An EXAFS study of the structure of the Zn1-xBexSe alloy system

Zn1-xBexSe is an interesting II-VI semiconductor showing unusual phonon behavior for 0.19<x<0.81which has been ascribed due to presence of chains of Be and Se with two slightly differing Be-Se bond distances. EXAFS data have been recorded for several compositions of Be in this mixed crystals at the Zn and Se K edges and analyzed to determine the nearest and next nearest neighbor distances for Zn and Se atoms as a function of 'x'. The effects of these chains is observed in the form of an increase in the σ2 value of the Be-Se bond at x = 0.42 and 0.55 as compared to smaller 'x' values of 0.06, 0.16 and 0.27. Theoretical estimates show that the bond length difference between the two Be-Se bonds is ∼ 0.04A, which seems to be too small to be resolved as two different bond lengths but could be observed only as increase in σ2 value for larger values of 'x'. The trends in the various bond angles as a function of 'x' have also been explained in terms of the distorted tetrahedral structure in the ternary.