Study of band-structure, optical properties and native defects in AIBIIIO2 (AI = Cu or Ag, BIII = Al, Ga or In) delafossites

In this work, employing a first-principles approach, the structural, electronic, optical, as well as the defect physics of AIBIIIO2 (AI = Cu or Ag, BIII = Al, Ga or In) compounds are discussed. We show that all these delafossite compounds have indirect band gaps with gap energy in the range Egind = 1.6–3.6 eV. We also estimate the lowest direct band gap energies to be in the range Egdir = 2.6–4.0 eV. Optical characteristics reveal that AIBIIIO2 compounds exhibit a significant anisotropy for both the real and imaginary parts of the dielectric function. Furthermore, we find that absorption onset for these compounds is energetically well above (>1.5 eV) the fundamental band gaps. Moreover, we demonstrate that the copper delafossites have larger absorption coefficients compared to the corresponding BIII cation silver delafossites in the visible range. Defect calculations reveal that Cu or Ag vacancy has the lowest formation energy followed by the O vacancy while the BIII cation vacancy has the highest formation energy. (paper)