Far infrared photoelectric thresholds of extrinsic semiconductor photocathodes

Far infrared detection is demonstrated in forward biased Ge (out to 240 pm), Si (220 pm) and InGaAs (90 ,um) p-i-n with D* up to 5 x 10” cm Hz < 1/2/W at 4.2 K. For silicon detectors, this is the longest response wavelength ever reported. Estimates for the responsivity and the detectivity for unoptimized commercial samples are provided by comparison with a silicon composite bolometer. The variations observed in the long wavelength threshold (il, suggest that if correlations with device processing parameters can be successfully established, this approach can be used to tailor detectors for different IR wavelength regions. Spectral response comparison with a single p-i structure strongly supports the detection mechanism and opens the possibility of detector optimization using multilayered structures.