Forming defect-free relaxed sige fins

A method comprising:

• forming strained silicon germanium (SiGe) fins on a first portion of a silicon (Si) substrate;
• forming Si fins on a second portion of the Si substrate;
• forming shallow trench isolation (STI) regions between adjacent SiGe fins and Si fins;
• forming a cladding layer over top and side surfaces of the SiGe fins and the Si fins and over the STI regions in the second portion of the Si substrate but not over the STI regions in the first portion of the Si substrate, wherein a third portion of the Si substrate, between an adjacent SiGe fin and a Si fin, covers only a portion of an STI region in the third portion of the Si substrate;
• and
• oxidizing a bottom portion of the SiGe fins through the STI regions until the STI regions at opposite sides of each SiGe fin are joined beneath the SiGe fin.

A device comprising:

• fully strained defect-free silicon germanium (SiGe) fins, each having a top portion and a bottom portion, on a first portion of a silicon (Si) substrate;
• Si fins, each having a top portion and a bottom portion, on a second portion of the Si substrate;
• shallow trench isolation (STI) regions between adjacent SiGe fins and Si fins, the STI regions being below a bottom surface of the SiGe fins and below the top portion of the Si fins;
• a cladding layer over top and side surfaces of the top portions of the SiGe fins and the Si fins and over the STI regions in the second portion of the Si substrate;
• and
• a dopant implanted into the Si substrate below the SiGe fins.

A device comprising:

• fully strained defect-free silicon germanium (SiGe) fins on a first portion of a silicon (Si) substrate;
• Si fins on a second portion of the Si substrate;
• shallow trench isolation (STI) regions between adjacent SiGe fins and Si fins;
• and
• a cladding layer over top and side surfaces of the SiGe fins and the Si fins and over the STI regions in the second portion of the Si substrate,
• wherein a bottom portion of the SiGe fins is oxidized.