Indium Selenide Research Articles

Enhancement of the structural, morphological, optical and thermoelectric power factor of polycrystalline BiInSe3 thin film

There is an immediate need for thermoelectric materials that are cost-effective and readily accessible. It has been recognized that semiconductors utilizing selenium can play a pivotal role in surmounting the barriers to their extensive commercial utilization. In this study, we demonstrate the synthesis of n-type bismuth indium selenide thin films on a glass substrate using a thermal evaporation technique, followed by post-annealing in a tube furnace at 200 °C for different durations (ranging from 1 to 5 h) in a Se atmosphere. Our primary focus is on the morphological, structural, optical, electrical, and thermoelectric power factor of both the as-deposited and post-annealed BiInSe3 thin films for varying durations. Morphological, structural, and optical analyses of the BiInSe3 films were performed using a scanning electron microscope, x-ray diffraction, and UV-spectroscopy. Furthermore, we used thermoelectric measurements to thoroughly investigate the mechanism of thermoelectric transportation at room temperature, focusing on the Seebeck coefficient and charge carrier mobility concerning the formation of thin film nanostructures. By tailoring the post-annealing process, we have optimized the structural, optical, and thermoelectric power factor of BiInSe3 films, enabling thermoelectric devices for energy applications to achieve commercial maturity.

Indium selenide/silver phosphate hollow microsphere S-scheme heterojunctions for photocatalytic hydrogen production with simultaneous degradation of tetracycline

Designing heterojunction photocatalysts with strong interfacial interactions is an effective way to reduce the recombination of photogenerated charge carriers. Here, silver phosphate (Ag3PO4) nanoparticles are coupled with hollow flower-like indium selenide (In2Se3) microspheres by a facile Ostwald ripening and in-situ growth method, resulting in the construction of In2Se3/Ag3PO4 hollow microsphere step-scheme (S-scheme) heterojunction with a large contact interface. The flower-like In2Se3 with hollow and porous structure provides a large specific surface area and numerous active sites for photocatalytic reactions to take place. The photocatalytic activity was tested by measuring the hydrogen evolution from antibiotic wastewater, and the H2 evolution rate of In2Se3/Ag3PO4 reached 4206.4 µmol g-1h−1 under visible light, which is approximately 2.8 times greater than that of In2Se3. In addition, the amount of tetracycline (TC) degradation when it was used as a sacrificial agent is about 54.4% after 1 h. On the one hand, Se-P chemical bonds act as electron transfer channels in the S-scheme heterojunctions, which can facilitate the migration and separation of photogenerated charge carriers. On the other hand, the S-scheme heterojunctions can retain the useful holes and electrons with higher redox capacities, which is very favorable for the generation of more •OH radicals and the photocatalytic activity is greatly enhanced. This work provides an alternative design approach for photocatalysts toward hydrogen evolution in antibiotic wastewater.

Tribo‐ferro‐optoelectronic neuromorphic transistor of α‐In2Se3

AbstractInspired by biological neural networks, the fabrication of artificial neuromorphic systems with multimodal perception capacity shows promises in overcoming the “von Neumann bottleneck” and takes advantage of the efficient perception and computation of diverse types of signals. Here, we combine a triboelectric nanogenerator with an α‐phase indium selenide (α‐In2Se3) optoelectronic synaptic transistor to construct a tribo‐ferro‐optoelectronic artificial neuromorphic device with multimodal plasticity. Based on the excellent ferroelectric and optoelectronic characteristics of the α‐In2Se3 channel, typical synaptic behaviors (e.g., pair‐pulse facilitation and short‐term/long‐term plasticity) are successfully simulated in response to the synergistic effect of mechanical and optical stimuli. The interaction of mechanical displacement and light illumination enables heterosynaptic plasticity and spatiotemporal dynamic logic. Furthermore, multiple Boolean logical functions and associative learning behaviors are successfully implemented using the paired stimuli of displacement pulses and light pulses. The proposed tribo‐ferro‐optoelectronic artificial neuromorphic devices have great potential for application in interactive neural networks and next‐generation artificial intelligence.

Direct Measurements of Anisotropic Thermal Transport in γ‐InSe Nanolayers via Cross‐Sectional Scanning Thermal Microscopy

AbstractVan der Waals (vdW) atomically thin materials and their heterostructures offer a versatile platform for the management of nanoscale heat transport and the design of novel thermoelectrics. These require the measurement of highly anisotropic heat transport in vdW‐based nanolayers, a major challenge for nanostructured materials and devices. In the present study, a novel effective method of cross‐sectional scanning thermal microscopy was used to map and quantify the anisotropic heat transport in nanoscale thick layers of vdW materials and the material‐substrate interfaces. This technique measures the heat conducted into a vdW crystal via the nanoscale apex of a heat‐sensitive probe. The crystal is nano‐polished via Ar ion beams generating an oblique nearly atomically flat surface. By measuring the thermal conductance variation as a function of increasing layer thickness, the transition between the cross‐plane and in‐plane heat transport (defined by heat conductivity anisotropy) is acquired. By using an analytical model validated by finite element simulations, anisotropic thermal transport in a gamma indium selenide crystal nano‐thin flake on a Si substrate was studied, obtaining results corresponding to anomalously low anisotropic thermal conductivities of kxy = 2.16 Wm−1 K−1 in‐plane and kz = 0.89 Wm−1 K−1 cross‐plane confirming its potential for thermoelectric applications.

Lattice Thermal Conductivity of Monolayer InSe Calculated by Machine Learning Potential.

The two-dimensional post-transition-metal chalcogenides, particularly indium selenide (InSe), exhibit salient carrier transport properties and evince extensive interest for broad applications. A comprehensive understanding of thermal transport is indispensable for thermal management. However, theoretical predictions on thermal transport in the InSe system are found in disagreement with experimental measurements. In this work, we utilize both the Green-Kubo approach with deep potential (GK-DP), together with the phonon Boltzmann transport equation with density functional theory (BTE-DFT) to investigate the thermal conductivity (κ) of InSe monolayer. The κ calculated by GK-DP is 9.52 W/mK at 300 K, which is in good agreement with the experimental value, while the κ predicted by BTE-DFT is 13.08 W/mK. After analyzing the scattering phase space and cumulative κ by mode-decomposed method, we found that, due to the large energy gap between lower and upper optical branches, the exclusion of four-phonon scattering in BTE-DFT underestimates the scattering phase space of lower optical branches due to large group velocities, and thus would overestimate their contribution to κ. The temperature dependence of κ calculated by GK-DP also demonstrates the effect of higher-order phonon scattering, especially at high temperatures. Our results emphasize the significant role of four-phonon scattering in InSe monolayer, suggesting that combining molecular dynamics with machine learning potential is an accurate and efficient approach to predict thermal transport.

Facile fabrication of amorphous-In2Se3/Si heterojunction for fast ultraviolet to near-infrared broadband photodetection

Indium selenide (In2Se3) has emerged as a promising candidate for broadband photodetection due to its suitable bandgap, high electron mobility, high optical absorption coefficient, and broad-spectrum absorption properties. Nevertheless, wafer-scale growth of single-component and pure-phase In2Se3 films remains challenging and requires stringent experimental parameters. Here, a facile approach for depositing amorphous-In2Se3 (a-In2Se3) on Si substrate by physical vapor deposition (PVD) process is proposed to fabricate high-performance a-In2Se3/Si heterojunction photodetectors. The as-produced devices are sensitive to a broad-spectrum (255–1300 nm), exhibiting superior overall performance with a low dark current of 0.54 nA, large current on/off ratio of 2.26 × 104, fast response with rise/decay time of 176/175 μs, decent responsivity of 1.50 A/W and detectivity of 6.46 × 1012 Jones under 1050 nm illumination at − 3 V bias. Such remarkable results can be attributed to the unique type-Ⅰ straddling energy band alignment and the strong coupling between a-In2Se3 and Si interface. In addition, decent responsivity and detectivity under 255 nm (0.29 A/W and 1.25 × 1012 Jones) and 630 nm (0.77 A/W and 3.32 × 1012 Jones) remedy the deficiency of Si in ultra-violet and visible light detection. Our work provides a facile and low-cost route for the realization of high-performance broadband photodetectors based on a-In2Se3/Si heterojunctions.

Giant Out-of-Plane Exciton Emission Enhancement in Two-Dimensional Indium Selenide via a Plasmonic Nanocavity

Out-of-plane (OP) exciton-based emitters in two-dimensional semiconductor materials are attractive candidates for novel photonic applications, such as radially polarized sources, integrated photonic chips, and quantum communications. However, their low quantum efficiency resulting from forbidden transitions limits their practicality. In this work, we achieve a giant enhancement of up to 34000 for OP exciton emission in indium selenide (InSe) via a designed Ag nanocube-over-Au film plasmonic nanocavity. The large photoluminescence enhancement factor (PLEF) is attributed to the induced OP local electric field (Ez) within the nanocavity, which facilitates effective OP exciton-plasmon interaction and subsequent tremendous enhancement. Moreover, the nanoantenna effect resulting from the effective interaction improves the directivity of spontaneous radiation. Our results not only reveal an effective photoluminescence enhancement approach for OP excitons but also present an avenue for designing on-chip photonic devices with an OP dipole orientation.

Probing Anisotropic Deformation and Near-Infrared Emission Tuning in Thin-Layered InSe Crystal under High Pressure.

Indium selenide (InSe) exhibits high lattice compressibility and an extraordinary capability of tailoring the optical band gap under pressure beyond other 2D materials. Herein, by applying hydrostatic pressure via a diamond anvil cell, we revealed an anisotropic deformation dynamic and efficient manipulation of near-infrared light emission in thin-layered InSe strongly correlated to layer numbers (N = 5-30). As N > 20, the InSe lattice is compressed in all directions, and the intralayer compression leads to widening of the band gap, resulting in an emission blue shift (∼120 meV at 1.5 GPa). In contrast, as N ≤ 15, an efficient emission red shift is observed from band gap shrinkage (rate of 100 meV GPa-1), which is attributed to the predominant uniaxial interlayer compression because of the high strain resistance along the InSe-diamond interface. These findings advance the understanding of pressure-induced lattice deformation and optical transition evolution in InSe and could be applied to other 2D materials.

Electroplating kinetics and mechanism of nanostructured indium selenide thin films

Electroplating kinetics and mechanism of nanostructured indium selenide thin films

Ballistic two-dimensional InSe transistors.

The International Roadmap for Devices and Systems (IRDS) forecasts that, for silicon-based metal-oxide-semiconductor (MOS) field-effect transistors (FETs), the scaling of the gate length will stop at 12 nm and the ultimate supply voltage will not decrease to less than 0.6 V (ref. 1). This defines the final integration density and power consumption at the end of the scaling process for silicon-based chips. In recent years, two-dimensional (2D) layered semiconductors with atom-scale thicknesses have been explored as potential channel materials to support further miniaturization and integrated electronics. However, so far, no 2D semiconductor-based FETs have exhibited performances that can surpass state-of-the-art silicon FETs. Here we report a FET with 2D indium selenide (InSe) with high thermal velocity as channel material that operates at 0.5 V and achieves record high transconductance of 6 mS μm-1 and a room-temperature ballistic ratio in the saturation region of 83%, surpassing those of any reported silicon FETs. An yttrium-doping-induced phase-transition method is developed for making ohmic contacts with InSe and the InSe FET is scaled down to 10 nm in channel length. Our InSe FETs can effectively suppress short-channel effects with a low subthreshold swing (SS) of 75 mV per decade and drain-induced barrier lowering (DIBL) of 22 mV V-1. Furthermore, low contact resistance of 62 Ω μm is reliably extracted in 10-nm ballistic InSe FETs, leading to a smaller intrinsic delay and much lower energy-delay product (EDP) than the predicted silicon limit.

Layer-dependent optically induced spin polarization in InSe

Optical control of spin in semiconductors has been pioneered using nanostructures of III-V and II-VI semiconductors, but the emergence of two-dimensional van der Waals materials offers an alternative low-dimensional platform for spintronic phenomena. Indium selenide (InSe), a group-III monochalcogenide van der Waals material, has shown promise for opto-electronics due to its high electron mobility, tunable direct bandgap, and quantum transport. There are predictions of spin-dependent optical selection rules suggesting potential for all-optical excitation and control of spin in a two-dimensional layered material. Despite these predictions, layer-dependent optical spin phenomena in InSe have yet to be explored. Here, we present measurements of layer-dependent optical spin dynamics in few-layer and bulk InSe. Polarized photoluminescence reveals layer-dependent optical orientation of spin, thereby demonstrating the optical selection rules in few-layer InSe. Spin dynamics are also studied in many-layer InSe using time-resolved Kerr rotation spectroscopy. By applying out-of-plane and in-plane static magnetic fields for polarized emission measurements and Kerr measurements, respectively, the $g$-factor for InSe was extracted. Further investigations are done by calculating precession values using a $\textbf{k} \cdot \textbf{p}$ model, which is supported by \textit{ab-initio} density functional theory. Comparison of predicted precession rates with experimental measurements highlights the importance of excitonic effects in InSe for understanding spin dynamics. Optical orientation of spin is an important prerequisite for opto-spintronic phenomena and devices, and these first demonstrations of layer-dependent optical excitation of spins in InSe lay the foundation for combining layer-dependent spin properties with advantageous electronic properties found in this material.

Subnanometer-Wide Indium Selenide Nanoribbons.

Indium selenides (InxSey) have been shown to retain several desirable properties, such as ferroelectricity, tunable photoluminescence through temperature-controlled phase changes, and high electron mobility when confined to two dimensions (2D). In this work we synthesize single-layer, ultrathin, subnanometer-wide InxSey by templated growth inside single-walled carbon nanotubes (SWCNTs). Despite the complex polymorphism of InxSey we show that the phase of the encapsulated material can be identified through comparison of experimental aberration-corrected transmission electron microscopy (AC-TEM) images and AC-TEM simulations of known structures of InxSey. We show that, by altering synthesis conditions, one of two different stoichiometries of sub-nm InxSey, namely InSe or β-In2Se3, can be prepared. Additionally, in situ AC-TEM heating experiments reveal that encapsulated β-In2Se3 undergoes a phase change to γ-In2Se3 above 400 °C. Further analysis of the encapsulated species is performed using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), and Raman spectroscopy, corroborating the identities of the encapsulated species. These materials could provide a platform for ultrathin, subnanometer-wide phase-change nanoribbons with applications as nanoelectronic components.

Nanosecond passively Q-switched Nd: YVO4 laser based on BP/InSe saturable absorber

We report on a compact 808 nm diode-pumped passively Q-switched (PQS) Nd:YVO4 laser at 1064 nm with black phosphorus (BP)/ indium selenide (InSe) heterostructure as a saturable absorber (SA). When the transmission of the output coupler (OC) was 30%, the maximum continuous-wave (CW) output power of 10.3 W was obtained with a slope efficiency of 52.4% under the incident pump power of 22 W. The maximum average output power of 3.1 W was obtained at 9.29 W pump power, corresponding to the repetition rate of 598 kHz and the pulse width of 455 ns during pulse operation, further power scaling was limited by the damage threshold of the saturable absorber mirror (SAM). The results sufficiently validated that two-dimensional (2D) BP/InSe heterostructure could be used as an optical modulator for near-IR pulsed laser sources.

First principles calculations of electronic and optical properties of InSe nanosheets doped with noble metal atoms

Monolayer Indium Selenide (ML-InSe) is studied for 4x4 supercell structure through ab initio calculations. The electronic and optical properties of ML-InSe for both pristine and substitutional doped ML-InSe with Palladium (Pd), Platinum (Pt), Silver (Ag), and Gold (Au) atoms have been calculated. With substitutional doping, ML-InSe has been observed to have a spin-dependent electronic structure. The flat energy bands near the Fermi level are observed in ML-InSe with doping elements placed in In site. The flat bands of d orbitals of some noble metal atoms are formed by the projected density of states (PDOS). The PDOS calculations show that the s-orbital of In and p-orbital of Se form the conduction band edge. The energetically favorable position of doping atoms is found to be the PtIn substitution atom according to formation energy calculations. For each studied structure, the bond length of the first neighbor of doping atoms in doped ML-InSe, static dielectric constant (ε0), refractive index, and energy band gap have been calculated. In the structure ML-InSe with AuSe, ε0 reaches ∼ 8.15. Another important result is that substitutional doping induces some peaks in the lower energy region of the imaginary part of the dielectric function. These peaks mainly refer to the absorption in related regions and may be important for the optoelectronic properties of ML-InSe.

Nanosized indium selenide saturable absorber for multiple solitons operation in Er3+-doped fiber laser.

With the advances in the field of ultrafast photonics occurring so fast, the demand for optical modulation devices with high performance and soliton lasers which can realize the evolution of multiple soliton pulses is gradually increasing. Nevertheless, saturable absorbers (SAs) with appropriate parameters and pulsed fiber lasers which can output abundant mode-locking states still need to be further explored. Due to the special band gap energy values of few-layer indium selenide (InSe) nanosheets, we have prepared a SA based on InSe on a microfiber by optical deposition. In addition, we demonstrate that our prepared SA possesses a modulation depth and saturable absorption intensity about 6.87% and 15.83 MW/cm2, respectively. Then, multiple soliton states are obtained by dispersion management techniques, including regular solitons, and second-order harmonic mode-locking solitons. Meanwhile, we have obtained multi-pulse bound state solitons. We also provide theoretical basis for the existence of these solitons. The results of the experiment show that the InSe has the potential to be an excellent optical modulator because of its excellent saturable absorption properties. This work also is important for improving the understanding and knowledge of InSe and the output performance of fiber lasers.

Remarkable plasticity and softness of polymorphic InSe van der Waals crystals

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.

Investigation of passively Q-switched and mode-locked operation using Cu nanoparticles doped Indium Selenide as saturable absorber at 1.5-μm region

A reliable Q-switched and mode-locked operation at the 1.5-μm region has been demonstrated using copper nanoparticles (Cu NPs)-doped Indium Selenide (In2Se3). The Cu NPs were produced using pulsed laser ablation (PLA) in a PVA solution before mixed it with In2Se3 solution. Then, the Cu/In2Se3 solution was dry casted into a petri dish and peeled off from the petri dish after it was completely dry to form a free-standing (without substrate) Cu/In2Se3 film as a saturable absorber since this technique offers simplicity and is easy to integrate into the laser cavity. Q-switched pulses were generated at the operating wavelength of 1561.9 nm with a threshold pump power of 24.13 mW. A short pulse width of 2.54 μs, with a repetition rate of 122.60 kHz, attained a maximum pump power of 125.63 mW. The highest pulse energy obtained is 145.84 nJ, with an output power maximum of 17.88 mW on average. A soliton was generated as 100 m SMF integrated into the EDF laser cavity with the center of a wavelength of 1562.2 nm, a pulse width of 3.59 ps, and a peak power of 1.68 kW. These results prove that Cu/In2Se3 shows excellent potential as a SA material that operates in the 1.5-µm region.

Uniaxial Strain Dependence on Angle-Resolved Optical Second Harmonic Generation from a Few Layers of Indium Selenide

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.

Selective Enhancement of Photoresponse with Ferroelectric-Controlled BP/In2 Se3 vdW Heterojunction.

Owing to the large built-in field for efficient charge separation, heterostructures facilitate the simultaneous realization of a low dark current and high photocurrent. The lack of an efficient approach to engineer the depletion region formed across the interfaces of heterojunctions owing to doping differences hinders the realization of high-performance van der Waals (vdW) photodetectors. This study proposes a ferroelectric-controlling van der Waals photodetector with vertically stacked two-dimensional (2D) black phosphorus (BP)/indium selenide (In2 Se3 ) to realize high-sensitivity photodetection. The depletion region can be reconstructed by tuning the polarization states generated from the ferroelectric In2 Se3 layers. Further, the energy bands at the heterojunction interfaces can be aligned and flexibly engineered using ferroelectric field control. Fast response, self-driven photodetection, and three-orders-of-magnitude detection improvements are achieved in the switchable visible or near-infrared operation bands. The results of the study are expected to aid in improving the photodetection performance of vdW optoelectronic devices.

Synthesis and characterization of (Sb0.05In0.95)Se crystals

The antimony doped indium selenide (Sb0.05In0.95)Se crystals have been grown using the direct vapour transport (DVT) technique. The grown (Sb0.05In0.95)Se crystals have been characterized by estimating its structural, optical and electrical properties using appropriate techniques. The (Sb0.05In0.95)Se crystal has a hexagonal crystal structure with a preferred orientation along the (004) direction from the X-ray diffraction (XRD) spectra. Also, the micro-structural parameters (crystallite size, lattice strain, dislocation density, domain population) have been analysed from XRD spectra. The optical parameters (optical band gap, extinction coefficient and refractive index) have been calculated from UV–vis absorption spectrum. The resulting optical direct band gap is 1.51 eV. The activation energy value of 0.71 eV has been obtained from resistance-temperature observations of (Sb0.05In0.95)Se crystal.