III-V materials are under serious consideration as a replacement of the Si channel in MOS transistors and draws great attention due to the potential for ultrahigh speed transistor devices. However, to date, a superior-quality MOS GaAs-device has been difficult to achieve and is attributed to low quality of the central part of the device, i.e., high-k/III-V interface. Among the III-V materials studied most extensively in this regard is GaAs. Specifically, the relatively poor performance of GaAs surface channel MOS transistors mainly arises from Fermi level pinning at the interface, which is caused by GaAs surface oxidation and the resultant interfacial bonding with high-k dielectrics. As a result, substantial research on the GaAs surface and the GaAs/HfO ₂ interface has been investigated in this dissertation. Moreover, oxide growth on GaAs will be discussed based on the latest investigations of first-principles molecular dynamics.

To further clarify the origin of the Fermi level pinning, electronic structures of GaAs/HfO₂ interfaces with various interfacial structural disorders are investigated. The As-As dimers, Ga-dangling bonds and partial oxidation states of Ga contribute to the gap states and pin the Fermi level. Control of the interface thermal stability and band offsets with respect to the amount of interfacial oxygen is elucidated as well. Finally, diverse passivation schemes includeing F, Cl, H and Si are proposed to explain the passivating mechanism at the interface.