Cornell researchers have made a groundbreaking discovery in the realm of high-power electronics, uncovering a minuscule layer of carbon contamination that has been impeding progress in the development of next-generation devices. This layer, often left behind by air exposure and fabrication methods, has been found to disrupt electrical flow in devices utilizing gallium oxide. However, the researchers have not only identified this issue but have also devised a solution to combat it.
Published in the journal APL Materials on June 20, the study sheds light on the nanometer-thin barrier that forms when metals are applied to semiconductors, a critical step in facilitating current flow within electronic devices. The presence of resistance at these interfaces has been a significant obstacle in achieving optimal device performance, particularly in beta gallium oxide, a semiconductor material with a wide band gap that holds promise for enhancing the efficiency of electric vehicles and grid infrastructure in the future.
Naomi Pieczulewski, a doctoral student in materials science and engineering and co-lead author of the study, emphasized the longstanding challenge posed by this issue within the gallium oxide field. The erratic nature of electrical conduction in these devices has puzzled researchers for some time, making it difficult to pinpoint the exact cause of the problem.
Pieczulewski and her team, drawing on the expertise of various Cornell labs specializing in oxide materials production and atomic-resolution microscopy, focused their investigation on the interface between beta gallium oxide and a titanium contact. By employing scanning transmission electron microscopy and other advanced techniques, they compared two common fabrication methods: the traditional lift-off process and a metal-first approach where the metal is deposited prior to patterning the semiconductor.
Their findings, depicted in atomic resolution ADF-STEM images published alongside the study, revealed critical insights into the nature of the interface between titanium and gallium oxide in different samples. While sample A exhibited a dark contamination layer separating the two materials, resulting in poor adherence, samples B-D displayed near-perfect contact between gallium oxide and titanium, highlighting the efficacy of certain fabrication methods in circumventing the carbon contamination issue.
Overall, this research represents a significant step forward in overcoming a longstanding hurdle in the development of high-power electronics, setting the stage for advancements in the utilization of gallium oxide in cutting-edge electronic devices. In a recent study published in APL Materials, researchers have made significant progress in improving the contact resistance in non-alloyed beta gallium oxide (β-Ga2O3) devices. The research, led by Naomi Pieczulewski and Kathleen Smith, focused on addressing carbon contamination issues in the metal-semiconductor interface, a common problem in the fabrication process.
The researchers observed a thin, patchy layer of carbon between the metal and the semiconductor in lift-off samples, which was attributed to residual photoresist materials used during processing. To combat this contamination, a one-hour UV-ozone exposure was found to effectively remove the carbon layer, resulting in a contact resistance as low as 0.05 ohm-millimeters. This achievement represents one of the lowest reported contact resistances for non-alloyed beta gallium oxide contacts.
Furthermore, the study identified a solution for carbon contamination that occurs during air exposure in the metal-first fabrication method. A five-minute active oxygen treatment was shown to significantly reduce the contact resistance and improve current flow in the devices.
“This research paves the way for the production of reliable, consistent ultra-wide bandgap devices,” Pieczulewski commented. “While it may seem like incremental progress, the impact of this work is significant in advancing towards commercialization.”
The collaborative nature of the study was evident in the involvement of all seven co-principal investigators of the AFRL-Cornell Center for Epitaxial Solutions (ACCESS), including Huili Grace Xing, David Muller, Debdeep Jena, Michael Thompson, Darrell Schlom, Farhan Rana, and Hari Nair. Boise State University and Micron, supported by the Semiconductor Research Corporation (SRC), also contributed advanced characterization techniques to the research.
Overall, this study represents a key advancement in the field of non-alloyed beta gallium oxide devices, offering insights into addressing carbon contamination issues and achieving low contact resistances. The collaboration between researchers from various institutions and the utilization of advanced techniques highlight the importance of interdisciplinary efforts in advancing semiconductor technologies.
