Quaternary InxAlyGa1-x-yN alloys with In mole fraction x ranging from 0 to 0.10 and Al mole fraction y in the range of 0.30-0.40 were grown by RF plasma-assisted molecular beam epitaxy (RF-MBE) by varying the growth temperature and the In flux. The surface morphology and structural quality of InAlGaN layers were optimized using metal-rich growth conditions and a relatively low growth temperature. The layers exhibited strong band-edge photoluminescence (PL) up to room temperature and a minimum line width of 61 meV for 20 K PL emission at 3.0 eV. Abrupt GaN/InAlGaN multiple quantum well structures were grown, with high-resolution X-ray diffraction curves exhibiting satellite peaks and interference fringes. Unwanted In incorporation in the GaN layers by In segregation effects was eliminated. Laser structures with active region consisting of InAlGaN wells and GaN barriers exhibited lasing under optical pumping at room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.