Characterization and modeling of strained silicon FET and gallium nitride HEMT devices

Metal-oxide-semiconductor field-effect transistors (MOSFETs) have shown impressive performance improvements over the past 10 years by incorporating strained silicon (Si) technology. Concurrently, interest in alternate device structures and channel materials has been increasing tremendously because of the scaling limitations on performance enhancement. This work focuses on the impact of strain on state-of-the-art Si planar MOSFETs, Si tri-gate (TG) FinFETs, and GaN HEMT devices.;Piezoresistive properties of Si n- and pMOSFETs are obtained by applying controlled external mechanical stress, using the four-point and concentric-ring wafer bending setups. The results are discussed by considering strain-induced band splitting, band warping, and consequently the carrier repopulation, and the altered conductivity effective mass and scattering rate. Strain experimental results on TG FinFETs, coupled with the understanding of strained planar MOSFET physics, are used to explain the strain-enhanced tri-gate device performance.;Gallium Nitride (GaN) high electron mobility transistors (HEMTs) are promising for high-power applications, such as microwave or RF amplifiers. However the application of these devices is limited by their reliability issues. A comprehensive study of the effects of mechanical stress on GaN HEMT channel resistance and gate leakage mechanisms is reported in this work. Using the tight binding method to calculate strained GaN band structure, the stress-altered channel resistance is simulated by considering two dimensional electron gas (2DEG) sheet carrier density and electron mobility variation. Several possible gate leakage mechanisms are modeled and compared to the experimental results. The Poole-Frenkel Emission from surface states is determined to be the dominant leakage mechanism and its stress dependence is investigated. Finally, the density functional theory (DFT) calculations based on various functionals are evaluated, and the HSE functional is employed to obtain the GaN band structure with correct bandgap. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html).