Enhancement Effect Of Co-Doping On Electro-Luminescence Of Light-Emitting Devices With Silicon-Based Erbium-Doped TiO₂ Films

In the past two decades,the light-emitting devices based on erbium-doped(Er)-based semiconductor have always attracted attention.TiO2,a wide band gap oxide n-type semiconductor material,has been proved to be a suitable host for achieving Er-related luminescence.In recent years,our research group has realized the electroluminescence(EL)from TiO 2:Er/p+-Si heterostructured devices and ITO/TiO2:Er/SiO2/n+-Si multilayered devices by using the Er-doped TiO2 film(TiO2:Er).Nevertheless,the Er-related EL intensity is yet to be enhanced.In this thesis,the enhancement of Er-related EL has been achieved by co-doping a certain amount of specific impurities in the Er-doped TiO2 films.The primary results obtained are described as follows:(1)The Zr-codped T1O2:Er[TiO2:(Zr,Er)]films with nominal Zr contents 2.5-7.5%were deposited on the p+-Si substrates and the n+-Si substrates thermally oxidized at 1100 ? for 5 min by radio frequency(RF)sputtering.The films on the p+-Si substrates were annealed at 650 ? for 2 h in the oxygen atmosphere,while those on the oxidized n+-Si substrates were annealed at 800? for 1 h in the oxygen atmosphere.On this basis,the TiO2:(Zr,Er)//p+-Si heterostructured devices and the ITO/Ti02:(Zr,Er)/SiO2/n+-Si multilayered devices were fabricated,respectively.For comparison,the TiO2:Er/p+-Si heterostructured devices ITO/TMO2:Er/SiO2/n+-Si multilayered devices were also fabricated.It is revealed that the Zr codoping does not alter the anatase phase of the TiO2:Er film.Compared with the devices based on the TD2:Er films,those based on the TiO2:(Zr,Er)films with nominal 5at%Zr content possess much higher EL intensities in the visible and near-infrared regions(?1540nm band).It is believed that the substitution of oversized Zr4+ ions for Ti4+ ions in the TiO2 lattice leads to the distortion of the crystal field around the Er3+ ions,thus reducing the crystal field symmetry.As a result,the probabilities of transitions among the 4f energy levels and the consequent luminescence intensities of the Er3+ ions are significantly increased.(2)The Hf-doped TiO2:Er[TiO2:(Hf,Er)]films were deposited on the p+-Si substrate and the n+-Si substrate thermally oxidized at 1100 ? for 5 min by RF sputtering,respectively.The former was annealed at 650 ? for 2 h while the latter was annealed at 800 ? for 1 h in the oxygen atmosphere.On this basis,the TiO2:(Hf,Er)//p+-Si heterostructured and ITO/TiO2:(Hf,Er)/SiO2/n+-Si multilayered devices were fabricated.Compared with the devices based on the TiO2Er films,those based on the TiO2:(Hf,Er)films possess much higher EL intensities in the visible and near-infrared regions(?1540nm band).The mechanism for such enhancement is similar to that related to the Zr-codoping as mentioned above.(3)The Yb-doped TiO2Er[TiO2:(Yb,Er)]films were deposited on the n+-Si substrates which was thermally oxidized at 1100 ? for 5 min by RF sputtering.Such films were then annealed at 800? for 1 h in the oxygen atmosphere.On this basis,the ITO/TiO2:(Yb,Er)/SiO2/n+-Si multilayered devices were fabricated.The visible and near-infrared EL intensities of the devices based on the TiO2:(Yb,Er)films were significantly increased compared with those of the devices based on the TiO2:Er films.It is found that Yb co-doping results in that the TiO2:Er film is transformed from the anatase phase into the rutile phase.The crystal field around the Er3+ ions in the rutile TiO2 has lower symmetry than that in the anatase TiO2.Moreover,the substitution of over-sized Yb3+ ions for Ti3+ ions in the TiO2 lattice further distorts the crystal field around Er3+ ions.Such two factors increase the probabilities of transitions among the 4f energy levels of Er3+ ions and the consequent Er-related luminescence intensities.