Role of ALD AlO Surface Passivation on the Performance of p-Type CuO Thin Film Transistors.

High-performance p-type oxide thin film transistors (TFTs) have great potential for many semiconductor applications. However, these devices typically suffer from low hole mobility and high off-state currents. We fabricated p-type TFTs with a phase-pure polycrystalline CuO semiconductor channel grown by atomic layer deposition (ALD). The TFT switching characteristics were improved by applying a thin ALD AlO passivation layer on the CuO channel, followed by vacuum annealing at 300 °C. Detailed characterization by transmission electron microscopy-energy dispersive X-ray analysis and X-ray photoelectron spectroscopy shows that the surface of CuO is reduced following AlO deposition and indicates the formation of a 1-2 nm thick CuAlO interfacial layer. This, together with field-effect passivation caused by the high negative fixed charge of the ALD AlO, leads to an improvement in the TFT performance by reducing the density of deep trap states as well as by reducing the accumulation of electrons in the semiconducting layer in the device off-state.