SPECIFIC ROLE OF IMPURITIES IN SEMIMETALS

We have shown that the Fermi energy dependence on temperature in semim etals keeps its well-known form, similar to that of semiconductors, do wn to T = 0. In the nearest vicinity of T = 0 this dependence is signi ficantly changed, and the Fermi level is displaced toward the top of t he valence band. The more different electron and hole effective masses in the model of the overlapped bands in semimetals are, the more suff icient is this displacement. We note the specific role of substitution al impurities in semimetals containing at least two atoms per elementa ry cell. Of particular interest is the case when an impurity is of don or type when it substitutes an atom in tile host elementary cell, and of acceptor type when it substitutes another atom. This phenomenon can be observed experimentally at low temperatures as oscillations of the kinetic coefficients as functions of the impurity concentration, if t he energies of the donor and acceptor levels are close to the Fermi en ergy. We present selected experimental data obtained in Bi, which exhi bit these oscillations.