Al-rich AlGaN layers and quantum well (QW) structures with a reasonable structural quality have been grown by plasma-assisted molecular beam epitaxy (PA-MBE) under metal-rich stoichiometric conditions directly on c-sapphire. The bowing parameter of 1.1 eV for the compositional dependence of AlGaN band gap energy has been determined using an electron-probe microanalysis, Raman spectroscopy and optical transmission spectroscopy. A successful application of a sub-monolayer digital-alloying (SMDA) technique in PA-MBE for fabrication of AlGaN-based multiple QW structures, including deep-UV MQW light-emitting diodes, has been demonstrated for the first time. These structures exhibit both photo- and electroluminescence in the spectral range of 300-320 nm at room temperature. (C) 2008 Elsevier B.V. All rights reserved.