Radiative and Non-Radiative Exciton Recombination Processes in a Chemical Vapor Deposition-Grown MoSe₂ Film

Abstract

In transition metal dichalcogenides (TMDs), defects and stress in thin films significantly affect the dynamic of exciton recombination. Here, we report that a MoSe 2 continuous film, grown on a SiO 2 /Si substrate by chemical vapor deposition (CVD), shows an exceptionally strong photoluminescence (PL) and a rather long lifetime (∼154 ns) at 6 K. However, when the film is transferred to another similar substrate, its PL intensity is remarkably reduced by almost 80. By analyzing temperaturedependent PL and time-resolved PL spectra for the as-grown and transferred films, it reveals that the strong PL of the as-grown MoSe 2 sample comes from the exciton recombination from the band tails. We believe that the tensile strain introduced during CVD growth can effectively suppress the non-radiative channels of the excitons in the localized band tails. Our studies demonstrate that the effect of defects and stress on the kinetics of exciton recombination in MoSe 2 is of great significance for the application of TMDs in optoelectronics.

Light-emitting devices based on atomically thin MoSe2

“…PL spectroscopy serves as a powerful characterization technique to investigate the exciton properties in 2D MoSe 2 . The excitonic emission behaviors of MoSe 2 can be modulated by changing the external physical conditions, such as temperature [48,49] , substrates [25, 50−52] , external physical fields [53−58] , and so on. [47] .…”

“…Godde et al investigated the effects of temperature on the X 0 and X * properties in 2D MoSe 2 by PL spectroscopy [48] : at a cryogenic temperature of 12 K, it is experimentally demonstrated that two distinct PL bands of X 0 peak at 1.658 eV and X * peak at 1.628 eV, respectively, in which the PL peak intensity of X * peak is significantly greater than that of X 0 peak due to the presence of carrier doping (Fig. 4(a)); the PL intensity of X 0 increases relative to X * peak with the increase in temperature.…”

“…5(d) can be observed, whose energies vary almost linearly at the high magnetic fields within the range of 15−30 T [56] . [48] . (b) Two pronounced PL peaks of monolayer MoSe 2 at 20 K: the higher-energy X 0 and the lower-energy X* at 1.659 and 1.63 eV, respectively.…”

Recent advances in molybdenum diselenide-based electrocatalysts: preparation and application in the hydrogen evolution reaction

“…Although the CVD method can effectively control the growth of atomically thin 2D materials such as MoSe 2 or MoS 2 , its detailed process is complicated and difficult to be monitored by in situ characterization and is not completely understood. In general, the optical properties of MoSe 2 characterized by near-field photoluminescence (PL), Raman, and X-ray photoelectron spectroscopy [80][81][82] can provide some pivotal information to explain the growth mechanism of MoSe 2 with heterogeneous morphology for further precisely controlling the growth process to obtain 2D materials with expected regular shape or special physicochemical property, and further reveal the correlation between morphology/surface structure and property of CVD-grown polycrystalline monolayer MoSe 2 as well as the key role of the substrate. When colloidal molybdenum nanoparticles (Mo NPs) prepared using a wet chemical method were spinning-coated onto graphite substrate and used as Mo precursor, the selenization of Mo NPs at different temperatures generated MoSe 2 film via the CVD approach.…”

Persistent room-temperature valley polarization in graphite-filtered WS2 monolayer

“…Interestingly, the intrinsic radiative decay time of initially hot excitons-which is in the range of ps or even sub-ps at high temperaturehas to be substituted with an effective radiative recombination time for thermalized excitons, that lies at the order of ns [15]. Following our experimental results characterized by long PL decay times, we consider four main factors that affect the PL dynamics: (i) effective exciton radiative recombination [15] (ii) bright-to-dark exciton conversion [31,32,37,38] (iii) exciton-exciton scattering [39,40] and (iv) nonradiative recombination [41,42]. Each of these factors is associated with a characteristic time that is properly chosen to fit the population of bright excitons, provided as solutions of the rate equations, to the PL data.…”