Intrinsic Band Gap Research Articles

Interlayer Transition Induced Infrared Response in ReS2/2D Perovskite van der Waals Heterostructure Photodetector.

The emerging Ruddlesden-Popper two-dimensional perovskite (2D PVK) has recently joined the family of 2D semiconductors as a potential competitor for building van der Waals (vdW) heterostructures in future optoelectronics. However, to date, most of the reported heterostructures based on 2D PVKs suffer from poor spectral response that is caused by intrinsic wide bandgap of constituting materials. Herein, a direct heterointerface bandgap (∼0.4 eV) between 2D PVK and ReS2 is demonstrated. The strong interlayer coupling reduces the energy interval at the heterojunction region so that the heterostructure shows high sensitivity with the spectral response expanding to 2000 nm. The large type-II band offsets exceeding 1.1 eV ensure fast photogenerated carriers separation at the heterointerface. When this heterostructure is used as a self-driven photodetector, it exhibits a record high detectivity up to 1.8 × 1014 Jones, surpassing any reported 2D self-driven devices, and an impressive external quantum efficiency of 68%.

A high-efficiency solar water evaporation-photocatalysis system achieved by manipulating surface wettability and constructing heterojunction

Recent developments in integrating photocatalysis into solar-driven interfacial water evaporation have attracted much attention. Herein, β-In2S3 nanosheets decorated 2H phase MoS2 nanosheet arrays (MSIS) were proposed for synchronous solar-driven water evaporation and photodegradation of organic pollutants. The modification of hydrophobic 2H phase MoS2 with In2S3 switched the surface wettability. The intrinsic narrow bandgaps of both MoS2 and In2S3 endowed the solar absorber with a solar absorptance of 96.0 %, and the light utilization of the MSIS was further improved due to its hydrophilicity during solar-driven interfacial water evaporation. Moreover, the MSIS not only boosted the solar-driven interfacial water evaporation by tailoring the wettability of the solar absorber, but also enhanced its photocatalytic degradation over organic pollutants by the formation of heterojunction interfaces between MoS2 and In2S3. Specifically, the optimal solar absorber, only composed of semiconductors, exhibited a 4.2-times enhancement in photocatalytic rate constant without the compromise on solar-driven water evaporation (achieving an evaporation rate of 1.56 kg·m−2·h−1 under one sun). The heterojunction-based solar absorber featuring favorable hydrophilicity offered exciting opportunities to construct the high-efficiency solar water evaporation-photocatalysis system for the treatment of contaminated water.

Optical properties of InI3: Density functional theory calculations and experimental results

The electronic and optical properties of InI3 have been investigated by both experimental and theoretical approaches. The First Principle electronic structure and optical properties were calculated by Density Functional Theory (DFT) formalism using Full Potential Linearized Augmented Plane Wave plus local orbitals (FP-LAPW + lo) implementing different appropriate exchange-correlation functionals in WIEN2k code. The calculations were also carried out implementing other functionals and only TB-mBJ results tally the closest with experimental results. The optical measurements of a well characterized InI3 films indicate the band gap as of direct type and residual strain dependant. The stress free intrinsic band gap Eg = 2.8 eV (average of Eg⊥c and EgIIc) has been determined from the residual strain dependence of the band gap in closest agreement with theoretically calculated value of 2.9 eV. Both theory and experiment show that the band gap is anisotropic along and perpendicular to c-axis. The electron effective mass me*=0.79m0 and the hole effective mass mh*=0.85m0 have been determined from the band structure. The experimental and theoretical optical properties match reasonably well.

Enhancement of thermoelectric power factor via electron energy filtering in Cu doped MoS2 on carbon fabric for wearable thermoelectric generator applications

The design and construction of state-of-the-art wearable thermoelectric materials are important for the development of self-powered wearable thermoelectric generators (WTEGs). Molybdenum disulfide (MoS2) has been reported as a noteworthy thermoelectric (TE) material because of its large intrinsic bandgap and high carrier mobility. In this work, Cu-doped two-dimensional layered MoS2 nanosheets were grown on carbon fabric (CF) via a hydrothermal method. The electrical conductivity, Seebeck coefficient, and power factor for the Cu-doped MoS2 were found to increase with increasing temperature. The maximum Seebeck coefficient was obtained for a MoS2 sample doped with 4 at% of Cu (CM4) was ∼10 μV/K at 303 K and ∼13 μV/K at 373 K. The enhancement in the Seebeck coefficient was attributed to an energy-filtering effect caused by the interfacial barrier between MoS2 and Cu. In addition, a thermoelectric device was designed with four pairs of TE materials, where CM4 (4 at%) was used as a p-type material and Cu wire was used as an n-type material. These p- and n-type materials were connected electrically in series and thermally in parallel to generate a voltage of 190.7 μV at a temperature gradient of 8 K.

First-principles determination of high thermal conductivity of PCF-graphene: A comparison with graphene

Poly-cyclooctatetraene framework (PCF)-graphene, an emerging all-sp2 hybridized two-dimensional (2D) carbon allotrope, possesses an intrinsic direct bandgap (0.77 eV) and excellent mechanical properties, indicating great potential in nanoelectronics. Understanding the thermal transport behavior of PCF-graphene is of vital importance for determining the reliability of related devices based on it. In this work, the thermal transport in PCF-graphene is systematically studied using the Boltzmann transport theory combined with first-principles calculations. The results show that the room-temperature thermal conductivity of PCF-graphene with only considering three-phonon scattering is as high as 1587.3 W/m K along the zigzag direction, and decreases by 27.1% (1157.4 W/m K) when including four-phonon scattering, indicating the four-phonon scattering plays a non-negligible role in in thermal transport. Although the thermal conductivity of PCF-graphene is not as large as that in graphene, it still exceeds most common 2D materials and makes it suitable for applications in the thermal management of microelectronics. Analyses of phonon group velocity and phonon scattering rates are conducted to reveal the high thermal conductivity of PCF. Moreover, as the temperature increases to 800 K, the reduction of thermal conductivity is close to 50% after including four-phonon scattering. The analysis of phonon group velocity and phonon scattering rates are conducted to reveal the underlying mechanism. Our results provide insights for constructing high-thermal-conductivity materials based on 2D carbon allotropes.

(Invited) Effect of Polaron Formation on Optical and Carrier Transport Properties of Transition Metal Oxides As Photoelectrodes from First-Principles Calculations

Transition metal oxides are promising photoelectrode materials for solar-to-fuel conversion applications. However, their performance is limited by the low carrier mobility (especially electron mobility) due to the formation of small polarons. Recent experimental studies have shown improved carrier mobility and conductivity by atomic doping; however the underlying mechanism is not understood. A fundamental atomistic-level understanding of the effects on small polaron transport is critical to future material design with high conductivity. In this talk, we will discuss the effect of small polaron formation on optical and carrier transport properties of transition metal oxides from first-principles calculations.First, we resolve the conflicting findings that have been reported on the optical gap of a well-known catalysis Co3O4 as an example[1]. We confirm that the formation of small hole polarons significantly influences the optical absorption spectra and introduces extra spectroscopic signature below the intrinsic band gap, leading to a 0.8 eV transition that is often misinterpreted as the band edge that defines the fundamental gap.Then we discuss the formation of small polarons' effect on carrier concentration, by resolving the controversy of nature of "shallow" or "deep" impurities of intrinsic oxygen vacancies in BiVO4 as an example[2], i.e. how to unify different experiments with the correct definition of ionization energy in polaronic oxides. We further discuss why certain dopants can have very low optimal concentrations (or very early doping bottleneck) in polaronic oxides such as Fe2O3, through a novel "electric-multipole" clustering between dopants and polarons[3]. These multipoles can be very stable at room temperature and are difficult to fully ionize compared to separate dopants, and thus they are detrimental to carrier concentration improvement. This allows us to uncover mysteries of the doping bottleneck in hematite and provide guidance for optimizing doping and carrier conductivity in polaronic oxides toward highly efficient energy conversion applications. In addition, we show the importance of synthesis condition such as synthesis temperature and oxygen partial pressure on dopant and polaron concentrations, and how to optimize the synthesis condition based on theoretical predictions[4].At the end, we show different theoretical models for polaron mobility calculations from a macroscopic dielectric continuum picture with an example of spin polarons in CuO[5] and a microscopic polaron hopping picture by combining generalized Landau-Zener theory and kinetic Monte-Carlo samplings for doped oxides[6].Our first-principles calculations provide important insights and suggest design principles for optimal optical and transport properties of polaronic oxides.

Experimental Observation of ABCB Stacked Tetralayer Graphene.

In tetralayer graphene, three inequivalent layer stackings should exist; however, only rhombohedral (ABCA) and Bernal (ABAB) stacking have so far been observed. The three stacking sequences differ in their electronic structure, with the elusive third stacking (ABCB) being unique as it is predicted to exhibit an intrinsic bandgap as well as locally flat bands around the K points. Here, we use scattering-type scanning near-field optical microscopy and confocal Raman microscopy to identify and characterize domains of ABCB stacked tetralayer graphene. We differentiate between the three stacking sequences by addressing characteristic interband contributions in the optical conductivity between 0.28 and 0.56 eV with amplitude and phase-resolved near-field nanospectroscopy. By normalizing adjacent flakes to each other, we achieve good agreement between theory and experiment, allowing for the unambiguous assignment of ABCB domains in tetralayer graphene. These results establish near-field spectroscopy at the interband transitions as a semiquantitative tool, enabling the recognition of ABCB domains in tetralayer graphene flakes and, therefore, providing a basis to study correlation physics of this exciting phase.

Concentric core-shell tracks and spectroscopic properties of SrTiO3 under intense electronic excitation

A deeper understanding of the intrinsic link between the irradiation-induced microstructures and the corresponding spectroscopic properties is becoming increasingly attractive for the research fields of materials science, physics, and information technology. In this work, the structural damage response, spectroscopic features, and associated physical mechanisms of SrTiO3 single crystals under swift heavy ion irradiation were comparatively analyzed using a combination of experimental and theoretical approaches. Corresponding to 0.11–5.00 MeV/u ion irradiation with electronic energy loss ranging from 4.0 to 29.3 keV/nm, the inelastic thermal spike calculations combined with molecular dynamics simulations are compared with the experimental observations, revealing the track fine structures (individual spherical defects with a disordered region, and discontinuous and continuous tracks consisting of an amorphous core and a disordered outer shell) and demonstrating the dominant effects of the deposition energy and lattice temperature on track damage formation and evolution; thus, two essential thresholds for defect formation of ∼0.60 eV/atom and amorphous region formation of ∼1.81 eV/atom were identified to better describe the concentric core-shell track structure. The enhanced nanohillock formation in the surface region is attributed to the combined action of kinetic and potential energy depositions, and the fluence dependence in regulating the hillock dimensions is also presented. The measured refractive index profiles along different crystal axes further indicate the anisotropy of irradiation-induced lattice expansion. With increasing ion fluence and damage level, the intrinsic bandgap gradually decreased, and the concentration of additional radiative recombination centers (1.81 eV, 2.31 eV, and 2.42 eV) accordingly increased in the SrTiO3 crystal, providing the possibility of regulating related defects to achieve tunable/selective photon emission for more critical technological applications.

Oxygen vacancy-regulated metallic semiconductor MoO2 nanobelt photoelectron and hot electron self-coupling for photocatalytic CO2 reduction in pure water

This communication describes metallic MoO2−x nanobelts intrinsic photocatalytic CO2 reduction performance in pure water. The intrinsic wide-bandgap endowed MoO2 nanobelts great potential for CO2 reduction in ultraviolet, while localized surface plasmonic resonance (LSPR) and the metallic feature induced by oxygen vacancies ensured energetic electrons transform and fast kinetic transfer. Credit to the unique degenerate doping properties of MoO2−x nanobelts, the absorbed wavelength of intrinsic semiconductor bandgap overlapped with the LSPR absorption. Therefore, the high performance was ascribed to the self-coupling of intrinsic excited photoelectrons and plasmonic hot electrons. The surface abundant oxygen vacancies also facilitated preferable adsorption of CO2 and hence promoted the chemical activation. The according intrinsic CO production rate was 62.75 µmol/g/h in pure water under ultraviolet light, which was 6 times higher than that of commercial P25 photocatalyst (11.13 µmol/g/h). Our findings provide new insights and inspirations for parsing the mechanism and developing new-type MoO2-based photocatalysts.

First-principles study of band alignment and electronic structure of Arsenene/SnS2 heterostructures

Currently, Stacking two or more 2D materials into a vertical heterostructures is currently a methods to obtain excellent electronic properties. In this work, the energy band alignment of Arsenene/SnS 2 heterostructures, electronic structure including strain and electric field effects are investigated in detail. The results show that the intrinsic band gap of the Arsenene/SnS 2 heterostructure is much smaller than Arsenene monolayer. The bilayer heterostructure is type II band alignment, which can effectively promote separation of the photo-generated electron-hole pairs. Its absorption range covers from visible light to ultraviolet light, and the light absorption intensity is up to 10 5 orders of magnitude. Meanwhile, the vertical strain and electric field between the layers can tune the band gap of the heterostructures, in which the electric field can realize the transition from semiconductor to metal. The results show that heterostructures has great potential for application in coming field of optoelectronic devices and the photovoltaic . • Electronic structure for Arsenene/SnS 2 heterostructure are studied systematically. • Heterostructure possesses a type-II band alignment and a narrow indirect band gap (0.20 eV). • Light absorption intensity of heterostructure is up to 10 5 orders of magnitude. • Electronic structure of heterostructure is flexibly controllable by vertical strain and electric field.

Cr2XTe4 (X = Si, Ge) monolayers: a new type of two-dimensional high-T C Ising ferromagnetic semiconductors with a large magnetic anisotropy

Two-dimensional (2D) ferromagnetic semiconductor (FMS) provides the ideal platform for the development of quantum information technology in nanoscale devices. However, most of them suffer from low Curie temperature and small magnetic anisotropic energy (MAE), severely limiting their practical application. In this work, by using first-principles calculations, we predicted two stable 2D materials, namely, Cr2SiTe4 and Cr2GeTe4 monolayers. Interestingly, both of them are intrinsic direct band gap FMSs (∼1 eV) with a large magnetization (8 µ B f.u.−1) and sizable MAE (∼500 μ eV Cr−1). Monte Carlo simulations based on Heisenberg model suggest markedly high Curie temperatures of these monolayers (∼200 K). Besides, their high mechanical, dynamical, and thermal stabilities are further verified by elastic constants, phonon dispersion calculations, and ab initio molecular dynamics simulations. The outstanding attributes render Cr2XTe4 (X = Si, Ge) monolayers broadening the candidates of 2D FMS for a wide range of applications.

Self-driven highly responsive p-n junction InSe heterostructure near-infrared light detector

Photodetectors converting light signals into detectable photocurrents are ubiquitously in use today. To improve the compactness and performance of next-generation devices and systems, low dimensional materials provide rich physics to engineering the light–matter interaction. Photodetectors based on two-dimensional (2D) material van der Waals heterostructures have shown high responsivity and compact integration capability, mainly in the visible range due to their intrinsic bandgap. The spectral region of near-infrared (NIR) is technologically important, featuring many data communication and sensing applications. While some initial NIR 2D material-based detectors have emerged, demonstrations of doping-junction-based 2D material photodetectors with the capability to harness the charge-separation photovoltaic effect are yet outstanding. Here, we demonstrate a 2D p-n van der Waals heterojunction photodetector constructed by vertically stacking p-type and n-type indium selenide (InSe) flakes. This heterojunction charge-separation-based photodetector shows a threefold enhancement in responsivity in the NIR spectral region (980 nm) as compared to photoconductor detectors based on p- or n-only doped InSe. We show that this junction device exhibits self-powered photodetection operation, exhibits few pA-low dark currents, and is about 3–4 orders of magnitude more efficient than the state-of-the-art foundry-based devices. Such capability opens doors for low noise and low photon flux photodetectors that do not rely on external gain. We further demonstrate millisecond response rates in this sensitive zero-bias voltage regime. Such sensitive photodetection capability in the technologically relevant NIR wavelength region at low form factors holds promise for several applications including wearable biosensors, three-dimensional (3D) sensing, and remote gas sensing.

Strong Neel Ordering and Luminescence Correlation in a Two‐Dimensional Antiferromagnet

AbstractMagneto‐optical effect has been widely used in light modulation, optical sensing, and information storage. Recently discovered 2D van der Waals layered magnets are considered as promising platforms for investigating novel magneto‐optical phenomena and devices, due to the long‐range magnetic ordering down to atomically thin thickness, rich species, and tunable properties. However, majority 2D antiferromagnets suffer from low luminescence efficiency which hinders their magneto‐optical investigations and applications. This work uncovers strong light‐magnetic ordering interactions in 2D antiferromagnetic MnPS3 using a newly‐emerged near‐infrared photoluminescence (PL) mode far below its intrinsic bandgap. This ingap PL mode shows strong correlation with the Neel ordering and persists down to monolayer thickness. Combining the density‐functional theory (DFT), scanning transmission electron microscopy (STEM), and X‐ray photoelectron spectroscopy (XPS), this work illustrates the origin of the PL mode and its correlation with Neel ordering, which can be attributed to the oxygen ion‐mediated states. Moreover, the PL strength can be further tuned and enhanced using ultraviolet‐ozone (UVO) treatment. The studies offer an effective approach to investigate light‐magnetic ordering interactions in 2D antiferromagnetic semiconductors.

Thermal-mechanical-photo-activation effect on silica micro/nanofiber surfaces: origination, reparation and utilization.

The exploration relevant to the surface changes on optical micro- and nanofibers (MNFs) is still in infancy, and the reported original mechanisms remain long-standing puzzles. Here, by recognizing the combined interactions between fiber heating, mechanically tapering, and high-power pulsed laser guiding processes in MNFs, we establish a general thermal-mechanical-photo-activation mechanism that can explain the surface changes on MNFs. Our proposed activation mechanism can be well supported by the systematical experimental results using high-intensity nanosecond/femtosecond pulsed lasers. Especially we find large bump-like nanoscale cavities on the fracture ends of thin MNFs. Theoretically, on the basis of greatly increased bond energy activated by the fiber heating and mechanically tapering processes, the energy needed to break the silicon-oxygen bond into dangling bonds is significantly reduced from its intrinsic bandgap of ∼9 eV to as low as ∼4.0 eV, thus high-power pulsed lasers with much smaller photon energy can induce obvious surface changes on MNFs via multi-photon absorption. Finally, we demonstrate that using surfactants can repair the MNF surfaces and exploit them in promising applications ranging from sensing and optoelectronics to nonlinear optics. Our results pave the way for future preventing the performances from degradation and enabling the practical MNF-based device applications.

Insights into controllable electronic properties of 2D type-II Twin-Graphene/g-C3N4 and type-I Twin-Graphene/hBN vertical heterojunctions via external electric field and strain engineering

Twin-graphene (Twin-G), an accessible carbon allotrope composed of sp2 hybridized carbon atoms, has attracted considerable interest due to its intrinsic bandgap and tunable electronic properties. This work evaluates the near-edge electronic structures and the carrier mobility of the Twin-G/g-C3N4 and Twin-G/hBN vdW heterojunctions employing the first-principles calculations. The results demonstrate that Twin-G/g-C3N4 retains a staggered type-II alignment, which may benefit the highly-efficient photogenerated carrier separation. Whereas the Twin-G/hBN exhibits type-I alignment. An external electrical field induces a semiconductor-to-metal and indirect-to-direct gap transition in Twin-G/g-C3N4 heterostructure. The type-II-to-type-I transition in Twin-G/g-C3N4 under tensile strain can be understood from the near-gap wave functions morphology. G-C3N4 substrate has a more significant effect to enhance the carrier mobility of Twin-G. The electron mobility along the zigzag-direction in Twin-G/g-C3N4 is ∼1751 cm2V−1s−1, far surpassing that of Twin-G monolayer. These results open up promising opportunities for the development of optoelectronic devices based on the Twin-G heterostructures.

Enhanced photoelectrochemical activity of WO3-decorated native titania films by mild laser treatment

The effectiveness of the electrochemical WO3-modification as a method for improving the photoactivity of native air-formed TiO2 layers was assessed. The way in which a mild laser treatment influences the photoelectrochemical performances of the thus obtained WO3/TiO2 systems was also investigated. At laser-treated electrodes (L-WO3/TiO2), the melting-solidification process induced by the treatment led to a smaller size of the deposited WO3 particles and to their better dispersion on the surface. The treatment also enhanced the surface oxygen deficiency and ensured better relative absorptivity of the oxygenated species on the surface. These features, together with the intrinsic narrower bandgap of the WO3-TiO2 composites, the higher donor density and the lower flat band potential of L-WO3/TiO2 enabled faster kinetic of the oxygen photoanodic evolution. Importantly, the same process exhibited a cathodic shift of its onset potential. The laser treatment also strongly enhanced the photoelectrocatalytic performances for UV-assisted methanol anodic oxidation.

Reducing the interfacial voltage loss in tin halides perovskite solar cells

Tremendous attention has been given to tin halide perovskite solar cells (TPSCs) due to the lower toxicity and similar electronic configuration compared with the lead perovskites. Nevertheless, on account of the intrinsic low bandgap, high defect density and surface/interface non-radiative recombination, the open-circuit voltage loss (Vloss) of TPSCs is comparatively large in all semiconductor solar cells. Herein, a hydrophobic bulky molecule of 3-(trifluoromethyl) phenethylamine hydroiodide (CF3PEAI) was utilized to passivate the lead-free perovskite surface by post-deposition treatment. The Vloss of the corresponding PSC devices was significantly reduced to afford a high open-circuit voltage (Voc) up to 0.73 V with a power conversion efficiency (PCE) of 10.35% in conjunction with the broadly utilized (6,6)-Phenyl C61 butyric acid methyl ester (PC61BM). Additionally, the CF3PEAI interlayer expressively suppressed the interfacial non-radiative recombination accompanying with extending photoexcited carrier lifetime. The formation of oriented 2D Sn-based perovskite could also facilitate the vertical charge-carrier transportation and improve the efficiency of Sn-based PSCs. The density of defect states and the amount of mid-gap states required to be filled were both dramatically reduced. Meanwhile, the surface reconstruction can effectively relax the tensile surface strain with the phenethyl ammonium iodide ligands. Therefore, this surface passivation strategy contributes to the development of high-quality lead-free perovskite film with low internal defects and residual stress.

An efficient solution-processable hybridized local and charge-transfer (HLCT)-based deep-red fluorescent emitter for simple structured non-doped OLED

The development of highly efficient deep-red fluorescent emitters is still a challenging task due to their intrinsic low bandgap characteristics resulting in low fluorescence emission in solid-state. Moreover, most of efficient deep-red organic light-emitting diodes (OLEDs) have complex device structures and are fabricated by high-cost vacuum deposition techniques. Herein, a novel solution-processable hybridized local and charge-transfer (HLCT) deep-red fluorescent molecule, TPA-NZF, is designed and synthesized as an emitter for low-cost and simple-structured OLEDs. TPA-NZF comprises a strong electron-deficient naphthothiadiazole (NZ) functionalized with triphenylamine (TPA) as a donor and dioctylfluorene as a solubilizing moiety. The photophysical results and theoretical calculations reveal a strong donor-acceptor feature and deep-red fluorescent emission with a solid-state photoluminescence quantum yield as high as 44%, decent hole-transporting mobility, good film morphology, and thermal and electrochemical stabilities. TPA-NZF is successfully fabricated as a solution-processed non-doped emitter in simple structured OLEDs. The device shows excellent electroluminescence (EL) performance (maximum external quantum efficiency (EQEmax) of 3.59%) and a deep-red emission with CIE coordinates of (0.66, 0.33).

Self‐Powered Visible‐Infrared Polarization Photodetection Driven by Ferroelectric Photovoltaic Effect in a Dion–Jacobson Hybrid Perovskite

AbstractFerroelectric materials, particularly the emerging layered hybrid ferroelectrics, have shown great potential for high‐sensitive polarization photodetection owing to their striking bulk photovoltaic effect (BPVE). Despite recent great achievements, the linear photoresponse range based on single‐mode BPVE is still limited in the shortwave region due to the large intrinsic bandgaps. Herein, first, the realization of self‐powered visible–infrared polarization photodetection by exploiting dual‐modal BPVE in a newly developed layered Dion–Jacobson (D‐J) hybrid ferroelectric (BDA)(EA)2Pb3Br10 (1, BDA is 1,4‐butadiammonium, EA is ethylammonium) is reported. Crystallographic investigations indicate that 1 adopts a typical trilayered D‐J perovskite structure with a fascinating ferroelectric feature and a giant two‐photon absorption coefficient as giant as 4.73 cm MW–1. Meanwhile, the bulk single crystal device of 1 exhibits excellent self‐powered direct detection performance under both visible light (405 nm) and near‐infrared light (800 nm), with a current on/off ratio as high as 103. More intriguingly, the device displays high sensitivity to the polarization of illuminated light, showing a considerable anisotropy up to 4.2 (405 nm) and 4.8 (800 nm), which are much larger than the detectors achieved by geometry anisotropy. The realization of self‐powered visible‐infrared dual‐modal polarization photodetection in 1 indicates the tremendous potential of hybrid ferroelectrics in various optoelectronic applications.

Tunable and giant valley-selective Hall effect in gapped bilayer graphene.

Berry curvature is analogous to magnetic field but in momentum space and is commonly present in materials with nontrivial quantum geometry. It endows Bloch electrons with transverse anomalous velocities to produce Hall-like currents even in the absence of a magnetic field. We report the direct observation of in situ tunable valley-selective Hall effect (VSHE), where inversion symmetry, and thus the geometric phase of electrons, is controllable by an out-of-plane electric field. We use high-quality bilayer graphene with an intrinsic and tunable bandgap, illuminated by circularly polarized midinfrared light, and confirm that the observed Hall voltage arises from an optically induced valley population. Compared with molybdenum disulfide (MoS2), we find orders of magnitude larger VSHE, attributed to the inverse scaling of the Berry curvature with bandgap. By monitoring the valley-selective Hall conductivity, we study the Berry curvature's evolution with bandgap. This in situ manipulation of VSHE paves the way for topological and quantum geometric optoelectronic devices, such as more robust switches and detectors.