Semiconductor nanowires and their field-effect devices
Abstract
Semiconductor nanowires have attracted significant attention in the last decade for their potential in improving existing or enabling novel devices. An important challenge in the field is to reproducibly control the electronic properties and to fabricate high purity nanowires. The goal of this thesis is to apply nanowires for the realization of field effect transistors and sensors, whose performance proves all the benefits of having high quality nanoscale materials. The nanowires used in this thesis are synthesized in our group and are mainly gallium arsenide (GaAs) nanowires grown by Molecular Beam Epitaxy (MBE) and germanium (Ge) nanowires grown by Chemical Vapor Deposition (CVD). Special in these nanowires is that they are synthesized by avoiding the use of gold in the nucleation and growth process, which should lead into higher purity and improved overall properties. The study is mainly realized by electrical measurements and by electronic microscopy in smaller part. In a first phase the nanowires are contacted in a 2-points configuration by means of optical lithography. In the following part, more complex methods, like Electron Beam Lithography (EBL), are applied in order to place the multiple contacts on the single nanowire. EBL technique enabled 4-point transport measurements which allowed accurate determination of the nanowire resistance and contact resistance. Even more than this, mentioned techniques allowed to understand what the effect of smaller size contact is and to realize devices in the size of few hundred nanometers. Additionally, we were able to realize more complex device geometries, for example by providing different gate configurations. We investigated different semiconductor materials (GaAs, Ge and Si), designed and realized multiple geometry field- effect transistors and sensors based upon them and characterized their properties, particularly regarding possible applications in future electronic devices architectures. Special attention was paid to ensure reliable and reproducible results.
