Abstract
This work presents the in-situ high energy electron diffraction (RHEED), low energy electron diffraction (LEED) and photoemission spectroscopy (PES) studies for the structural and interfacial chemical characterization of molecular beam epitaxy (MBE)-grown fresh n-GaAs(111)A-2x2 surface and MBE-grown 3ML Gd2O3/GaAs(111)A-2x2 interface. The LEED pattern shows that the GaAs(111)A-2x2 surface follows the “Ga vacancy-buckling model.” Surface As 3d and Ga 3d core-level binding energy shifts have been resolved by in-situ synchrotron radiation photoemission (SRPES) from the GaAs(111)A-2x2 surface. The core-level shifts are -231 meV and +282 meV for As and Ga, in agreement with the vacancy-buckling model. On the other hand, the chemical bonding for the Gd2O3/GaAs(111)A-2x2 interface is also resolved by SRPES. The interface is consisted of Ga-O (Ga1+, +771eV), As-O (As1+, +522eV) bonding, and a large amount of unreacted surface atoms. The Ga-O bond will induce excess negative charge on the nearby As atom and create a As 3d surface core-level shift at -635meV.

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