Si Semiconductor Research Articles

Unconventional Near-Equilibrium Nucleation of Graphene on Si-Terminated SiC(0001) Surface.

The transfer-free character of graphene growth on Silicon Carbide (SiC) makes it compatible with state-of-the-art Si semiconductor technologies for directly fabricating high-end electronics. Although significant progress has been achieved in epitaxial growth of graphene on SiC recently, the underlying nucleation mechanism remains elusive. Here, we present a theoretical study to elucidate graphene near-equilibrium nucleation on Si-terminated hexagonal-SiC(0001) surface. It is found that the ultra-large lattice mismatch between SiC(0001) surface and graphene and the highly localized electron distribution on SiC(0001) surface lead to a distinctive nucleation process: (i) Most of the magic carbon clusters on SiC(0001) show only C1 symmetry and are mainly composed of pentagonal rings; (ii) Two possible nucleation pathways are revealed, i.e., longitudinal and circular modes; (iii) Carbon clusters are more stable on flat terraces than near atomic step edges. Based on above findings, a graphene nucleation diagram on SiC(0001) is established and experimentally observed contradictories for graphene growth on SiC(0001) are answered. Our in-depth understanding on graphene nucleation on SiC(0001) extends nucleation mechanisms of 2D crystals and will benefit high-quality graphene growth on SiC(0001).

A Review of Wide Bandgap Semiconductors: Insights into SiC, IGZO, and Their Defect Characteristics.

Although the irreplaceable position of silicon (Si) semiconductor materials in the field of information has become a consensus, new materials continue to be sought to expand the application range of semiconductor devices. Among them, research on wide bandgap semiconductors has already achieved preliminary success, and the relevant achievements have been applied in the fields of energy conversion, display, and storage. However, similar to the history of Si, the immature material grown and device manufacturing processes at the current stage seriously hinder the popularization of wide bandgap semiconductor-based applications, and one of the crucial issues behind this is the defect problem. Here, we take amorphous indium gallium zinc oxide (a-IGZO) and 4H silicon carbide (4H-SiC) as two representatives to discuss physical/mechanical properties, electrical performance, and stability from the perspective of defects. Relevant experimental and theoretical works on defect formation, evolution, and annihilation are summarized, and the impacts on carrier transport behaviors are highlighted. State-of-the-art applications using the two materials are also briefly reviewed. This review aims to assist researchers in elucidating the complex impacts of defects on electrical behaviors of wide bandgap semiconductors, enabling them to make judgments on potential defect issues that may arise in their own processes. It aims to contribute to the effort of using various post-treatment methods to control defect behaviors and achieve the desired material and device performance.

Effect of temperature and magnetic field on the density of surface states in semiconductor heterostructures

In this article, the physical properties of the surface of the CdS/Si(p) material under the influence of a magnetic field were studied . The dependence of the density of surface states of the p-type Si(p) semiconductor on the magnetic field and temperature has been studied. For the first time, a mathematical model has been developed to determine the temperature dependence of the density of surface states of a semiconductor under the influence of a strong magnetic field. Mathematical modeling of processes was carried out using experimental values of the continuous energy spectrum of the density of surface states, obtained at various low temperatures and strong magnetic fields, in the band gap of silicon. The possibility of calculating discrete energy levels is demonstrated.

Occurrence of the collective Ziman limit of heat transport in cubic semiconductors Si, Ge, AlAs and AlP: scattering channels and size effects

In this work, we discuss the possibility of reaching the Ziman conditions for collective heat transport in cubic bulk semiconductors, such as Si, Ge, AlAs and AlP. In natural and enriched silicon and germanium, the collective heat transport limit is impossible to reach due to strong isotopic scattering. However, we show that in hyper-enriched silicon and germanium, as well as in materials with one single stable isotope like AlAs and AlP, at low temperatures, normal scattering plays an important role, making the observation of the collective heat transport possible. We further discuss the effects of sample sizes, and analyse our results for cubic materials by comparing them to bulk bismuth, in which second sound has been detected at cryogenic temperatures. We find that collective heat transport in cubic semiconductors studied in this work is expected to occur at temperatures between 10 and 20 K.

Self-Aligned Edge Contact Process for Fabricating High-Performance Transition-Metal Dichalcogenide Field-Effect Transistors.

The persistent challenges encountered in metal-transition-metal dichalcogenide (TMD) junctions, including tunneling barriers and Fermi-level pinning, pose significant impediments to achieving optimal charge transport and reducing contact resistance. To address these challenges, a pioneering self-aligned edge contact (SAEC) process tailored for TMD-based field-effect transistors (FETs) is developed by integrating a WS2 semiconductor with a hexagonal boron nitride dielectric via reactive ion etching. This approach streamlines semiconductor fabrication by enabling edge contact formation without the need for additional lithography steps. Notably, SAEC TMD-based FETs exhibit exceptional device performance, featuring a high on/off current ratio of ∼108, field-effect mobility of up to 120 cm2/V·s, and controllable polarity─essential attributes for advanced TMD-based logic circuits. Furthermore, the SAEC process enables precise electrode positioning and effective minimization of parasitic capacitance, which are pivotal for attaining high-speed characteristics in TMD-based electronics. The compatibility of the SAEC technique with existing Si self-aligned processes underscores its feasibility for integration into post-CMOS applications, heralding an upcoming era of integration of TMDs into Si semiconductor electronics. The introduction of the SAEC process represents a significant advancement in TMD-based microelectronics and is poised to unlock the full potential of TMDs for future electronic technologies.

Excellent Hole Mobility and Out-of-Plane Piezoelectricity in X-Penta-Graphene (X = Si or Ge) with Poisson's Ratio Inversion.

Recently, the application of two-dimensional (2D) piezoelectric materials has been seriously hindered because most of them possess only in-plane piezoelectricity but lack out-of-plane piezoelectricity. In this work, using first-principles calculation, by atomic substitution of penta-graphene (PG) with tiny out-of-plane piezoelectricity, we design and predict stable 2D X-PG (X = Si or Ge) semiconductors with excellent in-plane and out-of-plane piezoelectricity and extremely high in-plane hole mobility. Among them, Ge-PG exhibits better performance in all aspects with an in-plane strain piezoelectric coefficient d11 = 8.43 pm/V, an out-of-plane strain piezoelectric coefficient d33 = -3.63 pm/V, and in-plane hole mobility μh = 57.33 × 103 cm2 V-1 s-1. By doping Si and Ge atoms, the negative Poisson's ratio of PG approaches zero and reaches a positive value, which is due to the gradual weakening of the structure's mechanical strength. The bandgaps of Si-PG (0.78 eV) and Ge-PG (0.89 eV) are much smaller than that of PG (2.20 eV), by 2.82 and 2.47 times, respectively. This indicates that the substitution of X atoms can regulate the bandgap of PG. Importantly, the physical mechanism of the out-of-plane piezoelectricity of these monolayers is revealed. The super-dipole-moment effect proposed in the previous work is proved to exist in PG and X-PG, i.e., it is proved that their out-of-plane piezoelectric stress coefficient e33 increases with the super-dipole-moment. The e33-induced polarization direction is also consistent with the super-dipole-moment direction. X-PG is predicted to have prominent potential for nanodevices applied as electromechanical coupling systems: wearable, ultra-thin devices; high-speed electronic transmission devices; and so on.

(Invited) Metal Corrosion Mitigation in Fine Geometries during Chemical Mechanical Planarization

In the Si semiconductor industry, aggressive device geometry scaling has given rise to new processing challenges to each new technology nodes over the past 6 decades. When the feature size shrinks to nanometer regime, new phenomenon emerges whereby significant loss in metal vias and lines can be observed after CMP.Findings from our previous studies suggest just a few nanometers of metal loss imposes serious yield loss in sub-5nm technology nodes MOL and BEOL metallization. Post CMP clean process can be responsible for ~ 50% of the metal loss after CMP. The phenomenon was observed with W, Co, and Cu alike. It affects conductors as well as liner/barrier metals, and exhibits strong dependence on pattern density, feature size, and even underlying layer. [1, 2]. Properly formulated slurries and post CMP clean chemicals can modulate the amount of metal loss and partially alleviate the issue.In this study, we continue to assess how post CMP clean chemicals and modified de-ionized water can influence the amount of metal loss for Cu interconnects. As a starter, blanket wafers resembling several different Cu/liner/low-k stacks were evaluated. The were subjected to polish with the same alkaline slurry followed by various alkaline post clean chemicals (Clean 1, pH ~ 10.2; Clean 2, pH 9.8). It was observed on the attached figure that brush clean only process with DIW alone can induce small amount of Cu loss. For wafers with polish and post clean, on a comparison basis, Clean1 resulted in slightly more Cu loss than Clean2. However, when dilute NH4OH solution (pH ~ 9.6) was introduced to replace DIW during brush clean with Clean1, the amount of Cu loss is reduced, on par with that of Clean2. The observation suggests NH4OH-treated DIW can help alleviate part of Cu loss during post CMP clean process. Patterned wafers with various combination of liner stacks will be subjected to clean process with various combinations of chemistries and/or NH4OH-treated DIW. The amount of Cu or liner loss will be characterized.

Enhanced performance of quasi-solid-state silicon-air batteries through light-assisted anodic reactions

Silicon-air batteries (SABs) offer a promising energy storage solution due to their high theoretical energy density, cost-effectiveness, and environmental friendliness. However, practical applications are hindered by limitations in maximum discharge current density and discharge voltage, stemming from intrinsic electrochemical properties of the silicon (Si) anode and surface oxidation kinetics. This study addressed the low maximum discharge current density of SABs by leveraging the Si semiconductor properties and employing a light-assisted strategy. Introducing light to the silicon anode generates photogenerated electron-hole pairs. Furthermore, introducing light to the Si anode allowed for the generation of photogenerated electron-hole pairs. The resulting holes reacted with OH- ions to form hydroxyl radical (OH), which efficiently oxidized the Si surface, thereby facilitating electrochemical reactions. This enhancement increased the anodic reaction kinetics, thereby enhancing the maximum discharge current density of SABs. Furthermore, through this strategy, light-assisted SABs exhibited significant performance improvements: under 1 sun illumination, maximum discharge current density increased by 50.0 %, discharge voltage by 10.0 %, and power density by 45.0 %. Under 3 suns illuminations, these metrics improved further, with maximum discharge current density increasing by 87.5 %, discharge voltage by 20 %, and power density by 200 %. Additionally, quasi-solid-state SABs (QSSSABs) according to this strategy exhibited versatility across various application scenarios, thereby significantly expanding the practical potential of SABs technology.

Phonon-assisted charge carriers thermalization in semiconductor Si and metallic silicide NiSi2, CoSi2: A non-adiabatic molecular dynamics study

Recently, the cold source field-effect transistor (CSFET) has emerged as a promising solution to overcome Boltzmann tyranny in its ballistic regime, offering a steep-slope subthreshold swing (SS) of less than 60 mV/decade. However, challenges arise due to scattering, particularly from inelastic scattering, which can lead to significant degradation in SS through cold carrier thermalization. In this study, we delve into the theoretical investigation of the electronic excitation/relaxation dynamic process using the state-of-the-art nonadiabatic molecular dynamics (NAMD) method. The mixed quantum-classical NAMD proves to be a powerful tool for comprehensively analyzing cold carrier thermalization and transfer processes in semiconductor Si, as well as metallic silicides (NiSi2 and CoSi2). The approach of mixed quantum-classical NAMD takes into account both carrier decoherence and detailed balance, enabling the calculation of thermalization factors, relaxation times, scattering times, and scattering rates at various energy levels. The thermalization of carriers exhibits a gradual increase from low to high energy levels. Achieving partial thermalization from the ground state to reach the thermionic current window occurs within a sub-100 fs time scale. Full thermalization across the entire energy spectrum depends sensitively on the barrier height, with the scattering rate exponentially decreasing as the energy of the out-scattering state increases. Notably, the scattering rate of NiSi2 and CoSi2 is two orders of magnitude higher than that of Si, attributed to their higher density of states compared to Si. This study not only provides insights into material design for low-power tunnel field-effect transistors but also contributes valuable information for advancing CSFET in emerging technologies.

Defects and oxygen impurities in ferroelectric wurtzite Al1−xScxN alloys

III-nitrides and related alloys are widely used for optoelectronics and as acoustic resonators. Ferroelectric wurtzite nitrides are of particular interest because of their potential for direct integration with Si and wide bandgap semiconductors and unique polarization switching characteristics; such interest has taken off since the first report of ferroelectric Al1−xScxN alloys. However, the coercive fields needed to switch polarization are on the order of MV/cm, which are 1–2 orders of magnitude larger than oxide perovskite ferroelectrics. Atomic-scale point defects are known to impact the dielectric properties, including breakdown fields and leakage currents, as well as ferroelectric switching. However, very little is known about the native defects and impurities in Al1−xScxN and their effect on the dielectric and ferroelectric properties. In this study, we use first-principles calculations to determine the formation energetics of native defects and unintentional oxygen incorporation and their effects on the polarization switching barriers in Al1−xScxN alloys. We find that nitrogen vacancies are the dominant native defects, and unintentional oxygen incorporation on the nitrogen site is present in high concentrations. They introduce multiple mid-gap states that can lead to premature dielectric breakdown and increased temperature-activated leakage currents in ferroelectrics. We also find that nitrogen vacancy and substitutional oxygen reduce the switching barrier in Al1−xScxN at low Sc compositions. The effect is minimal or even negative (increases barrier) at higher Sc compositions. Unintentional defects are generally considered to adversely affect ferroelectric properties, but our findings reveal that controlled introduction of point defects by tuning synthesis conditions can instead benefit polarization switching in ferroelectric Al1−xScxN at certain compositions.

Photoelectrocatalytic Hydrogen Generation: Current Advances in Materials and Operando Characterization.

Photoelectrochemical (PEC) hydrogen generation is a promising technology for green hydrogen production yet faces difficulties in achieving stability and efficiency. The scientific community is pushing toward the development of new electrode materials and a better understanding of the underlying reactions and degradation mechanisms. Advances in photocatalytic materials are being pursued through the development of heterojunctions, tailored crystal nanostructures, doping, and modification of solid-solid and solid-electrolyte interfaces. Operando and in situ techniques are utilized to deconvolute the charge transfer mechanisms and degradation pathways. In this review, both materials development and Operando characterization are covered for advancing PEC technologies. The recent advances made in the PEC materials are first reviewed including the applied improvement strategies for transition metal oxides, nitrites, chalcogenides, Si, and group III-V semiconductor materials. The efficiency, stability, scalability, and electrical conductivity of the aforementioned materials along with the improvement strategies are compared. Next, the Operando characterization methods and cite selected studies applied for PEC electrodes are described. Operando studies are very successful in elucidating the reaction mechanisms, degradation pathways, and charge transfer phenomena in PEC electrodes. Finally, the standing challenges and the potential opportunities are discussed by providing recommendations for designing more efficient and electrochemically stable PEC electrodes.

Determination of the effective critical breakdown field for Si, wide, and extreme bandgap semiconductor superjunction devices

Designing high voltage superjunction (SJ) power devices with wide bandgap and extreme bandgap semiconductors, when compared to silicon, can enhance the trade-off between RON,sp and BV significantly, due to their >10× higher avalanche breakdown electric field. Nevertheless, because of the difference in the breakdown field profile and ionization path length, the effective breakdown field for these semiconductor SJ devices has not been determined theoretically. Consequently, we estimate and compare the effective critical breakdown electric field for SJ device structures in Si, 4H–SiC, 2H–GaN, β-Ga2O3, diamond, and AlN using Technology Computer Aided Design TCAD simulation. We also establish its dependence on the SJ devices’ structural parameters, such as the pillar thickness. Furthermore, we also quantitatively compare the on-state performance of these SJ devices, including their thermal capabilities, using a paramount figure-of-merit to underscore the potential improvement possible.

Optoelectronic properties of Au/n-type Si semiconductor structures with SiO2 interlayer

In this study, we investigated the effect of light intensity on electrical and photovoltaic properties using current-voltage (I–V) measurements at room temperature of Au/n-type Si structures with SiO2 interface layer. At each light intensity, the obtained main electrical characteristics such as ideality factors (n), barrier heights (Φbo), rectification ratios (RR), saturation currents (I0) and series resistances (RS) of Au/SiO2/n-type Si structures were calculated from both thermionic emission (TE) and Cheung methods using I–V measurements and compared to each other. Experimental results showed that while the n and I0 values increased with the increase in the light intensity, the Φbo and RR values decreased. While the ideality factor values obtained using the TE method ranged between 1.973 (at dark) and 2.250 (for 100 mW/cm2), these values were obtained between 3.227 and 3.482 using the Cheung method. At the same time, while the barrier height values obtained using the TE method ranged between 0.865 eV (at dark) and 0.817 eV (for 100 mW/cm2), these values were obtained between 0.773 eV and 0.742 eV using the Cheung method. It was observed that while the n values obtained from TE theory were smaller than the values obtained from the Cheung method, the Φbo values were larger than the values obtained from the Cheung function. Furthermore, for the Au/SiO2/n-type Si structures, the photovoltaic parameters such as short circuit current (Isc) and open circuit voltage (Voc) and photocurrent (Iph) were examined under dark, daylight and various light intensities (from 20 to 100 mW/cm2).

Optimization of the coupling efficiency under self-injection locking in a narrow linewidth hybrid wavelength tunable laser diode

In this study, a fiber Fabry–Perot (FFP) interferometer was connected to a hybrid wavelength-tunable laser diode consisting of a semiconductor optical amplifier chip and Si photonics chip, and spectral linewidth narrowing was achieved using the self-injection locking effect. The hybrid wavelength-tunable laser was equipped with a variable-reflectivity mirror, which allowed the optimization of κ, the coupling efficiency between the laser cavity and FFP interferometer. By optimizing κ, self-injection locking stabilized, and the linewidth was controlled between 4 and 300 kHz. This laser can be used to evaluate the linewidth required for communication systems such as digital coherent communication and the accuracy required for distance measurement.

Intrinsic surface states with electron–surface optical phonon interaction influence in wurtzite Zn-IV-N2 semiconductors

The electronic intrinsic surface states in wurtzite Zn-IV-N2 (with group-[Formula: see text], Ge and Si) semiconductors were investigated using an intermediate-coupling variational approach considering the electron–surface optical phonon interaction influence. The intrinsic surface state energy distribution and the average penetrating depth of surface state eigen-wave function of the electron have been evaluated numerically by changing the surface potential barrier [Formula: see text] for wurtzite ZnSnN2, ZnGeN2 and ZnSiN2, respectively. The results show that the electronic intrinsic surface state energy increased linearly with increasing surface potential barrier [Formula: see text] for all the calculated materials. The result also indicated that the electronic intrinsic surface state energies variations due to the influence of electron–surface optical phonon interaction are dozens of[Formula: see text]meV. The average penetrating depth of electronic surface state eigen-wave function is independent of [Formula: see text]. Its value is no more than the corresponding material’s lattice constant. The electronic scattering by surface optical phonon should be taken into account in the study of the intrinsic surface state of electrons in the group of Zn-IV-nitrides (with [Formula: see text], Ge and Si) semiconductors, especially for materials having strong electron–phonon interaction and wide band gap.

Monolithic Perovskite-Silicon Dual-Band Photodetector for Efficient Spectral Light Discrimination.

Selective spectral discrimination of visible and near-infrared light, which accurately distinguishes different light wavelengths, holds considerable promise in various fields, such as automobiles, defense, and environmental monitoring. However, conventional imaging technologies suffer from various issues, including insufficient spatial optimization, low definition, and optical loss. Herein, a groundbreaking advancement is demonstrated in the form of a dual-band photodiode with distinct near-infrared- and visible-light discrimination obtained via simple voltage control. The approach involves the monolithic stacking integration of methylammonium lead iodide (MAPbI3) and Si semiconductors, resulting in a p-Si/n-phenyl-C61-butyric acid methyl ester/i-MAPbI3/p-spiro-MeOTAD (PNIP) device. Remarkably, the PNIP configuration can independently detect the visible and near-infrared regions without traditional optical filters under a voltage range of 3 to -3V. In addition, an imaging system for a prototype autonomous vehicle confirms the capability of the device to separate visible and near-infrared light via an electrical bias and practicality of this mechanism. Therefore, this study pushes the boundaries of image sensor development and sets the stage for fabricating compact and power-efficient photonic devices with superior performance and diverse functionality.

MODIFICATION OF POLYPYRROLE FILM WITH GOLD MICROPARTICLES FOR GLUCOSE OXIDATION

This work presents the preparation of a gold-polypyrrole (Au-PPy) composite film on a silicon (Si) semiconductor supported by electrodeposition, and the study of its electrocatalytic activity as an anode catalyst for the glucose oxidation reaction in alkaline media. The microstructure of the as-prepared Au-PPy film is characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that the presence of the polymer film on the Si support improves the conductivity of the latter and enables better distribution of the Au microparticles on the electrode surface, thus helping to increase their catalytic activity for glucose oxidation.

Metal Nanoparticles Assisted Ultrafast Laser Plasmonic Microwelding of Oxide-Semiconductor Interconnects.

Integration of wafer-scale oxide and semiconductor materials meets the difficulties of residual stress and materials incompatibility. In this work, Ag NPs thin film is contributed as an energy confinement layer between oxide (Sapphire) and semiconductor (Si) wafers to localize the materials interaction during ultrafast laser irradiation. Due to the plasmonic effects generated within constructed dielectric-metal-dielectric structures (i.e., Sapphire-Ag-Si), thermal diffusion and chemical reaction between Ag and its neighboring materials facilitate the microwelding of Sapphire and Si wafers. Ag NPs can be totally sintered within the junction area to bridge oxide and semiconductor, while Al─O─Ag bond and Ag─Si bond are formed at Ag-Sapphire and Ag─Si interfaces, respectively. As-received heterogeneous joint exhibits a high shear strength up to 5.4MPa, with the fracture occurring inside Si wafer. Meanwhile, insertion of metal nanolayer can greatly relieve the residual stress-induced microcracking inside the brittle materials. Such wafer-scale Sapphire and Si interconnects thus show robust strength and excellent impermeability even after thermal shocking (-40 °C to 120 °C) for 200 cycles. This metal NPs layer-assisted plasmonic microwelding technology can extend to broad materials integration, which is promising for high-performance microdevices development in MEMS, MOEMS, or microfluidics.

Experimental investigation of electromagnetic interference impact on phase change material coated solar photovoltaic panel

ABSTRACT High Voltage Transmission Line Electromagnetic Field’s (HVTL-EMF) impact on solar PV performance is analyzed in the proposed work. Depending on HV-EMF, the electrical characteristics and conversion process of PhotoVoltaic (PV) panels are analyzed. Electromagnetic (EM) field from HV lines has a partially positive and somewhat negative impact on solar PV. When absorption probability is low, one photon and one phonon are required. Phonons are vibrational energy units. A solar PV cell made of Silicon (Si) semiconductor material requires phonons to have high conversion efficiency and electric field from HV transmission line induces phonon. In addition, electric field from HV line increases the solar cell temperature (10 to 15°C) to the ambient temperature. Because of high solar PV cell temperature and high EM field, solar PV power generation is affected by increasing panel temperature. The proposed system uses unnatural Phase Change Material (PCM-Glauber salt (Na2SO4.10 H2O)) coated to the backside of solar PV to normalize the temperature. The impact of electromagnetic fields produced by HV lines on solar cells coated with PCM is validated with experimental testing results. The experiment considers a HVTL of 230kV and solar PV rating of 20 W. The experimental results are measured at various distance ranging from 12 to 22 meters between solar PV and HV transmission lines. Conversion efficiency of solar PV with PCM coating under the impact of HVTL- EMF has increased by 3%.

Dual high-Q Fano resonances metasurfaces excited by asymmetric dielectric rods for refractive index sensing.

The metasurface refractive index sensor has a high degree of tunability and flexibility, providing excellent performance for high precision refractive index sensing applications. The metasurface absorber with metallic structure has been hindered in further sensor applications due to the inherent Ohmic loss of the metallic material. In this study, a dual nanorod metasurface structure based on semiconductor Si was designed, introducing a symmetry-breaking structure to excite dual ultra-narrow q-BIC resonance peaks with Fano line shapes. Both peaks are located in the near-infrared region, and multipole analysis shows that this strong field enhancement effect is induced by a magnetic dipole. Experimental results demonstrate the potential of this sensor to provide dual-channel detection while achieving high sensitivity and high Q-factor. We believe that this device exhibits outstanding performance and high practicality, providing a reference for the development and application of biological and environmental sensors.