Far-infrared (FIR) free-carrier absorption characteristics for epitaxially
grown p-type Si and GaAs thin films over a range of carrier concentrations
have been investigated, both experimentally and theoretically, and employed
to analyze the experimental results of FIR detection. The free-hole absorp
tion is found to be almost independent of the wavelength and a linear regre
ssion relationship between the absorption coefficient and the carrier conce
ntration has been obtained, which can be applied to well explain the behavi
or of GaAs FIR detectors with different number of layers, different applied
biases, as well as different layer concentrations.