Polarization dependent photocurrent in the Bi2Te3 topological insulator film for multifunctional photodetection

UV-VIS-NIR broadband flexible photodetector based on layered lead-free organic-inorganic hybrid perovskite

The flexible photodetector is viewed as a research hotspot for numerous advanced optoelectronic applications. Recent progress has manifested that lead-free layered organic-inorganic hybrid perovskites (OIHPs) are highly attractive to engineering flexible photodetectors due to the effective overlapping of several unique properties, including efficient optoelectronic characteristics, exceptional structural flexibility, and the absence of Pb toxicity to humans and the environment. The narrow spectral response of most flexible photodetectors with lead-free perovskites is still a big challenge to practical applications. In this work, we demonstrate the flexible photodetector based on a novel (to our knowledge) narrow-bandgap OIHP of (BA)₂(MA)Sn₂I₇, with achieving a broadband response across an ultraviolet-visible-near infrared (UV-VIS-NIR) region as 365-1064 nm. The high responsivities of 28.4 and 2.0 × 10^-2 A/W are obtained at 365 and 1064 nm, respectively, corresponding to detectives of 2.3 × 10¹⁰ and 1.8 × 10⁷ Jones. This device also shows remarkable photocurrent stability after 1000 bending cycles. Our work indicates the huge application prospect of Sn-based lead-free perovskites in high-performance and eco-friendly flexible devices.

Momentum-matching and band-alignment van der Waals heterostructures for high-efficiency infrared photodetection

Two-dimensional (2D) infrared photodetectors always suffer from low quantum efficiency (QE) because of the limited atomically thin absorption. Here, we reported 2D black phosphorus (BP)/Bi₂O₂Se van der Waals (vdW) photodetectors with momentum-matching and band-alignment heterostructures to achieve high QE. The QE was largely improved by optimizing the generation, suppressing the recombination, and improving the collection of photocarriers. Note that momentum-matching BP/Bi₂O₂Se heterostructures in k-space lead to the highly efficient generation and transition of photocarriers. The recombination process can be largely suppressed by lattice mismatching-immune vdW interfaces. Furthermore, type II BP/Bi₂O₂Se vdW heterostructures could also assist fast transport and collection of photocarriers. By constructing momentum-matching and band-alignment heterostructures, a record-high QE of 84% at 1.3 micrometers and 76.5% at 2 micrometers have been achieved in BP/Bi₂O₂Se vdW photodetectors.

Epitaxial Topological Insulator Bi2Te3 for Fast Visible to Mid-Infrared Heterojunction Photodetector by Graphene As Charge Collection Medium

Three dimensional topological insulators have a thriving application prospect in broadband photodetectors due to the possessed topological quantum states. Herein, a large area and uniform topological insulator bismuth telluride (Bi₂Te₃) layer with high crystalline quality is directly epitaxial grown on GaAs(111)B wafer using a molecular beam epitaxy process, ensuring efficient out-of-plane carriers transportation due to reduced interface defects influence. By tiling monolayer graphene (Gr) on the as-prepared Bi₂Te₃ layer, a Gr/Bi₂Te₃/GaAs heterojunction array prototype was further fabricated, and our photodetector array exhibited the capability of sensing ultrabroad photodetection wavebands from visible (405 nm) to mid-infrared (4.5 μm) with a high specific detectivity (D*) up to 10¹² Jones and a fast response speed at about microseconds at room temperature. The enhanced device performance can be attributed to enhanced light-matter interaction at the high-quality heterointerface of Bi₂Te₃/GaAs and improved carrier collection efficiency through graphene as a charge collection medium, indicating an application prospect of topological insulator Bi₂Te₃ for fast-speed broadband photodetection up to a mid-infrared waveband. This work demonstrated the potential of integrated topological quantum materials with a conventional functional substrate to fabricate the next generation of broadband photodetection devices for uncooled focal plane array or infrared communication systems in future.

Photothermal Control of Helicity-Dependent Current in Epitaxial Sb2Te2Se Topological Insulator Thin-Films at Ambient Temperature

Optical control of helicity-dependent photocurrent in topological insulator (TI) Sb₂Te₂Se has been studied at room temperature on epitaxial thin-films grown by pulsed laser deposition (PLD). Comparison with a theoretical model, which fits the data very well, reveals different contributions to the measured photocurrent. Study of the dependence of photocurrent on the angle of incidence (wave-vector) of the excitation light with respect to the sample normal helps to identify the origin of different components of the photocurrent. Enhancement and inversion of the photocurrent in the presence of the photothermal gradient for light incident on two opposite edges of the sample occur due to selective spin-state excitation with two opposite circularly polarized lights in the presence of the unique spin-momentum locked surface states. These observations render the PLD-grown epitaxial TI thin-films promising for optoelectronic devices such as sensors, switches, and actuators whose response can be controlled by polarization as well as the angle of incidence of light under ambient conditions. The polarization response can also be tuned by the photothermal effect by suitably positioning the incident light beam on the device.

2D Layered Material Alloys: Synthesis and Application in Electronic and Optoelectronic Devices

2D layered materials (2DLMs) have come under the limelight of scientific and engineering research and broke new ground across a broad range of disciplines in the past decade. Nevertheless, the members of stoichiometric 2DLMs are relatively limited. This renders them incompetent to fulfill the multitudinous scenarios across the breadth of electronic and optoelectronic applications since the characteristics exhibited by a specific material are relatively monotonous and limited. Inspiringly, alloying of 2DLMs can markedly broaden the 2D family through composition modulation and it has ushered a whole new research domain: 2DLM alloy nano-electronics and nano-optoelectronics. This review begins with a comprehensive survey on synthetic technologies for the production of 2DLM alloys, which include chemical vapor transport, chemical vapor deposition, pulsed-laser deposition, and molecular beam epitaxy, spanning their development, as well as, advantages and disadvantages. Then, the up-to-date advances of 2DLM alloys in electronic devices are summarized. Subsequently, the up-to-date advances of 2DLM alloys in optoelectronic devices are summarized. In the end, the ongoing challenges of this emerging field are highlighted and the future opportunities are envisioned, which aim to navigate the coming exploration and fully exert the pivotal role of 2DLMs toward the next generation of electronic and optoelectronic devices.

Multielement 2D layered material photodetectors

The pronounced quantum confinement effects, outstanding mechanical strength, strong light-matter interactions and reasonably high electric transport properties under atomically thin limit have conjointly established 2D layered materials (2DLMs) as compelling building blocks towards the next generation optoelectronic devices. By virtue of the diverse compositions and crystal structures which bring about abundant physical properties, multielement 2DLMs (ME2DLMs) have become a bran-new research focus of tremendous scientific enthusiasm. Herein, for the first time, this review provides a comprehensive overview on the latest evolution of ME2DLM photodetectors. The crystal structures, synthesis, and physical properties of various experimentally realized ME2DLMs as well as the development in metal-semiconductor-metal photodetectors are comprehensively summarized by dividing them into narrow-bandgap ME2DLMs (including Bi₂O₂X (X = S, Se, Te), EuMTe₃(M = Bi, Sb), Nb₂XTe₄(X = Si, Ge), Ta₂NiX₅(X = S, Se), M₂PdX₆(M = Ta, Nb; X = S, Se), PbSnS₂), moderate-bandgap ME2DLMs (including CuIn₇Se₁₁, CuTaS₃, GaGeTe, TlMX₂(M = Ga, In; X = S, Se)), wide-bandgap ME2DLMs (including BiOX (X = F, Cl, Br, I), MPX₃(M = Fe, Ni, Mn, Cd, Zn; X = S, Se), ABP₂X₆(A = Cu, Ag; B = In, Bi; X = S, Se), Ga₂In₄S₉), as well as topological ME2DLMs (MIrTe₄(M = Ta, Nb)). In the last section, the ongoing challenges standing in the way of further development are underscored and the potential strategies settling them are proposed, which is aimed at navigating the future advancement of this fascinating domain.

High-performance polarization-sensitive photodetectors on two-dimensional β -InSe

Two-dimensional (2D) indium selenide (InSe) has been widely studied for application in transistors and photodetectors, which benefit from its excellent optoelectronic properties. Among the three specific polytypes (γ-, ϵ- and β-phase) of InSe, only the crystal lattice of InSe in β-phase (β-InSe) belongs to a non-symmetry point group of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$D_{6h}^4$\end{document}, which indicates stronger anisotropic transport behavior and potential in the polarized photodetection of β-InSe-based optoelectronic devices. Therefore, we prepare the stable p-type 2D-layered β-InSe via temperature gradient method. The anisotropic Raman, transport and photoresponse properties of β-InSe have been experimentally and theoretically proven, showing that the β-InSe-based device has a ratio of 3.76 for the maximum to minimum dark current at two orthogonal orientations and a high photocurrent anisotropic ratio of 0.70 at 1 V bias voltage, respectively. The appealing anisotropic properties demonstrated in this work clearly identify β-InSe as a competitive candidate for filter-free polarization-sensitive photodetectors.

High performing flexible optoelectronic devices using thin films of topological insulator

Topological insulators (TIs) possess exciting nonlinear optical properties due to presence of metallic surface states with the Dirac fermions and are predicted as a promising material for broadspectral phodotection ranging from UV (ultraviolet) to deep IR (infrared) or terahertz range. The recent experimental reports demonstrating nonlinear optical properties are mostly carried out on non-flexible substrates and there is a huge demand for the fabrication of high performing flexible optoelectronic devices using new exotic materials due to their potential applications in wearable devices, communications, sensors, imaging etc. Here first time we integrate the thin films of TIs (Bi₂Te₃) with the flexible PET (polyethylene terephthalate) substrate and report the strong light absorption properties in these devices. Owing to small band gap material, evolving bulk and gapless surface state conduction, we observe high responsivity and detectivity at NIR (near infrared) wavelengths (39 A/W, 6.1 × 10⁸ Jones for 1064 nm and 58 A/W, 6.1 × 10⁸ Jones for 1550 nm). TIs based flexible devices show that photocurrent is linearly dependent on the incident laser power and applied bias voltage. Devices also show very fast response and decay times. Thus we believe that the superior optoelectronic properties reported here pave the way for making TIs based flexible optoelectronic devices.

Symmetry-Reduction Enhanced Polarization-Sensitive Photodetection in Core-Shell SbI3 /Sb2 O3 van der Waals Heterostructure

Structural symmetry is a simple way to quantify the anisotropic properties of materials toward unique device applications including anisotropic transportation and polarization-sensitive photodetection. The enhancement of anisotropy can be achieved by artificial symmetry-reduction design. A core-shell SbI₃ /Sb₂ O₃ nanowire, a heterostructure bonded by van der Waals forces, is introduced as an example of enhancing the performance of polarization-sensitive photodetectors via symmetry reduction. The structural, vibrational, and optical anisotropies of such core-shell nanostructures are systematically investigated. It is found that the anisotropic absorbance of a core-shell nanowire is obviously higher than that of two single compounds from both theoretical and experimental investigations. Anisotropic photocurrents of the polarization-sensitive photodetectors based on these core-shell SbI₃ /Sb₂ O₃ van der Waals nanowires are measured ranging from ultraviolet (UV) to visible light (360-532 nm). Compared with other van der Waals 1D materials, low anisotropy ratio (I_max /I_min ) is measured based on SbI₃ but a device based on this core-shell nanowire possesses a relatively high anisotropy ratio of ≈3.14 under 450 nm polarized light. This work shows that the low-symmetrical core-shell van der Waals heterostructure has large potential to be applied in wide range polarization-sensitive photodetectors.

2D material broadband photodetectors

Our review provides a comprehensive overview of the latest evolution of broadband photodetectors (BBPDs) based on 2D materials (2DMs). We begin with BBPDs built on various 2DM channels, including narrow-bandgap 2DMs, 2D topological semimetals, 2D charge density wave compounds, and 2D heterojunctions. Then, we introduce defect-engineered 2DM BBPDs, including vacancy engineering, heteroatom incorporation, and interfacial engineering. Subsequently, we summarize 2DM based mixed-dimensional (0D-2D, 1D-2D, 2D-3D, and 0D-2D-3D) BBPDs. Finally, we provide several viewpoints for the future development of this burgeoning field.

Fast-Response, Highly Air-Stable, and Water-Resistant Organic Photodetectors Based on a Single-Crystal Pt Complex

Organic semiconductors demonstrate several advantages over conventional inorganic materials for novel electronic and optoelectronic applications, including molecularly tunable properties, flexibility, low-cost, and facile device integration. However, before organic semiconductors can be used for the next-generation devices, such as ultrafast photodetectors (PDs), it is necessary to develop new materials that feature both high mobility and ambient stability. Toward this goal, a highly stable PD based on the organic single crystal [PtBr₂ (5,5'-bis(CF₃ CH₂ OCH₂ )-2,2'-bpy)] (or "Pt complex (1o)") is demonstrated as the active semiconductor channel-a material that features a lamellar molecular structure and high-quality, intraligand charge transfer. Benefitting from its unique crystal structure, the Pt-complex (1o) device exhibits a field-effect mobility of ≈0.45 cm² V^-1 s^-1 without loss of significant performance under ambient conditions even after 40 days without encapsulation, as well as immersion in distilled water for a period of 24 h. Furthermore, the device features a maximum photoresponsivity of 1 × 10³ A W^-1 , a detectivity of 1.1 × 10¹² cm Hz^1/2 W^-1 , and a record fast response/recovery time of 80/90 µs, which has never been previously achieved in other organic PDs. These findings strongly support and promote the use of the single-crystal Pt complex (1o) in next-generation organic optoelectronic devices.

Polarimetric Three-Dimensional Topological Insulators/Organics Thin Film Heterojunction Photodetectors

As a state of quantum matter with insulating bulk and gapless surface states, topological insulators (TIs) have huge potential in optoelectronic devices. On the other hand, polarization resolution photoelectric devices based on anisotropic materials have overwhelming advantages in practical applications. In this work, the 3D TIs Bi₂Te₃/organics thin film heterojunction polarimetric photodetectors with high anisotropic mobility ratio, fast response time, high responsivity, and EQE in broadband spectra are presented. At first, the maximum anisotropic mobility ratio of the Bi₂Te₃/organics thin film can reach 2.56, which proves that Bi₂Te₃ can serve as a sensitive material for manufacturing polarization photoelectric devices. Moreover, it is found that the device can exhibit a broad bandwidth and ultrahigh response photocurrent from visible to middle wave infrared spectra (405-3500 nm). The highest responsivity (R_i) of optimized devices can reach up to 23.54 AW^-1; surprisingly, the R_i of the device can still reach 1.93 AW^-1 at 3500 nm. In addition, the ultrahigh external quantum efficiency is 4534% with a fast response time (1.42 ms). Excellent properties mentioned above indicate that TIs/organics heterojunction devices are suitable for manufacturing high-performance photoelectric devices in infrared region.

Novel synthesis of topological insulator based nanostructures (Bi2Te3) demonstrating high performance photodetection

The rapid progress in 2D material research has triggered the growth of various quantum nanostructures- nanosheets, nanowires, nanoribbons, nanocrystals and the exotic nature originating through 2D heterostructures has extended the synthesis of hybrid materials beyond the conventional approaches. Here we introduce simple, one step confined thin melting approach to form nanostructures of TI (topological insulator) materials, their hybrid heterostructures with other novel 2D materials and their scalable growth. The substrate and temperature dependent growth is investigated on insulating, superconducting, metallic, semiconducting and ferromagnetic materials. The temperature dependent synthesis enables the growth of single, few quintuples to nanosheets and nanocrystals. The density of nanostructure growth is seen more on fabricated patterns or textured substrates. The fabricated nanostructure based devices show the broadband photodetection from ultraviolet to near infrared and exhibit high photoresponsivity. Ultimately, this unique synthesis process will give easy access to fabricate devices on user friendly substrates, study nanostructures and scalable growth will enable their future technology applications.

Layered tin monoselenide as advanced photothermal conversion materials for efficient solar energy-driven water evaporation

Solar energy-driven water evaporation lays a solid foundation for important photothermal applications such as sterilization, seawater desalination, and electricity generation. Due to the strong light-matter coupling, broad absorption wavelength range, and prominent quantum confinement effect, layered tin monoselenide (SnSe) holds a great potential to effectively harness solar irradiation and convert it to heat energy. In this study, SnSe is successfully deposited on a centimeter-scale nickel foam using a facile one-step pulsed-laser deposition approach. Importantly, the maximum evaporation rate of SnSe-coated nickel foam (SnSe@NF) reaches 0.85 kg m^-2 h^-1, which is even 21% larger than that obtained with the commercial super blue coating (0.7 kg m^-2 h^-1) under the same condition. A systematic analysis reveals that its good photothermal conversion capability is attributed to the synergetic effect of multi-scattering-induced light trapping and the optimal trade-off between light absorption and phonon emission. Finally, the SnSe@NF device is further used for seawater evaporation, demonstrating a comparable evaporation rate (0.8 kg m^-2 h^-1) to that of fresh water and good stability over many cycles of usage. In summary, the current contribution depicts a facile one-step scenario for the economical and efficient solar-enabled SnSe@NF evaporation devices. More importantly, an in-depth analysis of the photothermal conversion mechanism underneath the layered materials depicts a fundamental paradigm for the design and application of photothermal devices based on them in the future.

Spin Hall photoconductance in a three-dimensional topological insulator at room temperature

Three-dimensional topological insulators are a class of Dirac materials, wherein strong spin-orbit coupling leads to two-dimensional surface states. The latter feature spin-momentum locking, i.e., each momentum vector is associated with a spin locked perpendicularly to it in the surface plane. While the principal spin generation capability of topological insulators is well established, comparatively little is known about the interaction of the spins with external stimuli like polarized light. We observe a helical, bias-dependent photoconductance at the lateral edges of topological Bi₂Te₂Se platelets for perpendicular incidence of light. The same edges exhibit also a finite bias-dependent Kerr angle, indicative of spin accumulation induced by a transversal spin Hall effect in the bulk states of the Bi₂Te₂Se platelets. A symmetry analysis shows that the helical photoconductance is distinct to common longitudinal photoconductance and photocurrent phenomena, but consistent with optically injected spins being transported in the side facets of the platelets.

While the spin generation in topological insulators is well studied, little is known about the interaction of the spins with external stimuli. Here, Seifert et al. observe a helical, bias-dependent photoconductance at the lateral edges of topological Bi₂Te₂Se platelets for perpendicular incidence of light, distinct to common longitudinal photoconductance phenomena.

Polarization-Dependent Optoelectronic Performances in Hybrid Halide Perovskite MAPbX3 (X = Br, Cl) Single-Crystal Photodetectors

Hybrid organic-inorganic lead halide perovskites (HOIPs) have received significant attention because of their impressive performances in the fields of solar cells and photoelectric detection. In the past five years, great efforts have been made to improve the crystallinity, reduce grain boundaries, and enhance the stabilities of perovskite films. Compared with films, HOIP single crystals possess fewer grain boundaries and stronger optoelectronic properties and can be applied in optoelectronic devices. As the most popular HOIP member, single crystals of MAPbX₃ (X = Br, Cl) are deemed as important candidates for ultraviolet-visible photodetectors, in which the crystal structure anisotropy largely affects the detection performance. In this study, high-quality cubic single crystals of MAPbBr₃ and MAPbCl₃ were successfully grown from solutions. Taking advantages of their smooth (100) facets, planar metal-semiconductor-metal photodetectors were fabricated using Au interdigitated electrodes. The optoelectronic performances under nonpolarized and linearly polarized lights were explored. The optoelectronic performances were dependent on linearly polarized lights. Interestingly, both responsivity and external quantum efficiency were greatly enhanced under the excitation with linearly polarized lights. Moreover, the polarization-related optical absorptions and the electron densities within the (100) plane could be used to interpret different optoelectronic performances of single crystals of MAPbX₃ (X = Br, Cl) under various linearly polarized lights.

Band offset and an ultra-fast response UV-VIS photodetector in γ-In2Se3/p-Si heterojunction heterostructures

High-quality γ-In₂Se₃ thin films and a γ-In₂Se₃/p-Si heterojunction were prepared using pulse laser deposition (PLD).

Robust broad spectral photodetection (UV-NIR) and ultra high responsivity investigated in nanosheets and nanowires of Bi2Te3 under harsh nano-milling conditions

Due to miniaturization of device dimensions, the next generation's photodetector based devices are expected to be fabricated from robust nanostructured materials. Hence there is an utmost requirement of investigating exotic optoelectronic properties of nanodevices fabricated from new novel materials and testing their performances at harsh conditions. The recent advances on 2D layered materials indicate exciting progress on broad spectral photodetection (BSP) but still there is a great demand for fabricating ultra-high performance photodetectors made from single material sensing broad electromagnetic spectrum since the detection range 325 nm-1550 nm is not covered by the conventional Si or InGaAs photodetectors. Alternatively, Bi₂Te₃ is a layered material, possesses exciting optoelectronic, thermoelectric, plasmonics properties. Here we report robust photoconductivity measurements on Bi₂Te₃ nanosheets and nanowires demonstrating BSP from UV to NIR. The nanosheets of Bi₂Te₃ show the best ultra-high photoresponsivity (~74 A/W at 1550 nm). Further these nanosheets when transform into nanowires using harsh FIB milling conditions exhibit about one order enhancement in the photoresponsivity without affecting the performance of the device even after 4 months of storage at ambient conditions. An ultra-high photoresponsivity and BSP indicate exciting robust nature of topological insulator based nanodevices for optoelectronic applications.

Alloying-assisted phonon engineering of layered BiInSe3@nickel foam for efficient solar-enabled water evaporation

The fresh water crisis has emerged as one of the most urgent bottlenecks hindering the rapid development of modern industry and society. Solar energy-driven water evaporation represents a potential green and sustainable solution to address this issue. Herein, for the first time, centimeter-scale BiInSe₃-coated nickel foam (BiInSe₃@NF) as an efficient solar-enabled evaporator was successfully achieved and exploited for solar energy-driven water evaporation. Benefitting from multiple scattering-induced light trapping of the rough substrate, strong light-matter interaction and intermediate band (IB)-induced efficient phonon emission of BiInSe₃, the BiInSe₃@NF device achieved a high evaporation rate of 0.83 kg m^-2 h^-1 under 1 sun irradiation, which is 2.5 times that of pure water. These figures-of-merit are superior to recently reported state-of-the-art photothermal conversion materials, such as black titania, plasmonic assembly and carbon black. In addition, superior stability over a period of 60 days was demonstrated. In summary, the current contribution depicts a facile scenario for design, production and application of an economical and efficient solar-enabled BiInSe₃@NF evaporator. More importantly, the phonon engineering strategy based on alloying induced IB states can be readily applied to other analogous van der Waals materials and a series of superior vdWM alloys toward photothermal applications can be expected in the near future.

Helicity dependent photocurrent in electrically gated (Bi1-x Sb x )2Te3 thin films

Circularly polarized photons are known to generate a directional helicity-dependent photocurrent in three-dimensional topological insulators at room temperature. Surprisingly, the phenomenon is readily observed at photon energies that excite electrons to states far above the spin-momentum locked Dirac cone and the underlying mechanism for the helicity-dependent photocurrent is still not understood. Here we show a comprehensive study of the helicity-dependent photocurrent in (Bi_1-x Sb _x )₂Te₃ thin films as a function of the incidence angle of the optical excitation, its wavelength and the gate-tuned chemical potential. Our observations allow us to unambiguously identify the circular photo-galvanic effect as the dominant mechanism for the helicity-dependent photocurrent. Additionally, we use an analytical model to relate the directional nature of the photocurrent to asymmetric optical transitions between the topological surface states and bulk bands. The insights we obtain are important for engineering opto-spintronic devices that rely on optical steering of spin and charge currents.

Stable, Fast UV-Vis-NIR Photodetector with Excellent Responsivity, Detectivity, and Sensitivity Based on α-In2Te3 Films with a Direct Bandgap

Photoelectric conversion is of great importance to extensive applications. However, thus far, photodetectors integrated with high responsivity, excellent detectivity, large phototo-dark current ratio, fast response speed, broad spectral range, and good stability are rarely achieved. Herein, we deposited large-scale and high-quality polycrystalline indium sesquitelluride (α-In2Te3) films via pulsed-laser deposition. Then, we demonstrated that the photodetectors made of the prepared α-In2Te3 films possess stable photoswitching behavior from 370 to 1064 nm and short response time better than ca. 15 ms. At a source-drain voltage of 5 V, the device achieves a high responsivity of 44 A/W, along with an outstanding detectivity of 6 × 10(12) cm H(1/2) W(-1) and an excellent sensitivity of 2.5 × 10(5) cm(2)/W. All of these figures-of-merit are the best among those of the reported α-In2Te3 photodetectors. In fact, they are comparable to the state-of-the-art commercial Si and Ge photodetectors. For the first time, we established the theoretical evidence that α-In2Te3 possesses a direct bandgap structure, which reasonably accounts for the superior photodetection performances above. Importantly, the device exhibits a good stability against the multiple photoswitching operation and ambient environment, along with no obvious voltage-scan hysteresis. These excellent figures-of-merit, together with the broad spectral range and good stability, underscore α-In2Te3 as a promising candidate material for next-generation photodetection.

Promoting Photosensitivity and Detectivity of the Bi/Si Heterojunction Photodetector by Inserting a WS2 Layer

Layered transition metal dichalcogenides (TMDs) have been proven to be essential building blocks for the high-performance optoelectronic devices as a result of their favorable bandgaps, extraordinary light absorption, and closed surface electronic structures. However, the in-depth exploration of their operating mechanism as insertion layers in heterojunction photodetectors is scarce. Here, we demonstrate that a Bi/Si heterojunction photodetector can achieve a superior performance by inserting a WS2 layer. A high photosensitivity of 1.4 × 10(8) cm(2)/W and an outstanding detectivity of 1.36 × 10(13) cm Hz(1/2) W(-1) are obtained, which are comparable or even surpass those of state-of-art commercial photodetectors. The working mechanism of the Bi/WS2/Si sandwich-structured photodetector is unveiled, including the efficient passivation of the interface, enhancement of light absorption, and selective carrier blocking. Finally, a good voltage tunability of the photoresponse is also demonstrated. These findings are significant to the deep understanding on the integration of layered TMDs with conventional semiconductors, and they provide an attractive methodology to develop layered TMDs in a multi-junction system.