p -type Bi 2 Se 3 for topological insulator and low-temperature thermoelectric applications

The growth and elementary properties of $p$-type ${\text{Bi}}_{2}{\text{Se}}_{3}$ single crystals are reported. Based on a hypothesis about the defect chemistry of ${\text{Bi}}_{2}{\text{Se}}_{3}$, 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 ${\text{Bi}}_{1.98}{\text{Ca}}_{0.02}{\text{Se}}_{3}$ relative to the $n$-type material. $p$-type single crystals with $ab$-plane Seebeck coefficients of $+180\text{…