Abstract
Nanometer-thick Y 2 O 3 films were grown epitaxially on GaN (0 0 0 1) using molecular beam epitaxy (MBE). The structures of the oxide films were studied in situ by reflection high energy electron diffraction (RHEED) during the growth and ex situ by high resolution X-ray diffraction using synchrotron radiation. At atmospheric pressure, Y 2 O 3 exists in either cubic or hexagonal structure. For the first time, the high-pressure monoclinic phase of Y 2 O 3 , stabilized by epitaxy, was prepared and preserved under atmospheric pressure. The electrical characterization carried out on the Y 2 O 3 /GaN metal-oxide-semiconductor (MOS) capacitors showed a leakage current density of ∼3.3×10 -6 A/cm 2 at 1.5 MV/cm, which remained almost the same after 800°C annealing. A dielectric constant of ∼20 and a hysteresis of ∼250 mV were deduced from the capacitancevoltage (CV) curves for the epitaxial monoclinic Y 2 O 3 . © 2010 Elsevier B.V. All rights reserved.