Lead-telluride as well as two types of gold-germanium infrared detectors have been constructed and their characteristics analyzed. Parameters which distinguish one detector from another are spectral response, time constant, noise, and signal for a given incident power. All three materials must be cooled to about 90°K before they become useful. One type of gold-germanium detector has a long wavelength threshold at 9.5 μ, the other type and the lead telluride detector have a response extending to 6 μ. The germanium detectors owe their long wavelength response to excitation of carriers from the gold impurity states. In lead telluride, intrinsic excitation of carriers from valence to conduction band is responsible for the 6-μ threshold.
Time constants of the 9.5-μ detector beyond 1.5 μ are less than 1 µsec. Time constants of the 6-μ germanium detector vary between 10 µsec and 1 msec; in lead telluride they are of the order of 15 µsec. Noise equivalent power of all three detectors is of the order of 10−10 w, referred to a 500°K blackbody.
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