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 A(I)B(III)O(2) (A(I) = Cu or Ag, B-III = Al, Ga or In) compounds are discussed. We show that all these delafossite compounds have indirect band gaps with gap energy in the range E-g(ind) = 1.6-3.6 eV. We also estimate the lowest direct band gap energies to be in the range E-g(dir) = 2.6-4.0 eV. Optical characteristics reveal that A(I)B(III)O(2) 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 B-III 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 B-III cation vacancy has the highest formation energy.