MOCVD system to drive exploration of next-gen nitride materials

A laboratory upgrade at Cornell will help forge new directions for nitride semiconductors - materials best known for enabling LEDs and 5G communications - by expanding the capabilities of nitrides to support technologies such as quantum computers and next generation radiofrequency and power devices.

The upgrade includes the installation of a custom-built, metal-organic chemical vapor deposition (MOCVD) system in Duffield Hall. The system works by injecting vapors of carefully designed chemicals, known as precursors, onto a heated substrate, where the materials react and form ultra-thin crystalline layers. This process, known as epitaxial growth, allows researchers to build semiconductor structures with atomic-level precision and performance.

MOCVD has been used to grow the traditional family of nitride semiconductors - gallium nitride, aluminum nitride and indium nitride - that revolutionized energy-efficient lighting and high-frequency electronics. But with this new system, researchers aim to engineer an expanded, palette of nitrides with functionalities such as superconductivity, ferroelectricity and magnetism.

"The established family of nitrides do a fantastic job, but now we are at a point where we can move on to other nitrides, like niobium nitride, which is a superconductor," said Hari Nair, assistant professor of materials science and engineering and principal investigator for the MOCVD system. Co-principal investigators are Debdeep Jena, the David E. Burr Professor, and Huili Grace Xing, the William L. Quackenbush Professor, both in the School of Electrical and Computer Engineering and the Department of Materials Science and Engineering.

These new materials could pave the way for high-coherence microwave qubits, memory and radio-frequency devices, far ultra violet-C LEDs and next-generation quantum communication systems. One promising direction involves replacing the aluminum-aluminum oxide Josephson junctions - core building blocks of quantum computers - with versions that are all epitaxial nitride.

Another breakthrough involves making aluminum nitride ferroelectric by substituting in small amounts of scandium, an approach gaining significant traction in both academia and industry, and one that Nair said will be explored with the new MOCVD system.

Many of these new nitrides have only been produced using molecular beam epitaxy, a technique that is useful for research, but difficult to scale for industrial manufacturing. MOCVD, in contrast, is already the workhorse for commercial LED and gallium nitride-based power devices.

"Every single LED that's commercially made uses MOCVD," Nair said. "So if we can develop growth processes for these new nitrides using MOCVD, they'll be much easier to translate into industry. That's what makes this so exciting - it's not just about what we can study in the lab, it's about how we can scale it."

Building on recent advances in chemical precursors and high-temperature gas flow control, the Cornell team worked with the company AIXTRON to design a one-of-a-kind MOCVD system capable of handling the unique challenges posed by nitride materials. It is the first such system in the U.S. specifically configured from the outset for the purpose of growing the new nitrides along with the more established family of nitrides.

Unlike conventional systems, the machine features dual metal-organic delivery channels - one for traditional precursors and another for low vapor pressure precursors like scandium and niobium. A triple-plenum showerhead ensures that the traditional precursors and the low vapor pressure precursors do not mix until they are injected into the reactor.

"When we talk about a materials science breakthrough, it's many evolutionary steps that build up," Nair said. "This system is one of those steps. It gives us the platform to explore, discover and ultimately help drive a new era in materials for electronics, optoelectronics and quantum information systems."

The MOCVD system is expected to serve national priorities, enabling a range of research initiatives funded by the U.S. Department of Defense. The system was made possible through a grant from the U.S. Department of Defense with the advocacy of Kenneth Goretta, retired program manager at the U.S. Air Force Office of Aerospace Research and Development.

Cornell researchers anticipate the system will also advance technologies being developed by Soctera, a Cornell-based startup focused on millimeter-wave power amplifiers using high-quality aluminum nitride. The company's innovations are targeting defense applications, including advanced radar systems, autonomous vehicle communications and satellite networks.