Graded superlattice structure for gate all around devices

A method of forming a device structure, comprising:

• forming a superlattice structure on a substrate, comprising:
• forming a first superlattice stack over the substrate, comprising:
• forming a first silicon germanium structure using a first deposition process with a first precursor material and a second precursor material, comprising:
• forming a first silicon germanium cladding layer having a first germanium concentration and a first thickness;
• forming a silicon germanium core layer on the first silicon germanium cladding layer, the silicon germanium core layer having a second germanium concentration and a second thickness;
• and
• forming a second silicon germanium cladding layer on the silicon germanium core layer, the second silicon germanium cladding layer having a third germanium concentration and a third thickness,
• forming a first silicon layer using a second deposition process with a third precursor material,
• wherein the first germanium concentration and the third germanium concentration are greater than the second germanium concentration and the first thickness and the third thickness are less than the second thickness.

A method of forming a device structure, comprising:

• forming a superlattice structure on a substrate, wherein the substrate comprises silicon {110}, comprising:
• forming a plurality of superlattice stacks over the substrate, comprising:
• forming a first silicon germanium structure using a first deposition process with a first silicon-containing precursor material and a second germanium-containing precursor material, comprising:
• forming a first silicon germanium cladding layer having a first thickness;
• forming a silicon germanium core layer on the first silicon germanium cladding layer, the silicon germanium core layer having a second thickness;
• and
• forming a second silicon germanium cladding layer on the silicon germanium core layer, the second silicon germanium cladding layer having a third thickness, wherein the silicon germanium stack has a germanium concentration gradient that decreases with an increase in distance from dissimilar materials;
• and
• forming a first silicon layer over the first silicon germanium structure using a second deposition process with a second silicon-containing precursor material, wherein the first thickness and the third thickness are less than the second thickness.