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

TL;DR

This paper proposes a universal percolation-based framework for understanding phonon mode behavior in semiconductor alloys, supported by ab initio calculations, challenging traditional virtual crystal approximation models.

Contribution

It introduces a mesoscopic percolation model for phonon behavior in alloys, replacing the traditional microscopic virtual crystal approximation, and provides a practical ab initio protocol for parameter estimation.

Findings

Unified phonon mode behavior across different alloys

Validation of the percolation model with ab initio simulations

A self-sufficient semi-empirical model for alloy phonons

Abstract

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 towards 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 semi-empirical `percolation' model for the calculation of the 1-bond->2-mode vibration spectra of zincblende alloys. With this, the model turns self-sufficient.