n–p transformation in TlBi(1−x)SbxTe2 system

TlBi(1−x)SbxTe2 quaternary crystals that crystallize in a rhombohedral structure and according to their properties are classified between semimetals and narrow energy gap semiconductors, are studied. The study of their optical and electrical behavior reveal that they are quite sensitive to the Sb content x, and it is found that the substitution of Bi- with Sb-atoms in TlBiTe2 crystals leads initially to a decrease in the plasma frequency. However, for higher Sb contents, the plasma frequency increases. At room temperature, samples with x < 0.8 are n-type semiconductors, becoming p-type ones for x > 0.8.A model suggesting a suppression of the free electron concentration induced by the incorporation of Sb atoms into the crystal lattice of TlBiTe2 is used to explain this transition in the conductivity type.