Fabrication and optical properties of erbium-doped Group IV nanowires and their corresponding oxides

Abstract

As photolithography-based top-down methods are approaching their fundamental limits, new conceptual methods are emerging as possible alternatives to replace them. Alternatives based on bottom-up approach rely on the assembly of basic building blocks such as nanowires. One-dimensional Group IV semiconductors (Ge, SiGe) are very important electronic materials. However, they cannot be used in optoelectronics due to their intrinsic indirect band gap properties. One of the most effective approaches to make them luminescent is the introduction of impurities such as Er3+ ions. Er3+ is of technologically important because its emission lies at the transmission window of silica. Another focus of our research is to fabricate one-dimensional Er-doped Group IV oxide amplifiers. Ideally, these NWs could be used as building blocks in the field of near-IR nanophotonics. The basic building block Ge NWs were first fabricated via a vapor-liquid-solid synthetic route.^Next, these Ge NWs were doped with Er3+ ions. These NWs were characterized using electron microscopy and spectroscopy, showing that these nanowires possess a core-shell structure. Activation and possible underlying mechanism for the Er-related emission have also been explored. Since Ge NWs are readily oxidized, Si was introduced to form stable SiGe alloys in order to circumvent this problem. Three different alloyed architectures were prepared. A combination of electron microscopes in concert with both elemental and Raman microanalyses were used to investigate the composition and structure of these Er-doped SiGe NWs.The Er coordination environment and Er-related luminescence properties have also been investigated. Er-doped group IV oxide nanofibers were fabricated via an electrospinning approach. These nanofibers were then characterized using X-ray diffraction, electron microscopy, and spectroscopy to investigate their structures and compositions.^The Er3+ ions in Er-doped GeO2 nanofibers were found to be excited through a GeOx-mediated process. Lastly, the Er sensitizer, GeOx was introduced deliberately into Er-doped SnO2 nanofibers. These composite nanofiber structures were characterized using electron microscopy and spectroscopy, showing that SnO2 can be reduced by Ge to form Sn metal. A longer Ge deposition time leads to the formation of Ge nanorods. The Er-related luminescence from these sensitized nanofibers has been enhanced by almost 2 orders of magnitude.