Impact of terahertz short pulses on the oxygen defect state in TiO$_{2-x}$

TL;DR

This study investigates how terahertz short pulses influence oxygen defect states in TiO₂₋ₓ, revealing the conversion of localized electrons into metastable polarons with potential opto-electronic applications.

Contribution

It demonstrates the use of THz-pump/IR-probe techniques to control and understand defect states and polaron formation in oxygen-deficient TiO₂.

Findings

THz pump converts localized electrons into metastable polarons

Metastable states have a lifetime in the nanosecond range

Potential applications in opto-electronic devices

Abstract

Oxygen deficient titanium dioxide (TiO$_{2-x}$) is a very attractive material for several applications ranging from photocatalysis to resistive switching. Oxygen vacancies turn insulating anatase titanium dioxide into a polaronic conductor, while creating a defect state band below the ultraviolet semiconducting gap. Here we employ a combination of broadband infrared (IR) reflectivity and THz-pump/IR-probe measurements to investigate the relationship between localized defect states and delocalized conducting polaronic states. We show that the THz pump allows to convert deeply localized electrons into metastable polarons with a lifetime in the ns range. These long-lived metastable states may find application in novel opto-electronic applications exploiting the interplay of dc resistivity, with terahertz and infrared signals.