Ab initio calculation of excitons in ZnO

The optical absorption and excitonic properties of wurtzite ZnO are investigated by means of an ab initio approach taking into account electron-hole correlations. This is done by solving the Bethe-Salpeter equation, using the results of density functional theory calculations as a starting point. Our main focus is the calculation of the band edge optical spectra. We have identified ground states for three excitons (A, B, and C), with binding energies around 68 meV. Excitons A and B are excited mainly by light polarized perpendicular to the c crystallographic axis. The C exciton absorbs mainly light polarized parallel to the c axis. Due to spin-orbit interactions, excitons A and C show a tiny absorption for the parallel polarization and perpendicular polarizations, respectively.