Engineering Nonvolatile Polarization in 2D α-InSe/α-GaSe Ferroelectric Junctions.

The advent of two-dimensional (2D) ferroelectrics offers a new paradigm for device miniaturization and multifunctionality. Recently, 2D α-InSe and related III-VI compound ferroelectrics manifest room-temperature ferroelectricity and exhibit reversible spontaneous polarization even at the monolayer limit. Here, we employ first-principles calculations to investigate group-III selenide van der Waals (vdW) heterojunctions built up by 2D α-InSe and α-GaSe ferroelectric (FE) semiconductors, including structural stability, electrostatic potential, interfacial charge transfer, and electronic band structures. When the FE polarization directions of α-InSe and α-GaSe are parallel, both the α-InSe/α-GaSe P↑↑ (UU) and α-InSe/α-GaSe P↓↓ (NN) configurations possess strong built-in electric fields and hence induce electron-hole separation, resulting in carrier depletion at the α-InSe/α-GaSe heterointerfaces. Conversely, when they are antiparallel, the α-InSe/α-GaSe P↓↑ (NU) and α-InSe/α-GaSe P↑↓ (UN) configurations demonstrate the switchable electron and hole accumulation at the 2D ferroelectric interfaces, respectively. The nonvolatile characteristic of ferroelectric polarization presents an innovative approach to achieving tunable n-type and p-type conductive channels for ferroelectric field-effect transistors (FeFETs). In addition, in-plane biaxial strain modulation has successfully modulated the band alignments of the α-InSe/α-GaSe ferroelectric heterostructures, inducing a type III-II-III transition in UU and NN, and a type I-II-I transition in UN and NU, respectively. Our findings highlight the great potential of 2D group-III selenides and ferroelectric vdW heterostructures to harness nonvolatile spontaneous polarization for next-generation electronics, nonvolatile optoelectronic memories, sensors, and neuromorphic computing.