Vertical semiconductor device in narrow slots within trench

A device comprising:

• a substrate including a trench defined by a first sidewall and a second sidewall facing each other along a first direction, and a floor between one end of the first sidewall and one end of the second sidewall;
• one or more epitaxial layers in the trench, each of the one or more epitaxial layers extending along a second direction traversing the first direction, wherein the first sidewall, the second sidewall, the floor of the trench, and the one or more epitaxial layers define two or more slots within the trench;
• a first set of source/drain structures in the two or more slots above the floor of the trench along the second direction;
• a second set of source/drain structures in the two or more slots above the first set of source/drain structures along the second direction;
• and
• a set of gate structures in the two or more slots, each of the set of gate structures between a corresponding one of the first set of source/drain structures and a corresponding one of the second set of source/drain structures.

A device comprising:

• a substrate including a trench defined by a first sidewall and a second sidewall facing each other along a first direction, and a floor between one end of the first sidewall and one end of the second sidewall;
• a first epitaxial layer on the first sidewall along a second direction traversing the first direction;
• a second epitaxial layer on the second sidewall along the second direction, the first epitaxial layer and the second epitaxial layer being a first type;
• a third epitaxial layer on the first epitaxial layer along the second direction;
• and
• a fourth epitaxial layer on the second epitaxial layer along the second direction, the third epitaxial layer and the fourth epitaxial layer being a second type.