High-Mobility Ge N-MOSFETs and Mobility Degradation Mechanisms

Ge N-MOSFETs have exhibited poor drive currents and low mobility, as reported by several different research groups in the past. The major mechanisms behind poor Ge NMOS performance have not been completely understood yet. In this paper, mechanisms responsible for poor Ge NMOS performance in the past are investigated with detailed gate dielectric stack characterizations and Hall mobility analysis. High source/drain (S/D) parasitic resistance, inversion charge loss due to trapping in the high-K gate dielectric, and high interface trap density are identified as the mechanisms responsible for Ge NMOS performance degradation. After eliminating the degradation mechanisms, the highest electron mobility in Ge NMOS to date, which is, to the best of our knowledge, similar to 1.5 times the universal Si mobility, is experimentally demonstrated for the Ge N-MOSFETs fabricated with ozone-oxidation surface passivation and low temperature S/D activation processes.