Photoferroelectric Coupling and Polarization-Controlled Interfacial Band Modulation in van der Waal Compound CuInP2S6

TL;DR

This study demonstrates how optical excitation influences polarization and electronic band structure in the ferroelectric van der Waals material CuInP2S6, enabling light-controlled electronic and ionic functionalities for nanoelectronic applications.

Contribution

It provides the first nanoscale evidence of photoferroionic coupling in CuInP2S6, revealing how light modulates band bending, ferroelectric switching, and ionic relaxation in layered ferroelectric semiconductors.

Findings

Illumination increases surface work function and photovoltage.

Light reduces coercive field and shifts polarization stability.

Photoinduced effects involve photocarrier redistribution and Cu+ migration.

Abstract

Understanding how optical excitation couples with polarization and interfacial electrostatics in van der Waals (vdW) ferroelectrics (FEs) is essential for the development of light-programmable nanoelectronic and optoelectronic devices. Here, we present direct nanoscale evidence of photoferroionic coupling in the vdW FE semiconductor CuInP2S6 (CIPS), where optical excitation jointly modulates electronic band bending, FE switching, and Cu+ ionic relaxation. The use of correlated Kelvin probe force microscopy, piezoresponse force microscopy, and conductive atomic force microscopy under above-bandgap illumination reveals illumination-induced enhancement of surface work function, persistent surface photovoltage, reduced coercive field, and positive imprint shifts. These effects arise from synergistic photocarrier redistribution and slow Cu+ migration that reshape interfacial depletion widths and internal electric fields. Illumination-assisted barrier lowering further enhances carrier injection and produces sweep-rate-dependent ferroionic transport hysteresis. Our results establish photoferroionic coupling as the governing mechanism for light-controlled band modulation and polarization stability in CIPS, providing a nanoscale framework for designing light-addressable FE memories, optoelectronic switches, and neuromorphic devices based on layered ferroionic materials.