Fabrication and characterization of transparent oxide thin film

Abstract

Two types of transparent oxide thin film, namely, transparent ferroelectric thin film and transparent conductive oxide thin film has been studied. These transparent oxide thin films are commonly used in electro-optics applications. In this thesis, these two types of thin films were fabricated by various deposition methods such as pulsed laser deposition (PLD) and magnetron sputtering. Their structural, optical and electrical properties have been investigated. In the first part of the thesis, strontium barium niobate Sr0.5Ba0.5Nb2O6 (SBN) films doped with gadolinium (III) oxide were fabricated. These SBN films were grown epitaxially on either (100) MgO substrates or Pt-coated MgO (100) substrates. The effects of the Gd-doping concentration on the structural and ferroelectric properties of these films were investigated. Besides, the optical properties of the prepared Gd-doped SBN thin films i.e. the refractive index and extinction coefficient were characterized by UV-Vis spectrometer and spectroscopic ellipsometry to retrieve the thickness dependent effects on the optical properties of these films. The thickness dependent optical properties were also studied to fully evaluate the potential application of these films on various optoelectronic devices. The ferroelectric properties of SBN with different Gd-doping concentration were measured by using Pt bottom electrode and Au top electrode. The ferroelectric measurements showed that the 4%-Gd-SBN films had good ferroelectric properties. Ramanent polarization of +Pr =1.36 μC/cm² and -Pr =-5.73 μC/cm² and coercive field of +Ec=158.0kV and -Ec=-30.8kV were obtained. Two values of ramanent polarization are reported due to the asymmetric electrode materials has been used, causing the central shifting hysteresis loop. In the second part of the thesis, transparent conductive oxide Indium Tin Oxide plasmonic devices formed by inserting a thin gold spacer layer in between two ITO thin film i.e ITO/Au/ITO trilayer structure were fabricated. Symmetric Devices (i.e. have same top and bottom ITO layer thickness) with different top and bottom ITO thicknesses were fabricated in this thesis. The structural characterizations showed that the top and bottom ITO layers have different crystallinity due to the effect of inserted gold spacer. The electrical properties including the carrier concentration, mobility and resistivity were measured by using Van der Pauw configuration, and the optical properties such as refractive index, extinction coefficient and absorption spectra were studies by using spectroscopic ellipsometry and UV-Vis-NIR transmittance measurement. The results showed that increasing ITO thickness can tune the crossover wavelength from the near visible range (830 nm) to near infrared range (1490 nm), corresponding to over 600 nm of plasmonic tuning ability. The performance in different types of plasmonic devices using such multilayer structures were also being evaluated and reported. Finally, using the asymmetric structure (different in top and bottom ITO thickness in the trilayer structure), we differentiated the thickness contribution on bottom and top ITO layer to the trilayer structure on its electrical and optical properties. The asymmetric structure on the plasmonic properties can be fine-tuned on the epsilon-near-zero (ENZ) regimes.