Epitaxial integration of TiO2 with Si(100) through a novel approach of oxidation of TiN/Si(100) epitaxial heterostructur
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Epitaxial integration of TiO2 with Si(100) through a novel approach of oxidation of TiN/Si(100) epitaxial heterostructure A. Moatti1, R. Bayati2, S. Singamaneni1, 3, J. Narayan1 1. Department of Materials Science and Engineering, North Carolina State University, EB-1, Raleigh 27695-7906, NC, USA. 2. Intel Corporation, IMO-RA, Hillsboro, OR 97124, USA. 3. Department of Physics, University of Texas at El Paso, El Paso, Texas 79958, USA ABSTRACT In this study, we provide a novel approach to the epitaxial integration of TiO2 with Si(100) and investigate the defect mediated ferromagnetism in TiO2 structure. Epitaxial TiO2 thin films were grown on a TiN/Si(100) epitaxial heterostructure through oxidation of TiN where a single crystalline rutile-TiO2 (r-TiO2) with a [110] out-of-plane orientation was obtained. The epitaxial relationship is determined to be TiO2(1ͳത0)||TiN(100) and TiO2(110)||TiN(110). We rationalized this epitaxy using the domain matching epitaxy paradigm. First TiN is grown epitaxially on Si(100). Subsequently, TiN/Si(100) samples are oxidized to create r-TiO2/TiN/Si(100) epitaxial heterostructures. The details of the mechanism behind the oxidation of single crystalline TiN to TiO2 was investigated using atomic scale high resolution electron microscopy techniques. Defects introduced to the heterostructure during oxidation caused ferromagnetism in TiO2 thin film which is reversible and can be tuned by controlling oxygen partial pressure. The source of magnetization is correlated with the presence of oxygen vacancy leading to introduction of two localized states; hybrid and polaron among neighboring Ti atoms, and titanium vacancy providing four holes to form molecular oxygen. We present structure property correlations and its impact on the next generation solid state devices. INTRODUCTION Titanium dioxide has been used for a variety of applications, including photocatalysts, solar cells, optical coatings, capacitor-varistors for protection against high voltage transients, gate insulators in MOSFETS, spacers in magnetic spin-valve systems, biocompatible implants, Libatteries, and electrochromic devices [1-5]. Epitaxial form of TiO2 is of more importance due to its role in understanding the mechanisms in atomic scale and the need for controlling over transport properties in solid state devices. There are several reports on the epitaxial integration of TiO2 on the sapphire substrate [6,7]. However, in microelectronic industries, there is a growing demand on the integration of epilayers with Si(100) where there are very limited systematic studies. Thus, there is a need for systematic study on TiO2 epitaxy and its integration with Si(100). Intrinsic defects play an important role in defining properties of epitaxial heterostructures. Ferromagnetism has been detected in the semiconducting oxides like In2O3, HfO2, SnO2, ZnO, TiO2 without extrinsic doping [8-11]. The nature of ferromagnetism has been attributed to either oxygen or cation vacancy. Introduction of oxygen and titanium vacancies as donor and accepter in
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