Study of PbTe optical coatings

The properties of PbTe evaporable materials and deposited coatings are investigated experimentally. It is shown that the structural and optical characteristics of PbTe layers deposited from a given starting material are largely determined by the substrate temperature and the deposition rate. However, the characteristics of the starting PbTe material strongly influence the properties of the deposited layers and determine the precise way in which they vary with the substrate temperature during deposition. By using a certain kind of Te dopant, a 'mild' variety of PbTe has been obtained in which the balance between Pb and Te is maintained over a wide substrate temperature range and the concentration of free carriers is 25-40 times lower than in conventional PdTe material. The effect of ZnS and ZnSe on the properties of PbTe layers is discussed.