A method includes depositing a multi-layer stack on a semiconductor substrate, the multi-layer stack including a plurality of sacrificial layers that alternate with a plurality of channel layers; forming a dummy gate on the multi-layer stack; forming a first spacer on a sidewall of the dummy gate; performing a first implantation process to form a first doped region, the first implantation process having a first implant energy and a first implant dose; performing a second implantation process to form a second doped region, where the first doped region and the second doped region are in a portion of the channel layers uncovered by the first spacer and the dummy gate, the second implantation process having a second implant energy and a second implant dose, where the second implant energy is greater than the first implant energy, and where the first implant dose is different from the second implant dose.