Excitons bound to nitrogen pairs in GaAs as seen by photoluminescence of high spectral and spatial resolution

Abstract

High resolution photoluminescence (PL) spectroscopy was performed on high quality bulk GaAs, lightly doped with the nitrogen isoelectronic impurity. The shallowest nitrogen pair bound exciton center labeled as ${\mathrm{X}}_{1}$ revealed a total of six transitions. The photoluminescence lines from a small ensemble of nitrogen centers showed polarization dependent intensity. High spectral resolution PL spectroscopy was combined with confocal spectroscopy experiments performed on a $\mathrm{Ga}\mathrm{As}:\mathrm{N}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ heterostructure. The high spatial resolution achieved by this technique enables us to localize and examine individual nitrogen bound excitons. Similar spectral structure and polarization dependence was observed for individual N-pair centers in GaAs. Both techniques support the ${C}_{2v}$ symmetry of such isoelectronic impurity centers. The comparison between the PL spectra from an ensemble of nitrogen pairs and individual centers demonstrate the ability of the single impurity technique to lift the orientational degeneracy.