Semiconducting Properties of Single Crystals of n- and p-Type Tungsten Diselenide (WSe2)

The optical absorption, photoconductivity, contact photovoltage, electrical conductivity, and Hall coefficient of single crystals of WSe₂ have been studied over the temperature range 77°-295°K. It was found that the forbidden energy gap Eg was 1.35 eV at 295°K and that the temperature dependence of Eg was given by dEg/dT=-4.6×10^-4 eV/°K. The material as grown by iodine vapor transport in a sealed ampule is p-type with hole mobility μ_h∼80 cm²/V.sec and p∼10¹⁶/cc at 295°K. The carrier concentration could be reduced by pumping out excess selenium. Doping with rhenium during the crystal growth process resulted in n-WSe₂ with a carrier concentration n∼10¹⁷/cc and electron mobility μ_n∼100 cm²/V.sec at 295°K.