No band gap, no problem: Defects in InAs using a band-avoiding occupation-constrained density functional theory

Abstract

Density functional theory (DFT) underestimates the experimental band gap---the infamous band gap problem. As the band gap defines the energy scale of defect levels, this complicates computation of charge transition energies for atomic defects. In the extreme case of narrow-gap semiconductors, the DFT band gap collapses to zero, seemingly precluding quantitative predictions of defect levels. We present a band-avoiding occupation-constrained DFT (ba-occ-DFT) approach that prevents spurious occupation of band-edge states and enables reliable total energy calculations of atomic defects. Application to indium arsenide (InAs) shows that ba-occ-DFT circumvents the band gap problem, separates band-edge errors from defect level calculations, and enables rigorous defect level predictions in a narrow-gap semiconductor despite a zero DFT band gap.