Hannover, Universiẗat, Diss., 1998.

Chemnitz, Techn. Univ., Diss., 2006.

Darmstadt, Techn. Univ., Diss., 2004.

No description available.

Stuttgart, Univ., Diss., 2002.

Universiẗat, Diss., 2002--Stuttgart.

Oxide semiconductors have been envisaged to find applications in ubiquitous flexible electronics in daily life such as wearable electronic gadgets to offer novel user experiences. However, one of the bottlenecks to realise these applications is a lack of oxide-semiconductor components capable of wireless communications. As Bluetooth and Wi-Fi are the two dominant communication interfaces, fast enough front-end rectifiers must be developed to operate at their gigahertz (GHz) transmission frequencies. Furthermore, despite of significant developments of n-type oxide semiconductors in the last decade, widespread flexible electronics also requires high-performance p-type oxide semiconductors for use in complementary logic circuits. The objectives of this dissertation are to develop high quality Schottky barriers, achieve GHz speed Schottky diodes on rigid and flexible substrates, evaluate the noise properties of the Schottky diodes, develop p-type oxide semiconductor using sputtering technology, elucidate the hole transport mechanism in p type transistors, and demonstrate their potential applications such as radio receivers, complementary inverters and ring oscillators. First, indium gallium zinc oxide (IGZO) Schottky diodes were fabricated by using radio frequency magnetron sputtering. The oxygen content at the metal-IGZO interface was found to have a profound effect on the electrical performance. By introducing 3% O2 during the deposition of Pt or IGZO, the diodes exhibited excellent electrical properties without requiring any annealing treatment, thus allowing for the realisation of flexible IGZO Schottky diodes. The high-frequency properties of Pt-IGZO Schottky diodes on glass substrates were optimised by testing a range of IGZO thicknesses and diode active areas. The achieved highest cut-off frequency was beyond 20 GHz, which is to the best of our knowledge the fastest oxide-semiconductor device to date. On flexible substrates, the diodes also showed cut-off frequencies up to 6.3 GHz, well beyond the critical benchmark speed of 2.45 GHz for typical wireless communications. In order to assess the feasibility of using IGZO Schottky diodes in practical applications, measurements were taken to discern their low-frequency noise properties. In the as-deposited diodes, logarithmic dependence of the noise spectral density on the applied bias was observed, revealing that the dominant noise was generated in the space-charge region at low biases and in the series-resistance region at high biases, respectively. After annealing the diodes, very different noise mechanism was observed and the interface-trap-induced noise dominated the noise spectra. As one of the most promising p-type oxide semiconductors, SnO was also studied at low temperatures in this thesis. The experiment revealed that hole-transport mechanism was governed by either band conduction or variable range hopping in different temperature ranges. Finally, the potential for fully oxide-based electronics was demonstrated by an amplitude-modulation radio receiver comprising of an IGZO Schottky diode as the demodulator and a complementary ring oscillator based on IGZO and SnO transistors. In reference to IEEE copyrighted material which is used with permission in this thesis, the IEEE does not endorse any of the University of Manchester's products or services. Internal or personal use of this material is permitted. If interested in reprinting/republishing IEEE copyrighted material for advertising or promotional purposes or for creating new collective works for resale or redistribution, please go to http://www.ieee.org/publications_standards/publications/rights/rights_link.html to learn how to obtain a License from RightsLink.

In this work, organic solar cells of the configuration ITO/Pedot:PSS/CuPc/PTCBI/Al (Indium tin oxide/poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid/copper phthalocyanine/3,4,9,10-perylenetetracarboxylic bisbenzimidazole/aluminum) were investigated. A high open-circuit voltage (Voc) of 1.15 V was obtained when the PTCBI layer was 7 nm thick. Lower Voc values were observed for the same structure with silver, copper and gold electrodes instead of aluminum. However, short-circuit current density (Jsc) with these electrodes was much higher (4 mA/cm2) than in the case of aluminum (0.12 mA/cm2). Results were interpreted in terms of a modified CuPc/Al Schottky diode for the thin PTCBI case and a CuPc/PTCBI heterojunction for the thick PTCBI case. Also, the formation of a thin, protective aluminum oxide layer under the aluminum electrode was postulated. For devices with silver, copper and gold electrodes, absence of this protective layer was thought to be the cause of a relatively lower Voc and higher Jsc.

Organic solar cells are cheaper and much easier to fabricate than the conventional inorganic solar cells, but they suffer from low efficiencies due to low carrier mobilities in organic films. In this study Copper Phthalocyanine (CuPc) and Buckminster Fullerene (C60) based Schottky diodes were fabricated on ITO coated glass substrates to study their performance and a study of the effect of thickness on the cell parameters of CuPc Schottky diodes was made. Also, TiO2 based devices were studied to see the effect of TiO2 layer on the cell parameters. The J-V curves were analyzed for series resistance, diode ideality factor and reverse saturation current density. The devices were also characterized by SEM and XRD measurements.

This work aims to study the variation in electrical and optical properties of nanoscale Schottky diodes by varying their dimensions in the nanoscale. Experimental conditions for fabricating porous alumina with varying pore diameters and inter-pore distances were first optimized by anodizing Aluminum tape with variable currents. Cadmium Sulfide nanowires were then synthesized inside the membranes by dc electrodeposition. Finally a high work function metal was deposited on top as a contact for the metal-semiconductor Schottky diode junction. As a comparative study, Schottky diodes fabricated using the same metals and Cadmium Sulfide thin films deposited on conducting glass substrates using electro-deposition and annealed in different ambient were also studied. Device characterizations were carried out by field-emission scanning electron microscopy (FESEM), current voltage (I-V) measurements, ultraviolet-visual (UV-Vis) absorption spectroscopy and X-Ray diffraction.