Importance of the correct Fermi energy on the calculation of defect formation energies in semiconductors

Abstract

Density functional theory (DFT) is a major theoretical tool for the study of defects in semiconductors. However, the results suffer from the often too-small DFT band gap. The calculation of defect formation energy (ΔH) using more sophisticated DFT+GW and hybrid functional methods, however, suggest qualitatively different conclusions about the nature of the DFT error. Here we show that these discrepancies originate from large differences in the representation of the Fermi energy of bulk for the different methods and that they can be largely brought into agreement by correcting the DFT ionization energy.