Optical Properties of Lead Telluride

Optical constants of lead telluride films as a function of both temperature and oxygen content have been investigated. The films were evaporated onto sapphire disks subsequently exposed to air and also on sapphire disks maintained at pressures lower than 10^-6 mm of Hg. Film thickness, determined by Tolansky interference techniques and by weighing techniques, indicated that the density of evaporated layers of PbTe is about 10 percent smaller than for bulk. The optical constants were calculated from the reflection and transmission curves of the film. The addition of oxygen to the film was shown to give rise to an increase in absorption and a slight increase in the index of refraction. The optical properties were then shown to be strongly dependent on the temperature of the film. A mechanism has been proposed to explain the results.