An ab-initio study of electronic and optical properties of corundum Al2O3 doped with Sc, Y, Zr, and Nb

Abstract

Ab-initio calculations based on density functional theory have been employed to study the structural, electronic, and optical properties of yttrium (Y), scandium (Sc), zirconium (Zr), and niobium (Nb) doped α-Al2O3 with corundum structure. Exchange and correlation effects between electrons have been treated by generalized gradient approximation within the Perdew-Burk-Ezrenhof parameterization and by recently developed Tran-Blaha modified Becke-Johnson approach. Most attention in the work has been paid to the impurity d states, whose energy splitting has been analyzed in terms of the crystal field theory and whose influence on the gap size and the offset of the bands around it has been carefully evaluated. The influence of these states on modification of the optical absorption edge and the static dielectric constant of the doped systems has been also studied. It is concluded that only the Y doped α-Al2O3 (1) preserves the size of the band gap of the pure alumina, (2) does not change significantly the band offset around it, and (3) elevates the value of the static dielectric constant of the compound. These three conditions, necessary for usability of the doped material as a high-ε dielectric gate, are not satisfied by the Sc-, Zr-, and Nb-doped alumina compounds. Therefore, only the Y-doped α-Al2O3 exhibits potential to be further explored for employment in the semiconductor industry.