Scavenging Segregated Ge on Thin Single-Crystal Si Epitaxially Grown on Ge

Single-crystal Si with six monolayers in thickness was epitaxially grown on epi-Ge(001). The Si surface is characterized with the Ge atoms segregated from the underlying epi-Ge. Some of the Ge atoms bond with the Si inside the film. Upon O2 exposure at room temperature, both the Si and Ge surface atoms are simultaneously oxidized to give rise to four Si charge states and Ge suboxides, respectively. The subsequent in situ annealing at 500 °C under ultra-high vacuum moved the oxygen atom in the Ge suboxides to bond with the nearby Si atom. The annealing also caused the diffused Ge inside the epi-Si to segregate to the surface. The processes of O2 exposure followed by annealing were repeated three times resulting in an oxidized Si/Ge surface having only the four Si oxidized states without GeOx, but with a very small amount of segregated Ge. Using the scavenging process in reducing the segregated Ge prior to the high-κ deposition, the C–V hysteresis of the high-κ/epi-Si/n-Ge(001) metal-oxide-semiconductor (MOS) capacitors decreased more than two times, meaning that the electron traps contributed from the GeOx in the high-κ/epi-Si/Ge(001) are reduced.