Carrier Density Distribution Research Articles

A fully coupled system of generalized thermoelastic theory for semiconductor medium

This study presents a new mathematical framework for analyzing the behavior of semiconductor elastic materials subjected to an external magnetic field. The framework encompasses the interaction between plasma, thermal, and elastic waves. A novel, fully coupled mathematical model that describes the plasma thermoelastic behavior of semiconductor materials is derived. Our new model is applied to obtain the solution to Danilovskaya’s problem, which is formed from an isotropic homogeneous semiconductor material. The Laplace transform is utilized to get the solution in the frequency domain using a direct approach. Numerical methods are employed to calculate the inverse Laplace transform, enabling the determination of the solution in the physical domain. Graphical representations are utilized to depict the numerical outcomes of many physical fields, including temperature, stress, displacement, chemical potential, carrier density, and current carrier distributions. These representations are generated for different values of time and depth of the semiconductor material. Ultimately, we receive a comparison between our model and several earlier fundamental models, which is then graphically represented.

Carrier density distribution in AlGaAs/GaAs superlattices with different numbers of quantum wells determined by capacitance-voltage profiling

The charge carrier density distribution in uniformly doped AlGaAs/GaAs superlattices with layer thicknesses of 1.5/10 nm and different numbers of quantum wells was studied. Both energy band theory and capacitance–voltage profiling were used to determine the carrier concentration profiles of the structures. During the analysis of the experimental and simulated capacitance–voltage characteristics, it was found that the maximum electron concentrations increase with an increase in the number of quantum wells from ∼ 7.1⋅1016cm−3 for three wells to ∼ 9.3⋅1016cm−3 for 25 wells with an overall superlattice doping level of ∼ 1017cm−3.

Response of photo-elasto-electric semiconductor porosity medium according to changing thermal conductivity with two-temperature

This study examines a new model for a solid semiconductor porosity medium with variable thermal conductivity under photo-thermoelastic conditions using two-temperature theory. A normal mode analysis is carried out to solve the equations in two dimensions analytically while taking into account the linear relationship between thermal conductivity and temperature. Physical fields, such as carrier density distribution, temperature, stress, and displacement, are then determined. The interaction between plasma and elastic waves is also considered. The simulation is conducted using silicon material, and the numerical calculations are illustrated graphically. This study investigates the effects of different porosity parameters (with and without porosity), thermal variable conductivity, and the two-temperature parameter on the physical field values.

Compact plasmon modulator based on the spatial control of carrier density in indium tin oxide.

To keep pace with the demands of semiconductor integration technology, a semiconductor device should offer a small footprint. Here, we demonstrate a compact electro-optic modulator by controlling the spatial distribution of carrier density in indium tin oxide (ITO). The proposed structure is mainly composed of a symmetrical metal electrode layer, calcium fluoride dielectric layer, and an ITO propagating layer. The carrier density on the surface of the ITO exhibits a periodical distribution when the voltage is applied on the electrode, which greatly enhances the interaction between the surface plasmon polaritons (SPPs) and the ITO. This structure can not only effectively improve the modulation depth of the modulator, but also can further reduce the device size. The numerical results indicate that when the length, width, and height of the device are 14µm, 5µm, and 8µm, respectively, the modulation depth can reach 37.1dB at a wavelength of 3.66µm. The structure can realize a broadband modulation in theory only if we select a different period of the electrode corresponding to the propagating wavelength of SPPs because the modulator is based on the scattering effect principle. This structure could potentially have high applicability for optoelectronic integration, optical communications, and optical sensors in the future.

A failure mechanism of IGBT module in MMC and improvement

In modular multi-level converter valves, as the blocked mode happens, the failure in IGBT modules often causes a chain explosion reaction, which masks the initial failure mechanism. The root cause of the failure was that the voltage, consisting of the diode forward voltage and the induced voltage on the parasitic inductance, exceeded the reverse blocking capability of the anti-parallel IGBT. The methods against the failure were studied from three aspects: decreasing the diode’s peak forward voltage, increasing the reverse blocking capability of IGBT, and minimizing the parasitic inductance of the package. It was found that the doping concentration’s effect on the diode’s peak forward voltage is not monotonic. It can be explained from the carrier density distribution during forward recovery transient that lower doping concentration reduces the carrier injection, and higher doping concentration reduces the excess carrier concentration in the doping region. Then, the influence of two buffer designs on the reverse blocking capability of IGBT was compared. It was found that a higher reverse blocking voltage would be achieved when a multi-proton implantation buffer replaced the diffused buffer. And the new design has almost no degradation in forward blocking capability.

Photothermal interactions in a semiconducting fiber‐reinforced elastic medium with temperature‐dependent properties under dual‐phase‐lag model

AbstractThis article highlights the study of photothermoelastic interactions in a semiconducting fiber‐reinforced anisotropic medium with temperature‐dependent properties. The model is studied in the context of the photothermal transport process with dual‐phase‐lag theory of generalized thermoelasticity. The governing equations describe the interactions between elastic and plasma thermal waves. The normal mode analysis is employed to procure the exact expressions of the physical fields under investigation. A mechanical load is applied at the outer free surface of the medium to obtain the complete solution of the displacements, stresses, temperature, and carrier density distributions. Numerical results are obtained and displayed graphically with the help of MATLAB software. Some special cases of interest have been deduced from the present study and comparisons are also made among the different theories of thermoelasticity.

Propagation of plane waves in nonlocal semiconductor nanostructure thermoelastic solid with fractional derivative due to ramp-type heat source

In this paper, propagation of thermoelastic waves in semi-conducting nanostructure medium is studied. First, the governing equations are formulated with the help of coupled nonlocal elasticity theory, thermoelastic three-phase-lag model, and equation of motion. Heat equation with fractional order is incorporated to study thermal effects on the propagation of wave. The problem is solved using Fourier series and Laplace transform to obtain the exact expressions of physical fields. The distributions of the nondimensional carrier density and stresses are obtained and illustrated graphically. The effects of nonlocal parameter, fractional order parameter, and time parameter on these wave characteristics are concerned and discussed in detail. Some semiconductor materials as Silicon (Si) and Germanium (Ge) are used to make the numerical simulation and some comparisons in different thermal memories are made.

Linewidth narrowing for the distributed feedback nanoplasmonic laser

Ultra-narrow linewidth and single-mode output are vital for the further development of semiconductor nanolasers capable of excellent lasing performance. This paper addresses a systematic linewidth narrowing method for the design of a new type of nanoplasmonic laser coupled with distributed feedback (DFB) structure of nanogratings. Based on the physical model of DFB nanoplasmonic laser, the optical field distribution, carrier density distribution, relaxation oscillation and lasing spectra of the DFB laser were simulated with different parameters. The optimal device design for the DFB nanoplasmonic laser was achieved through a complete numerical simulation based on the multiple effects. By optimizing the influence of device parameters, the optimal structures for the DFB nanoplasmonic laser were achieved with the optimal optical properties of cavity mode, spectra and output power. The monochromatic DFB nanoplasmonic laser functions the optimum lasing performance with a single-mode peak at 514 nm, 3 dB linewidth of 0.1 pm, and the threshold current of 16 mA. This work provides a fundamental and technical support for the development of a new generation of efficient nanolaser devices with good spectra merits.

A Quantum Corrected Compact Model of Experimentally Fabricated GAA 2-D MBCFETs

Gate all around (GAA) 2-D material multibridge-channel (MBC) FET with the thinnest channel could lead to the ultimate scaling of transistor technology. In this work, a physics-based compact model including quantum correction and multiple other physical effects is developed for experimentally fabricated 2-D MBC FET. The model is formulated on the basis of symmetric double gate (DG) potential solutions. By considering the wave functions in the 2-D channel, the quantum mechanical confinement (QMC) is taken into account, and the quantum corrected potential is deduced in analytical form using perturbation approach. The model captures the carrier density distribution across channel accurately, which has been verified by first principle calculations. Furthermore, electrical characteristics, such as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> models, are created. The models are implemented in Verilog-A and they show good agreement with experimental data.

Construction of Ca-CuFeO2/TiO2(B) p–n Heterojunctions with Efficient Visible Light-Driven Photocatalysis

Ca-CuFeO2/TiO2(B) heterojunctions were constructed to improve the photocatalytic reduction efficiency of Cr(VI). The results suggest that Ca doping gives rise to the phase transition of 3R to 2H, increased surface area, and improved charge transfer ability of CuFeO2. Covering CuFeO2 with TiO2(B) effectively inhibits the partial oxidization of Cu1+ to Cu2+. The schematic energy band diagram and carrier density distributions for Ca-CFO/TiO2 heterojunctions were theoretically simulated using AMPS software. It suggests that photogenerated electrons in the CuFeO2 conduction band adjacent to the depletion region drift into TiO2(B) due to the presence of a built-in electric field to directly participate in the reducing process of Cr(VI) on the TiO2 surface. Photogenerated holes in CuFeO2 can hardly drift or diffuse into TiO2(B) due to the presence of an energy barrier in the valence band and will diffuse to the uncovered CuFeO2 surface and be captured by formic acid to generate reactive CO2·– free radicals to effectively reduce Cr(VI). The maximum photocatalytic efficiency using 5%Ca-CuFeO2/TiO2 (3:1) was 100% in 40 min. The study results can provide a new avenue for the efficient treatment of Cr(VI)-containing wastewater with Ca-CuFeO2/TiO2(B) p–n heterojunctions owing to the advantages of high efficiency, environmental friendliness, sustainability, and low energy consumption.

Two-dimensional analysis on the magnetic field adjusted electrical behaviors in composite semiconductor structures

To explore the exact electric properties and reveal the intrinsic interaction mechanisms among multi-fields in composite magneto-electric-semiconductor structures, two-dimensional analyses are performed based on the coupled field theory. Expanding the basic physical quantities to Fourier series along the length, the governing equations are simplified. And then, the discrete solutions are derived by utilizing differential quadrature method. As applications, three composite structures are designed via considering different poling directions. Respectively, the extension, piecewise deformation and bending are realized. Before analysis, the convergence and correctness of adopted method are discussed systematically. In numerical calculation, the effect of material proportion on the perturbation carrier density is investigated. It is found the variation rule of perturbation carrier density is controlled by material proportion and deformation form simultaneously. Importantly, there are optimal material proportion ranges producing the carriers, nevertheless, the ranges are different for three structures. Additionally, two-dimensional distributions of perturbation carrier density, electric field, electric displacement and polarization are discussed. Along the thickness, the field quantities are symmetric for extension and piecewise deformation, but is antisymmetric for bending. Specially, in the structure with piecewise deformation, the potential barriers are realized. This work could be the guidance designing magneto-electric devices.

Thermo-mechanical waves of excited microelongated semiconductor layer during photothermal transport processes

The governing equations for microelongated semiconductors are provided using a unique mathematical-physical approach. When the microelongated elastic semiconductor medium is energized, the model is investigated following the photo-generated transport processes. When microelongation is taken into consideration, the primary governing equations show the interplay between elastic, thermal, and plasma waves. The generalized photo-thermoelasticity hypothesis is taken into account in this context. The harmonic wave method has been used to translate the dimensionless formulas for temperature, carrier density, displacement, stresses, and microelongation distributions. The general solutions of the principal distributions are derived during the electronic and thermoelastic deformation processes in two dimensions (2D). The application of some thermal-mechanical stresses as well as plasma conditions occurs when the semiconductor medium is homogeneous, linear, and isotropic. A numerical simulation using the semiconductor material silicon (Si) is done to demonstrate the findings. Graphical representations of the variations in the wave propagations of the principal physical fields have been made.

Electrically tuning near-field heat flux using metal–oxide–semiconductor structure considering gradient dielectric function distribution

We build a model to determine the dependency of near-field heat flux on bias voltage using the metal–oxide–semiconductor structures considering gradient distribution of dielectric function. Quantitative dependency of near-field heat flux exchanged by two biased metal–oxide–semiconductor structures on bias voltage is established. The distribution of carrier density and the resultant dielectric function in the semiconductor layer caused by the bias are determined. The corresponding near-field heat flux is calculated using an effective multilayer model. Significant tuning performance is demonstrated, which is due to the increase or decrease in high-frequency surface polariton states induced by the injection or extraction of major carriers. This work deepens the understanding of electrical control of near-field heat transfer with metal–oxide–semiconductor structures, promising for nanoscale thermal management devices and thermal circuits.

Silicon–Organic Hybrid Tunable Fabry–Perot Filter for Electro-Optic Modulation

Recently, electro-optic integrated photonic elements have attracted considerable interest owing to their widespread application in optical communication and signal processing. The strong electro-optical properties and the complementary metal–oxide semiconductor (CMOS) technology compatibility of silicon–organic hybrid structures makes them promising photonic platforms. This study investigated a novel implementation of a high-speed electrically tuned bandpass optical filter using finite-difference time-domain and eigenmode expansion numerical methods. The proposed device was based on a Fabry–Perot cavity and was realized via an electro-optic organic molecular glass filled slot waveguide with Bragg gratings. Furthermore, the calculation considered the plasma dispersion effect, free-carrier absorption in the silicon component of the slot waveguide for different applied voltages, and doping profiles corresponding to ion implantation. It is shown that the spatial distribution of charge carrier density formed by the surface states accumulation/depletion layers has a significant effect on the optical properties of the slot waveguide. Lithographic distortions in the geometry of the proposed structures during fabrication were also considered. Therefore, this paper presents an optical filter designed for fabrication using CMOS-compatible processes on silicon-on-insulator wafers. The filter produced a 3 nm tunable range for a 10 V bias voltage swing, a 0.3 nm full width at half maximum (FWHM) passband with a center at 1550 nm at zero bias voltage, and a 12.5 nm free spectral range with a 27 dB extinction ratio. The proposed device outperforms many narrow passband analogs in terms of sensitivity (tunability: 0.3 nm/V) and can be applied extensively in the fields of optical communications and photonic spectral signal processing.

Revealing the Hidden Mechanism of Enhanced Responsivity of Doped p-i-n Perovskite Photodiodes via Coupled Opto-Electronic Model.

Organic-inorganic halide perovskites have demonstrated preeminent optoelectronic performance in recent years due to their unique material properties, and have shown great potential in the field of photodetectors. In this study, a coupled opto-electronic model is constructed to reveal the hidden mechanism of enhancing the performance of perovskite photodetectors that are suitable for both inverted and regular structure doped p-i-n perovskite photodiodes. Upon illumination, the generation rate of photogenerated carriers is calculated followed by carrier density distribution, which serves as a coupled joint to further analyze the recombination rate, electric field strength, and current density of carriers under different doping types and densities. Moreover, experiments were carried out in which the doping types and densities of the active layer were regulated by changing the precursor ratios. With optimal doping conditions, the inverted and regular perovskite photodiodes achieved an external quantum efficiency of 74.83% and 73.36%, and a responsivity of 0.417 and 0.404 A/W, respectively. The constructed coupled opto-electronic model reveals the hidden mechanism and along with the doping strategy, this study provides important guidance for further analysis and improvement of perovskite-based photodiodes.

Response of thermo-mechanical waves of an excited microelongated semiconductor layer according to photothermal transport processes

A novel mathematical-physical governing equations of microelongated semiconductor are presented. According to the photo-generated transport processes the model is studied when the microelongated elastic semiconductor medium is excited. The main governing equations display the interaction between elastic-thermal-plasma waves when the microelongation is taken into account. In this context, the generalized photo-thermoelasticity theory is considered. The dimensionless expressions for temperature, carrier density, displacement, stresses and microelongation distributions have been converted using the harmonic wave technique. During the electronic and thermoelastic deformation processes in two-dimensional (2D) the general solutions of the main distributions are obtained. Some thermal-mechanical loads and plasma conditions are applied when the semiconductor medium is isotropic, homogeneous, and linear. In order to display the obtained results, a numerical simulation for silicon (Si) as semiconductor material is carried out. The variations of the wave propagations of main physical fields have been depicted graphically.

Valley polarization control in WSe2 monolayer by a single-cycle laser pulse

Abstract The valley degree of freedom in two-dimensional materials provides an opportunity to extend the functionalities of valleytronics devices. Very short valley lifetimes demand the ultrafast control of valley pseudospin. Here, we theoretically demonstrate the control of valley pseudospin in WSe2 monolayer by single-cycle linearly polarized laser pulse. We use the asymmetric electric field controlled by the carrier-envelope phase (CEP) to make the valley polarization between K and K'-point in the Brillouin zone (BZ). Time-dependent density functional theory with spin-orbit interaction reveals that no valley asymmetry and its CEP dependence is observed within the linear-optical limit. In the nonlinear-optical regime, linearly polarized pulse induces a high degree of valley polarization and this polarization is robust against the field strength. Valley polarization strongly depends and oscillates as a function of CEP. The carrier density distribution forms nodes as the laser intensity increases, our results indicate that the position of the carrier density in the BZ can be controlled by the laser intensity. From the analysis by the massive Dirac Hamiltonian model, the nodes of the carrier density can be attributed to the Landau-Zener-St\"uckelberg interference of wave packets of the electron wave function.

A plasmon modulator by dynamically controlling the spatial distribution of carrier density in graphene

Light–matter interaction at the nanoscale is of particular interest for future photonic integrated circuits and devices with applications ranging from communication to sensing and imaging. In this letter, we proposed a plasmon modulator to enhance the Light–matter interaction by dynamically controlling the spatial distribution of carrier density at the nanoscale, which is demonstrated by a hybrid graphene-dielectric-grating structure. The numerical results show that both the applied voltage and the grating period can be utilized to modulate the surface plasmon polaritons (SPPs) effectively. The modulator can also work on an ultra-wideband in theory as the scattering effect is independent of the wavelength. Compared with the modulator via changing the whole carrier density, the modulation depth by controlling the spatial distribution of carrier density at the nanoscale has improved about 18.6 dB at the working wavelength of 12.4μm. This plasmon modulator triggers an approach for the enhancement of Light–matter interaction at the nanoscale and improves the modulation depth significantly, which will have a potential application in the fields of optical switches, sensor and photo-detection.

Bias dependent physics-based model of low-frequency noise for nanowire type gate-all-around MOSFETs

In this study, the bias dependence of low-frequency noise (LFN) in nanowire type gate-all-around (GAA) MOSFETs was physically modeled. In the model, the inversion carrier density distribution was considered based on the potential in the channel that changes according to the bias. The developed model was verified with measurement data of the fabricated device. The model could help circuit designers to optimize noise performance in analog/RF applications when designing integrated circuits using nanowire-type GAA MOSFETs.

Ion Motion Determines Multiphase Performance Dynamics of Perovskite LEDs

AbstractPerovskite light‐emitting diodes (PeLEDs) currently reach up to about 20% external quantum efficiency (EQE) and are becoming a promising technology for display and lighting applications. Still, many issues regarding their performance remain unresolved, particularly those related to stability, operation in non‐stationary regimes, and efficiency roll‐off at high current densities. Here, some of those issues in PeLEDs based on MAPbI3 perovskite are addressed. The authors analyze the electroluminescence (EL) and current dynamics after the first‐time voltage application and after application of sequences of voltage pulses, at different temperatures. Analysis of the results suggests that the complex dynamics observed on time scales from sub‐seconds to minutes and hours can be explained by the spatial redistribution of mobile species, most likely iodine interstitials, characterized by ≈175 meV activation energy. This redistribution alters the carrier injection, spatial electric field, and charge carrier density distributions as well as density of nonradiative recombination centers within the perovskite layer. Mathematical modeling of the ion motion and related processes enabled to reproduce the EL and current dynamics and to disentangle complex sequence of processes governing the PeLED operation.