A theoretical equation is given for the sensitivities or signal-to-noise ratios of infrared photodetectors as functions of area and sensitive time and long-wavelength cutoff λ0, assuming the materials approach within comparable factors of the fundamental limits set by radiation noise from their surroundings at a given temperature.
JOHN R. PLATT, "Wavelength Dependence of Radiation-Noise Limits on Sensitivity of Infrared Photodetectors," J. Opt. Soc. Am. 46, 609-610 (1956)