Semiconductor devices and methods for making the same include patterning a stack of layers that includes channel layers, first sacrificial layers between the channel layers, and second sacrificial layers between the channel layers and the first sacrificial layers, to form one or more device regions. The first sacrificial layers are formed from a material that has a same lattice constant as a material of the first sacrificial layers and the second sacrificial layers are formed from a material that has a lattice mismatch with the material of the first sacrificial layers. Source and drain regions are formed from sidewalls of the channel layers in the one or more device regions. The first and second sacrificial layers are etched away to leave the channel layers suspended from the source and drain regions. A gate stack is deposited on the channel layers.
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