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This article proposes various new approximate analytical solutions of the boundary value problem for the non-stationary system of Nernst–Planck–Poisson (NPP) equations in the diffusion layer of an ideally selective ion-exchange membrane at overlimiting current densities. As is known, the diffusion layer in the general case consists of a space charge region and a region of local electroneutrality. The proposed analytical solutions of the boundary value problems for the non-stationary system of Nernst–Planck–Poisson equations are based on the derivation of a new singularly perturbed nonlinear partial differential equation for the potential in the space charge region (SCR). This equation can be reduced to a singularly perturbed inhomogeneous Burgers equation, which, by the Hopf–Cole transformation, is reduced to an inhomogeneous singularly perturbed linear equation of parabolic type. Inside the extended SCR, there is a sufficiently accurate analytical approximation to the solution of the original boundary value problem. The electroneutrality region has a curvilinear boundary with the SCR, and with an unknown boundary condition on it. The article proposes a solution to this problem. The new analytical solution methods developed in the article can be used to study non-stationary boundary value problems of salt ion transfer in membrane systems. The new analytical solution methods developed in the article can be used to study non-stationary boundary value problems of salt ion transport in membrane systems. [ABSTRACT FROM AUTHOR]

Tuning the surface properties of catalysts is an effective method for accelerating water electrolysis. Herein, we propose a directional doping and interfacial coupling strategy to design two surface-functionalized Schottky junction catalysts for coordinating the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Directional doping with B/S atoms endows amphiphilic g-C3N4 with significant n-/p-type semiconductor properties. Further coupling with Fe3C modulates the energy band levels of B-C3N4 and S-C3N4, thus resulting in functionalized Schottky junction catalysts with specific surface-adsorption properties. The space-charge region generated by the dual modulation induces a local "OH-- and H+-enriched-environment, thus selectively promoting the kinetic behavior of the OER/HER. Impressively, the designed B-C3N4@Fe3C||S-C3N4@Fe3C pair requires only a low voltage of 1.52 V to achieve efficient water electrolysis at 10 ​mA ​cm-2. This work highlights the potential of functionalized Schottky junction catalysts for coordinating redox reactions in water electrolysis, thereby resolving the trade-off between catalytic activity and stability. [ABSTRACT FROM AUTHOR]

The problem of the potential, electrical field and charge density in a space charge region is revisited. Within the Boltzmann approximation, the asymptotic solution is found analytically. The exact solution everywhere can be found from numerically integrating an analytical function. The solution is compared to the popular abrupt (or depletion) approximation and an analytical approximation is given. [ABSTRACT FROM AUTHOR]

Understanding the defect characteristics that occur near the space‐charge regions (SCRs) of kesterite (CZTSSe) solar cells is important because the recombination loss at the CZTSSe/CdS interface is considered the main cause of their low efficiency. CZTSSe surfaces with different elemental compositions were formed without polishing (C00) and with polishing for 20 s (C20) and 60 s (C60). For C60, a specific region near the SCR was excessively Cu‐rich and Zn‐poor compared to C00 and C20. Various charged defects formed where the elemental variation was large. As the main deep acceptor defect energy level (Ea2) near the SCR increased, the efficiency, open‐circuit voltage deficit, and current density degraded, and this phenomenon was especially rapid for large Ea2 values. As the Ea2 near the SCR became deep, the carrier diffusion length decreased more for the CZTSSe solar cells with a low carrier mobility than for the CuInGaSe2 (CIGSe) solar cells. The large amplitude of the electrostatic potential fluctuation in the CZTSSe solar cells induced a high carrier recombination and a short carrier lifetime. Consequently, the properties of the CZTSSe solar cells were more strongly degraded by defects with deep energy levels near the SCR than those of the CIGSe solar cells. [ABSTRACT FROM AUTHOR]

Abstract Understanding the defect characteristics that occur near the space‐charge regions (SCRs) of kesterite (CZTSSe) solar cells is important because the recombination loss at the CZTSSe/CdS interface is considered the main cause of their low efficiency. CZTSSe surfaces with different elemental compositions were formed without polishing (C00) and with polishing for 20 s (C20) and 60 s (C60). For C60, a specific region near the SCR was excessively Cu‐rich and Zn‐poor compared to C00 and C20. Various charged defects formed where the elemental variation was large. As the main deep acceptor defect energy level (Ea2) near the SCR increased, the efficiency, open‐circuit voltage deficit, and current density degraded, and this phenomenon was especially rapid for large Ea2 values. As the Ea2 near the SCR became deep, the carrier diffusion length decreased more for the CZTSSe solar cells with a low carrier mobility than for the CuInGaSe2 (CIGSe) solar cells. The large amplitude of the electrostatic potential fluctuation in the CZTSSe solar cells induced a high carrier recombination and a short carrier lifetime. Consequently, the properties of the CZTSSe solar cells were more strongly degraded by defects with deep energy levels near the SCR than those of the CIGSe solar cells.

The paper investigates and analyzes the current–voltage characteristics of the CdO-CdTe-Mo heterostructure, which is photosensitive to visible and near infrared electromagnetic radiation, in a wide range of solar radiation illumination power with an AM1.5 spectrum. The effect of internal injection amplification of the primary photocurrent in the forward direction of the applied voltage to the heterostructure is established. This effect is explained in terms of the positive feedback mechanism when the resistance of the photosensitive region of the structure is modulated by injected charge carriers and the external applied bias voltage is redistributed between the p–n junction and the base region. The photosensitivity of the CdO-CdTe-Mo heterostructure, in the charge carrier injection mode, increases with an increase in the applied bias voltage and a decrease in the power of the incident solar radiation. This is explained by the effective modulation of the base of the structure by the injected charge carriers at low radiation powers. [ABSTRACT FROM AUTHOR]

The zone fluctuation potentials (ZFPs) in quantum wells located in the space charge region (SCR) of the p–n junction and the lateral ZFPs in quantum wells outside the SCR in blue, green, and UV LEDs based on nitrides have been experimentally determined. Green LEDs were used as an example to show that the low external quantum efficiency (EQE) of LEDs at the maximum correlated with an increase in the ZFP and disordering of heteroboundaries in quantum wells located in the SCR. The EQE at the maximum decreased because charge carriers were captured by charged centers localized at disordered heteroboundaries. The lateral ZFP in quantum wells located outside the SCR was the main parameter determining the decrease of the EQE from the moment the p–n junction opened until current densities reached 30–40 A/cm2. [ABSTRACT FROM AUTHOR]

The paper studies dark and light current–voltage characteristics of a polycrystalline solar cell with the Ag-n-Si/p-Si–Al/Ag structure, in a wide range of external applied electrical voltage and solar radiation power generating electron-hole pairs in the photoactive part of solar radiation. It has been established that the effect of amplification of the primary photocurrent is observed due to the presence of a "high-resistance region" at the boundary between crystallites, in the region of the space charge (p–n junction) and the base region of the p-Si layer, in the mode of charge carrier injection. The observed effect is explained by the positive feedback mechanism as a result of modulation of the resistance of the "high-resistance region" located at the boundary between the crystallites and the resistance of the base layer by injected and photogenerated charge carriers. The high-resistance regions found at the interface between the crystallites limit the power output of the solar cell. [ABSTRACT FROM AUTHOR]

Summary: Photocatalytic overall water splitting for converting solar energy into hydrogen is a potential means of pursuing a renewable, scalable, and eco-friendly energy source. It is challenging to achieve the 5%–10% solar-to-hydrogen (STH) efficiency needed to be economically viable for renewable solar hydrogen production. Here, we report a heterojunction in which the thickness within the space charge region can be precisely adjusted to enhance the redox capacity, increase light absorption, and reduce carrier transport distance. The fully stacked two catalysts and aqueous-solution-exposed surfaces exhibit advantages of an enhanced built-in-electric field and a highly effective surface area. Based on that, an Ag3PO4/CdS/Pt photocatalyst exhibits overall water splitting with an STH efficiency, dramatically improving from zero to 0.75% under visible light at ambient pressure by tuning CdS/Ag3PO4 thickness from 200 nm/120 nm to 60 nm/30 nm. The STH efficiency can be further enhanced to 2% under visible light in 0.01 mol L−1 Na2S solution.

Transistor structures are the basic elements of integrated circuitry and are often used to create not only transistors themselves, but also diodes, resistors, and capacitors. Determining the mechanism of the occurrence of inductive type impedance in semiconductor structures is an urgent task, the solution of which will create the prerequisites for the development of solid-state analogs of inductors. The purpose of the work is to establish the effect of extraction of non-equilibrium charge carriers from the base region on the reactive impedance of a bipolar p–n–p transistor.Using impedance spectroscopy in the frequency range 20 Hz–30 MHz, the structures based on p–n–p transistors KT814G manufactured by JSC “INTEGRAL” were studied. It is shown that in the transistor structures it is possible to observe the “effect of negative capacitance” (inductive type impedance). It is established that the most probable cause of the inductive type impedance is the accumulation of uncompensated charge of holes in the base, the value of inductive impedance is influenced by both the injection efficiency in the base–emitter junction and the extraction efficiency in the base–collector junction.The results can be applied in the elaboration of technologies for the formation of elements of silicon based integrated circuits with an impedance of inductive type.

Controlling of parameters of manufactured transistors and interoperational controlling during their production are necessary conditions for production of competitive products of electronic industry. Traditionally for controlling of bipolar transistors the direct current measurements and registration of capacity-voltage characteristics are used. Carrying out measurements on alternating current in a wide interval of frequencies (20 Hz–30 MHz) will allow to obtain additional information on parameters of bipolar transistors. The purpose of the work is to show the possibilities of the method of impedance spectroscopy for controlling of differential resistance of p–n-junctions of the bipolar p–n–p-transistor in active mode.The KT814G p–n–p-transistor manufactured by JSC “INTEGRAL” was studied by the method of impedance spectroscopy. The values of differential electrical resistance and capacitance for base–emitter and base–collector p–n-junctions are defi at direct currents in base from 0.8 to 46 µA.The results of the work can be applied to elaboration of techniques of fi checking of discrete bipolar semiconductor devices.

It is highly desirable to provide extra functionality for p-n junction to bypass the limits to Moore’s law. By combining magnetoelectric and photovoltaic effects of p-n junctions, we demonstrate a novel light-induced magnetoresistance (MR) effect, that the photovoltage in the conventional p-n junction can be significantly tuned by magnetic field. In contrast to the symmetric MR driven by external electric field, light-induced MR presents an asymmetric behavior at positive and negative magnetic induction. Theoretical fits using photovoltaic transport equations further reveal that the asymmetric MR induced by light directly reflects the asymmetric geometric of the space-charge region in p-n junction under the magnetic induction. The results not only further confirm our MR model of p-n junction, but also provide a new route by using magnetic control of energy flow in light harvest. [ABSTRACT FROM AUTHOR]

• Poisson-Boltzmann modeling of SnO 2 nanowire gas sensor response. • Early saturation of the depletion length versus nanowire surface charge. • Reproducing the experimental responses of nanowire gas sensors. • Calculating the range of the power-law exponent in the conductivity of nanowires. • Observing the 1/ d scaling of response versus nanowire diameter d. The response of single SnO 2 nanowire gas sensors with different diameters between 20 and 140 nm are evaluated by calculating the nanowire conductivity as a function of the surface charge density. The procedure involves the numerical solution of the Poisson-Boltzmann equation for the electrostatic potential in cylindrical geometry in order to model the depletion region and band bending at the SnO 2 nanowire surface. In the model we take into account varying surface charge densities σ and bulk electron concentrations n 0 to calculate the electrical conductivity. Considering the fact that the surface charge density depends on the nanowire surface interactions with ambient gas, the model allows us to simulate the sensor response when the nanowire is employed as gas sensing component. We report a saturation in depletion length λ versus surface charge density σ which is the principal reason for limiting the sensor responses. The results also show that the conductivity is decreasing by increasing surface charge density, the smaller the nanowire diameter the steeper the decrease. As a result the nanowire response is proportional to 1/d where d is the nanowire diameter. Furthermore, we argue about the validity of the modeling results and their relevance to experimental findings on SnO 2 nanowire based gas sensors reported in literature. [ABSTRACT FROM AUTHOR]

Within the framework of the problem of ensuring favorable conditions for normal operation of diode photodetector matrices, the influence of a step composition profile on the formation of inversion in mercury—cadmium—tellurium (MCT) films under the action of a built-in charge Qi of the isolating dielectric is studied. The problem of evaluating the maximum permissible charge Qi still not leading to the formation of inversion in the system is analyzed via the variation of involved problem parameters: the values of the band edge offsets for charge carriers in the MCT, the thickness of the broadband surface MCT layer, the operating temperature of the photodetector, and the doping level of the two-layer MCT film. [ABSTRACT FROM AUTHOR]

The effect of the illumination wavelength on the vertical parallel silicon solar cell n-p junction with electrical parameters by use extension space charge region method is theoretically analyzed. Based on the excess minority carrier's density, the photocurrent density and photovoltage across the junction was determined. From both photocurrent and the photovoltage, the series and shunt resistance expressions are deduced and the solar cell associated capacitance (open-circuit and short-circuit) and conversion efficiency are calculated. Wavelength dependence in the initial part with moderate junction recombination velocity modulation by use extended space charge region method. This influence is attenuated in polycrystalline silicon solar cells with wavelength in the space charge region. A theoretical discussion about the wavelength dependence of the cell efficiency is also reported. [ABSTRACT FROM AUTHOR]

A comparative study of small signal noise has been presented for n+-n-p-p+ double drift region (DDR) impact avalanche and transit time (IMPATT) diode. The comparison is made by taking different semiconductor materials such as silicon, germanium, gallium arsenide, indium phosphide, wurtzite gallium nitride and 4H-silicon carbide, as doping element throughout the Ka band frequency of 26.5-40 GHz. Also, a generalised idea for performing the small signal noise analysis for the IMPATT diode is presented, by taking a one-dimensional mathematical model of DDR IMPATT diode. The 4H-SiC material-based IMPATT diode is proven to be less noisy with noise measure (NM) variation of 17-29 dB in the Ka band, whereas Ge-based IMPATT diode is noisier with the NM value of 34-44 dB. This paper has studied the small signal noise behaviour and is helpful in selecting the proper semiconducting material for the optimum design of the IMPATT diode in the Ka band. [ABSTRACT FROM AUTHOR]

Due to the large surface specific area, tunable porosity and refractive index, porous germanium (Ge) has wide applications in optoelectronics, photovoltaics, anode materials in batteries. Electrochemical etching is the most used approach to fabricate porous Ge. However, previous work focused on bulk Ge wafer etching, which is not suitable for device integration on a Si substrate, and illumination had to be used for n -type porous Ge formation. In this paper, we show that by using bipolar potentiostatic etching, porous Ge with the thickness of more than 100 nm and the pore diameter in the range of 10 to 100 nm, can be obtained from both p - and n -type Ge-on-Si layers without illumination. The pore formation mechanism is interpreted by hydrogen evolution effect and Space Charge Region (SCR) model where pore nucleation, growth and dissolution are determined by the total etching time. Our work paves the way for porous Ge applications in Si based integrated photonics and microelectronics. [ABSTRACT FROM AUTHOR]

In recent years, transmission and reception systems of optical signals are widely used. Receiving the optical signal in such systems is carried by photoreceiving modules based on a photodetector, which defines the quality of the received signal, the range and speed of the entire system. However, hitherto used p–i–n- and avalanche photodiodes do not fully meet the growing demands. The present work is devoted to investigate the photovoltaic characteristics of semiconductor thin base transistor structure based on germanium, which is superior the silicon counterparts by speed and gain. Investigated p+–n–p-structures were obtained by diffusion of antimony onto the substrate of p-type germanium to a depth of 1 micron and alloying of indium to the part of its surface which creates diffusion layer of ?+-type and with thickness of 0,5 microns. Experiments have shown that the reverse biasing of a single p+-n-emitter-base junction leads to a smooth increase in reverse current, at the same time when it is connected in series to forward biased collector p-n-junction there is a sharp increase in the current by voltage, giving properties of voltage surge suppressor. This behavior of the current-voltage characteristics can be explained by the punch-through effect when the space charge regions of the emitter junction and the space charge region of collector junction touch each other and the conditions are realized for double carrier injection into a fully depleted region of the transistor. At the same time giving small fixed voltages 0,1—0,15 V to the collector-base junction the output static characteristics can be received with an operating voltage of 3—3,5 V. A characteristic feature of the investigated transistor is that when the base region under illumination by integrated light intensity (50 and 3000 lux) light current appears, whose magnitude with the increase of operating voltage (up to 1.7 V) increases nonlinearly, resulting in increased current photosensitivity up to 17 µA/lux, which is one and a half orders of magnitude greater than photosensitivity of germanium phototransistor “OOA-5”.