Atomic level insight into the variation and tunability of band alignment between Si and amorphous SiO₂/HfO₂

The band alignment between silicon and high-k dielectric, which is a key factor to device operation and device reliability, is still suffering from uncontrolled fluctuation and ambiguous understanding. Here by conducting atomic level ab initio calculations on realistic Si/SiO₂/HfO₂ stacks, we manage to reveal the physical origin of band alignment fluctuations, i.e. oxygen density dependent interface and surface dipoles, and demonstrate that the band offsets can be tuned without introducing other materials. This is instructive to reduce gate tunneling current, alleviate device-to-device variation, and tune threshold voltage. Besides, this study indicates that great attention should be paid to model construction in the emerging atomistic study of semiconductor devices.