Abstract
We report on electrically-active defects located between 0.054 and 0.69 eV below the conduction band edge in rutile single crystals subjected to reducing and hydrogenating heat treatments. Deep-level transient spectroscopy measurements recorded on samples subjected to different heat treatments are compared. In samples annealed in gas, three defect levels are commonly observed. One of these levels, , 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 display a larger number of defect levels and larger concentrations compared to samples heat-treated in gas. treatments are performed at considerably higher temperatures. Four energy levels located between 0.28 and 0.69 eV, induced by annealing in , are tentatively attributed to O vacancy- or Ti interstitial-related complexes with impurities.
Highlights
Rutile titanium dioxide (TiO2) is a wide bandgap semiconductor (Eg = 3.2 eV [1,2,3,4]) that is well-known for its photocatalytic properties [5, 6], enabling applications such as photocatalytic water-splitting and water purification [6,7,8,9,10]
We report on electrically-active defects located between 0.054 and 0.69 eV below the conduction band edge in rutile TiO2 single crystals subjected to reducing and hydrogenating heat treatments
Deep-level transient spectroscopy spectra of samples heat-treated in N2 display a larger number of defect levels and larger concentrations compared to samples heat-treated in H2 gas
Summary
Reduced and/or hydrogenated TiO2 (TiO2−x:H) has gained interest because it displays enhanced photocatalytic activity [11,12,13]. 36 (2020) 014006 which have been subjected to hydrogenating and/or reducing heat treatments might display a defect chemistry comparable to the one found in TiO2 used for photocatalysis, and are important to study. Using DLTS, we identified several defect-related charge state transition levels in TiO2−x:H [23], but no clear assignments to certain defects have so far been made. In samples annealed in FG flow, seven distinct levels in the range 0.057–0.63 eV were detected. In samples annealed in N2 flow, six distinct levels in the range 0.063–0.40 eV were detected. The present paper aims to further investigate electricallyactive defects in TiO2 single crystals subjected to reducing and/or hydrogenating heat treatments. The correlation between [Hi] and transition level concentrations is investigated
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