Advances in heteroepitaxy of oxides on silicon

Direct epitaxy of high-quality perovskite oxides on silicon paves the way for their integration with Si microelectronics. At Motorola Labs, we have achieved heteroepitaxy of high-quality perovskite oxide films and stacks on up to 8-in. Si and silicon-on-insulator (Sol) substrates by using molecular beam epitaxy. Alkaline earth metals are used to remove the native oxide on Si and Sol at 720-800 degreesC, well below the SiO2 thermal desorption temperatures. A stable (2 x 1) surface structure is the critical enabling template for oxide epitaxy on silicon. Unit cell-by-unit cell growth of SrTiO3 (STO) by using co-deposition of Sr and Ti in oxygen promotes Ti oxidation and produces higher-quality films on Si, compared to a layer-by-layer flux shuttering technique, especially at the initial nucleation stage. Characteristic half-order reconstructions of the perovskite oxide surface are useful in real-time stoichiometry monitoring and control during growth while the wafers are rotating. Amorphous interfacial layer between the epitaxial oxide and silicon can be tailored by controlling the oxide growth process and parameters. Al-doping is found to expand the band gap and reduce the leakage current density in the STO films. (C) 2004 Elsevier B.V. All rights reserved.