Characterization, functionalization, and assembly of silicon based nanowires and their applications in FETs and sensor devices

Abstract

Electronic devices are being in small sizes and of better performance. Yet, challenges come along since further miniaturization of devices require even higher precision technology and the traditional planar fabrication technology will soon reach its limit. One dimensional (1-D) nano-scale materials have brought possibilities for overcoming the difficulties and their potential to be applied in the electronic industry has created excitement all over the world. In this project, p-type and n-type silicon nanowires (SiNWs) were synthesized by electroless template method and thermal evaporation method respectively. To align the disordered nanowires, micro-fluidic system was used to assemble them to fabricate field effect transistors (FETs) based on SiNWs and silicon nanotubes (SiNTs), and gas sensor devices based on palladium (Pd) functionalized SiNWs. Micro-channels with widths of 500μm, 200μm and 100μm were used in the micro-fluidic system. Micro-channels of smaller widths were observed to lead to better nanowire alignment. More than 90% nanowires and nanoribbons can be aligned to the same direction within ±5% degree when the channel width is down to 100μm. With this kind of technique, 2,5,8 11-tetra-(t-butyl)-perylene (TBP) nanowires, 9,10-Diphenyl anthracene (DPA) nanoribbons, SiNWs, SiNTs and zinc oxide (ZnO) nanowires were aligned successfully. In order to investigate the properties of the SiNWs based FETs, template method was used to synthesis the p-type SiNWs by etching boron doped silicon wafers. The SiNW FETs shows an increase in the conductivity and higher saturation voltage with a more negative gate voltage. The P-type SiNWs have a hole mobility of 8.5 cm2/V-s, and an on-off ratio about 104 in air. The hole mobility increases one order to 76 cm2/V-s in vacuum, with an on-off ratio larger than 104. SiNWs decorated by Pd nano-particles were used for hydrogen detection. The SiNWs were fabricated via a thermal evaporation method using Tin (Sn) catalyst. The as-grown SiNWs were chemically treated to remove surface oxide and then coated with a thin layer of Pd nano-particles. A gas sensor was fabricated with the Pd-functionalized SiNWs. The sensor showed better sensitivity to hydrogen and faster responding time than the macroscopic Pd metal wire hydrogen sensor. Single-crystalline ZnS/Si core-shell nanowires have been synthesized via a two-step thermal evaporation method. The nanowires have uniform diameters of 80-200 nm with lengths range from several to several tens of micrometers. Single crystalline Si nanotubes can be obtained by chemical etching away the ZnS core from ZnS/Si structure. Investigation on FETs fabricated from the Si nanotube suggests that the non-doped Si tube shows weak n-type semiconductor properties, induced by point defects and surface states.

Date of Award	15 Feb 2008
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Chun Sing LEE (Supervisor)