High-Mobility CVD-Grown Ge/Strained Ge 0.9 Sn 0.1 /Ge Quantum-Well pMOSFETs on Si by Optimizing Ge Cap Thickness

The high peak mobility of 509 cm 2 / $\text {V}\cdot \text {s}$ of the chemical vapor deposition -grown GeSn pMOSFETs is obtained using 1-nm Ge cap. The Ge cap on GeSn can reduce the scattering of oxide/interface charges and surface roughness for the holes in the GeSn quantum wells. However, the thick cap induces holes in the Ge cap itself, leading lower mobility than GeSn channels. The on current is enhanced by external stress due to the effective mass reduction. The normalized noise power density of the GeSn devices decreases with increasing Ge cap thickness, indicating the carrier number fluctuation and correlated mobility fluctuation are suppressed when the holes are away from interface.