Study of Exciton Dynamics in MoS2 Monolayer and MoS2-QD Heterostructure

Abstract

The recent studies of two-dimensional semiconductors (2D) and their hybrid structure with zero-dimensional (0D) semiconductors have led to discovering of many fascinating properties that are absent in their bulk counterparts. Here in this thesis, we have looked into two such systems, monolayer MoS2 (2D), CdSe Quantum Dots (0D), and their hybrid structures. We start with the optoelectronic study of monolayer MoS2 FET devices fabricated in the cleanroom. We studied the dynamics of excitons (electron-hole pair), which have high binding energy at room temperature using steady-state photoluminescence (PL) and time-resolved photoluminescence (TRPL) in these devices by controlling the carrier density using both electrical and surface treatment using dopant. We observed neutral and charged exciton(trions) dominant regimes in some specific carrier density. In the second part of my thesis, I studied the optical properties of 2D-0D (MoS2-QD) hybrid structures using PL and TRPL characterization at room temperature. The 2D-OD heterostructure is of particular interest in understanding the various nonradiative energy channels such as FRET. In MoS2-QD hetero-structure, we control the emission efficiency of core QDs using the surface treatment for QDs, which controls the inter-dot separation, δ, and the separations between MoS2 and QD, d. At larger separations, we observe quenching of QD PL due to non radiative processes. At smaller separations, we observe enhanced emission from QDs on MoS2 compared to the larger separations despite the presence of significant non-radiative charge transfer and FRET. We observe some signatures of possible resonant radiative energy exchange between the 0D excitons in QDs and the 2D exciton in MoS2