Epitaxial Thin Films and Heterojunctions of Electron Doped Manganite La1-Xhfxmno3

This dissertation, "Epitaxial Thin Films and Heterojunctions of Electron Doped Manganite La1-xHfxMnO3" by Libin, Jin, 靳立彬, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled EPITAXIAL THIN FILMS AND HETEROJUNCTIONS OF ELECTRON DOPED MANGANITE La Hf MnO 1-x x 3 Submitted by Jin Libin For the Degree of Master of Philosophy at The University of Hong Kong in October 2015 The strong electron correlated system like perovskite oxides in transition metal oxides have been studied for many years. Most efforts have been focused mainly 3+ 4+ on the hole-doped manganites with Mn /Mn double exchange interaction. Recently, the tetravalent ions doping has attracted considerable attention to make electron doping LaMnO compounds. Such electron-doped manganites may be applied for fabrication of all-manganites devices potentially. The sensitivities to magnetic fields, currents, electric fields, photo illumination and mechanical strain make the electron-doped manganites of great interests for relevant applications. In this thesis, thin films and heterojunctions of tetravalent hafnium doped perovskite manganite La Hf MnO were fabricated. The hafnium shows a 1-x x 3 unique tetravalent state as well as an ion radius closed to trivalent lanthanum ion. These properties make the investigation on La Hf MnO system relatively 1-x x 3 simple and reliable. The structural and physical properties of La Hf MnO (x=0.1, 0.2, 0.3) thin 1-x x 3 films were studied systematically. The crystal structure and epitaxy of La 1- Hf MnO thin films were examined by X-ray diffraction. The temperature x x 3 dependent resistance and magnetization of different samples were investigated in detail. Both temperature dependent resistance and field dependent magnetization indicated the evident transition between paramagnetic and ferromagnetic states. The electronic structures of epitaxial La Hf MnO were measured by X-ray 0.9 0.1 3 Photoelectron Spectroscopy. Both spectrum of Mn 3s and Mn 2p demonstrated 2+ 3+ the composition of Mn /Mn ions. Such evidence strongly suggested the electron-conductive mechanism in La Hf MnO systems. 0.9 0.1 3 The heterojunctions composed of oxygen-deficient SrTiO and 3-δ La Hf MnO thin films have been studied. These heterojunctions demonstrate 0.9 0.1 3 good rectifying characteristics with very low leakage current and high breakdown voltage in a wide temperature range. X-ray diffraction and electron backscattering diffraction measurements reveal that both SrTiO and La Hf MnO layers 3-δ 0.9 0.1 3 have single crystal nature and [001]-orientation. Transmission electron microscope images show an excellent epitaxial growth of SrTiO and 3-δ La Hf MnO layers. Such all-oxides junctions utilizing the bi-layer 0.9 0.1 3 heterostructure may be applied in microelectronic devices. The n-i-p heterojunctions have been fabricated by depositing an n-type La Hf MnO layer on p-type Si with a thin SrTiO intermediate layer. These 0.9 0.1 3 3 junctions exhibit excellent rectifying properties for temperature from 20 K to 300 K. Under illumination of 630 nm light a remarkable photocurrent has been observed. The photosensitivity is over 1200% under -3 V bias and illumination of the light at room temperature, demonstrating very a pronounced photocurrent effect. The injection of photo-carriers could be responsible for the observed phenomenon. The obtained results in this thesis demonstrate the electron-conductive mechanism in La Hf MnO system. The La Hf MnO based heterojunctions 1-x x 3 0.9 0.1 3 show remarkable characteristics and may