Integration of functional oxide thin film heterostructures with silicon (100) substrates

The novel functionalities of metal oxides provide the opportunity for the development of next generation optoelectronic, spintronic and a host of other multifunctional devices. A critical issue in the development of practical devices based on metal oxides is the integration of high quality epitaxial oxide thin films with the existing silicon technology which is based on silicon (100) substrates. However, silicon is not suitable for epitaxial growth of oxides owing to its tendency to readily form an amorphous oxide layer at the film-substrate interface. The oxide films deposited directly on silicon exhibit poor crystallinity and are not suitable for device applications. To overcome this challenge, appropriate substrate templates must be developed for growth of oxide thin films on silicon substrates.;The present work is focused on developing integration methodology of functional oxides with Si (100) substrates using an yttria-stabilized zirconia (YSZ) template layer. If the deposition conditions are controlled properly, YSZ can be grown epitaxially on silicon substrates even if the native oxide is not etched prior to deposition. This is believed to occur by reaction between zirconium and native silicon dioxide. These Si (100) substrates with epitaxial YSZ template layer can be used to grow functional oxide thin films.;The above approach has been used to integrate zinc oxide (ZnO) thin films with Si (100) substrates. The wide band gap (∼3.4 eV), large exciton binding energy (60 meV) and room temperature ferromagnetism make ZnO a potential candidate for a host of next generation optoelectronic and spintronic devices. A thorough study on growth and properties of ZnO films on YSZ buffered Si (100) substrates was performed. The ZnO and YSZ films were deposited by pulsed laser deposition (PLD) technique. Detailed characterization of the deposited films was done using x-ray diffraction, transmission electron microscopy (TEM), electrical measurements and photoluminescence spectroscopy. Using YSZ buffer layer, we have been able to epitaxially integrate both non-polar (c-plane) and semi-polar (r-plane) ZnO films with Si (100) substrates. It was observed that, depending on the oxygen pressure during the deposition, ZnO can grow in two different crystallographic orientations (c-plane or r-plane) on YSZ buffered silicon. Experiments carried out to elucidate the role of oxygen pressure indicated that the crystallographic orientation of ZnO depends on the nature of atomic termination of YSZ layer. It has been proposed that crystallographic orientation of ZnO is controlled by chemical free energy associated with the ZnO/YSZ interface.;In order to form p-n junction with n-type ZnO, another multifunctional oxide La0.67Sr0.33MnO3 (LSMO) was epitaxially integrated with Si (100) substrates. LSMO is a p-type materials and exhibits interesting properties such as semiconductor to metal transition (SMT), room temperature ferromagnetism and colossal magneto resistance (CMR). Junctions based on CMR materials are of special interest, because their electrical and magnetic properties can be modulated by external electric and magnetic fields. It has been demonstrated that epitaxial nonpolar a-plane ZnO films can be grown on LSMO integrated with Si (100) substrates.