Simultaneous optimization of transmittance and resistivity for γ-CuI thin films via an iodination method at mild reaction condition

Abstract

In p-type γ-CuI thin films synthesized by the iodination of Cu layers with iodine vapor, a frosted-glass-like appearance with a rough surface is usually obtained, which makes it difficult to apply the γ-CuI films to transparent electronics. This paper proposes an innovative method for the preparation of highly transparent p-type γ-CuI films. A chemical reaction between Cu thin films and iodine vapor, combined with the layer-by-layer process at a temperature between room temperature and 120 °C are found to result in highly transparent polycrystalline γ-CuI films. The root-mean-square roughness values of the γ-CuI films prepared by this method are 8.5–21.2 nm, which are smaller than those for the γ- CuI films synthesized by the conventional method. The microstructure and optoelectronic properties of the γ-CuI thin films are sensitive to the temperature of iodine vapor. A high transmittance (80%) of the film obtained at an iodine vapor temperature of 80 °C has a low resistivity of 5 × 10−2 Ω cm and high mobility of 8.7 cm2/Vs. Moreover, a boosted figure of merit is realized due to the simultaneously low resistivity and high transparency: its value jumps from ∼488 to ∼1630 MΩ−1.