硅基掺铒二氧化钛薄膜发光器件的电致发光:共掺镱的增强发光作用

Electroluminescence from silicon-based light-emitting device with erbium-doped TiO2 films:Enhancement effect of ytterbium codoping

在我们以前的工作(Zhu C, Lü C Y, Gao Z F, Wang C X, Li D S, Ma X Y, Yang D R 2015 Appl.Phys.Lett.107 131103)中,利用掺铒(Er)二氧化钛薄膜(TiO2:Er)作为发光层,实现了基于ITO/TiO2:Er/SiO2/n+-Si结构的发光器件的Er相关可见及近红外(约1540 nm)电致发光.本文将镱(Yb)共掺入TiO2:Er薄膜中,显著增强了Er相关可见及近红外电致发光.研究表明,一定量Yb的共掺会导致TiO2:Er薄膜由锐钛矿相转变为金红石相,从而使得Er3+离子周围晶体场的对称性降低.此外,Yb3+离子比Ti4+离子具有更大的半径,这使TiO2基体中Er3+离子周围的晶体场进一步畸变.晶体场的对称性降低及畸变使得Er3+离子4f能级间的跃迁概率增大.由于上述原因,Yb在TiO2:Er薄膜的共掺显著增强了相关发光器件的电致发光.

In the past years, light-emitting devices(LEDs) based on erbium(Er)-doped insulators or wide-bandgap semiconductors have received intensive attention because the intra-4 f transition(4 I13/2→4 I15/2) of Er3+ ions at^1540 nm has potential applications in the optical interconnection for silicon-based circuits. The LEDs with rare-earth(RE)-doped SiOx(x ≤ 2) or SiNx(x ≤4/3) films have been well investigated as the siliconcompatible emitters. However, they suffer difficulty in injecting current and easing fatigue. In this context, the LEDs with RE-doped oxide semiconductors have been extensively investigated out of research interest in recent years. Among the oxide semiconductors, TiO2 is a desirable host for RE-doping because it is transparent for visible and infrared light, and cost-effective, and has considerably high RE solubility. In our previous work(Zhu C, Lii C Y, Gao Z F, Wang C X, Li D S, Ma X Y, Yang D R 2015 Appl. Phys. Lett. 107 131103), we have realized erbium(Er)-related visible and near-infrared(~1540 nm) electroluminescence(EL) from the LED with a structure of ITO/TiO2:Er/SiO2/n+-Si, in which TiO2:Er refers to the Er-doped TiO2film as the lightemitting layer. In this work, we co-dope ytterbium(Yb) into the TiO2:Er film in the aforementioned LED to significantly enhance the Er-related visible and near-infrared EL. It is revealed that a certain amount of Yb codoping enables the TiO2:Er film to transform its crystal phase from anatase to rutile. Such a phase transformation reduces the symmetry of crystal field surrounding the Er3+ ions incorporated into the TiO2 host.Moreover, the substitution of over-sized Yb3+ ions for Ti4+ ions in the TiO2 host leads to the distortion of the crystal field around the Er3+ ions. The aforementioned symmetry-reduction and distortion of the crystal field increase the probabilities of the intra-4 f transitions of Er3+ ions. Due to the aforementioned reason, the Yb codoping into the TiO2:Er film remarkably enhances the EL from the corresponding LED. It is believed that the strategy of Yb-codoping can be adopted to enhance the EL from the LEDs with other RE-doped TiO2 films.