Some measurements of the characteristics of germanium interband infrared detectors

In a recent paper the authors have described a new infrared detector which depends on light-to-heavy hole transitions in P-type germanium. The device is a photoresistor in which the mobility rather than the carrier concentration is varied. The transition between the degenerate hole bands produces a maximum absorption coefficient for photons with energy of about 0.12 ev, making this device particularly useful as a detector for the CO2laser. The enormous density of states in the bands permits efficient room temperature operation in spite of the fact that the photon energy is only 4kT. The degeneracy at k=0 produces very rapid relaxation of the non-equilibrium population of light holes. This implies both a very fast rise and fall time and also low sensitivity.