Extended X-Ray Absorption Fine Structure Studies of Co Doped ZnS and ZnSe Alloys

X-ray absorption experiments were performed at the Kedge of Co and Zn in Zn1-xCoxS and Zn1-mCoxSe compounds with x = 0.25, 0.16, 0.10, 0.05, 0.00 in the sulphides samples and x = 0.07, 0.02, 0.00 in the selenide ones. Anaysis of the extended X-ray absorptio fine structure oscillations using phase and amplitudes either from McKale code or from standard samples, gave the distance, number of atoms and the Debye-Waller factors for nearest neighbours. We found that the cation-anion distances Zn-S(Se) or Co-S(Se) are systematically shorter in ZnS than in ZnSe matrix, the Zn-anion distance is always larger than the Co-anion one without any significant Co content dependence. This allowed us to estimate the covalent radius of Co in the studied matrices to be 0.025 smaller than the Zn covaent radius and stated that covalent radius of Co is independent of the type of surrounding atoms. In addition the Debye-Waller factors indicated a better ordering in ternary compounds than in the binary standard ones in agreement with rocking curve measurements.