Band tail formation in mono and multilayered transition metal dichalcogenides: A detailed assessment and a quick-reference guide

TL;DR

This paper investigates how band tail states in transition metal dichalcogenides are influenced by layer thickness, temperature, doping, and substrates, providing detailed physical insights and a quick-reference guide for key parameters.

Contribution

It offers a comprehensive theoretical analysis of band tail formation in TMDs, including an analytical interpolation formula for Urbach parameters across different materials.

Findings

Band tails depend critically on layer number, temperature, doping, and substrate.

Physical mechanisms of band tail formation are elucidated in detail.

An analytical formula for Urbach parameters in TMDs is provided.

Abstract

Transition metal dichalcogenides (TMDs) are promising candidates for a wide variety of ultrascaled electronic, quantum computation, and optoelectronic applications. The exponential decay of electronic density of states into the bandgap, i.e. the band tail has a strong impact on the performance of TMD applications. In this work, the band tails of various TMD monolayer and multilayer systems when placed on various dielectric substrates is predicted with density functional theory based nonequilibrium Green's functions. Nonlocal scattering of electrons on polar optical phonons, charged impurities and remote scattering on phonons in the dielectric materials is included in the self-consistent Born approximation. The band tails are found to critically depend on the layer thickness, temperature, doping concentration and particularly on the chosen dielectric substrate. The underlying physical mechanisms are studied in high detail and an analytical interpolation formula is given to provide a quick-reference for Urbach parameters in $MoS_2$, $WS_2$ and $WSe_2$.