Efeitos de blindagem eletrostática sobre a energia de excitons em materiais semicondutores bidimensionais

Abstract

Two-dimensional semiconductor materials have been subject of intense studies in recent years, ans several technological applications for such materials are expected in near future. A very important class of two-dimensional semiconductors is transition metal dichalcogenides (TMDs), which have been show to be suitable for the development of optoelectronics. For a complete undestanding of the light-matter interaction, the absorption, and luminescence phenomena observed in experiments with these materials, we need a robust theorical model to describe the bound electron-hole pairs (excitons) in them. Experimental results have provided evidence that the exciton binding energy in this system is high and very dependent on the surrounding dielectric environment (substrate and upper layers). In this work, we study TMD optoelectronic properties, focusing on the effect of the dielectric environment on the properties of excitons. For that, from the eigenstates of the lattice Hamiltonian of the TMD, we obtained the energy bands and we approximated theses bands by parabolas in the effective mass model, where electrons can be effectively treated as free quasiparticles. We solve the time-independent Schrodinger equation to find the exciton energy levels by assuming an electron-hole interaction obtained through the solution of the Poisson equation, resulting no longer in a Coulomb potential (as it would be expected for free particles), but in a potential with a form similar to that of the Rytova-Keldysh potential. The results of our model for different TMD on substrates and covered with other materials in various configurations are compared with recent experimental observations.