Ab initio and semiempirical modeling of excitons and trions in monolayer TiS3

Abstract

We explore the electronic and the optical properties of monolayer TiS 3 , which shows in-plane anisotropy and is composed of a chain-like structure along one of the lattice directions. Together with its robust direct band gap, which changes very slightly with stacking order and with the thickness of the sample, the anisotropic physical properties of TiS 3 make the material very attractive for various device applications. In this study, we present a detailed investigation on the effect of the crystal anisotropy on the excitons and the trions of the TiS 3 monolayer. We use many-body perturbation theory to calculate the absorption spectrum of anisotropic TiS 3 monolayer by solving the Bethe-Salpeter equation. In parallel, we implement and use a Wannier-Mott model for the excitons that takes into account the anisotropic effective masses and Coulomb screening, which are obtained from ab initio calculations. This model is then extended for the investigation of trion states of monolayer TiS 3 . Our calculations indicate that the absorption spectrum of monolayer TiS 3 drastically depends on the polarization of the incoming light, which excites different excitons with distinct binding energies. In addition, the binding energies of positively and the negatively charged trions are observed to be distinct and they exhibit an anisotropic probability density distribution.

Excitonic complexes in anisotropic atomically thin two-dimensional materials: Black phosphorus and TiS3

“…For TiS 3 we find that the negative trion binding energy is larger than the positive trion binding energy, whereas the opposite behavior was found in Ref. [39]. There are only few experimental works studying excitonic systems in monolayer bP.…”

“…We see that the binding energy for identical electron and hole masses is always larger than that for opposite masses except when the masses in the k x -and k y -direction are equal, i.e. at m x e = 0.1m 0 , m x e = m 0 , and m x e = 4m 0 for the blue, red, and black curves, respectively, as in this case the two situations [39] are identical. This can be explained by the fact that the reduced mass µ x(y) = m ), implying that in the opposite mass case µ x = µ y will remain small when m x e = m y h becomes large.…”

“…differing at most 9%, with those from Ref. [39], which are obtained by numerically solving the relative Schrödinger equation either directly (excitons) or using an imaginary time evolution operator (trions). The authors also calculate the exciton binding energy for TiS 3 in vacuum by solving the Bethe-Salpeter equation and find 590 meV, which is in good agreement with our result.…”

Design and Optimize the Performance of Self-Powered Photodetector Based on PbS/TiS3 Heterostructure by SCAPS-1D

“…The physical parameters of PbS and TiS 3 layers used in this simulation are shown in Table 1. All these parameters are from previous reports and theories [12,[41][42][43]. The approximate thermal velocity of electrons and holes in PbS and TiS 3 semiconductor at room temperature is set at 10 7 cm/s for simplifying the numerical calculation.…”

Transition from band insulator to excitonic insulator via alloying Se into Monolayer TiS$_3$: A Computational Study

“…It has a direct gap around 1 eV with high carrier mobility and may find applications in future nanoelectronics, thermoelectric device and infrared light emission [17][18][19] . Due to the two-dimensional nature, the screening of electronhole interaction is significantly reduced in monolayer TiS 3 , leading to a large exciton binding energy 12,[20][21][22][23] . Even more interesting is that its band edge states have the same parity and thus transitions between them are dipole forbidden which further suppresses the screening effect.…”