Photoluminescence (PL) measurements and in situ reflection high-energy electron diffraction (RHEED) observations were used to optimize GaAs/AlAs multi-quantum-well (MQW) structures grown by molecular beam epitaxy (MBE) under different As fluxes. PL peaks were identified with computer simulations, intensity behavior as a function of temperature, and with previous results in literature. The room temperature PL intensity from our MQW samples first increases with the As flux and then decreases as the flux is increased. Combining our RHEED and PL observations, we propose that an optimum As flux for growth of GaAs/AlAs structures is close to the special As flux at which the GaAs(1 0 0) surface reconstruction changes from (2 x 4) to (4 x 2). The reasons for the findings are discussed. (C) 2008 Elsevier B.V. All rights reserved.