Two-dimensional Electron Gas At Oxide Interfaces Prepared By Spin Coating Chemical Methods

The two-dimensional electron gas?2DEG?at LaAlO₃?LAO?and SrTiO₃?STO?interface is of remarkable interest due to its numerous characteristics like ferromagnetism,superconductivity,tunable Rashba spin-orbit coupling,and highly efficient spin to charge conversion.Due to these properties,LAO/STO interface has attracted significant attention and has become promising candidate for next generation spintronics applications.The electronic properties in Si and III-IV group-based semiconductors are determined by p-orbitals and free electrons whereas in transition metal oxides,the electronic properties are defined by correlated electrons and delicately balanced hybridization between d-orbital of transition metals and p-orbital of oxygen atoms.Due to such hybridization and correlation,transition metal oxides exhibit special characteristics and hence will occupy a special place in future electronic and spintronics applications.In general,the LAO/STO interfaces have been fabricated by pulse laser deposition.In this thesis,we will introduce the spin coating chemical methods for the fabrication of 2DEG and later will show the effects of buffer layer and doping transition metal at Al site in LAO over layer films on the2DEG obtained by this method.Main achievements include:1.High mobility 2DEGs are obtained at the?001?,?011?and?111?-oriented LaAlO₃/SrTiO₃?LAO/STO?interfaces by utilizing spin coating chemical method,which is a gentle technique where plasma bombardment of the pulsed laser deposition is not applied.X-ray diffraction spectrum and x-ray reflectivity analysis reveal epitaxial growth of the LAO over layer on STO,with uniform thicknesses of¹5 nm,²0 nm and²6 nm for?001?,?011?and?111?orientations,respectively.The magnetotransport measurements show that the interfaces exhibit metallic behavior from room temperature down to 2 K and linear Hall resistances with applied magnetic field.The carrier mobilities for the?001?,?011?and?111?LAO/STO interfaces are²8 000 cm²/Vs,²2 000 cm²/Vs and⁸300 cm²/Vs at 2 K,respectively,and⁸cm²/Vs,⁴ cm²/Vs and⁴ cm²/Vs at room temperature.2.We report our investigations on the 2DEG fabricated by spin coating LAO layer on a?001?STO substrate where the interface is buffered by ultrathin La_2/3Sr_1/3MnO₃?LSMO?layer.Highly mobile 2DEG is observed at interfaces where the thickness of the buffer layer is below 3uc.Corresponding to the thickness of the buffer layer of 0,1,and 2uc,the Hall mobilities of 2DEG are²4 000 cm²/Vs,²8 000 cm²/Vs,and⁵9 600 cm²/Vs at 2 K.In contrast,the 2DEG at interface with a buffer layer of thickness of 3 uc shows a comparatively low mobility?³000 cm²/Vs at 2 K?.Moreover,anomalous Hall effect?AHE?is observed in this 2DEG below 20 K that is the indication of the existence of a long-range ferromagnetic order.3.We report the two-dimensional electron gas existing at interfaces of cobalt doped LAO and TiO₂-terminated STO using spin coating chemical methods.It is found the two-dimensional electron gas at LaAl_1-xCo_xO₃?x=0.1,0.3?and STO?001?interfaces is achieved after a vacuum annealing performed for pretty less time as compared to pure LAO/STO interfaces.The presence of cobalt in over layer films is confirmed by XPS measurements that shows clear Co 2p peaks when x=0.1 and x=0.3.The two-dimensional electron gas at LaAl_1-xCo_xO₃?x=0.1,0.3?and STO?001?interfaces shows ferromagnetic behavior below 30 K when x=0.1 and below 50 K when x=0.3.Moreover,the carrier density is 4.49×10¹³ cm^-2 and 2.39×10¹33 cm^-2 and Hall mobility is 73.4 cm²/Vs and 147.3 cm²/Vs at 2 K for x=0.1 and 0.3 respectively.This work shows the potential of chemical methods for securing spin polarized 2DEG at cobalt doped LaAlO₃ and SrTiO₃ interface.