Coherent light generators – Particular active media – Plural active media or active media having plural dopants
Reexamination Certificate
2001-04-17
2004-08-17
Wong, Don (Department: 2828)
Coherent light generators
Particular active media
Plural active media or active media having plural dopants
C372S023000, C372S043010, C372S050121
Reexamination Certificate
active
06778578
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface emitting laser which can emit laser beams in a direction perpendicular to a substrate, and more particularly, to a multi-wavelength surface emitting laser in which different types of surface emitting lasers emitting laser beams of different wavelengths are configured on the same substrate, and a method for manufacturing the same.
The present invention is based upon Korean Patent Application No. 00-41737, filed Jul. 20, 2000, which is incorporated herein by reference.
2. Description of the Related Art
In general, a surface emitting laser emits a laser beam in a direction normal to the surfaces of deposited semiconductor material layers, which is different from an edge emitting laser. Also, since the surface emitting laser emits a circular beam, unlike the edge emitting laser, an optical system is not needed to correct the cross-sectional shape of an emitted beam. Also, the surface emitting laser can be manufactured in a compact size, and a plurality of surface emitting lasers can be integrated on a single semiconductor substrate, thus enabling a two-dimensional arrangement. As a result, the surface emitting laser has a wide range of optical application fields such as electronic calculators, audio-visual apparatuses, laser printers, laser scanners, medical equipment, and communications apparatuses.
Referring to
FIG. 1
, a conventional surface emitting laser includes a substrate
10
, a lower reflector
12
, an active layer
14
and an upper reflector
16
, which are deposited in order on the substrate
10
.
The substrate
10
is formed of a semiconductor material such as gallium arsenide (GaAs) or indium phosphorous (InP) including a predetermined impurity, for example, an n-type impurity. The lower and upper reflectors
12
and
16
are distributed Bragg reflectors (DBRs) formed by alternately depositing pairs of semiconductor layers having different refractive indices. That is, the lower reflector
12
is formed on the substrate
10
and is formed of the same type of impurity as that of the substrate
10
, for example, n-type Al
x
Ga
1−x
As and AlAs are alternately deposited. The upper reflector
16
is formed of the same semiconductor material as that of the lower reflector
12
and includes a semiconductor material with the opposite type of charge carriers to that of the lower reflector
12
. For example, p-type Al
x
Ga
1−x
As and AlAs are alternately deposited. The active layer
14
has a single or multi-quantum well structure or a super lattice structure as an area for generating a light beam when energy transition is generated due to recombination of electrons and holes. An upper electrode
23
having a window
23
a
is provided on the upper surface of the upper reflector
16
and a lower electrode
21
is provided on the bottom surface of the substrate
10
.
Also, to improve the output of light L emitted through the window
23
a
, a high resistance portion
18
is formed by injecting protons into the upper reflector
16
except for a zone under the window
23
a
. Accordingly, the high resistance portion
18
limits the flow of holes so that laser oscillation is generated only in the zone under the window
23
a.
In the surface emitting laser having the above structure, the wavelength of a laser beam is determined by the materials of the upper and lower reflectors
16
and
12
, the structure of deposition, and the structure of the active layer
14
. Thus, when the surface emitting laser is manufactured in a single process with a single substrate, it is difficult to produce the surface emitting laser in an array form so as to emit laser beams of different wavelengths.
Also, in application fields of a semiconductor laser capable of emitting laser beams having different wavelengths, such as compatible optical pickups for DVD players which can also read CDs, and communications equipment in which the wavelengths for transmitting and receiving are different, a structure in which surface emitting lasers, which are manufactured to correspond to desired wavelengths, and are attached to an additional substrate, has been suggested. However, the above structure has a problem in that it generates a large optical alignment error due to an error in the combination of the respective surface emitting lasers.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a multi-wavelength surface emitting laser, and method of manufacturing the same, formed directly on a single substrate so that optical alignment errors are reduced and manufacturing is made easy.
Accordingly, to achieve the above object, there is provided a multi-wavelength surface emitting laser for emitting light having a first wavelength and light having a second wavelength. The multi-wavelength laser comprises a substrate, a first surface emitting laser for emitting light having a first wavelength, which is directly formed on a portion of an upper surface of the substrate. The first surface emitting laser includes a first lower reflector formed by alternately depositing two semiconductor material layers with the same type of impurities, but different refractive indices. A first active layer is provided. A first upper reflector is formed by depositing two semiconductor material layers having different refractive indices and the opposite type of impurities to that of the first lower reflector. Also provided is a second surface emitting laser for emitting light having a second wavelength, which is directly formed on a portion of an upper surface of the substrate neighboring the first surface emitting laser. The second surface emitting laser includes a second lower reflector formed by alternately depositing two semiconductor material layers having different refractive indices and the same type of impurities. A second active layer is provided. A second upper reflector is formed by depositing two semiconductor material layers having different refractive indices and the opposite type of impurities to that of the second lower reflector. A lower electrode layer is formed on one surface of the substrate, and first and second upper electrodes are formed on the first and second upper reflectors, respectively, for applying electric power.
Also, to achieve another aspect of the above object, there is provided a method for manufacturing a multi-wavelength surface emitting laser comprising the steps of forming a first surface emitting laser for emitting light having a first wavelength by sequentially depositing on a prepared substrate a first lower reflector formed by alternately depositing two semiconductor material layers with the same type of impurities, but different refractive indices, a first active layer, and a first upper reflector formed by alternately depositing two semiconductor material layers having the opposite type of impurities to that of the first lower reflector and different refractive indices. The method also includes partially removing the first upper reflector, the first active layer, and the first lower reflection layer by etching, and forming a protection film on the outer surface of the first surface emitting laser. A second surface emitting laser for emitting light having a second wavelength is formed by sequentially depositing on the substrate and the protection film, a second lower reflector formed by alternately depositing two semiconductor material layers having the same type of impurities, but different refractive indices, a second active layer, and a second upper reflector formed by alternately depositing two semiconductor material layers having the opposite type of impurities to that of the second lower reflector and different refractive indices. The method further includes removing the second lower reflector, the second active layer, and the second upper reflection layer formed on the protection film by etching, and removing the protection film and forming first and second upper electrodes on upper surfaces of the first and second upper reflection l
Chung Min-hyung
Lee Eun-kyung
Rodriguez Armando
Samsung Electronics Co,. Ltd.
Sughrue & Mion, PLLC
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