Si micro- and nano-structures for communication and energy applications

Abstract

In the past decades, Si has been the most important material for electronics. By exploiting this mature semiconductor fabrication technique, it is also highly desired to use Si for applications in other areas. Here we report the use of Si micro-structures for optical-communications and Si nano-structures for energy applications. Sub-micron Si waveguides is fabricated on Si substrates rather than SOI (silicon on insulator) substrate using laser reformation technique. This method helps solve the incompatible problem for the integration of optics and electronics on a single Si chip. The typical thickness of the oxide layer on the CMOS transistor layer is below 100nm which, however, creates excessive optical loss due to the light coupling into Si substrate. Besides, fabricating Si photonics on Si wafer is much cheaper than that on SOI wafer. The method is using high-power pulse laser to melt high-aspect ratio Si ridges. This creates a structure with wider upper portion and narrower lower portion, which can be further oxidized and forming waveguides. For energy applications, Si nanostructures are fabricated using the metal-assisted chemical etching (MacEtch) technique. Si nanostructures could greatly reduce the surface reflection to enhance light harvest. In addition, Si nanowires are further combined with organic materials to form hetero-junction solar cells using low-cost solution process. Furthermore, the Si nanostructures and MacEtch process are refined to form completely single-crystal Si thin film. Thus the material cost of Si solar cells can be potentially reduced to only 1/10 of current ones.