Narrow Bandgap Materials Research Articles

Ionic Liquid-Assisted Strategy for Morphology Engineering of Inorganic Cesium-Based Perovskite Thin Films Toward High-Performance Solar Cells.

The wide bandgap CsPbI2Br perovskite materials have attracted significant attention due to their high thermal stability and compatibility with narrow bandgap materials in tandem devices. The performance of perovskite solar cells (PSCs) is highly dependent on the quality of the perovskite layer, which is governed by the crystallization process during solution processing. However, the crystallization dynamics of CsPbI2Br thin films remain less explored compared to conventional organic-inorganic perovskites. Achieving high-quality CsPbI2Br films with uniform morphology and large perovskite grains remains challenging with standard solution techniques. This study applies the ionic liquid (IL) [EMIM]+[PF6]- as an additive within the bulk CsPbI2Br absorber layer. Within our experimental regime, [EMIM]+[PF6]- accelerates the crystallization process while promoting the formation of large perovskite grains, a feature not commonly observed in previous studies. Our experimental results suggest that the IL acts as heterogeneous nucleation sites, and varying IL incorporation amount significantly impacts the morphology of CsPbI2Br perovskite films. Consistent UV-vis and photoluminescence (PL) red-shifts are observed in the IL-incorporated CsPbI2Br films, with X-ray diffraction (XRD) data projecting an influence on the perovskite crystal structure. These findings provide new insights into the role of ILs in controlling crystallization and morphology that have been minimally discussed in the literature. The incorporation of an optimized amount of [EMIM]+[PF6]- promotes the formation of highly crystalline perovskite thin films with excellent morphology, reducing defect density, enhancing carrier transport, and yielding large grain sizes. As a result, PSCs fabricated with [EMIM]+[PF6]- achieved a power conversion efficiency (PCE) of 17.11% (stabilized at 15.87%) and an open-circuit voltage (VOC) of 1.39 V, along with improved stability compared to control devices. This work provides a straightforward approach for producing high-quality CsPbI2Br thin films with high reproducibility, contributing valuable advancements to Cs-based PSCs.

Giant infrared bulk photovoltaic effect in tellurene for broad-spectrum neuromodulation

Given the surpassing of the Shockley-Quiesser efficiency limit in conventional p-n junction photovoltaic effect, bulk photovoltaic effect (BPVE) has garnered significant research interest. However, the BPVE primarily focuses on a narrow wavelength range, limiting its potential applications. Here we report a giant infrared bulk photovoltaic effect in tellurene (Te) for broad-spectrum neuromodulation. The generated photocurrent in uniformly illuminated Te excludes other photoelectric effects and is attributed to the BPVE. The bulk photovoltaic wavelength in Te spans a wide range from the ultraviolet (390 nm) to the mid-infrared (3.8 µm). Moreover, the photocurrent density of 70.4 A cm−2 under infrared light simulation outperforms that in previous ultraviolet and visible semiconductors as well as infrared semimetals. Te attached to the dendrites or somata of the cortical neurons successfully elicit action potentials under broad-spectrum light irradiation. This work lays the foundation for the further development of infrared BPVE in narrow bandgap materials.

Comprehensive Review of FinFET Technology: History, Structure, Challenges, Innovations, and Emerging Sensing Applications.

The surge in demand for 3D MOSFETs, such as FinFETs, driven by recent technological advances, is explored in this review. FinFETs, positioned as promising alternatives to bulk CMOS, exhibit favorable electrostatic characteristics and offer power/performance benefits, scalability, and control over short-channel effects. Simulations provide insights into functionality and leakage, addressing off-current issues common in narrow band-gap materials within a CMOS-compatible process. Multiple structures have been introduced for FinFETs. Moreover, some studies on the fabrication of FinFETs using different materials have been discussed. Despite their potential, challenges like corner effects, quantum effects, width quantization, layout dependencies, and parasitics have been acknowledged. In the post-planar CMOS landscape, FinFETs show potential for scalability in nanoscale CMOS, which leads to novel structures for them. Finally, recent developments in FinFET-based sensors are discussed. In a general view, this comprehensive review delves into the intricacies of FinFET fabrication, exploring historical development, classifications, and cutting-edge ideas for the used materials and FinFET application, i.e., sensing.

Synergistic Effect of Ionic Liquid and Embedded QDs on 2D Ferroelectric Perovskite Films with Narrow Phase Distribution for Self-Powered and Broad-Band Photodetectors.

2D layered metal halide perovskites (MHPs) are a potential material for fabricating self-powered photodetectors (PDs). Nevertheless, 2D MHPs produced via solution techniques frequently exhibit multiple quantum wells, leading to notable degradation in the device performance. Besides, the wide band gap in 2D perovskites limits their potential for broad-band photodetection. Integrating narrow-band gap materials with perovskite matrices is a viable strategy for broad-band PDs. In this study, the use of methylamine acetate (MAAc) as an additive in 2D perovskite precursors can effectively control the width of the quantum wells (QWs). The amount of MAAc greatly affects the phase purity. Subsequently, PbSe QDs were embedded into the 2D perovskite matrix with a broadened absorption spectrum and no negative effects on ferroelectric properties. PM6:Y6 was combined with the hybrid ferroelectric perovskite films to create a self-powered and broad-band PD with enhanced performance due to a ferro-pyro-phototronic effect, reaching a peak responsivity of 2.4 A W-1 at 940 nm.

Hydrostatic Pressure as a Tool for the Study of Semiconductor Properties-An Example of III-V Nitrides.

Using the example of III-V nitrides crystallizing in a wurtzite structure (GaN, AlN, and InN), this review presents the special role of hydrostatic pressure in studying semiconductor properties. Starting with a brief description of high-pressure techniques for growing bulk crystals of nitride compounds, we focus on the use of hydrostatic pressure techniques in both experimental and theoretical investigations of the special properties of nitride compounds, their alloys, and quantum structures. The bandgap pressure coefficient is one of the most important parameters in semiconductor physics. Trends in its behavior in nitride structures, together with trends in pressure-induced phase transitions, are discussed in the context of the behavior of other typical semiconductors. Using InN as an example, the pressure-dependent effects typical of very narrow bandgap materials, such as conduction band filling or effective mass behavior, are described. Interesting aspects of bandgap bowing in In-containing nitride alloys, including pressure and clustering effects, are discussed. Hydrostatic pressure also plays an important role in the study of native defects and impurities, as illustrated by the example of nitride compounds and their quantum structures. Experiments and theoretical studies on this topic are reviewed. Special attention is given to hydrostatic pressure and strain effects in short periods of nitride superlattices. The explanation of the discrepancies between theory and experiment in optical emission and its pressure dependence from InN/GaN superlattices led to the well-documented conclusion that InN growth on the GaN substrate is not possible. The built-in electric field present in InGaN/GaN and AlGaN/GaN heterostructures crystallizing in a wurtzite lattice can reach several MV/cm, leading to drastic changes in the physical properties of these structures and related devices. It is shown how hydrostatic pressure modifies these effects and helps to understand their origin.

Photoreduction of carbon dioxide into methane and ethylene using TiO2 inverse opal-derived PCN-222(M)

Solar-driven photocatalytic CO2 reduction has significant potential to address the energy crisis and mitigate greenhouse gas emissions by producing valuable organic compounds. Narrow bandgap materials enhance photon absorption within the visible light spectrum, thereby improving exciton generation. Both the inverse opal (IOT) and the porphyrin-based MOF (PCN-222) exhibit biomimetic design concepts. The IOT has a highly ordered porous structure that increases the light-absorbing surface area, facilitating efficient light harvesting. Conversely, the PCN-222 structure, which is modelled on biological porphyrin molecules, has a highly ordered pore structure and abundant active centers. Under hydrothermal conditions, PCN-222 self-assembles on the IOT surface to form a P(Cu, Fe, Zn)/IOT heterostructure. The tight interface of this heterostructure promotes rapid electron-hole separation and transport. In addition, the slow-light effect is exploited to increase the light absorption efficiency, thus improving the overall photocatalytic reaction efficiency and stability. In this study, the morphology, structure and photoelectric properties of P(Cu, Fe, Zn)/IOT heterostructures are investigated, revealing enhanced photocatalytic efficiency. The P(Fe)/IOT composite demonstrated outstanding CO2 conversion rates under simulated sunlight, yielding carbon monoxide (62 %), methane (0.11 %), and ethylene (0.09 %). The Z-scheme charge transfer mechanism significantly enhances photocatalytic performance by improving the efficiency of carrier separation and transfer, thereby increasing the overall photocatalytic reaction efficiency. This advance offers significant benefits for environmental and renewable energy remediation. The study provides key insights and recommendations for enhancing the efficiency of Z-scheme photocatalytic systems in future research and development.

Harnessing Metal-Organic Frameworks for NIR-II Light-Driven Multiphoton Photocatalytic Water Splitting in Hydrogen Therapy.

The construction of near-infrared (NIR) light-activated hydrogen-producing materials that enable the controlled generation and high-concentration release of hydrogen molecules in deep tumor tissues and enhance the effects of hydrogen therapy holds significant scientific importance. To address the key technical challenge of low-efficiency oxidation-reduction reactions for narrow-bandgap photocatalytic materials, this work proposes an innovative approach for the controllable fabrication of multiphoton photocatalytic materials to overcome the limitations imposed by traditional near-infrared photocatalysts with "narrow-bandgap" constraints. Herein, an NIR-responsive multiphoton photocatalyst, ZrTc-Co, is developed by utilizing a post-synthetic coordination modification strategy to introduce hydrogenation active site CoII into a multiphoton responsive MOF (ZrTc). The results reveal that with the introduction of the CoII site, electron-hole recombination can be efficiently suppressed, thus promoting the efficiency of hydrogen evolution reaction. In addition, the integration of CoII can effectively enhance charge transfer and improve static hyperpolarizability, which endows ZrTc-Co with excellent multiphoton absorption. Moreover, hyaluronic acid modification endows ZrTc-Co with cancer cell-specific targeting characteristics, laying the foundation for tumor-specific elimination. Collectively, the proposed findings present a strategy for constructing NIR-II light-mediated hydrogen therapeutic agents for deep tumor elimination.

Nonlinear optical response and application of indirect narrow-bandgap SbTe nanosheets

The nonlinear optical properties of antimony telluride (SbTe) crystal with indirect narrow bandgap are investigated, which exhibits superior performance for nonlinear laser modulation in the infrared band. The nonlinear optical coefficients of SbTe nanosheets are determined to be −3.3 cm/GW, −2.3 cm/GW, −1.9 cm/GW and the modulation depths are 5.5 %, 2.0 %, 1.5 % at 400 nm, 800 nm, 1064 nm, respectively. Based on the SbTe-SA, a Yb:GdScO3 laser centered at 1064 nm is achieved with 633 mW maximum output power, 56 fs pulse width and 104 MHz repetition rate. The damage threshold of the SbTe nanosheets is calculated to be exceed 338 GW/cm2, revealing the great potential in high-power laser modulation. This investigation marks the inaugural theoretical and experimental analysis of SbTe’s optical properties and its application in laser modulation, laying the groundwork for future research into indirect narrow-bandgap materials in laser technology.

GaSb/Si Heterojunction Based Pocket Engineered Vertical Non-Uniform Channel Double Gate TFETs for Low Power Applications

This article compares the performance of two Vertical Non-Uniform Channel Double Gate Tunnel Field Effect Transistors (VNUCDGTFETs), a normal all-Silicon Tunnel Field-Effect Transistor (TFET) having a pocket and another one a Gallium Antimonide/Silicon heterojunction TFET with pocket. GaSb is a III-V narrow energy band gap material, employed in the source area of the TFET structure to decrease the tunneling width and thus to make more number of carriers capable enough to tunnel through the heterojunction. The proposed source pocket heterojunction non uniform channel TFET presents superior performance as compared to the conventional non uniform channel vertical TFET with a pocket, regarding a larger ION/IOFF ratio, a reduced sub-threshold swing, and a smaller threshold voltage at VDS = 0.5 V. Furthermore, the proposed TFET device undergoes a comprehensive analysis of both DC parameters and various analog/RF parameters.

Highly efficient CdS/SbVO4 composites for visible-light-driven Cr(VI) reduction

Heavy metal contamination is a grave environmental concern due to its severe implications for human health and ecosystems, causing carcinogenic and teratogenic effects. This study addresses this pressing issue by exploring the synthesis and application of CdS/SbVO4 composites as effective photocatalysts. These composites were synthesized by a streamlined two-step hydrothermal method, with investigations conducted on varying molar ratios. The composite with a molar ratio of 0.2:1 demonstrated superior Cr(VI) photoreduction properties under visible light irradiation, exhibiting an efficiency quadruple that of pure SbVO4. This enhancement in photocatalytic activity is credited to the augmented separation of electrons and holes facilitated by the integration of narrow band gap materials within the composite. Electrochemical tests indicated the electron transfer mechanism and identified the primary active centers of the samples. The detailed photocatalytic mechanism of the composite was further discussed, grounded on insights derived from free radical trapping experiments and electron spin resonance analyses.

Improved performance of ternary organic solar cells based on both bulk and pseudo-planar heterojunction active layer

The high photovoltaic conversion efficiency (PCE) of ternary organic solar cells (OSCs) based on PTB7-Th, PC71BM and IEICO-4F material is obtained, the short-circuit current density (J SC), fill factor (FF), and open-circuit voltage is 25.90 mA cm−2, 73.20% and 0.71 V, respectively. PCE is as high as 13.53%. It is the highest PCE of ternary OSCs based on PTB7-Th, PC71BM and IEICO-4F materials for all we know. The narrow bandgap material of IEICO-4F is deposited on PTB7-Th:PC71BM bulk heterojunction (BHJ) by layer-by-layer process. We constructed the dual bandgap active layer both BHJ and pseudo-planar heterojunction (P-PHJ), it could be defined as ternary BHJ/P-PHJ of OSCs. This type of OSCs is not only the complementary bandgap material of the active layer, but also increasing the donor/acceptor (D/A) interface. The excitons generation and collection of the device are increased leading a higher J SC and FF. The semitransparent OSCs (ST-OSCs) is prepared by varying the thickness of Ag electrode and PCE can reach 9.70%, and the average visible light transmittance and light use efficiency of ST-OSCs are improved effectively.

Extended Conjugation Strategy Enabling Red-Shifted and Efficient Emission of Orange-Red Thermally Activated Delayed Fluorescence Materials.

In account of the energy gap law, the development of efficient narrow-band gap thermally activated delayed fluorescence (TADF) materials remains a major challenge for the application of organic light-emitting diodes (OLEDs). The orange-red TADF materials are commonly designed with either large π-conjugated systems or strong intramolecular donor-acceptor (D-A) interactions for red-shift emission and small singlet-triplet energy gap (ΔEST). There are rare reports on the simultaneous incorporation of these two strategies on the same material systems. Herein, two orange-red emitters named 1P2D-BP and 2P2D-DQ have been designed by extending the conjugation degree of the center acceptor DQ and increasing the number distribution of the peripheral donor PXZ units, respectively. The emission peak of 1P2D-BP is red-shifted to 615 nm compared to 580 nm for 2P2D-DQ, revealing the pronounced effect of the conjugation extension on the emission band gap. In addition, the distorted molecular structure yields a small ΔEST of 0.02 eV, favoring the acquisition of a high exciton utilization through an efficient reverse intersystem crossing process. As a result, orange-red OLEDs with both 1P2D-BP and 2P2D-DQ have achieved an external quantum efficiency (EQE) of more than 17%. In addition, the efficient white OLED based on 1P2D-BP is realized through precise exciton assignment and energy transport modulation, showing an EQE of 23.6% and a color rendering index of 82. The present work provides an important reference for the design of high-efficiency narrow-band gap materials in the field of solid-state lighting.

Fabrication and interface properties of amorphous Ga2O3/GaAs heterojunction

Heterojunctions based on the combination of wide and narrow bandgap materials provide a basis for realizing high-performance electronic and optoelectronic devices. So, it is crucial to study the interface properties of heterojunctions. Inspired by this idea, an ultra-wide bandgap Ga2O3 film was grown on a narrow bandgap GaAs by atomic layer deposition (ALD) in this work. The morphology was analyzed by atomic force microscope (AFM), showing an excellent uniformity of the film. The thickness of Ga2O3 film was estimated to be 80 nm by Ellipsometry, and its unique adsorption in the solar blind wavelength range was also investigated. X‐ray photoelectron spectroscopy (XPS) was used to characterize the band alignment, and elememtal composition. The value of the valence band offset was 3.15 ± 0.04 eV, and the conduction band offset was 0.25 ± 0.02 eV. The work functions of Ga2O3, and GaAs were calculated by first principles based on density functional theory (DFT), building the carrier immigration mode at the interface of Ga2O3/GaAs heterojunction combined with the band alignment. The band configurations of Ga2O3/GaAs heterojunction illustrate the possibility of realizing high-speed photodetectors. Furthermore, the band offset provides the reference value of barrier height, facilitating the design of electronic and optoelectronic devices based on this heterojunction.

Crystal surfaces cooperate with F ion migration to improve the photocatalytic performance of Z-type Ag-Ag2S/F-TiO2 composites

The TiO2 has the problems of low utilization of visible light and high photogenerated carrier recombination rate. The photocatalytic activity of TiO2 can be significantly improved by introducing F ion and narrow band gap material Ag2S. When F ions are present on the {001} surface of TiO2, surface F ions drive positively charged holes across the {001} surface, creating a synergistic effect that promotes the separation of electron-hole pairs. During the sample composite process, a certain amount of Ag will be precipitated to form an all-solid Z-type heterojunction structure of Ag2S, Ag and F-TiO2, which can improve the electron-hole separation efficiency. The results of XPS characterization confirmed the migration of F ion and the precipitation of Ag. The Ag2S/F-TiO2 composite sample was referred to as AT for short, and the corresponding ratio was 1:10,1:20,1:30,1:40, the optimal sample AT 1:20 degraded 95.6% tetracycline hydrochloride within 2 hours. This work simultaneously realizes TiO2 self-modification (synergistic effect of F ion migration and TiO2{001} crystal surface) and composite modification (formation of all-solid Z-type heterojunction), a new idea of studying TiO2 self-modified cooperative heterostructures is proposed, and the good application potential of AT nanocomposites in photocatalytic water treatment technology is demonstrated.

Poly-Si/a-Si/4H-SiC p-n heterojunction broadband photodetector prepared by magnetron sputtering

With the increasing complexity of scenarios, there is a growing need for broadband photodetectors (PDs). In this work, we report a polycrystalline-Si (poly-Si)/amorphous-Si (a-Si)/4H-SiC p-n heterojunction PD with efficient response in a broad spectral range of ultraviolet–visible–near-infrared. The poly-Si/a-Si/4H-SiC heterojunction was achieved by magnetron sputtering and annealing. The fabricated heterojunction device has a low dark current of 1 pA at −40 V and a fast response time of 3 ns due to the outstanding rectification characteristics of the heterojunction combined with narrow bandgap and wide bandgap material. In addition, the carrier behavior of the heterojunction exposed to broadband light is analyzed in detail by constructing the energy band diagram.

A General Strategy for Enhancing Sensitivity and Suppressing Noise in Infrared Organic Photodetectors Using Non‐Conjugated Polymer Additives

AbstractPhotodetectors operating across the near‐ to short‐wave infrared (NIR–SWIR, λ = 0.9–1.8 µm) underpin modern science, technology, and society. Organic photodiodes (OPDs) based on bulk‐heterojunction (BHJ) active layers overcome critical manufacturing and operating drawbacks inherent to crystalline inorganic semiconductors, offering the potential for low‐cost, uncooled, mechanically compliant, and ubiquitous infrared technologies. A constraining feature of these narrow bandgap materials systems is the high noise current under an applied bias, resulting in specific detectivities (D*, the figure of merit for detector sensitivity) that are too low for practical utilization. Here, this study demonstrates that incorporating wide‐bandgap insulating polymers within the BHJ suppresses noise by diluting the transport and trapping sites as determined using capacitance‐frequency analysis. The resulting D* of NIR–SWIR OPDs operating from 600–1400 nm under an applied bias of −2 V is improved by two orders of magnitude, from 108 to 1010 Jones (cm Hz1/2 W−1), when incorporating polysulfone within the blends. This broadly applicable strategy can reduce noise in IR‐OPDs enabling their practical operation and the realization of emerging technologies.

Machine learning guided rapid discovery of narrow-bandgap inorganic halide perovskite materials

Machine learning guided rapid discovery of narrow-bandgap inorganic halide perovskite materials

Design and implementation of an infrared artificial visual neural synapse based on a p-WSe2/n-Ta2NiS5 van der Waals heterojunction

Inspired by human visual synapses, high performance and versatile infrared vision synapses can be achieved in the p-WSe2/n-Ta2NiS5 van der Waals heterojunction by introducing narrow band gap materials and bias-induced band bending.

The growth of Ge and direct bandgap Ge1-xSnx on GaAs (001) by molecular beam epitaxy.

Germanium tin (GeSn) is a tuneable narrow bandgap material, which has shown remarkable promise for the industry of near- and mid-infrared technologies for high efficiency photodetectors and laser devices. Its synthesis is challenged by the lattice mismatch between the GeSn alloy and the substrate on which it is grown, sensitively affecting its crystalline and optical qualities. In this article, we investigate the growth of Ge and GeSn on GaAs (001) substrates using two different buffer layers consisting of Ge/GaAs and Ge/AlAs via molecular beam epitaxy. The quality of the Ge layers was compared using X-ray diffraction, atomic force microscopy, reflection high-energy electron diffraction, and photoluminescence. The characterization techniques demonstrate high-quality Ge layers, including atomic steps, when grown on either GaAs or AlAs at a growth temperature between 500-600 °C. The photoluminescence from the Ge layers was similar in relative intensity and linewidth to that of bulk Ge. The Ge growth was followed by the growth of GeSn using a Sn composition gradient and substrate gradient approach to achieve GeSn films with 9 to 10% Sn composition. Characterization of the GeSn films also indicates high-quality gradients based on X-ray diffraction, photoluminescence, and energy-dispersive X-ray spectroscopy measurements. Finally, we were able to demonstrate temperature-dependent PL results showing that for the growth on Ge/GaAs buffer, the direct transition has shifted past the indirect transition to a longer wavelength/lower energy suggesting a direct bandgap GeSn material.

High‐Performance Photodetector Based on Bi2Se3/GeSe Heterojunction with Band Alignment Evolution

AbstractBand alignment engineering in 2D van der Waals heterostructures is a promising method for manufacturing high‐speed, high‐responsivity, and high‐gain photodetectors. Here, a heterojunction photodetector with the band alignment transition from type I to type II under the bias voltage using narrow bandgap material n‐Bi2Se3 and polarization‐sensitive material p‐GeSe is designed and prepared. This photodetector possesses excellent performance of broadband detection (532‐1550 nm), high responsivity (5.86 × 103 A W−1), high detectivity (1.50 × 1013 Jones), significant external quantum efficiency (1.15 × 106%) and fast response time (97 µs). Compared with the conventional type II band alignment, an additional triangular potential barrier is generated in this type II band alignment evolved from type I. Notably, this triangular barrier will block photogenerated carriers in Bi2Se3, which leads to high external quantum efficiency; Furthermore, photogenerated holes can tunnel through this barrier, effectively shortening the response time. Meanwhile, the device can achieve polarization detection (anisotropic ratio = 1.74 at 808 nm) and polarization imaging, which is of great significance for reducing the bit error rate in complex environments.