Epitaxial Electrodeposition of a Crystalline Metal Oxide onto Single-Crystalline Silicon

Epitaxial films of cuprous oxide, Cu 2 O, are electrodeposited from aqueous solution onto single-crystalline Si(001). The epitaxial growth of Cu 2 O onto Si is an unexpected result, because there is a strong driving force for the oxidation of Si to form a native amorphous SiO 2 layer. The Cu 2 O films are single-crystalline in nature, with little or no fiber texture. High-resolution X-ray diffraction shows that the very large lattice mismatch of −21.4% is reduced to +11.2% by the formation of a Cu 2 O(001)[100]//Si(001)[110] orientation relationship, in which the film is rotated 45° around the common [001] axis. Cross-sectional transmission electron microscopy studies suggest that the growth mechanism involves an initial electroless deposition of Cu 2 O epitaxial seeds in direct contact with the Si(001), with the concomitant oxidation of Si to form a layer of amorphous SiO 2 about 3 nm thick. Electrochemical deposition of Cu 2 O then proceeds on the epitaxial seeds, with the deposit growing not only perpendicular to the surface but also laterally across the SiO 2 interlayer. This type of lateral overgrowth is used in the production of semiconductor-on-insulator (SOI) structures to avoid defects due to misfit strains.