Role of ALD Al2O3 Surface Passivation on the Performance of p-Type Cu2O 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 Cu2O semiconductor channel grown by atomic layer deposition (ALD). The TFT switching characteristics were improved by applying a thin ALD Al2O3 passivation layer on the Cu2O channel, followed by vacuum annealing at 300 degrees C. Detailed characterization by transmission electron microscopy-energy dispersive X-ray analysis and X-ray photoelectron spectroscopy shows that the surface of Cu2O is reduced following Al2O3 deposition and indicates the formation of a 1-2 nm thick CuAlO2 interfacial layer. This, together with field-effect passivation caused by the high negative fixed charge of the ALD Al2O3, 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.

Automated summary

High-performance p-type oxide thin film transistors (TFTs) have great potential for semiconductor applications, but often suffer from low hole mobility and high off-state currents. By applying a thin ALD Al2O3 passivation layer on the Cu2O channel and vacuum annealing, the TFT switching characteristics can be improved. Characterization by TEM-EDX and XPS shows that Al2O3 deposition on Cu2O reduces surface and forms a CuAlO2 interfacial layer. This, along with field-effect passivation, leads to improved TFT performance by reducing trap states and electron accumulation in the off-state.