Molecular precursor derived and solution processed indium–zinc oxide as a semiconductor in a field-effect transistor device. Towards an improved understanding of semiconductor film composition

Abstract

Amorphous indium–zinc-oxide, IZO, of the composition indium–zinc 60/40, was prepared by a solution process using a combination of the two molecular precursors diaqua-bis[2-(methoxyimino)-propanoato]zinc(II) and tris[2-(methoxyimino)-propanoato]indium(III) followed by a rapid calcination step which leads to the conversion into an IZO ceramic. Thin IZO films of about 15 nm thickness deposited on field effect transistor substrates showed an excellent performance with a mobility μ of 7.4 cm² V⁻¹ s⁻¹, an I_on/off ratio of ∼4.7 × 10⁵ and a threshold voltage V_th of +4.8 V after rapid thermal processing up to 450 °C. Characterization of the IZO material by TEM, SEM, Auger, XPS, AFM, photoluminescence and impedance spectroscopy revealed the amorphous nature of the films. Nevertheless the IZO contained well separated and dispersed In₂O₃ nanocrystallites with cubic bixbyite structure of about 5 nm and smaller, which were embedded in the amorphous IZO host matrix. The concentration of these In₂O₃ nanocrystallites was too small to be detectable by EPR. Indium(III) in the amorphous phase exhibited a characteristic and significant line broadening of the signal of the ZnO component in IZO.