Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2001-03-13
2004-01-06
Leung, Quyen (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S046012
Reexamination Certificate
active
06674779
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a buried heterostructure type semiconductor laser device and a method for producing the same.
2. Description of the Related Art
A conventional buried heterostructure type semiconductor laser device (hereinafter, referred to as “BHLD”) includes a light emission region, which is formed by an active layer stripe, and a buried layer for burying the active layer stripe, and separation grooves. A separation groove is provided on each side of the light emission region for electrical isolation in order to prevent capacitance of peripheral elements from affecting the light emission region. Outside the separation grooves, no active layer stripe is provided, and only the buried layer is formed on a substrate.
A method for producing the conventional BHLD will be briefly described below. First, semiconductor layers for forming an active layer stripe are crystal-grown on the substrate, and a dielectric film is formed thereon in a stripe shape. Then, the semiconductor layers are etched using the dielectric film as a mask to form the active layer stripe. Thereafter, the dielectric film is removed, and the active layer stripe is buried by using a liquid growth method. In this process, the buried layer causes difficulty in locating the active layer stripe with accuracy. Therefore, in order to perform subsequent production steps, a portion of the buried layer on the substrate is removed by etching to expose the active layer stripe. After the active layer stripe has been located, an alignment key is formed on the active layer stripe for use in the steps of forming a p-type electrode, forming separation grooves, gold-plating, forming scribe lanes, mounting, etc.
In this conventional method for producing the BHLD, for example, the alignment key used in each of the above-described steps may cause at least two deviations, i.e.: an alignment key position formed on the exposed active layer stripe may deviate from a predetermined position; and a pattern position which is formed in each step using the alignment key as a reference line may deviate from a predetermined position.
In the case of flip chip-mounting of a semiconductor laser device, a light emission point of the semiconductor laser device is aligned with an optical axis of an optical fiber combined with a chip carrier by combining an alignment key for mounting, which has been formed on a surface of the semiconductor laser device, with an alignment key formed on the chip carrier. However, as described above, since the alignment key for mounting formed on the surface of the semiconductor laser device may cause at least two deviations, in principle, alignment of the optical fiber with the light emission point after the flip chip-mounting is affected by such deviations. Furthermore, when a plurality of active layer stripes are provided, a deviation &thgr; is caused between an alignment key
602
and an active layer stripe
601
as illustrated in
FIG. 7
, and accordingly, alignment accuracy is further degraded.
In recent years, development has been eagerly carried out for the purpose of reducing production costs of a module including a semiconductor laser device mounted thereon. In order to realize such a module, simplified production/assembly steps achieving high light-coupling efficiency are required. Conventionally, to this end, the semiconductor laser device is flip chip-mounted on a module by passive alignment in which the semiconductor laser device is aligned with an optical fiber of the module using only their alignment keys.
However, in such a conventional method, the positional accuracy of the alignment key used for mounting with respect to the light emission point is poor. Therefore, even if the alignment key alignment for mounting with an alignment key on the chip carrier is perfectly performed, the light emission point is not necessarily accurately placed on the optical axis of the optical fiber. That is, the optical axis of the optical fiber is misaligned with that of the semiconductor laser device. Thus, it is difficult to achieve high light-coupling efficiency. Moreover, when removing a portion of the buried layer on the active layer stripe by etching, organic contamination may occur on a surface of the active layer stripe. Such contamination reduces production yield.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a semiconductor laser device including a substrate, a light emission region provided on the substrate, and an alignment stripe provided on the substrate so as to be adjacent to the light emission region. The light emission region includes a first active layer stripe having a layered structure including a first waveguide layer, an active layer, and a second waveguide layer, a first buried layer formed so as to cover side faces of the active layer stripe, a second buried layer formed on the first buried layer, and a third buried layer formed on the second buried layer and the active layer stripe. The alignment stripe includes a second active layer stripe having a layered structure including the first waveguide layer, the active layer, and the second waveguide layer, and a selective growth mask formed on the second active layer stripe and formed of a material on which the first buried layer, the second buried layer and the third buried layer are incapable of growing.
According to one embodiment of the invention, at least one of faces of the third buried layer has a (
111
) face, a neighborhood face of the (
111
) face, a (
001
) face, and a neighborhood face of the (
001
) face which is present in the vicinity of both sides of selective growth mask in the alignment stripe.
According to another aspect of the invention, there is provided a semiconductor laser device including a substrate, a light emission region provided on the substrate, and an alignment region provided on the substrate so as to be adjacent to the light emission region. The light emission region includes an active layer stripe having a layered structure including a first waveguide layer, an active layer, and a second waveguide layer, a first buried layer formed so as to cover side faces of the active layer stripe, a second buried layer formed on the first buried layer, and a third buried layer formed on the second buried layer and the active layer stripe. The alignment region includes an active layer region having a layered structure including the first waveguide layer, the active layer, and the second waveguide layer, and a selective growth mask formed on the active layer region and formed of a material on which the first buried layer, the second buried layer and the third buried layer are incapable of growing.
According to one embodiment of the invention, at least one of faces of the third buried layer has a (
111
) face, a neighborhood face of the (
111
) face, a (
001
) face, and a neighborhood face of the (
001
) face which is present in the vicinity of the edges of selective growth mask in the alignment region.
According to another embodiment of the invention, the active layer stripe is formed so as to extend in a [
011
] direction, and the selective growth mask has at least one of the sides which includes a side which extends in a direction substantially parallel to the active layer stripe, a side which extends in a direction substantially perpendicular to the active layer stripe, and a side which extends in a direction crossing the active layer stripe at an angle of approximately 45 degrees.
According to still another aspect of the invention, there is provided a method for producing a semiconductor laser device including the steps of: growing a first semiconductor film which includes a first waveguide layer, an active layer, and a second waveguide layer on a substrate; forming on the first semiconductor film a selective growth film of a material on which second and third semiconductor films are incapable of growing; processing the selective growth film into two or more stripes; etching the first semiconductor film using
Leung Quyen
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
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