Abstract: Far infrared light is detected using semiconductor devices having at least two doped layers with adjacent doped layers separated by undoped layers. The technique includes doping to levels which establish work functions at interfacial barriers between the doped and undoped layers approximately equal to the photon energy of far infrared light of the longest wavelength to be detected. The devices are forward biased, cooled to a temperature at which thermal excitation of carriers in the doped layers is less than the work function, and exposed to far infrared light of a band width including the selected longest wavelength. Photo current produced by excitation of carriers over the interfacial barriers is then measured. The method can be applied to existing p-i-n diodes and superlattice structures as well as devices fabricated to respond to specific far infrared wavelength bands.