Prof. Lee's team demonstrates highly unconventional laser design

ECE News

Laura Schmitt, MNTL
1/20/2017 9:36:30 AM

Story Highlights

ECE ILLINOIS Associate Professor Minjoo Lawrence Lee and a team of researchers have 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).

Development of InAs MQW active region. (a) RT PL spectra from 4 QW sample with strain-balancing (blue), 1 QW sample (black), and 4 QW sample without strain-balancing (red). (b) Bright-field TEM image on 4 QW sample with strain-balancing, and (c) without strain-balancing.
Development of InAs MQW active region. (a) RT PL spectra from 4 QW sample with strain-balancing (blue), 1 QW sample (black), and 4 QW sample without strain-balancing (red). (b) Bright-field TEM image on 4 QW sample with strain-balancing, and (c) without strain-balancing.
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.

Minjoo Lawrence Lee
Minjoo Lawrence Lee

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 an ECE ILLINOIS faculty member at the Micro + Nanotechnology Lab, 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. You can also read the news release from MNTL.

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