Physical mechanisms of structural, morphological, and property changes in ZnS and ZnSe under electron irradiation

This work presents an analysis of the physical mechanisms of radiation-induced changes in the structural parameters, morphology, and properties of ZnS and ZnSe crystals irradiated with 2 MeV electrons at fluences ranging from 0.5 × 10¹⁷to 4.0 × 10¹⁷electrons cm^-2. The processes of defect formation (vacancies, interstitials, and dislocations) resulting from elastic (nuclear) and inelastic (electronic) collisions are analyzed. These processes lead to lattice compression, bandgap narrowing, and an increase in the Urbach energy with rising electron fluence, reflecting enhanced structural disorder, as well as to surface smoothing, higher microhardness, and intensification of the longitudinal optical phonon mode in the Raman spectra. Differences between ZnS and ZnSe are discussed with respect to the ionicity of chemical bonds and the defect dynamics influencing lattice relaxation. A conceptual physical model is proposed to explain the observed effects in ZnS and ZnSe, based on electron-phonon interactions and defect annihilation processes.