The interaction of arsenic with dislocations in gallium arsenide has been studied. By performing molecular dynamics simulations with a Tersoff-type interaction potential and simulating the microscopic diffusion drift aggregation process based on the kick-out mechanism, we obtained that arsenic clusters are preferably situated at dislocations from energetic and kinetic reasons. This formation of arsenic clusters explains why the radius of the cylinder with an increased free electron concentration around dislocations in n-type sulfur-doped gallium arsenide extends up to about 10 mm, as revealed by Raman scattering. ? 2003 American Institute of Physics.