Role of defect states in hopping transport and photoconductivity properties of WSe2-FeS2 nanocomposite thin films

Abstract

Transition metal dichalcogenides (TMDs) are one of the promising materials in the field of electronics and optoelectronics. The multifunctional TMD based nanocomposites such as WSe 2 -FeS 2 can also become a potential candidate for these applications. In this work, WSe 2 -FeS 2 nanocomposite thin films have been fabricated and studied for electrical transport and photoconductivity studies for the first time. Structural and optical analysis has been done, probing nanocomposite formation and defect states present in the deposited film. XPS analysis of WSe 2 -FeS 2 shows solid interfacial bonding in the deposited films. Raman analysis shows the presence of E 1 2 g mode for WSe 2 and E g , A g , T g modes for FeS 2 and shift in Raman peaks corresponds to the disorder in the film. Also, the blue (red) shift of FeS 2 (WSe 2 ) PL emission probes the presence of defect/trap states. Temperature-dependent (173–350 K) resistivity results reveal the presence of more than one type of carrier transport mechanism - thermally activated conduction and hopping transport. The chalcogenide vacancies in WSe 2 -FeS 2 affect the formation of trap states responsible for forming localized states. These localized states play a crucial role in the variable range hopping conduction at low temperatures. Whereas photoconductivity study yields a non-significant effect of light on photocurrent due to entrapment of carriers in trap states up to 250 K. Afterwards, a significant photocurrent increase was observed. The detailed mechanism considering all these aspects is explained in this work. It provides substantial new understandings for the carrier transport in WSe 2 -FeS 2 nanocomposite thin films. • Structural, morphological and optical analysis of WSe 2 - FeS 2 nanocomposite thin films. • Temperature dependent carrier transport studies by thermally activated and hopping conduction mechanism. • Persistent photoconductivity in WSe 2 - FeS 2 nanocomposite film due to entrapment of carriers in mid band gap trap states.