P -type Bi2 Se3 for topological insulator and low-temperature thermoelectric applications

The growth and elementary properties of p -type Bi2 Se3 single crystals are reported. Based on a hypothesis about the defect chemistry of Bi2 Se3, the p -type behavior has been induced through low-level substitutions (1% or less) of Ca for Bi. Scanning tunneling microscopy is employed to image the defects and establish their charge. Tunneling and angle-resolved photoemission spectra show that the Fermi level has been lowered into the valence band by about 400 meV in Bi1.98 Ca0.02 Se3 relative to the n -type material. p -type single crystals with ab -plane Seebeck coefficients of +180 μV/K at room temperature are reported. These crystals show an anomalous peak in the Seebeck coefficient at low temperatures, reaching +120 μV K-1 at 7 K, giving them a high thermoelectric power factor at low temperatures. In addition to its interesting thermoelectric properties, p -type Bi2 Se3 is of substantial interest for studies of technologies and phenomena proposed for topological insulators.