Electroluminescence from light-emitting devices based on erbium-doped ZnO/n-Si heterostructures: Enhancement effect of fluorine co-doping

Abstract

We report on erbium (Er) related electroluminescence (EL) in the visible and near infrared (NIR) regions from the light-emitting device (LED) based on the Er-doped ZnO (ZnO:Er)/n-Si isotype heterostructure formed by sputtering ZnO:Er film on n-Si/n⁺-Si epitaxial wafer. Herein, the ZnO:Er film exhibits n-type in electrical conduction. The aforementioned LED is electroluminescent only under sufficiently high forward bias with the negative voltage connecting to n⁺-Si substrate. Such forward bias enables the electrons from n-Si to enter into the ultra-thin SiO_x (x ≤ 2) layer inherently existing between the ZnO:Er film and n-Si via Poole-Frenkel conduction mechanism and, subsequently, to drift into the ZnO:Er film thus becoming hot electrons, which impact-excite the Er³⁺ ions to emit characteristic visible and NIR light. Furthermore, the Er-related EL from the aforementioned LED can be significantly enhanced through adopting the strategy of co-doping F^- ions into the ZnO host, which brings about twofold primary effects. Firstly, due to the atomic size compensation between F^- and Er³⁺ ions, the ZnO crystal grains become larger to accommodate much more optically active Er³⁺ ions. Secondly, the partial substitution of F^- ions for O^2- ions around the Er³⁺ ion reduces the symmetry of pseudo-octahedral crystal field of Er³⁺ ion, thus increasing the probabilities of intra-4f transitions of Er³⁺ ions. We believe that this work sheds light on developing efficient silicon-based LEDs using the Er-doped oxide semiconductors.