Carrier concentration gradient generated in p-type PbTe crystals by unidirectional solidification

The study was aimed at demonstrating the possibility of producing a graded charge carrier concentration in PbTe crystals by taking advantage of the concentration profile that is set up during solidification from a melt containing an excess of Te. This approach is based on the premise that the carrier concentration can be varied not only by doping with external impurity atoms but also by varying the relative concentration of the constituent elements. An excess of Te in the melt gives rise to crystals having a Pb vacancy (acceptor) concentration. Single PbTe crystals were grown by the Czochralski technique. Hall effect and electrical conductivity were studied in the 80-300K temperature range. The results showed that the carrier concentration increased from 1×10¹⁶cm^-3-5×10¹⁸ cm^-3 along the length of the 100mm long crystal. Nonetheless, in the present system, the various material constraints make it doubtful whether actual pre-designed carrier concentration gradients can be set up using this approach.