Semiconductor device and method for forming the same

A method, comprising:

• forming first and second semiconductor layers over a substrate, the first and second semiconductor layers being laterally separated from each other;
• forming a dummy material between the first and second semiconductor layers, wherein the dummy material covers a first sidewall of the first semiconductor layer facing the second semiconductor layer, and the dummy material covers a second sidewall of the second semiconductor layer facing the first semiconductor layer;
• forming first source/drain epitaxy structures in contact with the first semiconductor layer and forming second source/drain epitaxy structures in contact with the second semiconductor layer;
• removing the dummy material to expose the first sidewall of the first semiconductor layer and the second sidewall of the second semiconductor layer;
• forming a third semiconductor layer on the first sidewall of the first semiconductor layer and a fourth semiconductor layer on the second sidewall of the second semiconductor layer;
• and
• forming a gate electrode over the first and second semiconductor layers.

A method, comprising:

• forming a first semiconductor layer over a substrate;
• forming source/drain epitaxy structures in contact with opposite ends of the first semiconductor layer;
• forming a second semiconductor layer on a first sidewall of the first semiconductor layer;
• and
• after forming the second semiconductor layer, forming a gate electrode over the first semiconductor layer, wherein the gate electrode is further in contact with the second semiconductor layer.