Reduction of bulk carrier concentration in Bridgman-grown Bi2Se3 topological insulator by crystallization with Se excess and Ca doping

•Doping with Ca and crystallization with Se excess is applied to reduce carrier concentration in Bi2Se3.•Reduction of the electron concentration down to 1017 cm−3 is achieved.•Hole concentration up to 1018 cm−3 is achieved.•Large single-crystalline grains up to about 1 cm2×10 cm are obtained.•It is necessary to compromise between a low carrier concentration and a good crystal morphology.

Bismuth selenide topological insulator with a lowered bulk carrier concentration was grown by the vertical Bridgman method from stoichiometric or non-stoichiometric melt, both with and without calcium doping. Limits for the reduction of the carrier concentration were investigated. The non-stoichiometric growth allowed to reduce the room-temperature electron concentration from ~1019 cm−3 to ~1017 cm−3. The increase of the selenium-to-bismuth ratio led to a phase separation and formation of metallic selenium precipitates within the van der Waals gaps. Crystallization from the selenium-rich melt with calcium acceptor added allowed for a further donor compensation and obtaining of p-type material. The lowest hole concentration achieved was 1×1018 cm−3. It was thus shown that it is necessary to compromise between a low carrier concentration and a good crystal morphology—the electron concentration of 2×1018 cm−3 constitutes a limit below which precipitation of Se occurs in the growth from Se-rich melt. The case of p-type doping requires both adding the Ca acceptor and performing crystallization from non-stoichiometric melt, which is associated with the occurrence of precipitates of foreign phases.