Light enhanced electron-phonon coupling: Raman study with an analytical model

What is it about?

The impact of excitation laser-induced effects on measured Raman spectra has been discussed in the literature, but quantitative assessments of these effects remain limited. This work offers insights into the underlying mechanisms, focusing on the alteration of Urbach tail state density due to laser-induced heating. This heating can be triggered by non-radiative transitions in semiconductors under laser illumination, which, in turn, perturbs electron-phonon interactions within the sample. A theoretical model has been developed to describe these effects, and experimental data from silicon nanowires and bulk EuFeO3 have been analyzed using the derived relationships.

Featured Image

Photo by FlyD on Unsplash

Photo by FlyD on Unsplash

Why is it important?

This article builds on a previous model of Fano interference and its correlation with disorder in a system [Phys. Rev. B 104, 245205 (2021)], extending it to the effects of laser illumination on Raman line shapes. Fano interference, which arises from electron-phonon interactions, manifests in asymmetric line shapes, with the degree of asymmetry characterized by the parameter 'q'. In this work, the expression for 'q' is explicitly derived as a function of the sample's surface temperature, enabling the assessment of laser-induced heating effects across different systems. The parameters in this expression reflect the thermal and electronic properties of the sample, making it a valuable tool for comparing these properties using the non-contact, non-destructive technique of Raman spectroscopy. Given that laser illumination can introduce lattice perturbations, such as thermal disorder due to heating, the role of Urbach energy (which represents the width of smeared density of states near the band edges in a semiconductor due to lattice disorder) becomes relevant. This study, therefore, explores the connection between Urbach energy and Raman spectroscopy in semiconductors. Moreover, this work serves as an example of "measurement perturbing the system itself," highlighting the critical importance of selecting appropriate excitation laser power during measurements. The observed significant changes in 'q' with varying laser power also suggest the possibility of light-controlled electron-phonon coupling, which could be crucial for optoelectronic and transport applications in semiconductors.