Formation reactions of PbTe thin film deposition by close-spaced vapor transport (CSVT) technique

A study of the deposition reactions of PbTe thin films on soda lime glass substrate by close-spaced vapor transport (CSVT), using PbTe crystal, pellets or powder as source material and iodine as transport reagent, has been conducted. Based on the study of the thermodynamic properties of PbTe, of iodide compounds involved in the process, like PbI, PbI 2 and PbI 4, and the experimental conditions, different reversible reactions have been considered to explain the final composition of the thin films obtained. The mole fraction yield of solid compounds deposited (PbTe, PbI 2, Pb, Te, I 2) can be deduced at equilibrium from these reactions as a maximum value, taking into account the experimental thermodynamics parameters. On the experimental side, the thin films grown in various operational conditions have been characterized by X-ray diffraction, EDS and SEM. For optimal operational conditions: source temperature T so (540°C), substrate temperature T su (490°C), distance between source and substrate l (0.1 cm) and time of deposition t (10 minutes) we have obtained PbTe thin films free of iodide. For experimental conditions very different from the optimal conditions, especially at lower substrate temperatures, the films are dominated by the presence of PbI 2.