Integrated circuit structures having germanium-based channels

An integrated circuit structure, comprising:

• a fin comprising a lower silicon portion, an intermediate germanium portion on the lower silicon portion, an intermediate silicon germanium portion on the intermediate germanium portion, and an upper germanium portion on the intermediate silicon germanium portion;
• an isolation structure along sidewalls of the lower silicon portion of the fin;
• a gate stack over a top of and along sidewalls of the upper germanium portion of the fin and on a top surface of the isolation structure, the gate stack having a first side opposite a second side;
• a first source or drain structure at the first side of the gate stack;
• and
• a second source or drain structure at the second side of the gate stack.

A method of fabricating an integrated circuit structure, the method comprising:

• forming a trench in an isolation structure on a silicon substrate, the trench exposing a portion of the silicon substrate;
• forming a lower silicon portion of a fin in the trench and on the exposed portion of the silicon;
• forming an intermediate germanium portion of the fin in the trench and on the lower silicon portion of the fin;
• forming a silicon germanium portion of the fin in the trench and on the intermediate germanium portion of the fin;
• recessing the isolation structure to expose sidewalls of a portion of the fin;
• and
• forming a gate stack on and along the exposed sidewalls of the portion of the fin.