Deep-well structures in mid-IR QCLs improve efficiency

Jan. 1, 2011
The active regions of quantum-cascade lasers (QCLs) are made of a superlattice of quantum wells (QWs) and barrier layers.

The active regions of quantum-cascade lasers (QCLs) are made of a superlattice of quantum wells (QWs) and barrier layers. In conventional QCLs, the barriers all have the same alloy composition. For QCLs emitting continuous-wave (CW) in the 4.5 to 5.0 μm range, this results in thermally activated electron leakage from the upper laser level to the continuum, and low maximum wall-plug-efficiency values of around 12% at room temperature—short of the theoretical 28%. Researchers at the University of Wisconsin (Madison, WI), Lehigh University (Bethlehem, PA), and the Naval Research Laboratory (Washington, DC) say that this problem can be corrected by using metal-organic chemical vapor deposition to grow QWs and barriers that vary in composition.

The researchers fabricated 4.8-μm-emitting indium-phosphide-based QCLs using the deep (highly strained) well approach, using tall barriers in and around the active region for strain compensation. In addition, the conduction-band edges of the injector and extractor regions were tapered. The characteristic temperature coefficient T0 for the threshold current density Jth was boosted from 143 K for conventional QCLs to 253 K over the 20°–90°C temperature range. The design should allow single-facet room-temperature CW wall-plug efficiencies of up to 22%. Contact Dan Botez at [email protected].

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.

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