Pressure-stiffened Raman Phonons in Group III Nitrides

TL;DR

This paper develops an analytical model linking pressure-induced Raman phonon stiffening in Group III nitrides to atomic bonding changes, providing physical insight into the phenomenon and its polynomial description.

Contribution

It extends the bond-order-length-strength (BOLS) model to pressure effects, offering an atomic-level explanation for Raman phonon stiffening under pressure.

Findings

The model accurately predicts Raman phonon shifts under pressure.

Polynomial coefficients relate to atomic bonding energies.

The approach enables determination of atomic cohesive energies.

Abstract

It has long been puzzling regarding the atomistic origin of the pressure-induced Raman phonon stiffening that generally follows a polynomial expression with coefficients needing physical indication. Here we show that an extension of the bond-order-length-strength (BOLS) correlation mechanism to the pressure domain has led to an analytical solution to connect the pressure-induced Raman phonon stiffening directly to the bonding identities of the specimen and the response of the bonding identities to the applied stimulus. It is found that the pressure-induced blue-shift of Raman phonons arises from the bond compression and energy storage exerted by the compressive stress. Agreement between predictions and experimental measurement leads to the detailed form for the polynomial coefficients, which offer an atomic understanding of the physical mechanism of the external pressure induced energy gain, thermally induced bond expansion as well as means of determining the mode atomic cohesive energy in a specimen.