GaNAs/GaAs multiple quantum wells (MQWs) were fabricated on GaAs (0 0 1) substrates by molecular beam epitaxy using N radical beam source. We have used modulated N radical beam source method in which N plasma is ignited only when the GaNAs layer is grown. We have investigated the effects of growth interruption (GI) after GaNAs layer growth on the MQW structure. High-resolution X-ray diffraction (HRXRD), transmission electron microscopy and low-temperature photoluminescence (PL) spectroscopy were used to study the N composition, structural and optical properties of the MQW structures. From results of the HRXRD and PL measurements, the drastic reduction and redistribution of N atoms in the GaNAs layers were found even by introduction of very short GI. (c) 2007 Elsevier B.V. All rights reserved.