We explore the growth temperature dependence of GaAs/AlGaAs core/shell lanowires (NW) grown by metal-organic chemical vapor deposition (MOCVD) on (1 0 0) and (1 1 1)B GaAs substrates. In situ calibration of the growth temperature allows for a systematic variation with unprecedented resolution. Characterization by photoluminescence (PL) indicates that, at low growth temperatures, nanowires grown on (1 1 1)B substrates incorporate higher density of defects than wires on (1 00). On either substrate, nanowire core growth temperatures above 450 degrees C result in rising defect luminescence in the PL spectra concomitant with the increased cpiLaxial growth on the nanovvire sidevvalls at these higher temperatures. This work presents a systematic study of nanovvire growth conditions that reveals the correlation between the growth temperature of the GaAs core, the chosen substrate surface orientation, and the resulting optical properties of GaAs/AlGaAs nanowires. (c) 2015 Elsevier B.V. All rights reserved,