Surface Passivation of Ge MOS Devices by ${\rm SmGeO}_{\bf{x}}$ With Sub-nm EOT

Ge MOS devices passivated by SmGeO_x with equivalent oxide thickness of 0.61 nm were employed as the platform to evaluate the eligibility of SmGeO_x as Ge surface passivation layer. The SmGeO_x layer was formed by deposition of Sm₂O₃ on Ge substrate with a subsequent O₂ annealing and the formation of SmGeOx was confirmed by X-ray photoelectron spectroscopy. The tiny frequency dispersion in capacitance measurement and a low interface trap density of 5.1×10¹¹ cm^-2eV^-1 near midgap attest to desirable passivation effect and it can be ascribed to Sm-Ge-O bonding, which is favorable in mitigating dangling bonds at Ge surface. In addition, the small hysteresis in capacitance also suggests good quality of bulk dielectric. Due to the small amount of bulk traps and large conduction band offset with respect to Ge, it enjoys low leakage current of 0.36 A/cm² at gate bias of V_fb (flatband voltage)-1 V. Through the test of bias temperature instability, the passivation layer demonstrates reasonable reliability performance in terms of 65-mV flatband voltage shift at 85 ^°C after stressing with -16 MV/cm for 1000 s. With these characteristics, SmGeO_x is promising as a passivation layer for aggressively scaled Ge MOS devices.