High mobility strained-Ge pMOSFETs with 0.7-nm ultrathin EOT using plasma post oxidation HfO2/Al2O3/GeOx gate stacks and strain modulation

An ultrathin HfO₂/Al₂O₃/GeO_x gate stack has been fabricated on strained-Ge surfaces using the plasma post oxidation method. It is found that the strained-Ge MOS interface can be sufficiently passivated by inserting a 0.35-nm-thick GeO_x interfacial layer, with a low D_it at 10¹¹ cm^-2eV^-1 level. A peak hole mobility of 552 cm²/Vs and 2.2× enhancement of high field mobility (N_s=10¹³ cm^-2) over unstrained-Ge pMOSFETs has been revealed for bi-axial compressive strained-Ge pMOSFETs with an EOT of 0.82 nm. It is also observed that the hole mobility is further improved by partially releasing the compressive strain along the channel width direction. As a result, the asymmetric strained-Ge pMOSFETs show high peak hole mobility of 763 cm²/Vs and 3.4× enhancement of high field mobility over unstrained-Ge pMOSFETs.