Characterization of the atomic and electronic structures of oxide/III-V(001) interfaces

Despite the potential benefits of a commercially viable III-V based metal oxide semiconductor field-effect transistor (MOSFET) over current technology, development has proven to be an arduous task that has spanned four decades. A unique approach that combines an ultra-high vacuum chamber, scanning tunneling microscopy, scanning tunneling spectroscopy, and molecular beam epitaxy in situ was used to gain an atomic understanding of the early stages of surface oxidation. The chemisorption sites formed as well as their affect on the surface electronic structure of the material was determined. Density functional theory calculations were performed to confirm experimental findings as well as explain why certain chemisorption sites have adverse affects on the electronic structure of the material. The results obtained from this approach have led to great advancements in the understanding of Fermi level pinning (the inability to easily invert a semiconductor), by showing that oxygen chemisorbs onto the GaAs(001)-c(2x8)/(2x4) surface by displacing surface arsenic atoms and bonding in their place. The oxygen atoms withdraw charge from second layer gallium atoms to which they are bonded. The charge deficient second layer gallium atoms induce states within the band gap which cause Fermi level pinning. This result disproved the advanced unified defect model theory that has influenced the thinking in the development of a III-V based MOSFET since 1978. It has also been found that when Ga 2O is deposited on the clean GaAs(001)-c(2x8)/(2x4) surface it only bonds into or between arsenic dimer pairs. This bonding structure provides the surface arsenic atoms with a charge similar to arsenic in bulk GaAs, thereby unpinning the Fermi level. In2O, although very similar to Ga2O, inserts into or between arsenic dimer pairs, but also bonds within the trough. One trough site inserts an oxygen atom into the third layer arsenic dimers. This site greatly alters the charge on the trough arsenic atoms from their bulk GaAs charge, thereby pinning the Fermi level.