INDEPENDENT AND CORRELATED COMPOSITION BEHAVIOR OF MATERIAL PROPERTIES - APPLICATION TO ENERGY-BAND GAPS FOR THE GA-ALPHA-IN1-ALPHA-P-BETA-AS1-BETA AND GA-ALPHA-IN1-ALPHA-P-BETA-SB-GAMMA-AS1-BETA-GAMMA ALLOYS

A correlated function expansion (CFE) is introduced (a) to identify th e role of independent and correlated composition variations upon a des ired material property, and (b) to provide an efficient means to compu te the property throughout the composition space. As an example the co ntributions of independent and correlated composition behavior upon th e principal energy band gaps for the alloys GaalphaIn1-alphaPbetaAs1-b eta and GaalphaIn1-alphaPbetaSbgammaAs1-beta-gamma are calculated and analyzed by applying the CFE to the universal tight-binding (UTB) Hami ltonian model of the alloys. The convergence properties of the CFE ove r the entire composition variable space (alpha,beta,gamma) are examine d upon including independent, pair-, and triple-correlated terms. By r etaining only independent component contributions in the CFE it was po ssible to represent the UTB results to better than 90% accuracy for bo th the alloys GaalphaIn1-alphaPbetaAs1-B and GaalphaIn1-alphaPbetaSbga mmaAs1-beta-gamma. Pair composition correlations contributed approxima tely 5-10 % to the band gaps in both alloys and for GaalphaIn1-alphaPb etaSbgammaAs1-beta-gamma the triple correlations were at the level of similar to 3%. The CFE is a generic tool capable of simplifying effort s at finding desired alloy compositions for material properties.