Photon parameter characterization of infrared photodetectors

An alternative formulation of IR photodetector theory in photon parameter terms is examined and it is shown that within such a formulation, subsystem figures-of-merit such as SNR and NETD may be separated entirely into factors describing respectively the system geometry, noise bandwidth, signal-to-background contrast, atmospheric transmission, background-to-noise ratio and detector linearity. For the evaluation of signal current, a dimensionless photon responsivity is introduced, analogous to the standard current responsivity. A special feature is the specification of the IR background current as an inherent part of the formalism. In this respect, r.m.s. noise currents may be determined from values of an alternative specific quantity, the specific background-to-noise ratio B^∗, that is used in place of the standard specific detectivity D^∗. Simple relationships are derived for conversion between responsivity and photon responsivity, and between the standard detectivity D^∗ and B^∗.