Compact laser sources emitting in the mid-infrared wavelength range (i.e., 3-8 m) are currently of great interest for applications such as stand-off spectroscopic sensing of toxic-chemical agents, free-space communications, and LIDAR. However, the lack of sufficiently powerful, compact sources with high beam quality has so far drastically limited the development of these technologies. Scaling the CW single-mode output power requires optimization of the QCL active region as well as device architectures allowing for scaling the lateral device width. By taking advantage of the flexibility of MOCVD to easily grow quantum wells and barriers of multiple alloy compositions in the QCL core, we have implemented the step-taper active region (AR) – resonant-extraction (STA-RE) QCL which provides both carrier-leakage suppression and miniband-like extraction. To scale the single-mode output powers, we employ a phase-locked arrays of antiguides. Such devices represent high-index-contrast (Δn = 0.08-0.10) photonic crystals (PC) structures that allow global coupling between the array elements.
The highest performance QCLs employ strain compensated InGaAs/AlInAs active regions on InP substrates. Realizing such QCLs on either GaAs or Si substrates would enable a lower cost (larger substrate diameter) manufacturing process. Metamorphic buffer layers (MBLs) can be utilized as virtual substrates with a specified lattice constant, opening up the palette of III/V alloys available for new device architectures. For example, our simulations suggest that for emission wavelengths less than about 3.5 m, significant enhancement in performance is possible over conventional InP-substrate devices by employing an MBL design on a GaAs substrate. Improvement of the MBL surface morphology and the development of strained QWs subsequently grown atop the MBL are challenging materials issues, which need to be addressed for the QCL-device application. The growth and characterization of strain-compensated superlattices (SLs), representative of the QCL active region, atop a MBL structures will be discussed.
Luke J. Mawst received the B.S. degree in engineering physics and the M.S. and Ph.D. degrees in electrical engineering from the University of Illinois at Urbana-Champaign in 1982, 1984, and 1987, respectively. He joined TRW, Inc., Redondo Beach, CA, in 1987, where he was a senior scientist in the research center, engaged in design and development of semiconductor lasers using MOCVD crystal growth. He is co-inventor of the Resonant Optical Waveguide (ROW) antiguided array and has contributed to its development as a practical source of high coherent power, for which he received the TRW Group Level Chairman's award. He developed a novel single- mode edge-emitting laser structure, the ARROW laser, as a source for coupling high powers into fibers. He is currently a Professor (since 1996) in the Electrical and Computer Engineering Department at the University of Wisconsin-Madison, where he is involved in the development novel III/V compound semiconductor device structures, including quantum dot lasers, active photonic lattice structures, dilute-nitride lasers, lasers employing metamorphic buffer layers, and quantum cascade lasers. Prof. Mawst has authored or coauthored more than 250 journal publications and holds 26 patents. He was recipient of the Vilas associates Award at UW-Madison (2017) and he is a Fellow of IEEE.