Epitaxial growth of highly infrared-transparent and conductive CuScO2 thin film by polymer-assisted-deposition method

As an important wide bandgap p-type conductive delafossite material, CuScO2 (CSO) has been intensively investigated for its wide applications in multi-functional optoelectronic devices. In order to obtain both high infrared (IR) transparency and low resistivity, we report on, for the first time, the experimental preparation of single phase epitaxial CSO thin film by using polymer-assisted-deposition (PAD) method. As a key point in the PAD process, the used polymer materials (PEI and EDTA) not only control the desired viscosity for the process, but also bind the metal ions to prevent premature precipitation and formation of metal oxide oligomers. The technique results in a homogeneous distribution of the metal precursors in the solution as well as the formation of uniform metal organic film. Due to the uniaxial locked epitaxy mechanism, the epitaxial growth of CSO (0001) thin film on a-plane sapphire is achieved, and the orientation relationship of the film with respect to the substrate are confirmed to be CSO[3R](0001)//a-Al2O3(110). The obtained CSO thin film from the PAD technique exhibits a low electrical resistivity of 1.047 Ω cm at room temperature, and a high transmittance of 65–85% in the near-IR range and more than 85% in the mid-IR range. The presented technique does provide the possibility of preparing high-crystallinity oxide films which can be applicable over a wide wavelength range from visible band to infrared band.