PHYSICAL PROPERTIES OF MIXED SINGLE CRYSTALS OF CDS AND ZNS

Cd1-x-ZnxS single crystals have been grown by iodine vapor transport and their photoelectronic properties studied in order to help characterize analogous defect centers in CdS and ZnS. The n-type dark conductivity of the solid solutions exhibits a sharp decrease by 7-8 orders of magnitude at about x = 0·15. This is accompanied by an increase of ∼1 order of magnitude in the thermal activation energy for conduction. The photoconductivity decreases smoothly across the composition range. The band gap, as measured by the peak in the spectral response of photoconductivity and from the absorption edge, also shifts smoothly, from ∼2·4 eV in CdS to ∼3·7 eV in ZnS. The photoconductivity in the crystals can be quenched by simultaneous illumination with light of energy ∼1 eV; almost invariant with composition. Thermally stimulated current measurements have detected two dominant traps whose energy below the conduction band varies monotonically with composition. One of these traps is commonly observed in ZnS and is responsible for the long duration phosphorescence seen in Cd1-xZnxS crystals with high ZnS content. The other trap is probably one which is frequently reported in CdS as due to sulfur vacancies. © 1968.