Research on 4H-SiC Photoconductive Semiconductor Switch Employing Composite Anti-Reflection Coating

This paper proposes a novel 4H-SiC Photoconductive Semiconductor Switches (PCSS) with anti-reflection function for incident lasers, which depends on an AlN composite anti-reflection coating. The key innovation lies in the graded-index design of the anti-reflection coating, which is fabricated as a laminate of a uniform AlN film and a tilted nanopillar (TN) AlN film via reactive magnetron sputtering combined with Glancing Angle Deposition (GLAD). This mono-material structure not only creates a continuous refractive index transition from air to the 4H-SiC substrate—significantly suppressing Fresnel reflection—but also inherently avoids the interfacial reliability issues associated with conventional heterogeneous multilayer coatings. Measurement shows that, at the incident wavelength of 532 nm, the transmission rate of this coating for PCSS is increased by 65 % and 15% compared to no anti-reflection film and single uniform film. Furthermore, the optoelectronic characteristics of PCSS with composite anti-reflection coating are analyzed. It has been found that this PCSS exhibits a very high transient current of 10.3A, and the on-state resistance has been reduced to 17Ω when the optical power density of the incident laser is merely 2.5 MW/cm2. The introduction of this flexible composite anti-reflection coating with adjustable refractive index is a very promising solution for the laser absorption efficiency, device miniaturization and frequency improvement of PCSS.