Electrically-active defects in reduced and hydrogenated rutile TiO2

Abstract

We report on electrically-active defects located between 0.054 and 0.69 eV below the conduction band edge in rutile T i O 2 single crystals subjected to reducing and hydrogenating heat treatments. Deep-level transient spectroscopy measurements recorded on T i O 2 samples subjected to different heat treatments are compared. In samples annealed in H 2 gas, three defect levels are commonly observed. One of these levels, E 192 , located 0.43 eV below the conduction band edge is tentatively assigned to a hydrogen-impurity complex. Two levels at 0.054 and 0.087 eV below the conduction band edge, which were present after all different heat treatments, are tentatively assigned as being related to O vacancies or Ti self-interstitials. Deep-level transient spectroscopy spectra of samples heat-treated in N 2 display a larger number of defect levels and larger concentrations compared to samples heat-treated in H 2 gas. N 2 treatments are performed at considerably higher temperatures. Four energy levels located between 0.28 and 0.69 eV, induced by annealing in N 2 , are tentatively attributed to O vacancy- or Ti interstitial-related complexes with impurities.

Functional Modifications Induced via X‐ray Nanopatterning in TiO2 Rutile Single Crystals

“…A possible explanation for these two observations could be represented by the presence of a high density of oxygen vacancies in this region of the device, which induces a variety of electronic states located within 0.7 eV from the bottom of the conduction band. [47,55] Indeed, on one hand, this situation would offer nonradiative recombination paths to photoexcited electrons, which results in a local decrease in the luminescence signal. [45] On the other hand, it could increase the surface conductivity because of thermally excited electrons coming from these defective states, which could be considered as shallow donor levels for the conduction band and that can also affect the overall band structure at the rutile/metal Schottky barrier in such a way to favor the injection of mobile carriers, similarly to what has already been proved in SrTiO 3 and in ZrO x .…”