Semiconductor laser device in which compressive strain...

Details Semiconductor laser device in which compressive strain... Semiconductor laser device in which compressive strain...

2001-10-31

2003-11-04

Ip, Paul (Department: 2828)

Coherent light generators

Particular active media

Semiconductor

C372S046012

Reexamination Certificate

active

06643306

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser device having a compressive strain active layer.
2. Description of the Related Art
The active layers in the conventional semiconductor laser devices which are formed on a GaAs substrate and emit laser light having a wavelength of 0.9 to 1.2 micrometers have a composition which causes a compressive strain. Since the compressive strain produces crystal defects or the like, the above semiconductor laser devices cannot attain to satisfactory characteristics and high reliability in operation with high output power.
U.S. Pat. No. 5,671,242 (corresponding to Japanese Unexamined Patent Publication, No. 8(1996)-78786) discloses a stress-compensation semiconductor laser device including a stress-compensation strained quantum well layer in which compressive strain well layers and tensile strain barrier layers are alternately laminated so that the average strain of the entire active layer is a compressive strain. However, when the amount of the compressive strain is increased in this semiconductor laser device, the difference in the strain between the compressive strain well layers and the tensile strain barrier layers increases, and therefore the strong interlayer stress is produced. Thus, it is impossible to achieve satisfactory crystallinity without producing defects in vicinities of the boundaries between the layers.
T. Fukunaga et al. (“Reliable operation of strain-compensated 1.06 &mgr;m InGaAs/InGaAsP/GaAs single quantum well lasers,” Applied Physics Letters, Vol. 69, Issue 2, pp. 248-250, 1996) report a semiconductor laser device in which an InGaAs strained quantum well active layer is formed above a GaAs substrate, and tensile strain barrier layers are formed adjacent to the InGaAs strained quantum well active layer so as to compensate for the strain in the InGaAs strained quantum well active layer. Although the reliability of the semiconductor laser device is improved by the provision of the tensile strain barrier layers, the above semiconductor laser devices cannot attain to a practical reliability level or high output characteristics.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor laser device which can compensate for compressive strain in an active layer, and is reliable in a wide output power range from low to high output power.
(1) According to the first aspect of the present invention, there is provided a semiconductor laser device comprising a substrate and an active region being formed above the substrate. The active region includes an active layer and optical waveguide layers. The active layer has a predetermined amount of compressive strain and a predetermined thickness, and the optical waveguide layers have a predetermined amount of tensile strain and a predetermined total thickness, and are formed so that the active layer is sandwiched between the optical waveguide layers. The absolute value of the sum of the product of the predetermined amount of compressive strain and the predetermined thickness of the active layer and the product of the predetermined amount of tensile strain and the predetermined total thickness of the optical waveguide layers is equal to or smaller than 0.05 nm.
The strain &Dgr;a of the (single quantum well) active layer and the strain &Dgr;w of the tensile strain optical waveguide layers can be expressed by
&Dgr;
a
=(
c
a
−c
s
)/
c
s
, and
&Dgr;
w
=(
c
w
−c
s
)/
c
s
,
where c
a
, c
w
, and c
s
are lattice constants of the active layer, the tensile strain optical waveguide layers, and the substrate, respectively.
In this case, according to the first aspect of the present invention, the active layer and the tensile strain optical waveguide layers satisfy the inequality,
|&Dgr;
a·da+&Dgr;w·dw|≦
0.05
nm,
where da and dw are respectively the total thickness of the active layer and the total thickness of the tensile strain optical waveguide layers.
Preferably, the semiconductor laser device according to the first aspect of the present invention may also have one or any possible combination of the following additional features (i) to (viii).
(i) The substrate may be made of GaAs, the active layer may be made of In
x1
Ga
1−x1
As
1−y1
P
y1
, and the optical waveguide layers may be made of In
x3
Ga
1−x3
As
1−y3
P
y3
, where 0.4≧x1>0.49y1, 0≦y1≦0.1, 0<x3<0.49y3, and 0<y3≦0.5.
(ii) The semiconductor laser device according to the first aspect of the present invention may further comprise a cladding layer formed between the substrate and the active region, wherein the substrate may be made of GaAs, the cladding layer may be made of one of In
x4
Ga
1−x4
As
1−y4
P
y4
and Al
z1
Ga
1−z1
As, where x4=(0.49±0.01)y4, 0.9≦y4≦1, and 0.2≦z1≦0.7.
(iii) The semiconductor laser device according to the first aspect of the present invention may further comprise a current confinement layer which is formed above the active region, and includes a groove allowing current injection into the active layer so as to realize an index-guided structure.
(iv) In the semiconductor laser device having the additional feature (iii), the groove may have a width of 1 to 4 micrometers, and the difference in the equivalent refractive index between the portion of the active layer which is located under the groove and the other portions of the active layer which are not located under the groove may be 1.5×10
−3
to 7×10
−3
.
In the internal stripe structure, when the equivalent refractive index at the oscillation wavelength in the portions of the active layer which are not located under the groove is denoted by na, and the equivalent refractive index at the oscillation wavelength in the portion of the active layer which is located under the groove is denoted by nb, the difference &Dgr;n in an equivalent refractive index between the portions of the active layer which are not located under the groove and the portion of the active layer which is located under the groove is expressed by &Dgr;n=nb−na.
(v) In the semiconductor laser device having the additional feature (iii), the groove may have a width greater than 4 micrometers, and the difference in the equivalent refractive index between the portion of the active layer which is located under the groove and the other portions of the active layer which are not located under the groove may be 2×10
−3
or more.
(vi) Predetermined regions of the semiconductor laser device except for a predetermined stripe region of the semiconductor laser device may be removed so that a ridge-shaped current path and an index-guided structure are realized.
(vii) In the semiconductor laser device having the additional feature (vi), the predetermined stripe region may have a width of 1 to 4 micrometers, and the difference in the equivalent refractive index between the portion of the active layer which is located under the predetermined stripe region and the other portions of the active layer which are not located under the predetermined stripe region may be 1.5×10
−3
to 7×10
−3
.
In the ridge stripe structure, when the equivalent refractive index at the oscillation wavelength in the portions of the active layer which are not located under the ridge (predetermined) stripe region is denoted by nA, and the equivalent refractive index at the oscillation wavelength in the portion of the active layer which is located under the ridge (predetermined) stripe region is denoted by nB, the difference &Dgr;N in an equivalent refractive index between the portions of the active layer which are not located under the ridge (predetermined) stripe region and the portion of the active layer which is located under the ridge (predetermined) stripe region is expressed by &Dgr;N=nB−nA.
(viii) In the semiconductor laser device having the additional feature (vi), the predetermined stripe region may have a width greater

Affiliated with

Also associated with

Rating

Semiconductor laser device in which compressive strain... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Semiconductor laser device in which compressive strain..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor laser device in which compressive strain... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3166898