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Aggressive reduction in the thickness of SiO2-based gate dielectrics in ULSI devices brings about a number offimdamental problems, the most critical ones being reduced dielectric reliability and exponentially increasing leakage (tunneling) current with decreasing oxide thickness. This has induced an urgent search for alternatives dielectric materials (high-I( dielectrics). The common approach has involved amorphous materials with higher dielectric constants, :JUch as metal oxides and their silicates. The problem here is to keep the material amorphous even after post-depOsition high temperature processing. A different approach is based on the development of epitaxial metal oxides grown directly on silicon surfaces. An epitaxial oxide involves more effort, but it has the advantages of enabling defined interface engineering and higher thenna! stability. MBE is known for its superior capability in atomic level engineering and interface control, and is one of the techniques being investigated/or the epitaxial growth of various high-I( materials.