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

Spontaneous CuPt ordering induces a band-gap reduction Delta E-g relative to the random alloy, a crystal field splitting Delta(CF) at valence-band maximum, as well as an increase of spin-orbit splitting Delta(SO) We calculate these quantities for AlxIn1-xP, AlxIn1-xAs, GaxIn1-xP, and GaxIn1-xAs 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 Delta E-12 (between <(Gamma)over bar>(4,5u) and <(Gamma)over bar>((1)(6v))) and Delta E-13 (between <(Gamma)over bar>(4,5v) and <(Gamma)over bar>((2)(6v))) for these materials as a function of the degree eta of long range order. In the absence of an independent measurement of eta, experiment is currently able to deduce only the ratio Delta E-g/Delta(CF). Our LDA-corrected results for this quantity compare favorably with recent experiments for GaxIn1-xP and GaxIn1-xAs, but not for AlxIn1-xP, where our calculation does not support the experimental assignment. The "optical LRO parameter eta" can be obtained by fitting our calculated Delta E-g(eta) to the measured Delta E-g(eta), and by expressing the measured Delta E-12(eta) and Delta E-13(eta) in terms of our calculated Delta(CF)(eta) and Delta(SO)(eta). We also provide the calculated x-ray structure factors for ordered alloys that can be used experimentally to deduce eta independently. [S0163-1829(98)01715-9].