Investigation of Europium Doped Wide Band Gap Oxides and an Annealing Study of the Amorphous Oxide Semiconductor - Indium Gallium Zinc Oxide

Abstract

The electronic, optical and luminescent properties of europium doped wide band gap oxide thin films and the electronic properties of indium gallium zinc oxide (IGZO), a novel amorphous oxide semiconductor were investigated. The thin films of europium doped gallium and gadolinium oxides and indium gallium zinc oxide were deposited on c-axis oriented sapphire substrates by Pulsed Laser Deposition at various conditions of temperature, pressure and doping concentration. Europium doped gallium oxide was found to be in beta phase with monoclinic crystal structure and the films exhibited intense red emission under cathode ray excitation with a peak wavelength of emission at 611 nm which corresponds to the transitions from ⁵D₀ to ⁷F₂ levels in europium. Europium doped gadolinium oxide thin films were found to exhibit two different phases (cubic and monoclinic) with the one of the phases being dominant depending on the growth conditions. The peak wavelength of emission was either 611 nm or 613 nm depending on the phase of the films.

The amorphous indium gallium zinc oxide thin films were found to exhibit very high hall mobilities of the order of ˜15 cm²∙V⁻¹∙s⁻¹ and the conductivity could be controlled over several orders of magnitude from 5 x 10⁻³ S∙cm⁻¹ to 10 S∙cm⁻¹ in the amorphous phase. Annealing the films in presence of air was found to decrease the carrier concentration of the films due the incorporation of oxygen in the films thereby filling up the oxygen vacancies. Applications of amorphous indium gallium zinc oxide include Transparent Thin Film Transistors and use as transparent conducting oxide for optoelectronic devices.