The gamma phase of copper(I) iodide (γ-CuI) is a p-type semiconductor with a wide bandgap (Eg ≈ 3.1 eV). Conventionally, γ-CuI thin films have been synthesized by the iodination of Cu thin layers with iodine vapor. However, γ-CuI films fabricated by this method have a rough surface and thus frosted-glass-like appearance, which make it difficult to apply this material to transparent electronics. In this paper, a simple new method is proposed for the synthesis of truly transparent p-type γ-CuI films. The chemical reaction between Cu3N thin films and solid-phase iodine at 25 ºC was found to yield highly transparent polycrystalline γ-CuI films with shiny appearance. The γ-CuI films fabricated by this method had root-mean-square roughness values of 8-12 nm, which are less than one-third of those for γ-CuI films synthesized by the conventional method. As a result, specular transmittance of >75% in the visible region was attained. An as-prepared film had a resistivity (ρ) of 3.1 × 10 -2 Ω cm, hole density (nh) of 8.9 × 10 19 cm -3 , and mobility (μ) of 2.4 cm 2 V -1 s -1 . Mild heat treatment at 100-150 ºC under an inert atmosphere was found to suppress nh and enhance μ. The heat-treated films had μ values of 9-10 cm 2 V -1 s -1 , which are comparable to those of other wide-bandgap p-type semiconductors grown epitaxially at high temperatures above 400 ºC. These findings would assist studies on applications of γ-CuI thin films in transparent electronics.

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Transparent p‐type CuI layers with high hole mobility can be fabricated on flexible plastic sheets, a system which has been unattainable with p‐type transparent oxide semiconductors. Mildly heat‐treated CuI layers have mobilities of ≈20 cm2 V−1 s−1, which are comparable to those of p‐type GaN epilayers. Highly transparent p–n diodes with sufficient rectification ratio (106) can be manufactured by employing a heterojunction of p‐type CuI and amorphous n‐type In‐Ga‐Zn‐O layers on plastic sheets. Thus, CuI can be regarded as an excellent transparent p‐type semiconductor for flexible transparent electronics.

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Pseudo III-V nitride ZnSnN2 is an earth-abundant semiconductor with a high optical absorption coefficient in the solar spectrum. Its bandgap can be tuned by controlling the cation sublattice disorder. Thus, it is a potential candidate for photovoltaic absorber materials. However, its important basic properties such as the intrinsic bandgap and effective mass have not yet been quantitatively determined. This paper presents a detailed optical absorption analysis of disordered ZnSnN2 degenerately doped with oxygen (ZnSnN2−xOx) in the ultraviolet to infrared region to determine the conduction-band effective mass (m c *) and intrinsic bandgap (E g). ZnSnN2−xOx epilayers are n-type degenerate semiconductors, which exhibit clear free-electron absorption in the infrared region. By analysing the free-electron absorption using the Drude model, m c * was determined to be (0.37 ± 0.05)m 0 (m 0 denotes the free electron mass). The fundamental absorption edge in the visible to ultraviolet region shows a blue shift with increasing electron density. The analysis of the blue shift in the framework of the Burstein-Moss effect gives the E g value of 0.94 ± 0.02 eV. We believe that the findings of this study will provide important information to establish this material as a photovoltaic absorber.

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