Excitonic Stark effect inMoS2monolayers

Abstract

We theoretically investigate excitons in MoS2 monolayers in an applied in-plane electric field. Tight-binding and Bethe-Salpeter equation calculations predict a quadratic Stark shift, of the order of a few meV for fields of 10 V/µm, in the linear absorption spectra. The spectral weight of the main exciton peaks decreases by a few percent with an increasing electric field due to the exciton field ionization into free carriers as reflected in the exciton wave functions. Subpicosecond exciton decay lifetimes at fields of a few tens of V/µm could be utilized in solar energy harvesting and photodetection. We find simple scaling relations of the exciton binding, radius, and oscillator strength with the dielectric environment and an electric field, which provides a path to engineering the MoS2 electro-optical response.

Two-dimensional excitons in monolayer transition metal dichalcogenides from radial equation and variational calculations

“…For monolayer MoS 2 encapsulated in h-BN (average dielectric constant ε=(5+5)/2=5), we find that the ground state energy shift deviates from the quadratic field dependence for fields F exceeding 15 V/µm (not shown), similar to the finding in Ref. [41]; at low field strengths, we obtain for the ground state exciton a polarizability of 2.1× 10 −17 eV(m/V) 2 , a value smaller than 3.5× 10 −17 eV(m/V) 2 given in Ref. [41] but larger than 1.4× 10 −17 eV(m/V) 2 reported in Ref.…”

“…With an electric field applied, clearly the 1s energy level is redshifted while the 2p level splits into two. Using second-order perturbation theory, we obtain an analytical expression for the energy shift of the ground state, δE 10 = −αF 2 /2, i.e., the second-order Stark effect, where α is the electric polarizability of the exciton [40,41],…”

“…[41] for comparison of the exciton energies), the polarizability of the ground state exciton increases to 1.1× 10 −17 eV(m/V) 2 , corresponding to an energy redshift of 2.3 meV at F =20 V/µm, close to the 3 meV redshift in Ref. [41]. For monolayer MoS 2 encapsulated in h-BN (average dielectric constant ε=(5+5)/2=5), we find that the ground state energy shift deviates from the quadratic field dependence for fields F exceeding 15 V/µm (not shown), similar to the finding in Ref.…”

Dynamic theory of nanophotonic control of two-dimensional semiconductor nonlinearities

“…We find binding energies of about 850 meV, due to the weak screening of the Coulomb interaction in these materials. Our values are comparable to theoretical calculations for MoS 2 using density functional theory (DFT) methods [45][46][47][48] . The energetic splitting between the A and B exciton with 0.15 meV reflects mostly the valence band splitting with ∆ v = 0.16 meV (with ∆ c = 0), while a small difference appears due to the different effective masses of the two valence bands.…”

“…In our model the exciton binding energies follow roughly the solution of the 2D Coulomb potential. Studies of the exciton series in TMDC monolayers is still a very active research field, because strong deviations from the Rydberg series were found 20,47 .…”