Semiconductor Layers Research Articles

Electrical characterization of Ag/MoO3−x/p-Si Schottky diodes based on MoO3−x synthesized via sol–gel method: an investigation on frequency and voltage dependence

MoO3−x is a commonly used buffer layer in organic based optoelectronic devices to align energy level between active semiconductor and metal layer. The purpose of this study is to show the effects of the MoO3−x interlayer by comparing with a reference device without MoO3−x interlayer. To evaluate the effect of MoO3−x interlayer synthesized by sol–gel method, basic important parameters such as ideality factor (n), barrier height (∅\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varnothing$$\\end{document}B), interface states (Nss) and series resistance (Rs) of Ag/MoO3−x/p-Si and Ag/p-Si Schottky diodes were calculated by electrical characterization methods. The current–voltage (I–V) measurements show that the ideality factor for the p-Si/Ag reference diode was decreased from 2.4 to 1.9 while rectification factor increasing 44.6 times using MoO3−x interlayer, and frequency–dependent measurements (C–V–f, G–V–f) were carried out to elucidate this deviation at room temperature for MoO3−x-based diode. From the XPS analysis, it was seen that Mo+6 and Mo+5 oxidation states were intense on the surface of the MoO3−x film, and the Mo+4 oxidation state increased as it went into the bulk. The changes in Rs and Nss due to the energy levels formed by the Mo+6 and Mo+5 oxidation steps at the interface are depicted. In addition, the energy density distribution profile of Nss was obtained using the I–V characteristics for various forward bias voltages range from 2.1 × 1012 to 2.5 × 1012 eV−1 cm−2. Based on the experimental results, the sol–gel synthesized MoO3−x thin film exhibits favorable rectification characteristics and holds promise for application as a Schottky diode.

Bimetal Thin Film, Semiconductors, and 2D Nanomaterials in SPR Biosensors: An Approach to Enhanced Urine Glucose Sensing.

This work introduces a systematic approach for the development of Kretschmann configuration-based biosensors designed for non-invasive urine glucose detection. The methodology encompasses the utilization of various semiconductors, including Silicon (Si), Germanium (Ge), Gallium Nitride (GaN), Aluminum Nitride (AlN), and Indium Nitride (InN), in combination with a bimetallic layer (comprising Au and Ag films of equal thickness) to enhance the biosensor sensitivity. Additionally, 2D nanomaterials, such as Black Phosphorus and Graphene, are integrated into the semiconductor layers to enhance performance further. These configurations are meticulously optimized through the application of the transfer matrix method (TMM), and the sensing parameters are assessed using the angular modulation method. Among the semiconductors, AlN and GaN exhibit superior results. On these substrates, Graphene and Black phosphorous (BP) layers are applied, resulting in four final structures (thicknesses in nm): BK7/Au(26)/Ag(26)/Si(6)/BP(0.53)/Biosample, BK7/Au(26)/Ag(26)/AlN(14)/BP(0.53)/Biosample, BK7/Au(26)/Ag(26)/GaN(12)/BP(0.53)/Biosample, and BK7/Au(26)/Ag(26)/GaN(12)/Graphene(0.34)/Biosample. These biosensors achieve Sensitivity(° /RIU) and Figure of Merit (FoM) (1/RIU) of 380, 360, 440, 400, and 58.5, 90, 90.65, and 82.4, respectively. Subsequently, these high-performing sensors undergo testing with actual urine glucose samples. Among them, two biosensors, BK7/Au(26)/Ag(26)/AlN(14)/BP (0.53)/Biosample and BK7/Au(26)/Ag(26)/GaN(14)/Graphene(0.34)/Biosample, exhibit outstanding performance, with sensitivities (° /RIU) and FoM (1/RIU) of 394.44 & 294.44, and 112.6 & 92.01 respectively. A comparison is also made with relevant previously published work, revealing improved performance in glucose detection.

A minimalist approach to 3D photoemission orbital tomography: algorithms and data requirements

Photoemission orbital tomography provides direct access from laboratory measurements to the real-space molecular orbitals of well-ordered organic semiconductor layers. Specifically, the application of phase retrieval algorithms to photon-energy- and angle-resolved photoemission data enables the direct reconstruction of full 3D molecular orbitals without the need for simulations using density functional theory or the like. However, until now this procedure has remained challenging due to the need for densely-sampled, well-calibrated 3D photoemission patterns. Here, we present an iterative projection algorithm that completely eliminates this challenge: for the benchmark case of the pentacene frontier orbitals, we demonstrate the reconstruction of the full orbital based on a dataset containing only four simulated photoemission momentum measurements. We discuss the algorithm performance, sampling requirements with respect to the photon energy, optimal measurement strategies, and the accuracy of orbital images that can be achieved.

Photophore-Anchored Molecular Switch for High-Performance Nonvolatile Organic Memory Transistor.

Over the past decade, molecular-switch-embedded memory devices, particularly field-effect transistors (FETs), have gained significant interest. Molecular switches are integrated to regulate the resistance or current levels in FETs. Despite substantial efforts, realizing large memory window with a long retention time, a critical factor in memory device functionality, remains a challenge. This is due to the inability of an isomeric state of a molecular switch to serve as a stable deep trap state within the semiconductor layer. Herein, the study addresses this limitation by introducing chemical bonding between molecular switch and conjugated polymeric semiconductor, facilitating closed isomer of diarylethene (DAE) to operate as a morphologically stable deep trap state. Azide- and diazirine-anchored DAEs are synthesized, which form chemical bonds to the polymer through photocrosslinking, thereby implementing permanent and controllable trapping states nearby conjugated backbone of polymer semiconductor. Consequently, when diazirine-anchored DAE is blended with F8T2 and subjected to photocrosslinking, the resulting organic FETs exhibit remarkable memory performance, including a memory window of 22 V with a retention time over 106 s, a high photoprogrammable on/off ratio over 103, and a high operational stability over 100 photocycles. Further, photophore-anchored DAEs can achieve precise patterning, which enables meticulous control over the semiconductor layer structure.

Robust Dipolar Layers between Organic Semiconductors and Silver for Energy-Level Alignment.

The interface between a metal electrode and an organic semiconductor (OS) layer has a defining role in the properties of the resulting device. To obtain the desired performance, interlayers are introduced to modify the adhesion and growth of OS and enhance the efficiency of charge transport through the interface. However, the employed interlayers face common challenges, including a lack of electric dipoles to tune the mutual position of energy levels, being too thick for efficient electronic transport, or being prone to intermixing with subsequently deposited OS layers. Here, we show that monolayers of 1,3,5-tris(4-carboxyphenyl)benzene (BTB) with fully deprotonated carboxyl groups on silver substrates form a compact layer resistant to intermixing while capable of mediating energy-level alignment and showing a large insensitivity to substrate termination. Employing a combination of surface-sensitive techniques, i.e., low-energy electron microscopy and diffraction, X-ray photoelectron spectroscopy, and scanning tunneling microscopy, we have comprehensively characterized the compact layer and proven its robustness against mixing with the subsequently deposited organic semiconductor layer. Density functional theory calculations show that the robustness arises from a strong interaction of carboxylate groups with the Ag surface, and thus, the BTB in the first layer is energetically favored. Synchrotron radiation photoelectron spectroscopy shows that this layer displays considerable electrical dipoles that can be utilized for work function engineering and electronic alignment of molecular frontier orbitals with respect to the substrate Fermi level. Our work thus provides a widely applicable molecular interlayer and general insights necessary for engineering of charge injection layers for efficient organic electronics.

Introduction thioindigo as new high stability unit in Ru-complex for DSSCs: Theoretical and photovoltaic investigation

New Ru-dyes were designed with indoline and thioindigo groups for dye-sensitized solar cells (DSSCs). Thioindigo was used as an effective substitute for improving fastness properties, and the synthesis efficiency of dyes 1 and 2 was 78 and 82 %, respectively. Cyanoacrylic acid is a suitable electron-withdrawing group in the preparation of photosensitizers, which improved the conversion efficiency by about 88 % in this research. The optical response of the complexes was evaluated theoretically and experimentally. The presence of cyano groups effectively bonds with the semiconductor layer, resulting in a better photovoltaic response. Furthermore, the prepared complexes have two types of electron withdrawing groups, carboxylic acid and cyanoacrylic acid, which yield 3.29 % and 6.23 % efficiency, respectively. In addition, co-sensitization using two prepared complexes and N719 was studied and analyzed. The efficiency of DSSCs prepared with N719 and complexes 1 and 2 was 8.10 and 9.49 %, respectively.

High Performance Amorphous IGO Thin Film Transistors Grown at Low Temperature

Polycrystalline indium gallium oxide has been widely studied in the domain of oxide thin film transistors (TFTs) due to its high mobility. However, there are few researches focus on amorphous IGO (a‐IGO), which has the advantage of large area display. Herein, high‐performance a‐IGO TFTs are demonstrated by magnetron sputtering method with simple process. The efficiency of a‐IGO TFTs fabricated under various conditions are evaluated, and a‐IGO TFTs prepared by 27 nm thin films grown at 220 °C have the best electrical properties. It exhibits the mobility of 35 cm2 V−1 s−1, threshold voltage of 0.5 V, subthreshold swing of 0.8 V dec−1, and the on/off current ratio over 106. This is due to the precise control of the deposition energy state by temperature during sputtering and the influence of the semiconductor layer thickness on the distribution of the accumulation layer. The results present here demonstrate a simple fabrication method for high‐performance amorphous oxide TFT, providing a new option for display driver circuits.

Inorganic-Organic Hybrid Layered Semiconductor AgSePh: Quasi-Solution Synthesis, Optical Properties, and Thermolysis Behavior.

Two-dimensional inorganic-organic hybrid layered semiconductors are actively studied because of their naturally formed multiquantum well (MQW) structures and associated optical, photoelectric, and quantum optics characteristics. Silver benzeneselenolate (AgSePh, Ph = C6H5) is a new member of such hybrid layered materials, but has not fully been exploited. Herein, we present a quasi-solution method to prepare high quality free-standing AgSePh flake-like microcrystals by reacting diphenyl diselenide (Ph2Se2) with silver nanoparticles. The resultant AgSePh microflakes exhibit room-temperature (RT) resolvable MQW-induced quasi-particle quantization and interesting optical properties, such as three distinct excitonic resonance absorptions X1 (2.67 eV), X2 (2.71 eV), and X3 (2.83 eV) in the visible region, strong narrow-line width blue photoluminescence at ∼2.64 eV (470 nm) from the radiative recombination of the X1 exciton state, and a large exciton binding energy (∼0.35 eV). Furthermore, AgSePh microcrystals show high stability under water, oxygen, and heat environments, while above 220 °C, they will thermally decompose to silver and Ph2Se2 as evidenced by a combination of thermogravimetry and differential scanning calorimetry and pyrolysis-coupled gas chromatography-mass spectrometry studies. Finally, a comparison is extended between AgSePh and other metal benzeneselenolates, benzenethiolates, and alkanethiolates to clarify differences in their solubility, decomposition/melting temperature, and pyrolytic products.

Tunability of the photoelectric properties of CdSe thin films through doping with manganese toward photovoltaic applications

Tandem solar cells have been demonstrated to surpass the Shockley-Queisser limit, promising the transition to third-generation solar cell technology. Tandem solar cells comprise thin film layers of various band gap semiconductors, and CdSe is a promising candidate for the top cell. In this study, we explore the properties of thermally evaporated CdSe thin films doped with 0 to 5 wt% Mn and report a significant five-fold increase in carrier concentration. Furthermore, our optoelectrical studies indicate a band gap energy of 1.681eV, experiencing up to a 28 meV shift with 5 wt% Mn doping and identifies 1 wt% as the optimal doping concentration, offering the best electrical properties and photo-response while maintaining a stable band gap.

Inheritance of the exciton geometric structure from Bloch electrons in two-dimensional layered semiconductors

Inheritance of the exciton geometric structure from Bloch electrons in two-dimensional layered semiconductors

Interface polarity brings a way to modulate magneto-optical effect of cubic Ni2+/Fe3+ co-doped Bi25FeO40 film: Implications in piezoelectricity

Cubic Sillenite Bi25FeO40 (BFO) could become a new magneto-optical material due to its high concentration of Bi3+ and no birefringence. But its weak magnetism causes the magneto-optical properties to be far from the requirements of practical applications. Doping magnetic Fe3+ and Ni2+ ions to improve the magnetism and magneto-optical properties of BFO (Bi19Ni2.8Fe4.2O40) film on fluorine-doped tin oxide (BNFO/FTO) is discussed in this paper. Another focus of this paper is to discuss the magneto-optical properties modulated by the electric field. The cubic BNFO film has weak piezoelectric effects, which makes it difficult to modulate its magneto-optical effect by electric field. A polarity symmetry induced by the Schottky junction between Au metal layer and BNFO semiconductor layer (Au/BNFO) compensates for cubic symmetry, and the piezoelectric effect can be improved. By applying an electric field, its magnetic circular dichroism (MCD) ellipticity |ΨF| gradually decreases as a direct current voltage from 0 V to 10 V in a magnetic field of 2500 Oe, demonstrating the feasibility of this strategy. These results indicate a new way for highly symmetric magneto-optical materials to modulate magneto-optical effects in electric fields.

Environmental Effects on the Performance of Small‐Molecule Organic Thin‐Film Transistors

AbstractElectrical measurements are performed on a bottom‐gate bottom‐contact organic thin‐film transistor with 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl) anthradithiophene (diF‐TES ADT) (diF‐TES ADT) as the active layer, varying the relative humidity of the environment surrounding the transistor. The results strongly indicate that water negatively impacts the electrical performance of the transistor and that the ingress of water is dynamic provided that the organic semiconductor layer is not encapsulated. It is found that the change can be reversed and the performance restored by removing the source of water. The drain current and threshold voltage of the transistor varied linearly when the relative humidity is changed from 35% to 7%, suggesting that the transistor can be used as a humidity sensor.

Layered Wide Bandgap Semiconductor GaPS4 as a Charge‐Trapping Medium for Use in High‐Temperature Artificial Synaptic Applications

AbstractArtificial synaptic devices (ASDs) are attracting widespread attention as highly promising components for use in complex neuromorphic systems, playing crucial roles in addressing the challenges posed by the conventional von Neumann architecture. However, the instabilities of ASDs in high‐temperature environments diminish the reliabilities of the device performances, significantly inhibiting their practical application. Herein, a highly reliable 2D MoS2/GaPS4 ASD that maintains its functionality even after exposure to 400 °C is proposed. Moreover, due to the enhanced charge‐trapping effect of the GaPS4 layer, the memory window expands from an initial 42 to 55 V, accompanied by a substantial on/off ratio of 105, low off‐leakage current of 10−11 A, and high number of endurance cycles (103). The device effectively simulates various biological synaptic functions via electric and light stimulation. Notably, the high electric and light paired‐pulse facilitation indices suggest an exceptional synaptic performance. The findings introduce a novel approach to high‐temperature neuromorphic applications via defect engineering.

Novel copper(II) phthalocyanines as semiconductor layer in organic field effect transistors: Synthesis and investigation of electrical properties

New two tetra-peripheral/non-peripheral substituted copper(II)-phthalocyanines have been synthesized and characterized by using ATR-IR, MALDI-TOF/MS and UV–Vis spectroscopy. The electrical characterization and conducting properties of copper(II)-phthalocyanine compounds have been achieved in order to determine their use as a semiconductor layer in organic field effect transistors (OFETs). The OFETs characterization has been performed and the tetra-peripheral/non-peripheral substituted copper(II)-phthalocyanines OFET carrier mobility of about 1.31×10−3 cm2/V.s and 1.42×10−3 cm2/V.s, respectively. On/off current ratio of ∼103 and ∼102; threshold voltage of (-30 V, -32 V), respectively were measured.

Electrochemical impedance spectroscopy analysis of dye-sensitized solar cells composed of electrospun composite photoanodes: A comparative study of natural and synthetic sensitizers

In this study, a transmission line model is applied to the electrochemical impedance spectroscopy (EIS) data of the fabricated dye-sensitized solar cells (DSSCs) to evaluate the charge transfer mechanism through the cells. Natural dye from black plum (Syzygium cumini) fruit was used as a cell sensitizer (SC-DSSC) and compared its photovoltaic and electron transport capabilities to those of a cell using a synthetic sensitizer (N719-DSSC). TiO2/ZnO electrospun composite nanofibers were used as the semiconductor layer of the photoanode to enhance electron transfer. The EIS analysis revealed the role of electron resistances through shant, interfaces, and electrolyte solution by measuring the electron transfer kinetic parameters of each element. Based on the results, the SC-DSSC and N719-DSSC are appropriate photovoltaic cells because their ratios of effective electron diffusion length to photoanode thickness are 12.5 and 2.8, respectively. The EIS analysis showed that the electrospun composite nanofiber coated on the photoanode reduces the semiconductor layer's electrical resistance to the cell's total resistance. The extracted natural dye also boosted electron lifetime to 3.68 ms and diffusion coefficient to 54.3×10−6 m2/s while minimizing back-electron recombination at the semiconductor-electrolyte interface. Moreover, the semiconductor-electrolyte interface resistance is over 85% of the overall resistance for both DSSCs and controls electron transport through the cells, which is due to the dye-semiconductor binding intensity. Based on the photovoltaic data, the SC-DSSC cell efficiency was lower than N719-DSSC which is attributed to its higher electron transfer rate-controlling element. Thus, enhancing dye-semiconductor interactions will decrease the rate-controlling impedance and enhance cell performance.

Defect and doping properties of sliding ferroelectric γ-InSe for photovoltaic applications

Layered van der Waals (vdw) materials have been proposed as light-absorbing materials for photovoltaic applications. InSe is a layered vdw semiconductor with ultra-high carrier mobility, strong charge transfer ability, super deformability, thermoelectricity, and optoelectronic properties. Its γ phase, or γ-InSe, was greatly stabilized by doping recently, which also exhibits sliding ferroelectricity. In this study, we propose that γ-phase InSe (γ-InSe), which was recently synthesized in a high-quality bulk phase, could be an excellent light-absorbing material candidate. Based on the first-principles simulations, bulk γ-InSe is found to possess suitable bandgap, decent absorption, and low effective mass. The investigation of defect properties reveals the major defect types, defect levels, and deep-level defects that could possibly harm the efficiency, and the deep-level defects can be significantly suppressed under Se-rich conditions. In addition, γ-InSe is intrinsically n-type, which can be tuned into weak p-type by Zn and Cd doping. We also identify the defect types of Y and Bi doping, which have been experimentally used to adjust the mechanical property of γ-InSe, and find that Y interstices could play an important role in improving the stiffness of γ-InSe. Our study provides theoretical insights for photovoltaic and other photoelectronic applications based on this interesting ferroelectric layered vdw material.

Design and optimization of a high efficiency CdTe–FeSi2 based double-junction two-terminal tandem solar cell

This article theoretically demonstrates an enormously efficient CdTe–FeSi2 based dual-junction tandem solar cell accompanied by slender semiconductor layers. The peak efficiency of the device has been ensured through the optimization of its various attributes of window, CdTe (bandgap 1.5 eV) top absorber, FeSi2 (bandgap 0.87 eV) bottom absorber and back surface layers. Additionally, the impacts of thickness, doping and the level of defects in different window, base and rear surface layers have been examined to observe how different layers affect the solar cell's performance. The optimized n-CdS/p-CdTe/p+-MoS2--n-CdS/p-FeSi2/p+-Cu2SnS3 dual-junction tandem solar device displays an efficiency of 43.9% with a voltage at no load, VOC of 1.928 V, current density under a closed circuit, JSC of 25.34 mA/cm2, and fill factor of 89.88%, respectively. These results disclose the high potential of the suggested solar cell based on CdTe and FeSi2 compounds.

Effect of source and drain electrode positions on the performance of bottom gate organic thin film transistor

In recent years several novel technologies have emerged on commercial level. Organic electronics is one such technology that has created new avenues for the development of flexible, robust, and cost-effective electronic devices. Transistor developed using organic materials are called organic thin film transistors (OTFT). Transistor is elementary component of any electronic device, any variation in the size or performance of the transistors reflects directly on the overall performance of the electronic devices. Bottom gate bottom contact (BGBC) OTFT is commonly employed single gate organic transistor owing to its simple architecture and easy fabrications. Since in organic semiconductor material carrier mobility of charges is lower, hence its overall performance declines. As a result, its application in electronic circuits becomes limited. Therefore, to enhance the performance of BGBC OTFT and facilitate the optimal charge mobilisation inside organic semiconductor layer i.e., OSC, improvement in the architecture of BGBC is deemed necessary. In this research article the performance of BGBC OTFT is analysed for different positions of electrodes viz. source and drain embedded inside the OSC layer. The study signifies the effect of electrode positions on performance optimization of BGBC OTFT without changing the materials, dimensions, or the operating voltage regime. It has been found that for 30 nm thick OSC layer, the electrodes should ideally be placed between 5 nm to 10 nm above the junction of OSC and dielectric layer inside OSC layer for optimal results.

The Performance of Organic Field Effect Transistor Affected by Different Thickness of Active Semiconductor Layer and Thickness of Gate Insulator

The purpose of this paper is to fabricate organic field effect transistor and to investigate the effect of the thickness of the pentacene active layer and the thickness of gate insulator layer on MOSFET performance. The fabricated structure is top-contact. When the thickness of the insulator gate layer increases from 10 nm to 30 nm, the magnitude of the drain source current, when VGS = VDS = -4 V, decreases from 1813 nA to 214 nA and then the threshold voltage shifts from -1.4 V to -2.4 V. When the thickness of the pentacene increases from 9 nm to 40 nm, the threshold voltage voltage shifts slightly in the negative direction from -1.4 V to -1.6 V for SiO2 thickness of 10 nm. In case of SiO2 thickness of 20 nm, the threshold voltage voltage shifts from -1.9 V to -2.2 V. In case of SiO2 thickness of 30 nm, the threshold voltage voltage shifts from -2.4 V to -2.9 V. Besides that, the mobility decreases from around 0.31 cm2/(Vs) to 0.15 cm2/(Vs) when the pentacene thickness increases from 9 nm to 40 nm.

Roles of chalcogen sublayers of 1H transition metal dichalcogenides in metal-semiconductor van der Waals heterostructures

In this paper, the crystal and electronic structures are investigated using first-principles theory for metal-semiconductor van der Waals heterostructures 1H-transition-metal dichalcogenides (NbS2, NbSe2, TaS2, TaSe2, MoS2, MoSe2, WS2, and WSe2). The theoretical investigations reveal that chalcogen sublayers play crucial roles in the crystal and electronic structures though these sublayers are minor parts in the pristine crystals. Actually, selenide sublayers energetically stabilize the commensurate heterobilayers, whereas moiré structure gives a much lower electronic energy with sulfide sublayers. Moreover, the chalcogen sublayers dominate the charge distribution via the difference of work functions in the component layers, i.e., the charge transfer between the metallic and semiconducting layers in the heterobilayers. The theoretical results suggest that the chalcogen sublayers can be the key to control the crystal and electronic structures in the metal-semiconductor vdW heterostructure of TMDC monolayers. Published by the American Physical Society 2024