Highly Tunable Lateral Homojunction Formed in Two-Dimensional Layered CuInP₂S₆ via In-Plane Ionic Migration

Abstract

As basic building blocks for next-generation information technologies devices, high-quality p-n junctions based on van der Waals (vdW) materials have attracted widespread interest. Compared to traditional two-dimensional (2D) heterojunction diodes, the emerging homojunctions are more attractive owing to their intrinsic advantages, such as continuous band alignments and smaller carrier trapping. Here, utilizing the long-range migration of Cu + ions under an in-plane electric field, a lateral p-n homojunction was constructed in the 2D layered copper indium thiophosphate (CIPS). The symmetric Au/CIPS/Au devices demonstrate an electric-field-driven resistance switching (RS) accompanied by a rectification behavior without any gate control. Moreover, such rectification behavior can be continuously modulated by poling voltage. We deduce that the reversable rectifying RS behavior is governed by the effective lateral build-in potential and the change of the interfacial barrier during the poling process. Furthermore, the CIPS p-n homojuction is evidenced by the photovoltaic effect, with the spectral response extending up to the visible region due to the better photogenerated carrier separation efficiency. Therefore, this work provides a facile route to fabricate homojunctions through electric-field-driven ionic migration.

Cu+ Migration and Resultant Tunable Rectification in CuInP2S6

“…The same circumstance was observed for the sample which experienced a −15 V and 1 s poling process in the EFM experiment (See Figure S7b). This was consistent with a recent work on an in-plane CIPS homojunction working under a voltage of ∼30 V, where nanoparticles are generated on the electrode after many cycles . The topography of the sample after cycling also showed a profound change.…”

“…This was consistent with a recent work on an inplane CIPS homojunction working under a voltage of ∼30 V, where nanoparticles are generated on the electrode after many cycles. 25 The topography of the sample after cycling also showed a profound change. After several cycles at −5 V, an irreversible topography change could be observed, as shown in Figure S7c.…”

“…Being endowed with such a unique combination of FE and ionic conductivity, CIPS can be used for the construction of memristors and for performing neuromorphic computing . Compared with traditional memristors, whose structures usually consist of multilayers and multi-interfaces requiring complicated fabrication processes, CIPS can be used to construct a single-phase memristor with mobile ions, multiple polarization states, and low electronic leakage, based on a very simple structure. − It has also been reported that CIPS can form a device with unusual programmable rectifying direction via changing the sweep speed and voltage amplitude, which is critical for bidirectional operation and environment-adaptable learning.…”

Interface-Tuning of Ferroelectricity and Quadruple-Well State in CuInP2S6via Ferroelectric Oxide

“…Layered van der Waals (vdW) ferroelectric CuInP 2 S 6 (CIPS) hosts unconventional quadruple-well energy and high ionic conductivity, , which lead to various exotic phenomena, including negative piezoelectricity, thickness-dependent in-plane polarization, giant electrostriction enabled strain tunability, strong coupling of ferroelectric polarization with ionic migration and topography variation, − and the self-rectifying memristor effect . Compared with other vdW ferroelectric semiconductors, the above room temperature Curie temperature (bulk T C ∼ 42 °C), large band gap ( E g ∼ 2.9 eV), and large out-of-plane polarization ( P ∼ 4 μC/cm 2 ) make CIPS the most promising candidate for developing flexible and transparent nanoelectronic and optoelectronic devices, such as nonvolatile memory, − negative capacitance transistors, , memristors, , rectifiers, , photocatalysis, and photovoltaics …”

Robust Threshold-Switching Behavior Assisted by Cu Migration in a Ferroionic CuInP2S6 Heterostructure

“…Moreover, further studies have shown that the displacement of Cu in CIPS could not only induce the ferroelectricity but also contribute to the ionic conductivity under a high electric field: that is, the Cu ions can be driven out of the lattice and become mobile across the intra and inter layers. − Since the ions’ motion has been regarded as the basis for many resistive-switching devices, − the migration of Cu ions in CIPS makes it a potential candidate for developing ionic memristors. Indeed, recent studies have shown that the two-terminal CIPS device could mimic various neuroplasticity functions, and the flowing current can be manipulated through different bias stimuli, such as sweeping speed, direction, and amplitude. ,− However, while these works have shown the potential to make memristive devices utilizing the 2D layered CIPS, achieving stable resistive switching remains a challenge.…”