Effects of air-annealing on the electrical properties of p-type tin monoxide thin-film transistors

We have investigated the effects of air-annealing on the electrical performance of the p-type tin oxide thin-film transistors (TFTs). The air-annealing of the tin oxide thin-film was made using a mini furnace at various temperatures. From the x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) data, it is demonstrated that the phase of tin oxide partially transforms from SnO to SnO₂ with an air-annealing process, and it accelerates as the annealing temperature increases. The electrical performance of the p-type tin oxide TFT with a channel thickness of 25 nm exhibits much improved electrical performance when air-annealed at 230 °C for 1 h, but a decrease of the on-current is observed with an ambipolar operation in 260 and 290 °C air-annealed devices. Based on the XPS, XRD, and Hall measurement data, the reduced hole concentration inside the channel due to the recombination with electrons from SnO₂ is believed to be the reason for the electrical performance improvement in 230 °C air-annealed p-type tin oxide TFTs, and a partial formation of n-type SnO₂ channel is considered as the plausible reason for the ambipolar operation in tin oxide TFTs with high annealing temperatures. Our experimental results show that there is an optimum air-annealing temperature which can improve the electrical performance in p-type tin oxide TFTs. (paper)