Novel buffer-layer design yields room-temperature mid-IR InAs laser made on InP

Recently, ECE Associate Professor Minjoo Larry Lee and a team of researchers demonstrated the first room-temperature lattice-mismatched indium arsenide (InAs) quantum-well laser grown on an indium phosphide (InP) substrate. Their laser emits light at a wavelength (2.75µm) that is typically only achievable using the more expensive substrate gallium antimonide (GaSb).

In order to build their laser on InP, Lee and the team devised a highly unconventional design. Using molecular beam epitaxy, they grew a metamorphic buffer layer composed of indium, arsenide, and phosphide (InAsP) that served as a platform to grow strained InAs quantum wells, where light would be generated.

The buffer layer served a second purpose: it made up the bottom clad for optical confinement in a laser waveguide. With a typical laser design, the buffer layer that helps bridge the mismatch between substrate and active region is completely separate from the cladding layers.

 According to Lee, the lower optical cladding layer can constitute nearly 50% of the total laser thickness. By having a multi-purpose buffer layer, the researchers needed less epitaxial material to make their laser, which resulted in less processing time and expense.

Another benefit of Lee’s design approach is it gives researchers the ability to reach emission wavelengths that weren’t readily accessible on InP before.

 “Our design concept can theoretically now be applied to other materials, including III-V lasers on silicon,” said Lee, who plans to apply the new design approach to creating lasers that emit light in under-served infra-red wavelength ranges that are good for molecular gas sensing for environmental monitoring or defense applications.

Lee collaborated on this work with University of Texas faculty member Dan Wasserman, who had previously been a faculty member at the University of Illinois Micro + Nanotechnology Lab and Electrical & Computer Engineering Department, and graduate students Daehwan Jung and Lan Yu. Funding for the work was provided by the National Science Foundation and Toyota Motor Corp.

The team’s research was published in Applied Physics Letters in November 2016.

For more information, contact Larry Lee at mllee@illinois.edu.