Integrated circuit structures having source or drain structures with low resistivity are described. In an example, integrated circuit structure includes a fin having a lower fin portion and an upper fin portion. A gate stack is over the upper fin portion of the fin, the gate stack having a first side opposite a second side. A first source or drain structure includes an epitaxial structure embedded in the fin at the first side of the gate stack. A second source or drain structure includes an epitaxial structure embedded in the fin at the second side of the gate stack. Each epitaxial structure of the first and second source or drain structures include silicon, germanium and boron. The first and second source or drain structures have a resistivity less than or equal to 0.3 mOhm·cm.