Photoconductivity of WSe₂ layers deposited on mica and (0001) Sapphire with pulsed laser ablation

Refractory metal dichalcogenides of the van der Waals family have attracted much attention in recent years due to their novel electro-photonic properties that emanate from a direct bandgap and large exciton energy. Here we describe preparation of WSe₂ thin films on mica and c-plane sapphire substrates with pulsed laser ablation of a meltcast target of WSe_2.2. By precisely controlling the deposition rate per laser pulse and growth temperature we have successfully deposited WSe₂ films of thickness ranging from a few monolayers to several tens of monolayer. Raman spectroscopy of these films reveals characteristic vibrational modes corresponding to the 2H structure of WSe₂. We have also measured the photoconductivity response (PCR) of our films with laser excitations of wavelength 405, 532 and 915 nm. A robust PCR is seen in thicker films whereas the photo response of the thinner films is dominated by thermal effects. We have successfully modelled these data to separate out the contributions of thermal effects and the change in conductivity due to photoexcitation of carriers across the bandgap. Details of this analysis will be presented at the meeting.