On Fermi level pinning in lead telluride based alloys doped with mixed valence impurities

The galvanomagnetic (4.2≤T≤300 K, B≤0.1 T) properties of n-Pb1−yMnyTe (0.07≤y≤0.11) and n-Pb1−xGexTe (0.04≤x≤0.08) doped with In and Ga (CIn≈0.5 mol%, CGa≈1.5–2 mol%, respectively) before and after the irradiation with fast electron (E=6 MeV, Φ≤1.85×1017 cm−2) have been investigated. Impurity-induced deep levels EIn and EGa were observed in the alloys studied. Their energy position was determined and the energy level diagrams as a function of alloy composition were constructed. It was found that the electron irradiation has nearly no effect on the properties of Pb1−yMnyTe〈In〉, while in Pb1−xGexTe〈Ga〉 it causes a transition to metal-type conductivity. It was concluded that the gallium-induced level EGa, unlike the level EIn does not stabilize the Fermi level in PbTe based alloys.