Effect of Si capping layer on the interface quality and NBTI of high mobility channel Ge-on-Si pMOSFETs

The effects of a Si capping layer on the device characteristics and negative bias temperature instability (NBTI) reliability were investigated for Ge-on-Si pMOSFETs. A Ge pMOSFET with a Si cap shows a lower subthreshold slope (SS), higher transconductance ( G m) and enhanced drive current. In addition, lower threshold voltage shift and G m,max degradation are observed during NBTI stress. The primary reason for these characteristics is attributed to the improved interface quality at the high- k dielectric/substrate interface. Charge pumping was used to verify the presence of lower density of states in Ge pMOSFETs with a Si cap.