Hf defects in HfO2/Si

TL;DR

This study uses ab initio calculations to explore the stability and charge states of Hf defects in Si channels of HfO2/Si devices, revealing potential impacts on device mobility.

Contribution

It provides the first detailed analysis of Hf defect energetics and charge states in silicon, highlighting their possible effects on device performance.

Findings

Interstitial Hf defects are more stable than substitutional ones.

Multiple stable charge states exist within the silicon band gap.

Charged Hf impurities could cause Coulombic scattering, reducing mobility.

Abstract

We investigate the possibility that Hf defects exist in the Si channel of HfO2 Si-based metal-oxide-semiconductor devices. We have studied, using ab initio Density Functional Theory calculations, substitutional and interstitial Hf impurities in c-Si, for various charge states. Our results indicate that 1) the tetrahedral interstitial defect is energetically more favorable than the substitutional, and 2) there are various stable charge states in the Si gap. The possible presence of these charged impurities in the Si channel could lead to a mobility reduction, due to coulombic scattering.