InGaN/GaN single quantum wells (SQWs) are grown by molecular beam epitaxy using ammonia as a nitrogen precursor. The InGaN material quality is optimized through the photoluminescence (PL) properties. It is found that the growth temperature is critical for both the PL efficiency and the indium incorporation in the InGaN layer. InGaN/GaN SQWs with In compositions larger than 15% present high PL efficiencies at room temperature. Depending on the QW width, the InGaN PL energy can be tuned from blue to red. This behavior is ascribed to a strong quantum-confined Stark effect. (C) 2001 Elsevier Science B.V. All rights reserved.