Electronic bandstructure of in-plane ferroelectric van der Waals $\beta '-In_{2}Se_{3}$

TL;DR

This study measures and analyzes the electronic bandstructure of in-plane ferroelectric $eta'-In_{2}Se_{3}$, revealing its highly two-dimensional nature, moderate bandgap, and potential for high-mobility ferroelectric devices.

Contribution

First direct measurement of $eta'-In_{2}Se_{3}$ bandstructure using ARPES, supported by hybrid DFT calculations, highlighting its potential as a 2D ferroelectric semiconductor.

Findings

Bandstructure is highly two-dimensional with negligible c-axis dispersion.

Measured indirect bandgap is 0.97 eV and direct bandgap is 1.46 eV.

Fermi surface shows anisotropic electron pockets with small effective masses.

Abstract

Layered indium selenides ($In_{2}Se_{3}$) have recently been discovered to host robust out-of-plane and in-plane ferroelectricity in the $\alpha$ and $\beta$' phases, respectively. In this work, we utilise angle-resolved photoelectron spectroscopy to directly measure the electronic bandstructure of $\beta '-In_{2}Se_{3}$, and compare to hybrid density functional theory (DFT) calculations. In agreement with DFT, we find the band structure is highly two-dimensional, with negligible dispersion along the c-axis. Due to n-type doping we are able to observe the conduction band minima, and directly measure the minimum indirect (0.97 eV) and direct (1.46 eV) bandgaps. We find the Fermi surface in the conduction band is characterized by anisotropic electron pockets with sharp in-plane dispersion about the $\overline{M}$ points, yielding effective masses of 0.21 $m_{0}$ along $\overline{KM}$ and 0.33 $m_{0}$ along $\overline{\Gamma M}$. The measured band structure is well supported by hybrid density functional theory calculations. The highly two-dimensional (2D) bandstructure with moderate bandgap and small effective mass suggest that $\beta'-In_{2}Se_{3}$ is a potentially useful new van der Waals semiconductor. This together with its ferroelectricity makes it a viable material for high-mobility ferroelectric-photovoltaic devices, with applications in non-volatile memory switching and renewable energy technologies.