We have investigated the evolution of the photoluminescence intensity of different GaAs/GaAlAs quantum wells to probe the defect penetration during focused ion beam implantation at various sample temperatures. By implanting homogeneous areas, it was possible to evaluate the depth extension of the ion-induced damage, while by localizing the implantation at a submicrometric length scale, it was also possible to quantify the lateral damage extension. Both the depth and lateral damage extensions are found to be reduced when the sample temperature is changed from 300 to 80 K. This result is used to demonstrate that a fast diffusion of nonequilibrium defects is taking place in the irradiated sample. It is found that this diffusion is highly anisotropic with a lateral diffusion length ten times higher than the depth one, suggesting that the defects easily diffuse in the GaAlAs barrier layers. The results are interpreted as a manifestation of a radiation enhanced diffusion mechanism. The advantage of using low temperature irradiations to better localize the injected defects by focused ion beam is highlighted, specially for quantum nanostructure fabrication.