Low temperature carrier transport mechanism and photoconductivity of WSe2

TL;DR

This study investigates the temperature-dependent electrical transport and photoconductivity in WSe2 thin films, revealing distinct conduction mechanisms across temperature ranges and demonstrating stable photodetector performance.

Contribution

It provides a detailed analysis of conduction mechanisms in WSe2 across temperatures and explores its potential for stable photodetector applications.

Findings

Carrier localization at low temperatures due to Mott hopping

Low barrier height enhances carrier mobility between 190-273 K

Photocurrent increases with temperature, indicating effective photoconductivity

Abstract

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.