Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2001-11-16
2003-07-15
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S045013, C372S050121
Reexamination Certificate
active
06594295
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a semiconductor laser and more particularly to a semiconductor laser having disordered and non-disordered quantum well active regions for increased efficiency.
DESCRIPTION OF RELATED ART
Many areas of technology require compact, low-power sources of coherent light which can be coupled into a waveguide such as an optical fiber. To that end, semiconductor lasers and light-emitting diodes are widely used. Typically, a semiconductor laser includes a quantum well active region in which light is produced. However, carriers which have been injected into the quantum well active region can diffuse into surrounding areas of the semiconductor substrate, in which case they are wasted. Such diffusion increases the threshold current required for lasing and reduces the efficiency of the laser.
U.S. Pat. No. 4,805,179 to Harder et al teaches a lateral current injection laser formed in a semiconductor heterostructure. However, Harder et al does not provide a solution to the above-noted difficulty.
U.S. patent application Ser. No. 09/833,078 to Thompson et al, filed Apr. 12, 2001, entitled “A method for locally modifying the effective bandgap energy in indium gallium arsenide phosphide (InGaAsP) quantum well structures,” and published on Mar. 14, 2002, as U.S. 2002/0030185 A1, whose entire disclosure is hereby incorporated by reference into the present disclosure, teaches a method for locally modifying the effective bandgap energy of indium gallium arsenide phosphide (InGaAsP) quantum well structures. That method allows the integration of multiple optoelectronic devices within a single structure, each comprising a quantum well structure.
In one embodiment, as shown in
FIG. 1A
, an InGaAsP multiple quantum well structure
104
formed on a substrate
102
is overlaid by an InP (indium phosphide) defect layer
106
having point defects
108
, which are donor-like phosphorus antisites or acceptor-like indium vacancies. Rapid thermal annealing (RTA) is carried out under a flowing nitrogen ambient, using a halogen lamp rapid thermal annealing system. During the rapid thermal annealing, the point defects
108
in the defect layer
106
diffuse into the active region of the quantum well structure
104
and modify its composite structure. The controlled inter-diffusion process causes a large increase in the bandgap energy of the quantum well active region, called a wavelength blue shift.
Another embodiment, as shown in
FIG. 1B
, uses two defect types, one to generate a wavelength blue shift and the other to decrease carrier lifetime. A first InP defect layer
110
contains slowly diffusing vacancy defects
114
, while a second InP defect layer
112
includes rapidly diffusing group V interstitial defects
116
. Rapid thermal annealing causes both types of defects to diffuse into the quantum well active region.
However, the prior art has yet to provide a technique to address the issue of diffusion of injected carriers.
SUMMARY OF THE INVENTION
It will be readily apparent that a need exists in the art to overcome the problem of diffusion of injected carriers. It is therefore an object of the invention to provide a semiconductor laser which includes an element for blocking such diffusion.
To achieve the above and other objects, the present invention is directed to the realization of a disordered region of quantum well active region surrounding a region of non-disordered quantum well region in order to prevent diffusion of injected carriers from the non-disordered, light emitting quantum well active region. The method provides blocking of current in a vertical-cavity surface-emitting laser, lowering its threshold current and raising its efficiency. The method provides the formation of a lateral heterobarrier in lateral-current-injected edge-emitting lasers, lowering threshold and raising efficiency. The disordered region can be produced by any of the techniques of the above-cited Thompson et al patent application or by any other suitable intermixing or other disordering techniques.
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Blank Rome LLP
Fox-Tek, Inc.
Ip Paul
Vy Hung
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