Heterodyne detection of infrared radiation by cryogenically cooled extrinsic photoconductors is reviewed. Operational characteristics of a highly compensated Ge : Hg detector are calculated from experimentally determined material parameters. In many cases wideband, quantum noise limited performance can be obtained only if substantial refrigeration capacity is available at detector operating temperature.
S. L. Kurtin, G. S. Picus, and C. J. Buczek, "Wideband Optical Heterodyne Performance of Extrinsic Photoconductive Infrared Radiation Detectors," Appl. Opt. 9, 1848-1853 (1970)