Features of the real structure of doped PbTe crystals

T.A. Kuznetsova, O.I. Tananaeva, V.P. Zlomanov

Forth International Conference on Materials Science and Material properties for Infrared Optoelectronics (Kiyv, Ukraine, 1998), p. 163.

ABSTRACT. The real structure (dislocation density, inclusions, segregations, character of distribution of components) was studied in PbTe crystals doped with Cr, Co, Ni, and In. The relation between the real structure of crystals and the features of the T-x phase diagrams of the corresponding systems, doping level, and the rates of growth and cooling was established. Single crystals were grown by Bridgman and vapor-liquid-crystal methods. The conditions of growth from the melt were chosen from the T-x diagrams of PbTe--impurity telluride (Cr$_{0.47}$Te$_{0.53}$, Cr$_{0.55}$Te$_{0.45}$, CoTe, CoTe$_2$, Ni$_3$Te$_2$, NiTe$_2$, InTe, In$_2$Te$_3$) systems. All these diagrams belong to eutectic type with K>1. Tiller criterion was used to calculate the concentration range of stability of a crystallization surface during the crystal growth. The doping level in the source was varied over a wide range of 10-40 mol.% of impurity telluride. Growth rate was (2-4)*10^{-2} cm/hour. The crystals were cooled at a speed 10$^\circ$/hour in the switched-off furnace or air-quenched. The real structure were studied by the selective etching method and Auger electron spectroscopy. In general, crystals grown by vapor-liquid-crystal method had better quality of the real structure. When increasing the impurity concentration in crystals, the dislocation density decreased up to some minimum value (in the case of Cr$_{0.47}$Te$_{0.53}$ --- 1*10^4$ cm$^{-2}). The increase of the dislocation density at higher doping levels was due to occurrence of laminar segregations of the impurity telluride. Evidence of concentration recooling --- the dot and cellular structures --- were found in quenched material. At slow cooling rates these features were smoothed due to solid-phase diffusion. The work was supported by RFBR grant No. 96-03-32932.

Laboratory of Physics and Chemistry of Semiconductors