Pressure-induced delocalization-to-localization transition of excitons in AlN

The properties of excitons in the rocksalt high-pressure phase of AlN are investigated theoretically by means of a first-principles approach based on solution of the Bethe-Salpeter equation. The excitons, in that phase, change nature when the applied pressure is varied, from being very extended in space at low pressures to being significantly more localized at higher pressures. The transition is associated with a sudden increase in the exciton binding energy. The change of the character of the excitons is related to the pressure-induced rearrangement of the energy bands.