Microstructure, optical and electrical properties of CrAlN film as a novel material for high temperature solar selective absorber applications

• This paper reports a novel CrAlN material for high temperature solar selective absorber coatings with good thermal stability and oxidation resistance superior to TiAlN, which has recently been reported to be used as high-temperature solar selective absorber coatings. The CrAlN film crystallizes in B1 NaCl-typed CrN structure with the preferred growth orientations of (1 1 1) and (2 2 0) and CrAlN grains show perfectly crystalline pyramid-like structure. It shows similar reflectance and absorptance characteristics to those of TiN based films in the solar spectrum region (300–2600 nm) and exhibits semiconductor nature with a sheet resistance of 38 kΩ/sq.
• The results are also valuable to understand the metallic-like to semiconducting nature of transition metal nitrides such as CrN, TiN, etc., when they are doped with Al and to extend the application field of high-hardness CrN based materials.

The microstructure, optical and electrical properties of CrAlN and (Cr, Al) films synthesized by DC reactive magnetron sputtering method have been comparatively investigated. The results show that CrAlN film crystallizes in B1 NaCl-typed CrN structure with the preferred growth orientations of (1 1 1) and (2 2 0) and CrAlN grains show perfectly crystalline pyramid-like shape. The CrAlN film is determined as Al-doped CrN phase with the chemical formula of Cr0.9136Al0.0864N0.8999. It shows similar reflectance and absorptance characteristics to those of TiN based films in the solar spectrum region (300–2600 nm) and exhibits semiconductor nature with a sheet resistance of 38 kΩ/sq. Hence CrAlN can be used as a novel candidate material for high-temperature solar selective absorber coatings with good thermal stability and oxidation resistance.