Bound exciton luminescence in shock compressed GaP:S and GaP:N

Photoluminescence (PL) spectra of bound excitons were measured in uniaxially strained GaP by performing shock-wave experiments at liquid nitrogen temperatures. GaP samples doped with sulfur or nitrogen were compressed up to 3 GPa when subjected to uniaxial strains along the [100] crystallographic orientation. PL lines from shallow sulfur donors redshifted upon compression, tracking the reduction in the indirect band gap. PL lines related to the isoelectronic $NN1$ pairs, in contrast, exhibited splitting and nonlinear blueshift. An empirical approach was used to model the $NN1$ behavior. It was shown that the splitting pattern is consistent with the previously proposed symmetry of $NN1$ defects and nonlinearities resulting from the reduction in the exciton binding energy. At high stresses, the $NN1$ lines disappeared due to the ionization of bound excitons.