Photoconductive detectors wavelength cutoff

Hg Cd Te is an example of a ternary detector, in which the value of x controls the cutoff wavelength. Photoconductive detectors are generally simpler to couple to low noise amplifiers photodiodes generally have lower power consumption because these have no external bias, and better high frequency performance (15,16). 

This graph summarizes the wavelength response of some semiconductors used as detectors for infrared radiation. The quantity D (X) is the signal to noise ratio for an incident radiant power density of 1 W/cm and a bandwidth of 1 Hz (60° field of view). The Ge, InAs, and InSb detectors are photovoltaics, while the HgCdTe series are photoconductive devices. The cutoff wavelength of the latter can be varied by adjusting the relative amounts of Hg, Cd,... 

Fig. 2.15. Photon noise limited Df at peak wavelength (assumed to be cutoff wavelength), for a photovoltaic detector for selected background temperatures Tg. Values for a cooled photoconductive detector are 0.71 times those shown. (Assumes 27t steradian field of view and >/ = 1) (after Jacobs and Sargent [2.160])...

A comparison between the calculated values of specific detectivity of an exclusion detector and the BLIP values for a field of view of 180° at the same cutoff wavelength (equal to performance of a photoconductive device at 77 K) shows that all of the calculated values are significandy below the BLIP limit. The detectivity increase in comparison to a photoconductor without nonequilibrium Auger suppression (conventional sub-BLIP photoconductor) is less three times. 

---