Direct exciton emission from atomically thin transition metal dichalcogenide heterostructures near the lifetime limit

Abstract

We demonstrate the reduction of the inhomogeneous linewidth of the free excitons in atomically thin transition metal dichalcogenides (TMDCs) MoSe2, WSe2 and MoS2 by encapsulation within few nanometre thick hBN. Encapsulation is shown to result in a significant reduction of the 10 K excitonic linewidths down to ∼3.5 meV for n-MoSe2, ∼5.0 meV for p-WSe2 and ∼4.8 meV for n-MoS2. Evidence is obtained that the hBN environment effectively lowers the Fermi level since the relative spectral weight shifts towards the neutral exciton emission in n-doped TMDCs and towards charged exciton emission in p-doped TMDCs. Moreover, we find that fully encapsulated MoS2 shows resolvable exciton and trion emission even after high power density excitation in contrast to non-encapsulated materials. Our findings suggest that encapsulation of mechanically exfoliated few-monolayer TMDCs within nanometre thick hBN dramatically enhances optical quality, producing ultra-narrow linewidths that approach the homogeneous limit.

Exciton physics and device application of two-dimensional transition metal dichalcogenide semiconductors

“…The measurement at low temperatures revealed a radiative lifetime of excitonic transitions of approximately 200 fs, corresponding to a linewidth of 3 meV for monolayer WSe2 on a sapphire substrate [61]. In hexagonal boron nitride (hBN) encapsulated samples PL linewidths down to 1.7 meV have been observed [62,63].…”

Tuning carrier concentration in a superacid treated MoS2 monolayer

“…This means, in particular, keeping the surface free from chemical residues and avoiding defects which can negatively affect the desired optical properties of S-TMD layers. Recently, it has been reported that encapsulation of S-TMD monolayers in hexagonal boron nitride leads to suppression of the inhomogeneous contribution to the linewidths of excitonic resonances [12][13][14][15] . Another approach to heal the surface of N -layer S-TMDs is to subject them to a specific chemical treatment.…”

Van der Waals solid phase epitaxy to grow large-area manganese-doped MoSe 2 few-layers on SiO 2 /Si

“…Mechanical exfoliation [9] is one of the most popular methods to produce monolayer flakes, and though it is possible to produce very high quality flakes in this manner, the samples remain very small (<10 µm for TMDCs). So far, the highest quality flakes are produced by mechanical exfoliation and subsequent encapsulation in hBN [10,11]. Typically, encapsulation leads to even smaller flake sizes and involves very long process.…”