Carrier lifetime studies of semi-insulating silicon carbide for photoconductive switch applications

A contactless microwave photoconductivity decay (MPCD) method has been used to measure recombination lifetime and relative conductivity of semi-insulating (SI) silicon carbide (SiC) wafers. A pulsed laser, tunable from 210 nm to 2 μm, has been used to probe above and below band gap photoconductive responses of four SI SiC wafers. The carrier lifetimes were calculated by comparing the reflected microwave signal to the photo response of a fast (<; 300 ps) photodiode. Three vanadium-doped 6H-SiC wafers, with bulk resistivities ranging from 10⁵ Ω-cm to 10¹¹ Ω-cm, and one high purity semi-insulating (HPSI) 4H-SiC wafer (>; 10⁹ Ω-cm) were studied. The photoconductive response of each wafer set is presented. The HPSI wafer demonstrated longer carrier lifetime and improved above band gap photoconductivity compared to the vanadium-doped wafers. The difference in carrier lifetimes are attributed to higher densities of recombination centers (vanadium acceptors) in the 6H-SiC substrates.