Effect Of Surface Recombination Research Articles

Exploring the Effect of Microstructure and Surface Recombination on Hydrogen Effusion in Zn–Ni‐Coated Martensitic Steels by Advanced Computational Modeling

Exploring the Effect of Microstructure and Surface Recombination on Hydrogen Effusion in Zn–Ni‐Coated Martensitic Steels by Advanced Computational Modeling

Exploring the Effect of Microstructure and Surface Recombination on Hydrogen Effusion in Zn–Ni‐Coated Martensitic Steels by Advanced Computational Modeling

Ultrahigh‐strength steel (UHSS) structures are plated with Zn–Ni coatings because of their excellent corrosion resistance properties, but the plating process is accompanied by the production of hydrogen. The presence of hydrogen in steel results in hydrogen embrittlement. Hence, during the production of UHSS parts, dedicated outgassing steps are employed to remove the diffusible hydrogen from the steel. In a production environment, the real effect of the outgassing process and the outgassing efficiency is unknown for parts coated with Zn–Ni. Hence, a finite element model is developed to capture the evolution of the hydrogen concentration profile in coated UHSS parts during outgassing to study the influence of coating morphology and microstructural features of steel. In order to develop the geometry of the model, scanning electron microscope images are analyzed to understand the microstructure and morphology of the coating. Numerical samples are generated by combining different coating morphologies with steel substrates of varying microstructural features to attain a series of samples with varying features. The results of the outgassing simulations clearly demonstrate the major role of the coating morphology on the hydrogen flux.

Influence of surface nanostructures on the catalytic recombination of hyperthermal non-equilibrium flow

One of the key challenges for accurate prediction of hypersonic aerodynamic heating is the exothermic uncertainty due to the complex surface catalytic recombination effect, which is caused by the strong interactions between highly non-equilibrium dissociated gas and the thermal protection material surface. Employing engineered surface morphology to improve thermal protection effects has been proposed, but its effects on surface catalytic recombination remain unclear. To address this problem, this work employs the reactive molecular dynamics method to investigate the surface adsorption and recombination characteristics of continuous impingement of atomic oxygen upon eight different nano-structured silica surfaces. A parametric study of the influences of the gas incident angles and the surface structural parameters, i.e., roughness factor and surface fraction, is conducted. The results show that the surface catalytic recombination performance is very sensitive to the incident angle of the incoming gas, and the presence of nanostructures increases the recombination rate. The influence of surface morphology shows a complicated feature, where nanostructures with moderated fin height and high surface fraction are beneficial for the inhibition of surface recombination effects, leading to reduced exothermic heat release. Such microscopic revelation of the surface morphology effect is helpful for accurate prediction of aerodynamic heat and provides guidance for the surface engineering of optimized morphology to achieve improved thermal protection effect.

Cross‐Sectional Carrier Lifetime Profiling and Deep Level Monitoring in Silicon Carbide Films Exhibiting Variable Carbon Vacancy Concentrations

The carrier lifetime control over 150 μm thick 4H‐SiC epitaxial layers via thermal generation and annihilation of carbon vacancy (VC) related Z1/2 lifetime killer sites is reported. The defect developments upon typical SiC processing steps, such as high‐ and moderate‐temperature anneals in the presence of a carbon cap, are monitored by combining electrical characterization techniques capable of VC depth‐profiling, capacitance–voltage (CV) and deep‐level transient spectroscopy (DLTS), with a novel all‐optical approach of cross‐sectional carrier lifetime profiling across 4H‐SiC epilayer/substrate based on imaging time‐resolved photoluminescence (TRPL) spectroscopy in orthogonal pump‐probe geometry, which readily exposes in‐depth efficacy of defect reduction and surface recombination effects. The lifetime control is realized by initial high‐temperature treatment (1800 °C) to increase VC concentration to ≈1013 cm−3 level followed by a moderate‐temperature (1500 °C) post‐annealing of variable duration under C‐rich thermodynamic equilibrium conditions. The post‐annealing carried out for 5 h in effect eliminates VC throughout the entire ultra‐thick epilayer. The reduction of VC‐related Z1/2 sites is proven by a significant lifetime increase from 0.8 to 2.5 μs. The upper limit of lifetimes in terms of carrier surface leakage and the presence of other nonradiative recombination centers besides Z1/2, possibly related to residual impurities such as boron are discussed.

Investigation of the surface recombination rate in polycrystalline films from the A6B6 compound by the MW-PC method

In this article, the surface recombination rates in polycrystalline CdTe films obtained on oxidized substrates are studied. The results of the corona discharge effect on the CdTe-SiO2–Si-Al structure are presented. In this case, in the static mode, a shift of the short-circuit current spectra to the short-wave region was observed. To analyze the shift of the short-circuit current spectra, the method of microwave probe photoconductivity (MW-PC) was used and non-contact registration of decay transients for excess carriers was carried out. Considering that for CdTe in the wavelength range of about 800–1000 nm, the absorption coefficient increases sharply with the excitation photon energy at the absorption edge. It was found that the surface recombination rate was estimated at 19 ns. It has been determined that the filling of surface traps in CdTe leads to a decrease in the effect of surface recombination.

Comparing three numerical methods for current–voltage characteristics simulations of organic solar cells considering surface recombination effects

Comparing three numerical methods for current–voltage characteristics simulations of organic solar cells considering surface recombination effects

Analytical study of gradual photovoltaic CuInGaSe2 based solar cell performances

The most significant challenge for environment and renewable energy researchers is to achieve good performance, as well as cost efficiency in terms of solar generators especially in the PV sector. Regarding the thin film solar cells based on Cu(In,Ga)Se2, the present work dissertation is concerned with the performance of a graded band gap solar cell based on (CIGS). The aim is to determine the influence of physical and geometrical parameters on performance. Results indicate that the increase in electric field resulting from the gradient of the band gap dismantles the effects of surface recombination. The results obtained are an efficiency of 26 % for Eg0=1.67 eV, Eg1=1.02 eV and a thickness of layer p and n d1=1µm, d2=2µm respectively.

Analytical model of the modulated photoluminescence in semiconductor materials

Modulated photoluminescence (MPL) is an optoelectronic characterization technique of semiconductor materials. Going to high frequencies enables one to characterize fast phenomena, and so materials with a short lifetime such as chalcogenides or III–V absorbers. Some typical signatures have already been experimentally observed. However, physical mechanisms and quantitative analyses are not well understood yet. Here, using both an analytical approach and a full numerical modeling, we study how the energy position of a defect level, its electron and hole capture cross sections, its density, influence the frequency dependence of the MPL phase. We show that quantitative information can be extracted. We also study the effect of additional surface recombination, and of non homogeneities created by carrier generation profiles or asymmetric top surface and bottom surface recombination velocities, where diffusion of the carriers plays a role and can be limiting at high frequency. Finally we apply our model to an experimental result to extract defect parameters of the sample. Our analysis highlights the usefulness of MPL and the importance of having a proper modeling of the experiment.

How Thin Practical Silicon Heterojunction Solar Cells Could Be? Experimental Study under 1 Sun and under Indoor Illumination

The transition toward thinner microcrystalline silicon wafers for their potential performance gain has been of interest in recent years. Theoretical predictions have estimated a maximum efficiency for silicon wafers to be at about 100−110 μm thickness. The potential and losses in silicon heterojunction solar cells prepared on wafers with thickness in the range of 60−170 μm with focus on open‐circuit voltage (V OC) and fill factor (FF) are studied experimentally. The applicability of thinner wafers for low light and indoor applications using light emitting diode (LED) lighting is also studied. The implied V OC (iV OC) is observed to increase with a decrease in wafer thickness according to theoretical predictions with absolute values approaching the theoretical limit. Unlike the iV OC, the implied FF is observed to decrease with wafer thickness reduction opposite to the theoretical predictions which are related to the effect of surface recombination. A combination of gains and losses results in a broad range of high efficiency under 1 sun for wafer thicknesses ranging from 75 to 170 μm with maximum of 22.3% obtained at 75 μm. As for indoor performance, thinner wafers show slightly better efficiency at lower light intensity under sun and LED illumination, promising improved performance for even thinner devices.

Effect of Surface Recombination on Diffusion Length and Active Cavity Life time

This work presents an analytical study for simulating a Fabry-Perot Bi-stable etalon (F-P cavity) filled with a dispersive optimized nonlinear optical material (Kerr type) such as semiconductors Indium Antimonite (InSb). Depending on the obtained results and because of a trade-off between the optical path length of the sample and active cavity lifetime, an optimization procedure was applied on the InSb etalon/CO laser parameters; critical switching irradiance (Ic) was applied via simulation systems of optimization procedures of optical cavity (Matlap program was used to study the optical Bi-stability of a nonlinear Fabry-Perot cavity). In order to achieve minimum switching power and faster switching time, the optimization surface recombination on the diffusion length and effective cavity lifetime was studied.
 In addition, for a specific absorption value 400 cm-1, the lifetime coefficient values were 0.33 , 0.091 , 0.0172 ns for sample thickness (D) = 500 , 60 , 20 mm, respectively. Also, for a bulk recombination time (Tl) of 200 ns, specific absorption (α) of 50 cm1, and D of 20 mm, the surface recombination speed value was 2.845 x 105 cm/sec, whereas the active lifetime, which is defined as the thickness over the surface recombination speed (sυ) (D/2sυ), was equal to 3.5ns.

Structural Characterization of Fine γ′-Fe4N Nitrides Formed by Active Screen Plasma Nitriding

The paper presents the structural characterization of γ′-Fe4N nitrides produced by active screen plasma nitriding (ASPN) processes. Experiments were performed on the Fe-Armco model material at 693, 773, and 853 K for 6 h. Investigation of the properties of the substrate was realized using scanning electron microscopy (SEM, SEM–EBSD/Kikuchi lines), energy-filtered transmission electron microscopy (TEM-EFTEM), X-ray diffraction (GID, grazing incidence diffraction, micro-XRD), and secondary ion mass spectroscopy (SIMS). Results have confirmed that the γ′-Fe4N nitrides’ structure and morphology depend considerably on the nitriding process’s plasma conditions and cooling rate. In addition to that, γ′-Fe4N nitrides’ formation can be correlated with the surface layer saturation mechanism and recombination effect. It has been shown that the γ′-Fe4N structure depends considerably on several phenomena that occur in the diffusive layer (e.g., top layer decomposition, nitrogen, and carbon atoms’ migration). Our research proves that the nitrogen concentration gradient is a driving force of nitrogen migration atoms during the recombination of γ′-Fe4N nitrides. Finally, realized processes have allowed us to optimize active screen plasma nitriding to produce a surface layer of fine nitrides.

Influence of Surface Recombination on Open Circuit-Voltage of a Single Nanowire Solar Cell with Radial p-n Junction

An analytical model is proposed for the study of the effect of surface recombination on the characteristics of a solar cell made of a nanowire with a radial p-n junction formed between its ‘core’ and ‘shell’ with different types of the conductivity. The influence of the surface recombination on such important parameters of the solar cell as the short circuit current, open circuit voltage, and efficiency of conversion of the energy of solar radiation into electrical energy is considered when the shell width is varying over a wide range. It is shown that the relatively low open-circuit voltage, often observed experimentally in such solar cells, can be partially caused by significant surface recombination on the sidewall of the nanowire, the role of which increases with decreasing nanowire diameter and increasing surface to volume ratio.

Numerical analysis of the effect of surface recombination on N-atom in discharge and post-discharge region

In this paper, the effect of surface recombination on N-atom production is discussed through a one-dimensional simulation of Townsend dielectric barrier discharge in pure N2 based on a fluid model. By comparison of the experimental results, the recommended value of the sticking coefficient of N–N surface recombination is 0.5–1. The spatial-temporal distribution of N-atom of simulation results in discharge and post-discharge agree with experimental results. When the sticking coefficient is 0.5, the primary active species include N, N2(A), and N2(a′). N4+ is the densest positive ion, which can reach 4.77 × 109 cm−3. N-atom can reach the saturation level within about 30 ms. The highest number density is 3.14 × 1014 cm−3 at the position 0.25 mm away from the surface. The numerical simulation results are very consistent with the experimental results. The contribution of surface recombination and three-body recombination for the decay of N-atom are roughly equal in the post-discharge region.

Leakage Current in P N Junction Diode by Influent from SRFE Process

This paper present the effect from soft radiation flash exposure (SRFE) on electrical properties of semiconductor device. SRFE process take only few second on semiconductor device but it quite impact to device performance. The part we will study impact from SRFE such as surface and bulk. COMSOL is tool for help to understand more detail in term of surface recombination, temperature and bulk effect. Surface of device get impact from radiation and temperature generate from radiation. Also, silicon bulk get damage from radiation due to has high penetrate. From electrical results show that leakage current of device has reduce after SRFE process, mean radiation can help to improve or recover damage from fabrication process.

Simulation and Optimization Design of SiC-Based PN Betavoltaic Microbattery Using Tritium Source

In this paper, the Monte Carlo method and numerical model are used to build the electrical model of a SiC-based betavoltaic microbattery using a 3H source, and the influences of structural parameters and the surface recombination effect on the output characteristics of the SiC PN battery are simulated. According to Monte Carlo calculations based on the energy spectrum of the 3H source, the ionization energy deposition approaches the exponential distribution along the depth direction, and most of the 22rs are concentrated near the material surface. The ionization energy deposition data is converted into non-equilibrium carrier information for the numerical simulation of the battery’s output characteristics. The simulation results show that the conversion efficiency of the battery rises first, and then decreases with the increase of the doping concentration of the N region. This is because the N region-doping affects the depletion region width and the built-in electrical potential at the same time. After considering the surface recombination effect, the conversion efficiency decreased significantly. Thinning the thickness of or moderately reducing the doping concentration of the P region will weaken the surface recombination effect.

Composition-Dependent Passivation Efficiency at the CdS/CuIn1- x Gax Se2 Interface.

The bandgap of CuIn1- x Gax Se2 (CIGS) chalcopyrite semiconductors can be tuned between ≈1.0 and ≈1.7 eV for Ga contents ranging between x = 0 and x = 1. While an optimum bandgap of 1.34 eV is desirable for achieving maximum solar energy conversion in solar cells, state-of-the-art CIGS-based devices experience a drop in efficiency for Ga contents x > 0.3 (i.e., for bandgaps >1.2 eV), an aspect that is limiting the full potential of these devices. The mechanism underlying the limited performance as a function of CIGS composition has remained elusive: both surface and bulk recombination effects are proposed. Here, the disentanglement between surface and bulk effects in CIGS absorbers as a function of Ga content is achieved by comparing photogenerated charge carrier dynamics in air/CIGS and surface-passivated ZnO/CdS/CIGS samples. While surface passivation prevents surface recombination of charge carriers for low Ga content (x < 0.3; up to 1.2 eV bandgap), surface recombination dominates for higher-bandgap materials. The results thus demonstrate that surface, rather than bulk effects, is responsible for the drop in efficiency for Ga contents larger than x ≈ 0.3.

An Improved SPICE Model of SiC BJT Incorporating Surface Recombination Effect

The SiC bipolar junction transistor (BJT) offers an attractive alternative to the more popular SiC mosfet . It is important to develop an accurate SPICE model for the SiC BJT to enable its use in power electronic applications. The current gain of an SiC BJT may degrade considerably at high current levels and/or at high temperatures largely due to the surface recombination effect. In this paper, an improved SPICE behavioral model that accurately accounts for the current gain depending on the collector current and the junction temperature is proposed for the SiC BJT. In this paper, the conventional Gummel–Poon model is extended to include this important physical effect by adding a diode between the external base and emitter terminals of the BJT. A two-step model parameter extraction method is developed. First, the basic Gummel–Poon model parameters are extracted from low-current measurement data, and then, the new surface recombination model parameters are extracted by observing the difference between the measured high-level base current and the standard Gummel–Poon model prediction. The simulated static and switching characteristics of the new SiC BJT model match the measured data very well. Finally, the new SPICE model is used in the performance assessment of a proportional base driver technique embedded in a 3.6-kW boost converter, demonstrating its validity in helping with the optimum design of power electronic applications based on SiC BJTs.

On the effect of surface recombination in thin film solar cells, light emitting diodes and photodetectors

Radiative and non-radiative charge carrier recombination in thin-film diodes plays a key role in determining the efficiency of electronic devices made of next generation semiconductors such as organic, perovskite and nanocrystals. In this work, we show that lowering the bulk recombination does not necessarily result in enhanced performance metrics of electronic devices. From the perspective of charge carrier extraction and injection, the radiative limit of the open-circuit voltage of solar cells, noise current of photodetectors and lasing threshold of injection lasers cannot be improved if the contacts are not perfectly selective. A numerical drift-diffusion model is used to investigate the interplay between bulk recombination and surface recombination of minority carriers at the contacts in bipolar thin diode devices based on low-mobility semiconductors. The surface recombination becomes prominent in case of reduced bulk recombination strengths when non-selective contacts, i. e. contacts that are either metallic or have imperfect charge-selective interlayer, are employed. Finally, we derive analytical approximations for the case when diffusion-limited surface recombination of minority carriers at Ohmic contacts dominates the dark current. These results indicate that having perfectly selective contacts becomes crucial in systems with suppressed bulk recombination - a challenging requirement for future state-of-the-art thin-film solar cells, light-emitting devices and photodetectors made of next generation semiconductors.

Effects of surface recombination and excitation power on quantitative analysis of carbon in Si using room-temperature photoluminescence after electron irradiation

We have analyzed the effects of the surface recombination and the excitation power on the photoluminescence (PL) spectra in Si at room temperature in relation to the possible errors in the PL method after electron irradiation for the quantification of carbon in Si. The surface passivation enhances the band-to-band emission substantially but only slightly the carbon-related emission band. This variation produces an error in the carbon quantification, since the ratio between the two emissions is used as a measure of the carbon concentration. We show that the variation is caused by different excitation power dependence of the two emissions.

Electrochemistry of Sputtered Hematite Photoanodes: A Comparison of Metallic DC versus Reactive RF Sputtering.

The water splitting activity of hematite is sensitive to the film processing parameters due to limiting factors such as a short hole diffusion length, slow oxygen evolution kinetics, and poor light absorptivity. In this work, we use direct current (DC) magnetron sputtering as a fast and cost-effective route to deposit metallic iron thin films, which are annealed in air to obtain well-adhering hematite thin films on F:SnO2-coated glass substrates. These films are compared to annealed hematite films, which are deposited by reactive radio frequency (RF) magnetron sputtering, which is usually used for depositing metal oxide thin films, but displays an order of magnitude lower deposition rate. We find that DC sputtered films have much higher photoelectrochemical activity than reactive RF sputtered films. We show that this is related to differences in the morphology and surface composition of the films as a result of the different processing parameters. This in turn results in faster oxygen evolution kinetics and lower surface and bulk recombination effects. Thus, fabricating hematite thin films by fast and cost-efficient metallic iron deposition using DC magnetron sputtering is shown to be a valid and industrially relevant route for hematite photoanode fabrication.