Elucidating the high-k insulator α-Al2O3 direct/indirect energy band gap type through density functional theory computations

The measured band gap of the high-k insulator alpha-Al2O3 is direct (8.80 eV) but previous theoretical estimates were not conclusive regarding its direct/indirect character. Thus, we have performed density functional theory (DFT) computations of the structural and electronic properties of alpha-Al2O3 employing several exchange-correlation functionals and the A-sol scheme. Among the functionals tested, the best results were obtained for the sX-LDA calculation, which predicted an indirect gap of 8.826 eV. The lattice parameter dependence of the alpha-Al2O3 gap type, on the other hand, suggests a subtle transition for temperatures above 4001( due to thermal expansion. (C) 2015 Elsevier B.V. All rights reserved.