Percolation effect in copper- and nickel-doped Bi 2 Te 3 crystals

The (0001) surface morphology of Bi 2 Te 3 〈M〉 (M = Cu, Ni) layered crystals has been studied using atomic force microscopy (AFM) and scanning electron microscopy. Two- and three-dimensional AFM images reveal charge transport paths through inhomogeneities created by nanostructured elements (5–20 nm) in the Te(1)-Te(1) interlayer spaces. The nanoparticle distribution in the (0001) plane is similar to the arrangement of model two-dimensional percolation clusters on a square lattice. The carrier mobility in Bi 2 Te 3 〈0.5 wt % Ni〉 crystals varies anomalously between 80 and 120 K.