Semiconductor Transition Research Articles

Preparation of Organic N-Fused Perylenediimide-MXene Hybrid Material for Robust Versatile Memristive Device

Abstract Two-dimensional (2D) MXene nanomaterials have shown great promise for electronic devices, attributed to their metal-resembling conductivity and abundant surface functional groups. However, the utilization of intrinsic property of MXene into memristors remains challenging due to its free electron conducting behavior rather than semiconducting property. Here, a N-fused perylenediimide organic semiconductor (CBIN) with conjugated skeleton and heteroatoms (O, S, N) is designed to successfully actuate the surface modification of MXene. The organic CBIN-decorated MXene demonstrates remarkable bipolar memristive properties, such as low threshold voltages of approximate ±1.4 V, exalted retention time exceeding 104 s, and outstanding environmental stability even after exposure to ultraviolet and X-ray irradiations. Furthermore, the CBIN-MXene hybrid memristive device can mimic synaptic plasticity and holds potential for information encoding as QR codes and image recognition processing. This study provides efficient guidelines for implementing MXene-based memristors by organic semiconductor modulation and opens up possibilities of extending their functionalities into information encryption and neuromorphic computing applications.

A Widely and Continuously Tunable Single-Mode Transmitter Based on a Hybrid Microcavity Laser

A method for achieving the single-mode and efficient unidirectional emission of a whispering gallery mode (WGM) semiconductor laser is presented herein. Hybrid square-rectangular lasers (HSRLs) and hybrid square/rhombus-rectangular lasers (HSRRLs) consisting of a Fabry–Pérot (FP) cavity and a square or rhombus cavity microcavity are described. In addition, a transmitter optical subassembly (TOSA) based on an HSRRL chip was fabricated, which has a wide and continuous wavelength tuning range. Wavelength channels from 1555.75 nm to 1568.15 nm with a spacing of 50 GHz were demonstrated with a good side mode suppression ratio (SMSR) and good output power. These devices have the potential to meet the typical requirements of optical communication networks.

Electric‐Field‐ and Stacking‐Tuned Antiferromagnetic FeClF Bilayer: The Coexistence of Bipolar Magnetic Semiconductor and Anomalous Valley Hall Effect

AbstractValley polarization from broken inversion symmetry provides a new degree of freedom for carriers, bipolar magnetic semiconductor (BMS) generates a purely spin‐polarized current under a gate voltage, but few systems possess the coexistence of valley polarization and BMS. Based on the recent experimental FeCl2 flakes, reversible electric‐field effect on the valley‐ and spin‐polarized Janus FeClF bilayer with different stackings are investigated herein. Janus FeClF bilayers in all three stacks possess interlayer antiferromagnetic (AFM) and intralayer ferromagnetic (FM) couplings. The most stable A (Cl‐Fe‐F‐Cl‐Fe‐F) stack possesses concurrent and spontaneous BMS nature and valley polarization with perpendicular magnetic anisotropy (PMA), while B (Cl‐Fe‐F‐F‐Fe‐Cl) and C (F‐Fe‐Cl‐Cl‐Fe‐F) stacks exhibit AFM semiconductor characters without valley polarization. Electric‐field achieves a transition of BMS and AFM semiconductor. Large ferrovalley (≈108 meV) exists and is mainly contributed by Fe‐dxy and orbitals. With the out‐of‐plane to in‐plane to out‐of‐plane transition of the easy axis, anomalous valley Hall effect (AVHE) can be manipulated to presence and disappearance by perpendicular electric‐field, indicating the valley switch effect (VSE). The coexisting BMS feature, PMA, AVHE and VSE make Janus FeClF bilayer a promising candidate for multifunctional valleytronic and spintronic applications, favoring broad explorations for the low‐dimensional Janus family.

Flow boiling of HFE-7100 for cooling Multi-Chip modules using manifold microchannels

Two-phase manifold microchannel heat sinks have gained significant interest for their efficient use of the coolant’s latent heat. Despite this, manifold microchannel flow boiling heat transfer has not yet been applied to wide-bandgap semiconductor power modules with multiple chips, primarily due to the complexity of the process and challenges related to electrical insulation. This study introduces a novel embedded manifold microchannel design that ensures uniform mass flow distribution, tailored for the thermal management of multi-chip power modules. The microchannels were laser-etched onto direct bonded copper (DBC) to reduce thermal resistance while maintaining electrical insulation. Thermal test vehicles (TTVs) for multi-chip power modules, featuring two different microchannel widths, were assembled using silver sintering. Experimental tests were then conducted using HFE-7100 as the coolant to evaluate two-phase heat dissipation performance. Results indicate that during flow boiling heat transfer, the temperature difference between chips in a power module strongly correlates with the exit quality. A higher coolant mass flow rate significantly reduces temperature variation between chips, particularly under high chip heat flux. At a coolant mass flow rate of 9 g/s, with a chip heat flux of 357 W/cm2 and total heat dissipation of 536 W, the minimum thermal resistance reached 0.15 cm2∙K/W, yielding a COP of 1391. With a slight sacrifice in thermal resistance, 0.17 cm2∙K/W and 0.20 cm2∙K/W were achieved at mass flow rates of 6 g/s and 3 g/s, respectively. Correspondingly, the COPs reached 2179 and 6749. This research offers valuable insights for applying flow boiling heat transfer with dielectric coolants to cool multi-chip power modules.

Non-destructive orientation mapping of die-attach lead-free solder

Abstract Thermo-mechanical fatigue poses a serious challenge to the electrical operation of power semiconductor modules, manifested by the degradation of die-attach lead-free solder. So far, orientation microscopy (OM) using electron backscatter diffraction is considered a sensitive approach to characterizing the degradation of solder. However, its destructive character inhibits assessing solder inside the power modules. We propose a non-destructive OM method based on X-ray diffraction and successfully observed the changes in the orientation of the solder caused by thermo-mechanical fatigue. The proposed non-destructive OM method can facilitate the development of reliable power modules by evaluating the degradation of the solder inside the power modules.

Intralayer/Interlayer Codoping Stabilizes Polarity Modulation in 2D Semiconductors for Scalable Electronics.

2D semiconductors show promise as a competitive candidate for developing future integrated circuits due to their immunity to short-channel effects and high carrier mobility at atomic layer thicknesses. The inherent defects and Fermi level pinning effect lead to n-type transport characteristics in most 2D semiconductors, while unstable and unsustainable p-type doping by various strategies hinders their application in many areas, such as complementary metal-oxide-semiconductor (CMOS) devices. In this study, an intralayer/interlayer codoping strategy is introduced that stabilizes p-type doping in 2D semiconductors. By incorporating oppositely charged ions (F and Li) with the intralayer/interlayer of 2D semiconductors, remarkable p-type doping in WSe2 and MoTe2 with air stability up to 9 months is achieved. Notably, the hole mobility presents a 100-fold enhancement (0.7 to 92 cm2 V-1 s-1) with the codoping procedure. Structural and elemental characterizations, combined with theoretical calculations validate the codoping mechanism. Moreover, a CMOS inverter and more complex logic functions such as NOR and XNOR, as well as large-area device arrays are demonstrated to showcase its applications and scalability. These findings suggest that stable and straightforward intralayer/interlayer codoping strategy with charge-space synergy holds the key to unlocking the potential of 2D semiconductors in complex and scalable device applications.

Highly Robust, Pressureless Silver Sinter-Bonding Technology Using PMMA Combustion for Power Semiconductor Applications.

This study presents the development of a highly robust, pressureless, and void-free silver sinter-bonding technology for power semiconductor packaging. A bimodal silver paste containing silver nanoparticles and sub-micron particles was used, with polymethyl methacrylate (PMMA) as an additive to provide additional thermal energy during sintering. This enabled rapid sintering and the formation of a dense, void-free bonding joint. The effects of sintering temperature and PMMA content on shear strength and microstructure were systematically investigated. The results showed that the shear strength increased with rising sintering temperatures, achieving a maximum of 41 MPa at 300 °C, with minimal void formation due to enhanced particle necking facilitated by PMMA combustion. However, at 350 °C, the shear strength decreased to 35 MPa due to cracks and voids at the copper substrate-copper oxide interface caused by thermal expansion mismatch. The optimal PMMA content was found to be 5 wt.%, balancing sufficient thermal energy and void reduction. This pressureless sintering technology demonstrates significant potential for high-reliability applications in power semiconductor modules operating under high-temperature and high-stress conditions.

Scalable Metal–Organic Chemical Vapor Deposition of High Quality PtSe2

AbstractPlatinum diselenide (PtSe2), a 2D noble metal dichalcogenide, has recently received significant attention due to its outstanding properties. It undergoes a semimetal to semiconductor transition when thinned, offers a bandgap in the infrared range, and exhibits excellent stability in ambient conditions. These properties make it a prime active material in optoelectronic and chemical sensing devices. However, there is a high demand for a synthesis method that can produce large‐scale and reliable high‐quality PtSe2. In this study, the growth of PtSe2 is presented by metal–organic vapor deposition on a variety of substrates. Comprehensive Raman, X‐ray photoelectron, and X‐ray diffraction spectroscopy, as well as scanning tunneling microscopy characterization reveals the high quality of the deposited PtSe2. Domains within the films are found to be up to several hundreds of nanometers in size, and their highly ordered crystalline structure is evident from atomic‐scale measurements. Electrical characterization demonstrates improved conductivity relative to conventional synthesis methods. This study provides fundamental guidance for the scalable synthesis and implementation of high quality PtSe2 layers with controllable thickness, offering a key requirement for the implementation of PtSe2 in future applications.

Multiscale simulations of amorphous and crystalline AgSnSe2 alloy for reconfigurable nanophotonic applications

AbstractChalcogenide phase‐change materials (PCM) have been explored in novel nonvolatile memory and neuromorphic computing technologies. Upon fast crystallization process, the conventional PCM undergo a semiconductor–to–semiconductor transition. However, some PCM change from a semiconducting amorphous phase to a metallic crystalline phase with low conductivity (“bad metal”). In this work, we focus on new “bad metal” PCM, namely, AgSnSe2, and carry out multiscale simulations to evaluate its potential for reconfigurable nanophotonic devices. We study the structural features and optical properties of both crystalline and amorphous AgSnSe2 via density functional theory (DFT) calculations and DFT‐based ab initio molecular dynamic (AIMD) simulations. Then we use the calculated optical profiles as input parameters for finite difference time domain (FDTD) modeling of waveguide and metasurface devices. Our multiscale simulations predict AgSnSe2 to be a promising candidate for phase‐change photonic applications.

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.

Exploitation of the piezoelectricity-enabled sonophotocatalysis of Bi2Te3-Au nanosheets for efficient overall water splitting for energy and medical applications

The development of high-performance solar-photocatalysts/sonocatalysts for overall water splitting production of H2 and H2O2 is highly significant to their energy and medical applications, but remains challenging. Herein, we have discovered that Bi2Te3 nanosheets have a piezoelectricity, and experimentally confirmed the ultrasound-driven indirect-to-direct bandgap semiconductor transition which enables ultrasound stimulation to reconstruct band structure in competent for sonophotocatalytic overall water splitting production of H2 and H2O2. Under the assistance/driving of a low-density pulsed ultrasound, the solar-photocatalysis of Bi2Te3-Au nanosheets achieves extrahigh H2 and H2O2 production efficiencies (29.7 mmol/g/h H2 and 14.6 mmol/g/h H2O2), which are far higher than that previously reported about overall water splitting. For medical application, we have proposed a sonocatalytic strategy of combining hydrogen therapy and sonodynamic therapy for treatment of deep tumors, achieving a high outcome of orthotopic liver tumor treatment with a 100 % mice survival rate and a 100 % tumor eradication rate. High sonophotocatalytic performance, high biosafety and high anti-cancer efficacy endow Bi2Te3-Au nanosheets with a great potential for green energy and medical applications. These findings will provide an inspiration for exploitation and utilization of the piezoelectricity and sonophotocatalysis of A2VB3VI semiconducting nanomaterials.

Toward Mass Production of Transition Metal Dichalcogenide Solar Cells: Scalable Growth of Photovoltaic-Grade Multilayer WSe2 by Tungsten Selenization.

Semiconducting transition metal dichalcogenides (TMDs) are promising for high-specific-power photovoltaics due to their desirable band gaps, high absorption coefficients, and ideally dangling-bond-free surfaces. Despite their potential, the majority of TMD solar cells to date are fabricated in a nonscalable fashion, with exfoliated materials, due to the lack of high-quality, large-area, multilayer TMDs. Here, we present the scalable, thickness-tunable synthesis of multilayer WSe2 films by selenizing prepatterned tungsten with either solid-source selenium at 900 °C or H2Se precursors at 650 °C. Both methods yield photovoltaic-grade, wafer-scale WSe2 films with a layered van der Waals structure and superior characteristics, including charge carrier lifetimes up to 144 ns, over 14× higher than those of any other large-area TMD films previously demonstrated. Simulations show that such carrier lifetimes correspond to ∼22% power conversion efficiency and ∼64 W g-1 specific power in a packaged solar cell, or ∼3 W g-1 in a fully packaged solar module. The results of this study could facilitate the mass production of high-efficiency multilayer WSe2 solar cells at low cost.

Optimizing dielectric and electrical properties of graphene oxide thin film with temperature tuning: Insights from impedance spectra analysis on insulator to semiconductor transition

The study focused on exploring the impact of annealing temperatures on dielectric and electrical, and conductivity properties of Graphene Oxide (GO) thin films. The investigation involved measuring impedance spectra across a temperature range spanning from room temperature (T=300 K) to high temperature (T=560 K). The findings revealed intriguing trends in the behavior of GO thin films under varying annealing temperatures. Firstly, it was observed that the dielectric constant of the GO thin film exhibited an upward trend with increasing temperature within the specified range. This indicates a temperature-dependent response in the dielectric properties of the material. Secondly, the electrical conductance of the film was found to be influenced by both frequency and annealing temperature. Specifically, the AC conductance showcased semiconductor behavior across a broad temperature spectrum, with a notable increase in conductance as the annealing temperature rose. This suggests a correlation between electrical properties and the annealing temperature of the GO thin film. Furthermore, the impedance analysis of the GO films revealed distinct relaxation processes at different temperatures, indicating varying dynamics within the material under thermal conditions. Additionally, the study highlighted a direct relationship between dielectric behavior and factors such as dielectric loss, polarization effects, and enhancements in the dielectric constant. These findings underscore the intricate interplay between thermal treatment, dielectric properties, and conductivity in GO thin films. Hence, the research elucidates the complex nature of GO thin films’ electrical, dielectric, and conductivity characteristics under annealing temperature variations, shedding light on potential applications and further avenues for exploration in this field.

Understanding vapor phase growth of hexagonal boron nitride.

Hexagonal boron nitride (hBN), with its atomically flat structure, excellent chemical stability, and large band gap energy (∼6 eV), serves as an exemplary 2D insulator in electronics. Additionally, it offers exceptional attributes for the growth and encapsulation of semiconductor transition metal dichalcogenides (TMDCs). Current methodologies for producing hBN thin films primarily involve exfoliating multi-layer or bulk crystals and thin film growth via chemical vapor deposition (CVD), which entails the thermal decomposition and surface reaction of molecular precursors like ammonia boranes (NH3BH3) and borazine (B3N3H6). These molecular precursors contain pre-existing B-N bonds, thus promoting the nucleation of BN. However, the quality and phase purity of resulting BN films are greatly influenced by the film preparation and deposition process conditions that remain a substantial concern. This study aims to comprehensively investigate the impact of varied CVD systems, parameters, and precursor chemistry on the synthesis of high-quality, large scale hBN on both catalytic and non-catalytic substrates. The comparative analysis provided new insights into most effective approaches concerning both quality and scalability of vapor phase grown hBN films.

Reactive oxygen species, electrode potential and pH affect CoCrMo alloy corrosion and semiconducting behavior in simulated inflammatory environments

Crevice corrosion in modular taper junctions of hip or knee replacements using cobalt-chrome-molybdenum (CoCrMo) alloys remains a clinical concern. Non-mechanically-driven corrosion has been less explored compared to mechanically assisted crevice corrosion. This study hypothesized that solution chemistry within crevices, inflammation, and cathodic electrode potential shifts during fretting result in low pH and generate reactive oxygen species (ROS), affecting oxide film behavior. This study investigated how resistance and capacitance of the CoCrMo oxide film (i.e., corrosion resistance) are modified in simulated in vivo crevice environments of modular taper junctions. Six solutions were evaluated (two pH levels: 1 and 7.4 and four hydrogen peroxide (H2O2) concentrations: 0, 0.001, 0.01 and 0.1 M). Rp versus voltage and Mott–Schottky plots were created from symmetry-based electrochemical impedance spectroscopy (sbEIS). At pH 1, the semiconductor transition to p-type occurs at more anodic potentials and higher flat band potentials were found. H2O2 decreased the flat band potential and slope in the Mott–Schottky plot. Higher H2O2 in pH 7.4 solution significantly modified the oxide film, leading to increased donor density (p = 0.0004) and a 150-fold reduction in Rp in the cathodic potential range at -1 V (p = 0.0005). The most unfavorable condition (0.1 M H2O2 pH 1) resulted in a 250-fold lower resistance compared to phosphate buffered saline (PBS) pH 7.4 at -1 V (p = 0.0013). This study highlights the corrosion susceptibility of CoCrMo under adverse chemical and potential conditions, identifying increased defects in the oxide film due to ROS, hydrogen ions and electrode potential. Statement of significanceCorrosion of cobalt chrome molybdenum alloy caused by direct chemical attack in the crevice region of hip replacements, such as modular taper junctions, remains a clinical concern. The junction environment contains adverse chemical compositions, including high acidity and reactive oxygen species (ROS) due to inflammatory responses against the corrosion products. We simulate inflammatory environments with different pH levels and hydrogen peroxide, representative of ROS. We employ electrochemical impedance spectroscopy and apply stepwise voltage over the range induced by tribocorrosion processes. We relate the effect of adverse chemical components on corrosion and semiconducting behavior of the oxide film using Mott–Schottky analysis. This study shows how pH and ROS concentration compromises the oxide film potentially leading to non-mechanically induced corrosion.

(Invited) Electronic Doping in Two-Dimensional Semiconductors

Quantum-confined semiconductors provide highly tunable optical and electrical properties for a wide variety of emerging applications. Two-dimensional semiconductors possess tunable bandgaps, high charge carrier mobilities, and strong light-matter interactions that can enable applications in photovoltaics, quantum information processing, and spintronics. Electronic doping, the intentional introduction of controlled charge carrier density and type (electrons or holes) is a fundamental enabler for many emerging applications of two-dimensional semiconductors. While electrostatic doping in transistor geometries is useful for certain applications, it is important to develop additional methods based on e.g. molecular redox doping and substitutional atomic doping that can provide tunable Fermi level control in the absence of an applied bias. In this presentation, I will discuss our efforts to develop such doping strategies for a variety of two-dimensional semiconductors. I will discuss how electronic doping modulates opto-electronic properties, including ground-state absorbance, charge transport, and excited-state dynamics in these 2D semiconductors. These studies provide fundamental insights into the degree to which molecular and substitutional doping strategies can modulate Fermi level, charge transport, and excitonic optical transitions in 2D semiconductors.

Two-dimensional electrons at mirror and twistronic twin boundaries in van der Waals ferroelectrics

Semiconducting transition metal dichalcogenides (MX2) occur in 2H and rhombohedral (3R) polytypes, respectively distinguished by anti-parallel and parallel orientation of consecutive monolayer lattices. In its bulk form, 3R-MX2 is ferroelectric, hosting an out-of-plane electric polarisation, the direction of which is dictated by stacking. Here, we predict that twin boundaries, separating adjacent polarisation domains with reversed built-in electric fields, are able to host two-dimensional electrons and holes with an areal density reaching ~ 1013cm−2. Our modelling suggests that n-doped twin boundaries have a more promising binding energy than p-doped ones, whereas hole accumulation is stable at external surfaces of a twinned film. We also propose that assembling pairs of mono-twin films with a ‘magic’ twist angle θ* that provides commensurability between the moiré pattern at the interface and the accumulated carrier density, should promote a regime of strongly correlated states of electrons, such as Wigner crystals, and we specify the values of θ* for homo- and heterostructures of various TMDs.

Numerical Analysis for High-Speed Hybrid- Modulation Semiconductor Laser Integrated With Passive Waveguide

Numerical Analysis for High-Speed Hybrid- Modulation Semiconductor Laser Integrated With Passive Waveguide

Strain and orientation modulated optoelectronic properties of La-doped SrSnO3 epitaxial films

We have studied the structural, electrical, and optical properties of La0.05Sr0.95SnO3 thin films, which exhibited a strong dependence upon the substrate’s orientation and strain. X-ray diffraction results show that the LSSO films grow epitaxially on (001) and (011)-oriented LaAlO3 substrates, and the in-plane compressive strain decreases gradually upon increasing film thickness. Room-temperature resistivity varies from 4.23 (13.0) to 1.37 (4.76) mΩ cm as the film thickness increases for (001) orientation ((011) orientation). Temperature dependent resistivity curves of all the samples show a metal–semiconductor transition (MST), which can be explained by the electron–electron interactions below MST rather than weak localization. Both reducing the in-plane compressive strain and transferring the orientation from (011) to (001) can drive the MST point shifts toward lower temperature, indicative of the enhancement of the metallic transport in the films. The band gap increases upon increasing film thickness due to Burstein-Moss effect. The charge distributions of Sn and O from density functional theory (DFT) calculations illustrate that (001)-plane has a better conductivity. Furthermore, our DFT results also demonstrate that decreasing the in-plane strain will lead to a smaller electron effective mass, thus the increased carrier mobility can be obtained. These comprehensive investigations advance our knowledge of the optoelectronic characteristics and provide valuable insights for future research in related transparent materials.

Surface modification of XSe (X = Cu and Ag) monolayers by grope 1 elements: A metal to semiconductor transition by a first-principles perspective

Two-dimensional (2D) materials can be effectively functionalized by chemically modified using doping. Very recently, a flat AgSe monolayer was successfully prepared through direct selenization of the Ag(111) surface. Besides, the results indicate that the AgSe monolayer like CuSe, has a honeycomb lattice. Motivated by the experimental outcomes, in this work, employing first-principles calculations, we systematically investigate the electronic and optical properties of AgSe and CuSe monolayers, as well as the impact of alkali metals (Li, Na and K). Without functionalization, both the CuSe and AgSe monolayers exhibit metallic characteristics. The Li (Na)-CuSe and Na (K)-AgSe systems are dynamically stable while, the K- and Li-CuSe and Li-AgSe are dynamically unstable. Interestingly, the functionalized CuSe system with Li and Na atom as well as AgSe with K and Na atom, can open the band gaps, leading to the actualization of metal to semiconductor transitions. Our results show that, the electronic characteristics of the Na-CuSe/AgSe system can be modulated by adjusting the adsorption heights, which gives rise to the change in the electronic properties and the band gap may be controlled. Furthermore, from the optical properties we can find that the K-AgSe system is the best candidate monolayer to absorb infrared radiation and visible light. Consequently, our findings shed light on the functionalization of 2D materials based CuSe and AgSe monolayers and can potentially enhance and motivate studies in producing these monolayers for current nanodevices and future applications.