Solution processed ZnO homogeneous quasisuperlattice materials

Abstract

Heterogeneous multilayered oxide channel materials have enabled low temperature, high mobility thin film transistor technology by solution processing. The authors report the growth and characterization of solution-based, highly uniform and c-axis orientated zinc oxide (ZnO) single and multilayered thin films. Quasisuperlattice (QSL) metal oxide thin films are deposited by spin-coating and the structural, morphological, optical, electronic, and crystallographic properties are investigated. In this work, the authors show that uniform, coherent multilayers of ZnO can be produced from liquid precursors using an iterative coating-drying technique that shows epitaxial-like growth on SiO2, at a maximum temperature of 300 °C in air. As QSL films are grown with a greater number of constituent layers, the crystal growth direction changes from m-plane to c-plane, confirmed by x-ray and electron diffraction. The film surface is smooth for all QSLs with root mean square roughness <0.14 nm. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) of electronic defects in the QSL structure show a dependence of defect emission on the QSL thickness, and PL mapping demonstrates that the defect signature is consistent across the QSL film in each case. XPS and valence-band analysis shown a remarkably consistent surface composition and electronic structure during the annealing process developed here.