The lateral transport of excess carriers in metal organic chemical vapor deposition grown GaAs/AlxGa1-xAs(x=0.5) 20 angstrom thick single quantum well structures is studied by cathodoluminescence (CL) between 5 K less-than-or-equal-to T less-than-or-equal-to 170 K. Impurity and native defect related transitions are found to take place around grown-in dislocations where well thickness variations are also found. The CL intensity of free excitons and/or transitions involving impurities and native defects is measured as a function of distance from the dislocation to the point of excitation. Using a simple diffusion model, we are able to determine the hole diffusion length, L=1.5 mum, in slightly n-doped SQW. This represents a novel method for the direct determination of the diffusion length ih sufficiently defect-free material.