Single-crystal ternary wurtzite Al<sub>0.8</sub>In<sub>0.2</sub>N thin films were grown epitaxially onto lattice-matched (111)-oriented Ti<sub>0.2</sub>Zr<sub>0.8</sub>N seedlayers. The epilayers were grown onto single-crystal MgO (111) substrates by magnetron sputter epitaxy (MSE) using reactive direct current magnetron sputtering in an N<sub>2</sub> discharge under ultra-high-vacuum conditions. The growth temperatures ranged from 20 to 700 <sup>o</sup>C. Low-energy ion-assisted growth conditions, enhancing the epitaxy, were achieved by applying a negative substrate potential of 15-45 V. Film compositions and lattice parameters were determined using Rutherford Backscattering Spectroscopy (RBS) and High-Resolution X-ray diffraction (XRD), respectively. Cross-sectional High-Resolution Electron Microscopy of the interface regions verified the epitaxy and the crystallinity of the films. XRD ω-rocking scans of the Al<sub>0.8</sub>In<sub>0.2</sub>N 0002-peak showed full-width-at-half-maximum values of ~2400 arcs, indicating a high structural quality of the films. Opto-electronical properties were studied by cathodoluminescence at temperatures between 5 and 293 K. Luminescence was observed at wavelengths as short as 248 nm, corresponding to an energy of 5.0 eV. These results point towards the feasibility of metastable Al<sub>0.8</sub>In<sub>0.2</sub>N solid solutions as an active luminous material in opto-electronics. It also shows that MSE-grown Al<sub>0.8</sub>In<sub>0.2</sub>N can be an excellent choice for lattice-matched GaN heterostructures, with a resulting energy band-gap difference enabling strong charge carrier confinement. In addition to these new and original results, a brief review of the present work on Al(<sub>1-x</sub>)In<sub>x</sub>N growth at Linkoeping University is presented.