X-ray diffraction curves for the LT-GaAs samples δ-doped with P (1,2) and Sb (3,4). Curves 1 and 3 were recorded in the as-grown state. Curves 2 and 4 were taken after annealing at 873 K for 15 min. Arrows mark the positions of the SL-0 peak. The curves are shifted along the vertical axis for clarity.