Effective lateral isolation for hydrogen-terminated diamond field-effect transistors via nitrogen ion implantation

Field-effect transistors (FETs) based on hydrogen-terminated (H-terminated) diamond have attracted growing attention for their potential in power electronics and communication technologies. The conventional lateral isolation process in these FETs involves masking the conductive H-terminated regions with polymer resist or metal film, and then converting the unmasked regions into insulating oxygen-terminated diamond through oxygen plasma or other oxidizing treatments. However, this process carries a substantial risk of contaminating the H-terminated diamond surface with residues of the mask and its remover, which potentially degrades FET performance. Herein, we present a fundamentally different approach to lateral isolation in H-terminated diamond FETs through selective nitrogen ion implantation prior to the global H-termination. Electrical measurements confirm that the implanted regions remain highly resistive even after hydrogenation, providing effective and stable lateral isolation. Notably, H-termination is performed after ion implantation, which ensures a clean surface free from residues. This approach also facilitates fabrication of diamond FETs without exposing the hydrogenated surface to air, thus minimizing contamination from airborne impurities. Hence, the proposed lateral isolation technique offers a cleaner and more reliable pathway toward high-performance diamond-based electronic devices.