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Low-strain laser structures with group III nitride active layers
| Details |
Inventors: Edmond, John Adam; Bulman, Gary E.; Kong, Hua-Shuang;
Assignee: Cree Research, Inc. (Durham, NC)
Primary Examiner: Davie; James W.
Assistant Examiner:
Attorney, Agent or Firm: Summa; Philip
A Group III nitride laser structure is disclosed with an active layer that includes at least one layer of a Group III nitride or an alloy of silicon carbide with a Group III nitride, a silicon carbide substrate, and a buffer layer between the active layer and the silicon carbide substrate. The buffer layer is selected from the group consisting of gallium nitride, aluminum nitride, indium nitride, ternary Group III nitrides having the formula A.sub.x B.sub.1-x N, where A and B are Group III elements and where x is zero, one, or a fraction between zero and one, and alloys of silicon carbide with such ternary Group III nitrides. In preferred embodiments, the laser structure includes a strain-minimizing contact layer above the active layer that has a lattice constant substantially the same as the buffer layer. |
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DETAILED DESCRIPTION The present invention is a laser diode structure which is grown on a lattice mismatched silicon carbide substrate.
As used herein, the term "lattice mismatched" means that one or more layers of the laser structure have crystal lattice parameters different from the crystal lattice parameters of silicon carbide.
The structure of the invention balances the individual strains of each layer to produce a structure with minimal net strain.
FIG.
1 illustrates one embodiment of a separate-confinement heterostructure (SCH) indium gallium nitride laser broadly designated at 10 according to the present invention.
The laser structure 10 includes an indium gallium nitride active layer 11.
Upper and lower waveguide layers 12 and 13 respectively bracket the active layer and provide part of the waveguiding required for a laser of this type.
The waveguide layers 12 and 13 are preferably formed of aluminum gallium nitride.
Upper and lower cladding layers 14 and 15 respectively are on the respective upper and lower waveguide layers 12 and 13 and are also formed of aluminum gallium nitride, thus completing the optical waveguide structure.
In preferred embodiments, a strain minimizing layer 16 which is formed of aluminum gallium nitride and also serves as a top contact layer is on the upper cladding layer 14.
The structure also includes a buffer layer 17 and an appropriate substrate 20, preferably formed of silicon carbide.
Optionally a very thin layer of gallium nitride (not shown) can be added to the strain minimizing layer 16 and can serve as the top contact layer for the overall structure.
As known to those familiar with semiconductor laser structures, in order to enhance the laser capabilities of the device, particularly a separate confinement heterostructure such as the present invention, the active layer should desirably have a lower bandgap than the adjacent waveguide and cladding layers, and a higher refractive index than the adjacent waveguide and cladding layers.
Such a structure gives two benefits important for laser capability
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Quantum Computing 
