Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-05-14
2004-10-26
Harvey, Minsun Oh (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C438S016000, C438S040000, C438S745000, C257SE21221
Reexamination Certificate
active
06810059
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser and a method of manufacturing the same.
2. Related Background Art
Among conventional methods for manufacturing semiconductor lasers, the present invention relates to methods for manufacturing semiconductor lasers made on an In-P substrate and used for optical communication, more specifically, narrow radiation angle lasers that emit a laser beam with a narrow radiation angle. The narrow radiation angle laser is classified into a type having an active layer and a waveguide layer, which make up the laser, with film thicknesses varying along the cavity direction for narrowing a radiation angle, and a type having a taper shaped active layer stripe with the width varying in the cavity direction to have a taper shape for narrowing a radiation angle, without varying the film thicknesses of an active layer and a waveguide layer. In the latter type, the taper shaped active layer stripe is formed by etching laminated films including the active layer formed on a substrate through a taper shaped dielectric mask provided on the laminated films.
The following describes a method of manufacturing the above-mentioned narrow radiation angle laser of the taper shaped active layer type, with reference to FIG.
6
.
FIG. 6
is a front view of the semiconductor laser at the output end side of the semiconductor laser. Firstly, as shown in
FIG. 6A
, a n-InP layer
601
, an active layer
602
, and a p-InP layer
603
are formed on a n-InP substrate
600
in this order. On these layers, a SiO
2
film
604
is deposited, as shown in FIG.
6
B. Next, the SiO
2
film
604
is patterned in a stripe shape by ordinary photolithography and reactive ion etching methods, resulting in a SiO
2
mask
605
as shown in FIG.
6
C. The SiO
2
mask
605
is formed into a taper shape, so that the width of the mask is made narrower gradually, like a sector, from the rear end of the semiconductor laser toward the output end. The difference between the widths of the rear end and the output end of the SiO
2
mask
605
approximately is 1 &mgr;m. The cavity length is in a range between approximately 300 &mgr;m and 800 &mgr;m.
Next, the n-InP layer
601
, the active layer
602
, and the p-InP layer
603
are removed by a mixed solution including acetic acid, hydrochloric acid, and a hydrogen peroxide solution using the SiO
2
mask
605
(See FIG.
6
D). In this process, these layers are side-etched from the side edge portions of the SiO
2
mask
605
, so that the width of the active layer
602
becomes smaller than that of the SiO
2
mask
605
. This etching process is completed when the width of the active layer
602
becomes a predetermined value. A target value of the width of the active layer
602
is in a range between 0.5 &mgr;m and 1.0 &mgr;m. After that, in order to make the height of the upper surface of the n-InP layer
601
, which is exposed as a result of the etching process, from the surface of the n-InP substrate
600
a predetermined value, etching is conducted by a mixture solution including hydrochloric acid and phosphoric acid so as not to change the width of the active layer
602
. As a result of these wet-etching processes, a taper shaped active layer stripe is formed.
Next, as shown in
FIG. 6E
, a p-InP burying layer
606
, a n-InP burying layer
607
, a p-InP burying layer
608
, and a contact layer
609
are grown in this order by the vapor growth method. Finally, as shown in
FIG. 6F
, isolation grooves
610
and
611
and a p-type electrode
612
are formed on the surface and a n-type electrode
613
is formed on the rear surface so as to complete the laser.
However, the above conventional manufacturing method has the following problems.
In the wet-etching process for forming a taper shaped active layer stripe, where the width of the active layer
602
is patterned into a sub-micron size by carrying out side-etching from the side edges of the SiO
2
mask
605
, the end point where the etching is to be finished (hereafter simply called “etching end point”) is detected by measuring the width of the active layer
602
with an optical microscope so as to confirm that the width is within a predetermined dimension. In this case, it is difficult to measure the width of the active layer
602
with the optical microscope accurately. In addition, although the width of the taper shaped active layer stripe varies in the cavity direction, this stripe might be recognized as a stripe having a uniform width on the wafer, because the difference between the widths of the rear end and the output end thereof approximately is only 1 &mgr;m. Therefore, it is considerably difficult to identify the output end portion of the stripe by a visual inspection.
Due to this difficulty, it might take considerable time to identify the output end portion, which deteriorates a production efficiency, or an error in identifying the output end position might occur. Furthermore, due to the difficulty in measuring the width of the active layer of a sub-micron size, improper measurement often occurs, which causes poor qualities of patterning and laser characteristics.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a semiconductor laser and a method of manufacturing the same, by which the etching end point can be detected easily and thus improper measurement can be prevented when patterning the width of an active layer stripe at the output end into a sub-micron size.
The semiconductor laser according to present invention has a basic construction composed of an active layer stripe including a first semiconductor layer, an active layer, and a second semiconductor layer that are laminated in that order on a substrate and are formed into a stripe-shape; a burying layer in which the active layer stripe is buried; and a contact layer formed on the burying layer.
To cope with the above-stated problems, the semiconductor laser having the basic construction of the present invention further includes a monitor stripe that is formed in parallel to the active layer stripe and is composed of the first semiconductor layer only at an output end of the laser, the monitor stripe is buried in the burying layer on which the contact layer is formed, and the active layer stripe and the monitor stripe are isolated electrically by an isolation groove.
With this construction, the etching end point can be detected easily by using a timing when the active layer in the monitor stripe at the output end disappears as a criterion. As a result, the width of the active layer stripe can be formed with high accuracy.
In the basic construction, it is preferable that the monitor stripe changes in width in a cavity direction so as to have a narrow width region at the output end and a wide width region provided at least at one portion of the stripe other than at the output end, and the wide width region of the monitor stripe is composed of the first semiconductor layer and the second semiconductor layer. With this construction, it becomes easy to identify the output end in the monitor stripe.
In the above construction, preferably, the first semiconductor layer of the monitor stripe in the narrow width region is thicker at a center portion in a width direction than the other portions.
In addition, in the above basic construction, it is preferable that the monitor stripe is composed of the first semiconductor layer, and the first semiconductor layer in the monitor stripe is thicker at a center portion in a width direction than the other portions.
The method of manufacturing a semiconductor laser according to the present invention includes: forming a lamination film for stripe by depositing a first semiconductor layer, an active layer including a semiconductor multilayer, and a second semiconductor layer in this order on a substrate; forming a mask by depositing a dielectric film on the lamination film for stripe and shaping the dielectric film into a predetermined shape so as to form a first dielectric mas
Harvey Minsun Oh
Jackson Cornelius H.
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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