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

Abstract

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-4f transition (⁴I_13/2→⁴I_15/2) of Er³⁺ ions at ～ 1540 nm has potential applications in the optical interconnection for silicon-based circuits. The LEDs with rare-earth (RE)-doped SiO<i>_x</i> (<i>x</i> ≤ 2) or SiN<i>_x</i> (<i>x</i> ≤ 4/3) films have been well investigated as the silicon-compatible 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, Lü C Y, Gao Z F, Wang C X, Li D S, Ma X Y, Yang D R 2015 <i>Appl. Phys. Lett.</i> <b>107</b> 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 TiO₂ film as the light-emitting 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 co-doping 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-4f transitions of Er³⁺ ions. Due to the aforementioned reason, the Yb co-doping 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.