Band Gap Determination of Copper Doped Tungsten Diselenide Single Crystals by Optical Absorption Method

Absorption spectrum of copper (Cu) doped WSe2 (% of Cu = 0.0, 0.5, 1.0) single crystals were obtained in the range 700 nm to 1450 nm. The energy gap and phonon energies were determined for the crystals from the spectrum using two and three dimensional models. This study reflects that indirect transition is dominant in these crystals. On the basis of three dimensional models it was not possible for us to decide whether the indirect inter-band transition is forbidden or allowed type. Hence, different plots were made for two dimensional models, which showed that indirect forbidden transition holds accurately for this sample whereas indirect allowed type transition is not valid. The phonon energies calculated for these samples corresponds to the energies associated with optical phonons. The obtained results are discussed in details in this paper.