Injection Efficiency Research Articles

Numerical simulation of electrically-pumped overgrown III-V microwire lasers on silicon

Electrically-pumped III-V lasers on Si by aspect ratio trapping (ART) techniques have been a promising candidate for Si-based light sources. Although the lasers based on the ART approach enable large-scale integration and are compatible with complementary metal-oxide semiconductor processes, the sub-micron size laser structure suffers from severe metal absorption loss and heat accumulation. In this paper, we propose a novel Si-based III-V multi-quantum well laser by ART methods. The overgrowth of III-V microwires is adopted, with additional {110} quantum wells (QWs) generated during epitaxy. Through numerical simulation, the mode loss of the overgrowth structure is reduced from 3.59 dB/cm to 0.96 dB/cm, the threshold current is decreased by 42.5% and the output power is increased by 91.7% under pulsed conditions. Due to the growth of QWs on {110} planes, the injection efficiency of the device increases, leading to an improvement of performance. The effects of temperature and cavity length on the lasing characteristics of the device under continuous wave (CW) conditions are also analyzed that the proposed structure can realize CW lasing at room temperature. Moreover, the device deterioration caused by growth defects is discussed, which can be improved by high reflection coating. The suggested Si-based overgrowth III-V microwire laser has great potential to integrate high-density electrically-pumped light sources for silicon photonics.

Magnetic tunnel junction based on bilayer LaI2 as perfect spin filter device

The discovery of van der Waals intrinsic magnets has expanded the possibilities of realizing spintronics devices. We investigate the transmission, tunneling magnetoresistance ratio, and spin injection efficiency of bilayer LaI2 using a combination of first-principles calculations and the non-equilibrium Green’s function method. Multilayer graphene electrodes are employed to build a magnetic tunnel junction with bilayer LaI2 as ferromagnetic barrier. The magnetic tunnel junction turns out to be a perfect spin filter device with an outstanding tunneling magnetoresistance ratio of 653% under a bias of 0.1 V and a still excellent performance in a wide bias range. In combination with the obtained high spin injection efficiency this opens up great potential from the application point of view.

Swelling damage characteristics induced by CO2 adsorption in shale: Experimental and modeling approaches

Carbon dioxide (CO2) geological sequestration represents a critical technology in mitigating climate change. Shale reservoirs demonstrate a pronounced affinity for CO2, resulting in adsorption-induced swelling that significantly impacts permeability, mechanical strength, injection efficiency, and sequestration safety. For this, we tried to explore the key factors driving the swelling of shale upon CO2 injection and its subsequent impact on reservoir properties. Utilizing a self-developed high-temperature-pressure gas adsorption apparatus, we measured strain in Jurassic shale at 308 K under constant hydrostatic pressure with helium (He) at 1300 psi (1 psi = 6.895 kPa) and CO2 at 850 psi. Next, we investigated the influence of CO2 concentration on swelling protentional while maintaining constant pressure, uncovering the anisotropic deformation in relation to pressure. It shows that CO2 adsorption induces significant swelling in shale, following a Langmuir-type pressure relationship. Deformation is more pronounced perpendicular than that parallel to the bedding plane. At low pressure, vertical swelling is 2.28 times greater than the horizontal; while at high pressure, the vertical compression is 31.26 times greater than the horizontal. It seems that the anisotropic swelling enhances permeability predictions during CO2 injection. Mixed gases under constant compression can prompt gas desorption, stress redistribution, and alterations in pore structure, amplifying He compression effect. The strain induced after replacing CO2 with He exceeds that from pure He injection. The asynchronous response of CO2-induced swelling and mechanical compression can precipitate crack propagation and fracturing. Overall, anisotropic swelling from CO2 adsorption changes pore structure and permeability, affecting fluid flow and storage. Considering CO2 concentration and anisotropic characteristics in reservoir modeling is essential for optimizing injection strategies and enhancing reservoir efficiency.

Identification and characterization of dominant seepage channels in oil reservoirs after polymer flooding based on streamline numerical simulation

Reservoir heterogeneity, water-oil mobility ratio, cementation degree, and strong injection and production significantly influence long-term waterflooding and polymer flooding processes in oil reservoir development, leading to the formation of low-resistance dominant seepage channels in the lower part of thick oil layers without internal laminations. Understanding the spatial distribution and evolution of dominant seepage channels in oil reservoirs during waterflooding and polymer flooding is crucial for improving reservoir development and recovery rates. It uses a streamlined numerical simulation method to quantitatively show the spatial and temporal distribution of dominant seepage channels in the oil reservoir. A model and chart were created to demonstrate the relationship between permeability and throat radius, capturing changes in reservoir permeabilities over time. The study developed a comprehensive mathematical model to identify dominant seepage channels, considering parameters such as inter-well flow ratio, injection efficiency, permeability change value, and water saturation. Research findings indicate a 14.8 % increase in reservoir permeability after polymer flooding, with slight changes in porosity and a 20.3 % decrease in clay content. The established mathematical model and identification criteria were used to comprehensively quantitatively evaluate flow channels, describing the distribution characteristics and evolution process of dominant seepage channels in the experimental area over four periods: pre-polymer flooding, low water-saturation period during polymer flooding, post-polymer injection, and subsequent 10 years of water flooding. Both polymer flooding and subsequent water flooding have significantly altered the distribution pattern of predominant fluid pathways: 254 well layers now demonstrate robust predominant fluid pathways (19 %); another 272 well layers feature moderately predominant fluid pathways (22 %); while an additional 440 well layers display weaker predominant fluid pathways (approximately 35 %). There has been a noticeable increase in both weak and moderate predominant fluid pathways, which are now more widespread in the area. However, localized occurrences of strong predominant fluid pathways persist with no significant change in their distribution characteristics. Analysis at four different time points shows a clear trend of increasing intensity as we move from polymer to subsequent water flooding in this decade. Additionally, examination along an axis from upper left to lower right reveals a linear progression that indicates clear connections among different categories of dominant seepage channel. The verification results show a strong correlation between the calculated dominant seepage channel distribution and actual water-injection profile test results, indicating that the method effectively identifies dominant seepage channels in oil reservoirs after polymer flooding and has the potential to enhance oil recovery further.

Implementing nonlinear optics from Off-Energy closed orbit at NSLS-II

To characterize the second-order (chromatic sextupole) magnet lattice with high precision, we implemented nonlinear optics from off-energy closed orbit (NOECO) tool based on the linear optics from closed orbit modulation (LOCOM) method, named LOCOM-NOECO. The preliminary numerical study indicates that 1–2% precision can be achieved for the calibration of chromatic sextupoles. This accuracy could potentially help in resolving some long-standing challenges of NSLS-II (e.g., the discrepancy between the designed and measured dynamic apertures) if such high precision can be fulfilled. As an independent crosscheck, we also implemented NOECO based on the independent component analysis (ICA) method using turn-by-turn (TBT) BPM data, named ICA-NOECO. Both ICA-NOECO and LOCOM-NOECO have been successfully applied to identify the pre-dialed random errors of a chromatic sextupole family including five power supplies, and achieved the root mean square (RMS) residual error of 1% and peak error less than 2%. Moreover, to mitigate the chromatic sextupole error effect, we applied the correction and achieved significant improvements in the injection efficiency as well as the dynamic apertures.

Unraveling carrier distribution in far-UVC LEDs by temperature-dependent electroluminescence measurements

The hole transport and the carrier distribution in AlGaN-based far-ultraviolett (UVC) light emitting diodes (LEDs) emitting around 233 nm was investigated. Temperature-dependent electroluminescence measurements on dual wavelength AlGaN multiple quantum well (MQW) LEDs show a strong shift in the spectral power distribution from 250 to 233 nm with decreasing temperature. Comparing experimental data with simulation shows that the hole mobility and the electron to hole mobility ratios have a significant influence on the carrier injection efficiency (CIE) and that the change in the spectral power distribution is originating from a change in the hole distribution in the MQWs. Poor hole injection and charge carrier confinement in the AlGaN MQW active region was identified as one of the main reasons for the low CIE in far-UVC LEDs.

Improvement of the Internal Quantum Efficiency of III‐Nitride Blue Micro‐Light‐Emitting Diodes by the Hole Accelerator at the Low Current Density

The hole accelerator is proven to benefit the hole injection for traditional light‐emitting diodes (LEDs) because the induced electric field provides the holes with more kinetic energy to pass through the electron‐blocking layer, enhancing the hole injection efficiency. Herein, the effect of the hole accelerator (HA) layer on the micro‐LEDs by modeling the characteristics of the devices with a current density of lower than 10 A cm−2 is investigated. The simulation results show that the appended HA layer brings a knot of the electric field in the HA layer, leading to higher internal quantum efficiency (IQE) than the device without HA under the low current density. The thickness and composition of HA, the quantum number, and the material of quantum barrier are also simulated and analyzed. The simulated radiative, Shockley–Read–Hall, and Auger recombination rates show that the IQE of the micro‐LED with the HA layer is higher than that without the HA layer under the current density of lower than 10 A cm−2.

Dual polarization for efficient III-nitride-based deep ultraviolet micro-LEDs

The deep ultraviolet (DUV) micro-light emitting diode (μLED) has serious electron leakage and low hole injection efficiency. Meanwhile, with the decrease in the size of the LED chip, the plasma-assisted dry etching process will cause damage to the side wall of the mesa, which will form a carrier leakage channel and produce non-radiative recombination. All of these will reduce the photoelectric performance of μLED. To this end, this study introduces polarized bulk charges into the hole supply layer (p-HSL) and the electron supply layer (n-ESL) respectively (dual-polarized structure) of the DUV μLED at an emission wavelength of 279 nm to enhance the binding of carriers and increase the injection efficiency of carriers. This is because the polarization-induced bulk charge can shield the polarized sheet charge on the interface and reduce the polarization electric field. The reduced polarization electric field in p-HSL can increase the effective barrier height of the conduction band in the p-type region and reduce the effective barrier height of the valence band. The decrease in the polarized electric field of n-HSL can reduce the thermal velocity of electrons, thereby enhancing the electron injection efficiency, reducing the Shockley–Read–Hall (SRH) recombination, and increasing the effective barrier height of the valence band. The study results indicate that the electron concentration and hole concentration of a μLED with dual polarization were increased by 77.93% and 93.6%, respectively. The optical power and maximum external quantum efficiency of μLED reached 31.04 W/cm2 and 2.91% respectively, and the efficiency droop is only 2.06% at 120 A/cm2. These results provide a new approach to solving the problem of insufficient carrier injection and SRH recombination in high-performance DUV μLEDs.

Simulation of Carrier Injection Efficiency in AlGaN-Based UV-Light-Emitting Diodes

Simulation of Carrier Injection Efficiency in AlGaN-Based UV-Light-Emitting Diodes

Stimulation of tight basalt reservoirs using supercritical carbon dioxide: Implications for large-scale carbon sequestration

Although supercritical carbon dioxide (SC-CO2) fracturing shows tremendous potential for maximizing injection efficiency and enhancing storage volumes, few investigations have been reported on the SC-CO2 fracturing characteristics of tight basalts and the reactions between fractured basalt and SC-CO2. In this study, hydraulic fracturing experiments were conducted on cylindrical basalt specimens using water and SC-CO2 as fracturing fluids. Geometric parameters were proposed to characterize the fracture morphologies based on the three-dimensional (3D) reconstructions of fracture networks. The rock slices with induced fractures after SC-CO2 fracturing were then processed for fluid (deionized water/SC-CO2)-basalt reaction tests. The experimental results demonstrate that SC-CO2 fracturing can induce complex and tortuous fractures with spatially dispersed morphologies. Other fracturing behaviors accompanying the acoustic emission (AE) signals and pump pressure changes show that the AE activity responds almost simultaneously to variation in the pump pressure. The fractured basalt blocks exposed to both SC-CO2 and water exhibit rough and uneven surfaces, along with decreased intensities in the element peaks, indicating that solubility trapping predominantly occurs during the early injection stage. The above findings provide a laboratory research basis for understanding the fracturing and sequestration issues related to effective CO2 utilization.

Microphysics of Particle Reflection in Weibel-mediated Shocks

Particle-in-cell (PIC) simulations have shown that relativistic collisionless shocks mediated by the Weibel instability accelerate ∼1% of incoming particles, while the majority are transmitted through the shock and become thermalized. The microphysical processes that determine whether an incoming particle will be transmitted or reflected are poorly understood. We study the microphysics of particle reflection in Weibel-mediated shocks by tracking a shell of test particles in a PIC simulation of a shock in pair plasma. We find that electrons in positron-dominated filaments and positrons in electron-dominated filaments efficiently reflect off of strong magnetic structures at the shock. To participate in diffusive shock acceleration, however, these reflected particles headed toward the upstream must avoid getting advected downstream. This is enabled by incoming filaments, which trap reflected particles carrying the same sign of current as the filaments. The final injection efficiency on the order of ∼1% thus results from the effectiveness of the initial reflection at the shock and the reflected particles’ probability of survival in the upstream postreflection. We develop a model that predicts the fraction of high-energy particles as a function of the properties of Weibel filamentation.

Regulating coordinatively unsaturated Co active sites in TA@ZIF-L(Co) via tannic acid for efficient photoelectrochemical water oxidation

Metal-organic frameworks (MOFs) as a cocatalyst can enhance the photoelectrochemical (PEC) water oxidation performance to a certain extent, but still suffer from deficient exposure of active sites and low electron mobility. In this work, 2D Leaf-like zeolitic imidazolate frameworks (ZIF-L) were selected as a precursor for the generation of defective structures by tannic acid (TA) functionalization-assisted etching, and then coupling it with BiVO4 to prepare a novel and highly efficient TA@ZIF-L(Co)/BiVO4 photoanode by a simple impregnation method. The photocurrent density of TA@ZIF-L(Co)/BiVO4 composite photoanode achieves 4.21 mA cm−2 at 1.23 VRHE under AM 1.5 G illumination, which is superior to that of ZIF-L(Co)/BiVO4, and three times that of the bare BiVO4, with a charge injection efficiency of up to 80 %, and its stability is also remarkably improved. Experimental results and DFT calculations showed that the introduction of TA not only improved the light absorption efficiency, but also exposed more active sites, increased the electron density of the coordinatively unsaturated Co active sites, and enhanced the polarized electric field on the surface, thus accelerating electron mobility. This work demonstrates that TA as a surface modifier has great potential to activate metal sites and change the electronic environment of MOFs for BiVO4-based photoanode in PEC water oxidation, providing valuable insights into the rational design of photoanodes.

Contact engineering for two-dimensional metal/qHP C60 van der Waals heterostructure

The fabrication of two-dimensional (2D) quasi-hexagonal phase (qHP) C60 semiconductor material offers a promising candidate for high-performance electronic devices. Selecting appropriate metals is crucial for achieving Ohmic contact (OhC) to enhance carrier injection efficiency. In this Letter, we used first-principles calculations to study the contact properties of seven 2D metal/qHP C60 van der Waals heterostructures. Metals with suitable work functions can form p-type Schottky contacts (p-ShCs), n-type Schottky contacts (n-ShCs), and OhCs. Differences in work function affect interface charge transfer, creating interface dipoles and causing band alignment deviations from the ideal Schottky–Mott limit. The calculated Fermi level pinning factors for n-type and p-type 2D metal/qHP C60 vdWh are 0.528 and 0.521, respectively. By regulating Φn and Φp based on electrostatic potential difference ΔV, we have achieved the ideal Schottky–Mott limit. We also studied the Schottky barrier height of the germanene/qHP C60 vdWh, finding that using electric field is an effective way to convert n-ShC to OhC or p-ShC. These findings provide theoretical guidance for constructing efficient 2D qHP C60 electronic devices.

Janus MoSH/WSi2N4 van der Waals Heterostructure: Two-Dimensional Metal/Semiconductor Contact.

Constructing heterostructures from already synthesized two-dimensional materials is of significant importance. We performed a first-principles study to investigate the electronic properties and interfacial characteristics of Janus MoSH/WSi2N4 van der Waals heterostructure (vdWH) contacts. We demonstrate that the p-type Schottky formed by MoSH/WSi2N4 and MoHS/WSi2N4 has extremely low Schottky barrier heights (SBHs). Due to its excellent charge injection efficiency, Janus MoSH may be regarded as an effective metal contact for WSi2N4 semiconductors. Furthermore, the interfacial characteristics and electronic structure of Janus MoSH/WSi2N4 vdWHs can not only reduce/eliminate SBH, but also forms the transition from p-ShC to n-ShC type and from Schottky contact (ShC) to Ohmic contact (OhC) through the layer spacing and electric field. Our results can offer a fresh method for optoelectronic applications based on metal/semiconductor Janus MoSH/WSi2N4 vdW heterostructures, which have strong potential in optoelectronic applications.

Achieving ultra-low contact barriers in MX2/SiH (M = Nb, Ta; X = S, Se) metal-semiconductor heterostructures: first-principles prediction.

Minimizing the contact barriers at the interface, forming between two different two-dimensional metals and semiconductors, is essential for designing high-performance optoelectronic devices. In this work, we design different types of metal-semiconductor heterostructures by combining 2D metallic MX2 (M = Nb, Hf; X = S, Se) and 2D semiconductor SiH and investigate systematically their electronic properties and contact characteristics using first principles calculations. We find that all the MX2/SiH (M = Nb, Ta; X = S, Se) heterostructures are energetically stable, suggesting that they could potentially be synthesized in the future. Furthermore, the generation of the MX2/SiH metal-semiconductor heterostructures leads to the formation of the Schottky contact with ultra-low Schottky barriers of a few tens of meV. This finding suggests that all the 2D MX2 (M = Nb, Ta; X = S, Se) metals act as effective electrical contact 2D materials to contact with the SiH semiconductor, enabling electronic devices with high charge injection efficiency. Furthermore, the tunneling resistivity of all the MX2/SiH (M = Nb, Ta; X = S, Se) MSHs is low, confirming that they exhibit high electron injection efficiency. Our findings underscore fundamental insights for the design of high-performance multifunctional Schottky devices based on the metal-semiconductor MX2/SiH heterostructures with ultra-low contact barriers and high electron injection efficiency.

Multiwavelength Modeling for the Shallow Decay Phase of Gamma-Ray Burst Afterglows

We simulate the emission in the shallow decay phase of gamma-ray burst afterglows using a time-dependent code. We test four models: the energy injection model, evolving the injection efficiency of nonthermal electrons, evolving the amplification of the magnetic field, and the wind model with a relatively low bulk Lorentz factor. All of the four models can reproduce the typical X-ray afterglow lightcurve. The spectral shape depends on not only the parameter values at the time corresponding to the observer time but also the past evolution of the parameters. The model differences appear in the evolution of the broadband spectrum, especially in the inverse Compton component. Future gamma-ray observations with imaging atmospheric Cherenkov telescopes such as the Cherenkov Telescope Array will reveal the mechanism of the shallow decay phase.

Highly Efficient Photoelectrochemical Alkene Epoxidation on a Dye-Sensitized Photoanode.

In photoelectrochemical (PEC) cells, selective oxidation of organic substrates coupled with hydrogen evolution represents a promising approach for value-added chemical production and solar energy conversion. In this study, we report on PEC epoxidation of alkenes at a ruthenium dye-sensitized photoanode in a CH3CN/H2O mixed solvent with LiBr as a mediator and water as the oxygen source. The dye-sensitized photoanode was found to exhibit significant advantages in the simultaneous improvement of charge separation and suppression of charge recombination. First, LiBr as a redox mediator plays a critical role in charge separation, leading to an excellent excited electron injection efficiency of 95% and a high dye regeneration efficiency of 87%. Second, the predominant charge recombination pathway on the dye-sensitized photoanode is efficiently blocked by the reaction between alkene and the in situ generated bromine oxidant. As a result, the current system achieved a remarkable photocurrent density of over 4 mA cm-2 with a record-high incident photo-to-current efficiency (IPCE) of 51% and extraordinary selectivity of up to 99% for the epoxidation of a wide range of alkenes. Meanwhile, nearly 100% Faradaic efficiency for hydrogen evolution was obtained. The performance shown here exceeds that obtained by metal oxide-based semiconductor photoanodes under comparable conditions, demonstrating the great potential of dye-sensitized photoelectrodes for organic synthesis owing to their diversity and tunability.

Two fast multiturn injection models for synchrotron injection efficiency optimization

A multiturn injection scheme is used in the XiPAF-Upgrading synchrotron, with beam loss mainly occurring at the injection septum. The paper presents two theoretical models for calculating the efficiency of multiturn injection in compact synchrotrons, with a focus on the situation of dispersion mismatch at the injection point. The first model is the beam phase ellipse rotation model, which is based on the beam projection distribution. The second model is the injection septum rotation model, which is based on the particle coordinate criterion. The deviation in efficiency between both injection models and the simulation results is less than 5%, and the calculation speed has increased by a factor of 1000 compared to PyORBIT simulations. The models are used to optimize the multiturn injection efficiency of the XiPAF-Upgrading synchrotron, resulting in an optimal injection efficiency of 92%.

Near-infrared detection based on the excitation of hot electrons in Au/Si microcone array

Although the photoresponse cut-off wavelength of Si is about 1100 nm due to the Si bandgap energy, the internal photoemission effect (IPE) of the Au/Si junction in Schottky detector can extend the absorption wavelength, which makes it a promising candidate for the Si-based infrared detector. However, due to low light absorption, low photon–electron interaction, and poor electron injection efficiency, the near-infrared light detection efficiency of the Schottky detector is still insufficient. The synergistic effect of Si nano/microstructures with a strong light trapping effect and nanoscale Au films with surface plasmon enhanced absorption may provide an effective solution for improving the detection efficiency. In this paper, a large-area periodic Si microcone array covered by an Au film has successfully been fabricated by one-time dry etching based on the mature polystyrene microspheres lithography technique and vacuum thermal deposition, and its properties for hot electron-based near infrared photodetection are investigated. Optical measurements show that the 20 nm-thick Au covered Si microcone array exhibits a low reflectance and a strong absorption (about 85%) in wide wavelength range (900–2500 nm), and the detection responsivity can reach a value as high as 17.1 and 7.0 mA W−1 at 1200 and 1310 nm under the front illumination, and 35.9 mA W−1 at 1310 nm under the back illumination respectively. Three-dimensional finite difference time domain (3D-FDTD) simulation results show that the enhanced local electric field in the Au layer distributes near the air/Au interface under the front illumination and close to the Au/Si interface under the back illumination. The back illumination favors the injection of photo-generated hot electrons in Au layer into Si, which can explain the higher responsivity under the back illumination. Our research is expected to promote the practical application of Schottky photodetectors to Si-compatible near infrared photodetectors.

Small sized of anion doping effect on semiconducting single-walled carbon nanotube network for field-effect transistors

Carbon nanotubes have shown great promise for high-performance, large-area, solution processable field-effect transistors due to their exceptional charge transport properties. In this study, we utilize the spin-coating method to form networks from selectively sorted semiconducting single-walled carbon nanotubes (s-SWNTs), aiming for scalable electronic device fabrication. The one-dimensional nature of s-SWNTs, however, introduces significant roughness and charge trap sites, hindering charge transport due to the van der Waals gap (∼0.32 nm) between nanotubes. Addressing this, we explored the effects of anion doping on the spin-coated s-SWNT random network, with a focus on the influence of the small size of halogen anions (0.13–0.22 nm) on these electronic properties. Raman and ultraviolet–visible–near-infrared optical spectroscopy results indicate that smaller anions significantly enhance doping effects through strong non-covalent anion–π interactions, improving charge transport and carrier injection efficiency in s-SWNTs, especially for n-type operation. This improvement is inversely proportional to the size of the halogen anions, with the smallest anion (fluorine) effectively transitioning the electrical characteristics of the s-SWNT network from ambipolar to n-type by reducing both junction and contact resistances through anion doping, based on anion–π interaction.