Band-Gap Tunability in Anharmonic Perovskite-like Semiconductors Driven by Polar Electron-Phonon Coupling

TL;DR

This study demonstrates how electric-field-driven polar phonon modes in anharmonic perovskite-like semiconductors can be used to achieve significant, controllable band-gap tunability, enabling advanced optoelectronic device applications.

Contribution

It introduces a high-throughput screening method and detailed physical analysis to identify and understand materials with tunable band gaps via polar phonon coupling.

Findings

Identified 310 promising candidates for band-gap tunability.

Achieved up to 70% band-gap reduction in Ag₃SBr.

Observed nearly 23% band-gap increase in BaTiO₃.

Abstract

The ability to finely tune optoelectronic properties in semiconductors is crucial for the development of advanced technologies, ranging from photodetectors to photovoltaics. In this work, we propose a novel strategy to achieve such tunability by utilizing electric fields to excite low-energy polar optical phonon modes, which strongly couple to electronic states in anharmonic semiconductors. We conducted a high-throughput screening of over $10,000$ materials, focusing on centrosymmetric compounds with imaginary polar phonon modes and suitable band gaps, and identified $310$ promising candidates with potential for enhanced optoelectronic tunability. From this set, three perovskite-like compounds --Ag$_3$SBr, BaTiO$_3$, and PbHfO$_3$-- were selected for in-depth investigation based on their contrasting band-gap behavior with temperature. Using first-principles calculations, \textit{ab initio} molecular dynamics simulations, tight-binding models, and anharmonic Fr\"ohlich theory, we analyzed the underlying physical mechanisms. Our results show that polar phonon distortions can induce substantial band-gap modulations at ambient conditions, including reductions of up to $70\%$ in Ag$_3$SBr and increases of nearly $23\%$ in BaTiO$_3$, relative to values calculated at zero temperature, while PbHfO$_3$ exhibits minimal change. These contrasting responses arise from distinct electron-phonon coupling mechanisms and orbital hybridization at the band edges. This work establishes key design principles for harnessing polar lattice dynamics to engineer tunable optoelectronic properties, paving the way for adaptive technologies such as wavelength-selective optical devices and solar absorbers.