Electrical and optical properties of TiO2 anatase thin films

Abstract

Electrical and optical spectroscopic studies of TiO2 anatase thin films deposited by sputtering show that the metastable phase anatase differs in electronic properties from the well-known, stable phase rutile. Resistivity and Hall-effect measurements reveal an insulator–metal transition in a donor band in anatase thin films with high donor concentrations. Such a transition is not observed in rutile thin films with similar donor concentrations. This indicates a larger effective Bohr radius of donor electrons in anatase than in rutile, which in turn suggests a smaller electron effective mass in anatase. The smaller effective mass in anatase is consistent with the high mobility, bandlike conduction observed in anatase crystals. It is also responsible for the very shallow donor energies in anatase. Luminescence of self-trapped excitons is observed in anatase thin films, which implies a strong lattice relaxation and a small exciton bandwidth in anatase. Optical absorption and photoconductivity spectra show that anatase thin films have a wider optical absorption gap than rutile thin films.

Effects of Cr and Fe co-doping on structural, optical, electrical and magnetic properties of titanium dioxide (TiO2)

“…4a. It is revealed that these loops show antiferromagnetic behavior which may be due to the presence of hematite phase [12]. This phase is also confirmed by XRD micrographs.…”

Tunable optical properties of hybrid inorganic–organic [(TiO2)m(Ti–O–C6H4–O–)k]n superlattice thin films

“…The obtained band gap estimate for the pure TiO2 film of 3.25 eV is in accord with the literature value of 3.2 eV for anatase TiO2. 31 The TiO2 band gap was found to blue-shift in the superlattice films with decreasing superlattice period with an onset between periods of 1:20 (0.96 nm) and 1:40 (1.9 nm) 13 finally reaching 3.75 eV for the m=0 hybrid. The blue-shift is probably due to quantum confinement of electrons with decreasing TiO2 domain size in analogy to nanocrystalline materials in which a decrease in grain size leads to an increase in the band gap.…”

Optical studies on sol–gel derived titanium dioxide films

“…Values of the optical band gap Eo are comparable to those previously reported for Ti02 films. Values of Eo are found to be 3.2eV and 3.0eV for reactively triode sputtered Ti@ films in anatase and rutile, respectively [22]. Leinen et al [23] have recently reported a band gap in the range of 3.3-3.42eV for induced chemical vapour deposited anatase films.…”