Model of annealing-induced short-range order effects in (GaIn)(NP) alloys

The nearest-neighbor bond configuration affects decisively many important characteristics of semiconductor metastable alloys, in particular the width of the band gap. We study effects of formation of a short-range order in (GaIn)(NP)∕GaP heterostructures. Annealing experiments on (GaIn)(NP)∕GaP quantum wells reveal a blueshift of the photoluminescence spectra and an enhancement of the photoluminescence quantum efficiency as compared to the as-grown material. We show that the replacement of Ga-N bonds by In-N bonds upon annealing can account for the observed phenomena, in particular for the enhancement of the band gap. Calculations carried out in the frame of the density-functional theory and also using an empirical energy functional show that the driving force for the rearrangement in the nitrogen local environment is reduction of the strain contribution to the alloy total energy functional. Analytical treatment of correlation effects on the configurational entropy contribution to the alloy free energy is suggested. We show that the entropy factor is not negligible and it plays a crucial role when determining the thermodynamically favorable atomic configuration.