Fingerprints of CuPt ordering in III-V semiconductor alloys: Valence-band splittings, band-gap reduction, and x-ray structure factors

Abstract

Spontaneous CuPt ordering induces a band-gap reduction (Formula presented) relative to the random alloy, a crystal field splitting (Formula presented) at valence-band maximum, as well as an increase of spin-orbit splitting (Formula presented) We calculate these quantities for (Formula presented) and (Formula presented) using the local density approximation (LDA), as well as the more reliable LDA-corrected formalism. We further provide these values and the valence-band splittings (Formula presented) (between (Formula presented) and (Formula presented)) and (Formula presented) (between (Formula presented) and (Formula presented)) for these materials as a function of the degree η of long range order. In the absence of an independent measurement of η, experiment is currently able to deduce only the ratio (Formula presented) Our LDA-corrected results for this quantity compare favorably with recent experiments for (Formula presented) and (Formula presented) but not for (Formula presented) where our calculation does not support the experimental assignment. The “optical LRO parameter η” can be obtained by fitting our calculated (Formula presented) to the measured (Formula presented) and by expressing the measured (Formula presented) and (Formula presented) in terms of our calculated (Formula presented) and (Formula presented) We also provide the calculated x-ray structure factors for ordered alloys that can be used experimentally to deduce η independently. © 1998 The American Physical Society.