Charge carrier coupling to the soft phonon mode in a ferroelectric semiconductor

TL;DR

This study demonstrates that in a ferroelectric semiconductor, charge carriers strongly couple with soft phonon modes, which enhances screening and reduces recombination, potentially improving optoelectronic device performance.

Contribution

It provides direct experimental evidence of electron-soft phonon coupling in a ferroelectric semiconductor using coherent phonon spectroscopy.

Findings

Charge carriers are long-lived and interact with soft phonons.

Electron-soft phonon coupling aids in charge screening.

Reduced charge recombination rates observed.

Abstract

Many crystalline solids possess strongly anharmonic soft phonon modes characterized by diminishing frequency as temperature approaches a critical point associated with a symmetry breaking phase transition. While electron-soft phonon coupling can introduce unique scattering channels for charge carriers in ferroelectrics, recent studies on the non-ferroelectric lead halide perovskites have also suggested the central role of anharmonic phonons bearing resemblance to soft modes in charge carrier screening. Here we apply coherent phonon spectroscopy to directly study electron coupling to the soft transverse optical (TO) phonon mode in a ferroelectric semiconductor SbSI. Photo-generated charge carriers in SbSI are found to be exceptionally long lived and are associated with a transient electro-optical effect that can be explained by interactions between charge carriers and thermally stimulated soft-phonon excitations. These results provide strong evidence for the role of electron-soft phonon coupling in the efficient screening of charge carriers and in reducing charge recombination rates, both desirable properties for optoelectronics.