Tunable Photodetectors via In Situ Thermal Conversion of TiS3 to TiO2.

Foad Ghasemi,Andres Castellanos-Gomez,Takashi Taniguchi,Eduardo Flores,David Perez De Lara,Jose R Ares,Kenji Watanabe,Roberto D’Agosta,Carlos Sánchez,Nikos Papadopoulos,Riccardo Frisenda,Herre S J Van Der Zant,Robert Biele,Isabel J Ferrer

doi:10.3390/nano10040711

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 (TiS3), a layered semicon-ductor that has attracted much attention recently thanks to its quasi-1D electronic and optoelectron-ic properties and its direct bandgap of 1.1 eV. Heating TiS3 in air above 300 °C gradually converts it into TiO2, a semiconductor with a wide bandgap of 3.2 eV with applications in photo-electrochemistry and catalysis. In this work, we investigate the controlled thermal oxidation of indi-vidual TiS3 nanoribbons and its influence on the optoelectronic properties of TiS3-based photodetec-tors. We observe a step-wise change in the cut-off wavelength from its pristine value ~1000 nm to 450 nm after subjecting the TiS3 devices to subsequent thermal treatment cycles. Ab-initio and many-body calculations confirm an increase in the bandgap of titanium oxysulfide (TiO2-xSx) when in-creasing the amount of oxygen and reducing the amount of sulfur.

Highlights

Low-dimensional semiconductors are attracting increasing interest in the scientific community working on optoelectronic devices thanks to their outstanding optical and electronic properties combined with reduced dimensionality [1,2,3]
Control experiments performed on TiS3 nanoribbons fully encapsulated between hexagonal boron nitride flakes confirm that the direct contact between TiS3 and air is necessary for the oxidation process to happen
By monitoring the change in its current–voltage characteristics and in its spectral photoresponse, we find that the cut-off wavelength is blue-shifted upon oxidation, reaching a cut-off wavelength of 450 nm

Summary

Introduction

Low-dimensional semiconductors are attracting increasing interest in the scientific community working on optoelectronic devices thanks to their outstanding optical and electronic properties combined with reduced dimensionality [1,2,3]. An experimental demonstration was given by Molina-Mendoza et al, who reported thermogravimetric analysis (TGA) of bulk TiS3 in oxygen atmosphere showing the partial conversion of the material into TiO2, a large bandgap (3.2 eV) insulator with a wide range of applications [19,27,28,29]. After establishing the change in material properties we demonstrate the controlled oxidation of a TiS3 nanoribbon photodetector that allows tuning the cut-off wavelength and sensitivity of the device. Ab-initio and many-body calculations confirm an increase in the bandgap near to that of titanium oxysulfide (TiO2-xSx) when increasing the amount of oxygen and reducing the amount of sulfur

Materials Synthesis

Bandgap Energy Calculation

Electronic and Optoelectronic Characterization

Conclusions