A status report on infrared detectors∗

Abstract

Infrared photondetectors may be placed into two categories: intrinsic and impurity activated detectors. Intrinsic detectors include film detectors PbS, PbSe, PbTe, and single crystal detectors InSb and InAs. Their spectral response generally rises linearly to the spectral peak, then drops sharply. Typical PbS detectors operated at room temperature have a long wavelength threshold at 3 μ and a detectivity of 10 11 cm c/s 1 2 W −1 at 2 μ., their spectral peak. Time constants are of the order of 100 μsec. PbSe and PbTe detectors when operated at liquid nitrogen temperature have a detectivity of about 2 x 10 10 cm c/s 1 2 W −1 at their spectral peak between 4 and 6 μ. Time constants vary between 20 and 100 μsec. InSb detectors, when cooled to liquid nitrogen temperature, have a spectral peak in the vicinity of 5 μ and a detectivity of about 4 x 10 10 cm c/s 1 2 W −1.Their time constants are of the order of 1 μsec. Impurity activated detectors include Ge and Ge-Si single crystals with impurities such as Au, Cu, Zn, Sb. The spectral response of Ge with the peak at 1.5μ and a cut-off at 1.8 μ is superimposed on the response characteristic of the impurity. Gold extends the response to 9μ, Cu to 30 μ, Zn to 40 μ., and Sb to 120μ. When these detectors are cooled until they are background limited, their detectivity is about 2 x 10 10 cm c/s 1 2 W −1 atspectral peak. Time constants of Ge: Au and Ge: Zn detectors are less than 0.1 μsec. Evaluation of the theoretical limit of detectivity indicates that most currently available single crystal detectors approach the theoretical limit to within a factor of two-three; average film detectors, however, differ by a greater amount.