Investigation of optoelectronic properties of pure and Co substituted α-Al₂O₃ by Hubbard and modified Becke-Johnson exchange potentials

Advanced GGA+U (Hubbard) and modified Becke-Johnson (mBJ) techniques are used for the calculation of the structural, electronic, and optical parameters of α-Al_2-xCo_xO₃ (x= 0.0, 0.167) compounds. The direct band gaps calculated by GGA and mBJ for pure alumina are 6.3 eV and 8.5 eV, respectively. The mBJ approximation provides results very close to the experimental one (8.7 eV). The substitution of Al with Co reduces the band gap of alumina. The wide and direct band gap of the doped alumina predicts that it can efficiently be used in optoelectronic devices. The optical properties of the compounds like dielectric functions and energy loss function are also calculated. The rhombohedral structure of the α-Al_2-xCo_xO₃ (x= 0.0, 0.167) compounds reveal the birefringence properties.