Enhancing electronic properties by suppressing nucleation delay for low-temperature processed atomic-layer-deposited amorphous zinc–tin-oxide thin films

Atomic-layer-deposited (ALD) zinc-tin-oxide (ZTO) thin films offer promising electronic properties for many applications, but their development has been limited by their tendency to experience significant nucleation delay—which tends to introduce impurity—during deposition. This study utilized in-situ quartz crystal microbalance (QCM) analysis combined with ex-situ compositional analysis to examine the nucleation-delay characteristics of ZTO ALD and their dependence upon the oxidant-precursor settings. The results indicated that nucleation delay occurred solely during the ZnO-on-SnO2 deposition step as a result of persisting ethyl ligands of the organozinc precursor, diethylzinc, which could be mitigated by using H2O2 instead of H2O as the oxidant precursor and introducing a discrete-feeding or exposure procedure for the H2O2 half cycle to increase the effective oxidant dose. The effects of nucleation delay on the electronic properties of ALD ZTO films was examined with thin-film transistor (TFT) devices, where suppression of nucleation delay yielded substantial improvement in the device performance, achieving a high field-effect mobility of 21.5 cm2/V s, low sub-threshold swing of 0.16, high on/off ratio of 2 × 108, and enhance-mode operation without needing elevated-temperature post-processing. The findings present valuable improvements over the state of the art and provide insights useful for the development of other types of ALD multi-component films.