Investigation of defects in indium doped TiO₂thin films using electrical and optical techniques

Existence of defect levels into the band gap of titanium oxide (TiO₂) due to indium (In) doping was investigated by Deep level transition spectroscopy (DLTS), Raman Spectroscopy and photoluminescence (PL). Particularly, two distinct e-beam grown TiO₂thin film (TF) samples on Si substrates were doped using In films with thicknesses of 5 nm and 50 nm instantaneous source. It was observed that the increasing in In doping concentration has changed the TiO₂crystal structure from anatase to rutile phase. In addition, the low doped Ti/Au/5 nm In/TiO₂TF samples showed at −5 V reverse-bias lower leakage current (3.0 × 10⁻⁷A) as compared to the highly doped Ti/Au/50 nm In/TiO₂TF devices (7.0 × 10⁻⁵A). The free carrier concentration was increased from about 10¹⁴cm⁻³to 10¹⁵cm⁻³for 5 nm In/TiO₂TF to 50 nm In/TiO₂TF devices, respectively. DLTS results have revealed a unique behaviour where a substantial reduction in deep trap concentration was observed in the samples having larger In doping. A PL band around 2.4 eV and 1.9 eV was observed for 5 nm and 50 nm In/TiO₂TF samples, respectively A blue shift of photoluminescence (PL) energy peak with the increase of temperature was also observed for both samples and was associated to defect related emissions. Finally, the shallow activation energy was determined from the temperature dependence of PL spectra. It was observed that the activation energy increased from 25 meV for the low In-doped TiO₂TF samples to 65 meV for the highly In-doped TiO₂TFs.