Energy Distribution of Positive Charges in ${\rm Al}_{2}{\rm O}_{3}{\rm GeO}_{2}/{\rm Ge}$ pMOSFETs

The high hole mobility of Ge makes it a strong candidate for end of roadmap pMOSFETs and low interface states have been achieved for the
${\rm Al}_{2}{\rm O}_{3}/{\rm GeO}_{2}/{\rm Ge}$
gate-stack. This structure, however, suffers from significant negative bias temperature instability (NBTI), dominated by positive charge (PC) in
${\rm Al}_{2}{\rm O}_{3}{\rm GeO}_{2}$
. An in-depth understanding of the PCs will assist in the minimization of NBTI and the defect energy distribution will provide valuable information. The energy distribution also provides the effective charge density at a given surface potential, a key parameter required for simulating the impact of NBTI on device and circuit performance. For the first time, this letter reports the energy distribution of the PC in
${\rm Al}_{2}{\rm O}_{3}{\rm GeO}_{2}$
on Ge. It is found that the energy density of the PC has a clear peak near Ge Ec at the interface and a relatively low level between Ec and Ev. Below Ev at the interface, it increases rapidly and screens 20% of the Vg rise.