The structural, morphological, electrical and optical properties of In-rich AlxIn1−xN(0 < x < 0.39) layers grown by reactive radio-frequency (RF) sputtering on sapphire areinvestigated as a function of the deposition parameters. The RF power applied to the aluminumtarget (0 W–150 W) and substrate temperature (300 °C–550 °C) are varied. X-ray diffractionmeasurements reveal that all samples have a wurtzite crystallographic structure oriented withthe c-axis along the growth direction. The aluminum composition is tuned by changing thepower applied to the aluminum target while keeping the power applied to the indium targetfixed at 40 W. When increasing the Al content from 0 to 0.39, the room-temperature opticalband gap is observed to blue-shift from 1.76 eV to 2.0 eV, strongly influenced by the Burstein–Moss effect. Increasing the substrate temperature, results in an evolution of the morphologyfrom closely-packed columnar to compact. For a substrate temperature of 500 °C and RFpower for Al of 150 W, compact Al0.39In0.61N films with a smooth surface (root-mean-squaresurface roughness below 1 nm) are produced.