Preparation and characterization of large niobium-doped MoSe2 single crystals

Chemical vapor transport (CVT) process with bromine as a transporting agent has been utilized for growing large-size MoSe2 single crystals by adding niobium dopant (nominal concentration ∼0.5%) during the growth process. The maximum-size crystals are about 10×10 mm2 in surface area and 2 mm in thickness. The large edge plane facilitates an easier study of the influence of crystal anisotropy on the electrical and optical properties of the layered crystals. Anisotropy of the conductivity and indirect band gap parallel and perpendicular to the crystal c-axis due to the interlayer van der Waals interaction and red shift of the indirect and direct band gaps due to doping have been measured. It is found that the electrical and optical properties of niobium-doped MoSe2 are almost similar to those of the pure MoSe2 single crystal apart from a drastic reduction in the conductivity anisotropy and red shift of the band gap.