Thermal solid-phase crystallization of amorphous CuCrO2:N thin films deposited by reactive radio-frequency magnetron sputtering

In order to fabricate highly-oriented delafossite CuCrO2 (CCO) thin film which is one of the candidate materials for a p-type transparent conductive oxide, thermal solid-phase crystallization of an amorphous N-doped CCO (CCO:N) film was investigated. The amorphous CCO:N films were deposited at room temperature by reactive radio-frequency sputtering in an Ar/N2 gas mixture atmosphere, and they were subsequently calcined in N2. A N2 partial pressure (αN2) during the film deposition and a calcination temperature (TC) were varied within the range from 0 to 90% and 500 to 900 °C, respectively. By the calcination at 550 °C and above, c-axis orientation was observed regardless of αN2. Furthermore, at αN2 of 70 and 90%, a six-fold symmetry of CuCrO2[110]//Al2O3[300] was confirmed at TC of 800 °C and above. Average optical transmittance (λ = 450-800 nm) of the as-deposited CCO:N films was 45% and increased to 60% and over simultaneously with c-axis orientation. Resistivity of the calcined CCO:N film decreased with increasing TC up to 600 °C but it rebounded drastically at TC of 650 °C. This implies that resistivity was mainly affected by the number of intrinsic defects. From X-ray diffraction and X-ray photoelectron spectroscopy measurements, metal nitrides were formed in the as-deposited CCO:N film and it effectively acted to assist the generation of Cu+ and CuCrO2 bonds. N atoms were desorbed during the calcination but it was confirmed the initial formation of these desirable bonds effectively improved orientation of the delafossite structure.