Continuity Equation Research Articles

Investigating the prediction ability of the ionospheric continuity equation during the geomagnetic storm on May 8, 2016

Abstract Ionospheric electron density (IED) and vertical total electron content (VTEC) are two of the most important characteristics that interpret the ionosphere. Today, satellite geodesy plays an important role in providing these data. Apart from monitoring the ionosphere by means of Global Navigation Satellite System observations, predictions of these ionospheric characteristics have also been taken into consideration. The majority of prediction methods in the ionosphere are focused on VTEC prediction. The continuity equation in the ionosphere is a spatiotemporal partial differential equation that can be used to predict both IED and VTEC. In this study, we address this issue during May 8, 2016, which was a day of high geomagnetic activity. For this purpose, first, high-accuracy IED grids with a spatial resolution of 0.5° × 0.5° in longitude and latitude, 50 km in altitude, and a temporal resolution of 10 min are prepared. These IED grids are called analysis grids and are derived by assimilation of GPS-derived VTECs into the background IED grids provided by international reference ionosphere. Second, the analysis grids can be utilized as the initial and boundary values in the continuity equation to predict IED for the next 3 h with a step of 10 min. The analysis grids are constructed over the Iran region, and the performance of the continuity equation in the ionosphere prediction is investigated during the strongest geomagnetic storm of 2016. Finally, the accuracy of the predictions has been evaluated in two ways. First, analysis grids with high accuracy are available for each epoch in which the prediction is presented. On average, the root mean square (RMS) of the differences between the predicted IEDs and the analysis IEDs is 1.66 × 1010 el/m3 for 1-h predictions and 5.33 × 1010 el/m3 for 3-h predictions. Second, by numerical integration of the predicted grids in the vertical direction, VTECs are estimated and compared with VTEC values of test data that were already known. On average, the RMS of their difference was 1.29 total electron content unit (TECU) for 1-h predictions and 2.57 TECU for 3-h predictions. An acceptable accuracy for both IED and VTEC prediction by a continuity equation has been obtained up to 3 h on the most active ionospheric day.

Darcy-Forchheimer Flow of Hybrid Carbon Nanotube over a Permeable Stretching/Shrinking Curved Surface

The Darcy-Forchheimer flow of hybrid carbon nanotube over a permeable curved stretching/shrinking surface is investigated in this work. The Darcy-Forchheimer phrase is used to describe porous spaces with different porosity and permeability. The current problem is modelled using curvilinear coordinates due to the curved form of the geometry. A similarity transformation will be applied to the partial differential equations (PDEs) of the fluid flow to convert them to ordinary differential equations (ODEs). The numerical solutions of the equations of continuity, momentum, and energy are obtained using the bvp4c solver in MATLAB. To examine the impact of various physical parameters, including nanoparticle volume fraction, suction, inertia coefficient, and porosity, on temperature and velocity profiles, as well as the local Nusselt number and skin friction, a comprehensive graphical analysis is conducted. By carefully modifying these parameters and scrutinizing their effects on the flow and heat transfer properties, a dual solution was observed on the graphs. The results suggest that increasing the single-wall carbon nanotube (SWCNT) nanoparticle and inertia coefficient parameters narrow the range of solutions. When the SWCNT of a shrinking curved sheet is raised, the skin friction increases. Meanwhile, the inertia coefficient showed the opposite pattern. The increased SWCNT and inertia coefficient parameters decrease the local Nusselt number. Moreover, the findings are compared and rigorously confirmed with previous reported findings in the literature.

Holographic thermodynamic relation for dissipative and non-dissipative universes in a flat FLRW cosmology

Horizon thermodynamics and cosmological equations in standard cosmology provide a holographic-like connection between thermodynamic quantities on a cosmological horizon and in the bulk. It is expected that this connection can be modified as a holographic-like thermodynamic relation for dissipative and non-dissipative universes whose Hubble volume V varies with time t. To clarify such a modified thermodynamic relation, the present study applies a general formulation for cosmological equations in a flat Friedmann–Lemaître–Robertson–Walker (FLRW) universe to the first law of thermodynamics, using the Bekenstein–Hawking entropy SBH and a dynamical Kodama–Hayward temperature TKH. For the general formulation, both an effective pressure pe of cosmological fluids for dissipative universes (e.g., bulk viscous cosmology) and an extra driving term fΛ(t) for non-dissipative universes (e.g., time-varying Λ(t) cosmology) are phenomenologically assumed. A modified thermodynamic relation is derived by applying the general formulation to the first law, which includes both pe and an additional time-derivative term f˙Λ(t), related to a non-zero term of the general continuity equation. When fΛ(t) is constant, the modified thermodynamic relation is equivalent to the formulation of the first law in standard cosmology. One side of this modified relation describes thermodynamic quantities in the bulk and can be divided into two time-derivative terms, namely ρ˙ and V˙ terms, where ρ is the mass density of cosmological fluids. Using the Gibbons–Hawking temperature TGH, the other side of this relation, TKHS˙BH, can be formulated as the sum of TGHS˙BH and [(TKH/TGH)-1]TGHS˙BH, which are equivalent to the ρ˙ and V˙ terms, respectively, with the magnitude of the V˙ term being proportional to the square of the ρ˙ term. In addition, the modified thermodynamic relation for constant fΛ(t) is examined by applying the equipartition law of energy on the horizon. This modified thermodynamic relation reduces to a kind of extended holographic-like connection when a constant TKH universe (whose Hubble volume varies with time) is considered. The evolution of thermodynamic quantities is also discussed, using a constant TKH model, extending a previous analysis (Komatsu in Phys Rev D 108:083515, 2023).

Slip Flow in Hydrophilic Nanopores of Silica Colloidal Crystals.

Slip flow, a fluid flow enhanced in comparison to that calculated using continuum equations, has been reported for many nanopores, mostly those with hydrophobic surfaces. We investigated the flow of water, hexane, and methanol through hydrophilic nanopores in silica colloidal crystals. Three silica sphere sizes were used to prepare the crystals: 150 ± 30, 500 ± 40, and 1500 ± 100 nm. The spheres were pressure-packed in a fused silica capillary with an inner diameter of 75 μm. The resulting colloidal crystals had an average pore radius of 18 ± 4, 66 ± 6, and 215 ± 14 nm for the three silica sphere sizes used. The colloidal crystals were demonstrated to possess almost perfect packing. The fluids were flown through the colloidal crystals, and the pressure drop was measured using a pressure transducer. The flow rates varied from 10 to 80 nL/min. Water showed no-slip Hagen-Poiseuille flow with no enhancement for all of the pore sizes. Hexane showed a 20-fold flow enhancement for the smallest pore size, and the enhancement diminished for the medium pore size and was absent for the largest pore size. Methanol also showed a 20-fold flow enhancement for the smallest pores, about a 15-fold enhancement for the medium pores, and no enhancement for the largest pore size. The reduction in flow enhancement was significantly steeper for hexane than for methanol with an increasing pore size. These results demonstrate a significant slip flow in small (15 nm) hydrophilic nanopores for non-wetting fluids, which is size- and fluid-property-dependent. These observations are important for understanding fluid dynamics in liquid chromatography and naturally occurring nanoporous media.

Correct characteristics curves of Vlasov equation, fully respecting Maxwell equations in plasma kinetic simulation in lagrangian approach

Abstract We strictly demonstrate that the conflict between ordinary differential equations (ODEs) converted, through characteristic curve method, from one of coupled partial differential equations (PDEs) in Vlasov-Maxwell system and other coupled PDEs arises from inappropriate and habitual choice of one of two classes of characteristic curves and can be overcome by choosing another class. More comprehensive consideration on the characteristic curves of Vlasov equation can warrant kinetic simulation in Lagrangian approach getting rid of a well-known downside which refers to violation of Maxwell equations and continuity equation. This yields a sound/robust scheme of kinetic simulation in Lagrangian approach applicable to study a variety of topics. PACS: 52.65.-y.

Multiparticle collision framework for active polar fluids

Sufficiently dense intrinsically out-of-equilibrium suspensions, such as those observed in biological systems, can be modeled as active fluids characterized by their orientational symmetry. While mesoscale numerical approaches to active nematic fluids have been developed, polar fluids are simulated as either ensembles of microscopic self-propelled particles or continuous hydrodynamic-scale equations of motion. To better simulate active polar fluids in complex geometries or as a solvent for suspensions, mesoscale numerical approaches are needed. In this work, the coarse-graining multiparticle collision dynamics (MPCD) framework is applied to three active particle models to produce mesoscale simulations of polar active fluids. The first active-polar MPCD (AP-MPCD) is a variant of the Vicsek model, while the second and third variants allow the speed of the particles to relax towards a self-propulsion speed subject to Andersen and Langevin thermostats, respectively. Each of these AP-MPCD variants exhibits a flocking transition at a critical activity and banding in the vicinity of the transition point. We leverage the mesoscale nature of AP-MPCD to explore flocking in the presence of external fields, which destroys banding, and anisotropic obstacles, which act as a ratchet that biases the flocking direction. These results demonstrate the capacity of AP-MPCD to capture the known phenomenology of polar active suspensions and its versatility to study active polar fluids in complex scenarios. Published by the American Physical Society 2025

Течение ньютоновской жидкости в смесителях различных конфигураций

The flow of a viscous incompressible fluid in agitators with solid and anchor blades is analyzed. Mathematical formulation for the problem involves Navier-Stokes and continuity equations in the plane approximation. A solution algorithm is developed based on the control volume method and a SIMPLE correction procedure. The differential equations are discretized with unstructured triangular meshes that take into account the geometric features of the flow region. Tests were performed to verify the approximation convergence and to estimate the order of accuracy of the numerical scheme, as well as to verify the original calculation program. Parametric studies were carried out for Reynolds numbers in range of 0.1-100, which is characteristic of the technology of fluid materials processing in industrial mixers. Distributions of the kinematic and dynamic characteristics of the flow were obtained, and the flow patterns, whose specific feature is the presence of circulation zones in paddle agitators of different configurations, were demonstrated. Calculations are done to determine the position of marker particles and the evolution of reference lines, which give a visual representation of the process and demonstrate the presence of areas of uniform and non-uniform mixing. A quantitative mixing quality parameter is introduced to compare agitators of different configurations with each other and to consider the process of mixing over time. The process is evaluated quantitatively by the values of the integral of the dissipative function, which shows the energy consumption, and by the value of the quantitative parameter of the inhomogeneity of the marker particle distribution. The latter allows a more detailed study of the mixing process over the volume over time.

Modified Green-Ampt model for infiltration analysis in loess area and its parameter determination and verification

Water infiltration into soil is important in geotechnical engineering. The classical Green-Ampt (GA) infiltration model is widely used in soil infiltration due to its physical significance, but it ignores the actual unsaturated layer in the infiltration process and has some deficiencies. Thus, the present study established a modified GA infiltration model (MLGA model) using Darcy’s infiltration law and continuity equation to fully consider the variation characteristics of the soil water profile in the infiltration process. The Philip model and the GA model have the same physical basis. By combining the internal relationship between the infiltration rate and cumulative infiltration of the two models, the expression of matrix suction of the MLGA model was obtained. The existing measured data was used to verify the correctness and applicability of the MLGA model. Finally, the sensitivity analysis of the critical parameters of the model was performed. The results showed that the MLGA model is reliable and can be used for water infiltration analysis in loess sites. When the MLGA model is used to calculate the infiltration depth, the maximum relative error between the calculated value and the measured data is less than 10%, and the average relative error is 5.54%, which indicates that the model has a high calculation accuracy. The average error of the MLGA model is 24.47% of the Kostiakov model and 80.42% of the existing modified GA model (LGAM model). Sensitivity analysis of the saturated permeability coefficient, initial water content, saturated water content, and matrix suction was performed using the single-factor disturbance method. The influence of each parameter on infiltration depth was summarized, and the sensitivity of each parameter was quantitatively evaluated, which revealed that saturated water content is a highly sensitive parameter. When using the MLGA model to calculate infiltration depth, the accuracy of saturated water content should be ensured first. Finally, the difference between the MLGA model and the LGAM model in describing the whole process of water infiltration is discussed, and the influence mechanism of critical parameters on the water infiltration process is deeply analyzed. The established MLGA model provides theoretical support for further study of the loess water infiltration mechanism.

Entropy-minimizing dynamical transport on Riemannian manifolds

Given a smooth Riemannian manifold (M, g), compact and without boundary, we analyze the dynamical optimal mass transport problem where the cost is given by the sum of the kinetic energy and the relative entropy with respect to a reference volume measure e-Vdx. Under the only assumption that the prescribed marginals lie in L1(M), and a lower bound on the Ricci curvature, we characterize the minimal curves as unique weak solutions of the optimality system coupling the continuity equation with a backward Hamilton–Jacobi equation (with source given by the logarithm of the density). We give evidence that the entropic cost enhances diffusive effects in the evolution of the optimal densities, proving L1→L∞ regularization in time for any initial-terminal data, and smoothness of the solutions whenever the marginals are positive and smooth. We use displacement convexity arguments (in the Eulerian approach) and gradient bounds from quasilinear elliptic equations. We also prove the convergence of optimal curves towards the classical Wasserstein geodesics, as the entropic term is multiplied by a vanishing parameter, showing that this kind of functionals can be used to build a smoothing approximation of the standard optimal transport related to the Wasserstein distance.

Efficient Method for Improving Fully Implicit Scheme in Smoothed Particle Hydrodynamics for Highly Viscous and Non‐Newtonian Polymer Flow

ABSTRACTSmoothed particle hydrodynamics (SPH), a fully Lagrangian particle method, has been widely used in various applications, such as the simulation of incompressible flow with a free surface. For highly viscous flow, which typically appears in polymer processing, a fully implicit scheme, which implicitly treats both the predictor and corrector procedures of the projection method in the SPH framework, is efficient and numerically stable. This study proposes a simple and efficient fully implicit scheme that improves predictive accuracy for highly viscous flow. The proposed scheme utilizes a recently developed scheme for highly viscous flow that performs the pressure calculation before the viscosity diffusion calculation, unlike the conventional projection method. This study further improves the viscosity diffusion calculation by considering a viscous diffusion term that is usually ignored due to the continuity equation. Including this term enables us to correctly perform calculations for non‐Newtonian flows. The increase in the computational cost that results from the inclusion of the term is alleviated by introducing a two‐step method for calculating the viscous diffusion terms. The developed scheme is applied to injection molding of a polymer melt between two parallel plates. The results show that the proposed two‐step implicit scheme reproduces the fountain flow behavior near the advancing front. In addition, a three‐dimensional molding simulation of a plate with a hole shows a significant improvement in the prediction of the filling pattern in the mold.

Solution theory of fractional SDEs in complete subcritical regimes

Abstract We consider stochastic differential equations (SDEs) driven by a fractional Brownian motion with a drift coefficient that is allowed to be arbitrarily close to criticality in a scaling sense. We develop a comprehensive solution theory that includes strong existence, path-by-path uniqueness, existence of a solution flow of diffeomorphisms, Malliavin differentiability and $\rho $ -irregularity. As a consequence, we can also treat McKean-Vlasov, transport and continuity equations.

Fluid–structure interaction analysis of a piezoelectric wave energy converter positioned at the wave surface

The hydroelastic effects of an elastic plate and its piezoelectric characteristics under wave forces are examined in this study. The hydroelastic analysis models fluid motion and hydrodynamic pressure using viscous flow theory, solved through a combination of the Reynolds–averaged Navier–Stokes equations, the continuity equation, and the shear stress transport turbulence model. The finite element method is employed both to solve the hydroelastic motion of the plate and to calculate the static electric field. Unlike previous studies where the piezoelectric plate was fully submerged in water, this work places the plate on the wave surface. This approach serves two purposes: to increase the static pressure difference between the upper surface and lower surface of the plate and to amplify the wave-induced forces. A detailed analysis of strain energy, plate deformation, and electric voltage distribution is also presented.

Numerical study on the melting behavior of annular fuel under accident conditions

The use of annular fuel in nuclear power plants has been developed to improve their efficiency, safety, and economic viability. Therefore, studying the thermal hydraulic issues of annular fuel is crucial. The melting of annular fuel under accident conditions is equally important. This study uses a novel numerical technique called the Half Boundary Method (HBM) to tackle this issue. With new variables introduced, this method avoids the need for additional continuity equations at the boundary when solving multi-layer composite problems. First, the HBM is used to model a multi-layer composite ring and solve its transient thermal problems, which are then verified. Next, the temperature distribution of annular fuel under operational conditions is calculated, and the results are compared to validate HBM's accuracy. Based on these findings, simulations are conducted to model the melting phase transitions of annular fuel during Loss of Coolant Accidents (LOCAs) and Reactivity Insertion Accidents (RIAs).

Calculation of Efficiency Limit of Heterojunction Solar Cells Based on S-Q Theory

The ideal solar cell defined by the Shockley-Queisser (S-Q) theory is an important milestone in the analysis of photovoltaic devices based on some assumptions. One or more of the above assumptions are gradually evaded and even exceed or close to S-Q efficiency limit, so the development and improvement of S-Q theory is necessary. Heterojunction solar cells are one of the hot research fields in photovoltaics. In order to address the hindering effect of energy band discontinuity in the spatial barrier region of heterojunction solar cells on the transport of photogenerated carriers, this paper revised the assumptions of S-Q theory based on the original S-Q theory of photovoltaic cells. It is assumed that the carrier mobility in the barrier region is finite and the infinite mobility in the S-Q model is abandoned. But the mobility in the N-type and P-type neutral region is still infinite. The lumped relationship between carrier mobility and resistance in the barrier region is derived. Thus the physical process of charge transport is described in detail in this paper based on the continuity equation for semiconductors considering the effect of absorption coefficients to prevent the quasi-Fermi level from crossing the conduction or valence band. Thus, the revised S-Q theoretical limit model of heterojunction solar cell was constructed. The diode equivalent circuit diagram is deduced and the photovoltaic conversion efficiency is evaluated eventually. The loss effects of charge transmission and band gap mismatch on the performance of heterojunction solar cells are analyzed in detail in this paper. The calculation results under the condition of 5780K blackbody radiation and 300K cell temperature with N-type wide bandgap(EH) and P-type narrow bandgap(EL) materials show that the highest conversion efficiency is about 31% with hole resistance of 0.01 Ω·cm^2 and electronic resistance of 0.01 Ω·cm^2. The electronic resistance has more negative and complicated effects on solar cell performance than hole resistance based on the results of the calculation. When Re and Rh are small, the best conversion efficiency is achieved between 1.22 and 1.32 of the narrow bandgap. Increasing Re can increase the open circuit voltage of solar cells, but there are losses in efficiency and fill factor of solar cells. When Re is large enough, for example, Re=1000, the open circuit voltage of solar cells is not limited by EL and can exceed the bandgap limit of the narrow bandgap material. Increasing Rh also reduces efficiency and fill factor but has less effects than Re. The change of absorption coefficient makes the photogenerated current of L and H branches change, and the radiation recombination loss of both branches can be regulated.

Chaotic convection in an Oldroyd-B nanofluid for the Horton–Rogers–Lapwood problem with nonlinear Boussinesq approximation and gravity modulation

The Horton–Rogers–Lapwood problem for a non-Newtonian Oldroyd B nanofluid with modulated gravity effects under isothermal boundary conditions is investigated. Both linear and nonlinear stability analyses are performed, with numerical results presented graphically. The nonlinear Boussinesq approximation (NBA) is applied to the buoyancy term in the momentum equation, providing a more accurate representation of fluid behavior under high-temperature gradients, which is essential in advanced heat transfer applications. Consequently, the governing system includes the continuity equation, the Navier–Stokes momentum equation, the equation of state, the energy equation, and the nanoparticle volume fraction equation. A comprehensive stability analysis is conducted for free-free, rigid-free, and rigid-rigid boundary conditions. Additionally, a weakly nonlinear stability study employing the spectral Fourier method under isothermal, tangential stress-free boundary conditions quantifies heat and nanoparticle transport. The analysis reveals the transition from periodic convection to chaotic convection and bifurcation. A reduced Lorenz model is developed to explore the underlying dynamics further, offering deeper insights into the onset and progression of chaotic convection within the system. The NBA can be interpreted as lowering the critical Rayleigh number, thereby facilitating the onset of convection. This behavior contrasts with findings in many studies based on the linear Boussinesq approximation commonly reported in the literature. Gravity modulation enhances heat transfer and induces chaotic patterns within the nonlinear domain. The Darcy number (Da) and scaled nanoparticle Rayleigh number (Rn) promote chaos, while the modified diffusivity ratio (NA) supports periodicity.

A pseudo-transient pressure gradient method for solving the incompressible Navier–Stokes equations

The fundamental problem behind the numerical solutions of incompressible viscous flow equations lies in the lack of an update equation for the pressure field. In essence, there is no explicit relation that can be utilized to update the pressure field from a given velocity field. Following the principle of the artificial compressibility method and considering that it is the pressure gradient that drives incompressible flows, this study introduces a new primitive variables method to solve the incompressible Navier–Stokes equations. This method ensures that the continuity condition is rigorously satisfied at every grid point within the flow domain. Its principle lies in modifying the continuity equation to include a pseudo-transient pressure gradient term that vanishes upon convergence, which allows the incompressibility constraint to be satisfied to machine zero. This method eliminates the numerical difficulties associated with pressure-based solvers and improves the convergence of all dependent variables. Numerical solutions for three steady-state validation problems, namely fully developed channel flow, lid-driven cavity flow (2D and 3D), and flow in a constricted channel, are obtained to validate the proposed method. The results show good agreement with solutions available in the literature and demonstrate substantially improved convergence.

TEMPPERATURE AND IRRADIANCE EFFECTS, IN QUASI-STATIC REGIME, ON THE CONVERSION EFFICIENCYOF A BIFACIAL SILICON SOLAR CELL UNDER POLYCHROMATIC ILLUMINATION

In this work, a theoretical study of the effects of temperature and irradiance on a bifacial silicon solar cell is presented. To achieve this, the bifacial solar cell placed under polychromatic illumination, is the site of a photocreation of minority carriers whose movement is governed by the continuity equation. Solving this continuity equation allowed us to determine the density of the minority carriers photogenerated in the base of the cell as a function of temperature, irradiation and junction recombination velocity. From the expression of the minority carrier density, those of the photocurrent density, photovoltage, power and conversion efficiency have been deduced. When the ambient temperature of the medium varies from 290 K to 320 K, the power and efficiency of the solar cell decrease. On the other hand, for irradiance values between 100 W.m-2 and 400 W.m-2, we see an increase in power and conversion efficiency.

Exploration of Fusion and Fission of Molecular Assemblies in Aqueous Solution through a Dynamic Clustering Approach.

To understand the mechanism of self-assembly and to predict the evolutionary pattern of the fusion-fission system over a long period of time, studying the dynamics of these processes is of great significance. The trajectories from molecular dynamics (MD) simulations of self-assembly processes contain numerous latent fusion and fission events. To analyze the fusion and fission events from the simulated trajectory, in this article, a dynamic clustering approach was developed by comparing the changes of monomer composition within clusters over simulated time. The rates of fusion and fission events obtained from dynamic clustering analysis were further coupled with the population balance model (PBM), and the evolution of the molecular assemblies calculated is reasonably consistent with the corresponding MD simulation results. This approach provides a new idea to analyze the big data of molecular self-assembly dynamics obtained from MD simulations, and it offers a computationally achievable approach to connect discrete events at the molecular scale with continuum equations such as the PBM at the macroscale.

Comprehensive Spectroscopic Investigation of MoS2‐Solar Cells with Exclusive Zn3P2 as HTL Having Least Lattice Mismatches for 32.55% PCE

AbstractIn this analytical study, four‐layer MoS2‐based renewable energy photovoltaic cell has been first introduced using SCAPS‐1d. Proposed cell has FTO as window layer, ZnSe as electron transport layer (ETL), MoS2 as absorber layer, and an exclusive Zn3P2 hole transport layer (HTL) with least lattice mismatch of about 1.8%. To explore highest performance through proposed novel solar cell configuration, simulation studies have been done on best possible optimized physical and electrical parameters. Simulated power conversion efficiency, short circuit current, open circuit voltage, and fill factor are 32.55%, 37.75 mA/cm2, 1038.4 mV, and 83.01% respectively. Further to investigate defect states between band levels, admittance, and impedance spectroscopic analysis has been done with an equivalent electrical circuit model obtained from EIS module. Present studies help to identify the carrier accumulation behavior at various least‐lattice mismatched interfaces and in bulk of four‐layer solar device. For this analysis, proposed renewable solar device is simulated for characteristics such as capacitance‐voltage (C‐V), capacitance‐frequency (C‐F), conductance‐voltage (G‐V), and conductance‐frequency (G‐F) under different suitable and practical physical conditions. In this technique, AC signal is applied to the solutions obtained from the semiconductor and continuity equations in SCAPS‐1d. Further, we have done an in‐depth analysis through these measurements.

Analytic modeling of sensitivity in diffusion-limited type-II superlattice mid-wave infrared nBn photodetectors for design optimization for low-irradiance conditions

An analytical model for diffusion-limited detector sensitivity under low-irradiance conditions is derived from carrier continuity equations and verified with Silvaco TCAD drift-diffusion software. The model is used to determine the optimal design parameters for a mid-wave infrared InAs/InAsSb type-II superlattice nBn photodetector for maximum sensitivity under both topside- and backside-illumination conditions. A minimum attainable noise-equivalent irradiance of 4.5 × 1010 photons/cm2 s is found for InAs/InAsSb nBn at 130 K, roughly 2.4× higher than a detector exhibiting Rule 07 dark current density and unity quantum efficiency. A design heuristic, offering a simple and practical approach to designing a high-sensitivity detector, is then developed and performance is found to be comparable to the optimally designed structures. Finally, an evaluation of the impact of each material parameter on noise-equivalent irradiance is performed, revealing that the intrinsic carrier concentration, effective minority carrier lifetime, and absorption coefficient exhibit the largest impacts on sensitivity for diffusion-limited detectors.