Stress-Relieving Flexible Encapsulation for Avalanche-Mode GaAs Photoconductive Semiconductor Switches: Toward Enhanced Reliability and Longevity

Gallium arsenide photoconductive semiconductor switches (GaAs PCSS) face significant reliability and longevity challenges that hinder their practical deployment in pulse power system applications. A primary issue is thermomechanical stress at critical dielectric-electrode-GaAs interfaces, particularly under high-field operation and repetitive high-current stresses. This stress arises from the mismatch in the coefficient of thermal expansion between rigid traditional encapsulants like epoxy and GaAs, accelerating crack propagation, contact delamination, and eventual anode failure. This letter demonstrates a breakthrough in reliability enhancement for avalanche-mode GaAs PCSS via flexible polydimethylsiloxane (PDMS) encapsulation. Replacing conventional rigid traditional epoxy resins, PDMS mitigates thermomechanical stress at critical interfaces under large current operation (> hundreds of amperes). Experimental results show a 5× extended operational longevity (over 6×10³ pulses vs. 1×10³ for epoxy resin).