Semiconductor devices and data storage systems including the same

A semiconductor device, comprising:

• a stack structure that includes interlayer insulating layers and gate electrodes stacked in a vertical direction;
• a first material layer disposed on the stack structure and that includes a first semiconductor material that has a first conductivity;
• a second material layer disposed between the first material layer and the stack structure and that includes a second semiconductor material that has a second conductivity that differs from the first conductivity;
• channel structures that each include a first portion that penetrates through the stack structure in the vertical direction, and a second portion that extends upward from the first portion, penetrates through the second material layer, and is disposed below the first material layer;
• and
• a buffer layer disposed between second portion of the channel structures and the second material layer, and between the second portion of the channel structures and the first material layer.

A data storage system, comprising:

• a semiconductor storage device that includes a first semiconductor structure that includes a substrate and circuit devices disposed on the substrate;
• a second semiconductor structure that includes a stack structure that includes interlayer insulating layers and gate electrodes stacked in a vertical direction and channel structures that penetrate through the stack structure;
• and an input/output pad electrically connected to the circuit devices;
• and
• a controller that is electrically connected to the semiconductor storage device through the input/output pad and that controls the semiconductor storage device,
• wherein the first semiconductor structure further includes:
• a lower interconnection structure that is electrically connected to the circuit devices;
• and
• a lower bonding structure connected to the lower interconnection structure,
• wherein the second semiconductor structure includes:
• an upper interconnection structure disposed below the stack structure;
• an upper bonding structure connected to the upper interconnection structure and bonded to the lower bonding structure;
• a first material layer disposed on the stack structure and the channel structure and that has a first conductivity;
• and
• a second material layer disposed between the first material layer and the stack structure and that has a second conductivity that differs from the first conductivity,
• wherein each of the channel structures includes a first portion that penetrates through the stack structure in the vertical direction and a second portion that extends upward from the first portion, and
• wherein the first material layer overlaps the second portion of the channel structures in the vertical direction, and the second material layer does not overlap the second portion of the channel structures in the vertical direction.