Epitaxial ferromagnetic oxide thin films on silicon with atomically sharp interfaces

Abstract

Epitaxial growth of atomically-sharp interfaces serves as one of the main building blocks of nanofabrication. Such interfaces are crucial for the operation of various devices including transistors, photo-voltaic cells, and memory components. In order to avoid charge traps that may hamper the operation of such devices, it is critical for the layers to be atomically-sharp. Fabrication of atomically sharp interfaces normally requires ultra-high vacuum techniques and high substrate temperatures. We present here a new self-limiting wet chemical process for deposition of epitaxial layers from alkoxide precursors. This method is fast, cheap, and yields perfect interfaces as we validate by various analysis techniques. It allows the design of heterostructures with half-unit cell resolution. We demonstrate our method by designing hole-type oxide interfaces SrTiO3/BaO/LaAlO3. We show that transport through this interface exhibits properties of mixed electron-hole contributions with hole mobility exceeding that of electrons. Our method and results are an important step forward towards a controllable design of a p-type oxide interface. Growth methods of epitaxial thin films can be roughly categorized as physical and chemical. While physical methods (i.e. molecular beam epitaxy, pulsed laser de-position (PLD)[1]) are based on creating a beam of the film material and transporting it in vacuum onto the sub-strate. Chemical methods such as: chemical vapor depo-sition and atomic layer deposition (ALD) use a chemical precursor, a compound containing the film growth material. The precursor is transferred in vacuum onto the substrate, where the surface catalyzes the precursor dis-sociation reaction, and the deposition of the film. While giving very good results for film growth, these methods lack the versatility and become increasingly complex [2] when a wide variety of surface monolayers is required. (A) (B) (C) FIG. 1: Solution monolayer epitaxy process. The TiO2 terminated SrTiO3 is submersed in a solution of Ba II iso-propoxide (A) in ethylene glycol, which is kept slightly below the decomposition temperature of the precursor Ba II iso-propoxide. Surface catalysis results in decomposition of of the precursor, which results in epitaxial deposition of BaO on the surface (B). This process is terminated when a complete layer of BaO covers the surface (C). FIG. 2: (color online). Two models of SrTiO3/LaAlO3 interfaces. On the right the conventional n-type interface. On the left our new p-type interface which incorporates a mono-layer of BaO between the SrTiO3 substrate and the polar LaAlO3 film. The presence of the Ba film forces a growth with inverted LaAlO3 polarity. In Solution monolayer epitaxy (SoME) the substrate of choice, in this case a (100) TiO 2 terminated SrTiO 3 , is submersed in a solution of a dissolved precursor of choice, at a temperature slightly lower than its decomposition temperature. Under these conditions the precursor molecules do not decompose in the solution unless they are in close proximity to the surface ...

Atomically Flat Ultrathin Cobalt Ferrite Islands

“…Strategies for fabricating high quality CFO nanostructures while preserving the ability to tune its physical properties are thus highly appealing even though extremely demanding. Substantial progress has been made in the development of high‐quality CFO thin films through a variety of methods, recently also at low growth temperatures . However, the issue of APBs remains.…”