The Region of gallium solubility in lead telluride films grown on silicon substrates

This work is aimed at finding the boundaries of the region of the existence of the solid solutions of Ga in PbTe films prepared on Si substrates with the use of the modified “hot wall” technique. The quantitative results on the composition of the Pb1-y GayTe films with a thickness of more than 1 µm indicate that the gallium concentration yGa in our samples ranges from 0.0004 yGa 0.045, depending on the ratio of the partial pressures of the metallic components, which maybe specified by the temperature and composition of the Ga1–xPbx liquid melts. By varying the partial pressures of the metallic components and the chalcogen, we succeeded in synthesizing Pb1-yGayTe layers with a Te concentration ranging from 0.495 to 0.515 mol %. According to the results of a complex investigation with the use of X-ray diffraction, scan ning electron microscopy, and local X-ray spectrum analysis, the region of the existence of homogeneous Pb1 - y GaTe films is substantially narrower than the specified composition range: the limiting Ga concentration in these samples is no more than yGa = 0.011 ± 0.0005. It has been shown that the study of gallium solubility in PbTe should include not merely a quasi-binary PbTe-GaTe section, but also PbTe-Ga2Te3 and PbTe-Ga2Te5 polythermic sections. As indicated by the experimental data, the homogeneity region of the solid solutions of gallium in lead telluride is asymmetric with respect to the quasi-binary PbTe-GaTe section. It has been found that the deviation of the Pb1-yGayTe films from stoichiometry toward excessive concentration of tellurium promotes increased solubility of gallium in the lead telluride matrix.