AlGaAs/GaAs quantum wells (QWS) Structures were grown by molecular beam epitaxy (MBE) on semi-insulating-and Si-doped GaAs (100) substrates subjected to different surface treatments. The substrate treatments employed were: (a) H2SO4-based chemical etching, (b) hydrogen flux exposition at 650 degrees C tinder an arsenic overpressure, and (C) ultraviolet (UV) light irradiation in ambient conditions. In order to evaluate the impact of the substrate treatment on the samples properties the QWs were grown directly on the substrates with no buffer layer. Secondary ion mass spectroscopy (SIMS) was used to detect oxygen and carbon impurities at the QWs/substrate interface. From an analysis of the full-width at half-maximum (FWHM) of 10 K-photoluminescence (PL) peaks, we estimated the roughness at the interfaces in each QW. Photoreflectance spectroscopy (PR) at 300K was employed to evaluate the optical quality of the structures. The lowest concentration of C and 0 contaminants, and the QWs with the lowest interfacial roughness were achieved employing the H+As exposition. On the other hand, we found that UV irradiation is effective with brief exposition times (<= 1 min), but for longer UV exposition times the QWs are severely damaged. (C) 2008 Elsevier B.V. All rights reserved.