P-type transparent conducting characteristics of delafossite Ca doped CuScO₂ prepared by hydrothermal synthesis

Ca doped CuScO2 (CSO) delafossite oxides of 3-4 μm were synthesized through the hydrothermal method using Cu(NO3)2·3H2O, Sc(NO3)3·xH2O as the precursor at 240 °C for 24 h in this work. The influence of the process parameters (reaction temperature, Cu/Sc molar ratios, EG (ethylene glycol) quantity, NaOH mineralizer, reactant concentration) on the structure and morphology of CSO was studied systematically. The crystal structure, morphology, and chemical composition of these Ca doped CSO (0, 1 at%, 3 at%, and 5 at%) sheets were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). With increasing Ca dopant, the Ca doped CSO sheets become much thinner; the thickness decreased from 568 nm (CSO) to 190 nm (3 at% Ca doped CSO). Moreover, the conductivity of Ca doped CSO sheets decreased with increasing Ca dopant. The CSO powders (19.91 S m-1) have higher conductivity than Ca doped CSO sheets (9.89, 15.69, and 16.51 S m-1) at room temperature. All these CSO based samples exhibit a weak absorption ability with the absorptance around 20-40% in the visible light region (400-780 nm). The optical band gap values exhibited a blue shift with increasing Ca dopant. The calculated band gaps of Ca-doped CSO sheets are 3.88 eV, 3.91 eV, 3.90 eV and 3.93 eV, respectively. This result indicates that all these CSO based samples have potential applications as p-type transparent materials in optoelectronic devices, owing to their comparable optical transmittance in the UV-vis region.