ABSTRACT
The first infrared photoconductor of high responsivity was developed by Case in 1917. He discovered that a substance composed of thallium and sulfur exhibited photoconductivity.10 Later he found that the addition of oxygen greatly enhanced the response.11 However, instability of resistance in the pres ence of light or polarizing voltage, loss of responsivity due to over-exposure to light, high noise, sluggish response and lack of reproducibility seemed to be inherent weaknesses. Since about 1930 the development of IR technology has been dominated by the photon detectors. In about 1930, the appearance of the Cs-O-Ag phototube, with more stable characteristics, to a great extent dis couraged further development of photoconductive cells until about 1940.
