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Molecular beam epitaxy growth of Si thin films on CaF2/Si(111) substrates has been studied. A surfactant-modified solid-phase epitaxy method, where the room temperature Si deposition was followed by annealing under Sb flux, resulted in a continuous, smooth epitaxial crystalline Si film with a sharp (√3×√3)R30° reconstruction and a surface roughness of 0.15-nm rms for a 2.8-nm Si thin film. This growth technique was used to fabricate CaF2/Si/CaF2 double-barrier resonant tunneling diodes in SiO2 windows patterned on Si(111) substrates. A negative differential resistance (NDR) peak was found at ∼0.35 V at 77 K, and the current density at the NDR peak was estimated to be 3-4 orders of magnitude higher than in earlier reports.