Acoustic phonon assisted free-carrier optical absorption in an n-type monolayer MoS2 and other transition-metal dichalcogenides

Abstract

The theory of free-carrier absorption (FCA) is given for monolayers of transition-metal dichalcogenides, particularly for molybdenum disulphide (MoS2), when carriers are scattered by phonons. Explicit expressions for the absorption coefficient α are obtained and discussed for acoustic phonon scattering via screened deformation potential and piezoelectric coupling taking polarization of the radiation in the plane of the layer. It is found that α monotonously decreases with the increasing photon frequency Ω, increases with the increasing temperature T, and linearly depends on two-dimensional electron concentration ns. Effect of screening, which is ignored in all the earlier FCA studies, is found to reduce α significantly, attributing to the larger effective mass of the electrons. Results are also obtained in the classical and quantum limit giving the power laws α ∼ Ω−2 and T. Comparison of the results is made with those in bulk semiconductors and semiconductor quantum wells.

Magneto-optical transport properties of monolayer MoS2 on polar substrates

“…When MoS 2 is situated on a substrate, carriers couple with three different types of phonons: intrinsic MoS 2 acoustic and optical phonons [7,[37][38][39], and SO phonons induced by polar substrates [42,67]. In the following, the analytic expressions for MOAC are determined when the carriers are assumed to interact with these three different types of phonons.…”

“…For intrinsic MoS 2 acoustic (AP) and optical (OP) phonons, the carrier-phonon coupling matrix element is given by [39] g λ q,ν…”

“…where e 11 is the piezoelectric constant, erfc(x) is the complementary error function, σ is the effective width of the electronic wave functions, and A λ (q) is an anisotropy factor. In the long-wavelength limit, where erfc(qσ /2) ∼ 1 [38,39] and [37], the matrix element for the piezoelectric interaction goes as…”

“…Besides leading to the renormalization in band gap and introducing the extra peaks in the magneto-optical conductivity [34][35][36], the electron-phonon interaction plays also a salient role in the investigation into transport properties of monolayer MoS 2 such as: phonon limited mobility [7,37], hot-electron cooling [38], free-carrier optical absorption [39], thermoelectric transport coefficients [40], electrical transport properties [41], and magneto-optical transitions [42]. Recently, using a density-functional-based approach, Kaasbjerg et al [7] have calculated the electron-phonon couplings in monolayer MoS 2 for acoustic and optical deformation potentials as well as the Fröhlich interaction.…”

Transient SHG Imaging on Ultrafast Carrier Dynamics of MoS2 Nanosheets

“…For example, electron–acoustic phonon coupling dominates low‐energy carriers, which limits carrier mobility in TMDC‐based electronic applications . The optical absorption coefficient of MoS 2 is predicted to monotonously decrease with the increase in acoustic phonon frequency; further, the acoustic phonon plays a crucial role in connecting two adjacent valleys to generate a net valley depolarization in MoS 2 . The PIAPs, which are generated as a form of vibrational quantum, have been theoretically categorized into in plane longitudinal acoustic (LA), in‐plane transverse acoustic (TA), and out‐of‐plane acoustic (ZA) modes.…”