Defects and high bulk resistivities in the Bi-rich tetradymite topological insulator Bi2+xTe2-xSe

Defects in the topological insulator Bi2Te2Se are studied by scanning tunneling microscopy. Small numbers of Te-Bi antisite defects are found and are postulated to be the origin of n-type carriers in this tetradymite composition near the n-to-p crossover. Based on this defect chemistry, we design an alternative method for obtaining resistive Bi2+xTe2-xSe samples, by the introduction of compensating p-type carriers through BiTe antisite defects induced by making the material slightly Bi rich. Our resistivity and Hall coefficient measurements of Bi2+xTe2-xSe crystals grown by the Bridgeman-Stockbarger method show that the carrier concentration at base temperature is significantly reduced from that of stoichiometric samples. Analysis of the measurements reveals the possible underlying chemical distribution along the boules during growth.