p-Type conducting transparent characteristics of delafossite Mg-doped CuCrO2 thin films prepared by RF-sputtering

Abstract

The growth of technologically relevant compounds, Mg-doped CuCrO₂ delafossite thin films, on a quartz substrate by radio-frequency sputtering is reported in this work. The deposition, performed at room temperature, leads to a nanocrystalline phase with extremely low roughness and high density. Delafossite characteristic diffraction peaks were obtained as a function of the thermal treatment under primary vacuum. The electrical conductivity was optimized until 1.6 S cm⁻¹ with an optical transmittance of 63% in the visible range by a 600 °C annealing treatment under primary vacuum applied for 4 h. The transport properties were analyzed by Seebeck and Hall measurement, integrated spectrophotometry and optical simulation. These measurements highlighted degenerated semiconductor behavior using a hopping mechanism with a high hole concentration (10²¹ cm⁻³) and a low mobility (0.2 cm² V⁻¹ s⁻¹). The direct optical bandgap of 3.3 eV has been measured according to Tauc's relationship. A refractive index of 2.3 at a wavelength of 1100 nm has been determined by spectroscopic ellipsometry and confirmed by two independent modellings of the optical transmittance and reflectance spectra. All these p-type TCO optoelectronic characteristics have led to the highest Haacke's figure of merit (1.5 × 10⁻⁷ Ω⁻¹) reported so far for such delafossite materials.