Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-01-04
2004-10-12
Wong, Don (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S043010, C372S044010, C372S045013, C372S046012, C372S049010, C372S049010, C372S049010, C372S050121, C372S099000
Reexamination Certificate
active
06804279
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface emitting laser apparatus usable as a light source in the fields of large-capacity optical communication, optical interconnection, optical information processing, parallel optical recording, and the like, its fabrication method, and its driving method.
2. Description of the Related Background Art
The arrangement of arrayed laser devices for parallel transmission of optical information has been recently studied to achieve large-capacity optical communication and optical interconnection. Also, a structure utilizing plural recording light sources has been studied to further advance the printing speed of laser beam printers. Particular interest has been shown in the use of vertical cavity surface emitting lasers (VCSELs) as light emitting devices suitable for the array arrangement of those light sources.
Recently, the following surface emitting laser has been energetically researched and developed to improve the performance of the laser. In such a surface emitting laser, a semiconductor layer containing aluminum (Al) is provided near the active layer, and this Al-containing layer is selectively oxidized to form a current confinement structure. An example of such a laser is disclosed in “Appl. Phys. Lett. 1995, 66, (25), pp.3413-3415”.
FIG. 1
is a schematic diagram of this structure, which includes an n-type semiconductor multi-layer mirror
1001
, an active layer
1003
, a semiconductor layer
1005
containing Al, a p-type semiconductor multi-layer mirror
1007
, and a p-side electrode with an opening.
In the above structure of
FIG. 1
, the Al-containing semiconductor layer
1005
is selectively oxidized, and its peripheral portion is altered so as to form an insulating layer
1006
that is chiefly formed of Al
x
O
y
to form the current confinement structure. Due to the current confinement structure, current can be effectively and efficiently injected into the active layer
1003
, and hence, low threshold current and single-mode oscillation can be achieved in this type of surface emitting laser.
The resistance of that laser is, however, high since the resistance of the p-type semiconductor multi-layer mirror
1007
is large and the current passing region in the current confinement structure is small in area (about several micrometers×several micrometers, or twenty (20) square micrometers). As a result, the laser inevitably has disadvantages that its operation voltage needed to obtain a desired light power increases and that its characteristics are lowered due to a great amount of heat generated in the device.
Several methods have been researched and developed to reduce the resistance of the device. One of those methods is a method of injecting a current through a path escaping the semiconductor multi-layer mirror, which is disclosed in “Electron. Lett., 1995, 31, (11), pp.886-888”.
FIG. 2
is a schematic diagram of this structure, which includes an n-type substrate
2001
, ann-type semiconductor multi-layer mirror
2003
, an active layer
2005
, a semiconductor layer
2007
containing Al, a p-type contact layer
2009
, and an undoped semiconductor multi-layer mirror
2011
. In this example, the Al-containing semiconductor layer
2007
is selectively oxidized, and its peripheral portion is altered so as to form an insulating layer
2008
chiefly formed of Al
x
O
y
to form the current confinement structure. Further, a p-side electrode
2013
is deposited on the p-type contact layer
2009
, and an n-side electrode
2015
is deposited on the bottom surface of the n-type substrate
2013
. The p-side electrode
2013
is formed on the contact layer
2009
in this structure. The p-type semiconductor multi-layer mirror
2011
having a high resistance is not present in a current path between the n-side electrode
2015
and the p-side electrode
2013
.
In another method for reducing the resistance of the device, a p-type semiconductor multi-layer mirror, a semiconductor layer containing Al, an active layer, and an n-type semiconductor multi-layer mirror are layered on a p-type substrate, etching is conducted from the side of the n-type semiconductor multi-layer mirror to expose the side of the Al-containing semiconductor layer and form a protruded pole, and the Al-containing semiconductor layer is oxidized toward its central portion to construct the current confinement structure. In this structure, the resistance can be reduced since the area of a current flow through the p-type semiconductor multi-layer mirror can be enlarged.
In the above-mentioned conventional surface emitting lasers, however, an increase in the resistance due to a small area of the current flow through the current confinement structure is not considered, though the resistance can be decreased by escaping the p-type semiconductor multi-layer mirror as a current path.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a surface emitting laser apparatus in which its operation voltage and consumption electric power can be reduced due to its low resistance, a common-anode construction is possible, a high-speed modulation can be achieved, and a construction capable of wavelength division multiplexing can be readily attained, its fabrication method, and its driving method.
The present invention is generally directed to a surface emitting laser apparatus having at least a light-emitting device, which includes a substrate, a cavity structure of the light-emitting device including a first n-type semiconductor multi-layer mirror, a first active layer, a p-type spacer layer, a second active layer, and a second n-type semiconductor multi-layer mirror formed on the substrate. First and second current confinement structures are formed in the vicinity of the first and second active layers, respectively, a p-side electrode is electrically connected to the p-type spacer layer, a first n-side electrode is electrically connected to the first n-type semiconductor multi-layer mirror, and a second n-side electrode is electrically connected to the second n-type semiconductor multi-layer mirror.
In the above structure, since no p-type semiconductor multi-layer mirror is needed, the resistance of the laser apparatus can be reduced. Accordingly, the operation voltage and consumption power can be reduced. Further, where a plurality of light-emitting devices are arranged in the laser apparatus, a structure of the common-anode type can be constructed by putting the p-side electrodes of the respective devices on an equipotential level.
Where first and second current confinement portions are formed in the vicinity of the first and second active layers, respectively, resistors of the current confinement portions having a high resistance are connected in a parallel form. Therefore, the resistance of the laser apparatus can be further decreased.
The current confinement structure near the active layer can be established by forming an ion-injected region in a peripheral portion of the device. This structure can preferably be formed as follows. A first p-type current confinement layer including a first Al-containing semiconductor layer is formed between the first active layer and the p-type spacer layer, a second p-type current confinement layer including a second Al-containing semiconductor layer is formed between the second active layer and the p-type spacer layer, and the first and second Al-containing semiconductor layers are selectively oxidized, respectively. The current structure can be flexibly established with good controllability by this method.
Specifically, the substrate can be an n-type semiconductor substrate, and the first n-type semiconductor multi-layer mirror can be electrically connected to the first n-side electrode through the substrate. In such a structure, where a plurality of light-emitting devices are arranged, the first n-side electrodes and the p-side electrodes of the devices can be readily connected electrically, respectively.
The substrate can also be a semi-insulating-type semiconductor substrat
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Flores-Ruiz Delma R.
Wong Don
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