Study of the local structure of II-VI-based ternary alloys by extended x-ray absorption fine structure (EXAFS) and reflection high-energy electron energy loss spectrum (RHEELS)

Bondlengths, Debye-Waller factors, and site occupancy in the diluted magnetic semiconductors Zn{dollar}sb{lcub}rm 1 - x{rcub}{dollar}Mn{dollar}sb{lcub}rm x{rcub}{dollar}Se and Hg{dollar}sb{lcub}rm 1 - x{rcub}{dollar}Mn{dollar}sb{lcub}rm x{rcub}{dollar}Te, and the narrow-gap semiconductor Hg{dollar}sb{lcub}rm 1 - x{rcub}{dollar}Cd{dollar}sb{lcub}rm x{rcub}{dollar}Te have been measured using extended x-ray absorption fine structure (EXAFS). The nearest-neighbor bond lengths in all of these alloys are found to be constant as a function of alloy composition within the experimental uncertainty of 0.01A. Because the average cation-cation distance changes with Mn composition, these results necessarily imply distortion of the tetrahedral bond angles.; In the case of Zn{dollar}sb{lcub}rm 1 - x{rcub}{dollar}Mn{dollar}sb{lcub}rm x{rcub}{dollar}Se, the anion sublattice is shown to suffer the largest distortion, but the cation sublattice also exhibits some relaxation. The repercussions of these results are discussed, in terms of the amount of cation and anion sublattice distortion at low temperature and its connection to the superexchange mechanism occurring between the Mn{dollar}sp{lcub}+2{rcub}{dollar} ions and mediated by the intervening anion in Zn{dollar}sb{lcub}rm 1 - x{rcub}{dollar}Mn{dollar}sb{lcub}rm x{rcub}{dollar}Se.; From the NN bond length relaxation results shown in this study and those reported elsewhere for the III-V-based and II-VI-based ternary compounds and DMS alloys, it appears that substitution of Mn{dollar}sp{lcub}+2{rcub}{dollar} ions into II-VI-based compounds causes greater local distortion, in general, than otherwise observed when group II cations are substituted for one another. We believe that the tetrahedral bond weakening in DMS is due to MN 3d-orbital (t{dollar}sb2{dollar}) and anion p-orbital hybridization in DMS, leaving fewer p-orbitals available for tetrahedral bonding. This leads to the weakening of the bond force constants {dollar}alpha{dollar},{dollar}beta{dollar}, as well as the bond becoming more ionic as Mn{dollar}sp{lcub}+2{rcub}{dollar} is substituted into the II-VI-based compounds.; Finally, the experimentally extended electron energy loss fine structure (EXELFS) technique, with modulations in the differential inelastic electron scattering cross-section above an absorption core edge, has been used in recent years to study the local structure of condensed matter systems. Basically, the EXELFS phenomenology is the same as that for EXAFS, because the excited electron undergoes the same interference process when the experimental probe is either an electron or a photon. It has been demonstrated to be a complementary tool to EXAFS for obtaining accurate values for the surface structural parameters of materials.