Near-Infrared Photoelectric Properties of Multilayer Bi2O2Se Nanofilms

Nonvolatile Modulation of Bi2O2Se/Pb(Zr,Ti)O3 Heteroepitaxy

The pursuit of high-performance electronic devices has driven the research focus toward 2D semiconductors with high electron mobility and suitable band gaps. Previous studies have demonstrated that quasi-2D Bi2O2Se (BOSe) has remarkable physical properties and is a promising candidate for further exploration. Building upon this foundation, the present work introduces a novel concept for achieving nonvolatile and reversible control of BOSe's electronic properties. The approach involves the epitaxial integration of a ferroelectric PbZr0.2Ti0.8O3 (PZT) layer to modify BOSe's band alignment. Within the BOSe/PZT heteroepitaxy, through two opposite ferroelectric polarization states of the PZT layer, we can tune the Fermi level in the BOSe layer. Consequently, this controlled modulation of the electronic structure provides a pathway to manipulate the electrical properties of the BOSe layer and the corresponding devices.

Direct growth Bi2O2Se nanosheets on SiO2/Si substrate for high-performance and broadband photodetector

Bi2O2Se, a newly emerging two-dimensional (2D) material, has attracted significant attention as a promising candidate for optoelectronics applications due to its exceptional air stability and high mobility. Generally, mica and SrTiO3substrates with lattice matching are commonly used for the growth of high-quality 2D Bi2O2Se. Although 2D Bi2O2Se grown on these insulating substrates can be transferred onto Si substrate to ensure compatibility with silicon-based semiconductor processes, this inevitably introduces defects and surface states that significantly compromise the performance of optoelectronic devices. Herein we employ Bi2Se3as the evaporation source and oxygen reaction to directly grow Bi2O2Se nanosheets on Si substrate through a conventional chemical vapor deposition method. The photodetector based on the Bi2O2Se nanosheets on Si substrate demonstrates outstanding optoelectronics performance with a responsivity of 379 A W-1, detectivity of 2.9 × 1010Jones, and rapid response time of 0.28 ms, respectively, with 532 nm illumination. Moreover, it also exhibits a broadband photodetection capability across the visible to near-infrared range (532-1300 nm). These results suggest that the promising potential of Bi2O2Se nanosheets for high-performance and broadband photodetector applications.

Bi2O2Se-based CBRAM integrated artificial synapse

Integrating two-dimensional (2D) semiconducting materials into memristor structures has paved the way for emerging 2D materials to be employed in a vast field of memory applications. Bismuth oxyselenide (Bi2O2Se), a 2D material with high electron mobility, has attracted significant research interest owing to its great potential in various fields of advanced applications. Here, we explore the out-of-plane intrinsic switching behavior of few-layered Bi2O2Se via a cross point device for application in conductive bridge random access memory (CBRAM) and artificial synapses for neuromorphic computing. Via state-of-the-art methods, CVD-grown Bi2O2Se nanoplate is applied as a switching material (SM) in an Al/Cu/Bi2O2Se/Pd CBRAM structure. The device exhibits ∼90 consecutive DC cycles with a tight distribution of the SET/RESET voltages under a compliance current (CC) of 1 mA, a retention of over 10 ks, and multilevel switching characteristics showing four distinct states at Vread values of 0.1, 0.2, 0.25, and 0.3 V. Moreover, an artificial synapse is realized with potentiation and depression by modulating the conductance. The switching mechanism is explained via Cu migration through Bi2O2Se based on HRTEM analysis. The present structure shows potential for future integrated memory applications.

Ultrahigh responsivity of non-van der Waals Bi2O2Se photodetector

Bismuth oxyselenide has recently gained tremendous attention as a promising 2D material for next-generation electronic and optoelectronic devices due to its ultrahigh mobility, moderate bandgap, exceptional environmental stability, and presence of high-dielectric constant native oxide. In this study, we have synthesized single-crystalline nanosheets of Bismuth oxyselenide with thicknesses measuring below ten nanometers on Fluorophlogopite mica using an atmospheric pressure chemical vapor deposition system. We transferred as-grown samples to different substrates using a non-corrosive nail polish-assisted dry transfer method. Back-gated Bi2O2Se field effect transistors showed decent field effect mobility of 100 cm2V-1s-1. The optoelectronic property study revealed an ultrahigh responsivity of 1.16 × 106A W-1and a specific detectivity of 2.55 × 1013Jones. The samples also exhibited broadband photoresponse and gate-tunable photoresponse time. These results suggest that Bi2O2Se is an excellent candidate for future high-performance optoelectronic device applications.

Engineering electrode interfaces for telecom-band photodetection in MoS2/Au heterostructures via sub-band light absorption

Transition metal dichalcogenide (TMD) layered semiconductors possess immense potential in the design of photonic, electronic, optoelectronic, and sensor devices. However, the sub-bandgap light absorption of TMD in the range from near-infrared (NIR) to short-wavelength infrared (SWIR) is insufficient for applications beyond the bandgap limit. Herein, we report that the sub-bandgap photoresponse of MoS2/Au heterostructures can be robustly modulated by the electrode fabrication method employed. We observed up to 60% sub-bandgap absorption in the MoS2/Au heterostructure, which includes the hybridized interface, where the Au layer was applied via sputter deposition. The greatly enhanced absorption of sub-bandgap light is due to the planar cavity formed by MoS2 and Au; as such, the absorption spectrum can be tuned by altering the thickness of the MoS2 layer. Photocurrent in the SWIR wavelength range increases due to increased absorption, which means that broad wavelength detection from visible toward SWIR is possible. We also achieved rapid photoresponse (~150 µs) and high responsivity (17 mA W-1) at an excitation wavelength of 1550 nm. Our findings demonstrate a facile method for optical property modulation using metal electrode engineering and for realizing SWIR photodetection in wide-bandgap 2D materials.

Salt-Assisted Low-Temperature Growth of 2D Bi2 O2 Se with Controlled Thickness for Electronics

Bi₂ O₂ Se is the most promising 2D material due to its semiconducting feature and high mobility, making it propitious channel material for high-performance electronics that demands highly crystalline Bi₂ O₂ Se at low-growth temperature. Here, a low-temperature salt-assisted chemical vapor deposition approach for growing single-domain Bi₂ O₂ Se on a millimeter scale with thicknesses of multilayer to monolayer is presented. Because of the advantage of thickness-dependent growth, systematical scrutiny of layer-dependent Raman spectroscopy of Bi₂ O₂ Se from monolayer to bulk is investigated, revealing a redshift of the A_1g mode at 162.4 cm^-1 . Moreover, the long-term environmental stability of ≈2.4 nm thick Bi₂ O₂ Se is confirmed after exposing the sample for 1.5 years to air. The backgated field effect transistor (FET) based on a few-layered Bi₂ O₂ Se flake represents decent carrier mobility (≈287 cm²  V^-1 s^-1 ) and an ON/OFF ratio of up to 10⁷ . This report indicates a technique to grow large-domain thickness controlled Bi₂ O₂ Se single crystals for electronics.

Horizontally Self-Standing Growth of Bi2 O2 Se Achieving Optimal Optoelectric Properties

Air-stable 2D Bi₂ O₂ Se material with high carrier mobility appears as a promising semiconductor platform for future micro/nanoelectronics and optoelectronics. Like most 2D materials, Bi₂ O₂ Se 2D nanostructures normally form on atomically flat mica substrates, in which undesirable defects and structural damage from the subsequent transfer process will largely degrade their photoelectronic performance. Here, a new synthesis route involving successive kinetic and thermodynamic processes is proposed to achieve horizontally self-standing Bi₂ O₂ Se nanostructures on SiO₂ /Si substrates. Fewer defects and avoidance of transfer procedure involving corrosive solvents ensure the integrity of the intrinsic lattice and band structures in Bi₂ O₂ Se nanostructures. In contrast to flat structures grown on mica, it displays reduced dark current and improved photoresponse performance (on-off ratio, photoresponsivity, response time, and detectivity). These results indicate a new potential in high-quality 2D electronic nanostructures with optimal optoelectronic functionality.

Synthesis, characterization, and visible light photocatalytic activity of solution-processed free-standing 2D Bi2O2Se nanosheets

Owing to their unique structural and electronic properties such as layered structure with tuneable bandgap and high electron mobility, 2D materials have emerged as promising candidates for photocatalysis. Recently, bismuth oxyselenide (Bi₂O₂Se), a member of bismuth oxychalcogenide's family has shown great potential in high-speed field-effect transistors, infrared photodetectors, ferroelectric devices, and electrochemical sensors. However, the potential of Bi₂O₂Se in photocatalysis has not yet been explored. In the current work, Bi₂O₂Se nanosheets with an average size of ∼170 nm and a lattice strain of 0.01 were synthesized at room temperature using a facile solution-processed method and the as-synthesized material was investigated with various characterization techniques such as x-ray diffraction, FE-SEM, UV-vis spectroscopy. The bandgap for the indirect transition in Bi₂O₂Se nanosheets was estimated to be 1.19 eV. Further, the visible-light-driven photocatalytic degradation of methylene blue (MB) dye using Bi₂O₂Se as a photocatalyst is presented. The photocatalytic experiments demonstrate the promising photocatalytic ability of Bi₂O₂Se as it leads to 25.06% degradation of MB within 80 min of light illumination. The effect of active species trapping agents (carrier and radical scavengers) on photocatalytic activity is also presented and discussed.

Low-Temperature and High-Quality Growth of Bi2O2Se Layered Semiconductors via Cracking Metal-Organic Chemical Vapor Deposition

Ternary metal-oxy-chalcogenides are emerging as next-generation layered semiconductors beyond binary metal-chalcogenides (i.e., MoS₂). Among ternary metal-oxy-chalcogenides, especially Bi₂O₂Se has been demonstrated in field-effect transistors and photodetectors, exhibiting ultrahigh performance with robust air stability. The growth method for Bi₂O₂Se that has been reported so far is a powder sublimation based chemical vapor deposition. The first step for pursuing the practical application of Bi₂O₂Se as a semiconductor material is developing a gas-phase growth process. Here, we report a cracking metal-organic chemical vapor deposition (c-MOCVD) for the gas-phase growth of Bi₂O₂Se. The resulting Bi₂O₂Se films at very low growth temperature (∼300 °C) show single-crystalline quality. By taking advantage of the gas-phase growth, the precise phase control was demonstrated by modulating the partial pressure of each precursor. In addition, c-MOCVD-grown Bi₂O₂Se exhibits outstanding electrical and optoelectronic performance at room temperature without passivation, including maximum electron mobility of 127 cm²/(V·s) and photoresponsivity of 45134 A/W.

Ultrathin Bi2O2S nanosheet near-infrared photodetectors

Recently, a zipper two-dimensional (2D) material Bi₂O₂Se belonging to the layered bismuth oxychalcogenide (Bi₂O₂X: X = S, Se, Te) family, has emerged as an alternate candidate to van der Waals 2D materials for high-performance electronic and optoelectronic applications. This hints towards exploring the other members of the Bi₂O₂X family for their true potential and bismuth oxysulfide (Bi₂O₂S) could be the next member for such applications. Here, we demonstrate for the first time, the scalable room-temperature chemical synthesis and near-infrared (NIR) photodetection of ultrathin Bi₂O₂S nanosheets. The thickness of the freestanding nanosheets was around 2-3 nm with a lateral dimension of ∼80-100 nm. A solution-processed NIR photodetector was fabricated from ultrathin Bi₂O₂S nanosheets. The photodetector showed high performance, under 785 nm laser illumination, with a photoresponsivity of 4 A W^-1, an external quantum efficiency of 630%, and a normalized photocurrent-to-dark-current ratio of 1.3 × 10¹⁰ per watt with a fast response time of 100 ms. Taken together, the findings suggest that Bi₂O₂S nanosheets could be a promising alternative 2D material for next-generation large-area flexible electronic and optoelectronic devices.