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 μh∼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 μn∼100 cm2/V·sec at 295°K.