Ferroelectric-Driven Exciton and Trion Modulation in Monolayer Molybdenum and Tungsten Diselenides

Abstract

In this work, we show how domain engineered lithium niobate can be used to selectively dope monolayer MoSe2 and WSe2 and demonstrate that these ferroelectric domains can significantly enhance or inhibit photoluminescence (PL) with the most dramatic modulation occurring at the heterojunction interface between two domains.A micro-PL and Raman system is used to obtain spatially resolved images of the differently doped transition metal dichalcogenides (TMDs). The domain inverted lithium niobate causes changes in the TMDs due to electrostatic doping as a result of the remnant polarization from the substrate. Moreover, the differently doped TMDs (ntype MoSe2 and p-type WSe2) exhibit opposite PL modulation. Distinct oppositely charged domains were obtained with a 9-fold PL enhancement for the same single MoSe2 sheet when adhered to the positive (P + ) and negative (P -) domains. This sharp PL modulation on the ferroelectric domain results from different free electron or hole concentrations in the materials conduction band or valence band. Moreover, excitons dissociate rapidly at the interface between the P + and Pdomains due to the built-in electric field. We are able to adjust the charge on the P + and Pdomains using temperature via the pyroelectric effect and observe rapid PL quenching over a narrow temperature range illustrating the observed PL modulation is electronic in nature. This observation creates an opportunity to harness the direct bandgap TMD 2D materials as an active optical component for the lithium niobate platform using domain engineering of the lithium niobate substrate to create optically active heterostructures that could be used for photodetectors or even electrically driven optical sources on-chip.

Polar coupling enabled nonlinear optical filtering at MoS2/ferroelectric heterointerfaces

“…5). Such modulation of PL spectra in TMDCs via neighboring ferroelectric domains has previously been attributed to the polarizationinduced doping effect 23,24 and confirms the close interfacial contact between MoS 2 and PZT in our samples. The relative strength of the modulation, however, can be affected by the interfacial charge screening condition for PZT 27 and thus depends on the preparation details of the composite structures (Supplementary Note 2) 26 .…”

“…When 2D TMDC is interfaced with a ferroelectric gate, the spontaneous ferroelectric polarization offers the unique opportunity to induce nonvolatile charge modulation in the channel [18][19][20] . Combining the polarization doping with nanoscale ferroelectric domain patterning further allows local tuning of the electronic [20][21][22] and optical properties [23][24][25] of the vdW channel layer. Beyond the charge-mediated interfacial coupling, synergy between the polar nature of TMDCs and ferroelectric has never been explored to date.…”

Valley depolarization in downconversion and upconversion emission of monolayer WS2 at room temperature

“…Recently, monolayer transition metal dichalcogenides (TMDCs) are found to be direct bandgap semiconductors with visible PL [10][11][12][13][14][15][16] and much higher quantum efficiency than traditional semiconductor materials [17,18], where solid dipoles of excitons dominate the optical properties due to strong Coulomb binding effect [19][20][21][22][23][24][25]. Benefiting from enhanced photon-exciton [26][27][28][29][30][31][32][33][34][35][36][37] and phonon-exciton interaction strength [38][39][40][41] in a low dimensional scale, as observed in graphene and V-V binary materials [42,43], TMDCs are viewed as one promising platform for exploring UC PL at the monolayer limit. And there are some research studies reporting the UC PL observed in monolayer TMDCs, for example, two-photon absorption-induced UC PL of B-exciton at 4 K [44] and phonon-mediated doubly resonant UC PL with an energy gain of 30 meV up to 250 K [45] in monolayer WSe 2 , as well as multiphonon-induced UC PL with an energy gain of 150 meV in monolayer WS 2 at room temperature [46].…”

Recent advances on hybrid integration of 2D materials on integrated optics platforms

“…Speaking of their optical properties, monolayer TMDs possess particularly strong photoluminescence, where the single-layer emission is more than three orders of magnitude brighter compared with that of the bulk [45,46]. Unlike the broadband optical absorption due to conductivity of graphene, the optical absorption of monolayer TMDs can reach ~10% from near infrared (NIR) to UV frequencies, which is mainly caused by the excitonic transitions [12,39].…”