Negative spin-exchange splitting in the exciton fine structure of AlN

Abstract

The exact energy position of the free exciton transition and thus the lowest band gap in bulk wurtzite AlN are still under discussion. By combined high resolution optical emission and absorption experiments on a sample with (11¯00) surface, we resolve the fine structure of the lowest energy free exciton and determine an electron-hole spin-exchange interaction constant of j=−4 meV. This results in a low energy Γ1 exciton at 6.032 eV and a high energy Γ5 component at 6.040 eV. Only the latter one is observable for (0001) oriented AlN films due to selection rules.