Defect-annealing-induced optical gain recovery in electron-irradiated 4H-SiC UV phototransistors

Abstract

The ultraviolet (UV) response of a floating-base 4H-SiC n–p–n phototransistor is characterized before and after 10 MeV electron irradiation. The pristine device demonstrates visible-blind UV detection at 275 nm, achieving a UV/dark current ratio of ∼106, a specific detectivity of 1.37 × 1012 Jones, and a responsivity of 1.36 A/W. Responsivity monotonically increases with incident optical power density. After 500 kGy irradiation, responsivity degrades by 80%, with dose dependence following a double-exponential decay. Vacuum annealing at 800 K restores 79% of the pre-irradiation optical gain, confirming a partial reversibility of irradiation-induced defects. Deep level transient spectroscopy reveals defect evolution post-annealing, identifying corresponding energy levels, identities, and annihilation dynamics. High-temperature annealing primarily annihilates irradiation-induced point defects, enabling significant recovery, while thermally stable defect complexes prevent full restoration.