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

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 mu of 7.4 cm(2) V-1 s(-1), an I-on/off ratio of similar to 4.7 x 10(5) and a threshold voltage V-th of +4.8 V after rapid thermal processing up to 450 degrees 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.