Fabrication of silicon germanium channel and silicon/silicon germanium dual channel field-effect transistors

A semiconductor structure comprising:

• a plurality of fins disposed on a substrate, respective fins of the plurality of fins comprising:
• a silicon germanium core portion;
• and
• a silicon germanium surface portion on a surface of the silicon germanium core portion, wherein the silicon germanium surface portion has a lower concentration of germanium than the silicon germanium core portion;
• wherein the respective fins comprise respective channel regions of respective transistors of a plurality of transistors;
• and
• a plurality of source/drain regions of the respective transistors, wherein respective top source/drain regions of the plurality of source/drain regions are disposed on the respective fins and wherein respective bottom source/drain regions of the plurality of source/drain regions are disposed adjacent to and contacting the respective fins and comprise:
• a doped silicon germanium portion;
• and
• a germanium condensed portion disposed on the doped silicon germanium portion.