Deactivation of silicon surface states by Al-induced acceptor states from Al–O monolayers in SiO2

Al–O monolayers embedded in ultrathin SiO2 were shown previously to contain Al-induced acceptor states, which capture electrons from adjacent silicon wafers and generate a negative fixed charge that enables efficient Si-surface passivation. Here, we show that this surface passivation is just in part attributed to field-effect passivation, since the electrically active interface trap density Dit itself at the Si/SiO2 interface is reduced by the presence of the acceptor states. For sufficiently thin tunnel-SiO2 films between the Si-surface and the Al–O monolayers, Dit is reduced by more than one order of magnitude. This is attributed to an interface defect deactivation mechanism that involves the discharge of the singly-occupied dangling bonds (Pb0 defects) into the acceptor states, so that Shockley-Read-Hall-recombination is drastically reduced. We demonstrate that the combined electronic and field-effect passivation allows for minority carrier lifetimes in excess of 1 ms on n-type Si and that additional H2-passivation is not able to improve that lifetime significantly.