The Next Wonder Semiconductor

With scanning ultrafast electron microscopy, researchers unveil promising hot photocarrier transport properties of cubic boron arsenide

From:  University of California - Santa Barbara

October 25, 2022 -- In a study that confirms its promise as the next-generation semiconductor material, UC Santa Barbara researchers have directly visualized the photocarrier transport properties of cubic boron arsenide single crystals.

"We were able to visualize how the charge moves in our sample," said Bolin Liao, an assistant professor of mechanical engineering in the College of Engineering. Using the only scanning ultrafast electron microscopy (SUEM) setup in operation at a U.S. university, he and his team were able to make "movies" of the generation and transport processes of a photoexcited charge in this relatively little-studied III-V semiconductor material, which has recently been recognized as having extraordinary electrical and thermal properties. In the process, they found another, beneficial property that adds to the material's potential as the next great semiconductor.

Their research, conducted in collaboration with physics professor Zhifeng Ren's group at the University of Houston, who specialize in fabricating high-quality single crystals of cubic boron arsenide, appears in the journal Matter.

'Ringing the Bell'

Boron arsenide is being eyed as a potential candidate to replace silicon, the computer world's staple semiconductor material, due to its promising performance. For one thing, with an improved charge mobility over silicon, it easily conducts current (electrons and their positively charged counterpart, "holes"). However, unlike silicon, it also conducts heat with ease.

"This material actually has 10 times higher thermal conductivity than silicon," Liao said. This heat conducting -- and releasing -- ability is particularly important as electronic components become smaller and more densely packed, and pooled heat threatens the devices' performance, he explained.

"As your cellphones become more powerful, you want to be able to dissipate the heat, otherwise you have efficiency and safety issues," he said. "Thermal management has been a challenge for a lot of microelectronic devices."

What gives rise to the high thermal conductivity of this material, it turns out, can also lead to interesting transport properties of photocarriers, which are the charges excited by light, for example, in a solar cell. If experimentally verified, this would indicate that cubic boron arsenide can also be a promising material for photovoltaic and light detection applications. Direct measurement of photocarrier transport in cubic boron arsenide, however, has been challenging due to the small size of available high-quality samples.

The research team's study combines two feats: The crystal growth skills of the University of Houston team, and the imaging prowess at UC Santa Barbara. Combining the abilities of the scanning electron microscope and femtosecond ultrafast lasers, the UCSB team built what is essentially an extremely fast, exceptionally high-resolution camera.

"Electron microscopes have very good spatial resolution -- they can resolve single atoms with their sub-nanometer spatial resolution -- but they're typically very slow," Liao said, noting this makes them excellent for capturing static images.

"With our technique, we couple this very high spatial resolution with an ultrafast laser, which acts as a very fast shutter, for extremely high time resolution," Liao continued. "We're talking about one picosecond -- a millionth of a millionth of a second. So we can make movies of these microscopic energy and charge transport processes." Originally invented at Caltech, the method was further developed and improved at UCSB from scratch and now is the only operational SUEM setup at an American university.

        https://www.sciencedaily.com/releases/2022/10/221025150242.htm