Probabilistic analysis of site-occupation preferences in GaxIn1-xAsySb1-y and Cd1-xMnxSeyTe1-y quaternary compounds

Site-occupation preferences in quaternary GaInAsSb and CdMnSeTe compounds in tetrahedrally coordinated zinc-blende structures are discussed. Probabilistic eigenfunctions are defined to determine individual component pair-populations from measured average-pair distributions. The methodology and possible traps in interpreting site-occupation preferences of published EXAFS experimental overall average-pair distributions are discussed. The approach allows a deeper understanding of individual pair selective preferences in semiconducting multinary compounds. EXAFS reported departures from Bernoulli random distributions point to changes within elemental tetrahedral average-populations. Resolution requires that for tetrahedral structures experimental data best-fit be a 4th degree polynomial, product of a parabola by the factor x(1 - x). The analysis shows that both materials have a marked preference for elemental tetrahedra with odd numbers of competing species of ions around a central ion.