Exciton Properties Of Thin MoS₂ Films

Transition metal dichalcogenides as a family member of layered semiconductors have been a subject of intense research mainly due to its outstanding optoelectronic properties in thin films.Molybdenum disulfide is a typical member of transition metal dichalcogenides.Flourescence in MoS2 results from radiative recombination of excitons,therefore,it is important to research the effect of dielectric environment and layer number on exciton properties of single-and few-layer MoS2.In this work,we studied the Raman and Flourescence spectrum of single-,few-layer and bulk MoS2 on SiO2,Si3N4 and Al2O3 substrates.MoS2 thin films on SiO2 substrate are obtained by mechanical exfoliation and are transferred to Si3N4 and Al2O3 substrate by using PMMA.We analyzed the vibration mode of the four peaks in Raman strctrum and determined the relationship of their peak position and substrate.As for flourescence spectrum,we obtained the transition energy of excitons by peak fitting.We calculated the binding energy of excitons and studied the impact of layer number and dielectric environment on exciton binding energy.At last,we quantitatively determined the the expression of exciton peak intensity and dielectric constant,and explained the expression by analyzing the impact of dielectric screening.