Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-09-12
2004-08-10
Wong, Don (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S043010
Reexamination Certificate
active
06775311
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device, more specifically a semiconductor laser device capable of realizing high power and high reliability, and to an optical disk recording and reproducing apparatus using the same.
In recent years, with demands for faster and larger-capacity semiconductor laser devices applied to optical communications devices and optical recording apparatuses, research and development have been promoted for improving various properties of the semiconductor laser devices.
Among the semiconductor laser devices, those having an oscillation wavelength of 780 nm band for use in optical disk reproducing apparatuses and optical disk recording and reproducing apparatuses such as CD and CD-R/RW are conventionally made of AlGaAs based materials and typically have ridge stripe shape.
Generally in such semiconductor laser device, in superimposing a current constriction layer, a portion in the vicinity of a lateral face of a ridge stripe is positioned below an overhang of a contact layer, which prevents material gas from sufficiently reaching the vicinity of the lateral face of the ridge stripe. Further, due to plane orientation of the lateral face of the ridge stripe, there is an area whose crystal growth rate is slow. As a result, the portion in the vicinity of the lateral face of the ridge stripe is not fully filled up and a hollow portion is generated therein.
The above has been disclosed in Japanese Patent Laid-Open Publication HEI No. 3-64980, in which a means for eliminating the hollow portion has been proposed to solve a problem that the hollow portion has a low refractive index and therefore a single transverse mode oscillation is difficult to produce, and the like. A schematic view thereof is shown in
FIG. 8
, with reference to which outlined description will be made hereinbelow.
The semiconductor laser device is so structured that on top of a GaAs substrate
501
, there are laminated in sequence an AlGaAs first cladding layer
502
, an AlGaAs active layer
503
, an AlGaAs second cladding layer
504
, and a GaAs contact layer
505
. Further, there is spattered an SiO
2
film (unshown), which is formed into a stripe shape by a usual photo step. Then, with the SiO
2
film as a mask, the contact layer
505
and the second cladding layer
504
are etched by chemical etching to make the second cladding layer
504
into ridge stripe shape.
With the SiO
2
film as a mask for selective growth, there is formed a GaAs current constriction layer
506
on the both sides of the ridge stripe-shaped second cladding layer
504
. After that, the SiO
2
film is removed and the other contact layer
505
is laminated on the entire surface of the already formed contact layer
505
and the GaAs current constriction layer
506
so that the laminated contact layer
505
is integrated with them.
In the above conventional example, the hollow portion is eliminated to stabilize transverse mode oscillation. However, an inventor of the present invention actually manufactured as an experiment an AlGaAs based high-output semiconductor laser device based on the conventional technique, as a result of which it was confirmed that a maximum optical output thereof is approx. 180 mW, and end face destruction occurs at this optical output level. This is because the presence of active Al tends to generate Al oxide on a laser end face, which prevents implementation of higher output, higher reliability and longer life.
Also in the above conventional example, the contact layer
505
and the second cladding layer
504
are etched into ridge stripe shape with an etchant modified to prevent the stripe-shaped contact layer
505
from protruding from the ridge-strip-shaped second cladding layer
504
in lateral direction like an overhang. This method, however, suffers difficulty in management of etchant and etching time.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a high-output semiconductor laser device using a GaAs substrate, more specifically a 780 nm-band high-output semiconductor laser device for use in CD-R/RW and the like capable of implementing a single transverse mode oscillation and also implementing high reliability and long life in high-output driving state, as well as to provide an optical disk recording and reproducing apparatus with use of the semiconductor laser device.
In order to accomplish the above object, there is provided a semiconductor laser device comprising in sequence on a GaAs substrate: a first cladding layer having a first conduction type; a quantum well active layer; a second cladding layer having a second conduction type; and a ridge stripe-shaped third cladding layer having a same conduction type as the second cladding layer, as well as a current blocking layer having a first conduction type located on both sides of the third cladding layer,
the quantum well active layer being structured from III-V group compound semiconductor containing at least P as V group element,
the first cladding layer, the second cladding layer, the third cladding layer, and the current blocking layer being structured from III-V group compound semiconductor containing only As as V group element, and wherein
a hollow portion is provided inside the current blocking layer in the vicinity of and approximately parallel to the ridge stripe-shaped third cladding layer.
According to the above configuration, there is implemented a 780 nm-band high-output semiconductor laser device having stabilized transverse mode oscillation, high reliability in high output operation and long life. This is because in the quantum well active layer having an oscillation wavelength of 780 nm band, III-V group compound semiconductor containing P, e.g. InGaAsP based compound semiconductor, has a refractive index smaller than that of AlGaAs based compound semiconductor. More particularly, use of, for example, InGaAsP based materials in the quantum well active layer decreases difference in refractive index between the hollow portion and the quantum well active layer compared to the case of using an active layer made of conventional AlGaAs based materials, which generates acceptable difference of refractive index sufficient for stabilizing a single transverse mode oscillation.
Also in the semiconductor laser device, the hollow portion formed inside the current blocking layer saves an effort at preventing an overhang formed over the ridge stripe-shaped third cladding layer, which facilitates management of etchant and etching time for forming the ridge stripe-shaped third cladding layer.
In one embodiment, right above the ridge stripe-shaped third cladding layer, there is laminated a cap/intermediate layer having a width larger than a width of a lowermost portion of the ridge stripe-shaped third cladding layer.
According to the above embodiment, the hollow portion is located in more suitable position for stabilizing transverse mode oscillation in high-output driving state.
In one embodiment, the ridge stripe-shaped third cladding layer has a reverse mesa shape in cross section.
The reverse mesa shape in cross section herein refers to the shape of a cross section vertical to extending direction of the ridge stripe-shaped third cladding layer, in which the width of the ridge stripe-shaped third cladding layer is narrowed toward the GaAs substrate, or narrowed in the middle.
According to the above embodiment, the ridge stripe-shaped third cladding layer has a reverse mesa shape in cross section, so that the hollow portion is formed in an optimum position. This may provide a semiconductor laser device implementing stabilized transverse mode oscillation in high-output driving state as well as having high reliability and long life.
In one embodiment, a width of the semiconductor layer right above the ridge stripe-shaped third cladding layer is larger than a width of a lowermost portion of the ridge stripe-shaped third cladding layer in a range from 0.48 &mgr;m to 1.08 &mgr;m in one side.
According to the above embodiment, a width of the semicond
Morrison & Foerster / LLP
Nguyen Phillip
Sharp Kabushiki Kaisha
Wong Don
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