Papers by Keyword: Photoconductive Semiconductor Switches (PCSS)

Abstract: Annealing of high purity semi-insulating (HPSI) 4H-SiC is investigated as a method to improve bulk photoconductive semiconductor switches through recombination lifetime modification. Five samples of HPSI 4H-SiC were annealed at 1810 °C for lengths of time ranging from 3 to 300 minutes. The recombination lifetime of the unannealed and annealed samples was measured using a contactless microwave photoconductivity decay (MPCD) system. The MPCD system consists of a 35 GHz continuous microwave probe and a tripled Nd:YAG pulsed laser. The recombination lifetime was increased from 6 ns, as received, up to 185 ns by annealing for 300 minutes. To experimentally verify switch improvements, identical switches from unannealed and annealed material were fabricated and tested at low voltage. The unannealed device generated a 15 ns pulse with a 2 ns rise-time. The annealed device conducted for upwards of 300 ns with a comparable 2 ns rise-time. The increased recombination lifetime resulted in lower on-state resistance and increased energy transfer.

Abstract: The photoconductive semiconductor switches (PCSS) were fabricated on V-doped semi-insulating 6H-SiC. We studied the effect of surface morphology on the on-state resistance of SiC PCSS. The SiC wafers with quite similar physical properties were processed by mechanical polishing, chemical mechanical polishing and H2 etching for producing different surface morphologies. All the SiC PCSS were excited by a 355 nm laser with a frequency of 10 Hz and a pulse intensity of 132 μJ/mm². We found that the surface morphology had an obvious effect on the on-state resistance. The PCSS fabricated on mechanical polished SiC wafer with an average surface roughness (rms) of 1.0 nm showed the largest on-state resistance of 45.6 ohms, while a low value of 13.3 ohms was observed for the wafer processed by H2 etching at high temperature of 1550 °C.