Segregation of the Eu impurity as function of its concentration in the melt for growing of the lead telluride doped crystals by the Bridgman method

Behaviour of a rare earth impurity of Eu in the PbTe single crystals grown by the Bridgman method from the melt with different initial concentrations of impurity N about 1*10+19 cm-3 and less is investigated with X-ray fluorescent element analysis, Secondary Neutral Mass Spectroscopy (SNMS), and magnetic measurements. The impurity distributions along and across the doped ingots are established. It is revealed that doping impurity enters into the bulk of doped crystals only if its initial concentration in the melt is high enough, approximately 1*10+20 cm-3. If this concentration is lower, about 1*10+19 cm-3 and less, the doping Eu impurity is pushed out onto the surface of doped ingot. The thickness of the doped surface layer is estimated to be in the order of several microns or somewhat more. The longitudinal distributions of Eu impurity along the axis of doped ingot for N=1*10+20 cm-3, as well as the transverse one in the surface layer where entire doping impurity is pushed out for N=1*10+19 cm-3, are strongly non-monotonic. Possible reasons for this unusual behaviour of Eu doping impurity during the growth of PbTe:Eu crystals from the melt are analyzed.