Semiconductor device structure and methods of forming the same

A semiconductor device structure, comprising:

• a first semiconductor layer disposed over a substrate portion;
• a second semiconductor layer disposed on the substrate portion below the first semiconductor layer, wherein the first and second semiconductor layers comprise a same material, and the second semiconductor layer and the substrate portion comprise different materials;
• a first source/drain region disposed on the second semiconductor layer;
• and
• a second source/drain region disposed on the second semiconductor layer, wherein the first semiconductor layer is disposed between the first and second source/drain regions.

A method for forming a semiconductor device structure, comprising:

• forming a sacrificial gate structure over a first portion of a fin structure, wherein the fin structure comprises alternating first and second semiconductor layers;
• recessing a second portion of the fin structure to expose a substrate portion;
• removing the second semiconductor layers in a first region;
• trimming the first semiconductor layers in the first region;
• depositing a cap layer around the first semiconductor layers in the first region;
• and
• forming first and second source/drain regions on opposite sides of the cap layer.