Semiconductor Layers Research Articles

High Mobility, High Carrier Density SnSe2 Field‐Effect Transistors with Ultralow Subthreshold Swing and Gate‐Controlled Photoconductance Switching

Abstract2D and layered semiconductors are considered as promising electronic materials, particularly for applications that require high carrier mobility and efficient field‐effect switching combined with mechanical flexibility. To date, however, the highest mobility has been realized primarily at low carrier concentration. Here, it is shown that few‐layer/multilayer SnSe2 gated by a solution top gate combines very high room‐temperature electron mobility (up to 800 cm2 V−1s−1), along with large on‐off current ratios (>105) and a subthreshold swing below the thermodynamic limit (50 mV per decade) in field‐effect devices, at exceptionally large sheet carrier concentrations of ≈1013 cm−2. Observed mobility enhancements upon partial depletion of the channel point to near‐surface defects or impurities as the mobility‐limiting scattering centers. Under illumination, the resulting gap states give rise to gate‐controlled switching between positive and negative photoconductance. The results qualify SnSe2 as a promising layered semiconductor for flexible and wearable electronics, as well as for the realization of advanced approaches to photodetection.

Nanoscale Mapping of Carrier Distribution Regulated by Polarization in 2D FeFETs.

The emergence of 2D ferroelectrics, sliding ferroelectrics, and 2D ferroelectric semiconductors has greatly expanded the potential applications of two-dimensional ferroelectric field-effect transistors (2D FeFETs) in nonvolatile memory, neuromorphic synapses, and negative capacitance. However, the interaction between ferroelectric and semiconductor layers remains not well understood, and characterization methods to correlate carriers and polarization dynamics at the nanoscale are still lacking. Utilizing in situ scanning microwave impedance microscopy and piezoresponse force microscopy measurements, we employed a Pb(Zr0.2Ti0.8)O3/MoS2-based 2D FeFET as an example to reveal, with high spatial resolution, the microscopic redistribution of carriers. This study uncovers the microscopic behavior of ferroelectric-semiconductor heterojunctions, paving the way for a deeper understanding of ferroelectric-gating effects and retention issues at the nanoscale in 2D FeFETs.

Research on the Carrier Characteristics of Power Cables Considering the Aging Status of Insulation and Semiconducting Layers

The 10 kV XPLE cable is widely used in highly cabled transmission and distribution networks. It is necessary to closely monitor the transient current, harmonic content, and electric field distribution of each layer of the insulation and semiconductive layers of the cable when they age and deteriorate, so as to promptly carry out circuit breaking treatment and prevent safety accidents. Considering the frequency sensitivity and dielectric sensitivity of the distributed Runit, Lunit, Gunit, and Cunit parameters of long cables, this paper quantitatively analyzes the frequency variation of 10 kV cable parameters under different aging states. Reconstructing the frequency variation process of typical electrical quantities through MATLAB PSCAD joint simulation, constructing fault circuits for cable insulation and semiconducting layers, obtaining transient currents in each layer of the cable under aging conditions, and conducting total harmonic distortion (THD) analysis to provide theoretical guidance for the subsequent monitoring and fault diagnosis of distribution cable status.

Enhancement of Synaptic Behavior in Organic Electrochemical Transistors via the Introduction of Layer‐by‐Layer Grown Metal‐Organic Framework

AbstractOrganic electrochemical transistors (OECTs) are promising for neuromorphic architectures as they can generate multiple electrical states through the control of ion transport. However, conventional OECTs face limitations in mimicking a fully functional biological synapse due to their inability to achieve long‐term plasticity. In this study, a metal‐organic framework (MOF)‐enhanced OECT (MOECT) is fabricated by introducing MOF into the ion‐organic semiconductor (OSC) layer. MOFs are synthesized using the layer‐by‐layer (LBL) method, and additional cross‐linked OSC is introduced to prevent damage to the semiconductor layers during synthesis. The synthesized MOF layers hinder the rediffusion of ions in OECT, allowing ions to remain in the OSC for an extended period. In this study, the MOECT showed a change in current depending on the doping level, recording a current state 4.4 × 107 times higher than that of pristine OECT. Ultimately, the developed MOECTs are applied as synaptic transistors. MOECTs show 14% higher excitatory postsynaptic current (EPSC) after 130 s compared to pristine OECT, thereby strengthening the long‐term plasticity characteristics of neuromorphic devices. This method enhances the performance of synaptic transistors by introducing MOF, offering various possibilities through the selection of different MOF structures and ions, indicating it is a methodological approach with high potential.

The Impact of Non‐Monolithic Semiconductor Capacitance on Organic Electrochemical Transistors Performance and Design

AbstractThe existing device models for organic electrochemical transistors (OECTs) fail to provide any device design guidelines for optimized performance parameters such as transconductance that are pivotal for the applications OECTs in sensing. Moreover, the current models are based on the questionable assumption of a homogenous organic semiconductor layer, and all predict a linear behavior of the resistance with the OECT channel length. Consequently, the experimentally observed nonlinear resistance behavior in OECTs has been overlooked thus far. Here, an OECT device model is developed that accurately describes the nonlinear behavior of the OECT channel resistance and offers the first guidelines for maximizing transconductance. The model is inherently nonlinear and the nonlinearity stem from the non‐monolithic capacitance of the organic semiconductor layer. Moreover, the model provides a consistent and reliable estimations for the contact resistance in OECTs. The success of the model in accurately describing and providing predictions of the OECT operation by relating the device's geometrical parameters with electrochemical parameters of the semiconductor layer paves the way toward unlocking OECT potentials in diverse applications, from biosensing to neuromorphic computing and flexible electronics.

Quasi-particle Propagation Across Semiconductor–Mott Insulator Interfaces

As a prototypical example for a heterostructure combining a weakly and a strongly interacting quantum many-body system, we study the interface between a semiconductor and a Mott insulator. Via the hierarchy of correlations, we derive and match the propagating or evanescent (quasi) particle solutions on both sides and assume that the interactions among the electrons in the semiconducting regions can be absorbed by an effective potential. While the propagation is described by a band-like dispersion in both the weakly and the strongly interacting case, the inverse decay length across the interface follows a different dependence on the band gap in the Mott insulator and the semiconductor. As one consequence, tunnelling through a Mott insulating layer behaves quite differently from a semiconducting (or band insulating) layer. For example, we find a strong suppression of tunnelling for energies in the middle between the upper and lower Hubbard band of the Mott insulator.

Atom-Vacancy-Defect-Derived Electric Hysteresis Loops and Stochastic Low-Frequency Noises in Few-Atom Layer MoS2.

Atom-vacancy-defects present in various materials yield numerous interesting physical phenomena, even obstructing high performance in some cases. On the other hand, their valuable applications to novel devices, such as nitrogen vacancy centers in diamond for quantum bits, have gathered significant attention. In particular, these tendencies become more substantial in two-dimensional (2D) (atomically) thin van der Waals layers. However, correlations with various kinds of atom defects are still under exploration. Herein, we find the stochastic behaviors of large hysteresis loops with strong photoresponse in the static electrical properties in few-atom layer semiconductors, molybdenum disulfide (MoS2). The temperature dependence and transmission electron microscopy reveal that they arise from pairs of two neighboring in-plane S-vacancy defects, which predominantly present only around the interface at the MoS2 flake/substrate, with activation energies ∼0.35 eV. The low-frequency (f) (LF) noise measurements clarify a high f shift in the two 1/f2-dependent regimes, implying stochastic behaviors of electric charges through the S-vacancy pairs with high-speed charge(spin) transitions across low kinetic energy barriers between narrow discrete states. The shallow energy sates are formed from the highly uniform S-vacancy pairs interacting with Mo atoms, which act like quantum dots. The observed stochastic operation holds promise for various application, particularly for probabilistic neuromorphic computation in artificial intelligence.

Heterogeneous Integration of Complementary Field-Effect Transistors for High-Performance Micro LED Displays.

This study investigates a micro light-emitting diode (µLED) pixel circuit using the heterogeneous integration of complementary field-effect transistors (CFETs). The CFETs are fabricated using a semiconductor layer composed of tellurium (Te) and indium-gallium-zinc oxide (IGZO) layers. Te and IGZO layers in the heterostructure IGZO/Te film exhibit hexagonal and amorphous phases, respectively, indicating that each layer maintains independent material characteristics. The fabricated IGZO/Te CFETs exhibit ambipolar behavior with a turn-on voltage of 2.0V and field-effect mobility of 0.74 and 1.42 cm2 V-1 s-1 for p-type and n-type channels, respectively. Inverters comprising IGZO/Te CFET and IGZO TFT exhibit inverting behavior. A µLED pixel circuit is designed using IGZO/Te CFETs based on pulse width modulation (PWM). The proposed circuit uses an inverter structure with IGZO/Te and IGZO to control the emission time, suppressing the wavelength shift of µLEDs depending on the µLED current levels. The operation of the proposed pixel circuit is investigated through simulation and measurement of the fabricated circuit. The fabricated µLED pixel circuit successfully exhibits PWM operation, controlling the emission time and luminance. Consequently, IGZO/Te CFETs show promise as devices for high-quality µLED displays.

Emergence of mixing-induced polymorphic phase with higher mobility in alkylated layered organic semiconductors

Emergence of mixing-induced polymorphic phase with higher mobility in alkylated layered organic semiconductors

Self-activated epitaxial growth of ScN films from molecular nitrogen at low temperatures

Unlike naturally occurring oxide crystals such as ruby and gemstones, there are no naturally occurring nitride crystals because the triple bond of the nitrogen molecule is one of the strongest bonds in nature. Here, we report that when the transition metal scandium is subjected to molecular nitrogen, it self-catalyzes to break the nitrogen triple bond to form highly crystalline layers of ScN, a semiconductor. This reaction proceeds even at room temperature. Self-activated ScN films have a twin cubic crystal structure, atomic layering, and electronic and optical properties comparable to plasma-based methods. We extend our research to showcase Sc’s scavenging effect and demonstrate self-activated ScN growth under various growth conditions and on technologically significant substrates, such as 6H–SiC, AlN, and GaN. Ab initio calculations elucidate an energetically efficient pathway for the self-activated growth of crystalline ScN films from molecular N2. The findings open a new pathway to ultralow-energy synthesis of crystalline nitride semiconductor layers and beyond.

Design and simulation of highly efficient CZTS/CZTSSe based thin-film solar cell

Thin-film solar cells are a substitute for more common crystalline silicon solar cells, which consist of thin semiconductor layers. Thin-film materials comprise direct bandgap and can absorb sunlight more efficiently than silicon. In this article, a double-absorber-based thin-film solar cell comprising CZTS/CZTSSe is designed and optimized through numerical simulation. The proposed solar cell structure consists of a transparent window layer made of aluminum-doped zinc oxide, followed by an intrinsic zinc oxide layer, an n-type cadmium sulfide layer, and a p-type combined absorber layer of copper zinc tin sulfide (Cu2ZnSnS4) (CZTS) and copper zinc tin sulfur-selenium alloy (Cu2ZnSn(S,Se4)) (CZTSSe). The structure is further optimized by introducing two interfacial layers between CZTSSe/CZTS and CZTS/CdS. The highest conversion efficiency is achieved by adjusting the thicknesses of the layers, the doping densities in different layers, and the defect densities in the two absorber layers. The optimized model, with a total thickness of 2.01 μm, demonstrates an open-circuit voltage (Voc) of 0.7669 V, a short-circuit current (Jsc) of 48.57740 mA/cm2, a fill factor (FF) of 70.61%, and efficiency (η) of 26.31%. These results suggest that CZTS is a promising candidate for replacing other thin-film photovoltaic materials, such as CdTe. The proposed double-absorber thin-film solar cell optimizes doping concentration, thickness, and defect density to enhance performance metrics and efficiency while utilizing non-toxic materials to promote cost-effective, environmentally friendly energy solutions.

Device simulation study of multilayer MoS2 Schottky barrier field-effect transistors

Molybdenum disulfide (MoS2) is a representative two-dimensional layered transition-metal dichalcogenide semiconductor. Layer-number-dependent electronic properties are attractive in the development of nanomaterial-based electronics for a wide range of applications including sensors, switches, and amplifiers. MoS2field-effect transistors (FETs) have been studied as promising future nanoelectronic devices with desirable features of atomic-level thickness and high electrical properties. When a naturallyn-doped MoS2is contacted with metals, a strong Fermi-level pinning effect adjusts a Schottky barrier and influences its electronic characteristics significantly. In this study, we investigate multilayer MoS2Schottky barrier FETs (SBFETs), emphasizing the metal-contact impact on device performance via computational device modeling. We find thatp-type MoS2SBFETs may be built with appropriate metals and gate voltage control. Furthermore, we propose ambipolar multilayer MoS2SBFETs with asymmetric metal electrodes, which exhibit gate-voltage dependent ambipolar transport behavior through optimizing metal contacts in MoS2device. Introducing a dual-split gate geometry, the MoS2SBFETs can further operate in four distinct configurations:p - p,n - n,p - n, andn - p. Electrical characteristics are calculated, and improved performance of a high rectification ratio can be feasible as an attractive feature for efficient electrical and photonic devices.

Monte Carlo Simulation of Electron Beam Induced Current in Au/Si Schottky Diodes: effects of metal layer thickness and minority carrier diffusion length

The Electron Beam Induced Current (EBIC) technique, when combined with scanning electron microscopy (SEM), offers valuable insights into the electronic properties of semiconductor materials at the nanoscale. This study leverages EBIC and Monte Carlo simulations to investigate the behavior of Schottky diodes, particularly focusing on the influence of gold layer thickness on current gain and backscatter electron (BSE) yield. The simulation results reveal the significant effects of depletion depth and minority carrier diffusion length on the diode’s performance. A key finding is that the EBIC current decreases with increased gold layer thickness, due to a higher BSE fraction. Additionally, at low beam energies, the current is negligible when the interaction volume is confined within the metal layer, while at higher energies, some penetration into the semiconductor occurs, generating a measurable EBIC current. These findings provide a better understanding of the interplay between metal layer thickness and semiconductor performance, which is crucial for optimizing semiconductor devices.

Determining Bandgaps in the Layered Group‐10 2D Transition Metal Dichalcogenide PtSe2

AbstractUnlike traditional group‐6 transition metal dichalcogenides (TMDs), group‐10 TMDs such as PtSe2 and PdTe2 possess highly tuneable indirect bandgaps, transitioning from semiconducting in the near‐infrared to semimetal behavior with a number of monolayers (MLs). This opens up the possibility of TMD‐based mid‐infrared and terahertz optoelectronics. Despite this large potential, the optical properties of such materials have shown an extremely large disparity between that predicted and measured. For example, simulations show that a few MLs is required for the semiconductor–semimetal transition, whilst tens of MLs is found experimentally. This is a result of widely used optical extrapolation methods to determine bandgaps, such as the Tauc plot approach, that are not adapted here owing to i) nearby direct transitions, ii) the material dimensionality and iii) large changes in the non‐parabolic bandstructure with MLs. Here, uniquely combining optical ellipsometry to determine the complex permittivity, terahertz time resolved spectroscopy for the complex conductivity and in‐depth density functional theory (DFT) simulations, it is shown that the optical properties and bandstructure can be determined reliably and demonstrate clearly that the semiconductor‐semimetal transition occurs for PtSe2 layers ≈5 MLs. The microscopic origins of the observed transitions and the crucial role of the Coulomb interaction for thin semiconducting layers, and that of interlayer van der Waals forces for multilayer semimetallic samples are also demonstrated. This work of combining complimentary experimental techniques and extensive simulations avoids the application of constrained extrapolation methods to determine the optical properties of group‐10 TMDs, and will be of importance for future mid‐infrared and terahertz applications.

Heart Engineering of Photovoltaic Devices: Preparation of New Ru Dyes Using Thioindigo and Phenothiazine

ABSTRACTPhenothiazine and thioindigo were used as substitutes to make new Ru dyes for DSSCs. The thioindigo unit is a notable molecule with strong technical qualities in these photosensitizers. As a result, research was done on the cyano substituent as an electron‐donating group. Both theoretical and experimental methods were used to assess the complexes' optical response. A better photovoltaic response is achieved by the cyano groups' efficient bonding with the semiconductor layer. Additionally, the complexes that were formed contain two different kinds of electron accepter substituents: cyanoacrylic acid and carboxylic acid, with efficiencies of 7.42% and 4.17%, respectively. Additionally, cosensitization was investigated and analyzed utilizing N719 and two generated complexes. DSSCs made with Complex 1 and 2 and N719 have corresponding efficiency percentages of 8.86% and 9.74%.

Insulator-to-Metal Transition and Isotropic Gigantic Magnetoresistance in Layered Magnetic Semiconductors.

Magnetotransport, the response of electrical conduction to external magnetic field, acts as an important tool to reveal fundamental concepts behind exotic phenomena and plays a key role in enabling spintronic applications. Magnetotransport is generally sensitive to magnetic field orientations. In contrast, efficient and isotropic modulation of electronic transport, which is useful in technology applications such as omnidirectional sensing, is rarely seen, especially for pristine crystals. Here a strategy is proposed to realize extremely strong modulation of electron conduction by magnetic field which is independent of field direction. GdPS, a layered antiferromagnetic semiconductor with resistivity anisotropies, supports a field-driven insulator-to-metal transition with a paradoxically isotropic gigantic negative magnetoresistance insensitive to magnetic field orientations. This isotropic magnetoresistance originates from the combined effects of a near-zero spin-orbit coupling of Gd3+-based half-filling f-electron system and the strong on-site f-d exchange coupling in Gd atoms. These results not only providea novel material system with extraordinary magnetotransport that offers a missing block for antiferromagnet-based ultrafast and efficient spintronic devices, but also demonstrate the key ingredients for designing magnetic materials with desired transport properties for advanced functionalities.

Design and analysis of central gate organic thin film transistor

Abstract This paper presents a novel central gate organic thin-film transistor (OTFT) with electrodes in top-bottom configuration and its comparative performance analysis with conventional single and dual gate OTFTs. The central gate OTFT is comprised of a single gate electrode configured to be the center thin film. A pair of identical dielectric layers viz. top dielectric layer and a bottom dielectric layer on both sides of gate electrode to facilitate the further deposition top and bottom organic semiconductor layer over them respectively. The organic semiconductor layers (OSC) are configured as top OSC layer and a bottom OSC to accommodate two independent conduction channels. The source and drain electrodes are also deposited in pairs in top and bottom configurations. Due to the subtle modifications in the architecture the resultant output drain current of the central gate (CG) OTFT has increased manifold. It has been found in the study that the CG OTFT produces 94%, 76.36%, 80.58% higher drain current than bottom gate bottom contact (BGBC), top gate bottom contact (TGBC) and bottom gate top contact (BGTC) OTFT respectively of similar size, operating under identical voltage regime. Similarly in the case of dual gate (DG) OTFT an improvement of 5.10% has been recorded without any additional gate electrode at the same operating voltages.

Broadband self-powered MoS2/PdSe2/WSe2 PSN heterojunction photodetector for high-performance optical imaging and communication

Two-dimensional (2D) semi-metal transition metal dichalcogenides (TMDs) have drawn significant attention for their distinctive physical properties. However, the inherent high dark current of these materials and the single structure of detectors hinder the further development of photodetectors with high performance. Here, we construct a PSN (p-type semiconductor/semi-metal/n-type semiconductor) architecture by sandwiching 2D semi-metal between two semiconductor layers. In this architecture, the top and bottom layers generate an internal built-in electric field, while the middle layer serves as an absorption layer for low-energy photons and facilitates the dissociation of photo-generated carriers. As a result, the heterojunction device demonstrates a wide spectrum optical response from visible to infrared light (405 nm to 1550 nm) without requiring an external voltage. Working in self-powered mode at room temperature, the device achieves a responsivity of 0.56 A/W, a detectivity of 5.63 × 1011 Jones, and a rapid response speed of 190/74 µs. Additionally, the device shows potential for applications in fast optical communication and multi-wavelength optical imaging. This work presents a novel approach for developing a new type of broadband, self-powered, high-performance miniaturized semi-metal-based photodetector.

Semiconductor Nanoporous Anodic Alumina Photonic Crystals as a Model Photoelectrocatalytic Platform for Solar Light‐Driven Reactions

In this study, nanoporous anodic alumina distributed‐Bragg reflectors (NAA–DBRs) functionalized with tungsten trioxide (WO3) are used as prototype photoelectrocatalysts (PEC) for harnessing the slow photon effect to maximize photon‐to‐electron conversion efficiency under UV–visible–NIR illumination. NAA–DBR structures are structurally engineered by anodization, where their characteristic photonic stopband is precisely tuned along specific positions of the UV–visible spectrum. Subsequent atomic layer deposition is employed to coat the inner surface of these porous structures with WO3 semiconductor layers. Upon the application of overpotential bias, these platforms reveal excellent electron–hole pair separation to boost photoelectrocatalytic reactions. Photoelectrochemical degradation of methylene blue is used as a model reaction to elucidate enhancements associated with structural and optoelectronic arrangements. Notably, precise spectral alignment between the photonic stopband's red edge and the absorbance band of methylene blue enhances the degradation performance through the slow photon effect. Applying an overpotential bias further improves the photodegradation performance through efficient charge separation. These systems outperform comparable structures in this model reaction, achieving a maximum kinetic rate of 13.7 ± 2.0 h−1. The findings create new opportunities to develop high‐performing PEC technologies harnessing light–matter interactions.

Differential Hall Effect Metrology for Electrical Characterization of Advanced Semiconductor Layers

Semiconductor layers employed in fabricating advanced node devices are becoming thinner and their electrical properties are diverging from those established for highly crystalline standards. Since these properties also change as a function of depth within the film, accurate carrier profiling solutions are required. The Differential Hall Effect (DHE) technique has the unique capability of measuring mobility and carrier concentration (active carriers) through the depth of a semiconductor film. It comprises making successive sheet resistance and sheet Hall coefficient measurements as the thickness of the electrically active layer at a test region is reduced through successive material removal steps. Difference equations are then used to process the data and plot the desired depth profiles. The fundamentals of DHE were established in 1960s. Recently, the adaption of electrochemical processing for the material removal steps, and the integration of all other functionalities in a Differential Hall Effect Metrology (DHEM) tool, has made this technique more practical and accurate and improved its depth resolution to a sub-nm range. In this contribution, we review the development history of this important technique and present data from recent characterization work carried out on Si, Ge and SiGe layers.