Evidence of SiSiGe heterojunction roughness scattering

The separation distance between the electron channel at oxideSi interface and the strained- Sirelaxed -SiGe heterojunction can significantly affect the effective electron mobility of metal-oxide-silicon field-effect transistors due to the roughness scattering of the underneath SiSiGe heterojunction. The mobility degradation due to the SiSiGe heterojunction with the roughness of 7 nm becomes insignificant when the strained-Si thickness is larger than ~20 nm. A clear hole confinement shoulder is observed in the accumulation region of the capacitance-voltage curves, indicating that the abrupt transition from the SiGe buffer to strained Si is maintained at the rough heterojunction. The heterojunction roughness scattering not only degrades the electron mobility, but also degrades the device characteristics such as the transconductance and cut-off frequency.