High mobility Ge pMOSFETs with amorphous Si passivation: impact of surface orientation

We report the amorphous Si passivation of Ge pMOSFETs fabricated on (001)-, (011)-, and (111)-orientated surfaces for advanced CMOS and thin film transistor applications. Amorphous Si passivation of Ge is carried out by magnetron sputtering at room temperature. With the fixed thickness of Si tSi, (001)-oriented Ge pMOSFETs achieve the higher on-state current ION and effective hole mobility μeff compared to the devices on other orientations. At an inversion charge density Qinv of 3.5 × 1012 cm−2, Ge(001) transistors with 0.9 nm tSi demonstrate a peak μeff of 278 cm2/V × s, which is 2.97 times higher than the Si universal mobility. With the decreasing of tSi, ION of Ge transistors increases due to the reduction of capacitive effective thickness, but subthreshold swing and leakage floor characteristics are degraded attributed to the increasing of midgap Dit.