The current master thesis describes the synthesis of silicon nanowires via the Vapor-Liquid-Solid (VLS) growth mechanism. The goal of this work is the achievement of an efficient postgrowth doping method for silicon nanowires.
The first chapter explains the needs for further miniaturization of electronic devices. An introduction into structural methods, and the properties and advantages of nanowires is given. The second chapter describes theoretical principles of the VLS growth mechanism, the important role of gold as catalyst, and epitaxial nanowire growth, followed by a section about the characterization of electrical properties of silicon nanowires. Finally, in-situ, diffusion, and ion implantation doping are described in detail.
After these theoretical considerations with regard to the experimental work, the test assemblies are presented in the third chapter. This part covers the setup of the low pressure chemical vapor deposition (LPCVD) system, the sample preparation, and the influence of the surface pretreatment for epitaxial nanowire growth. The following section describes the contact formation to silicon nanowires via electron beam lithography, metal deposition and lift-off techniques. Next, the doping processes of VLS grown silicon nanowires are shown. This chapter is concluded by the description of the used setup for the electrical characterization of silicon nanowires. The results of the experimental work are illustrated in the fourth chapter. The synthesized silicon nanowires were observed via SEM and TEM, and finally characterized by electrical measurements. The last section deals with the electrical characterization of doped silicon nanowires. Used doping methods are diffusion doping via Spin-On-Dopant (SOD), thermal evaporation doping via phosphoric acid, and ion implantation.
The last chapter concludes with a summary and gives an outlook to future developments of nanowire integration and devices.