Influence of doping and substrate type on the metastable phase growth in pulsed-laser evaporated PbTe films

PbTe films, undoped and doped with 0.02, 0.3 mol% Cr and 0.02 mol % Co, grown by pulsed-laser evaporation (PLE) on different types of substrates have been investigated. The crystal structure of the films was studied by X-ray diffraction. Along with the stable fee phase, metastable GeS- and CsCl-type phases of PbTe were detected in the films. The growth of the metastable phases as well as the influence of the substrate type and temperature and the doping on the growth have been analyzed in the framework of the classical thermodynamic theory of crystallization. It was found that the influence of doping consists in the change of the surface free energy of the deposited material, while the substrate-type influence depends on its linear thermal expansion coefficient-when it is equal to that of the deposited compound the substrate stimulates the growth of the metastable phases. It is concluded that the growth mechanism is graphoepitaxy.