DIFFERENTIAL ANOMALOUS X-RAY-SCATTERING STUDIES OF AMORPHOUS CD59AS41AND CD26AS74

The local structure of amorphous cadmium arsenide semiconducting films has been studied by differential anomalous X-ray scattering. Intensit y measurements were carried out on two samples, containing 41 and 74 a t.% As, in the vicinity of the absorption K edges of both constituents using synchrotron radiation. The computational procedure, similar to that proposed by Warren for an amorphous sample with more than one kin d of atom, was applied to obtain the structural parameters from the ex perimental data. It has been found that atoms in the amorphous Cd-As f ilms remain almost tetrahedrally coordinated and that the investigated films are chemically ordered. The structural changes going from cadmi um- to arsenic-rich composition have been revealed. The differential a nomalous X-ray scattering technique proved to be effective, providing the evidence for the Cd-Cd and As-As near neighbour correlations in Cd 59As41 and Cd26As74, respectively. The simulations of the differential radial distribution functions have shown that for the amorphous film containing 41 at.% As the distorted tetrahedral structure, intermediat e between the CdAs and Si III type structures, is adequate to account for the experimental data. At 74 at.% As, the atomic arrangement can b e described satisfactorily by the structural model based on the tetrag onal CdAs, structure. The structural parameters obtained from the pres ent study and those previously derived using the extended X-ray absorp tion fine structure and conventional large angle X-ray scattering tech niques are compared.