Arsenic interstitial defect-induced gap states in LT-GaAs and the STM characterization from first-principles methods

We performed DFT calculations with advanced exchange-correlation treatments to study the electronic properties of arsenic interstitial (As i ) in the [110]-split configuration in low temperature GaAs (LT-GaAs) and compared them with experiments. We also calculated the STM images of As i in different layers of GaAs(110) to guide atomic-scale characterization. We found that As i expands Ga-Ga distances more than As-antisite (As Ga ) expands As-As bonds, supporting the observed Raman blue shift in annealed samples. Formation energy of As i is higher than As Ga in As-rich conditions, consistent with its formation during low-temperature annealing. Bandstructure analysis shows that As i introduces a mid-gap donor level matching the ~1300nm band observed by ultrafast transient absorption spectroscopy (UFTS) and a low-lying state, consistent with the band narrowing inferred from UFTS. STM images reveal distinct contrast patterns, with the subsurface As i showing the most prominent, bias-insensitive spherical contrast, indicating it could be the most detectable configuration on GaAs (110).