Optical nonlinear absorption characterization of bulk semi-insulating 4H-SIC at and above the band edge

Nonlinearity of optical absorption in semi-insulating bulk 4H-SiC has been investigated. Of interest was the optical bleaching behavior of 4H-SiC at and just above the band edge in the range 3.11-3.33 eV (wavelength 380-355 nm). Results of experiments on 200 μm and 490 μm thickness samples indicate partial bleaching in the optical fluence range from 70 W/cm
²
to 1.8 kW/cm
²
, and the absorption coefficient was found to vary by approximately 10% within this range. These experimental findings are supported by simulation results obtained from a first order semi-empirical rate based model linking excitation-induced change in density of states with the absorption coefficient over the range of tested power densities. As expected, this effect scales with photon energy. Characterization of 4H-SiC absorption behavior under varying fluence will aid in design optimization of a Photoconductive Semiconductor Switch (PCSS).