Low temperature carrier transport mechanism and photoconductivity of WSe2
This work reports the electrical transport and temperature-dependent photoconductivity in tungsten diselenide (WSe2) thin films. The electrical conductivity analysis shows the presence of the three regions with temperature variation. At lower temperatures (<190K), carriers become localized to small regions in the film due to the Mott hopping mechanism. The middle region (190 to 273 K) follows Seto parameters and obtained low barrier height (0.0873 eV) may be responsible for the improved carrier mobility. At higher temperature (>273K) region, thermally activated conduction is dominated with two activation energies of ~138 meV and 98 meV. The peaks obtained in photoluminescent analysis attributes to the presence of mid-bandgap states or defect states which play an important role in the photoconductivity of WSe2. The transient photoconductivity measurements show consistent temperature-dependent behaviour. The effect of light intensity and wavelength variation on the photoconductivity of WSe2 thin films is also discussed. The photocurrent is 1.19*10-5 A at 125 K while at 350 K it was observed to be 3.12*10-4 A. The light-on/off current cycles show that the current can recover to its initial state which points to the stable and outstanding reversible properties of the WSe2 thin film device to be used in photodetector applications.