M.S. Thesis Defense: Ittai Baum
Monday, August 5, 2019
Room 2332 AVW
301 405 3681
Quantum mechanics is applied to the study and simulation of two features of group IV semiconductor devices: metal/n-type 4H-SiC interfaces for SiC-based Schottky diodes and GeO$_2$ for Ge-based Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs).
SiC is well suited for power electronics due to its relatively wide bandgap and high breakdown field. In Schottky power diodes, one consideration in device performance is reverse saturation leakage. For metal/4H-SiC interfaces, reverse saturation leakage current is modeled using a calculated quantum mechanical transmission coefficient via the Symmetrized Transfer Matrix Method (STMM). The classical thermionic emission model and quantum model are compared for multiple donor concentrations. The quantum model is then compared to experimental results for Ti/4H-SiC measurements, and the effect of Fermi pinning is included to account for the correct barrier height. Multiple donor concentrations are again modeled to best fit the bias dependence of the measured curves to find an effective doping level that reflects barrier thinning possibly due to defects.
Ge is considered as a possible replacement for Si in MOSFET design as device lengths continue to scale down to match Moore's Law and Si MOSFETs become increasingly difficult to fabricate. Ge is considered due to its relatively high electron and hole mobilities, and its ability to grow a native oxide like Si. However, GeO$_2$ and the Ge/GeO$_2$ interface suffer from high defect densities, with one such defect being the oxygen vacancy defect. For GeO$_2$, the oxygen vacancy defect, and corresponding fluorine passivation, are modeled by calculating the atomic configurations and energies using Density Functional Theory (DFT). Incorporation of fluorine atoms in the vicinity of the defect is modeled, as well as the incorporation of fluorine atoms within the oxide network. Hydrogen passivation is also calculated and found to not be as energetically favorable. Finally, fluorine diffusion through the oxide network is investigated by calculating the reaction pathway between two fluorine incorporation sites in the network.