Exploring Layer Thinning of Exfoliated \b{eta}-Tellurene and Room Temperature Photoluminescence with Large Exciton Binding Energy Revealed in TeO2

TL;DR

This study develops a controlled thinning process for exfoliated tellurene nanosheets via thermal annealing, leading to the formation of ta-TeO2 with large exciton binding energy and promising optoelectronic properties.

Contribution

It introduces a reliable method for layer thinning and ta-TeO2 formation, revealing their optical properties and excitonic effects in 2D tellurene systems.

Findings

Controlled thinning occurs at 325b0C to 350b0C.

ta-TeO2 exhibits broad PL spectrum from 1.76 eV to 2.08 eV.

Large exciton binding energy up to 1.62 eV in monolayer ta-TeO2.

Abstract

Due to its tunable band gap, anisotropic behavior, and superior thermoelectric properties, device applications using layered tellurene (Te) are becoming attractive. Here, we report a thinning technique for exfoliated tellurene nanosheets using thermal annealing in an oxygen environment. We characterize different thinning parameters including temperature and annealing time. Based on our measurements, we show that controlled layer thinning occurs in the narrow temperature range of 325 oC to 350 oC. We also show a reliable method to form \b{eta}-tellurene oxide (\b{eta}- TeO2), which is an emerging wide band gap semiconductor with promising electronic and optoelectronic properties. This wide band gap semiconductor exhibits a broad photoluminescence (PL) spectrum with multiple peaks covering the range 1.76 eV to 2.08 eV. This PL emission coupled with Raman spectra are strong evidence of the formation of 2D \b{eta}- TeO2. We discuss the results obtained and the mechanisms of Te thinning and \b{eta}-TeO2 formation at different temperature regimes. We also discuss the optical band gap of \b{eta}-TeO2 and show the existence of pronounced excitonic effects evident by the large exciton binding energy in this 2D \b{eta}-TeO2 system that reach 1.54 eV to 1.62 eV for bulk to monolayer, respectively. Our work can be utilized to have better control over Te nanosheet thickness. It also sheds light on the formation of well-controlled \b{eta}-TeO2 layered semiconductor for electronic and optoelectronic applications.