Analyses of Surface and Interfacial Layers in Polycrystalline $\hbox {Cu}_{2}\hbox {O}$ Thin-Film Transistors

Effects of low temperature (300^°C) annealing on Cu₂O films were investigated by analyzing the film stacking structures with photoemission spectroscopy, X-ray reflectivity spectroscopy and spectroscopic ellipsometory in relation to p-channel TFT characteristics and possible origins of trap states. The Hall mobility of optimum Cu₂O films was 2.1 cm²/(V·s); however, the bottom-gate Cu₂O TFT exhibited a much lower field effect mobility of the order of 10 ^-4 cm²/(V·s) and an on/off drain current ratio of 10 ³. This work detected a surface layer and an interface layer in the Cu₂O/ SiO₂ samples, i.e., the surface layer included the 2+ state of Cu ions that would form subgap hole trap states at the back channel region. In addition, the low-density layer at the Cu₂O-SiO₂ interface would produce extra interfacial trap states.