Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-08-27
2001-05-29
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S046012
Reexamination Certificate
active
06240115
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semiconductor lasers, and more particularly, to edge emitting lasers based on GaN or other III-V material systems.
Background of the Invention
III-V materials such as GaN are particularly useful in constructing lasers and LEDs in the blue and green wavelengths. These layers are typically deposited on a sapphire substrate. Facets in the GaN layers provide the mirrors for the ends of the laser cavity. These facets must be parallel to one another and have smooth surfaces.
There are two prior art techniques for creating the facets. The first technique involves cleaving the GaN layers and the underlying sapphire substrate. The lattice constants of GaN and sapphire differ by 13%. In addition, the sapphire substrate is very hard. As a result, the cleavage plane is not always precisely perpendicular to the active layer plane of the laser. This leads to facets that are not perfectly parallel to one another. Hence, additional processing is needed in the form of time consuming polishing operations to correct for the cleavage errors. In addition, prior to cleavage, the sapphire substrate must be thinned in the region in which the cleavage is to take place. This thinning operation also increases the cost of the processing.
The second prior art method involves masking the GaN layers and reactive ion etching the stack to form the mirror facets. Unfortunately, the masks often have small imperfections that result in striations on the facet surface. These striations cause the mirrors to be optically lossy.
Broadly, it is the object of the present invention to provide an improved GaN laser.
It is a further object of the present invention to provide a laser that does not require the facets to be generated by cleavage of the underlying substrate and GaN layers.
It is a still further object of the present invention to provide a laser that does not require the mirror facets to be etched or polished.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention is a laser having a first layer of a III-V semiconducting material of a first semiconductor type on which a mask having an opening therein is deposited. A second layer of a III-V semiconducting material of the first semiconductor type is grown from the portion of the first layer underlying the opening in the mask and extends over the mask. A first cladding layer of a III-V semiconducting material of the first semiconductor type is grown over the second layer so as to cover the second layer. The active layer that generates light upon the recombination of holes and electrons therein is grown over the first cladding layer. A second cladding layer of a III-V semiconducting material is grown over the active layer, the second cladding layer includes a III-V semiconducting material of the opposite semiconductor type from the first layer. A third layer of a III-V semiconducting material is grown over the second cladding layer. The third layer of a III-V semiconducting material includes a III-V semiconducting material of the opposite semiconductor type, and the third layer of a III-V semiconducting material includes a crystalline layer covering the cladding layer. Two facets of the crystalline layer form the mirrors at opposite ends of an optical cavity that includes the active layer. The preferred III-V semiconducting material is GaN. The mask is constructed from a material on which the III-V semiconducting materials will not nucleate.
REFERENCES:
patent: 5880485 (1999-03-01), Marx et al.
patent: 0 551 721 (1993-07-01), None
patent: 0 874 405 (1998-10-01), None
Ando, Seigo et al., “Novel Hexagonal-Facet GaAs/AIGaAs Laser Grown by Selective Area Metalorganic Chemical Vapor Deposition”, Japanese Journal of Applied Physics, vol. 32, Sep. 15, 1993, No. 9b, Part 2, Tokyo, Japan, pp. 1293-1296.
Ando, Seigo et al., “Selective Area Metalorganic Chemical Vapor Deposition Growth for Hexagonal-Facet Lasers”, Journal of Crystal Growth, vol. 145, Dec. 11, 1994, Nos. 1/4, Amsterdam, NL, pp. 302-307.
Kato, Yoshiki et al., “Selective Growth of Wurtzite GaN and AIxGa1-xN on GaN/Sapphire Substrates by Metalorganic Vapor Phase Epitaxy”, Journal of Crystal Growth, Dec. 11, 1994, Nos. 3/4, Amsterdam, NL, pp. 133-140.
Chen Yong
Wang Shih-Yuan
Agilent Technologie,s Inc.
Arroyo Teresa M.
Leung Quyen P.
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