Effect of electric fields on Cr redistribution at GaAs surfaces

During the annealing of ion-implanted Cr-doped GaAs, Cr often redistributes and accumulates at the surface. Although this behavior has been attributed to strain fields and other mechanisms, the widths of these accumulation regions suggest that electric fields due to surface states are a limiting factor in Cr redistribution. For this reason we have developed a thermodynamic model for Cr redistribution which takes into account the electric field due to surface states. A qualitative fit to SIMS data on annealed unimplanted GaAs samples can be obtained with this model. We have also used applied voltages during annealing to modify the amount of band bending and Cr buildup at the surface. This experiment indicates that the accumulated ions are positively charged. We conclude from these experiments that electric fields play a significant role in the redistribution of Cr at GaAs surfaces.