Understanding the temperature-dependent evolution of solution processed metal oxide transistor characteristics based on molecular precursor derived amorphous indium zinc oxide
Amorphous indium zinc oxide (IZO) thin films are accessible by solution-deposition of mixtures of molecular single-source precursors with dimethyl 2-hydroxyimino- and 2-nitromalonato ligands (dmm-NOH and Hdmm-NO2, respectively). Thermal combustion of the precursor molecules In3O3(dmm-NO2)3·(toluene) and [Zn4O(dmm-NO)6] leads to a highly exothermic decomposition reaction yielding amorphous indium zinc oxide (IZO) even at a temperature of 150 °C. The main aim of the present investigation is to correlate the electronic performance in such solution processed field-effect transistors (FET) with the presence of surface groups and bulk defects depending on the processing temperatures of the resulting IZO films (250 to 400 °C). In depth electronic characterization using X-Ray- and Photoelectron Emission Spectroscopy (XPS and UPS) reveals major electronic changes during thin film formation in the temperature range between 275 and 300 °C. These findings are confirmed by Positron Annihilation Spectroscopy (PAS) which allows the monitoring of defects in a picometer range in the resulting functional IZO thin films. Resulting transistor mobilities (μ) of the semiconducting IZO films are in the range of those of amorphous silicon even at a processing temperature of 250 °C and increase up to 6 and 9.5 cm2 (V s)−1 at 350 and 400 °C with on/off ratios of 105 up to 107, respectively.