Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1999-02-25
2001-10-02
Leung, Quyen P. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S044010
Reexamination Certificate
active
06298078
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to laser diodes and more particular to laser diodes which include composite material systems.
BACKGROUND OF THE INVENTION
A composite material system is a material system that includes materials which consist of different elements, but have the same band gap. For example, Al
x
Ga
1-x
As has the direct band gap energy of 1.42 eV to 1.98 eV for 0 <x <0.45. Ga
x
In
1-x
As
y
P
1-y
lattice matched to GaAs has the direct band gap energy of 1.42 eV to 1.89 eV and AlGaInP lattice matched to GaAs has the direct band gap energy higher than 1.89 eV. Therefore, AlGaAs/GaInAsP or AlGaAs/AlGaInP forms a composite material system.
Prior art laser diodes use only one single material system where the deposited layers which define the laser are of the same material system except that the layers include the various compositions of the elements which adjusts the energy gap profile of the layers as is well understood. Thus the familiar material systems include, for example, GaAs/AlGaAs, GaInAsP/GaInP and GaInAsP/AlGaInP.
In diodes where a single material system is used, the refractive index is a single function of the band gap of the material. That is to say, the lower the refractive index, the higher the band gap.
For the composite material system, the refractive index is not only a function of the band gap, but also is a function of material system.
FIG. 3
shows the refractive index of AlGaAs and AlGaInP, which belong to different material systems. For the same bandgap energy, the difference of refractive index between AlGaAs and AlGaInP can be as large as 0.08. This difference in refractive index is enough to achieve some laser structures with preferred characteristics.
BRIEF DESCRIPTION OF THE INVENTION
In accordance with the principles of this invention, composite material systems, such as AlGaAs/GaInAsP and AlGaAs/AlGaInP, are used to form laser diodes where the materials are chosen to decouple the refractive index profile and the band gap profile, in other word, the electrical confinement profile and the optical confinement profile will be engineered separately to provide a new flexibility in laser diode structure design.
In one embodiment, an AlGaAs/AlGaInP composite material system is used to produce a laser diode which emits a large diameter light spot at the diode facet to significantly lower the optical density in the quantum well. A similar structure with only a single material system suffers from the difficulty of the injection of carriers into the quantum well.
In another embodiment, a passive waveguide structure is produced by a composite material system in which case the passive waveguide will not cause carrier trapping at the passive waveguide region because the band gap of the wave guiding area is the same as that of the cladding layer because of the composite material system. The advantage with passive waveguide structure is the significantly lower transverse far field divergence even with the same optical confinement factor at quantum well.
REFERENCES:
patent: 4740977 (1988-04-01), Ikeda
patent: 5105236 (1992-04-01), Hayakawa
patent: 5222090 (1993-06-01), Serreze
Leung Quyen P.
Opto Power Corporation
Shapiro Herbert M.
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