JPH09129967A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser, which has a wide ridges but is capable of stabilized fundamental lateral mode oscillation during high-output operation, by forming a high-loss, lateral-mode control region that has a narrow optical path. SOLUTION: A semiconductor laser comprises an n-type GaAs substrate 10, an n-type AlGaAs clad layer 20 on the substrate 10, an active layer 30 on the n-type AlGaAs clad layer 20, and a p-type AlGaAs clad layer 40a with a ridge 70. The p-type AlGaAs clad layer 40a includes recesses 90 for lateral mode control on both sides of the ridge 70.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-power semiconductor laser (hereinafter sometimes abbreviated as LD), and particularly to a ridge waveguide type semiconductor capable of obtaining stable fundamental transverse mode oscillation at high output. It relates to the structure of a laser.

[0002]

2. Description of the Related Art Conventionally, techniques in such a field include:
For example, literature name: RECENT DEVELOPMEN
TS OF 980-nm PUMP LASERS
FOROPTICAL FIBER AMPLIFIE
RS. Author: Heinz Meier, IBM Res
search Division, Zurich Res
search Laboratory, Proc. of
20th European Conf. on Opt
ical Communication (ECOC 1
994), Florence, Italy, Sept.
25-29, 1994.

The structure of the semiconductor laser disclosed in this document will be briefly described below with reference to FIG.
On the n-GaAs substrate 101, n-Al is formed in order from the substrate side.
GaAs cladding layer 102, InGaAs / AlGaA
s active layer 103, p-AlGaAs cladding layer 104,
A p-GaAs contact layer 105 is formed. Although not shown, the active layer 103 is InGa in which a quantum well layer made of InGaAs and an AlGaAs barrier layer are laminated.
It is composed of a semiconductor layer having an As / AlGaAs quantum well structure. In addition, the p-AlGaAs cladding layer 104
And the p-GaAs contact layer 105 form a ridge. Reference numeral 106 is an insulating film (SiO ₂ film).

Further, an n-side electrode 108 is formed on the lower surface of the n-GaAs substrate 101, and a p-side electrode 107 is formed on the upper surface of the p-GaAs contact layer 105.

[0005]

However, the conventional ridge waveguide type semiconductor laser has the following problems. The laser light propagates in the refractive index waveguide formed by the effective refractive index difference between both sides of the ridge and the ridge portion. For this reason,
In order to obtain stable fundamental transverse mode oscillation during high power operation, according to the effective refractive index difference determined by the material and structure,
It is necessary to narrow the width of the refractive index waveguide. In the conventional structure, this reduces the width of the ridge. However, when the ridge width is narrowed, the area of the ridge head becomes small, so that the contact resistance at the p-type electrode increases and the optical density at the optical waveguide increases, so that the temperature rise of the element becomes remarkable during laser oscillation. This causes a problem that the device life is shortened and the operation becomes unstable.

The present invention eliminates the above-mentioned problems and increases optical loss in the transverse mode control region, and effectively narrows the optical propagation path to stabilize the ridge width even during high output operation. It is an object of the present invention to provide a semiconductor laser capable of obtaining the fundamental transverse mode oscillation described above.

[0007]

In order to achieve the above object, the present invention provides [1] a compound semiconductor substrate, a first clad layer on the upper side of the substrate, and an active layer on the upper side of the first clad layer. And a second clad layer above the active layer, wherein a ridge portion is formed in the second clad layer above the active layer.
In the vicinity of the side surface of the ridge portion of the cladding layer, lateral mode control regions where the thickness of the second cladding layer is thin are formed on both sides of the ridge portion.

[2] In the semiconductor laser described in [1] above, the compound semiconductor substrate is a GaAs substrate, and the first semiconductor laser is the GaAs substrate.
The clad layer is an n-type AlGaAs clad layer, and the second clad layer is a p-type AlGaAs clad layer. According to the present invention, as described above, by providing the lateral mode control region in which the thickness of the AlGaAs cladding layers on both sides of the ridge on both end faces is reduced, the optical propagation path is substantially narrowed and the ridge width is narrowed. In this way, stable fundamental transverse mode oscillation can be obtained during high output operation.

Further, since the ridge width can be widened, the contact resistance at the p-side electrode at the ridge head increases, and the light density in the optical waveguide increases, so that the temperature of the device remarkably rises during laser oscillation. Is suppressed, and stable operation at high output operation is obtained.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In these drawings, each component merely shows the shape, size, and positional relationship of each component to the extent that the present invention can be understood. FIG. 1 is a perspective view schematically showing the structure of an element constituting a ridge waveguide type semiconductor laser which is an embodiment of the present invention,
2 is a manufacturing process diagram (1) of the semiconductor laser, FIG.
FIG. 3 is a manufacturing process diagram (2) of the semiconductor laser.

First, as shown in FIG. 2A, n-Ga
On the As substrate 10, n-Al_xGa _1-xAs first crack
Layer (eg, x = 0.2, carrier concentration 5 × 10¹⁷c
m^-3) 20, active layer 30, p-Al_xGa_1-xAs second
Cladding layer (eg, x = 0.2, carrier concentration 5 × 1
0¹⁸cm^-3, Thickness about 1.5 to 2 μm) 40, p-Ga
As contact layer (for example, carrier concentration 1.5 × 10
¹⁹cm^-3Below, thickness 0.3-0.5 μm) 50 MOV
It is grown by a known method such as PE method and MBE method.

Although not shown, the active layer 30 has a quantum well (for example, carrier concentration 0.15 ≦ x ≦ 0.2, thickness 8-10 nm) made of undoped In _x Ga _1-x As made of undoped GaAs. Barrier layer (e.g.
80 nm) sandwiched between undoped InGaAs / GaAs
It is composed of a semiconductor layer having a single quantum well structure.

Next, as shown in FIG. 2B, an oxide film such as SiO ₂ is formed on the p-GaAs contact layer 50 by the plasma CVD method or the like, and the usual photolithography method and buffer evaporation are used. A SiO ₂ stripe mask 60 having a width of 6 to 8 μm is formed by hydrogen etching. Next, as shown in FIG. 2C, wet etching (for example, sulfuric acid: 1, hydrogen peroxide solution: 8, water: 100) is performed.
Liquid mixture) and dry etching RIE (Reacti
ve Ion Etching) and the like, p-GaA
The s contact layer _{50, p-Al X Ga 1} -X As second cladding layer 40 are etched to form a ridge portion 70.

In this case, the remaining p after etching.
-Al _x Ga _1-x As second cladding layer 40a thickness,
The etching conditions and time are controlled so that the width of the ridge 70 is about 0.5 μm and 5 to 7 μm. In the figure, 4
0a is etched in _{p-Al x Ga 1-X} As second cladding layer, 50a denotes the etched of the p-GaAs contact layer.

Next, as shown in FIG. 3A, the upper SiO ₂ stripe mask 60 of the ridge portion 70 is removed, an oxide film of SiO ₂ or the like is formed again on the entire surface, and the ordinary photolithography method and SiO _{2 from} which SiO ₂ was removed over the width of 4 to 6 μm and the length of 10 to 20 μm on both sides of the ridge on both end faces of the resonator by buffered hydrogen fluoride etching.
_{2 A} mask 80 is formed.

Next, wet etching (for example, a mixed solution of sulfuric acid: 1, hydrogen peroxide: 8, water: 100),
SiO ₂ mask 80 by dry etching RIE or the like
P-Al _x Ga ₁ -x As second etched using
A part of the clad layer 40a is etched to have a thickness of about 0.2 μm to form a lateral mode control region 90. Incidentally, 100 is a ridge region.

Then, as shown in FIG.
_TwoThe mask 80 is removed with hydrogen fluoride. In the figure,
40b is p-Al on which the transverse mode control region 90 is already formed._X
Ga _1-XThe As 2nd clad layer is shown. After this,
However, the etched p-GaAs contact layer 50
a, p-Al on which the transverse mode control region 90 has been formed_XGa
_1-XInsulation of SiN or the like on the As second clad layer 40b
After film formation, etched p-GaAs contour
The insulating film on the insulating layer 50a is removed to form the p-side electrode
Then, the n-side electrode is formed on the substrate side. After cleavage, A on the cleavage plane
Apply R and HR coating.

The operation of the semiconductor laser thus obtained will be described below. When this element is operated normally, the laser light propagates in the refractive index waveguide formed by the effective refractive index difference between both sides of the ridge and the ridge portion. The propagated laser light has increased optical loss in the transverse mode control regions formed on both sides of the ridge at both ends of the resonator, effectively narrowing the optical propagation path, controlling the transverse mode, and operating at high output. Also becomes the oscillation of the fundamental transverse mode.

With this structure, by providing the lateral mode control region in which the thickness of the AlGaAs cladding layers on both sides of the ridge at both end faces is reduced, the optical propagation path is substantially narrowed and the ridge width is narrowed. In this way, stable fundamental transverse mode oscillation can be obtained during high output operation. Furthermore, since the ridge width can be widened, a remarkable temperature rise of the element during laser oscillation due to an increase in contact resistance at the p-side electrode at the ridge head and an increase in optical density in the optical waveguide can be suppressed. A stable operation can be obtained at the time of high output operation.

Further, the semiconductor laser of the present invention can be used in the following forms. (1) In the above embodiment, an n-type substrate is used, but a p-type substrate can be used by changing the conductivity types of n and p. (2) The embodiment using the GaAs-based laser has been described.
It can also be applied to other material systems such as InP system.

(3) Although the embodiment in which the lateral mode control region is formed on both end faces is shown, the present invention can be applied to the case where it is formed on one end face or the other region. In this case, parameters such as width, length, and depth of the lateral mode control region need to be optimized in each case. Note that the present invention is not limited to the above embodiment,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0022]

As described above in detail, according to the present invention, by providing the transverse mode control region in which the thickness of the AlGaAs cladding layers on both sides of the ridges on both end faces is reduced, the optical propagation path is substantially formed. Narrowing occurs, and stable fundamental transverse mode oscillation can be obtained during high-power operation without narrowing the ridge width.

Further, since the ridge width can be widened, a remarkable increase in temperature of the device during laser oscillation due to an increase in contact resistance at the p-side electrode at the ridge head and an increase in light density in the optical waveguide can be suppressed. A stable operation can be obtained at the time of high output operation.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing the structure of an element constituting a ridge waveguide type semiconductor laser which is an embodiment of the present invention.

FIG. 2 is a manufacturing process diagram (1) of a ridge waveguide type semiconductor laser according to an embodiment of the present invention.

FIG. 3 is a manufacturing process diagram (2) of the ridge waveguide type semiconductor laser according to the embodiment of the present invention.

FIG. 4 is a perspective view schematically showing the structure of an element that constitutes a conventional ridge waveguide type semiconductor laser.

[Explanation of symbols]

10 n-GaAs substrate _{20 n-Al x Ga 1-} x As first cladding layer 30 active layer _{40 p-Al x Ga 1-} x As second cladding layer 40a etched of the p-AlGaAs second cladding layer 40b transverse mode P-AlGa with a control region already formed
As second cladding layer 50 p-GaAs contact layer 50a etched of the p-AlGaAs contact layer 60 SiO ₂ stripe masks 70 ridge 80 SiO ₂ mask 90 transverse mode control region 100 ridge region

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroki Yaegashi 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (2)

[Claims] 1. A compound semiconductor substrate, a first cladding layer above the substrate, an active layer above the first cladding layer,
At least a second cladding layer above the active layer,
A ridge waveguide type semiconductor laser in which a ridge portion is formed in a second cladding layer above the active layer, wherein the second cladding layers on both sides of the ridge portion are provided in the vicinity of a side surface of the ridge portion of the second cladding layer. A semiconductor laser characterized in that a lateral mode control region having a reduced thickness is formed. 2. The semiconductor laser according to claim 1, wherein
A semiconductor laser, wherein the compound semiconductor substrate is a GaAs substrate, the first cladding layer is an n-type AlGaAs cladding layer, and the second cladding layer is a p-type AlGaAs cladding layer.