Two-regime degradation associated with carrier compensation and structural instability in NiO/ β -Ga2O3 heterojunction diodes under 1864 MeV Ta-ion irradiation

We report a two-regime degradation behavior in NiO/β-Ga2O3 heterojunction diodes subjected to 1864 MeV Ta swift heavy ions (linear energy transfer in Si ≈ 75 MeV cm2/mg) over a fluence range from 1 × 108 to 1 × 1011 ions/cm2. At low fluences (≤1 × 109 ions/cm2), the devices retain rectification while exhibiting reduced forward current density (JF), increased specific on-resistance (Ron,sp), and enhanced reverse leakage current (JR), consistent with donor compensation in the β-Ga2O3 drift layer. Capacitance–voltage (C–V) analysis reveals a monotonic reduction in the net carrier concentration (Nnet) with carrier-removal rates (Rc) on the order of 107 cm−1, indicating a quasi-linear compensation regime. When the fluence approaches 1 × 1010 ions/cm2, rectification collapses and normal turn-on behavior is lost. The capacitance becomes weakly voltage dependent, suggesting deviation from linear compensation. Cross-sectional scanning transmission electron microscopy reveals densely distributed nanoscale latent tracks in the drift layer, while cross-sectional scanning electron microscopy shows pronounced ∼2 μm interfacial warping near the NiO/β-Ga2O3 junction. These results indicate a transition from a low-fluence quasi-linear carrier-compensation regime to a high-fluence failure regime associated with structural instability, where severe carrier compensation and failure-associated structural perturbations are both observed.