Tunable Photodetectors via in situ Thermal Conversion of TiS$_3$ to TiO$_2$

TL;DR

This study demonstrates how controlled in situ thermal oxidation of TiS3 nanoribbons can tune their optoelectronic properties, enabling the development of photodetectors with adjustable spectral response by converting TiS3 into TiO2.

Contribution

It introduces a method for tuning 2D material properties through controlled thermal oxidation, specifically converting TiS3 into TiO2 to modify photodetector performance.

Findings

Step-wise increase in bandgap from ~1.1 eV to 3.2 eV.

Shift in photodetector cut-off wavelength from ~1000 nm to 450 nm.

Theoretical calculations confirm bandgap increase with oxidation.

Abstract

In two-dimensional materials research, oxidation is usually considered as a common source for the degradation of electronic and optoelectronic devices or even device failure. However, in some cases a controlled oxidation can open the possibility to widely tune the band structure of 2D materials. In particular, we demonstrate the controlled oxidation of titanium trisulfide (TiS$_3$), a layered semiconductor that has attracted much attention recently thanks to its quasi-1D electronic and optoelectronic properties and its direct bandgap of 1.1 eV. Heating TiS$_3$ in air above 300 {\deg}C gradually converts it into TiO$_2$, a semiconductor with a wide bandgap of 3.2 eV with ap-plications in photo-electrochemistry and catalysis. In this work, we investigate the controlled thermal oxidation of individual TiS$_3$ nanoribbons and its influence on the optoelectronic properties of TiS$_3$-based photodetectors. We observe a step-wise change in the cut-off wavelength from its pristine value ~1000 nm to 450 nm after subjecting the TiS$_3$ devices to subsequent thermal treatment cycles. Ab-initio and many-body calculations confirm an increase in the bandgap of titanium oxysulfide (TiO$_{2-x}$S$_x$) when increasing the amount of oxygen and reducing the amount of sulfur.