Quantum well confinement and competitive radiative pathways in the luminescence of black phosphorus layers

TL;DR

This study investigates the optical properties of black phosphorus layers across a wide thickness range, revealing quantum well confinement effects and the influence of defects on radiative pathways, with implications for optoelectronic applications.

Contribution

It provides comprehensive experimental and theoretical analysis of black phosphorus photoluminescence over an extended thickness range, highlighting quantum confinement and defect effects.

Findings

Photoluminescence energy follows a quantum well model at ~25 nm thickness.

Defect states from exfoliation compete with bound exciton emission.

Emission energy is minimally affected by dielectric environment in heterostructures.

Abstract

Black phosphorus (BP) stands out from other 2D materials by the wide amplitude of the band-gap energy (Delta(Eg)) that sweeps an optical window from Visible (VIS) to Infrared (IR) wavelengths, depending on the layer thickness. This singularity made the optical and excitonic properties of BP difficult to map. Specifically, the literature lacks in presenting experimental and theoretical data on the optical properties of BP on an extended thickness range. Here we report the study of an ensemble of photoluminescence spectra from 79 passivated BP flakes recorded at 4 K with thicknesses ranging from 4 nm to 700 nm, obtained by mechanical exfoliation. We observe that the exfoliation steps induce additional defects states that compete the radiative recombination from bound excitons observed in the crystal. We also show that the evolution of the photoluminescence energy versus thickness follows a quantum well confinement model appreciable from a thickness predicted and probed at 25 nm. The BP slabs placed in different 2D heterostructures show that the emission energy is not significantly modulated by the dielectric environment. Introduction Confinement effects