Trap states induced hopping transport and persistent photoconductivity in WSe2/MoS2 nanocomposite thin films

Abstract

In this work, temperature-dependent electrical transport and photoconductivity studies of WSe2/MoS2 nanocomposite thin films have been analyzed. An n-type semiconductor film of ≈150 nm with a carrier concentration of ≈1023cm−3 is prepared by a thermal evaporation technique. Temperature-dependent (150–350 K) conductivity results present more than one type of carrier transport mechanisms. Trap states from chalcogenide vacancies in WSe2/MoS2 play an important role in the formation of localized states. The electrical conductivity of the composite conforms to Mott’s variable range-hopping model due to these localized states in the temperature range of 150–250 K. Nearest-neighbor hopping and a thermally activated conduction mechanism are responsible for electrical transport in the higher temperature range. The role of defect/trap states and random local potential fluctuations in persistent photoconductivity has also been studied. Also, the effect of vacuum and air atmosphere shows that acceptor states resulting from incorporation of oxygen in sulfur vacancies results in more photocurrent in air than vacuum. The results deepen the understanding of the conduction mechanism in such multifunctional transition-metal dichalcogenide based nanocomposites.