The mechanism of Fermi level pinning/unpinning at high k Oxide/GaAs interface

Unpinning of Fermi level at oxide/GaAs interface is the one of the key issues of realizing GaAs-based III-V metal-oxide-semiconductor field-effect-transistors (MOSFETs) for high-speed and high power applications due to inherent advantages of high electron mobility, semi-insulating substrates, and high breakdown fields. In this study several important high dielectric constant materials, Al$_{2}$O$_{3}$, HfO$_{2}$, Ga$_{2}$O$_{3}$(Gd$_{2}$O$_{3})$ and Y$_{2}$O$_{3}$, were \textit{in-situ} deposited on GaAs(001), and exhibited the different Fermi level pinning/unpinning behavior of current-capacitance (C-V) characteristics. In order to correlate the relationship between the oxide/GaAs interfacial structure and their electrical behavior,\textit{ in-situ} XPS analysis was conducted shortly after nano high $\kappa $ oxides were deposited on GaAs. Our studies suggest that Fermi level unpinning in the oxide/GaAs hetero-structure is attributed to the exclusion of the As-As and the As-O bonding during the initial interfacial formation.