifted from the active layer (remote junction), so that the luminous efficiency is deteriorated and a large operating current is required. In extreme cases, laser oscillation may not be performed.

Further, since the refractive index of the active layer is several% higher than that of the first clad layer and the second clad layer, light waves can be confined in the active layer having a high refractive index. The emitted light wave can propagate without absorption if the band gap of the cladding layer is large, but the refractive index is small because the Al _x Ga _1-x As composition difference between the active layer and the first and second cladding layers is small. The difference becomes smaller and the confinement of the light wave becomes weaker. Alternatively, the band gap difference becomes smaller,
When the hole gets over the barrier in the cladding layer, the operating value current becomes large, and in extreme cases such as deterioration of luminous efficiency, the device becomes defective such as not oscillating laser.

An object of the present invention is to provide a pn junction in an active layer, to optimize the spread of current from the cladding layer to the active layer, and to optimize the confinement of light in the active layer. Another object of the present invention is to provide an LD element which is excellent in current-light output characteristics and voltage-current characteristics, has a small temperature change of the former, and has small coherence, and provides a manufacturing method with a high yield.

[0011]

In order to achieve the above object, a first conductivity type Al _x Ga _{1 -x} As (0 ≦ x ≦ 1) is formed on one principal surface of a first conductivity type GaAs substrate. ), A first cladding layer of Al _x Ga _1-x As (0 ≦ x ≦ 1) composition of the first conductivity type, and an Al _y Ga _1-y As (0 ≦ y ≦ x ≦ 1) composition. An active layer, a second cladding layer of a second conductivity type Al _x Ga _{1 -x} As composition,
GaAs cap layer of the second conductivity type, current confinement layer of the first conductivity type divided into two sections parallel to the laser optical axis, and third composition of Al _x Ga _{1 -x} As of the second conductivity type Cladding layer, second
AlGa in which conductive type GaAs contact layers are sequentially stacked
In the As-based semiconductor laser device, of the first or second cladding layer, the cladding layer having a p-type conductivity type includes a plurality of inner layers having different dopants, and the diffusion coefficient of the dopant in each of the inner layers is away from the active layer. It is assumed that they increase in order in accordance with.

The dopant is C from the active layer side.
It is preferable to use a combination of two or more of Mg and Zn in this order. This combination is C-Mg, C-Zn, Mg-Z
n or C-Mg-Zn. The thickness of the p-type cladding layer is in the range of 0.3 to 0.45 μm, and the Al composition difference (Δx) in the mixed crystal of the cladding layer with respect to the active layer is 0.35 to 0.6. It is good to be in the range.

A first conductive type GaAs substrate is provided on one main surface with a first conductive type GaAs substrate.
Conductivity type _{Al x Ga 1-x As (} 0 ≦ x ≦ 1) buffer layer having the composition, of a first conductivity type _{Al x Ga 1-x As (} 0 ≦ x ≦ 1) first cladding layer of the composition, Al _y An active layer of Ga _1-y As (0 ≦ y ≦ x ≦ 1) composition, a second cladding layer of Al _x Ga _{1- x} As composition of the second conductivity type, a cap layer of GaAs of the second conductivity type, A current confinement layer of a conductivity type divided into two areas parallel to the laser optical axis, a third cladding layer of a second conductivity type Al _x Ga _{1 -x} As composition,
GaAs contact layers of the second conductivity type are sequentially stacked
In the AlGaAs-based semiconductor laser device, a second conductive type second portion divided into two sections in parallel with the laser optical axis between the buffer layer and the first cladding layer or in the first cladding layer. Is formed.

Preferably, the current confinement layer and the second current confinement layer are mirror-image-symmetric with respect to the active layer. It is preferable that the stripe portion sandwiched between the current constriction layers has a mesa structure.
In the method for manufacturing a semiconductor laser device according to the above,
It is preferable to form a layer in which the dopant of the cladding layer is C at a V / III ratio of 10 to 30 and the other layers of the second cladding layer at a V / III ratio of 180 to 220.

The above-mentioned mesa structure of the stripe portion includes a step of laminating an etching stop layer, a clad layer and a cap layer, a step of forming a stripe mask on the clad layer, and a step of forming a cap layer and a clad in a portion not covered by the stripe mask. It may be formed by a step of removing the layer up to the etching stop layer.

[0016]

According to the present invention, a certain p-type cladding layer is formed by laminating a plurality of inner layers having different dopants, and the diffusion coefficient of the dopant in each inner layer increases in order as the distance from the active layer increases. Even after the high temperature during the subsequent film formation, the dopant having a large diffusion coefficient does not diffuse to the active layer, and the diffusion surface is steep.
Therefore, the pn junction is formed in the active layer in a stepwise manner with high accuracy by a dopant having a small diffusion coefficient, and a reduction in operating current and an improvement in yield can be expected.

Suitable dopants and diffusion coefficients are
And C is 6.0 × 10^-15cm^Two/ s (900 ° C), Mg
1.0 × 10^-13cm^Two/ s (900 ° C), Zn 5.3 ×
10 ^-8cm^Two/ s (900 ° C), and C and Mg are compared with Zn.
Since C or Mg is smaller by several orders of magnitude, the inner layer adjacent to the active layer
Can be used. Also, the thickness of the second cladding layer
Is too thin, the refractive index difference with the active layer becomes large (horizontal
Equivalent refractive index difference ≧ 1.0 × 10^-3) Single mode oscillation
And the coherence increases. Thick and multi-mo
Oscillation, and the coherence is reduced.
Injection current spreads in the lateral direction of the cladding layer and the oscillation start value
Current and operating current tend to increase. According to the present invention
If the thickness of the cladding layer meets all of these characteristics,
(See FIG. 6).
The oscillation start value of the body laser greatly depends on the temperature.
Carriers contributing to oscillation are near the quasi-Fermi level in the conduction band.
It is a nearby electron, but at high temperatures the excited carrier
The average energy is much higher than the pseudo-Fermi level,
As a result, the proportion of carriers that contribute to oscillation decreases,
It is considered that the starting value becomes large. Oscillation start current
(J_th) Is expressed by the following equation.

[0018]

J _th ∝exp (T / T ₀ ) T ₀ is a characteristic temperature (a constant unique to the element), and the smaller this value, the greater the temperature dependence of J _th . According to the present invention, the Al composition in the cladding layer is set in the optimum range (see FIG. 8), and the pn junction interface is formed in the active layer to efficiently inject carriers. A film with few defects can be obtained, and an LD element having good characteristics can be obtained.

Conversely, if the Al composition difference is too large, a difference in the thermal expansion coefficient due to the composition difference will occur, and strain will increase in the film, causing crystal defects and deteriorating the film morphology. In addition, the current confinement layer has a two-stage structure in the active layer and the cladding layer in order to provide a binding effect of injected carriers, so that the carriers in the active layer can be spread by two current confinement layers. Since the current confinement layer is narrowed on both sides, the current confinement layer is narrower than in the case of one stage, the injection efficiency is improved, and the oscillation start current is reduced.

Further, the mirror image is symmetrical, so that the light density in the light confinement region becomes uniform, and the oscillation start current is reduced.
Differential efficiency with respect to operating current is improved. When C is used as a dopant, C present in a trimethyl group such as trimethylgallium (TMG) or triethylgallium (TEG) or a triethylgallium (TEG), which is a raw material of a grown crystal, is present in the film if the V / III ratio is in accordance with the present invention. And is doped into the As site to become an acceptor. If the V / III ratio is around 200, the amount taken in is small and the conductivity type is determined according to the characteristics of the other doped dopants.

Next, the present invention will be described based on embodiments. Embodiment 1 FIG. 1 is a sectional view of a semiconductor laser device of an embodiment according to the present invention. The layers other than the second cladding layer have the same layer configuration as the conventional one, and the same reference numerals are used, so that the description is omitted. The second cladding layer 5 according to the present invention is a laminated layer of a C-doped layer 5a, an Mg-doped layer 5b and a Zn-doped layer 5c in order from the active layer 4 side.

Hereinafter, a description will be given along a manufacturing process. Since the manufacturing method of the semiconductor laser device of this embodiment is the same as the conventional manufacturing process except for the second clad layer portion, FIG. 18 used in the description of the conventional manufacturing process is also used, and the description of the reference numerals is omitted. First, an n-type GaAs substrate 1 (Si-doped, carrier concentration 2 × 10 ¹⁸ cm ⁻³ , thickness 300 μm) is formed by metalorganic vapor phase epitaxy (MOCVD) to form an n-type GaAs substrate 0.2 μm thick.
GaAs buffer layer 2, first cladding layer 3 (n-type
Al _0.5 Ga _0.5 As Carrier concentration 5 × 10 ¹⁷ cm ^-3 , thickness 1μ
m), active layer 4 (non-doped Al _0.1 Ga _0.9 As, thickness 0.
1 μm).

Further, a multilayer second clad layer 5 according to the present invention was formed. Other than the dopant, it is the same as the conventional second clad layer formation. The composition of the entire second cladding layer 5 is p
The mold was made of Al _0.5 Ga _0.5 As and the carrier concentration was 1 × 10 ¹⁸ cm ⁻³ . The first inner layer 5a is a C-doped layer using carbon tetrabromide as a doping source gas and has a thickness of 0.15.
The second inner layer 5b is a Mg-doped layer using biscyclopentadienylmagnesium as a doping source gas, and has a thickness of 0.15 nm. The third inner layer 5c uses diethylzinc as a doping source gas. , Zn-doped layer having a thickness of 0.15 nm. The V / III ratio during growth was 200.

[0024] Next GaAs cap layer 6 (p-type GaAs, a carrier concentration of 1 × 10 ¹⁸ cm ^-3, thickness _0. 03μm) was formed. The GaAs cap layer 6 is provided in order to prevent a high-resistance Al oxide film from being formed when the subsequent oxide film forming step and its patterning step are directly applied to the GaAlAs layer. . Next, a thickness of 0.0
A 4 μm silicon oxide layer was applied by EB and then to a thickness of 0.1
A 0 μm silicon oxide layer was formed by sputtering.

A stripe-shaped mask 7 having a width of 3 μm is formed by ordinary photo-process patterning (FIG. 18A). Since a silicon dioxide layer formed by EB has an etching rate 20 times that of a silicon dioxide film formed by sputtering, if a double mask is used,
No groove is formed on the side surface of the next current confinement layer. Alternatively, a stripe can be formed even with a single sputtered film having a thickness of about 0.1 μm.

Next, a mask 7 is a selective growth mask. The current confinement layer 8 (n-type GaAs, carrier concentration 1 × 10 ¹⁹ cm ⁻³ , thickness 0.3 μm) is removed by MOCVD under reduced pressure except for the mask portion. ) Was formed (FIG. 18B). Next, the mask 7 is removed, and the third cladding layer 9 (p
Type Al _0.5 Ga _{0. 5} As, carrier concentration 5 × 10 ¹⁷ cm ^-3) and the contact layer 10 (p-type GaAs, a carrier concentration of 1 × 10
¹⁹ cm ^-3 , thickness 5.0 μm).

Finally, a p-side electrode 11 and an n-side electrode 12 on the upper and lower sides of the wafer were formed (FIG. 18C). After the above manufacturing process, the wafer was cleaved into bars (parallel to the plane of FIG. 18), and the bars were scribed to obtain individual LD elements. The laser characteristics (light output-current (IL) characteristics and voltage-current (VI) characteristics) of the semiconductor laser device manufactured according to this example were evaluated and compared with a conventional LD device. FIGS. 2A and 2B are graphs showing the laser characteristics of the LD element. FIG. 2A shows the case of the LD element according to the present invention, and FIG. 2B shows the case of the conventional LD element. In the conventional LD element, the oscillation start value current is high and is 50 mA or more, and the operating current at the time of 3 mW output (hereinafter, the operation is 3 mW output and the note is omitted) is as high as 65 mA or more. there were. In contrast, in the device of the present invention,
The oscillation start value current was about 45 mA, and the operation current was about 55 mA, which proved to be good characteristics.

Further, secondary ion mass spectrometry (SIMS) is performed in the depth direction (perpendicular to the layer) of the laminated portion of the cladding layer of the first conductivity type, the active layer, and the cladding layer of the second conductivity type, and The distribution was examined. FIGS. 3A and 3B are graphs showing impurity distributions in the first conductivity type clad layer, the active layer and the second conductivity type clad layer. FIG. 3A shows the case of the LD device according to the present invention, and FIG. This is the case of an LD element. In the case of the prior art, Zn and Se coexist at a high concentration in the active layer, but in the case of the present invention, C and S in the active layer are present.
e does not coexist at a high concentration but crosses each curve at a low concentration, indicating that the pn junction is in the active layer. Also,
Neither Zn nor Mg diffused into the active layer. Example 2 By setting the V / III ratio in the range of 10 to 30 at the time of MOCVD film growth, C
Can be used as a carrier generation source impurity to control the carrier concentration. FIG. 4 shows V in the manufacturing method according to the present invention.
4 is a graph of the carrier concentration versus the / III ratio. The layer configuration was the same as that of Example 1, the V / III ratio at the time of forming the lower layer of the second conductivity type second cladding layer was 20, and the carrier concentration was 6.0 × 10 ¹⁸ cm ⁻³ . The other layers in the second cladding layer were the same as in Example 1.

FIG. 5 is a graph showing laser characteristics of an LD device according to another embodiment of the present invention. It is almost the same as Example 1, and it can be seen that the operating voltage is lower because the carrier concentration of the second cladding layer is higher than in the conventional case. Embodiment 3 In the layer configuration of Embodiment 1, the current-light output (IL) characteristics and the coherence (α)% of the laser light change depending on the thickness of the second cladding layer of the second conductivity type. I understood. FIG.
5 is a graph showing the dependency of the coherence (α) of the LD element according to the present invention on the thickness of the second cladding layer.

The thickness of the second cladding layer is 300 to 450 nm
In the current-light output (IL) characteristic, the oscillation start value current is 40 mA or less, the operating current is 50 mA or less, and V
The operating voltage (Vop) was as good as 2.0 V or less even in the -I characteristics. FIG. 7 shows a second clad layer thickness 40 according to the present invention.
4 is a graph of laser characteristics of a 0 nm LD element. Also, in this thickness range, the coherence (α) is 70% or less, which sufficiently satisfies α ≦ 95% required for an optical pickup or the like. Example 4 In the layer configuration of Example 1, it was found that the temperature characteristics of the laser characteristics depended on the Al composition difference (ΔX) between the second cladding layer and the active layer. FIG. 8 is a graph showing the dependence of the characteristic temperature (T ₀ ) of the LD element according to the present invention on the Al composition difference between the second cladding layer and the active layer.

It is understood that a characteristic temperature (T ₀ ) of 120 K or more can be obtained in the range of 0.35 ≦ ΔX ≦ 0.57. FIG. 9 is a graph of the laser characteristics of the LD device according to the present invention where ΔX = 0.57. When the Al composition difference is in the above range, in the current-light output (IL) characteristics, the oscillation start value current is 50 mA or less, the operating current is 60 mA or less, and the voltage-current (V
In the -I) characteristics, the operating voltage Vop was as good as 2.0 V or less. Example 5 In an LD device having a second cladding layer having the same layer configuration as the conventional one, by providing a second current confinement layer between the buffer layer and the first cladding layer, the injection efficiency of carriers into the active layer was improved. Can be improved.

FIG. 10 is a sectional view showing the vicinity of the second current confinement layer of the LD device having the second current confinement layer according to the present invention. The sign of the second current confinement layer is 7a. The positional relationship between the buffer layer 2 and the first cladding layer 3 of the second current confinement layer 7a and the manufacturing process are the same as those of the conventional current confinement layer 7
This is the same as the positional relationship between the cladding layer 5 and the third cladding layer 8 and the manufacturing process.

The carrier concentration of the first cladding layer is 2.0 ×
It is the same as the LD element of Example 1 except that it is 10 ¹⁸ cm ⁻³ or less. Since the active layer 4 is sandwiched between the two current confinement layers, the current spread is more restricted than before, the current density flowing through the active layer is increased, that is, the carrier injection efficiency is improved, and the current-light output characteristics are improved. Was improved, and characteristics superior to those of Example 1 could be obtained. FIG. 11 is a graph of laser characteristics of an LD device having the second current confinement layer according to the present invention. The oscillation start value current is 35 mA or less, the operating current is 45 mA or less, the luminous efficiency is about 30% higher than that of the conventional LD element, and the operating voltage (Vo
p) was also good at 2.0 V or less. Embodiment 6 FIG. 12 is a cross-sectional view of an LD device according to the present invention in which two current confinement layers are symmetric with respect to an active layer. The second current confinement layer 7a is placed between the first cladding layer lower layer 3a and the first cladding layer upper layer 3b so as to have a symmetrical (equidistant) positional relationship with the first current confinement layer 7 and the active layer. I did it. Further, in order to make the shape symmetrical, the stripe portion sandwiched between the first current confinement layers 7 has a mesa structure, and the side surface of the stripe portion has a gradient opposite to that in the related art.

FIGS. 13A and 13B are cross-sectional views showing a manufacturing process for obtaining a mesa structure according to the present invention. FIG. 13A shows a state after forming a stripe-shaped mask, FIG. 13B shows a state after mesa etching, and FIG. After the formation of the cladding layer. The mesa etching for forming the mesa structure Ms is performed on the second cladding lower layer 5a (thickness 4).
(00 nm), an etching stop layer Es (50 nm thick) is formed on the second cladding lower layer 5a.
Further, the second clad upper layer 5c and the cap layer 6 were laminated. The stripe has a trapezoidal shape with the stripe mask M on the upper side, and the side surface of the current confinement layer 7 has a gradient opposite to that in the related art. After the formation of the third cladding layer, the same steps as in the related art are performed.

The relationship between the second current confinement layer 7a, the first clad lower layer 3a, and the first clad upper layer is the same as that of the conventional current confinement layer 7, the second clad layer 5, and the third clad layer 8 (FIG. 1).
7, 18). The light confinement effect was improved, and the laser characteristics were improved. FIG. 14 is a graph showing laser characteristics of an LD device having a second current confinement layer in a first cladding layer according to the present invention. In the current-optical output characteristics, the oscillation start value current is 35 mA or less, and the operating current is 45
mA or less, operating voltage (Vop) is 2.0 in voltage-current characteristics
V or better.

FIG. 15 is a graph showing the distance dependency between the coherent active layer and the current confinement layer of an LD device in which two current confinement layers according to the present invention are symmetrical with respect to the active layer. The coherence is 95 when the distance is in the range of 0.27 to 0.5 μm.
%. FIG. 16 is a graph showing the clad layer thickness dependence of the characteristic temperature of the LD device in which the two current confinement layers according to the present invention are symmetric with respect to the active layer. It can be seen that the characteristic temperature is 120K or more when the distance is in the range of 0.23 to 0.52 μm.

In the sixth and seventh embodiments, the second clad layer is a conventional single-doped layer.

[0038]

According to the present invention, the first conductivity type Al _x Ga _{1 -x} As (0 ≦ x ≦) is formed on one principal surface of the first conductivity type GaAs substrate.
Buffer layer having composition of 1), Al _x Ga _1-x As of first conductivity type
First cladding layer having composition (0 ≦ x ≦ 1), Al _y Ga _1-y As
(0 ≦ y ≦ x ≦ 1) active layer, second conductivity type Al _x Ga
_1-x As composition second cladding layer, second conductivity type GaAs cap layer, first conductivity type current confinement layer divided into two sections parallel to the laser optical axis, second conductivity type Al _x Ga _1-x As
In the AlGaAs semiconductor laser device in which a third cladding layer having a composition of and a GaAs contact layer of the second conductivity type are sequentially stacked, the cladding layer having a p-type conductivity among the first or second cladding layers is The dopant is composed of a plurality of different inner layers, and the diffusion coefficient of the dopant in each of the inner layers is increased in order as the distance from the active layer increases, so that the dopant having a large diffusion coefficient does not reach the active layer, and is contained in the active layer. The pn junction is formed with high accuracy, and the laser characteristics are excellent. The production yield is high.

Further, since the thickness of the p-type cladding layer and the Al composition difference with respect to the active layer are made appropriate, the temperature change of laser characteristics is small, and the coherence of laser light is small. Therefore, it is suitable for an optical pickup. Further, by providing two current confinement layers and forming a symmetrical structure with respect to the active layer, it is possible to provide an LD device having not only good laser characteristics with low oscillation start current and operating current but also low coherence.

[Brief description of the drawings] [Explanation of symbols]

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a graph showing laser characteristics of an LD element;
(A) is the case of the LD element according to the present invention, (b) is the case of the conventional LD element

FIGS. 3A and 3B are graphs showing impurity distributions in a first conductivity type cladding layer, an active layer and a second conductivity type cladding layer. FIG. 3A shows the LD element according to the present invention, and FIG. For element

FIG. 4 is a graph of carrier concentration versus V / III ratio in the manufacturing method according to the present invention.

FIG. 5 is a graph showing laser characteristics of an LD device according to another embodiment of the present invention.

FIG. 6 shows the second example of the coherence (α) of the LD element according to the present invention.
Graph showing the thickness dependence of the cladding layer

FIG. 7 shows a second clad layer having a thickness of 400 nm according to the present invention.
Graph of laser characteristics of D element

FIG. 8 is a graph showing the dependence of the characteristic temperature (T ₀ ) of the LD element according to the present invention on the Al composition difference between the second cladding layer and the active layer.

FIG. 9 is a graph showing laser characteristics of an LD element having ΔX = 0.57 according to the present invention.

FIG. 10 shows an LD having a second current confinement layer according to the present invention.
Sectional view near the second current confinement layer of the device

FIG. 11 shows an LD having a second current confinement layer according to the present invention.
Graph of laser characteristics of device

FIG. 12 is a sectional view of an LD device in which two current confinement layers according to the present invention are symmetrical with respect to an active layer.

13A and 13B are cross-sectional views showing a manufacturing process for obtaining a mesa structure according to the present invention, wherein FIG. 13A shows a state after forming a stripe mask, FIG. 13B shows a state after mesa etching, and FIG. After film formation

FIG. 14 is a graph showing laser characteristics of an LD device having a second current confinement layer in a first cladding layer according to the present invention.

FIG. 15 is a graph showing a distance dependency between a coherent active layer and a current confinement layer of an LD device in which two current confinement layers according to the present invention are symmetrical with respect to the active layer.

FIG. 16 is a graph showing the dependence of the characteristic temperature of an LD element in which two current confinement layers according to the present invention are symmetrical on the active layer on the distance between the active layer and the current confinement layer

FIG. 17 is a sectional view parallel to a cleavage plane of a conventional LD element.

FIGS. 18A and 18B are cleaved cross-sectional views showing one device of a wafer after a main manufacturing process of a conventional LD device. FIG. 18A is a diagram showing a silicon oxide layer patterning process, and FIG. After epitaxial growth, (c) shows after forming metal film for electrode

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 GaAs substrate 2 buffer layer 3 first cladding layer 3a first cladding lower layer 3b first cladding upper layer 4 active layer 5 second cladding layer 5a second cladding lower layer 5b second cladding middle layer 5c second cladding upper layer 6 cap layer 7 current confinement Layer 7a Second current blocking layer M Mask 9 Third cladding layer 10 Contact layer 11 P-side electrode 12 N-side electrode 13 Diffusion prevention layer 14 Diffusion prevention layer Es Etching stop layer

Claims (8)

[Claims] A first conductive type GaAs substrate on one main surface thereof,
Buffer layer of the composition of the conductivity type _{Al x Ga 1-x As (} 0 ≦ x ≦ 1), of a first conductivity type _{Al x Ga 1-x As (} 0 ≦ x ≦ 1) first cladding layer of the composition, Al an active layer having a composition of _y Ga _1-y As (0 ≦ y ≦ x ≦ 1), a second cladding layer having a composition of Al _x Ga _1-x As of a second conductivity type, a cap layer of GaAs having a second conductivity type, A current confinement layer of one conductivity type divided into two sections parallel to the laser optical axis, a third cladding layer of Al _x Ga _1-x As composition of second conductivity type, and a contact of GaAs of second conductivity type In the AlGaAs-based semiconductor laser device in which the layers are sequentially stacked, the cladding layer having the p-type conductivity of the first or second cladding layer is composed of a plurality of inner layers having different dopants, and the diffusion of the dopant in each of the inner layers is performed. A semiconductor laser device wherein the coefficient increases in order as the distance from the active layer increases. 2. The method according to claim 1, wherein the dopant is C,
2. The semiconductor laser device according to claim 1, wherein a combination of two or more of Mg and Zn in this order. 3. The p-type cladding layer has a thickness of 0.3.
The Al composition difference (Δx) in the mixed crystal of the cladding layer with respect to the active layer is in the range of 0.35 to 0.6. 14. The semiconductor laser device according to claim 1. 4. A method according to claim 1, wherein the first conductive type GaAs substrate has a first main surface and a first main surface.
Conductivity type _{Al x Ga 1-x As (} 0 ≦ x ≦ 1) buffer layer having the composition, of a first conductivity type _{Al x Ga 1-x As (} 0 ≦ x ≦ 1) first cladding layer of the composition, Al _y An active layer of Ga _1-y As (0 ≦ y ≦ x ≦ 1) composition, a second cladding layer of Al _x Ga _1-x As composition of second conductivity type, a cap layer of GaAs of second conductivity type, A current confinement layer of a conductivity type divided into two areas parallel to the laser optical axis, a third cladding layer of a second conductivity type Al _x Ga _{1 -x} As composition,
GaAs contact layers of the second conductivity type are sequentially stacked
In the AlGaAs-based semiconductor laser device, a second conductive type second portion divided into two sections in parallel with the laser optical axis between the buffer layer and the first cladding layer or in the first cladding layer. A semiconductor laser device characterized by forming a current confinement layer. 5. The semiconductor laser device according to claim 4, wherein said current confinement layer and said second current confinement layer are mirror-image-symmetric with respect to an active layer. 6. The semiconductor laser device according to claim 5, wherein the stripe portion sandwiched between the current confinement layers has a mesa structure. 7. The method of manufacturing a semiconductor laser device according to claim 1, wherein the dopant of the second cladding layer is a layer of C in the supply of a group V element gas and a group III element gas. The second cladding layer is formed at a molar ratio of group element (hereinafter referred to as V / III ratio) of 10 to 30, and the other layers of the second cladding layer are formed at a V / III ratio of 180 to 220. A method for manufacturing a semiconductor laser device. 8. The mesa structure of a stripe portion according to claim 6, wherein a step of laminating an etching stop layer, a cladding layer and a cap layer, a step of forming a stripe mask on the cladding layer, and then not covering the stripe mask. A method for manufacturing a semiconductor laser device, comprising: forming a portion of a cap layer and a cladding layer up to an etching stop layer.