Metalorganic Molecular Beam Epitaxy of Magnesium Oxide on Silicon
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METALORGANIC MOLECULAR BEAM EPITAXY OF MAGNESIUM OXIDE ON SILICON F. Niu, B.H. Hoerman, and B.W.Wessels Department of Materials Science and Engineering and Materials Research Center, Northwestern University, Evanston, Illinois 60208 ABSTRACT Epitaxial cubic MgO thin films were deposited on single crystal Si (001) substrates by metalorganic molecular beam epitaxy (MOMBE) using the solid precursor magnesium acetylacetonate as the source and an RF excited oxygen plasma as the oxidant. The growth process involved initial formation of an epitaxial r3-SiC interlayer followed by direct deposition of a MgO overlayer. The film structure was characterized by X-ray diffraction as well as conventional and high-resolution transmission electron microscopy. Both the MgO overlayer and O3-SiC interlayer had an epitaxial relationship such that MgO (001) (or SiC (001)) // Si (001) and MgO [110] (or SiC [110])// Si [110]. No evidence of an amorphous layer was observed at either the MgO/SiC or SiC/Si interface. Dielectric properties of the epitaxial MgO thin films on Si (001) were evaluated from capacitance-voltage (C-V) characteristic of metal-oxide-semiconductor (MOS) structures. The C-V measurements indicated an interface trap density at midgap as low as 1011 to 1012 cm 2 eV1 and fixed oxide charge of the order of 101/ cm 2 , respectively. These results indicate that epitaxial MgO deposited by MOMBE has potential as a gate insulator. INTRODUCTION Epitaxial MgO layers on silicon substrates have potential applications in ultra-large scale integration and in microphotonics. Because of the thermodynamic stability of MgO with both silicon [1] and ferroelectric oxide thin films, it can be used as an ideal buffer layer between ferroelectric oxides and Si in optical integrated circuits. Furthermore since its dielectric constant of 9.65 is 3 times larger than Si0 2, crystalline thin film MgO is a potential alternative gate dielectric to Si0 2 in metal-oxide-semiconductor (MOS) devices and in metal / ferroelectric / insulator / semiconductor field effect transistor devices [2]. Despite the large lattice mismatch of 22.5% between MgO and silicon, which should preclude epitaxy, epitaxial films of MgO have been prepared by both pulsed laser deposition (PLD) [3] and RF magnetron sputtering [4]. We have been investigating metal-organic molecular beam epitaxy (MOMBE) as alternative approach for deposition of epitaxial MgO [5-6]. This technique utilizes highly volatile metalorganic compounds as the metal source. A major advantage of MOMBE is that the background pressure is very low (
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