Influence of Substrate-Induced Charge Doping on Defect-Related Excitonic Emission in Monolayer MoS₂

Many applications of transition metal dichalcogenides (TMDs) involve transfer to functional substrates that can strongly impact their optical and electronic properties. We investigate the impact that substrate interactions have on free carrier densities and defect-related excitonic (X^D) emission from MoS₂ monolayers grown by metal-organic chemical vapor deposition. C-plane sapphire substrates mimic common hydroxyl-terminated substrates. We demonstrate that transferring MoS₂ monolayers to pristine c-plane sapphire dramatically increases the free electron density within MoS₂ layers, quenches X^D emission, and accelerates exciton recombination at the optical band edge. In contrast, transferring MoS₂ monolayers onto inert hexagonal boron nitride (h-BN) has no measurable influence on these properties. Our findings demonstrate the promise of utilizing substrate engineering to control charge doping interactions and to quench broad X^D background emission features that can influence the purity of single photon emitters in TMDs being developed for quantum photonic applications.