High-spin configuration of Mn in Bi2Se3 three-dimensional topological insulator

Electron paramagnetic resonance was used to investigate Mn impurity in Bi2Se3 topological insulator grown by the vertical Bridgman method. Mn in high-spin S=5/2, Mn2+, configuration was detected regardless of the conductivity type of the host material. This means that Mn2+(d5) energy level is located within the valence band, and Mn1+(d6) energy level is outside the energy gap of Bi2Se3. The electron paramagnetic resonance spectrum of Mn2+ in Bi2Se3 is characterized by the isotropic g-factor |g|=1.91 and large axial parameter D=−4.20 GHz h. This corresponds to the zero-field splitting of the Kramers doublets equal to 8.4 GHz h and 16.8 GHz h, respectively, which is comparable to the Zeeman splitting for the X-band. Mn in Bi2Se3 acts as an acceptor, effectively reducing native-high electron concentration, compensating selenium vacancies, and resulting in p-type conductivity. However, Mn-doping simultaneously favors formation of native donor defects, most probably selenium vacancies. For high Mn-doping it may lead to the resultant n-type conductivity related with strong non-stoichiometry and degradation of the crystal structure - switching from Bi2Se3 to BiSe phase.