Quantitative Understanding of the Photoluminescence Modulation and Doping of Monolayer WS<sub>2</sub> by Heterostructuring with Non-van der Waals 2D Bi<sub>2</sub>O<sub>2</sub>Se Quantum Dots
Abhilasha Bora, Sumana Paul, Md Tarik Hossain, P. K. Giri
Abstract
Heterostructures (HS) of van der Waals two-dimensional (2D) semiconductors with non-van der Waals 2D semiconductors can be an exciting avenue for exploring their innovative optoelectronic applications. Neutral and charged exciton dynamics play a significant role in understanding the optical interband transitions in two-dimensional monolayer transition-metal dichalcogenides (TMDs). We investigate the effect of non-van der Waals 2D Bi2O2Se quantum dot (QDs) decoration on the monolayer WS2 (1L-WS2) film grown using chemical vapor deposition (CVD). The high photoluminescence (PL) emission of 1L-WS2 gets systematically quenched on the variation of the concentration of the QDs. We study the associated charge transfer dynamics in the system using a four-energy-level model. The PL measurements at different QD concentrations show that the exciton decay becomes faster as the concentration increases. Likewise, the trion formation rate increases. The trion decay involves trapping by defect states, which plays a vital role in the coupled charge transfer. Thus, the evolution of the emission features of 1L-WS2 in the heterostructure (HS) is attributed to the conversion of neutral excitons to negatively charged trions via electron transfer from the Bi2O2Se QDs. The simulation based on a set of decay rate equations replicates the experimental data for different concentrations of QDs. The 1L-WS2 becomes n-type doped, with an increase in the electron density by ∼6.6 × 1013 cm–2. The charge transfer from Bi2O2Se to WS2 due to the type II band alignment is confirmed by Kelvin probe force microscopy (KPFM). The study lays out a suitable approach to tune the optical properties of 1L-WS2 by doping using QDs. The charge transfer potentially enables researchers further to study the fundamentals of light–matter interaction at nanoscale heterostructures.