Width Of Space Charge Region Research Articles

Photoelectrochemical properties of anatase TiO2 nanostructures prepared by hydrothermal method: Effect of illumination and external bias on charge transport

A systematic study of photoelectrochemical properties in terms of carrier transport was conducted for TiO2 nanostructure films fabricated on Ti foil at different temperatures (130 °C–210 °C) through alkaline hydrothermal technique, along with the morphological, structural, and optical properties. For samples, the morphology transformed from nanosheets to nanowires, the phase converted from bi-phase of brookite and anatase to pure anatase along with the reduction in the amount of oxygen vacancies as temperature increases. Among them, the dark blue bi-phased TiO2 (brookite and anatase) prepared at 130 °C of hydrothermal treatment (TiO2-130) with nanosheets morphology displayed the optimum photoelectrochemical performance with the highest photocurrent density of 265 μA/cm2 at 1 V (vs. Ag/AgCl), largest carrier density of 1.809 × 1019cm−3 and narrowest space charge region of 11.73 nm. Besides, the large reduction in charge transfer resistance and the width of space charge region caused by simulated solar illumination facilitate the charge transport in photoelectrode especially the TiO2-130 with the largest reduction, indicating the great influence of illumination on carrier dynamics. Moreover, the external bias caused the reduction of resistance under irradiation, the increase in the resistance in the dark. Importantly, the TiO2-210 showed p-type conductivity under illumination inferred from the negative slope of Mott-Schottky plots, which is first observed and further confirm the influence of light on the charge transfer process.

Enhancement of photodetection performance of Ga2O3/Si heterojunction solar-blind photodetector using high resistance homogeneous interlayer

Creating homojunctions using Ga2O3 material presents a significant challenge, primarily because of the inherent difficulty in achieving stable p-type Ga2O3. The pn heterojunctions based on n-Ga2O3 materials offer a promising alternative for developing solar-blind photodetectors. In this work, our strategy is to fabricate a n-Ga2O3/p-Si heterojunction solar-blind photodetector with interface layers of high resistance and low resistance through using a magnetron sputtering system. The results indicate that a Ga2O3 layer with high resistance as an interface layer contributes to broadening the width of space charge region of this pn heterojunction, resulting in the enhancement of photodetection responsivity (61.7 mA/W @-5 V). Furthermore, the pn heterojunction photodetector exhibits a photo-response to 254 nm UV light at zero bias voltage, showcasing robust stability. This suggests significant potential for applications in the challenging environments. The synergistic blend of the enhanced photodetector performance and the well-established technology of Si integrated circuits is generating considerable enthusiasm.

Exploring the Impact of Fe-Implantation on the Electrical Characteristics of Al/p-Si Schottky Barrier Diodes

The effects of Fe-implantation on the electrical characteristics of Au/p-Si Schottky barrier diodes (SBDs) were studied using current–voltage (I–V) and capacitance–voltage (C–V) techniques. The Rutherford Backscattering Spectrometry (RBS) and Energy Dispersive Spectroscopy (EDS) results showed that Fe ions are well implanted and present in the Fe-implanted Si material. The acquired results from I–V and C–V analysis showed that the diodes were well fabricated, and Fe-implantation changed the normal diode’s I–V behaviour from typical exponential to ohmic. The ohmic behaviour was described in terms of the defect levels induced by Fe in the middle of the band gap of Si. The conduction mechanism for both forward and reverse currents was presented, and the effect of Fe-implantation on the conduction mechanisms was investigated. The C–V results show that Fe generates a high density of minority carriers in p-Si, which agreed with the increase in reverse current observed in the I–V results. The diode parameters in terms of saturation current, ideality factor, Schottky barrier height, doping density, and space charge region (SCR) width were used to investigate the effect of Fe in p-Si based diode. Owing to the observed changes, which were analogous to those induced by dopants that improve the radiation hardness of silicon, it was safe to say that Fe can also assist in the quest to improve the radiation hardness of silicon using the defect-engineering method.

Simultaneous S-scheme promoted Ag@AgVO3/g-C3N4/CeVO4 heterojunction with enhanced charge separation and photo redox ability towards solar photocatalysis

Photocatalytic removal of toxic contaminants is one of the emerging techniques for water remediation, but it suffers from low redox ability, charge recombination and poor light harvesting efficiency. The present work reports a simultaneous S-scheme promoted by CeVO4/g-C3N4/Ag@AgVO3. The formation of the S-scheme mechanism enhanced the generation of photogenerated carriers and also improved the redox ability of the electrons and holes in the reduction and oxidation photocatalysts. The ternary demonstrated remarkable photo switching properties along with efficient charge separation which was achieved through dual interfacial interaction within the ternary (Ag@AgVO3/g-C3N4 and CeVO4/g-C3N4). The heterojunction formation was verified through the shift in binding energy spectra in the X-ray Photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy analysis (HR-TEM). The ternary demonstrated reduced PL intensity, width of space charge region and an upsurge in photogenerated current density in the order of 93 μA/cm2 (∼6X higher than all the pristine). This resulted in efficient removal of methyl orange, methylene blue and endocrine disruptive bisphenol-A with a removal rate of 0.02 min−1, 0.03 min−1 and 0.0087 min−1 and an apparent quantum yield of 4.6 × 10−9 (Methylene Orange), 6.89 × 10−9 (Methylene Blue) and 2 × 10−9 (Bisphenol A/H2O2).

The effect of passivation to etching duration ratio on bipolar electrochemical etching of porous layer stacks in germanium

The effect of the passivation to etching duration ratio on the bipolar electrochemical etching of highly p-doped germanium on its pore structures has been investigated. The final goal is the development of porous multi-layer stacks consisting of a closed growth template and separation layer for lift-off. In particular, changing the passivation duration allows different types of porous structures to be obtained. These range from a strong crystallographic orientation dependent dissolution to multi-layer structures consisting of “sponge” and “pine-tree” shapes. In this work, the degree of passivation was considered first and foremost since it is one way of controlling the formation of molecular hydrogen and surface atom protection. In addition, certain areas of the porous structure can be protected and, assuming a different space charge region width, selective etching is possible. Finally, by combining various successive processes, a porous multi-layer structure can be etched, including separation layers. In this work the most dominant reoccurring structures have been described using a model that contains the aforementioned assumptions.

Potential distribution over temperature sensors of p-n junction diodes with arbitrary doping of the base region

In p-n-junction temperature sensors connected in the forwardbiased, the temperature dependence of the built-in potential is important, while in the reverse biased p-n-junction temperature sensors, it is necessary to study the temperature dependence of the built-in potential and space-charge region width.For this case, as well as for homogeneous and gradient alloyed cases, the temperature dependence of built-in potential and space-charge region widthare studied and mathematical analysis is presented for these cases.Based on these mathematical analysis, the results are obtained for cases where the base region of p-n-junction temperature sensors is doped at different concentrations with a homogeneous or inhomogeneous distributions of impurities. It is well known that in conventional temperature sensors, when the main current transport mechanism is determined by generation-recombination processes in space charge region, the dependence of the space charge region width on the temperature can affect the linearity of temperature response curve of sensor, it is desirable to increase the doping rate of the base region to weaken this effect, or it is necessary to use p-n junction.

Z-scheme promoted heterojunction photocatalyst (Ag@AgVO3 /rGO/CeVO4) with improved interfacial charge transfer for efficient removal of aqueous organics irradiated under LED light

A facile hydrothermal route was followed to obtain a ternary composite Ag@AgVO3/rGO/CeVO4 with in-situ deposition of Ag nanoparticles over the AgVO3 nano-belts. The in-situ deposition was promoted and enhanced with the introduction of GO. The as-synthesized composite demonstrated remarkable visible light harvesting efficiency greater than 75% in the visible region. The charge separation and light harvesting properties were achieved through the Z-scheme mechanism mediated through rGO and the electron trapping/Schottky barrier effect from Ag nanoparticles. The reduction in the width of space charge region (∼2.5 times) and simultaneous increase in the density of charge carriers (2.3∗1018) promoted the LED irradiated photocatalytic performance. The decay time of the charge carriers were prolonged in the order of 4.46 s implying the enhancement in the charge separation. The studies were extended to charge trapping and the band structure modelling. The later emphasized on the prominence of Z-scheme mechanism with hole mediated degradation pathway. The LED photocatalysis demonstrated a removal efficiency of 87.20% for MB and 55.51% for phenol with a average AQE of 29.28% (MB) and 13.90% (phenol) for the ternary. The mineralization efficiency determined through TOC analysis was found to be 71.72%, and 66.43% for MB and phenol system respectively.

Facet-dependent spatial charge separation with rational cocatalyst deposition on BiVO4

Rational assembly of cocatalyst on the photocatalyst with exposed functional crystal facets has been demonstrated to be viable in enhancing the photocatalytic activity. However, greater attention is paid to the property of the loaded cocatalyst while the effect of varied functional facet exposure is relatively less discussed. Herein, dual-faceted BiVO4 with well-defined {010} and {110} facets but with varied {010}/{110} exposure extent ratios are coupled with CoOx which is known as a cocatalyst for water oxidation. The enhancement induced by the cocatalyst loading depends on both its deposit location and the ratio of {010}/{110} facet exposure. When selectively deposited on oxidation {110} facet, CoOx generates over two-fold enhancement on BiVO4 in photocatalytic oxygen evolution as compared to its randomly deposited analogue. Meanwhile, the {010}-dominant BiVO4 is more obviously benefited from the cocatalyst loading to both photocatalytic water oxidation and hydrogen peroxide generation reactions with respect to the {110}-dominant BiVO4. Further investigation reveals that CoOx functions more effectively in PL quenching and generating greater band bending on {010}-dominant BiVO4, substantiating the better enhancement in reducing charge recombination and forming larger space charge region width for charge separation, which deliver greater photocatalytic activity enhancement on {010}-dominant BiVO4.

Current-voltage and capacitance-voltage characteristics of cadmium-doped p-silicon Schottky diodes

This study reports on a change in current-voltage (I–V) and capacitance-voltage (C–V) characteristics of silicon (Si) diodes due to doping Si with cadmium (Cd). Effects of Cd-doping on diode parameters and conduction mechanism are investigated. The results obtained here indicate that the diodes are well fabricated and introducing Cd in Si results in a diode I–V behaviour changing from normal exponential to ohmic. An ohmic behaviour indicates that the diode conduction mechanism is dominated by defect levels at the centre of the Si energy gap. These defects are responsible for generation of minority carriers to recombine majority carriers resulting in an increase in material resistivity. A change in a direction of a C–V trend showing an inversion of a material conductivity-type confirms the generation of minority carriers after doping Si with Cd. A high resistivity material is important for radiation detection since a full space charge region width can be attained at a reasonable operating voltage. The ohmic behaviour and a conductivity-type inversion have been observed on diodes that are resistant to radiation damage. Cd is, therefore, a suitable dopant in defect-engineering studies to improve radiation hardness of Si for high energy physics experiments.

A General Compact Pinned Photodiode Model Capable of Miniature PPD Modeling

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.

Heterojunction photocatalyst of cavity shaped Bi2S3/g-C3N4 for bisphenol a degradation: Regulation of internal electric field via assistance of interfacial functional groups

The p-n heterojunction with internal electric field (IEF) is flourishingly developed in photocatalysis. Enlarging the space charge region width can effectively improve the migration/separation of charge carriers. Here, adequate functional groups (–COOH, -N-(C)3, -C-N–H) were generated from graphitic carbon nitride (GCN) decomposition, worked as the dispersant and electric charge contributor in the heterojunction. Bi ions were adsorbed on –COOH to achieve localized nucleation, formed Bi2S3 can be uniformly dispersed on GCN surface to form FGBS/GCN. Additionally, the incorporation of functional groups not only ameliorated the 3D cavity structure and optimized the band structure of functional groups modified Bi2S3 (FGBS) but also widened the space charge region of IEF in FGBS/GCN and resulted in efficient carriers separation. Benefit from functional groups, the initial rate of bisphenol A (BPA) degradation over 2FGBS/GCN was 0.0280 mmol⋅gcat-1⋅h−1. This work provides new insight into the regulation of the space charge region in the p-n heterojunction.

Silicon Solar Cell Space Charge Region and Capacitance Behavior under Electric Field

This paper investigates theoretically the behavior of the space charge region of a silicon solar cell and its associated capacitance under the effect of an external electric field. The purpose of this work is to show that under illumination the solar cell’s space charge region width varies with both operating point and the external induced electric field and how the solar cell capacitance varies with the space charge region width. Based on a 1D modelling of the quasi-neutral p-base, the space charge region width is determined and the associated capacitance is calculated taking into account the external electric field and the junction dynamic velocity. Based on the above calculations and simulations conducted with Mathcad, we confirmed the linear dependence of the inverse capacitance with space charge region width for thin space charge region and we exhibit an exponential dependence for large space charge region.

Nickel incorporated graphitic carbon nitride supported copper sulfide for efficient noble-metal-free photo-electrochemical water splitting

Solar hydrogen generation through photo-electrochemical (PEC) water splitting is potential technology but equally challenging to address the growing energy demand as well as the concerns related to the use of fossil fuels, and several strategies have been devised to address these concerns. Herein, we report a nanohybrids of copper sulfides supported on nickel-incorporated graphitic carbon nitride (Ni/g-C3N4@CuS) sheets for enhanced activity towards PEC water oxidation. The TEM images confirm the presence of intimate contact between nickel doped graphitic carbon nitride and CuS, forming an interface which is favorable for an effective separation of charge-carriers. The electrochemical properties of the prepared samples are investigated through linear sweep voltammetry, electrochemical impedance spectroscopy, Mott-Schottky analysis, and chopped photo-current measurements. The Ni/g-C3N4@CuS nanohybrids depicts almost three-fold enhancement in current density under light illumination reaching to 15.5 mA cm−2 at an over potential of ca. 600 mV than in the dark and almost fifteen-fold enhancement as compared to its parent materials, CuS and g-C3N4. The enhanced activity towards PEC water splitting is assigned to the larger extent of band bending as illustrated by larger space charge region width, formation of p-n junction between CuS and g-C3N4, lowering of effective band gap of the resulting hetero-structures, and facile charge transfer kinetics due to Ni-incorporation into the g-C3N4 matrix.

Electrical and optical characterizations of erbium doped MPS/PANI heterojunctions

Macroporous silicon (MPS) films were yielded by electrochemical anodization of p-type crystalline silicon in HF:DMF. Following, a Schottky structure was obtained by depositing polyaniline (PANI), which was doped with different contents of erbium (Er) using cyclic voltammetry method. The structural analysis showed the formation of pores with diameters ranging between 0.25 and 1.20 μm and length around 15 μm and, after PANI deposition, the diameter became about 17% lower. The chemical characterization by Energy dispersive X-ray spectroscopy (EDS) and Rutherford Backscattering Spectroscopy (RBS) pointed out that the erbium is primarily incorporated at polyaniline surface, but it spreads through the polymer layer and achieves the MPS/PANI interface. According to the Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) analysis, the presence of Er gave rise to the formation of additional functional groups besides that corresponding to polyaniline and silicon oxide phases. The optical characterization within the UV–vis region revealed a modified optical bandgap of PANI as a function of the Er doping concentration. The results of the electrical measurements pointed out to a lowering of the space charge region width in the silicon as well as a change of the PANI workfunction as a function of the Er doping. On the other hand, the current flow through the MPS/PANI Schottky junction was lowered by the increase of the Er doping and by the tunneling mechanism through a thin silicon oxide (≈1–2 nm) grown on MPS during PANI deposition in aqueous solution.

Thermodynamic and Kinetic Influence of Oxygen Vacancies on the Solar Water Oxidation Reaction of α-Fe2O3 Photoanodes.

To reveal the role of oxygen vacancies in the solar water oxidation of α-Fe2O3 photoanodes, the kinetic and thermodynamic properties that are closely related to the water oxidation reaction of the α-Fe2O3 photoanode containing oxygen vacancies were investigated. Compared with the pristine α-Fe2O3 photoanode, the presence of surface oxygen vacancies can improve the water oxidation activity and stability of the α-Fe2O3 photoanode simultaneously, but the bulk oxygen vacancies have a negative effect on the water oxidation performance of the α-Fe2O3 photoanode. In thermodynamics, our investigations revealed that the presence of surface oxygen vacancies narrows the space charge region width of the α-Fe2O3 photoanode, which could boost the charge separation and transfer efficiency of the α-Fe2O3 photoanode during water oxidation. Because the surface property and hydrophilicity of α-Fe2O3 are modified owing to the presence of surface oxygen vacancies, the water oxidation kinetics of the α-Fe2O3 photoanode with surface oxygen vacancies is obviously boosted. Our findings in the present work provide comprehensive understanding of the thermodynamic and kinetic differences for α-Fe2O3 photoanodes with and without oxygen vacancies for solar water oxidation.

Effects of External Magnetic Field and Air Mass on Space Charge Region Width Extension of a Bifacial Solar Cell Front Side Illumination

The environmental and economical merits of converting solar energy into electricity via photovoltaic cells have caused an ever increasing interest among developed and developing countries to allocate more budget on photovoltaic systems in order to boost up their efficiency in recent years. Besides the material and design parameters, there are several external factors such as magnetic field, air mass, intense light, external electric field, solar spectrum…. that can influence the PV cell’s performance. There have been a handful of studies conducted on the effect of various influential parameters on the efficiency and performance of photovoltaic cells; however none has taken these two parameters (magnetic field and air mass) into account simultaneously. In this 3D study the effects of magnetic field and the air mass illumination on space charge region width extension of a bifacial polycristalline solar cell front side illumination will be elaborated. Based on the columnar model of the grain and the quasi-neutral base, the continuity equation is established and the boundaries conditions are defined in order to use Green’s functions to solve this equation. New analytical expression of charge carriers’ density is found and the diffusion capacitance to the junction is calculated. The normalized carriers’ density plot versus base depth and magnetic field with various air mass illumination are presented and analyzed. The effects of magnetic field and air mass illumination on space charge region width extension are then deducted. The influences of magnetic field and air mass illumination on the junction capacitance and on the reverse of junction capacitance are also shown and analyzed.

Effect of CdTe crystal thickness on the efficiency of Cr/CdTe/Au Schottky-diode detectors

The effect of CdTe crystal thickness on the detection efficiency and energy resolution of Cr/CdTe/Au diode X/γ-ray detectors has been studied. The Schottky (Cr electrode) and near Ohmic (Au electrode) contacts were created using Ar plasma treatment of the B- and A-faces of CdTe(111) single crystals at different regimes, respectively. Detector-grade CdTe wafers with an area of 5 × 5 mm2 and thicknesses d of 0.5 mm, 0.75 mm, 1.0 mm and 2.0 mm were used. High energy resolution (FWHM) in the 137Cs spectra (662 keV peak) was achieved: from 0.5 % for thin detectors to 3.0 % for thick ones. From the comparison of the detection efficiency dependences on the CdTe crystal thickness with the corresponding calculated dependences, the uncompensated impurity concentration in CdTe was obtained as N ≈ 4 × 1010 cm−3. N determines the space–charge region width W in Schottky diodes, therefore the effect of this value on the detection efficiency was analyzed. A key feature of the efficiency calculation was the correct evaluation of the electric field strength in the crystals and also using the integration limit d rather than W when W >d (in contrast to the earlier works).

Analytical Modeling of Carbon Nanoparticle-Based Symmetric p–n Junction

Outstanding physical and electrical properties such as quantum transport, high carrier mobility, excellent electrical and thermal conductivity, high surface area, good optical transparency, strong mechanical strength and easy fabrication make carbon nanoparticles appropriate on nanoelectronic applications. Carbon nanoparticle based p–n junction, as a fundamental structure of nanoscale devices, is analytically presented in this study. The carbon nanoparticle p–n interface reveals an improved transport along the junction in comparison with the conventional p–n junction. Controlling the doping of p–n junction based device partially permit the foundation of carbon nanoparticle based bipolar technology and can overcome application of current in silicon based technology. This paper analytically demonstrates findings on electric field, space charge region width, scalar potential, built-in potential and transport along carbon nanoparticle based p–n junction. The uniqueness of this method is to create a well identified carbon nanoparticle based p–n junction which opens new opportunities for researching high field transport limit in nanoscale devices.

Design of thin film solar cells based on a unified simple analytical model

Polycrystalline thin film solar cells made with absorber materials such as CdTe, CIGS, CZTS and metalorganic halides (perovskites) are currently important alternatives for the silicon solar cell technology, which still dominates the photovoltaic market. Then, it is important to have tools which can be used to design this kind of solar cells. For this purpose, we have developed a unified simple analytical model that can be applied to thin film solar cells. The model is based on the basic physics of hetero-junction devices, but it takes into consideration that the space charge region can extend along the major part of the cell length, particularly for very thin cells, causing important effects that typically are not observed in conventional junction devices. Photo-generated carriers are collected by electric field-drift instead of diffusion, and simultaneously strong recombination at this region may dominate the electrical I–V characteristic of the cell. Since the space-charge region width varies with the applied voltage, the illumination current density and the saturation dark current density are no longer independent of the voltage as is assumed for conventional solar cells. When the model is applied to CIS and CdTe solar cells as examples, it is found that it is possible to design very thin film solar cells (absorber less than 1 μm thick) with high efficiencies, whenever the recombination velocity at the back surface becomes small (102 cm/s), instead of the highrecombination velocities present at ohmic contacts (107 cm/s). This fact implies the cost reduction of thin film solar cells by reducing absorber material thickness, and therefore it poses a challenge to develop deposition methods for very thin CdTe and CIGS absorber materials without pinholes, so that improved efficiencies are obtained when the surface recombination velocity is made small at the back by having a p+ or an electron blocking region before the ohmic contact. This result also explains the high efficiencies achieved by very thin perovskite solar cells.

Experiment and Theoretical Calculation of the Surface Space Charge Region Effect on Photocurrent Generation of SnO2 Bilayer Photodiode Devices

AbstractIn this work, a SnO2 bilayers photodiode device is designed, which consists of a thin SnO2 photocurrent generation layer and a SnO2 thick layer on the glass substrate. The SnO2 photocurrent generation layer with high oxygen vacancy concentration is intentionally prepared. With annealing in oxygen ambient, an electrical potential would be built in the surface space charge region in the thin SnO2 photocurrent generation layer, which would drive the photocarriers down to and flow in the photocarrier transportation layer, i.e., the high‐mobility SnO2 thick film on the glass substrate. The designed SnO2 bilayers photodiode device could enhance photocurrent generation and resolution for the SnO2‐based UV‐photodetectors. It is concluded that the width of surface space charge region is the key factor for the enhancement of lifetime of photocarriers and photocurrent generation of the current SnO2 bilayers photodiode. Based on the present experimental results, the width of the surface space charge region is expected to be nearly or less than 3 nm. Moreover, in this work, a theoretical model is developed to calculate the width of the surface space charge region. The calculated width of the surface space charge region (3.26 nm) is close enough to support the present experimental observation.