Electroluminescence From Silicon-based Erbium-doped TiO₂ Films

Over the years, the light-emitting devices based on erbium (Er)-doped insulators or semiconducotrs have been extensively investigated due to the significance of-1540 nm light for optical communication. As a wide bandgap oxide semiconductor, TiO2 has been proved to be a desirable host for the doping of Er3+ ions. In recent year, the electroluminescence from the Er-doped TiO2 (TiO2:Er)/p+-Si heterostructured device has been achieved. In this thesis, through the different treatments of the TiO2:Er films, the EL performances and the related mechanisms for the TiO2:Er/p+-Si heterostructured devices have been further studied. The main results obtained in this thesis are described as follows.(1) The EL mechanisms of TiO2:Er/p+-Si heterostructure devices with the TiO2:Er films annealed at 550,650,750 and and 850℃ have been comparatively investigated. Under sufficiently high forward bias with the positive voltage connecting to the p+-Si substrate, the device with the 550 or 650 ℃-annealed TiO2:Er film exhibits the EL related to the Er3+ ions and the oxygen vacancies in the TiO2 host and, moreover, the Er-related EL is acivated by the energy transferring from the TiO2 host to the Er3+ ions via the sentilizers of oxygen vacancy; while the device with the 650 or 750 ℃-annealed TiO2:Er film is not electroluminescent. Under sufficiently high reverse bias with the negative voltage connecting to the p+-Si substrate, the device with the 750 or 850 ℃-annealed TiO2:Er film exhibits only the Er-related EL, which is ascribed to the impact excitation of Er3+ ions by the hot electrons, while the device with the 550 or 650℃-annealed TiO2:Er film is not electroluminescent. With increasing annealing tempreature of TiO2:Er film, the thickeness of the intermdiate SiOx (x≤2) layer between the TiO2:Er and p+-Si substrate increases, which alter the carrier transportation means in the device, thus leading to different EL mechanisms.(2) The photoluminescence (PL) performances of the TiO2 films without and with Ar plasma treatment, repectively, and the EL performances of the TiO2/p+-Si heterostructured devices using such two kinds of TiO2 films have been comparatively investigated. As the TiO2 film receives the treatment of Ar plasma generated with the working pressure of 3.5 Pa and the charging power of 30 W, its PL intensity increases over twice. Moreover, the EL intensity of the device with such treated TiO2 film is above twice that of the device with the pristine TIO2 film under the same injection current. The aformentioned PL and EL is due to that the oxgyen vacancy concentration in the TiCh film is significantly increased by the Ar plasma treatment and, moreovr, either PL or EL arises from the recombination of excitons trapped by the oxygen vacancies.(3) The PL performances of the TiO2:Er films without and with Ar plasma treatment, repectively, and the EL performances of the TiO2:Er/p+-Si heterostructured devices using such two kinds of TiO2:Er films have been comparatively investigated. As the TiO2:Er film receives the treatment of Ar plasma generated with the working pressure of 3.5 Pa and the charging power of 30 W, its PL intensity increases over one time. Moreover, the EL intensity of the device with such treated TiO:Er film is above twice that of the device with the pristine TiO2:Er film under the same injection current. The aformentioned Ar plasma treatment increases the oxygen vacancy concentration in the TiO2:Er film, which on one hand ehances the oxygen-vacancy-related EL from the TiO2 host, on the other hand, facilitates the energy transfer from the TiO2 host to the Er3+ ions via the sensitizers of oxygen vacancies, thus leading to the enhanced Er-related EL.