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Organic and molecular electronics is a promising field for many applications, particularly flexible electronics, since it allows for the processing of electronic circuits at low temperatures on a variety of different substrates, including flexible sheets. Despite continuous improvements in the charge carrier mobility of both n- and p-type thin-film transistors, the performance of these devices is not yet attractive for commercial applications. A substantial hurdle to the realization of effective organic-based digital circuits is the lack of scalable, reproducible high-charge carrier-mobility organic semiconductors with a low contact resistance and controllable threshold voltage in transistors. The threshold voltage control is required to optimize the performance of digital circuits. Previous approaches used doping or self-assembled monolayers to provide threshold voltage control in organic field-effect transistors (OFETs). However, neither of these methods offers a proper fine-tuning of the threshold voltage or a substantial on/off ratio. Both of these problems have been successfully solved in inorganic electronics by using the concept of remote doping. This doping results in a so-called modulation-doped field-effect transistor (MODFET). Thus, in the first part of this work, we present the concept of remote doping for controlling and fine-tuning the threshold voltage without compromising charge carrier mobility by using a hole-type conduction architecture at the junction between two organic semiconductors. The second part of this work is dedicated to developing, fabricating, and characterizing high-mobility single and polycrystalline rubrene OFETs by using scalable growth methods. Finally, in the last part, we apply the knowledge gained from the first two parts and design digital circuits of rubrene OFETs aiming for high-frequency applications.

Current leakage in GaN thin films limits reliable device fabrication. A variety of Ga and N rich MBE GaN thin films grown by Rf, NH3, and Rf+ NH3, are examined with electrical measurements on NiIAu Schottky diodes and CAFM. Current-voltage (IV) mechanisms will identify conduction mechanisms on diodes, and CAFM measurements will investigate the microstructure of conduction in GaN thin films. With CAFM, enhanced conduction has been shown to decorate some extended defects and surface features, while CAFM spectroscopy on a MODFET structure indicates a correlation between extended defects and field conduction behavior at room temperature. A remedy for poor conduction characteristics is presented in molten KOH etching, as evidenced by CAFM measurements, Schottky diodes, and MODFET's. The aim of this study is to identify anomalous conduction mechanisms, the likely cause of anomalous conduction, and a method for improving the conduction characteristics. Keywords: 111-Nitride, 111-V, Gallium Nitride, GaN, Electrical Properties, Conduction, Conductivity, Mobility, Hall Measurements, Resistivity, Schottky Diode, Modulation Doped Field Effect Transistor (MODFET), Conductive Atomic Force Microscopy (AFM), Defects, Molten Potassium Hydroxide (KOH) etching, Silvaco, Atlas, and Illumination.

The objective of proposed research is to investigate the potential of strained silicon and silicon-germanium (SiGe) based devices for RF/mixed-signal applications. Different device topologies, namely strained buried channel modulation doped field effect transistor (MODFET) and silicon-on-insulator (SOI) based MOSFETs, are studied in this context. Our preliminary results on SiGe MODFETs indicate strong dependence of device performance on displacement damage, which is critical for extreme environment applications. This research will be an effort towards understanding the physics of these devices in extreme environment conditions.

The objective of this work is to provide a comprehensive analysis of the small-signal and broadband noise performance of highly scaled silicon-based field-effect transistors (FETs), and develop high-frequency noise models for robust radio frequency (RF) circuit design. An analytical RF noise model is developed and implemented for scaled Si-CMOS devices, using a direct extraction procedure based on the linear two-port noise theory. This research also focuses on investigating the applicability of modern CMOS technologies for extreme environment electronics. A thorough analysis of the DC, small-signal AC, and broadband noise performance of 0.18 um and 130 nm Si-CMOS devices operating at cryogenic temperatures is presented. The room temperature RF noise model is extended to model the high-frequency noise performance of scaled MOSFETs at temperatures down to 77 K and 10 K. Significant performance enhancement at cryogenic temperatures is demonstrated, indicating the suitability of scaled CMOS technologies for low temperature electronics. The hot-carrier reliability of MOSFETs at cryogenic temperatures is investigated and the worst-case gate voltage stress condition is determined. The degradation due to hot-carrier-induced interface-state creation is identified as the dominant degradation mechanism at room temperature down to 77 K. The effect of high-energy proton radiation on the DC, AC, and RF noise performance of 130 nm CMOS devices is studied. The performance degradation is investigated up to an equivalent total dose of 1 Mrad, which represents the worst case condition for many earth-orbiting and planetary missions. The geometric scaling of MOSFETs has been augmented by the introduction of novel FET designs, such as the Si/SiGe MODFETs. A comprehensive characterization and modeling of the small-signal and high-frequency noise performance of highly scaled Si/SiGe n-MODFETs is presented. The effect of gate shot noise is incorporated in the broadband noise model. SiGe MODFETs offer the potential for high-speed and low-voltage operation at high frequencies and hence are attractive devices for future RF and mixed-signal applications. This work advances the state-of-the-art in the understanding and analysis of the RF performance of highly scaled Si-CMOS devices as well as emerging technologies, such as Si/SiGe MODFETs. The key contribution of this dissertation is to provide a robust framework for the systematic characterization, analysis and modeling of the small-signal and RF noise performance of scaled Si-MOSFETs and Si/SiGe MODFETs both for mainstream and extreme-environment applications.