JPH0677594A - Semiconductor laser - Google Patents

Abstract

(57) [Summary] [Object] To realize an internal stripe type semiconductor laser having a low operating current, a simple manufacturing process, and a current confinement structure capable of determining the width of a current stripe portion with high controllability. [Structure] A p-type In _x Ga _1-x P layer 7 as an etching stop layer is epitaxially grown on a p-type Al _0.2 Ga _0.8 As layer 6 as an optical waveguide layer which also serves as a p-type cladding layer,
After on the n-type Al _0.3 Ga _0.7 As layer 8 as a current stop layer is epitaxially grown thereon, the n-type Al _0.3 Ga
Stripe-shaped openings 8a are formed in the _0.7 As layer 8 by wet etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to an internal stripe type semiconductor laser having a current confinement structure with a current stop layer.

[0002]

2. Description of the Related Art As a semiconductor laser manufactured by a vapor phase growth method such as a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxy (MBE) method, control of epitaxial growth on an uneven surface having large steps Therefore, a so-called self-alignment is performed in which a current confinement structure is formed by forming a stripe-shaped opening in a current stop layer epitaxially grown on a flat double hetero growth layer to form a current confinement structure. The (self-aligned) type is becoming mainstream.

One of such self-aligned semiconductor lasers is the SAN (Self-Align) proposed by the present applicant.
ed Narrow Stripe) laser, which has a structure as shown in, for example, FIG.
0-66894).

As shown in FIG. 4, in this conventional SAN laser, an n-type AlGaAs layer 102 as an n-type cladding layer, for example, n-type or p-type, is formed on an n-type GaAs substrate 101.
An active layer 103 made of a p-type AlGaAs layer, a p-type AlGaAs layer 104 as a p-type optical waveguide layer which also serves as a p-type cladding layer, and an n-type GaAs layer 105 as a current stop layer are sequentially laminated. The n-type GaAs layer 105 as this current stop layer
A stripe-shaped opening 105a that defines a current stripe portion is formed in the. And this n-type GaAs layer 1
05 and the p-type AlGaAs layer 104 inside the opening 105a, a p-type AlGaAs layer 106 as a p-type clad layer is laminated, and on the p-type AlGaAs layer 106, a p-type GaAs layer 107 as a cap layer. Are stacked.

Although not shown, the p-type GaAs layer 1 is actually used.
The p-side electrode is provided on 07, and the n-side electrode is provided on the back surface of the n-type GaAs substrate 101.

[0006]

In the conventional SAN laser shown in FIG. 4 described above, light is effectively absorbed by the n-type GaAs layer 105 as a current stop layer so that it is effectively moved in the lateral direction (direction parallel to the pn junction). Since light is guided by providing a refractive index difference, n-type Ga generated by the oscillated laser light is used.
There is current leakage due to the generation of minority carriers in the As layer 105. Therefore, the operating current of the conventional SAN laser described above has a drawback that it is considerably larger than the operating current of a so-called real index guided semiconductor laser. For example, the operating current required to obtain an optical output of 30 mW is about 60 mA for a real index guided semiconductor laser, whereas it is about 100 mA for a SAN laser.

The above-mentioned problem is caused by the fact that n is used as a current stop layer.
The carrier concentration of the n-type GaAs layer 105 is set to 2 × 10 ¹⁸ cm ⁻³ or more, and the thickness thereof is set to the diffusion length of minority carriers in the n-type GaAs layer 105 or more, specifically about 1.5 μm or more. It is possible to solve it. However, if the thickness of the n-type GaAs layer 105 is set to 1.5 μm or more in this way, the step difference in the stripe-shaped opening 105a formed in the n-type GaAs layer 105 becomes considerably large.
Problems occur during the electrode forming process performed after the epitaxial growth process. Therefore, normally, after the epitaxial growth of the p-type GaAs layer 107 as the cap layer is completed, the surface of the p-type GaAs layer 107 is flattened, and then the p-side electrode is formed on the flattened surface. However, it is not preferable to use such a flattening process because it increases the labor of manufacturing the semiconductor laser.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a semiconductor laser which has a low operating current and does not require a flattening process so that the manufacturing process is simple.

Another object of the present invention is to provide a semiconductor laser capable of determining the width of the current stripe portion with high controllability.

[0010]

To achieve the above object, one invention of the present invention provides a first conductivity type first cladding layer (2, 4) laminated on a compound semiconductor substrate (1). )
An active layer (5) laminated on the first cladding layer (2, 4), a second conductivity type second cladding layer (6) laminated on the active layer (5), In an internal stripe type semiconductor laser having a first conductivity type current stop layer (8) having a stripe-shaped opening (8a) laminated on the second cladding layer (6), the current stop layer (8) is An etching stop formed of a compound semiconductor layer transparent to oscillated laser light and having an etching rate lower than that of the current stop layer (8) between the second cladding layer (6) and the current stop layer (8). A layer (7) is provided.

Another aspect of the present invention is to provide a first clad layer (2, 4) of the first conductivity type laminated on a compound semiconductor substrate (1) and a first clad layer (2, 4). An active layer (5) laminated on the active layer (5), an optical waveguide layer (6) of the second conductivity type laminated on the active layer (5) and also serving as a second cladding layer of the second conductivity type, and an optical waveguide layer. (6) A laser in which the current stop layer (8) is oscillated in an internal stripe type semiconductor laser having a first conductivity type current stop layer (8) having a stripe-shaped opening (8a) laminated thereon. An etching stop layer (7) formed of a compound semiconductor layer transparent to light and having an etching rate lower than that of the current stop layer (8) is provided between the optical waveguide layer (6) and the current stop layer (8). It is what has been.

[0012]

According to the semiconductor laser of the present invention configured as described above, the current stop layer (8) made of the compound semiconductor layer transparent to the oscillated laser beam allows the lateral direction (direction parallel to the pn junction). ) Is provided, but in this case, current leakage due to generation of minority carriers as in a conventional SAN laser in which a lateral refractive index difference is effectively provided by light absorption by the current stop layer is caused. Therefore, the operating current can be reduced accordingly. Further, by eliminating the current leakage in this way, the thickness of the current stop layer (8) can be reduced, so that the stripe-shaped opening (8a) portion formed in the current stop layer (8) is reduced. The step can be made small, and therefore, the flattening process after the epitaxial growth process is unnecessary, and the manufacturing process is simplified accordingly.

Further, a current stop layer (8) is laminated on the second cladding layer or the optical waveguide layer (6) via an etching stop layer (7) having an etching rate lower than that of the current stop layer (8), By forming a stripe-shaped opening (8a) in the current stop layer (8) by lithography and etching, the stripe-shaped opening (8a) can be prevented while preventing the second cladding layer or the optical waveguide layer (6) from being etched. ), And hence the width of the current stripe portion, can be determined with high controllability.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 1, 2 and 3 show a real index guided semiconductor laser according to an embodiment of the present invention. FIG. 1 is a sectional view perpendicular to the cavity length direction at the center of the cavity. 2 is a cross-sectional view perpendicular to the resonator length direction in the window portions at both ends of the resonator, and FIG. 3 is a cross-sectional view parallel to the resonator length direction at a position deviated from the current stripe portion.

As shown in FIGS. 1, 2 and 3, in the semiconductor laser according to this embodiment, for example, n-type GaAs is used.
On the substrate 1, n-type Al _0.42 Ga _0.58 as an n-type cladding layer
As layer 2, n-type In _x Ga _1-x as an etching stop layer
An n-type Al _0.2 Ga _0.8 As layer 4 serving as an n-type optical waveguide layer that also serves as the P layer 3 and the n-type cladding layer, for example, undoped Al _0.12 Ga
_An active layer 5 made of _0.88 As layer, a p-type Al _0.2 Ga _0.8 As layer 6 as a p-type optical waveguide layer which also serves as a p-type cladding layer, a p-type In _x Ga _1-x P layer 7 as an etching stop layer, and An n-type Al _0.3 Ga _0.7 As layer 8 as a current stop layer is sequentially laminated. Here, n as an etching stop layer
The In composition ratio x of the type In _x Ga _1-x P layer 3 and the p-type In _x Ga _1-x P layer 7 is preferably selected to be 0.5, for example. The n-type Al _0.3 Ga _0.7 As layer 8 serving as the current stop layer is provided with stripe-shaped openings 8a that define the current stripe portion. Then, this n-type Al _0.3 Ga _0.7 As layer 8 and its opening 8
On the p-type In _x Ga _1-x P layer 7 inside a, p-type Al _0.2 Ga _0.8 As as a p-type optical waveguide layer that also serves as a p-type cladding layer
A layer 9 is laminated, and a p-type Al _0.42 Ga _0.58 As layer 10 as a p-type cladding layer and a p-type GaAs layer 11 as a cap layer are sequentially laminated on the p-type Al _0.2 Ga _0.8 As layer 9. .

The thickness of each layer of the semiconductor laser according to this embodiment is selected according to the characteristics required for this semiconductor laser. One example thereof is n-type Al.
_0.42 Ga _0.58 As Layer 2 has a thickness of 1.5 μm and n-type In _x Ga _1-x
The P layer 3 has a thickness of 5 nm, the n-type Al _0.2 Ga _0.8 As layer 4 has a thickness of 0.1 μm, and the active layer 5 has a thickness of 0.04 μm.
The thickness of the _0.2 Ga _0.8 As layer 6 is 0.1 μm, p-type In _x Ga _1-x
The P layer 7 has a thickness of 5 nm, the n-type Al _0.3 Ga _0.7 As layer 8 has a thickness of 0.2 μm, and the p-type Al _0.2 Ga _0.8 As layer 9 has a thickness of 0.3.
The p-type Al _0.42 Ga _0.58 As layer 10 has a thickness of 1.5 μm, and the p-type GaAs layer 11 has a thickness of 0.5 μm.

As shown in FIGS. 2 and 3, the semiconductor laser according to this embodiment has a so-called window structure.
That is, in the semiconductor laser according to this embodiment, both end faces of the resonator are undoped which constitutes the active layer 5.
The energy gap is larger than that of the Al _0.12 Ga _0.88 As layer,
Therefore, n-type Al _0.3 G, which is transparent to the emitted laser light
It has a structure covered with a _0.7 As layer 8, and this portion forms a transparent window.

Next, a method of manufacturing the semiconductor laser according to this embodiment having the above-mentioned structure will be described.

To manufacture the semiconductor laser according to this embodiment, as shown in FIGS. 1, 2 and 3, first, n-type Ga is used.
The n-type Al _0.42 Ga _0.58 As layer 2 serving as an n _- type cladding layer, the n _- type In _x Ga _1-x P layer 3 serving as an etching stop layer, and the n-type cladding layer are also used on the As substrate 1 by MOCVD, for example. An n-type Al _0.2 Ga _0.8 As layer 4 as an n-type optical waveguide layer, for example, an active layer 5 composed of an undoped Al _0.12 Ga _0.88 As layer, and a p-type optical waveguide layer also serving as a p-type cladding layer.
Type Al _0.2 Ga _0.8 As layer 6, p-type In _x Ga _1-x P layer 7 as an etching stop layer, and n-type as a current stop layer
The Al _0.3 Ga _0.7 As layer 8 is sequentially epitaxially grown.

Next, by lithography and etching, stripe-shaped openings 8a are formed in the n-type Al _0.3 Ga _0.7 As layer 8.
To form. This etching is performed for AlGa with respect to the InGaP layer.
The wet etching method is performed using an etching solution capable of ensuring a sufficiently high As layer etching selectivity, for example, a hydrochloric acid-based etching solution (for example, HCl: H ₂ O = 1: 1). As a result, this n-type Al _0.3 Ga _0.7
When the As layer 8 is etched, etching is almost completely completed when the etching stop layer provided under the n-type Al _0.3 Ga _0.7 As layer 8, that is, the p-type In _x Ga _1-x P layer 7 is exposed. It stops and prevents the underlying p-type Al _0.2 Ga _0.8 As layer 6 from being etched. Thus, p-type In _x Ga
_{Since the 1-x} P layer 7 is hardly etched, the thickness of the p-type In _x Ga _1-x P layer 7 is, for example, 5 as described above.
Even a very small value of about nm is sufficient.

Next, by lithography and etching, an n-type Al _0.3 Ga _0.7 As layer 8, a p-type In _x Ga _1-x P layer 7,
p-type Al _0.2 Ga _0.8 As layer 6, active layer 5 and n-type Al _0.2 Ga
_{The 0.8} As layer 4 is sequentially patterned into a predetermined shape. In this case, the n-type Al _0.2 Ga _0.8 As layer 4 is etched by using a wet etching method, and the etching solution at that time is the same as that used for etching the n-type Al _0.3 Ga _0.7 As layer 8 described above. For example, a hydrochloric acid-based etching solution is used. As a result, when the etching stop layer provided below the n-type Al _0.2 Ga _0.8 As layer 4, that is, the n-type In _x Ga _1-x P layer 3 is exposed, the etching is almost completely stopped, and The n-type Al _0.42 Ga _0.58 As layer 2 is prevented from being etched.

Next, the entire surface is p-doped by MOCVD again.
The type Al _0.2 Ga _0.8 As layer 9, the p-type Al _0.42 Ga _0.58 As layer 10 and the p-type GaAs layer 11 are sequentially epitaxially grown.

Next, although not shown, the p-type GaAs layer 11 is formed.
After forming the p-side electrode on the upper surface and the n-side electrode on the back surface of the n-type GaAs substrate 1, the n-type GaAs substrate 1 having the laser structure formed thereon is cleaved into a bar shape as described above, and This bar is made into chips and the desired semiconductor laser is completed.

According to this embodiment, since the n-type Al _0.3 Ga _0.7 As layer 8 transparent to the oscillated laser beam is used as the current stop layer, the current stop layer is n
Unlike the above-described conventional SAN laser formed by the GaAs layer, there is no current leak due to the generation of minority carriers in the current stop layer due to the laser light, and therefore the operating current can be reduced accordingly. Further, since the thickness of the n-type Al _0.3 Ga _0.7 As layer 8 serving as the current stop layer can be small, the step difference in the stripe-shaped opening 8a formed in the n-type Al _0.3 Ga _0.7 As layer 8 can be eliminated. P-type Al which becomes smaller and is therefore epitaxially grown thereafter
_0.2 Ga _0.8 As layer 9, p-type Al _0.42 Ga _0.58 As layer 10 and p-type
The step difference on the surface of the GaAs layer 11 is also reduced, and the subsequent step, that is, the step of forming the p-side electrode does not occur. Therefore, it is not necessary to flatten the surface of the p-type GaAs layer 11 after the epitaxial growth step of the p-type GaAs layer 11 as the cap layer, and the manufacturing process of the semiconductor laser can be simplified accordingly.

Further, in the semiconductor laser according to this embodiment, p-type In _x Ga serving as an etching stop layer is formed on the p-type Al _0.2 Ga _0.8 As layer 6 serving as the p-type optical waveguide layer which also serves as the p-type cladding layer. _Since the n-type Al _0.3 Ga _0.7 As layer 8 serving as the current stop layer is laminated via the _1-x P layer 7, the p-type In _x Ga _1-x P layer 7 serves as a base p-layer. While preventing the etching of the type Al _0.2 Ga _0.8 As layer 6, the stripe-shaped openings 8a can be formed in the n-type Al _0.3 Ga _0.7 As layer 8 by etching with high controllability.
As a result, the width of the current stripe portion can be determined with high controllability, and the high light output characteristics of the semiconductor laser can be obtained with good reproducibility.

Further, since the semiconductor laser according to this embodiment has the window structure, it is possible to prevent the deterioration due to the destruction of the laser end face, and it is possible to greatly improve the maximum light output. Moreover, in the semiconductor laser according to this embodiment, since the waveguide is used, the spread of the laser beam is smaller than that of the semiconductor laser having a simple window structure, and the position of the light emitting point should be substantially aligned with the laser end face. Is possible.
In addition, it is desirable that the effective refractive index of the region in the vicinity of the active layer 5 at both ends of the resonator and the refractive index of the window region are the same,
By doing so, the waveguide loss can be suppressed to be small, and the instability of laser oscillation due to the composite resonator structure can be suppressed.

Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above embodiment, and various modifications can be made based on the technical idea of the present invention. .

For example, the p-type In _x Ga _1-x P layer 7 and the n-type In _x G serving as the etching stop layer in the above-described embodiments.
As described above, x = 0.5 is preferably used as the a _1-x P layer 3, but more generally, (Al _x Ga _1-x ) is used as the etching stop layer. _0.5 In
_{A 0.5} P layer may be used.

The composition of each AlGaAs layer constituting the semiconductor laser according to the above-mentioned embodiment is only an example, and the composition can be changed as required.

If necessary, in the above-described embodiment, a striped opening 8a is formed in the n-type Al _0.3 Ga _0.7 As layer 8 as a current stop layer, and then, as an etching stop layer in the opening 8a. P-type In _x Ga
_{The 1-x} P layer 7 may be removed by etching.

In the above-mentioned embodiments, the case where the semiconductor laser has the window structure has been described, but it is not always necessary to have the window structure.

Further, in the above embodiment, AlGaAs
Although the case where the present invention is applied to a semiconductor laser of the type has been described, the present invention can also be applied to a semiconductor laser other than the AlGaAs semiconductor laser, for example, a ZnSe semiconductor laser.

[0034]

As described above, according to the present invention, an internal stripe type semiconductor laser having a low operating current, a simple manufacturing process, and a high controllability of the current stripe width can be realized. be able to.

[Brief description of drawings]

FIG. 1 is a cross-sectional view perpendicular to a cavity length direction in a cavity central portion of a real index guided semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view perpendicular to the cavity length direction in the window portions at both ends of the cavity of the real index guided semiconductor laser according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view parallel to the cavity length direction at a position deviated from the current stripe portion of the real index guided semiconductor laser according to the embodiment of the present invention.

FIG. 4 is a sectional view showing a conventional SAN laser.

[Explanation of symbols]

1 n-type GaAs substrate 2 n-type Al _0.42 Ga _0.58 As layer 3 n-type In _x Ga _1-x P layer 4 n-type Al _0.2 Ga _0.8 As layer 5 active layer 6 p-type Al _0.2 Ga _0.8 As layer 7 p-type In _x Ga _1-x P layer 8 n-type Al _0.3 Ga _0.7 As layer 8 a Striped opening 9 p-type Al _0.2 Ga _0.8 As layer 10 p-type Al _0.42 Ga _0.58 As layer 11 p-type GaAs layer

Claims (2)

[Claims] 1. A first conductivity type first clad layer laminated on a compound semiconductor substrate, an active layer laminated on the first clad layer, and a second layer laminated on the active layer. An internal stripe type semiconductor laser having a conductive type second cladding layer and a first conductivity type current stop layer having a stripe-shaped opening laminated on the second cladding layer, wherein the current stop layer Is formed of a compound semiconductor layer transparent to oscillated laser light, and an etching stop layer having an etching rate smaller than that of the current stop layer is provided between the second cladding layer and the current stop layer. A semiconductor laser characterized in that 2. A first conductivity type first clad layer laminated on a compound semiconductor substrate, an active layer laminated on the first clad layer, and a second layer laminated on the active layer. Internal stripe type having a second conductivity type optical waveguide layer that also serves as a conductivity type second clad layer, and a first conductivity type current stop layer having a stripe-shaped opening laminated on the optical waveguide layer In the semiconductor laser described above, the current stop layer is formed of a compound semiconductor layer transparent to oscillated laser light, and has an etching rate smaller than that of the current stop layer between the optical waveguide layer and the current stop layer. A semiconductor laser having an etching stop layer.