Tunneling through silicon dioxide thermally grown on silicon carbide and silicon substrates

A comprehensive theoretical and experimental examination of tunneling through silicon dioxide (SiO₂) is presented.; The detailed theoretical examination of tunneling includes physical effects involved in the first order theory as well as second order effects that are often neglected in the literature. These second order effects include conservation of transverse momentum, dispersion relations within the bandgap of SiO ₂, image force barrier lowering, and multidimensional analysis of the transmission probability. Furthermore, I show that the Fowler-Nordheim equation, derived in 1928 as a theoretical prediction of field emission from metals into a vacuum, is not valid when carriers are emitted from a semiconducting substrate. A new formalism to describe the field emission of carriers emitted from a semiconductor has been developed.; Experimental tunneling results are obtained for SiO₂ grown on both silicon carbide (SiC) and silicon (Si) substrates. To compare results with those reported in literature, barrier heights are extracted using the standard Fowler-Nordheim analysis. An aluminum/SiO₂ barrier height of 2.7 eV is found for SiO₂ grown on both SiC and Si substrates indicating that the SiO₂ is the same for both substrate types. In addition, I report for the first time on the tunneling of holes from the valence band of SiC into the valence band of SiO₂. The extracted barrier height for holes is 2.38 eV using a parabolic dispersion relation and a mass for holes within the oxide of 0.42 m₀. The measured hole current is the dominant current mechanism through the structure. Furthermore, I analyze the temperature dependent tunneling of carriers through MOS structures fabricated on n-type SiC. The results yield a room temperature barrier height for electrons in the conduction band of 2.12 eV and 1.92 eV for 6H and 4H-SiC respectively and a temperature dependent barrier lowering of 1.1 meV/K for 6H-SiC and 2.2 meV/K for 4H-SiC. The small room temperature barrier heights along with the large temperature-dependent barrier lowering for oxides grown on n-type SiC limit the usefulness of these structures for high temperature and high power applications.