Defect Studies in Thin-Film SiO₂ of a Metal-Oxide-Silicon Capacitor Using Drift-Assisted Positron Annihilation Lifetime Spectroscopy

This work investigates the impact of an internal electric field on the annihilation characteristics of positrons implanted in a (Formula presented.) SiO₂ layer of a Metal-Oxide-Silicon (MOS) capacitor, using Positron Annihilation Lifetime Spectroscopy (PALS). By varying the gate voltage, electric fields up to (Formula presented.) were applied. The measurements reveal a field-dependent suppression of positronium (Ps) formation by up to (Formula presented.), leading to an enhancement of free positron annihilation. The increase in free positrons suggests that vacancy clusters are the dominant defect type in the oxide layer. Additionally, drift towards the SiO₂/Si interface reveals not only larger void-like defects but also a distinct population of smaller traps that are less prominent when drifting to the Al/SiO₂ interface. In total, by combining positron drift with PALS, more detailed insights into the nature and spatial distribution of defects within the SiO₂ network and in particular near the SiO₂/Si interface are obtained.