Mechanism of Gamma-Ray Irradiation Effects on the Transient Characteristics of Photoconductive Semiconductor Switches

This study investigates the gamma-ray irradiation effects on the transient characteristics of vanadium-compensated semi-insulating (VCSI) 4H-SiC photoconductive semiconductor switches (PCSS). Controlled irradiation experiments (0–800 krad(Si) and 5 kV bias) demonstrate dose-dependent degradation of on-state resistance (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub>), load power, and full-width at half-maximum (FWHM), revealing a three-phase evolution: initial deterioration (0–200 krad(Si)), transient recovery via field-assisted defect recovery (200–300 krad(Si)), and severe degradation (>500 krad(Si)). Photoluminescence spectroscopy identifies Z₁/₂ (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_C</i> -0.67 eV) and EH₆/₇ (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_C</i> -1.55 eV) deep traps as dominant recombination centers. Simulations confirm that under 532-nm laser excitation, deep-level defects reduce carrier lifetime via the Shockley-Read-Hall recombination mechanism, thereby degrading transient on-state characteristics. Crucially, shallow-donor deep-acceptor (SDDA) PCSS exhibits superior radiation tolerance with only a 6% on-state resistance increase at 800 krad versus 25.5% in deep-donor–shallow-acceptor (DDSA) devices, attributed to the substrate compensation type. These findings elucidate the radiation damage mechanism in 4H-SiC PCSS and provide design guidelines for radiation-hardened pulsed power systems in aerospace applications.