Trion Binding Energy Variation on Photoluminescence Excitation Energy and Power during Direct to Indirect Bandgap Crossover in Monolayer and Few-Layer MoS₂

Abstract

The behavior of the trion and exciton photoluminescence (PL) under various laser excitation conditions, that is, energy and power, is studied in monolayer and few-layer (FL) chemical vapor deposition (CVD)-MoS2 flakes grown on SiO2/Si. The room-temperature μ-PL spectroscopy of the flakes shows that the A exciton at 1.86 eV is overlapped by the trion component. First, the thickness-dependent characterization of the flakes has been carried out. The trion spectral weight and dissociation energy are observed to increase with the number of layers, which is correlated with an increase in nonequilibrium electron density. We propose the presence of many-body effects explaining this unusual dependence in CVD-MoS2 on n-type SiO2/Si. In the power-dependent μ-PL measurements, the deconvolution of spectra for the exciton and trion bands shows a faster intensification of the trion component compared to the A exciton with increasing laser power. The trion binding (dissociation) energy varied from 28 to 33 meV in the monolayer and from 32 to 46 meV in FL MoS2, when increasing the power of excitation light. The phenomenon is found to be more prominent when increasing the energy of excitation from 2.33 to 3.06 eV. The enhancement of the trion binding energy leads to a strong intensification of the trion component. Thereby, the intense A exciton/trion PL band redshifts and becomes more asymmetric when increasing the power of excitation at both energies of 2.33 or 3.06 eV. Simultaneously, the B exciton contribution to the spectrum also increases. Such an enhanced formation of the trions and B excitons is explained by a rate of photogenerated electron–hole pairs, leading to a higher population of nonequilibrium electrons. In the measurements under a higher excitation energy of 3.06 eV, the PL redshift is more prominent because the trion component is more intense compared to the A band. This is explained by considering a higher absorption of MoS2 at higher energies.

Different healing characteristics of thiol-bearing molecules on CVD-grown MoS2

“…The as-grown sample is characterized by a strong A − peak, typical of single-layer MoS 2 on SiO 2 /Si [38]. The presence of an intense trion peak (A − ) in fact is related to the excitation power of the laser light employed for the measurements, as explained by Golovynskyi et al [39] for experimental condition comparable with ours. Besides this, there is also a strong D peak due to the presence of MoO 3 precursor residuals, in agreement with the XPS analysis discussed above, while the contribution of the A 0 and B peaks is almost negligible.…”

Electrically Tunable Localized versus Delocalized Intralayer Moiré Excitons and Trions in a Twisted MoS2 Bilayer

“…The separation between X I and T II is about ∼5–7 meV higher than that between X II and T I indicating a stronger trion binding energy with the moiré trapped exciton. X II –T I is about ∼30 meV (see Figure S9), similar to the trion binding energy in 1L-MoS 2 . , …”

Quantitatively Deciphering Electronic Properties of Defects at Atomically Thin Transition-Metal Dichalcogenides

“…Note that the A − /A value may change when the incident laser power is high. 50 Fortunately, the laser power used in our measurement is mild, which will not obviously influence the ratio (see Supporting Information for details).…”

“…In fact, our TEPL measurements reveal a higher A – / A ratio, indicating a higher n e (5.0 × 10 13 cm –2 ) at the wrinkle compared with that at the basal plane (3.2 × 10 13 cm –2 ) (see Table S1). Note that the A – / A value may change when the incident laser power is high . Fortunately, the laser power used in our measurement is mild, which will not obviously influence the ratio (see Supporting Information for details).…”