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

摘要

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/N-2 gas mixture atmosphere, and they were subsequently calcined in N-2. A N-2 partial pressure (alpha(N2)) during the film deposition and a calcination temperature (T-C) were varied within the range from 0 to 90% and 500 to 900 degrees C, respectively. By the calcination at 550 degrees C and above, c-axis orientation was observed regardless of alpha(N2). Furthermore, at alpha(N2) of 70 and 90%, a six-fold symmetry of CuCrO2[110]// Al2O3[300] was confirmed at T-C of 800 degrees C and above. Average optical transmittance (lambda = 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 T-C up to 600 degrees C but it rebounded drastically at T-C of 650 degrees 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.