Proton radiation effects on hydrogen-terminated diamond field-effect transistors

Hydrogen-terminated diamond field-effect transistors (H-diamond FETs) are promising for space electronics because of their high breakdown field, thermal stability, and radiation tolerance. However, their response to proton irradiation and the associated degradation mechanisms remain insufficiently understood. Here, depletion-mode H-diamond FETs are irradiated with 5 MeV protons at fluences of 1 × 1011, 1 × 1012, and 1 × 1013 p/cm2. At the highest fluence, the on-state current evaluated at a fixed gate overdrive decreases by approximately 43%, the peak transconductance decreases from 7.74 to 2.77 mS/mm, the subthreshold swing increases from 300 to 960 mV/dec, the gate leakage current increases by approximately four orders of magnitude, and the 99% current-stabilization time increases from 0.84 to 4.56 ms. Capacitance–voltage measurements reveal a positive flatband voltage shift consistent with radiation-induced negative trapped charge. Gate-controlled deep-level transient spectroscopy identifies three hole trap states at ET − EV = 0.354, 0.462, and 0.662 eV, including two states that emerge after irradiation and one preexisting state enhanced by irradiation. These results support two coupled degradation pathways: gate-stack ionization damage primarily affects threshold voltage, leakage, subthreshold behavior, and carrier stabilization, whereas displacement-related defects in diamond are associated with mobility and transconductance degradation.