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 t_Si, (001)-oriented Ge pMOSFETs achieve the higher on-state current I_ON and effective hole mobility μ_eff compared to the devices on other orientations. At an inversion charge density Q_inv of 3.5 × 10¹² cm^-2, Ge(001) transistors with 0.9 nm t_Si demonstrate a peak μ_eff of 278 cm²/V × s, which is 2.97 times higher than the Si universal mobility. With the decreasing of t_Si, I_ON 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 D_it.