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PhD Defence Tamer Doğan

nano-structured hybrid organic / inorganic electronic devices

Tamer Doğan is a PhD student in the NanoElectronics Group (NE). His supervisor is W.G. van der Wiel from the faculty of Electrical Engineering, Mathematics and Computer Science.

Organic semiconductors have attracted a lot of attention with their unique electrical (tunable bandgap), optical (photoluminescence) and physical (flexibility) abilities. A number of applications, such as organic light-emitting diodes, flexible electronic devices, biodegradable sensors etc. are realized thanks to these properties. However, fundamental understanding of organic semiconductor materials and devices is still necessary in order to obtain near-ideal performance from current and future applications. In light of this quest, this thesis presents a variety of fabrication procedures that provides better device performances or pathways to investigate unique features of organic semiconductors. The proposed methodologies rely on silicon substrates and also utilize a number of inorganic dielectric materials and metal electrodes. Combining organic and inorganic materials creates an easy-to-fabricate hybrid devices. In addition, using nanofabrication processing technologies, devices with nanostructured substrate and confined organic materials are realized. When one or more dimensions of the organic and inorganic materials measure below 100 nm and 20 nm respectively, they provide unique phenomena. For example, when silicon is confined in three-dimensions, it shows increased photoluminescence, and organic semiconductors present increased diffusion of charge carriers when confined between two electrodes.

The thesis starts with introducing motivation in Chapter 1. The band structure of (organic) semiconductors and transport characteristics of organic FETs are discussed in Chapter 2. Chapter 3 explains nano-fabrication techniques used throughout the thesis. In Chapter 4, high-density arrays of crystalline silicon nanostructures are fabricated using lithography techniques of DTL and edge lithography (EL). In Chapter 5 a method based on a high-quality nanoscale template for patterning 1D organic nanostructures is introduced. Chapter 6 describes the fabrication of vertical organic field-effect transistors that has 100 nm thick P3HT nano-pillars with a surrounding gate dielectric (alumina, Al2O3) and gate electrode (aluminum, Al) around them. A unique vertical organic field-effect transistor structure in which highly doped silicon nanopillars are utilized as a gate electrode is demonstrated in Chapter 7. Lastly, Chapter 8 concludes the thesis with a useful outlook.