In this study we have investigated the damage distribution induced by a focused ion beam irradiation on a GaAlAs/GaAs heterostructure. The samples were kept at various temperatures during ion bombardment: room temperature (RT), 80 and 22 K. The samples were then characterized, after being warmed up at RT, using photoluminescence (PL) experiments without any subsequent annealing. Stable, reproducible, and localized modulation of the PL characteristics of several GaAlAs/GaAs heterostructures are demonstrated. The defect localization is found to be considerably improved for a sample kept at 22 K during irradiation.