Theory of edge-state optical absorption in two-dimensional transition metal dichalcogenide flakes

TL;DR

This paper presents an analytical model for sub-bandgap optical absorption in 2D transition metal dichalcogenide flakes, focusing on edge-state transitions and their dependence on carrier population and fluence.

Contribution

It introduces a novel analytical framework describing edge-state optical absorption in s-TMD nanoflakes, including linear and nonlinear effects, aiding photonic device design.

Findings

Absorption involves direct edge-to-bulk state transitions.

Absorption depends strongly on carrier population and saturates at high fluence.

Excess energy above half the bandgap heats edge-state electrons.

Abstract

We develop an analytical model to describe sub-bandgap optical absorption in two-dimensional semiconducting transition metal dichalcogenide (s-TMD) nanoflakes. The material system represents an array of few-layer molybdenum disulfide crystals, randomly orientated in a polymer matrix. We propose that optical absorption involves direct transitions between electronic edge-states and bulk-bands, depends strongly on the carrier population, and is saturable with sufficient fluence. For excitation energies above half the bandgap, the excess energy is absorbed by the edge-state electrons, elevating their effective temperature. Our analytical expressions for the linear and nonlinear absorption could prove useful tools in the design of practical photonic devices based on s-TMDs.