We have investigated the effects of vacuum annealing on the optical and electrical properties of the p-type copper-oxide thin-film transistors (TFTs). The vacuum annealing of the copper-oxide thin-film was performed using the RF magnetron sputter at various temperatures. From the x-ray diffraction and UV-vis spectroscopy, it is demonstrated that the high-temperature vacuum annealing reduces the copper-oxide phase from CuO to Cu 2 O, and increases the optical transmittance in the visible part of the spectrum. The fabricated copper-oxide TFT does not exhibit the switching behavior under low-temperature vacuum annealing conditions. However, as the annealing temperature increases, the drain current begins to be modulated by a gate voltage, and the TFT exhibits a high current on-off ratio over 10 4 as the vacuum annealing temperature increases over 450 • C. These results show that the vacuum annealing process can be an effective method of simultaneously improving the optical and electrical performances in p-type copper-oxide TFTs.

We investigate the charge transport mechanism and subgap density of states (DOS) in p-type Cu2O thin-film transistors (TFTs) using the bias and temperature dependence of the drain currents. Among several charge transport mechanisms, the experimental data are well matched with a multiple trapping and release model, which suggests that the charge transport in the Cu2O TFT is mainly limited by trap states at grain boundaries or dielectric/semiconductor interface. The subgap DOS is extracted based on the Meyer-Neldel rule. Large density of subgap states is extracted, which is considered to be the reason of low mobility in fabricated Cu2O TFTs.

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The authors investigated the effects of active layer thickness on the structual, optical, and electrical characteristics of p-type Cu2O thin-film transistors (TFTs). It was observed that as the channel thickness increases, the average grain size and root mean square roughness of the Cu2O thin films increase, but the optical transmittance notably decreases, especially in the short wavelength range below 500 nm. The p-type Cu2O TFT device exhibits the cleanest transfer function with only a small subthreshold slope when the channel thickness is 45 nm, whereas notable subthreshold slope humps are observed in the transfer curves for devices with thicker channels.

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