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To widen the photo-responsivity range of niobium pentoxide photodetectors, InSe thin films were deposited by thermal evaporation technique under high vacuum pressure and used as substrates for growing Nb2O5 thin films. The resulting InSe/Nb2O5 (ISNO) stacked layers formed amorphous/amorphous structure. Optical analyses showed that the niobium pentoxide layers successfully suppressed the free carrier absorption observed in InSe substrates. A new direct allowed transitions energy band gap of 0.85 eV was formed at the interface between InSe and Nb2O5. The ISNO interfaces exhibited conduction and valence band offsets in the ranges of 0.25–0.65 eV and 1.85 - 1.47 eV, respectively. Depositing Nb2O5 onto InSe extended the light responsivity range of Nb2O5 from the ultraviolet to the near infrared range. Notably, ISNO photodetectors displayed impressive features, with large current responsivities and large external quantum efficiencies of 4.7 A/W and 9.7 A/W and 1000% and 3000%, under visible-infrared and ultraviolet radiations, respectively.These characteristics make the ISNO heterojunction devices promising candidates for broadband photodetectors and other optoelectronic applications. [ABSTRACT FROM AUTHOR]

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Due to the high carrier mobility and direct bandgap character, indium selenide (InSe) exhibits great advantages for advanced optoelectronic applications. However, the unique optical section rule in InSe weakens the light‐matter interaction when the electric field of illuminated light is perpendicular to the c‐axis of planar InSe flake. To overcome this constraint, ultramicrotome technique is introduced to achieve vertically aligned InSe ribbons, aiming to reconfigure the optical paths for improved optical absorption and device performance. The well‐designed InSe ribbons are acquired with uniform morphology, showing an integrated structure free of cracks or fragments. First, the structural symmetry, crystal orientation, and optical anisotropy of InSe ribbon are carefully revealed by polarization‐dependent Raman spectrum, second harmonic generation (SHG), and photoluminescence measurements. Then, the back focal plane (BFP) imaging of photoluminescence distinguishes the in‐plane and out‐of‐plane dipole emission of InSe ribbons and planar InSe flakes, respectively. Notably, the ribbon exhibits new PL peaks with energy lower than the exciton peak of InSe at low temperature, which is attributed to Se vacancies. The work by introducing vertically aligned InSe nanoribbons provides a new strategy to manipulate the light‐matter interactions and defect engineering for novel optoelectronics, which can be also extended to other 2D semiconductors. [ABSTRACT FROM AUTHOR]

Neuromorphic devices that parallelize perception, preprocessing, and computation functions are expected to play a significant role in future non‐von Neumann architecture computers. Herein, a new retina‐inspired broadband self‐powered optoelectronic synaptic device based on 2D/3D heterojunction of epitaxial InSe on GaN(0001) is reported. Few‐layer n‐type InSe is grown on p‐type GaN by physical vapor deposition in an ultra‐high vacuum (UHV) environment. The devices are fabricated using a shadow mask assisted UHV electrode deposition technique. High‐resolution transmission electron microscopy images reveal that an atomically thin amorphous layer, which induces highly efficient charge trapping, is formed at the InSe/GaN interface. The photoresponse spans from visible to near‐infrared, and the response time is prolonged to 103 ms owing to the deep trapping levels. Thus, synaptic functions, including excitatory postsynaptic current, paired‐pulse facilitation with a high index of up to 170%, short‐term plasticity, and high‐pass filtering characteristics, are realized. Additionally, the synapses demonstrated the merit of realizing image sharpening and arithmetic operations on the same device under infrared and visible light illumination. This study provides a new platform of 2D/3D heterostructures for robust optoelectronic synapses that may find applications in post‐Moore era neuromorphic vision systems. [ABSTRACT FROM AUTHOR]

Our study delves into the nuanced effects of strain on hBN/InSe heterostructures, known for their exceptional wide-spectrum absorption capabilities. Employing uniform biaxial strain in the range of −6% to 6%, our investigation reveals a powerful method for manipulating the band gap. Notably, intense tensile strain leads to the near-complete elimination of the band gap—an outcome with profound implications. Comparison with hBN/InTe and hBN/GaTe heterostructures underscores the unique behaviour of hBN/InSe, showing a striking resemblance to hBN/GaTe but achieving lower band gap values under tensile strain. These findings provide crucial insights for experimental work and serve as a guide for more intricate theoretical explorations. With its outstanding electronic properties, tunable band gap, and remarkable absorption characteristics, hBN/InSe emerges as a key player in the development of future novel devices. [ABSTRACT FROM AUTHOR]

Group IIIA metal chalcogenides are an auspicious material system due to their variability of properties and hence the multitude of application options, for example, in the fields of optoelectronic, thermoelectric, piezo‐, and ferroelectric devices. Indium and gallium selenide films are innovatively grown in a sequential PVD (physical vapor deposition) process starting from metal precursor layers of various thicknesses, which are then subject to chalcogenization in different selenium contents. The resulting thin films are investigated for structural and optical properties by Raman, XRD (X‐ray diffraction), and UV–Vis–NIR spectrometry, revealing that all the compounds In2Se3, InSe, In4Se3, Ga2Se3, and GaSe as well as different polytypes can be achieved depending on the metal/chalcogen ratio. Results from Raman and XRD spectroscopy are highly consistent, and also from the optical measurements changes in absorption characteristics can be correlated. The results indicate, that by fine‐tuning the selenium content, deliberately growing ultra‐thin layers of the different indium and gallium phases will be possible, thus opening up a promising route for 2D material fabrication. Given the scalability of the fabrication method, it is highly promising for large‐scale deployment of the materials. [ABSTRACT FROM AUTHOR]

The many‐body GW combined with the Bethe–Salpeter equation (BSE) method including the spin‐orbit coupling (SOC) effect has been adopted to revisit the band structure and optical absorption spectra evolution of single‐layer, double‐layer, three‐layer, and bulk InSe. The many‐body effect is found to play an important role in both the band structure and the optical properties of InSe structures. Not only the band gap but also the energy dispersion is influenced by the electron–electron many‐body interaction. Electron–hole interaction strongly affects the optical properties of InSe structures, especially the single‐layer InSe. Compared with previous reports, the calculations show that, including SOC, two bound excitonic peaks have emerged for monolayer InSe, with the strong bound exciton being s‐state‐like, while the other p‐state‐like. BSE also predicts abundance of bounded "dark" excitons exists for monolayer InSe, indicating that monolayer InSe is a proper platform for studying excitons. Although the spin‐orbit interaction influence on the highest valence band and the lowest conducted band seems trivial, its effect on the optical properties of InSe is remarkable. [ABSTRACT FROM AUTHOR]

Abstract Group IIIA metal chalcogenides are an auspicious material system due to their variability of properties and hence the multitude of application options, for example, in the fields of optoelectronic, thermoelectric, piezo‐, and ferroelectric devices. Indium and gallium selenide films are innovatively grown in a sequential PVD (physical vapor deposition) process starting from metal precursor layers of various thicknesses, which are then subject to chalcogenization in different selenium contents. The resulting thin films are investigated for structural and optical properties by Raman, XRD (X‐ray diffraction), and UV–Vis–NIR spectrometry, revealing that all the compounds In2Se3, InSe, In4Se3, Ga2Se3, and GaSe as well as different polytypes can be achieved depending on the metal/chalcogen ratio. Results from Raman and XRD spectroscopy are highly consistent, and also from the optical measurements changes in absorption characteristics can be correlated. The results indicate, that by fine‐tuning the selenium content, deliberately growing ultra‐thin layers of the different indium and gallium phases will be possible, thus opening up a promising route for 2D material fabrication. Given the scalability of the fabrication method, it is highly promising for large‐scale deployment of the materials.

Indium selenide (InSe) crystals are reported to show exceptional plasticity, a new property to two-dimensional van der Waals (2D vdW) semiconductors. However, the correlation between plasticity and specific prototypes is unclear, and the understanding of detailed plastic deformation mechanisms is inadequate. Here three prototypes of InSe are predicted to be plastically deformable by calculation, and the plasticity of polymorphic crystals is verified by experiment. Moreover, distinct nanoindentation behaviors are seen on the cleavage and cross-section surfaces. The modulus and hardness of InSe are the lowest ones among a large variety of materials. The plastic deformation is further perceived from chemical interactions during the slip process. Particularly for the cross-layer slip, the initial In-Se bonds break while new In-In and Se-Se bonds are newly formed, maintaining a decent interaction strength. The remarkable plasticity and softness alongside the novel physical properties, endow InSe great promise for application in deformable and flexible electronics.

Abstract The type‐II band‐aligned van der Waals (vdW) heterostructures are favorable for photocarrier separation and are often used for designing high‐performance photodetectors. Inspired by this, a metal‐mirror electrode enhanced HfSe2‐InSe vdW heterostructure photodetector is designed and demonstrated excitement performance in UV light detection. It is demonstrated the moderate bandgap heterostructure can be configured as a high‐performance UV photodetector with excellent light on/off ratio of 106, high photoresponsivity of 47.3 AW−1, competitive high specific detectivity of 3.2 × 1012 cmHz1/2W−1 and very low noise equivalent power of 2.8 × 10−16 WHz−1/2. Notably, the photoresponse speed of the device is very fast, with a rise time of 4.1 µs and a decay time of 5.4 µs. The results indicate that 2D HfSe2‐InSe vdW heterostructure possesses great potential applications in UV photodetection.

γ-InSe is a semiconductor that holds promising potential in high-performance field-effect transistors and optoelectronic devices. Large-scale, single-phase γ-InSe deposition has proven challenging because of the difficulty in precise control of stoichiometry and the coexistence of different indium selenide phases. In this study, we demonstrate the wafer-scale combinatorial approach to map out the growth window as functions of the Se/In ratio and growth temperature for γ-InSe on the Si(111) 7 × 7 substrate in molecular beam epitaxy. X-ray diffraction (XRD) was used to identify the indium selenide phases, while atomic force microscopy revealed four distinct surface morphologies of γ-InSe, enabling a discussion of the growth mechanisms associated with each morphology. Cross-sectional atomic resolution scanning transmission electron microscopy confirmed that the film was of high crystalline quality and had nearly single-phase γ-InSe. Our comprehensive study elucidates the In–Se phase map for thin film growth parameters, providing invaluable landmarks for the reproducible synthesis of high-quality γ-InSe layers. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals (vdW) AIIIBVI semiconductor materials, such as InSe and GaSe, are of considerable interest due to their potential use in various microelectronics applications. The range of properties of materials of this class can be extended further through the use of quasi-binary alloys of the InSe(Te)-GaSe(Te) type. In this work, we study the effect of compositional and structural disorder in 2D In(Ga)Se(Te) on the band structure and electronic properties using first principles modeling. The results for In(Ga)Se demonstrate a noticeable decrease in the band gap for structures with a random distribution of indium and gallium cations, while for In(Ga)Te with a random cation distribution, metallization occurs. Changes in the compositional arrangement of chalcogens (there can be either the same or different atoms on each side of the vdW gap) lead to pronounced changes in the band gap, but no significant changes in topology are observed. In addition, a significant effect of the distance between the layers on the band gap under compression along the c axis was found for both alloys under study. An important point of our study is that van der Waals gap engineering is a very powerful tool to control the properties of 2D materials and its alloys. [ABSTRACT FROM AUTHOR]

2D materials, with distinct characteristics compared to their conventional bulk counterparts, have been a popular topic in various optoelectronic research fields. Herein, indium selenide (InSe), a monochalcogenide van der Waals layered semiconductor, which has been studied due to its thickness dependent optical characteristics is explored. For InSe to be used as a versatile light source, enhancing the emission of InSe is required. Here, enhanced photoluminescence (PL) from multi‐layer InSe is demonstrated using a gap plasmon induced between Ag nanocube dimer and an Au substrate. Such plasmonic structures support multiple resonances, one of those overlapping with InSe's band edge PL emission. The calculated Purcell factor shows a 200‐fold increase on the short edge of nanocube dimers. Experimentally, PL enhancement of 6‐fold is demonstrated at room temperature. In addition, a method for determining the thickness of 2D materials via dark‐field spectroscopy using white light illumination is shown. This study paves the way for the incorporation of 2D InSe into nanophotonic structures. [ABSTRACT FROM AUTHOR]

Low‐dimensional material field‐effect transistor (FET)‐based biosensors have the advantages of high sensitivity, high detection speed, small size, low cost, and excellent compatibility with integrated circuits. The sensing mechanism is extremely important in the design and fabrication of high‐performance FET biosensors in practical applications. Herein, an InSe‐FET biosensor is designed and its dominant sensing mechanism during detection and (mi)RNA detection performance are investigated. Finite element analysis reveals the electrostatic potential distribution in the InSe channel with DNA probe assembly showing that Coulomb scattering is the dominant sensing mechanism for carrier scattering‐sensitive InSe. The simulation and experimental results indicate that carriers in InSe are extremely sensitive to the scattering of surface impurities because of their small electron mass. The firstly reported back‐gate bias working mode of an InSe‐FET biosensor has a linear relationship with an extra‐large detectable range of 1 fM–10 nM, high specificity for identifying 1‐nucleotide polymorphisms, and excellent repeatability and reusability. The detection of biomarker miRNAs in clinical serum samples and specific RNA in SARS‐CoV‐2 pseudovirus samples indicate promising applications of InSe‐FET biosensors in critical disease screening and the fast diagnoses of infectious diseases. This study can be useful for the design and fabrication of high‐performance FET biosensors. [ABSTRACT FROM AUTHOR]

Bandgap engineering and quantum confinement in semiconductor heterostructures provide the means to fine‐tune material response to electromagnetic fields and light in a wide range of the spectrum. Nonetheless, forming semiconductor heterostructures on lattice‐mismatched substrates is a challenge for several decades, leading to restrictions for device integration and the lack of efficient devices in important wavelength bands. Here, it is shown that the van der Waals epitaxy of 2D GaSe and InSe heterostructures occur on substrates with substantially different lattice parameters, namely silicon and sapphire. The GaSe/InSe heteroepitaxy is applied in the growth of quantum wells and superlattices presenting photoluminescence and absorption related to interband transitions. [ABSTRACT FROM AUTHOR]

Bi2O2Se nanosheets, an emerging ternary non-van der Waals two-dimensional (2D) material, have garnered considerable research attention in recent years owing to their robust air stability, narrow indirect bandgap, high mobility, and diverse intriguing properties. However, most of them show high dark current and relatively low light on/off ratio and slow response speed because of the large charge carrier concentration and bolometric effect, hindering their further application in low-energy-consuming optoelectronics. Herein, a homotype van der Waals heterostructure based on exfoliated n-InSe integrated with chemical vapor deposition (CVD)-grown n-Bi2O2Se nanosheets that have type II band alignment was fabricated. The efficient interfacial charge separation, strong interlayer coupling, and effective built-in electric field across the heterointerface demonstrated excellent, stable, and broadband self-driven photodetection in the range 400–1064 nm. Specifically, a high responsivity (R) of 75.2 mA·W–1 and a high specific detectivity (D*) of 1.08 × 1012 jones were achieved under 405 nm illumination. Additionally, a high R of 13.3 mA·W–1 and a high D* of 2.06 × 1011 jones were achieved under 980 nm illumination. Meanwhile, an ultrahigh Ilight/Idark ratio over 105 and a fast response time of 5.8/15 ms under 405 nm illumination confirmed the excellent photosensitivity and fast response behavior. Furthermore, R could be enhanced to 13.6 and 791 mA·W–1 under 405 and 980 nm illumination at a drain–source voltage (Vds) of 1 V, respectively, originating from a lower potential barrier. This study suggested that the Bi2O2Se nanosheet/InSe nanoflake homotype heterojunction can offer potential applications in next-generation broadband photodetectors that consume low energy and exhibit high performance. [ABSTRACT FROM AUTHOR]

Post-transition metal chalcogenides, such as SnSe, SnSe2, InSe, In2Se3, and In4Se3, are recently suggested as good candidates for high performance thermoelectric materials. In this present study, we investigated the influence of Cl doping on the electrical and thermal transport of n-type polycrystalline InSe samples in an effort for searching new thermoelectric materials. A series of InSe1-xClx (x = 0, 0.01, 0.03, and 0.05) were synthesized by a conventional solid–state reaction. By Cl doping in the Se site, the power factor is significantly increased to 0.13 mW/mK2 for InSe0.97Cl0.03 from 0.044 mW/mK2 of undoped InSe, primarily owing to the unconventional simultaneous increase in both electrical conductivity and magnitude of Seebeck coefficient. The increase of power factor is discussed in regard with substantial increase of effective mass and weighted mobility by the Cl doping, along with the electronic dispersions calculated by density functional theory. As a result, the thermoelectric figure of merit zT is increased to 0.052 at 690 K in InSe0.97Cl0.03, which is improved by 208% compared to the undoped InSe sample.

Indium selenide (InSe) is an emerging van der Waals material, which exhibits the potential to serve in excellent electronic and optoelectronic devices. One of the advantages of layered materials is their application to flexible devices. How strain alters the electronic and optical properties is, thus, an important issue. In this work, we experimentally measured the strain dependence on the angle-resolved second harmonic generation (SHG) pattern of a few layers of InSe. We used the exfoliation method to fabricate InSe flakes and measured the SHG images of the flakes with different azimuthal angles. We found the SHG intensity of InSe decreased, while the compressive strain increased. Through first–principles electronic structure calculations, we investigated the strain dependence on SHG susceptibilities and the corresponding angle-resolved SHG pattern. The experimental data could be fitted well by the calculated results using only a fitting parameter. The demonstrated method based on first–principles in this work can be used to quantitatively model the strain-induced angle-resolved SHG patterns in 2D materials. Our obtained results are very useful for the exploration of the physical properties of flexible devices based on 2D materials. [ABSTRACT FROM AUTHOR]

Two-dimensional materials-based field-effect transistors (FETs) are promising biosensors because of their outstanding electrical properties, tunable band gap, high specific surface area, label-free detection, and potential miniaturization for portable diagnostic products. However, it is crucial for FET biosensors to have a high electrical performance and stability degradation in liquid environments for their practical application. Here, a high-performance InSe-FET biosensor is developed and demonstrated for the detection of the CA125 biomarker in clinical samples. The InSe-FET is integrated with a homemade microfluidic channel, exhibiting good electrical stability during the liquid channel process because of the passivation effect on the InSe channel. The InSe-FET biosensor is capable of the quantitative detection of the CA125 biomarker in breast cancer in the range of 0.01–1000 U/mL, with a detection time of 20 min. This work provides a universal detection tool for protein biomarker sensing. The detection results of the clinical samples demonstrate its promising application in early screenings of major diseases. [ABSTRACT FROM AUTHOR]

The two-dimensional (2D) van der Waals indium selenide (InSe) exhibits the ultra-low intralayer Young's modulus yet the high interlayer cleavage and slipping energy, which could thus be obtained by the liquid phase exfoliation (LPE) method. Here, we designed 48 experiments to systematically achieve its optimum LPE parameters including the exfoliating solvent of N-Methyl-2-pyrrolidinone (NMP), ultrasonic power of 180 ​W, ultrasonic time of 12 ​h and exfoliating concentration of 6.25 ​mg/mL. The resulting optimal 2D InSe nanosheets show a uniform lateral size distribution of about 200 ​nm without impurities. We further analyzed the underlying exfoliating mechanism through the scanning electron microscopy (SEM) investigations. The results show that NMP has the more suitable Hansen solubility parameters to disperse and stabilize the 2D nanosheets. Increasing the ultrasonic power and time can provide plenty of energy to destroy the van der waals' force that exist between the interlayers of InSe and induce intralayer fragmentation. This work would provide a significant guideline for selecting exfoliating parameters to obtain the expected InSe nanosheets and thus extend its applications in optical sensors and nanocomposites. [ABSTRACT FROM AUTHOR]

Van der Waals layered indium selenide (InSe) is an emerging star of the 2D semiconducting materials because of its excellent fundamental properties, such as ultrahigh carrier mobility, layer‐tunable bandgap, large elastic deformability, and rich polytypes. In addition, 2D layered indium selenide has demonstrated outstanding device performance including photodetector, field‐effect transistor, memory and synapse, mechanical and gas sensor, which has offered a new chance to next‐generation electrical and optoelectronic devices. This review presents a comprehensive summary of recent progress in 2D layered indium selenide. The novel fundamental properties and synthetic methods are summarized. Also, the indium selenide‐based state‐of‐the‐art electronic/optoelectronic devices, such as a functional field‐effect transistor, photodetector, and mechanical and gas sensors are systematically summarized. The techniques to enhance the performances of devices are also discussed. Finally, a brief discussion on the challenges and future opportunities as a guideline for this field is provided. [ABSTRACT FROM AUTHOR]

Identification of trap centers in semiconductors takes great importance for improving the performance of electronic and optoelectronic devices. In the present study, we employed the thermally stimulated current (TSC) method within a temperature range of 10–280 K to explore trap centers in InSe crystal—a material with promising applications in next-generation devices. Our findings revealed the existence of two distinct hole trap centers within the InSe crystal lattice located at 0.06 and 0.14 eV. Through the leveraging the T stop method, we offered trap distribution parameters of revealed centers. The results obtained from the experimental methodology employed to investigate the distribution of trap centers indicated that one of the peaks extended between 0.06 and 0.13 eV, while the other spanned from 0.14 to 0.31 eV. Notably, our research uncovers a remarkable variation in trap density, spanning one order of magnitude, for every 10 and 88 meV of energy variation. The results of our research present the characteristics of shallow trap centers in InSe, providing important information for the design and optimization of InSe-based optoelectronic devices. • TSC measurements were performed on InSe crystal in the below room temperature. • The presence of two hole traps at 0.06 and 0.14 eV was revealed. • The distribution of trap centers was investigated by applying T stop - T m method. • The results provide important information for design of InSe-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Two-dimensional materials are increasingly recognized for their distinctive nonlinear optical properties. Indium selenide (InSe), a notable optoelectronic material, demonstrates unique advantages in terms of nonlinear absorption behavior, making it a promising candidate in mid-infrared mode-locked lasers. By preparing a InSe saturable absorber (SA) and applying it in a Er: ZBLAN fiber laser, we demonstrate a stable mode-locked mid-infrared fiber laser at 2.8 μm. The obtained mode-locked pulses have a repetition frequency and pulse duration of 29.875 MHz and 13.6 ps, respectively. The obtained maximum value of pulse energy is 4.3 nJ. The signal-to-noise ratio (SNR) is 55 dB, indicating the high stability of the laser system. Our experimental results validate that InSe is a promising SA in the near 3 μm band. This work paves the way for further investigations and applications of InSe-based devices in nonlinear optics and mode-locked laser systems. [ABSTRACT FROM AUTHOR]

InSe, a member of the layered materials family, is a superior electronic and optical material which retains a direct bandgap feature from the bulk to atomically thin few-layers and high electronic mobility down to a single layer limit. We, for the first time, exploit strain to drastically modify the bandgap of two-dimensional (2D) InSe nanoflakes. We demonstrated that we could decrease the bandgap of a few-layer InSe flake by 160 meV through applying an in-plane uniaxial tensile strain to 1.06% and increase the bandgap by 79 meV through applying an in-plane uniaxial compressive strain to 0.62%, as evidenced by photoluminescence (PL) spectroscopy. The large reversible bandgap change of ∼239 meV arises from a large bandgap change rate (bandgap strain coefficient) of few-layer InSe in response to strain, ∼154 meV/% for uniaxial tensile strain and ∼140 meV/% for uniaxial compressive strain, representing the most pronounced uniaxial strain-induced bandgap strain coefficient experimentally reported in 2D materials. We developed a theoretical understanding of the strain-induced bandgap change through first-principles DFT and GW calculations. We also confirmed the bandgap change by photoconductivity measurements using excitation light with different photon energies. The highly tunable bandgap of InSe in the infrared regime should enable a wide range of applications, including electro-mechanical, piezoelectric and optoelectronic devices.

Dopant levels in layered compound InSe have considerable potential in optoelectronic devices. Dopant‐induced trap states are essential in determining the optoelectrical properties of semiconductors. However, detailed studies of the persistent photoconductivity (PPC) and related mechanism in doped InSe are still not available. Here, the dependence of excitation energy on the shallow donor level caused by the dopants (Ge, Sn) in InSe is systematically investigated. Notably, prolonged decay time originates from extrinsic Ge, Sn dopants and these doping‐assisted states improve the optoelectrical performance of pristine InSe. Those photogenerated carriers are trapped in the Ge, Sn shallow impurities states, which are long‐lived enough to be extracted into Au contacts before annihilation. This renders Ge‐, Sn‐doped InSe photoconductive gain and maximized photocurrent. Sn‐doped InSe single crystal device can achieve a maximum responsivity of around 1.7 × 106 A W−1 under red light and detectivity of 6.18 × 1013 Jones. In addition, Hall measurements identify the carrier concentration and the Hall mobility of pristine InSe is significantly changed by Ge and Sn dopants. It is demonstrated that doping Ge, Sn atoms is responsible for the obvious photoconductivity and beneficial for the high‐performance photodetector, offering intriguing opportunities for novel holographic memory applications. [ABSTRACT FROM AUTHOR]

Indium selenide (InSe), a layered semiconductor with direct band gap and high carrier mobility, holds promising applications in bendable electronics and ultrafast optoelectronics. Yet its crystal structure exhibits polytypism with four different stacking orders (γ‐, ε‐, β‐ and δ‐phases), arising from the weak van der Waals interlayer coupling. These phases are nearly‐degenerate in energy but are predicted to have contrasting electronic structures for versatile applications. It remains highly challenging to distinguish between these polytypes due to the lack of noninvasive tools that are sensitive enough to the interlayer structural variations. Here, the unambiguous discrimination of different InSe polytypes using symmetry‐sensitive oblique incident optical second harmonic generation (SHG) is demonstrated. Surprisingly, the ε‐phase is found to be dominant, although the samples from two popular commercial vendors (2D Semiconductors and Six Carbon Technology) are claimed to be the γ‐phase. These results would help promoting the precise application of InSe crystal for piezoelectric transducer and strain sensing, as well as showing the oblique incident SHG to be a powerful structural analytical tool for van der Waals layered materials. [ABSTRACT FROM AUTHOR]

Ⅲ-Ⅵ group InSe crystal is a very important compound semiconductor material, which is widely used in the fields of high-performance nano electronic devices, infrared light detection, photoelectric devices and flexible electronics. The development of In-Se phase diagram is briefly reviewed. InSe has incongruent melting characteristics that can be obtained by peritectic reaction from the quasi stoichiometric or non-stoichiometric solution, and the mole ratio of In/Se has an important influence on the productivity of InSe. In order to prepare InSe crystal, several techniques have been adopted in the past, such as vertical Bridgman method, Czochralski method, horizonal gradient freeze method, low temperature liquid phase method and vapor transfer method. In order to better understand the development of InSe crystal growth, this review summarizes the process principle, technical points, production of these techniques, and discsuses their advantages and disadvantages. It is shown that the vertical Bridgman method has become a mainstream method for preparing high quality and large size InSe crystals by virtue of the simple apparatus and feasible operation. The horizonal gradient freeze method is a special way for growing ε-InSe crystal, which would play a role of supplement to the vertical Bridgman method in the research and application of new material in the future. [ABSTRACT FROM AUTHOR]

Intercalation and doping are promising routes to tune properties of van der Waals (vdW) semiconductors and pave the way for their applications in digital electronics beyond Moore's law, sensors and spintronics. The indium selenide (InSe) vdW crystal shows great promise for use in next-generation semiconductor technologies. For these applications to be realized, the effects of impurities on properties of InSe must be understood. Here, we present a comparative experimental study of electron transport in n-type InSe semiconductor doped and electrochemically intercalated with magnetic cobalt (Co) impurities. It is shown that the presence of Co decreases the free electron density, the Hall mobility along layers and the conductivity anisotropy σ⊥C/σ‖C. Furthermore, this leads to a change of the behavior of σ⊥C(T) dependence from a metallic one in pristine samples to a semiconducting one in samples with Co. We also demonstrate that the interaction of electrons with space-charge regions is an effective scattering mechanism, which should be taken into account in doped and intercalated crystals. The present work is important for the basic physics knowledge of the effect of Co impurities on physical properties of InSe, which is needed to tailor the parameters of this semiconductor for applications in electronics and spintronics. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals (vdW) AIIIBVI semiconductor materials, such as InSe and GaSe, are of considerable interest due to their potential use in various microelectronics applications. The range of properties of materials of this class can be extended further through the use of quasi-binary alloys of the InSe(Te)-GaSe(Te) type. In this work, we study the effect of compositional and structural disorder in 2D In(Ga)Se(Te) on the band structure and electronic properties using first principles modeling. The results for In(Ga)Se demonstrate a noticeable decrease in the band gap for structures with a random distribution of indium and gallium cations, while for In(Ga)Te with a random cation distribution, metallization occurs. Changes in the compositional arrangement of chalcogens (there can be either the same or different atoms on each side of the vdW gap) lead to pronounced changes in the band gap, but no significant changes in topology are observed. In addition, a significant effect of the distance between the layers on the band gap under compression along the c axis was found for both alloys under study. An important point of our study is that van der Waals gap engineering is a very powerful tool to control the properties of 2D materials and its alloys.

Single-phase two-dimensional (2D) indium monoselenide (γ-InSe) film is successfully grown via solid phase epitaxy in the molecular beam epitaxy (MBE) system. Having high electron mobility and high photoresponsivity, ultrathin 2D γ-InSe semiconductors are attractive for future field-effect transistor and optoelectronic devices. However, growing single-phase γ-InSe film is a challenge due to the polymorphic nature of indium selenide (γ-InSe, α-In2Se3, β-In2Se3, γ-In2Se3, etc.). In this work, the 2D α-In2Se3 film was first grown on a sapphire substrate by MBE. Then, the high In/Se ratio sources were deposited on the α-In2Se3 surface, and an γ-InSe crystal emerged via solid-phase epitaxy. After 50 min of deposition, the initially 2D α-In2Se3 phase was also transformed into a 2D γ-InSe crystal. The phase transition from 2D α-In2Se3 to γ-InSe was confirmed by Raman, XRD, and TEM analysis. The structural ordering of 2D γ-InSe film was characterized by synchrotron-based grazing-incidence wide-angle X-ray scattering (GIWAXS). [ABSTRACT FROM AUTHOR]

The BP/InSe heterojunction has attracted the attention of many fields in successful combined high hole mobility of black phosphorus (BP) and high electron mobility of indium selenide (InSe), and enhanced the environmental stability of BP. Nevertheless, photonics research on the BP/InSe heterostructure was insufficient, while both components are considered promising in the field. In this work, a two-dimensional (2D) BP/InSe heterostructure was fabricated using the liquid-phase exfoliation method. Its linear and non-linear optical (NLO) absorption was characterized by ultraviolet−visible−infrared and Open-aperture Z-scan technology. On account of the revealed superior NLO properties, an SA based on 2D BP/InSe was prepared and embedded into an erbium-doped fiber laser, traditional soliton pulses were observed at 1.5 μm with the pulse duration of 881 fs. Furthermore, harmonic mode locking of bound solitons and dark-bright soliton pairs were also obtained in the same laser cavity due to the cross-coupling effect. The stable mode-locked operation can be maintained for several days, which overcome the low air stability of BP. This contribution further proves the excellent optical properties of 2D BP/InSe heterostructure and provides new probability of developing nano-photonics devices for the applications of double pulses laser source and long-distance information transmission. [ABSTRACT FROM AUTHOR]

[Display omitted] We investigate van der Waals (vdW) heterojunctions by combining InSe and zigzag carbon nanotubes (CNT(n,0)) by first-principle calculations. When n ranges from 5 to 7, The heterojunctions show n-type Schottky contact. However, for n of 8, 9, and 11, the heterojunctions still retain the characteristic of semiconductors with bandgaps. The metallized InSe/CNT(10,0) heterojunction has the most amount of charge transfer and the highest tunneling probability. Ohmic contact can be formed in InSe/CNT(n,0) (n = 5–7) heterojunctions under the external electric field. The charge transfer is enhanced and Schottky barrier heights are significantly reduced in heterojunctions with Se vacancy defect. In vacancy defect causes the disappearance of Schottky barrier because of metallization of InSe and more charge transfer than Se vacancy defect in InSe/CNT. Our findings provide a direction for the application of InSe/CNT in tunable nanoelectronic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spontaneous formation of defect states in γ-InSe/(C 4 H 9 NH 3) 2 (CH 3 NH 3)Pb 2 I 7 van der Waals heterostructures. • Theoretical calculation and experiment suggest the dynamic generation of iodine vacancy and charge states. • Electron–phonon coupling of the 2D perovskite is weakened from −127 meV to −90 meV in the heterostructure. • The band offset causes the built-in electrical field, then strengthens the optoelectrical response of heterostructure. Van der Waals (vdW) heterostructure composed of two-dimensional (2D) materials and 2D perovskite has shown excellent optoelectrical properties recently, while the interfacial coupling is less investigated. Here, van der Waals InSe/(C 4 H 9 NH 3) 2 (CH 3 NH 3)Pb 2 I 7 heterostructure is fabricated and systemically investigated by photoluminescence (PL) spectroscopy. An optical broadband emission is generated due to the formation of heterostructure. The first principle calculation and variable PL spectra suggest the dynamic generation of defects such as iodine vacancy and charge states. Electron–phonon coupling of the 2D perovskite is weakened from −127 meV to −90 meV in the heterostructure. The band offset causes the built-in electrical field, which strengthens the optoelectrical response of heterostructure devices. The results deepen the understanding of the interfacial optoelectrical dynamic of 2D perovskite-related vdW heterostructure and help develop superior optoelectrical vdW heterostructure devices. [ABSTRACT FROM AUTHOR]

Nonlinear absorption of light and its time evolution in InSe under the influence of picosecond laser excitation have been investigated experimentally. It was shown that the decrease in exciton absorption in InSe at high levels of optical excitation is due to the exciton–exciton interaction and screening of the Coulomb potential by free carriers, generated by laser light. Observations of induced absorption in the energy region between the exciton level and the edge of the conduction band are associated with the appearance of a continuum of states due to a shift in the edge of the energy band. [ABSTRACT FROM AUTHOR]

2D semiconductors are promising candidates for next generation electronics and optoelectronics. However, their exposure to air and/or resists during device fabrication can cause considerable degradation of material quality, hindering their study and exploitation. Here, field effect transistors (FETs) are designed and fabricated by encapsulation of the 2D semiconductor indium selenide (InSe) with alumina (Al2O3) and by self‐aligned electrical contacts. The Al2O3‐film is grown directly on InSe immediately after its exfoliation to provide a protecting capping layer during and after device fabrication. The InSe‐FETs exhibit a high electron mobility of up to ≈103 cm2 V−1 s−1 at room temperature for a 4‐nm‐thick InSe layer, a low contact resistance (down to 0.18 kΩ) and a high, fast, and broad‐band photoresponsivity. The photoresponsivity depends on the InSe‐layer thickness and photon wavelength, reaching a value of up to 108 A W−1 in the visible spectral range, at least one order of magnitude larger than previously reported for similar photodetectors. The proposed fabrication is scalable and suitable for high‐precision pattern definition. It could be extended to other 2D materials and multilayer structures where alumina could also provide effective screening of the electric field induced by polar molecules and/or charged impurities present near the surface of the 2D layer. [ABSTRACT FROM AUTHOR]

SnSe as a van der Waals (vdW) layered material has an extremely low light‐dark current ratio and renders its application in high‐performance optoelectronics. Herein, a SnSe/InSe vertical‐vdW heterojunction with built‐in electrical field favorable for suppressing the dark current is achieved. The SnSe/InSe heterojunction behaves as a self‐driven photodetector with a typical rectification behavior, photovoltaic effect, and broadband detection ranging from visible to near infrared light (405–808 nm). Moreover, the SnSe/InSe photodetector at near infrared 808 nm still exhibits excellent and balanced photoresponse performance with R of 350 mA W−1, external quantum efficiency of 48% and detectivity of 5.8 × 1010 Jones, respectively. The results pave the way for the applications of the novel SnSe/InSe vdW heterostructures in broadband photodetectors and photovoltaic devices. [ABSTRACT FROM AUTHOR]

In this work, we present findings on the syntheses and study of properties of InSe nanohybrid. The introduction of guest component in GaSe matrix leads to an increase in inhomogeneities, which is clearly confirmed by the strengthening of the low-frequency horizontal branch of Nyquist diagrams. A constant magnetic field counteracts this effect and changes the behavior of the impedance hodograph at low frequencies to the opposite. Illumination leads to a colossal increase in quantum capacitance, which is clearly demonstrated in the Nyquist diagram. For the synthesized InSe nanohybrid the interesting behavior of the current-voltage characteristic is reported. As a result of studies of the synthesized InSe nanohybrid the effect of "negative capacity" is observed, the magnitude of which can be controlled by the electric field. Based on the constructed impedance model and proposed N-barrier model, the physical mechanisms of the investigated processes are suggested. [ABSTRACT FROM AUTHOR]

This work reports the nonlinear optical properties and ultrafast carrier dynamics of indium selenide (InSe) nanosheets obtained via liquid‐phase exfoliation under pulsed excitation with different durations. InSe nanosheets exhibit a better saturable absorption response under 6 ns pulse excitation than that under 380 fs excitation. In addition, the scattering phenomena of InSe dispersions with different mechanisms under various pulse durations are discovered, which are caused by the thermal effect under ns pulse excitation and dynamic spatial self‐phase modulation affected by laser streaming under fs pulse excitation. The pump‐probe measurements reveal that the InSe dispersion has ultrafast saturable absorption and photoinduced absorption processes, which may be caused by free carrier absorption or bandgap renormalization. [ABSTRACT FROM AUTHOR]

The hierarchical structure of InSe> composition with 4-fold grade expansion was synthesized with the intercalation-deintercalation technique. Electrical properties of the structure obtained were examined using impedance and thermostimulated current spectroscopy methods. Influence of temperature, static magnetic field and illumination on electrical properties of the synthesized compound was investigated. Changes in the impurity spectrum of the expanded hierarchical structure were analyzed and extraordinary magneto- and photoimpedance behavior of InSe> at room temperature was explained.

In this work, we present findings on the syntheses and study of properties of InSe nanohybrid. The introduction of guest component in GaSe matrix leads to an increase in inhomogeneities, which is clearly confirmed by the strengthening of the low-frequency horizontal branch of Nyquist diagrams. A constant magnetic field counteracts this effect and changes the behavior of the impedance hodograph at low frequencies to the opposite. Illumination leads to a colossal increase in quantum capacitance, which is clearly demonstrated in the Nyquist diagram. For the synthesized InSe nanohybrid the interesting behavior of the current-voltage characteristic is reported. As a result of studies of the synthesized InSe nanohybrid the effect of “negative capacity” is observed, the magnitude of which can be controlled by the electric field. Based on the constructed impedance model and proposed N-barrier model, the physical mechanisms of the investigated processes are suggested.

Indium selenide (InSe) is an emerging van der Waals material, which exhibits the potential to serve in excellent electronic and optoelectronic devices. One of the advantages of layered materials is their application to flexible devices. How strain alters the electronic and optical properties is, thus, an important issue. In this work, we experimentally measured the strain dependence on the angle-resolved second harmonic generation (SHG) pattern of a few layers of InSe. We used the exfoliation method to fabricate InSe flakes and measured the SHG images of the flakes with different azimuthal angles. We found the SHG intensity of InSe decreased, while the compressive strain increased. Through first–principles electronic structure calculations, we investigated the strain dependence on SHG susceptibilities and the corresponding angle-resolved SHG pattern. The experimental data could be fitted well by the calculated results using only a fitting parameter. The demonstrated method based on first–principles in this work can be used to quantitatively model the strain-induced angle-resolved SHG patterns in 2D materials. Our obtained results are very useful for the exploration of the physical properties of flexible devices based on 2D materials.

Two-dimensional materials-based field-effect transistors (FETs) are promising biosensors because of their outstanding electrical properties, tunable band gap, high specific surface area, label-free detection, and potential miniaturization for portable diagnostic products. However, it is crucial for FET biosensors to have a high electrical performance and stability degradation in liquid environments for their practical application. Here, a high-performance InSe-FET biosensor is developed and demonstrated for the detection of the CA125 biomarker in clinical samples. The InSe-FET is integrated with a homemade microfluidic channel, exhibiting good electrical stability during the liquid channel process because of the passivation effect on the InSe channel. The InSe-FET biosensor is capable of the quantitative detection of the CA125 biomarker in breast cancer in the range of 0.01–1000 U/mL, with a detection time of 20 min. This work provides a universal detection tool for protein biomarker sensing. The detection results of the clinical samples demonstrate its promising application in early screenings of major diseases.

Mixed-phased InxSey thin film containing InSe, In2Se3 and In6Se7 phases was prepared by M-CBD method and characterized by X-ray diffraction, AFM, optical spectroscopy and J-V measurements. Structural, optical and electrical conductance properties were modified by annealing the films at different temperatures. Optical and morphological properties were also investigated dependently on temperature and concentration of cationic precursor solution. It has been observed with annealing that, the compositions of the phases changed, particle sizes increased, energy band gaps decreased and electrical conductivity increased. The photoconductivity of thin film was revealed by J-V measurements and slightly increased by annealing. From temperature-dependent J-V measurements, activation energies (Ea) were calculated in low and high temperature regions and, found to be 0.03 eV for low temperature region and 0.8 eV for high temperature one. [ABSTRACT FROM AUTHOR]

Intercalation and doping are promising routes to tune properties of van der Waals (vdW) semiconductors and pave the way for their applications in digital electronics beyond Moore’s law, sensors and spintronics. The indium selenide (InSe) vdW crystal shows great promise for use in next-generation semiconductor technologies. For these applications to be realized, the effects of impurities on properties of InSe must be understood. Here, we present a comparative experimental study of electron transport in n-type InSe semiconductor doped and electrochemically intercalated with magnetic cobalt (Co) impurities. It is shown that the presence of Co decreases the free electron density, the Hall mobility along layers and the conductivity anisotropy σ⊥C/σ‖C. Furthermore, this leads to a change of the behavior of σ⊥C(T) dependence from a metallic one in pristine samples to a semiconducting one in samples with Co. We also demonstrate that the interaction of electrons with space-charge regions is an effective scattering mechanism, which should be taken into account in doped and intercalated crystals. The present work is important for the basic physics knowledge of the effect of Co impurities on physical properties of InSe, which is needed to tailor the parameters of this semiconductor for applications in electronics and spintronics.

Abstract Two-dimensional (2D) InSe-based field effect transistor (FET) has shown remarkable carrier mobility and high on-off ratio in experimental reports. Theoretical investigations also predicated the high performance can be well preserved at sub-10 nm nodes in the ballistic limit. However, both experimental experience and theoretical calculations pointed out achieving high-quality ohmic has become the main limiting factor for high-performance 2D FET. In this work, we proposed a new sandwiched ohmic contact with indium for InSe FET and comprehensively evaluated its performance from views of material and device based on ab initio methods. The material properties denote that all of fundamental issues of ohmic contact including tunneling barrier, the Schottky barrier, and effective doping are well concerned by introducing the sandwiched structure, and excellent contact resistance was achieved. At device performance level, devices with gate length of 7, 5, and 3 nm were investigated. All metrics of sandwiched contacted devices far exceed requirement of the International Technology Roadmap for Semiconductors (ITRS) and exhibit obvious promotion as compared to conventional structures. Maximum boost of current with 69.4%, 50%, and 49% are achieved for devices with 7, 5, and 3 nm gate length, respectively. Meanwhile, maximum reduction of the intrinsic delay with 20.4%, 16.7%, and 18.9% are attained. Moreover, a benchmark of energy-delay product (EDP) against other 2D FETs is presented. All InSe FETs with sandwiched ohmic contact surpass MoS2 FETs as well as requirement from ITRS 2024. The best result approaches the upper limit of ideal BP FET, denoting superior preponderance of sandwiched structures for InSe FETs in the next generation of complementary metal-oxide semiconductor (CMOS) technology.

Single-phase two-dimensional (2D) indium monoselenide (γ-InSe) film is successfully grown via solid phase epitaxy in the molecular beam epitaxy (MBE) system. Having high electron mobility and high photoresponsivity, ultrathin 2D γ-InSe semiconductors are attractive for future field-effect transistor and optoelectronic devices. However, growing single-phase γ-InSe film is a challenge due to the polymorphic nature of indium selenide (γ-InSe, α-In2Se3, β-In2Se3, γ-In2Se3, etc.). In this work, the 2D α-In2Se3 film was first grown on a sapphire substrate by MBE. Then, the high In/Se ratio sources were deposited on the α-In2Se3 surface, and an γ-InSe crystal emerged via solid-phase epitaxy. After 50 min of deposition, the initially 2D α-In2Se3 phase was also transformed into a 2D γ-InSe crystal. The phase transition from 2D α-In2Se3 to γ-InSe was confirmed by Raman, XRD, and TEM analysis. The structural ordering of 2D γ-InSe film was characterized by synchrotron-based grazing-incidence wide-angle X-ray scattering (GIWAXS).

In contrast to the majority of two-dimensional semiconductors such as transition metal dichalcogenides, indium selenide (InSe) possesses an intrinsic large out-of-plane oriented band-edge luminescent dipole. This unique anisotropic feature of band-edge optical emissions can be exploited to achieve enhanced optical signal in bent regions of materials created by geometrical modification. We herein investigate based on first-principle calculations the mechanism of this optical emission enhancement by modelling the photoluminescence processes in bent and flat regions of the InSe thin film. We propose in our model that the shorter-wavelength interband transition, labelled as transition B′, between the second-highest valence band and the bottom of conduction band plays an important role in the enhancing process. Our model robustly describes the dependence of optical emission enhancement in the bent InSe thin films on thickness, incident light orientation, and excitation photon energy. In particular, we found that when excitation photon energy is lower than the energy of transition B′, strong enhancement up to hundreds of times can be obtained by applying an incident light at an angle less than 70° to the InSe layers. Our results provide useful references for modulating luminescent properties of InSe films toward flexible optoelectronic device applications. [ABSTRACT FROM AUTHOR]