Exciton binding energy and hydrogenic Rydberg series in layered ReS2

Abstract

Unlike monolayers of transition metal dichalcogenides such as MoS2, which possess high in-plane symmetry, layered ReS2 exhibits reduced in-plane crystal symmetry with a distorted 1 T structure. This unique symmetry leads to anisotropic optical properties, very promising for light polarization devices. Here, we report on low temperature polarization-resolved emission and absorption measurements of excitons in ReS2 from bulk to monolayer. In photoluminescence and reflectivity contrast spectra we distinguish two strongly polarized excitons X1 and X2 with dipole vectors along different crystal directions, which persist from bulk down to monolayer. Basing on the PL and RC spectra of bulk crystals we determine the energy of the ground and first four excited states of both excitons, which follow the usual hydrogenic Rydberg series of energy levels of 3D excitonic states (En = Ry*/n2). From the numerical fit we estimate that the energy gap is direct and equal to 1671.7 meV and binding energy of X1 and X2 is equal to 117.5 and 86.6 meV, respectively. In magneto-PL spectra of bulk ReS2 up to B = 10 T, the energy shift of all the states is below 2 meV. On reducing the crystal thickness from bulk to monolayer the ground state experience a strong blue shift.

The optical signature of few-layer ReSe2

“…This strongly suggests that the origin of these two investigated transitions is the same in both the emission and absorption measurements. Analogous low-temperature PL spectra were measured on thin layers of ReS 2 24 . Those spectra also comprise two well-defined peaks.…”

Stacking‐Order‐Driven Optical Properties and Carrier Dynamics in ReS2

“…[16] The uniqueness of ReS2 lies in its in-plane anisotropic properties, which have been demonstrated as early as 2001 in bulk. [9] In 2D ReS2, properties observed are polarizationdependent excitons, [17,18] non-linear absorption, [19] electron transport and SHG emission, [20,21] etc. Compared with black phosphorous (BP), which also shows in-plane anisotropic properties, ReS2 is more stable in ambient environments, which makes it more suitable for optoelectronic devices.…”

ReS2 Charge Trapping Synaptic Device for Face Recognition Application

“…However, ReS 2 within ten layers are all considered to have a direct bandgap [11], which means ReS 2 within ten layers can all perform well. Besides, the asymmetric lattice structure leads to weaker interlayer coupling energy, which benefits the exfoliation work, and thus makes the synaptic device much easier to fabricate [12][13][14][15]. In this study, ReS 2 film is used as a channel material.…”