Tunable Color System Based on Vertical Silicon Nanowire Array

Abstract

Due to interesting electrical and optical characteristics of semiconductor nanowires, they have attracted enormous attention in various fields including color filters, photodetectors, non-linear optical converters, and microcavity lasers. Among recently investigated semiconductor nanowires, Si nanowires are the most important piece of the puzzle for a novel optical device with high performance since those can be produced with existing semiconductor fabrication procedures. Recently, several studies on the multi-color generation and multispectral imaging with vertical Si nanowire arrays (Si NWAs) have been reported. The Si NWAs reveal wavelength dependence of spatial field distribution of the guide mode. The coupling of incident light and the guide mode of Si NWA provides wavelength-selective colors. However, those studies are only focused on the subtractive Si NWA color filters. Here, we present tunable color systems which show both subtractive and addictive colors by using Si NWA embedded in PDMS together with an adequate selection of substrate materials. In order to investigate the interaction between the PDMS embedded Si NWA and the substrate, we transferred the PDMS embedded Si NWAs onto both Au thin film (100 nm, yellow colored) and ZnO film (100 nm, blue colored), respectively, deposited on the Si wafers. We measured reflectance spectra of the Si NWAs with different diameters (120 nm to 150 nm with 10 nm steps) integrated with two different substrates (i.e., Au and ZnO). For the Au film with a thickness of 100 nm, the Si NWA shows concave reflectance spectra equal to subtractive color from 600 to 900 nm wavelength due to the strong reflection properties of Au film. On the contrary, when Si NWA is mounted on the ZnOcoated Si wafer, the reflectance of the Si NWA is a convex function from 600 to 900 nm wavelength which yields addictive colors. Additional experiments with various colored substrates will be discussed in the presentation. We believe that this tunable color system can be used for various applications including flexible color filters, decorative devices, and photodetectors.