Fabricating GeO₂ passivation layer by N₂O plasma oxidation for Ge NMOSFETs application

In this paper, oxidation of Ge surface by N₂O plasma is presented and experimentally demonstrated. Results show that 1.0-nm GeO₂ is achieved after 120-s N₂O plasma oxidation at 300 ℃. The GeO₂/Ge interface is atomically smooth. The interface state density of Ge surface after N₂O plasma passivation is about ～ 3×10¹¹ cm^-2·eV^-1. With GeO₂ passivation, the hysteresis of metal-oxide-semiconductor (MOS) capacitor with Al₂O₃ serving as gate dielectric is reduced to ～ 50 mV, compared with ～ 130 mV of the untreated one. The Fermi-level at GeO₂/Ge interface is unpinned, and the surface potential is effectively modulated by the gate voltage.