Effect of erbium-doping concentration on the electrical, structural and morphological properties of heterostructures based on TiO₂ thin films

Effect of erbium (Er) doping on the electrical, structural and morphological properties of TiO₂ thin films deposited by the combination of a simple sol–gel process and spin-coating technique on p-type silicon substrates, has been investigated. A systematic study of the effect of concentration of Er on the properties of heterostructures was carried out. Raman spectroscopy and atomic force microscopy have been used to study the structural and morphology properties of devices based on Er-doped TiO₂/Si heterostructures. Deep level transient spectroscopy (DLTS) has been also employed to study the electrically active defects within the band gap of Er-doped TiO₂ thin films. DLTS that has proved to be a powerful tool in analysing traps in semiconductors devices showed that undoped TiO₂-based devices exhibit five defects. However, three defects have been detected in the low erbium-doped TiO₂ devices and only one defect was observed in the higher erbium-doped devices. These results provide strong evidence that Er doping annihilates oxygen-related defects and demonstrate the effective proof of doping process in TiO₂ thin film. This finding contributes to the improved activities (e.g., photocatalytic) of TiO₂ since the increase in charge traps can reduce bulk recombination and consequently, separates photogenerated electrons and holes more efficiently. Furthermore, it is found that the overall electrical properties of the devices are improved by increasing Er doping concentration. This study provides an important understanding of the deep and shallow level defects in Er-doped TiO₂ thin films, which is essential for the manufacturing of future devices including UV detectors.