Microwave synthesis and field effect transistor performance of stable colloidal indium-zinc-oxide nanoparticles

Abstract

Indium zinc oxide nanoparticles were prepared by microwave-assisted decomposition employing solutions of molecular air stable In and Zn precursors of Schiff base type. Stable colloidal ready to use dispersions with shelf-lives of several months were obtained at comparably low temperature of 140 °C by heating mixtures of indium and zinc complexes with Schiff base oximato ligands in 2-ethoxyethanol. IZO particles prepared therefrom with an In : Zn ratio of 60 : 40 display an average diameter of about 5 nm and appeared amorphous in nature. Thin films of the colloidal particles with a uniform surface coverage and low roughness could be obtained by spin-coating on silicon dioxide substrates. X-ray photoelectron spectroscopy showed that oxide formation had occurred after the microwave reaction, but could be improved further by annealing the films at elevated temperatures. The removal of adherent organic and hydroxy moieties at 450 °C thus led to an excellent semiconducting behaviour of the finally resulting IZO films. Obtained thin film transistors exhibited a n-type enhancement mode performance, with a mobility of 8.7 cm² V⁻¹ s⁻¹, an I_on/off ratio of 2.8 × 10⁵ and a threshold voltage V_th of +3.3 V.