REAP Labs publish molecular beam epitaxy research

Many Tufts School of Engineering researchers aim to make the world a more sustainable and efficient place. In the Renewable Energy and Applied Photonics (REAP) Labs, that work is often done at the atomic level. Molecular beam epitaxy directs atoms into a crystalline structure on a substrate to engineer thin film materials. Perfecting the qualities of these deposited materials and figuring out the optimal conditions and features of these materials can lead to more efficient production of optoelectronic devices which can be used for things such as solar panels, LED lighting, and quantum computers.

Led by Professor Tom Vandervelde, Chair of the Department of Electrical and Computer Engineering, researchers in REAP Labs are working towards defining the characteristics of specific materials that can be epitaxially grown. Their work, “Determination of the Complex Refractive Index of GaSb1-xBix by Variable Angle Spectroscopic Ellipsometry” was recently published in the journal Physica Status Solidi (a). The team included Vandervelde, PhD students John H. McElearney and Pan Menasuta, and Kevin Grossklaus, a technical staff scientist at MIT Lincoln Laboratory who was previously a Tufts research assistant professor and laboratory manager.

The researchers studied an alloy known as GaSbBi, which includes three elements: gallium, antimony, and bismuth. They used variable angle spectroscopic ellipsometry to determine the different qualities of bismuth and how it affects the alloy as a whole. Their work had a specific focus on eliminating Auger recombination while reducing bandgap energy, which can inhibit the efficiency of devices fabricated out of epitaxially grown materials. They also examined the effects of surface droplets on both the complex refractive index and the critical point energies.

GaSbBi holds potential in mid- to far-infrared optoelectronic devices such as LEDs, solar cells, and more. While there is still more research to be done, this work represents an important step in understanding the epitaxial growth of this alloy and could extend to improving the efficiency of epitaxially grown materials in general.

At Tufts, REAP Labs study how light fundamentally interacts with matter and then applies that knowledge to novel technologies. Directed by Vandervelde, the lab works towards next generation image detection and energy independence with a focus on materials physics and optoelectronic technologies.