Effective mobilities in pseudomorphic Si/SiGe/Si p-channel metal-oxide-semiconductor field-effect transistors with thin silicon capping layers

The room-temperature effective mobilities of pseudomorphic ${\mathrm{Si/Si}}_{\mathrm{0.64}}{\mathrm{Ge}}_{\mathrm{0.36}}\mathrm{/Si}$ $p\mathrm{-metal-oxidesemiconductor}$ field effect transistors are reported. The peak mobility in the buried SiGe channel increases with silicon cap thickness. It is argued that ${\mathrm{SiO}}_{\mathrm{2}}\mathrm{/Si}$ interface roughness is a major source of scattering in these devices, which is attenuated for thicker silicon caps. It is also suggested that segregated Ge in the silicon cap interferes with the oxidation process, leading to increased ${\mathrm{SiO}}_{\mathrm{2}}\mathrm{/Si}$ interface roughness in the case of thin silicon caps.