By Josh Perry, Editor
[email protected]

Researchers at the Massachusetts Institute of Technology (MIT) in Cambridge, Mass. developed a technique for fabricating ultrathin semiconducting films from materials such as gallium arsenide, allium nitride, and lithium fluoride, which outperform silicon but had previously been too expensive to use in devices.

MIT researchers have devised a way to grow a single crystalline compound semiconductor on its substrate through two-dimensional materials. (Wei Kong and Kuan Qiao/MIT)

This cost-effective method developed at MIT, according to a report from the school, opens up the possibility of flexible electronics that outperform silicon-based devices. Scientists from Sun Yat-sen University (Guangzhou, China), the University of Virginia, the University of Texas at Dallas, the U.S. Naval Research Laboratory, Ohio State University, and the Georgia Institute of Technology also took part in the study.

The research began in 2017 with the publication of a report demonstrating the viability of using remote epitaxy, stacking graphene on top of a wafer of semiconductors (like gallium arsenide) then flowing atoms of the semiconductor through the stack, to produce copies of expensive semiconducting materials.

It turned out that the process did not work with all semiconductors. Researchers believed that an ionic charge was necessary to get the atoms flowing through the graphene layer.

“For instance, in the case of gallium arsenide, gallium has a negative charge at the interface, compared with arsenic’s positive charge,” the report explained. “This charge difference, or polarity, may have helped the atoms to interact through graphene as if it were transparent, and to copy the underlying atomic pattern.”

Researchers found that the stronger the polarity, the stronger the interaction between atoms. They also experimented with different intermediate layers, swapping graphene for hexagonal boron nitride, but the polarity of the new interface impacted the efficiency of the interaction with the wafer.

The article added, “Researchers can now simply look at the periodic table and pick two elements of opposite charge. Once they acquire or fabricate a main wafer made from the same elements, they can then apply the team’s remote epitaxy techniques to fabricate multiple, exact copies of the original wafer.”

The research was recently published in Nature Materials. The abstract stated:

“The transparency of two-dimensional (2D) materials to intermolecular interactions of crystalline materials has been an unresolved topic. Here we report that remote atomic interaction through 2D materials is governed by the binding nature, that is, the polarity of atomic bonds, both in the underlying substrates and in 2D material interlayers.

“Although the potential field from covalent-bonded materials is screened by a monolayer of graphene, that from ionic-bonded materials is strong enough to penetrate through a few layers of graphene. Such field penetration is substantially attenuated by 2D hexagonal boron nitride, which itself has polarization in its atomic bonds. Based on the control of transparency, modulated by the nature of materials as well as interlayer thickness, various types of single-crystalline materials across the periodic table can be epitaxially grown on 2D material-coated substrates.

“The epitaxial films can subsequently be released as free-standing membranes, which provides unique opportunities for the heterointegration of arbitrary single-crystalline thin films in functional applications.”