Nanotechnology opens up novel opportunities to develop sensors and energy convertors that can be used in a wide range of applications. Due to their small size and increased functionality they can be integrated into systems with low “real-estate” cost while offering real-time asset monitoring for increased control and energy efficiency. An area where nanotechnology can have a large impact is phononics – the science of controlling heat conduction in systems – and thermoelectric (TE) applications. Decreasing the structure size allows electrical transport but hinders phonon (heat) transport. Thus, nanowire (NW)-based systems can boost the performance of TE generation and cooling, and may enable key absent technologies such as on-chip heat management and storage, heat recovery and information processing in thermal form for systems such as heat sensors and generators. In the proposed work, the combined control of phonon and electron transport will be used to implement temperature sensing and data processing. This will be achieved by fabricating semiconducting NWs for phonon-filtering with Schottky barrier contacts for electron energy filtering. Nanoscale metal-semiconductor (MS) contacts have the ability to increase the Schottky barrier height that controls hot electron injection from the metal into the semiconductor. It is known that the introduction of high potential barriers in the carrier stream increases the Seebeck coefficient and thus increases the open circuit voltage for a given temperature difference. The NW structure itself blocks the phonon transport to maintain a large temperature difference. Electron energy filtering via potential barriers has been previously explored in semiconductor-semiconductor junctions. MS junctions have been found to be less efficient. However, nanoscale Schottky contacts are expected to change the physical processes at the interface that could lead to increased potential barriers and better energy filtering. This makes NWs, in which the phonon transport is hindered, a suitable candidate for temperature sensing. In order to make the sensor active, it can be integrated in reconfigurable NW FETs (RFETs). RFETs are built on intrinsic NWs and have Schottky source and drain contacts. RFETs can operate with both n and p-type functionality depending on the program gate. Our hypothesis is that gating the source and drain contact junctions can control the energy filtering process and control electrical and thermal transport through the NWs. The combination of reconfigurable NWs with Schottky barrier energy filtering for temperature sensing has not yet been explored but offers future possibilities for monolithically integrated on-chip heat management, recovery and storage systems. The PhD research involves simulations studies and design of reconfigurable NWs, followed by fabrication and characterisation of the system.
Ali Hamid was born in Iran in 1993. He lived in Iran for 14 years and then moved to Dubai to complete high school. During this time, he and his friends held many discussions on the need for low power devices for portable applications such as mobile phones. Small devices, low power and good heat management systems are essential to maintain long battery life and reliability in portable electronics. These discussions triggered an interest in micro- and nanochip design and manufacturing. He then studied Nanoscience and Nanotechnology (Bsc) at the University of Leicester (2012-2015), to understand the basics of nanotechnology. That course was followed by an MSc in Nanoscience and Nanotechnology in the University of Glasgow (2015-2016), to learn more about nanoelectronics and its fabrication methods. He joined the Electrical and Electronic Engineering Department in Imperial College London in November 2016 to work as a PhD student on the use of nanodevices for heat management applications. In his project he will investigate the use of reconfigurable nanowire field effect transistor technology for thermal management to increase the lifetime of integrated circuits and explore ways in which the thermo-electric/-ionic effect can simultaneously be exploited for battery charging.
Dr. Kristel Fobelets is an expert in the field of fabrication and characterisation of different types of semiconductor devices including fabrication/characterisation of NW FETs. She also has an excellent track record in thermoelectric power generation using Si nanowire arrays, having published extensively in this area in recent years. Her research record includes 82 journal papers and 85 conferences in different areas of semiconductor research.
Dr M. Kiziroglou has over ten years of experience in microfabrication of devices including spin injection nanostructures and nanostructured Schottky contacts, carbon nanotube fabrication, monolithic integration of Au inductors on CMOS and micro-generators for energy harvesting applications. He has experience in technology transfer with industrial partners including Semefab and Airbus Group Innovations. His research record includes 19 journal papers, 25 conference papers, 2 book chapters and 18 other contributions to conferences.