Optical and structural properties of CuCrO2 thin films on c-face sapphire substrate deposited by reactive RF magnetron sputtering

Abstract

Reactive sputtering with Ar/N2 mixture gas was introduced to improve stoichiometry of p-type transparent CuCrO2 films, and effects of N2 partial pressure ratio (αN) on optical and structural properties were investigated. Film composition was changed from Cu rich (i.e. Cr poor) to Cr rich (i.e. Cu poor) by N2 addition, and the stoichiometric film was grown at αN of about 20%. Although N atoms were not incorporated into the films from analyses of crystal structure and chemical bonding state, both transmittance from visible to near-infrared wavelength and crystallinity were improved at αN up to 10%. These improvements were attributed to suppression of the CuO formation and promotion of the O-Cu-O dumbbell bonds formation. This was confirmed by the decrease of diffraction intensity from CuO and the increase of vibrational intensity corresponding A1g mode. From these results, it can be considered that N atoms decreased not only Cu but also excess O in the film. At αN of 20% or above, transmittance at wavelength of 450nm and crystallinity deteriorated. This is supposed that excessive N2 addition probably generated both O and Cu deficiencies. As a result, it was found that slightly Cu-rich composition is suitable to obtain high-transparency CuCrO2 thin films for practical use.