Photoluminescence excitation spectroscopy of quantum wire-like dislocation states in ZnS

Abstract

Recent ab initio calculations predict one-dimensional (1D) dispersive electronic bands confined to the atomic scale cores of dislocations in the wide bandgap (3.84 eV) semiconductor ZnS. We test these predictions by correlating sub-bandgap optical transitions with the density of dislocations formed during strain relaxation in epitaxial ZnS grown on GaP. The densities for four predicted partial dislocations are quantified using scanning electron microscopy-based electron channeling contrast imaging. Room-temperature ellipsometry reveals absorption peaks that scale with dislocation density and align with theoretical predictions. Low-temperature photoluminescence spectra show deep emission peaks matching dislocation 1D band-to-band transitions. Photoluminescence excitation spectroscopy reveals six distinct emission lines with contrasting excitation dependence. Four peaks (2.78, 2.41, 2.20, 1.88 eV), assigned to dislocations, exhibit only modest suppression (≤5×) when excited below the ZnS bandgap, while two other peaks (3.11, 1.53 eV) are strongly quenched (>10×). These findings support the existence of efficient, 1D band-to-band radiative transitions within quantum wire-like dislocation core states in ZnS, distinct from typical non-radiative deep level defects in wide gap semiconductors.