The electrical and optical anisotropy of rhenium-dopedWSe2 single crystals

Abstract

Single crystals of rhenium-dopedWSe2 with large edge plane have been grown by the chemical vapour transport method usingbromine as the transporting agent. From the x-ray diffraction patterns, boththe doped and undoped crystals are found to crystallize in the 2H structure.The role of rhenium in affecting both the electrical and optical properties of theWSe2 crystals is examined.The thicker Re-doped WSe2 samples enable easier exploration of the electrical and optical anisotropiesof the materials both parallel and perpendicular to the crystalc-axis. The samples are n-type in nature from Hall measurements andthe conductivity anisotropy decreases drastically as a result of doping.Photovoltage measurements revealed that both undoped and Re-dopedWSe2 are indirect semiconductors. The indirect band gap of the doped sample showed considerable redshift compared with the undoped sample and also exhibited anisotropy along and perpendicular tothe c-axis. The anisotropy in the band gap is attributed to crystal anisotropy, which was alsostudied via the polarization-dependent electrolyte electroreflectance measurements takenalong the van der Waals plane (; ) and the as-grown edge plane (, ; ). The strong dependence of excitonic transitions A and B on polarization compared withthat of the undoped samples.