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Space charge dynamics under sinusoidal voltages are calculated based on bipolar charge transport model. The effects of AC voltage amplitude and frequency on current densities, electroluminescence intensities and space charge densities are investigated. It is shown that the carrier densities increase with the increase of AC voltage amplitude, but the thickness of the space charge layer approximately unchanged. The frequency of AC voltage has no effects on space charge dynamics when the frequency reaches the order of ten.

In this paper, the development of two-dimensional metal dichalcogenide WO3-WS2 nanoplates for highly selective oxygen sensing application was reported. A facile precipitation method to produce self-assembled WO3 nanoplates and one-step solid-state synthesis of self-assembled WO3-WS2 nanoplates was described. X-ray diffraction (XRD) confirms the formation of WO3 and WO3-WS2 hybrid structure. The as-synthesized nanoplates were investigated for sensing applications of ethanol, methanol, n-butanol, LPG, and O2 gas. Study revealed that both as-synthesized WO3 and WO3-WS2 nanoplate sensors are highly selective for oxygen sensing application. Response percentage of WO3 nanoplates and WO3-WS2 nanoplates measured at 500-ppm oxygen concentration was 40% and 95% respectively. The measured response time and recovery times of WO3-WS2 nanoplate sensor was shorter than WO3 nanoplate sensor at all concentrations. The improved performance of as-synthesized WO3-WS2 nanoplates was attributed to the formation of deeper depletion layer between WS2 and WO3 p-n junction which provide additional adsorption sites for oxygen species.

To improve the sensor response to low concentrations of methane (CH4) at low operating temperatures in humid atmospheres, we prepared Pd-loaded SnO2 (Pd-SnO2) nanoparticles via two different Pd-loading processes: (i) a general impregnation method and (ii) a new loading method using poly(N-vinyl-2-pyrrolidone) (PVP) as a protective agent for Pd receptor particles. According to the measured electric resistances, the Pd particles limited the hydroxyl-poisoning of the SnO2 particle surface. Because Pd is oxidized to PdO, a p–n junction is formed at the interface between PdO and SnO2, and such interface gives the enlargement of the electron depletion layer. Therefore, Pd further improved the resistance against hydroxyl poisoning of the SnO2 surface in humid air. In addition, although the sensor based on neat SnO2 did not respond to low-concentration CH4 at 200–400 °C, both the sensors based on the Pd-loaded SnO2 samples exhibited high sensor response to 200 ppm CH4 in a humid atmosphere. The Pd-SnO2 obtained by the new loading method exhibited a higher response to CH4 at lower concentrations in the lower operating temperature range (200–250 °C). This improvement in the sensor response is probably due to the catalytic activity of the larger Pd nanoparticles. According to high-resolution transmission electron microscopy–energy-dispersive X-ray spectroscopy images, the new loading method successfully provided Pd-loaded SnO2 nanoparticles with Pd nanoparticles dispersed uniformly on the SnO2 particle surface. The average particle size of Pd nanoparticles loaded on the surface of SnO2 by the new loading method was slightly larger than that of the Pd nanoparticles loaded by the impregnation method. As the Pd particle size increases, it is thought that crystalline PdO particles are formed more easily, thereby improving the combustion activity of CH4 under humid conditions. These results are of great significance for further decreasing the energy consumption of the CH4 sensor and increasing its sensor response in humid atmospheres.

This article presents a simple yet powerful general pinning process model for 3-D pinned photodiodes (PPDs), which can be used to model PPDs with small dimensions (miniature PPDs). For the development of a pinning model, capable of dealing with different PPD shapes and dimensions, the charge population in the space charge region (SCR) is calculated. Moreover, to improve the model’s accuracy, the PPD inner region depletion mechanism is investigated, and the inner SCR width is extracted analytically. The model’s application in analyzing PPDs is verified with six previously published experimental results.

In this article, in addition to two commonly known noise parameters—dark count rate (DCR) and afterpulsing (AP)—we explore another interesting phenomenon–random telegraph signal (RTS) noise—during the transitional phase of the avalanching process. We present the properties of the RTS noise and their dependence on the biasing voltage and temperature. An analytical model is used to extract the dimension of the defects in the depletion region from the variation of the RTS noise current amplitude with biasing voltage. By comparing the DCR and AP of single-photon avalanche diode (SPAD) samples with different defect dimensions derived from the RTS noise properties, a trend that the SPAD with a larger defect dimension shows a higher DCR and AP is found.

Gate reliability and its degradation mechanism were studied for the normally off high-electron-mobility transistors (HEMTs) with regrown p-GaN gate and AlN/SiN x stack passivation. Through comparing the forward leakage current in two designed structures, the conduction mechanism is determined to be Fowler-Nordheim tunneling whose current is independent of temperature when the Pd/p-GaN Schottky junction is under high electric field. Even for the regrown p-GaN gates, this Schottky junction fails at first, resulting in an abrupt increase in gate current. The maximum gate operation voltage with a failure rate of 1% for 10-year lifetime is estimated to be about 6.87 and 6.07 V at room temperature by adopting power law and exponential law as extrapolation fitting, respectively. Degradation process monitoring reveals that the net acceptor concentration $N_{\mathrm {A}}$ extracted through $C$ – $V$ fitting presents an apparent decreasing trend from $3.8\times 10^{19}$ to $1.1\times 10^{19}$ cm−3 with the stress time increased from 30 to 2600 s. This is assumed to be related with the defects generation in the Schottky depletion region under high tunneling current and high electric field. These analyses show the feasibility of the normally off HEMTs with a regrown p-GaN gate and AlN/SiN x stack passivation for practical applications, giving directions for further improving the gate breakdown voltage and lifetime.

Recent advances in CMOS scaling have made circuits more and more sensitive to errors and dysfunction caused by ionizing radiation, even at ground level, requiring accurate modeling of such effects. Besides generation, transport, and collection of radiation-induced excess carriers, another phenomenon, called funneling, has to be modeled for an accurate prediction of soft errors. The funneling effect occurs when the radiation track crosses a space charge region and generates excess carriers with a density higher than the doping close to it. These carriers distort the electric field of the space charge region, deeply changing the transport mechanism, from diffusion in a field-free semiconductor to drift. The objective of this work is to include funneling as part of the generalized lumped devices model in order to obtain a complete tool for SPICE-compatible simulations of single-event effects (SEEs). The latter approach has been recently proposed to simulate radiation-induced charges in the silicon substrate and is based on the so-called generalized lumped devices that simulate charge generation, propagation, and collection using standard circuit simulators. The generalized devices are here extended to include funneling and used to simulate an alpha particle impinging on the bulk of nMOS and pMOS transistors. The results obtained are validated with TCAD numerical simulations. Finally, an static random-access memory (SRAM) struck by an alpha particle is analyzed. The model predicts that the occurrence of a soft error, i.e., flipping of memory state, may depend on whether or not there is funneling. This justifies the need for accurate modeling of funneling phenomena to predict SEEs in ICs.

The main focus of this framework is the preparation of CdTe nanocrystalline thin films (~120 nm) on single crystal p-Si wafers (270 μm) with Miller index (100) using thermal evaporation. Then, the In/n-CdTe/p-Si/Al solar cell was successfully fabricated. The dark I–V characteristics for the fabricated solar cell have been determined in range of 300–375 K and an applied voltage range of − 2 to 2 V. The fabricated solar cell's behavior was thoroughly explained. As a result, the important parameters for the fabricated solar cell such as the rectification ratio $${\text{RR}}$$ , the junction resistance $$R_{{\text{J}}}$$ , ideality factor of solar cell n, the shunt resistance $$R_{{{\text{sh}}}}$$ , the series resistance $$R_{{\text{s}}}$$ , the barrier height created at the interface between the CdTe thin film and the p-Si wafer $$\phi_{b}$$ , the energy of trap level $$E_{{\text{t}}}$$ and the activation energy of carriers’s recombination in the depletion region $$\Delta E$$ were determined. Finally, the Poole–Frenkel $$\beta_{{{\text{PF}}}}$$ and Schottky $$\beta_{{\text{S}}}$$ parameters were computed.

Sensors are part of a safe laboratory, working space and closed environment. In view of this, a sensing material for ammonia (NH3) vapour, nickel oxide (NiO) has been investigated to improve its quality as a sensor. The transparent nanostructured NiO thin films were deposited on glass substrates by sol-gel spin coating method at different molar concentrations (0.4 M, 0.6 M and 0.8 M). The NH3 sensing studies reveal that 0.6 M film shows admirable response of 403 (75 ppm), and also it has good response and recovery times (110 s and 33 s) for 25 ppm at room temperature. These features of the film are attributed to low surface roughness, small grain size and higher surface to volume ratio compared to other films. In presence of air ambience, the electrons at film surface are chemisorbed by oxygen molecules and thereby cause an increase of the depletion layer. Once the film is exposed to the analyte gas NH3, the depletion layer decreases because of electrons returning back to the conduction band (CB). These electrons are then de-excited to the valence band (VB) and recombine with holes (annihilation of holes). At the same time, the trapping of electrons by Ni(OH)2 and creation of holes by oxidation of Ni2+ into Ni3+ increases the hole concentration at VB, followed by a reduction of recombination rate of electrons and holes. All these processes decrease the potential barrier between the grains and thereby cause the Fermi level (EF) to shift towards VB. These processes remarkably enhance the sensing behaviour of the film. Importantly, the prepared NiO thin film behaves as a n-type sensor at room temperature for NH3; and therefore, termed as pseudo-n-type.

To improve the performance of semiconductor photoelectrodes for water splitting, the amount of band bending in the depletion layer of a semiconductor should be accurately ascertained, since it dete...

In2O3 vertical nanostructures (VNS) are fabricated using a glancing angle deposition (GLAD) technique upon an In2O3 thin film (TF) on a n-type silicon (n-Si) substrate. Analysis using high-resolution transmission electron microscopy (HRTEM) and high-resolution x-ray diffraction (HRXRD) revealed that the In2O3 VNS are amorphous in nature. An average ~4.5-fold enhancement in absorption was observed and a microscopic origin was proposed for observed bandgap changes for the n-Si/In2O3 TF/GLAD In2O3 VNS and bare n-Si/In2O3 TF samples in the visible region due to surface-related trap states or oxygen vacancies. The improvement in photodetection was attributed to the presence of a large number of surface-related trap states at the edge of metal contacts. The fabricated VNS detector possesses enhanced photosensitivity (~1.7-fold) due to an efficient photogating effect in the depletion region. A maximum detectivity of ~12.8 × 107 Jones was observed for the n-Si/In2O3 TF/GLAD In2O3 VNS device, which possesses ~15.6-fold enhanced detectivity as compared to the bare n-Si/In2O3 TF device.

We review designs of a solar cell constructed from pn junctions, quantum dots and quantum wells. In the first instance we show that quantum wells of varying size embedded in the depletion region yields spatial variation of the energy gap that can be controlled. An advantage of the proposed structure is efficient utilization of the broad solar spectrum, lessening of lattice matching problems and generation of electron-hole pairs in narrow depletion regions which yields fast spatial separation of charges and, thus, reduces recombination losses. In another model we show how quantum coherence can be used, in principle, to eliminate radiative recombination and increase photocell power.

International audience; Developing nanoscale electrical characterization techniques adapted to three-dimensional (3D) geometry is essential for optimization of the epitaxial structure and doping process of nano- and microwires. In this paper, we demonstrate the assessment of the depletion width as well as the doping profile at the nanoscale of individual microwire core–shell light-emitting devices by capacitance–voltage measurements. A statistical study carried out on single wires shows the consistency of the doping profile values measured for individual microwires compared to assemblies of hundreds of wires processed on the same sample. The robustness of this method is then demonstrated on four epitaxial structures with different growth and doping conditions. Finally, electron-beam-induced current and secondary electron profiles are used to validate the depletion region width and the position in the core–shell structure.

The n–n heterojunction is formed at the interfaces of FeVO4 and ZnO under hydrothermal conditions to increase the mobility of electrons and to decrease the barrier of oxygen activation. The results from X-ray powder diffraction and X-ray photoelectron spectroscopy analyses confirm the co-existence of the FeVO4 and ZnO phases in the composite. The formation of n–n heterojunction and electron transfer behavior are explored by applying electrochemical techniques and corresponding simulation calculation. The FeVO4/ZnO (Fe:Zn = 1:0.5) sensor shows a high response value of Sg = 42 at 300 °C, excellent selectivity, fast response, stable, and superior sensitivity for ethanol detection. The effect of the formed n–n heterojunction on enhancing the gas sensitivity for detecting ethanol is discussed by electron depletion theory. When the gas atmosphere is changed from air to ethanol gas, the depletion layer on the sensor surface is also changed significantly, altering the macroscopic resistance of the material. This work offers a new mechanistic understanding of the role of n–n heterojunction in detecting target gases and paves the way for designing excellent selectivity, fast response, and stable sensors based on n–n heterojunctions.

In this paper, we propose a novel Silicon on Insulator (SOI) Metal Semiconductor Field Effect Transistor (MESFET) with an embedded GaN layer (GL-SOI-MESFET) for modifying the electric field distribution. The main idea of this work is based on using a high breakdown field material (GaN), for amending the electric field and potential distribution near the drain region, and as a result, the breakdown voltage of the proposed structure will be higher than a conventional structure (C-SOI-MESFET). The breakdown voltage (VBR) of the GL-SOI-MESFET at the Ids = 55 mA/mm and Vgs = − 1 V has been achieved ~21 V whereas the VBR in the C-SOI-MESFET is 16 V. The proposed structure shows the improvement of DC and RF characteristics versus the C-SOI-MESFET. For obtaining the best results to improve the structure performance, dimensions of the GaN layer have been optimized. Also, by amending potential distribution and changing the depletion region between the gate and drain sides, the gate-drain capacitance reduces. The effects like the electric field, the potential distribution, breakdown voltage, the kink effect, the self-heating effect, power gains, and parasitic capacitances are investigated and the proposed structure results have superior DC and radio frequency (RF) performances compared with the conventional MESFET structure.

In this work, we fabricated vertical organic thin film transistors (VOTFTs) with lead phthalocyanine (PbPc) as the active layer and analyzed the operating characteristics and current transfer mechanism of VOTFTs. The results show that the quiescent output current of VOTFTs is not saturated, and the output current can be modulated by requiring different gate voltages. The switching parameters of the VOTFTs are ton = 2.5 μs, toff = 3.5μs, and the switching characteristic time reaches the microsecond level. When a sine wave dynamic signal is applied to the gate electrode, the cut-off frequency fc = 77 kHz. The experimental results demonstrate that short channel and vertical structure of VOTFTs make up for organic semiconductor material defects of low carrier mobility and realize high speed and low driving voltage of organic devices. Electric field intensity of depletion layer in the gate region is 7×107V/m, and high electric field intensity makes carriers tunneling become the major transport mode. The tunnel injection model is used to analyze the carrier transport inside the transistor. The results show that the operating current of the transistor conforms to the tunneling effect theory.

Pristine ZnO based hydrogen sensors pose low sensitivity (~ 43%) at the operating temperature of 150°. Herein, we explore the decoration of Phosphorene oxide quantum dots (POQDs) on RF sputtered grown ZnO nanostructures for hydrogen gas sensing application. A simplistic approach such as drop cast method is employed to decorate electrosynthesized POQDs (2- $8~\mu \text{L}$ ) onto interdigitated electrodes over ZnO nanostructures. The suggested hydrogen sensor based on POQDs ( $6~\mu \text{L}$ )/ZnO nanostructures exhibits an outstanding sensing response (~70.6%) as compared to all the sensors for 100 ppm at 150°C. Enhanced sensing response from the POQDs( $6~\mu \text{L}$ )/ZnO nanostructure might be due to the enormous active surface area of POQDs (provides more active sites for hydrogen gas) and modulation of depletion region at the interface of POQDs and ZnO. The proposed sensor can be operated at mild temperature and consume low power which is the need of the hour for the hydrogen sensors for industrial applications.

Silicon technology is dominant in electronics and optoelectronics. The cut-off wavelength of silicon is less than 1.1 $$\upmu$$ m due to the bandgap, limiting applications of silicon in communication, sensing, and light harvesting. A new strategy for infrared photodetection is presented by integrating silicon and PbSe colloidal quantum dots (CQDs), which combines advantages of silicon devices and PbSe-CQDs. In this study, we introduce a silicon-based photodetector that is sensitive to infrared light with spectral response from 405 nm to 1550 nm. The device can deliver a high responsivity of 648.7AW− 1 and a fast response of 32.3 $$\upmu$$ s at 1550 nm. Besides, the detectivity and the external quantum efficiency of the device reached 7.48 × 1010 Jones and 6.47 × 104%, respectively. The performance of the device originates from the photovoltage generated at the interface between the silicon and the quantum dots. This photovoltage changed the width of the depletion layer to realize detection. These results indicate that the silicon-based quantum dot infrared photodetectors prepared by this method have application prospects in the field of optoelectronics.

The micro-electro-mechanical system (MEMS)-based field effect transistor (FET) sensor for hydrogen detection was fabricated by modifying the gate electrode with boron nitride nanotubes (BNNTs) decorated Pd-ternary alloy (Pd63·2Ni34·3Co2.5) as a hydrogen sensing layer Electro-thermal properties of the micro-heater embedded under sensor membrane were analyzed by a finite element method (FEM) simulation. The structural and morphological properties of the gate electrode were studied by Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM). A variation in gate potential is observed due to the H2 atmosphere that leads to the variation in the depletion region, therefore, changing the current in the channel (BNNTs decorated Pd-ternary alloy). The BNNTs-decorated Pd ternary alloy displayed high sensing response, fast response and recovery time for H2 gas, low power consumption, long-term stability, and wide detection range from 1 to 5000 ppm H2. The drain current of the H2 FET sensor varied significantly at hydrogen gas exposure and increased with H2 concentration. As proposed H2 FET sensor can be utilized to the H2 leak detection system for safe applications.

2D materials and their heterojunctions have been explored for gas sensing applications due to their tremendous surface-to-volume ratio, active edges with atomic thickness, and tunable electrical properties. Heterostructures of 2D materials exhibit absolutely novel physics and versatility with accelerated device performance by integrating the atomic scale properties of individual materials. Traditional gas sensors use homogeneous materials as the sensing interface in which the surface adsorbed oxygen ion species play an important role in its performance. But the performance of the sensors suffers greatly due to their selectivity and high working temperature leading to poor stability and short-term uses; the van der Waals 2D p-n heterojunction-based gas sensors hold several advantages since both the materials and the depletion layer formed at the junction can actively tune the sensing performance. By choosing 2D materials with different band structures, charge polarity, carrier concentration, and work function, band alignment at the interface can be precisely engineered to achieve the selective gas sensing performance with low operating temperature. Herein, we have reviewed the working principles, recent developments, and future perspectives of p-n heterojunctions of 2D materials for gas sensing applications.

Topological materials that possess spin-momentum locked surface states provide an ideal platform to manipulate the quantum spin states by electrical means. However, an antisymmetric magnetoresistance (MR) superimposed on the spin-polarized transport signals is usually observed in the spin potentiometric measurements of topological materials, rendering more power loss and reduced signal-to-noise ratio. Here we reveal the mechanism of surface-bulk interaction for the observed antisymmetric linear MR in the spin transport of Dirac semimetal Cd3As2 nanoplates. The antisymmetric linear MR can be eliminated through sample surface modifications. As a consequence, clean signals of charge current induced spin-polarized transport are observed, robust up to room temperature. The purification of spin signals can be attributed to the isolation of surface and bulk transport channels via forming a charge depletion layer with surface modifications. This surface engineering strategy should be valuable for high-performance spintronic devices on topological materials.

Perovskite solar cells (PSCs) have triggered a research trend in solar energy devices in view of their high power conversion efficiency and ease of fabrication. However, more delicate strategies are still required to suppress carrier recombination at charge transfer interfaces, which is the necessary path to high-efficiency solar cells. Here, a p-p+ homojunction was constructed on basis of NiO film to enhance hole transfer in an inverted planar perovskite solar cell. The homojunction was generated by fabricating a NiO/Cu:NiO bilayer film. The density functional theory calculation demonstrated the charge density difference in the two layers, which could generate a space charge region and a band bending at the junction, and the result was further proved by energy level structure analysis of NiO and Cu:NiO films. The designed homojunction could accelerate the hole transfer and inhibit carrier recombination at the interface between hole transfer layer and perovskite layer. Finally, the inverted planar perovskite solar cell with p-p+ homojunction showed an efficiency of 18.30 % and a high fill factor of 0.81, which were much higher than the counterpart of the PSCs individually using NiO or Cu:NiO as hole transfer layer. This work developed a new structure of hole transport layer to enhance the performance of PSCs, and also provided new ideas for design of charge transfer films.

In this research, for determining the effects of the (Gr-PVP) interfacial layer, two types of diodes (Au/n-Si and Au/(Gr-PVP)/n-Si) were performed on the same n-Si wafer with the same ohmic and rectifier contacts. Graphene-doped PVP nanocomposite film was grown on the n-Si wafer by a spin-coating method. Therefore, the basic electrical parameters of them were extracted from the I-V and Z-V-f characteristics and compared in detail. The higher values of n and lower values of BH obtained from Cheung's functions compared to TE theory were ascribed to their voltage-dependent. The frequency-dependent diffusion potential (V-D), doping-donor atoms (N-D), depletion layer width (W-D), surface potential (psi(s)), R-s, and BH values of the MPS diode were also extracted from the impedance characteristics in the frequency range of 10-10(3) kHz.

Understanding the interfacial impedance between the solid electrolyte and the electrode is a critical issue for the design of solid-state batteries. We propose a new equivalent circuit model that treats the interface not only as a capacitor but also includes the space charge layer resistance and the resultant polarization resistance. Moreover, the elements of the circuit model are quantified by the physical quantities based on the recently proposed modified Planck-Nernst-Poisson (MPNP) model, which includes the effect of the unoccupied regular lattice sites (vacancies) in the electro-diffusion problem and takes both the ion and electron contributions into the account. We provide a new analytical solution for the space charge layer capacitance. Comparative numerical results demonstrate that our proposed model with additional polarization resistance can explain well the real impedance tail at the low-frequency region, for which the pure capacitor interface model fails. The model is verified against the experimental impedance spectra of LiPON.