Anisotropy in Electroluminescence and Conductivity of Single Crystals of ZnS

Synthetic ZnS single crystals possess highly anisotropic electrical properties. The dark conductivity may be as much as a factor of ${10}^6$ larger in directions perpendicular to the $c$-axis than parallel to it. Photoconductivity and electroluminescent emission are also anisotropic but in smaller degree. It is proposed that these effects are caused by barriers due to stacking faults.