Gamma-ray radiation hardness of Ir contacts in H-terminated diamond MESFETs

We investigate the radiation hardness and electrical stability of Ir-based source and drain contacts employed in hydrogen-terminated diamond MESFETs under 100 kGy γ-ray irradiation followed by thermal annealing. The Ir/diamond interface remains electrically stable under the present combined radiation and thermal stress conditions. In contrast, γ-ray exposure induces a positive threshold voltage shift, accompanied by changes in channel conduction consistent with ionization-induced modification of the near-surface electrostatics. A statistical evaluation across multiple devices further shows that the dominant post-irradiation changes are not contact-related, but instead appear in gate-controlled parameters, including a systematic threshold voltage shift and increased variation in subthreshold characteristics after repeated annealing at 200 °C. Taken together, these results identify Ir metallization as a robust source/drain contact strategy for radiation-tolerant diamond electronics and highlight gate-stack engineering as the critical pathway for further reliability improvement.