Majority Charge Carriers Research Articles

Transition from p-type to n-type semiconductor in V₂O₅ nanowire-based gas sensors: Synthesis and understanding of the sensing mechanism

Vanadium pentoxide (V2O5) nanowires (NWs) were grown via hydrothermal method, followed by annealing treatment at 500 °C in air. Morphological characterization showed that the V2O5 material consists of nanowires with a diameter of 200 nm and an average length of 2.5 μm. The nanowires were used to make an NH3 sensor that operates at room temperature (28 °C) and relative humidity of 40 % RH, giving a relative response of 6.0 % to 500 ppm. The V2O5 nanowires show a change in behavior from p-type semiconductor to n-type semiconductor when the temperature exceeds 50 °C. The maximum response (35 %) was recorded at a working temperature of 200 °C (when the semiconductor behaves as an n-semiconductor) and showed good response and recovery speed over 500 ppm NH3. The performance of the sensor was studied and a sensing mechanism that takes into account the change of majority charge carriers in the semiconductor was hypothesized.

The origins of nonlinear peculiarities on the IV characteristics of multi-junction solar cells

The paper presents an overview of studies of the multi-junction (MJ) solar cells (SC) with IV characteristics having nonlinear peculiarities. It is shown that such peculiarities can arise either due to hetero-interface barriers (HB) for majority charge carriers or due to problems with tunnel diodes (TD). It is usually difficult to identify which of these hetero-structural objects is the cause of this nonlinearity, since the peculiarities appear similarly in the IV characteristics of MJ SC. The experimental method presented in this work is based on the study of IV characteristics during the overheating of MJ SCs. The behavior of nonlinear peculiarities caused by an imperfect TD or an HB is fundamentally different during the overheating of SCs, which makes it possible to identify the type of hetero-structural object. Since the number of hetero-interfaces in MJ SC is large, a method determining the position of problematic objects in the MJ structure was also developed. The method is based on the illumination of individual subcells using different laser wavelengths. Both methods considered were tested experimentally on GaInP/GaAs/Ge SCs.

All‐Electronic Memristor Based on Charge Carrier Confinement in Bulk Semiconductor of Metal–Semiconductor–Metal Structure

AbstractMemristors have gained significant attention in recent years due to their potential applications in computing and memory technology by offering higher performance, lower power consumption, and increased storage capacity. In this paper, a new type of volatile memristor is presented by analyzing the dynamic behavior of charge carriers within a metal–semiconductor–metal (MSM) structure. It is shown that an all‐electronic memristor is achieved through the confinement of majority charge carriers within the bulk semiconductor by the favor of high barrier Schottky contacts. The findings reveal a remarkable current offset between forward and backward scans, along with exceptional current pulse consistency with a tunable current level using pulse frequency. These characteristics greatly simplify the process of designing electrical circuits incorporating this memristor variant. Furthermore, this research paves the way for the development of crystalline semiconductor‐based memristors. While various semiconductors with controllable doping densities can be considered as potential candidates for this type of memristor, the calculations using silicon demonstrate the integration of this semiconductor with the current technology holds significant promise for two terminal memristors.

Tetracycline removal via photo-Fenton processes using Fe-based metal-organic frameworks loaded with Bi2S3: Performance evaluation and insights into the charge-transfer mechanism

Combining photocatalytic technology with the Fenton system may help overcome these technologies’ limitations. Photo-Fenton catalysis is economical and eco-friendly. The Fe based heterogeneous photo-Fenton process appears to be a promising wastewater treatment technology. Herein, an Fe based metal–organic framework (MIL-101 (Fe)) was produced via hydrothermal processing. Subsequently, Bi2S3 was loaded onto the surface of MIL-101 (Fe) to form a composite catalyst. A type-II heterojunction was established between MIL-101 (Fe) and Bi2S3. The 10 % Bi2S3-loaded MIL-101 (Fe) (MBS-10) was effective in the photocatalytic degradation of tetracycline, particularly after H2O2 addition. This outcome was due to the enhanced generation of radical species through the photo-Fenton process. The MBS-10 photocatalyst promoted Fe (II)/Fe (III) cycling in the presence of H2O2 and under visible light irradiation. MBS-10 also showed a higher kinetic rate constant during the photocatalytic reaction compared to MIL-101 (Fe) and Bi2S3, suggesting enhanced activity through greater electron-hole separation. Furthermore, MBS-10 proved to be stable and reusable photocatalyst after four testing cycles. The charge-transfer mechanism was elucidated through radical scavenging experiments which demonstrated that superoxide and hydroxyl radicals are the major charge carriers. Therefore, the Bi2S3-MIL-101 (Fe) composite exhibits great potential for degrading tetracycline antibiotics.

In-Depth Study of Ambipolar Charge-Transport Regime through External Triggers and Gas Sensing.

Ambipolar devices are a hot topic in research tables due to their unique advantage in reducing the size of the electrical system and enhancing its efficiency. Here, we report a bilayer heterojunction device constructed using octafluoro-vanadyl-phthalocyanine (VOF8Pc) and lutetium bisphthalocyanine (LuPc2), which exhibits both p- and n-type behaviors under oxidizing (NO2 and O3) and reducing gas (NH3) species depending on the humidity level and temperature variations. The initial polarity of the device is identified as n-type by measuring a current decrease under oxygen exposure. Most interestingly, we were capable of observing the zero state (no response) where both opposite charge carriers fight for the majority to dominate the electrical properties of the device when it goes from n- to p-type or vice versa. The inversion in the nature of the majority charge carriers in this ambipolar device was achieved by optimizing the external trigger. The unique property of controllable polarity inversion in a VOF8Pc/LuPc2-based bilayer heterojunction device makes it the most effective ambipolar device for real-world applications.

Influence of Dimensional Quantization Effects on the Effective Mass of Major Charge Carriers in LED Heterostructures with InxGa1−xN/GaN Multiple Quantum Wells

By numerically solving the self-consistent system of the Schr¨odinger equations and Poisson electroneutrality, zone diagrams of LED heterostructures with InxGa1−xN/GaN multiple quantum wells have been calculated. The effect of electron–phonon interaction, nonparabolicity of the dispersion relation, and hybridization of the wave function on the values of the effective mass of major charge carriers in the InxGa1−xN/GaN quantum wells has been studied. The long-wave shift of 2D-plasmon resonances is associated with the temperature renormalization of the effective mass of two-dimensional carriers. To describe the temperature dependence of the effective mass, the function for the displacement of the 2D-plasmon resonance frequency is introduced.

Tailoring Li-ion transport in hybrid biopolymer electrolyte from Maydis stigma for supercapattery applications

Corn Silk Biopolymer (CSBP), a potent biomaterial shed light on offering a sustainable solution to agrowaste and achieve waste valorization. Hybrid Biopolymer Electrolyte (HBPE) was synthesized using corn silk extract by simple solution casting strategy. Freshly synthesized [30wt % CSBP+70 wt % PVDF-Co-HFP] system exemplifies conductivity of 2.35 × 10−8 Scm−1 and while loading 3.2 v/v % LiClO4 salt, the conductivity increased to 4.05 × 10−4 Scm−1 at 25 °C. Structural studies indicate complex formation between the Li+ and polar groups within polymer-salt system. From FTIR studies, prominent peaks noticed at 1651 and 1628 cm−1 are due to the interaction of –C=O group with Li+ and 625 cm−1 for unbound ClO4−.Our best conducting system reveal Li+ ions (tion = 0.98) are the major charge carriers. Electrochemical behaviour from CV demonstrates a good reversibility with a specific capacity (Qs = 25.6 Cg-1) and specific capacitance (Csp = 10.67 Fg-1) at a scan rate of 1 mV s−1. Also, the relation between the peak current with different scan rates for CPL 2 system is estimated from the slope as b = 0.7 suggesting the extraordinary behavior of a hybrid battery and super capacitor offering a unique platform for the sustainable energy storage technology.

Electronic structure and thermoelectric properties of epitaxial Sc1−xVxNy thin films grown on MgO(001)

The electronic structure of Sc1−xVxNy epitaxial films with different alloying concentrations of V are investigated with respect to effects on thermoelectric properties. Band structure calculations on Sc0.75V0.25N indicate that V 3d states lie in the band gap of the parent ScN compound in the vicinity of the Fermi level. Thus, theoretically, the presence of light (dispersive) bands at the Γ point with band multiplicity is expected to lead to lower electrical resistivity, while flat (heavy) bands at X−W−K symmetry points are associated with higher Seebeck coefficients than that of ScN. Hence, to probe the thermoelectric properties experimentally, epitaxial Sc1−xVxNy thin film samples were deposited on MgO(001) substrates. All the samples showed N substoichiometry and pseudocubic crystal structure. The N-vacancy-induced states were visible in the Sc 2p x-ray absorption spectroscopy spectra. The reference ScN and Sc1−xVxNy samples up to x=0.12 were n type, exhibiting carrier concentration of 1021 cm−3, typical for degenerate semiconductors. For the highest V alloying of x=0.15, holes became the majority charge carriers, as indicated by the positive Seebeck coefficient. The underlying electronic structure and bonding mechanisms in Sc1−xVxNy influence the electrical resistivity, Seebeck coefficient, and Hall effect. Thus, this paper contributes to the fundamental understanding to correlate defects and thermoelectric properties to the electronic structure in the Sc-N system with V alloying. Published by the American Physical Society 2024

Enhancement in power factor through rare-earth samarium doping in Cu2SnSe3 system

Cu2SnSe3 has drawn enough attention as a potential thermoelectric material due to its unique electronic and thermal properties. We present the impact of Sm doping on the Cu2SnSe3 system’s Sn site. The polycrystalline samples of Cu2Sn1-x Sm x Se3 (0 ≤ x ≤ 0.08) were prepared using the solid-state reaction technique followed by conventional sintering. The crystal structure was characterized using XRD and the results reveal that the samples have a diamond cubic structure with a space group of F4̄3m. Scanning Electron Microscopy (SEM) analysis indicates a uniform surface homogeneity within the sample. Furthermore, the introduction of Sm causes a reduction in porosity. The electrical transport characteristics were studied in the mid temperature range of 300–650 K. The Seebeck coefficient of all the samples were found to be positive within the temperature range under study, suggesting that holes constitute the majority charge carriers. This is also confirmed by the Hall measurements as the carrier concentration was positive for all the samples. The inclusion of Sm has led to a reduction of electrical resistivity and Seebeck coefficient and hence power factor of ~539 μW mK−2 for x = 0.08 at 630 K which is ten times greater as compared to x = 0 whose power factor is ~56 μW mK−2 at 630 K is achieved which makes it suitable for thermoelectric applications.

Efficient Ionovoltaic Energy Harvesting via Water-Induced p-n Junction in Reduced Graphene Oxide.

Water motion-induced energy harvesting has emerged as a prominent means of facilitating renewable electricity from the interaction between nanostructured materials and water over the past decade. Despite the growing interest, comprehension of the intricate solid-liquid interfacial phenomena related to solid state physics remains elusive and serves as a hindrance to enhancing energy harvesting efficiency up to the practical level. Herein, the study introduces the energy harvester by utilizing inversion on the majority charge carrier in graphene materials upon interaction with water molecules. Specifically, various metal electrode configurations are employed on reduced graphene oxide (rGO) to unravel its distinctive charge carriers that experience the inversion in semiconductor type upon water contact, and exploit this characteristic to leverage the efficacy of generated electricity. Through the strategic arrangement of the metal electrodes on rGO membrane, the open-circuit voltage (Voc) and short-circuit current (Isc) have exhibited a remarkable augmentation, reaching 1.05V and 31.6µA, respectively. The demonstration of effectively tailoring carrier dynamics via electrode configuration expands the practicality by achieving high power density and elucidating how the water-induced carrier density modulation occurs in 2D nanomaterials.

Optical Studies of Doped Two-Dimensional Lead Halide Perovskites: Evidence for Rashba-Split Branches in the Conduction Band.

Two-dimensional (2D) hybrid organic/inorganic perovskites are an emerging materials class for optoelectronic and spintronic applications due to strong excitonic absorption and emission, large spin-orbit coupling, and Rashba spin-splitting effects. For many of the envisioned applications, tuning the majority charge carrier (electron or hole) concentration is desirable, but electronic doping of metal-halide perovskites has proven to be challenging. Here, we demonstrate electron injection into the lower-energy branch of the Rashba-split conduction band of 2D phenethylammonium lead iodide by means of n-type molecular doping at room temperature. The molecular dopant, benzyl viologen (BV), is shown to compensate adventitious p-type impurities and can lead to a tunable Fermi level above the conduction band minimum and increased conductivity in intrinsic samples. The doping-induced carrier concentration is monitored by the observation of free-carrier absorption and intraband optical transitions in the infrared spectral range. These optical measurements allow for an estimation of the Rashba splitting energy ER ≈38 ± 4 meV. Photoinduced quantum beating measurements demonstrate that the excess electron density reduces the electron spin g-factor by ca. 6%. This work demonstrates controllable carrier concentrations in hybrid organic/inorganic perovskites and yields potential for room temperature spin control through the Rashba effect.

Comparative analysis of radiation-induced effects on the performance of p-type PERC and TOPCon solar cells for space applications

This work presents a comprehensive numerical evaluation of PERC and TOPCon technologies, focusing on the impact of radiation-induced defects. This assessment is conducted for p-type silicon solar cells as they are intrinsically more resistant to radiation defects. By rigorously calibrating recombination parameters, radiation-induced defect profiles, and other pertinent details, a robust basis is established for an in-depth comparison of the performance characteristics displayed by both architectures under space conditions. The investigation reveals that when utilizing substrates with high doping levels, both PERC and TOPCon cells exhibit nearly identical beginning-of-life (BOL) and end-of-life (EOL) performance. However, with lower substrate doping concentrations, both technologies show improved BOL efficiency. Notably, this enhanced BOL efficiency does not translate into superior EOL efficiency. This distinction in EOL efficiency can be attributed to two primary factors triggered by radiation exposure. Firstly, the emergence of defects leads to a reduction in open-circuit voltage. Secondly, dopant compensation contributes to an increase in series resistance. Specifically, for PERC cells, the challenge of elevated series resistance is further exacerbated by the requirement for majority carriers to traverse both vertically and laterally to reach the rear metal contact. When a robust defect recovery mechanism or resilient cover glass is absent, substrates characterized by lower doping levels display increased susceptibility to the adverse effects of radiation-induced defects and the subsequent dopant compensation. Under these circumstances, the TOPCon technology demonstrates a significant advantage over PERC, particularly for high electron fluence due to its full area contacts for both minority and majority charge carriers.

Dual Exciton Polarization in Bipolar CeO2-x Nanocrystals Controlled by Defect-Based Redox Processes.

Discovering alternative means to control electronic states in semiconductor nanostructures is the key to the development of new quantum technologies. Controlling the cyclotron motion of free charge carriers in semiconductor nanocrystals using an external magnetic field generates a tunable angular momentum, as a collective electronic degree of freedom, which can be imparted to the electronic band states to achieve complete exciton polarization. The sign of this polarization is determined by the type of majority charge carriers in a given lattice. Using magnetic circular dichroism spectroscopy, we demonstrate a simultaneous polarization of excitonic states in substoichiometric oxygen-deficient CeO2-x nanocrystals associated with electrons and holes, which can be controlled by the thermal treatment of colloidal nanocrystals in oxidizing or reducing conditions. The presence of both occupied and unoccupied midgap states, due to Ce3+ 4f and Ce4+ 4f orbitals, respectively, allows for selective probing of the effect of holes in the valence band (VB → Ce4+ 4f) and electrons in the conduction band (Ce3+ 4f → CB). The two transitions show the opposite sign at 300 K due to the opposite angular momenta associated with cyclotron electrons and holes. The ability to manipulate Ce 4f-derived midgap states by defect formation during the synthesis or postsynthesis treatment allows for a range of new technological applications of CeO2-x nanocrystals in optoelectronics.

Modeling Ion Transport across Thin-Film Composite Membranes During Saltwater Electrolysis.

Affordable thin-film composite (TFC) membranes are a potential alternative to more expensive ion exchange membranes in saltwater electrolyzers used for hydrogen gas production. We used a solution-friction transport model to study how the induced potential gradient controls ion transport across the polyamide (PA) active layer and support layers of TFC membranes during electrolysis. The set of parameters was simplified by assigning the same size-related partition and friction coefficients for all salt ions through the membrane active layer. The model was fit to experimental ion transport data from saltwater electrolysis with 600 mM electrolytes at a current density of 10 mA cm-2. When the electrolyte concentration and current density were increased, the transport of major charge carriers was successfully predicted by the model. Ion transport calculated using the model only minimally changed when the negative active layer charge density was varied from 0 to 600 mM, indicating active layer charge was not largely responsible for controlling ion crossover during electrolysis. Based on model simulations, a sharp pH gradient was predicted to occur within the supporting layer of the membrane. These results can help guide membrane design and operation conditions in water electrolyzers using TFC membranes.

Oxygen vacancy migration and impact on high voltage DC polarization in 0.8BaTiO3–0.2BiZn0.5Ti0.5O3

AbstractElectrical polarization and defect transport are examined in 0.8BaTiO3–0.2BiZn0.5Ti0.5O3, an attractive capacitor material for high power electronics. Oxygen vacancies are suggested to be the majority charge carrier at or below 250°C with a grain conduction hopping activation energy of 0.97 eV and 0.92 eV for thermally stimulated depolarization current (TSDC) and impedance spectroscopy measurements, respectively. At higher temperature, thermally generated electronic conduction with an activation energy of 1.6 eV is dominant. Significant oxygen vacancy concentration is indicated (up to ∼1%) due to cation vacancy formation (i.e., acceptor defects) from observed Bi (and likely Zn) volatility. Oxygen vacancy diffusivity is estimated to be 10−12.8 cm2/s at 250°C. Low diffusivity and high activation energies are indicative of significant defect interactions. Dipolar oxygen vacancy defects are also indicated, with an activation energy of 0.59 eV from TSDC measurements. The large oxygen vacancy content leads to a short lifetime during high voltage (30 kV/cm), high temperature (250°C) direct current (DC) electrical measurements.

New insights into the photoassisted anodic reactions of n-type 4H SiC semiconductors

This study aims to investigate the photoelectrochemical behavior of the n-type 4H-SiC, focusing on aqueous, hydroxide-based electrolytes. Despite its high stability, this wide-bandgap semiconductor material undergoes electrochemical reactions, such as anodic oxidation or etching, under specific conditions. Since electrons are the majority charge carriers in n-type semiconductors, oxidation processes require above-bandgap illumination. Then, the reaction rate is influenced by the number of electron holes available for an oxidation process and the velocity of the transport of hydroxide ions to/from the surface. The goal is to focus on the essential reaction parameters (i.e., potential and electrolyte concentration) to clarify the reaction mechanism in aqueous (alkaline) electrolytes. Methods with controllable hydrodynamic conditions are required to investigate the transport processes in the electrolyte. Even though the rotating disk electrode (RDE) is a commonly used and powerful method, it is not well suited for our purpose. Photoelectrochemical etching of SiC is extraordinary because it involves both mass transfer phenomena and gas evolution but also needs high-intensity illumination from an appropriate light source. Hence, a new concept for an inverted rotating cell was developed and implemented. This setup was used to study the effect of the mass transport of hydroxide ions on the photoelectrochemical behavior of SiC in each potential region at varying rotation speeds. In order to interpret the experimental findings, a distinct electrical network model was formulated for simulating the results, aiding in unraveling the underlying reaction mechanism. Electrochemical measurements were complemented by surface-sensitive analytical techniques. XPS was the method of choice to investigate the composition of the sample surface before and after etching. SEM and AFM allow the characterization of the surface morphology in the initial stages of etching. The totality of this information provides a complete picture of the complex processes in the vicinity of the semiconductor electrode.Graphical abstract

A study of the effect of cerium ion doping concentration on the structural, electrical, and thermoelectric properties of CaMnO3 nanoparticles

Abstract Universally, energy loss in the form of heat is predominant and this heat is irrecoverable waste heat that leads to global warming. Clean, green, eco-friendly, cost-effective, and renewable energy sources are the possible solutions for this energy crisis and global warming issues. Thermoelectric power generation is a promising technology by converting this irrecoverable waste heat directly into electricity without any greenhouse gas emission. Nanostructured CaMnO3 at various cerium concentrations have been successfully prepared by sol–gel hydrothermal method followed by annealing and sintering. Pure and doped samples were systematically characterized by DSC, powder XRD, RAMAN, SEM with EDAX and FTIR spectroscopy. Electrical and thermoelectrical measurements were carried out on the sintered pellets. The XRD analyses confirmed the formation of orthorhombic perovskite structure for all the samples and the average particle size lies in the range of 50–60 nm. FTIR analysis shows the presence of CaMnO3 nanoparticles without any impurities. The temperature dependence of physical properties was performed and analyzed between room temperature and 600 °C. Electrical resistivity strongly depends on the nature of substituent ions and negative values indicate that the electrons are major charge carriers. Large Seebeck coefficient value and high-power factor make Ca1−x Ce x MnO3 an efficient thermoelectric material for energy storage applications.

Effects of Visible Light on Gas Sensors: From Inorganic Resistors to Molecular Material-Based Heterojunctions.

In the last two decades, many research works have been focused on enhancing the properties of gas sensors by utilising external triggers like temperature and light. Most interestingly, the light-activated gas sensors show promising results, particularly using visible light as an external trigger that lowers the power consumption as well as improves the stability, sensitivity and safety of the sensors. It effectively eliminates the possible damage to sensing material caused by high operating temperature or high energy light. This review summarises the effect of visible light illumination on both chemoresistors and heterostructure gas sensors based on inorganic and organic materials and provides a clear understanding of the involved phenomena. Finally, the fascinating concept of ambipolar gas sensors is presented, which utilised visible light as an external trigger for inversion in the nature of majority charge carriers in devices. This review should offer insight into the current technologies and offer a new perspective towards future development utilising visible light in light-assisted gas sensors.

Enhanced Photoelectrochemical Activity Realized from WS2 Thin Films Prepared by RF‐Magnetron Sputtering for Water Splitting

AbstractWe report the synthesis of tungsten sulfide (WS2) films using RF‐magnetron sputtering at different RF powers. X‐ray diffraction (XRD) data confirm the hexagonal crystal structure of WS2 with an average crystallite size of ∼44.54 Å. With increased RF power, the preferred orientation of WS2 crystallites shifts from (002) to (100). Linear sweep voltammetry (LSV) was used to assess the Photoelectrochemical (PEC) activity of WS2 films. The film deposited at 150 W demonstrated the highest photocurrent density of 5.44 mA/cm2. The 150 W film also showed a lower Tafel slope of ∼0.374 V/decade, indicating superior PEC activity. Mott Schottky's (MS) analysis revealed a notable shift in the flat band potential towards the negative side, suggesting a shifting of the Fermi level towards the conduction band. WS2 film grown at 150 W demonstrated a majority charge carrier density of 6.2×1021 cm−3 and a depletion layer width of 1.54 nm. The observed low charge transfer resistance of 155 Ω contributed to the enhanced PEC activity with a relaxation time constant of 37 ms. These properties suggest that WS2 can be suitable for PEC water splitting.

Modulating the majority charge carrier type and performance of organic heterojunction ammonia sensors by increasing peripheral fluorination of the silicon phthalocyanine sublayer

Silicon phthalocyanines (R2-SiPcs) are an emerging class of high-performance organic semiconductors which have recently found application in highly sensitive and selective bilayer organic heterojunction devices for ammonia (NH3) sensing. We report bilayer heterojunction devices based on axially-substituted bis(pentafluorophenoxy)silicon phthalocyanines of increasing peripheral fluorination ((F5PhO)2-FXSiPc) as a bottom layer and lutetium bis-phthalocyanine (LuPc2) and demonstrate how increased peripheral fluorination changes device operation from p-type to n-type in response to NH3. Sensors fabricated with (F5PhO)2-F16SiPc exhibits the smallest apparent energy barrier for interfacial charge transport by impedance spectroscopy due to better alignment of the semiconductor molecular orbitals with the semi-occupied molecular orbital of LuPc2. Bilayer heterojunction devices all demonstrated a limit of detection (LOD) below 1 ppm with (F5PhO)2-SiPc/LuPc2 yielding an LOD of 307 ppb and a sensitivity of −0.72%·ppm−1. Postdeposition thermal annealing of the (F5PhO)2-SiPc/LuPc2 device is shown to further enhance sensor performance with a 1.5-fold increase in sensitivity to −1.15%·ppm−1 and a LOD of 198 ppb.