Unification of the phonon mode behavior in semiconductor alloys:: Theory and ab initio calculations

We demonstrate how to overcome serious problems in understanding and classification of vibration spectra in semiconductor alloys, following from traditional use of the virtual crystal approximation (VCA ). We show that such different systems as InGaAs (1- bond -> 1- mode behavior), InGaP (modified 2- mode) , and ZnTeSe (2- bond. 1- mode ) obey, in fact, the same phonon mode behavior - hence probably a universal one - of a percolation type (1- bond. 2- mode ). The change of paradigm from the VCA insight (an averaged microscopic one ) to the percolation insight (a mesoscopic one ) offers a promising link toward the understanding of alloy disorder. The discussion is supported by ab initio simulation of the phonon density of states at the zone center of representative supercells at intermediary composition (ZnTeSe ) and at the impurity- dilute limits (all systems ). In particular, we propose a simple ab initio protocol to estimate the basic input parameters of our semiempirical percolation model for the calculation of the 1- bond -> 2- mode vibration spectra of zinc blende alloys. With this, the model turns self- sufficient.