High-Sensitivity Crystal Infrared Detectors*

Germanium infrared detectors are cut from a large zone leveled crystal. Compensation with antimony donors is used to obtain n-type material. The gold-antimony doped detectors have a long wavelength cutoff at 6 microns and a photoconductive time constant which is dependent on the wavelength of the incident radiation. A table is given which shows the sensitivity characteristics of a number of these detectors. Indium antimonide detectors have been made with sensitivities comparable to those of the gold-doped germanium. The indium antimonide detector is made either by alloying or diffusing a thin layer of impurities into the surface layer of a single crystal of material. Cadmium is presently being used, giving a thin p-type surface on n-type indium antimonide. If light is allowed to fall on the front surface of the alloyed material, a photovoltage may be measured between the n and p parts of the detector. The cutoff wavelength for this type of detector when cooled to liquid nitrogen temperature also is of the order of 6 microns.A comparison is made between the characteristics of the two types of cells and a description is given of a multiple contact cell which can locate a target as well as detect it. A section is included on the standard measuring techniques used in evaluating infrared detectors.