HMN 2025: How carbon contamination is a key barrier in gallium oxide electronics

Cornell researchers have uncovered a virtually invisible perpetrator hindering the event of next-generation, high-power electronics: a microscopic layer of carbon contamination, usually left behind by air publicity and fabrication strategies, that impairs electrical movement in gadgets made with gallium oxide. They have additionally discovered an answer.

A study revealed June 20 within the journal APL Materials is among the many first to instantly visualize this nanometer-thin barrier that may happen when metals are patterned onto semiconductors, a necessary interface for getting present out and in of digital gadgets. When these contacts have resistance, system efficiency suffers.

The problem is particularly pronounced in beta gallium oxide, a semiconductor materials with an ultra-wide band gap that would in the future permit gadgets like electrical autos and grid infrastructure to extra effectively deal with greater voltages.

“It’s been an issue within the gallium oxide area for fairly a while,” mentioned Naomi Pieczulewski, a doctoral scholar in supplies science and engineering and the research’s co-lead writer. “Sometimes you get good conduction and generally you get completely no conduction in any respect, and nobody might actually pinpoint why.”

Pieczulewski’s analysis spans a number of Cornell labs uniquely positioned to analyze the issue, together with one specializing within the manufacturing of oxide supplies and one specializing in atomic-resolution microscopy.

Focusing on the interface between a beta gallium oxide and titanium contact, Pieczulewski and colleagues used scanning transmission electron microscopy and different strategies to check two widespread strategies for fabricating the contact: a conventional lift-off course of, and a metal-first course of through which metallic is deposited earlier than the semiconductor is patterned.

In the lift-off samples, the researchers noticed a skinny, patchy layer of carbon between the metallic and the semiconductor left over from photoresist supplies used throughout processing. To deal with the contamination, a one-hour UV-ozone publicity successfully eliminated the carbon layer, enabling a contact resistance as little as 0.05 ohm-millimeters, among the many lowest reported for non-alloyed beta gallium oxide contacts.

Carbon contamination ensuing from air publicity within the metal-first fabrication methodology was remediated with a five-minute energetic oxygen therapy, considerably decreasing the contact resistance and enhancing present movement.

“This analysis allows a solution to produce dependable, constant ultra-wide bandgap gadgets,” Pieczulewski mentioned. “It’s an incremental progress, however I believe it is vital when it comes to shifting towards commercialization.”

The study’s different co-lead writer is Kathleen Smith, Ph.D. ’24. Corresponding authors embrace Huili Grace Xing, the William L. Quackenbush Professor of Electrical and Computer Engineering and of Materials Science and Engineering; and David Muller, the Samuel B. Eckert Professor of Engineering within the School of Applied and Engineering Physics.

The study was the primary to unite on one analysis paper all seven co-principal investigators of the AFRL-Cornell Center for Epitaxial Solutions, also referred to as ACCESS, which together with Xing and Muller embrace Debdeep Jena, the David E. Burr Professor of Engineering; Michael Thompson, the Dwight C. Baum Professor in Engineering; Darrell Schlom, the Tisch University Professor; Farhan Rana, the Joseph P. Ripley Professor of Engineering; and Hari Nair, assistant professor of supplies science and engineering.

Boise State University and Micron, by the Semiconductor Research Corporation (SRC), contributed superior characterization strategies to the research.