Engineering Light Outcoupling in 2D Materials

Abstract

When light is incident on 2D transition metal dichalcogenides (TMDCs), it engages in multiple reflections within underlying substrates, producing interferences that lead to enhancement or attenuation of the incoming and outgoing strength of light. Here, we report a simple method to engineer the light outcoupling in semiconducting TMDCs by modulating their dielectric surroundings. We show that by modulating the thicknesses of underlying substrates and capping layers, the interference caused by substrate can significantly enhance the light absorption and emission of WSe2, resulting in a ∼11 times increase in Raman signal and a ∼30 times increase in the photoluminescence (PL) intensity of WSe2. On the basis of the interference model, we also propose a strategy to control the photonic and optoelectronic properties of thin-layer WSe2. This work demonstrates the utilization of outcoupling engineering in 2D materials and offers a new route toward the realization of novel optoelectronic devices, such as 2D LEDs and solar cells.

High Luminescence Efficiency in MoS2 Grown by Chemical Vapor Deposition

“…For samples measured on Si/SiO 2 substrates (not transferred), the external quantum efficiency was also corrected for using a previously reported multiple reflection model. 30 Time-resolved measurements were performed using pulsed light at 10 MHz generated by a supercontinuum laser (Fianium WhiteLase SC-400). A wavelength of 514 nm was selected using a double monochromator and focused on the sample using an 80× objective lens (NA = 0.9).…”

Excitonic Linewidth Approaching the Homogeneous Limit in MoS2 -Based van der Waals Heterostructures

“…In contrast, the typical spectrum of a MoS 2 ML deposited directly onto the SiO 2 substrate (black curve) exhibits a very large and broad defect-related emission followed by charged exciton (trion) emission (FWHM 38 meV) and a neutral exciton emission (FWHM 16 meV) [56] whose intensity drops dramatically after a few minutes of laser exposure due to laser-induced doping of these MLs [40] (here, the spectrum was recorded within the first 0.5 sec following laser exposure). The intensity stemming from the neutral exciton in our hBN-protected samples is at least 1 order of magnitude higher than in unprotected ones; for a fully quantitative comparison cavity effects need to be taken into account [57].…”

Engineering light emission of two-dimensional materials in both the weak and strong coupling regimes

“…Such environmental-induced effects have also been observed for the G and 2D Raman signals of graphene [29][30][31] and the Raman modes of TMDs [32][33][34], as summarized in Figures S5 and S6 (see Supplementary Information). Again, the MST accurately accounts for the Raman intensities of the G and 2D modes of SL graphene ( Figure S5a) and the A 1g and E mode measured in MoS 2 nanoflakes of different thicknesses supported on SiO 2 /Si substrates, as extracted from Ref.…”

“…Compared to the minimum PL intensity at ~230 nm SiO 2 , there is a ~30-fold increase Results shown in Figure 3A and B evidence the already reported effects of substrate-related optical interference in the PL signals of 2D materials. The origin of such interference effects has been extensively discussed in several 2D systems on the basis of the interference model [32][33][34]. Within this model and assuming that the PL emission intensity is proportional to the excitation (absorption), the resulting modulation of light emission can be understood as the combination of the optical interference produced in both excitation and emission processes due to the multiple reflections within underlying substrates.…”

“…Finally, another intuitive approach used to optically tune the incoupling and outcoupling of light in atomically thin 2D materials has been the modification of their dielectric surroundings. In fact, the Raman signals of graphene [29][30][31] and 2D TMDs [32][33][34], as well as the PL signals of 2D TMDs [33,34], have revealed a strong intensity dependence on the thickness of the underlying silicon dioxide (SiO 2 ) layer of Si/SiO 2 substrates, due to substrate-related optical interference effects.…”