After the optional dopant implantation process, a thermal treatment 233 is performed to activate the dopants in the source/drain regions 292. The thermal treatment 233 may further re-crystallize any of the source/drain regions that were amorphous. For example, the thermal treatment 233 may reorder the crystal structure of the amorphous regions 219, re-distribute the dopant atoms (e.g., first and second species) by incorporating the dopant atoms into the crystalline lattice of the source/drain regions 292. Ordering the crystal lattice and activating dopants can reduce resistivity of the doped regions. Upon completion of the thermal treatment 233, the amorphous regions 219 can turn into crystalline regions 223, as shown in FIG. 7. The crystalline regions 223 may have the first species and the second species randomly redistributed therein. In some embodiments, the crystalline regions 223 may have a peak or higher concentration of the first species and the second species proximate the top surface 215 of the source/drain regions 292, and a lower concentration (e.g., an order magnitude lower than the peak concentration) of the first species and the second species deeper into the crystalline regions 223 (e.g., towards a direction away from the top surface 215). In an example, the crystalline regions 223 may be silicon germanium doped with first and second species. In cases where the first species is gallium and the second species is boron, the crystalline regions 223 may be gallium-doped and/or boron-doped silicon germanium.