Transparent Thin Film Transistors Based on Parallel Array of Si Nanowires

Abstract

Optically transparent and mechanically flexible semiconductors allow unusual applications in invisible and portable electronics. For such applications, organic materials or polycrystalline thin films deposited on glass or plastic substrates have been used. However, these films exhibit low carrier mobility due to the scattering caused by defects, thus thin-film devices have poor electrical characteristics. An alternative approach is to use one-dimensional (1D) inorganic nanomaterials, such as silicon nanowires (SiNWs), since the 1D nanostructures provide a significant enhancement in mechanical flexibility, while their single crystalline structures hold the promise of high device performance. On the other hand, numerical analysis based on effective-medium model predicts that periodic SiNW arrays have much lower reflectivity than thin films, revealing an increase in transmittance of incident light in SiNWs if the nanowire diameter is small enough to minimize the light absorption. Here, we report on the fabrication of fully transparent thin-film transistors by implementing the aligned SiNWs and Ga-doped ZnO thin films as transparent channels and transparent conducting electrodes, respectively. The SiNWs aligned on the glass substrates are highly transparent in the visible spectral range, with a transmittance of ~90 % for the NW density of ~2?3 ?m-1. In addition, polarization-dependent measurements reveal the variation of transmittance in the range of 75?95 % with respect to the angle between polarization of incident light and the NW axis. Gate dependent transport measurements demonstrated that the boron-doped SiNW devices behaved as p-type TFTs with good characteristics in terms of transconductance and switching behavior.