Multi-gate devices and fabricating the same with etch rate modulation

A semiconductor device, comprising:

• first and second channel members vertically stacked above a substrate;
• a gate structure wrapping around each of the first and second channel members;
• a gate sidewall spacer disposed on a sidewall of the gate structure;
• and
• an epitaxial feature abutting a first end portion of the first channel member and a second end portion of the second channel member,
• wherein the first end portion of the first channel member includes a dopant, and a concentration of the dopant in the first end portion of the first channel member is higher than in the second end portion of the second channel member.

A semiconductor device, comprising:

• a channel member disposed over a substrate;
• a gate structure wrapping around the channel member;
• a gate sidewall spacer disposed on a sidewall of the gate structure;
• and
• an epitaxial feature abutting the channel member,
• wherein:
• an end portion of the channel member includes a dopant of a first concentration,
• an outer portion of the epitaxial feature includes the dopant of a second concentration,
• an inner portion of the epitaxial feature includes the dopant of a third concentration,
• the first concentration is higher than the second concentration, and
• the second concentration is lower than the third concentration.