Electron Transport Behavior Research Articles

Photoluminescence and Electrical Properties of n-Ce-Doped ZnO Nanoleaf/p-Diamond Heterojunction.

The n-type Ce:ZnO (NL) grown using a hydrothermal method was deposited on a p-type boron-doped nanoleaf diamond (BDD) film to fabricate an n-Ce:ZnO NL/p-BDD heterojunction. It shows a significant enhancement in photoluminescence (PL) intensity and a more pronounced blue shift of the UV emission peak (from 385 nm to 365 nm) compared with the undoped heterojunction (n-ZnO/p-BDD). The prepared heterojunction devices demonstrate good thermal stability and excellent rectification characteristics at different temperatures. As the temperature increases, the turn-on voltage and ideal factor (n) of the device gradually decrease. The electronic transport behaviors depending on temperature of the heterojunction at different bias voltages are discussed using an equilibrium band diagram and semiconductor theoretical model.

Electron transport characteristics in dual gate-controlled 30 nm-thick silicon membrane

The exploration of multi-gate-controlled electron transport characteristics is always a research focus in Si-based device development and optimization. In this work, we report individual and dual gate-controlled energy band regulations of 30 nm-thick Si membrane and the resulted electron transportations at 10–300 K. It is discovered that the fine energy band structure is a key element to determine electron transport behaviors in fully-depleted silicon-on-insulator. Furthermore, either the front or the back gate bias can modify the energy band bending and sub-band gap, change charged body distribution and intersub-band transition probability, and thus adjust electron mobility and device performance. This dual gate coupling effect together with the proposed gate-controlled sub-band structure model is confirmed by magnetotransport experiments at 1.6 K. Notably, our work presents the coupled gate controlling effects within ultrathin Si film, and gives a physical insight into electron structure modulating, which may promote the evolution of Si-based device applications in many domains.

Photon and magnetic field controlled electron transport of a multiply-resonant photon-cavity double quantum dot system

We study electron transport through double quantum dots (DQD) coupled to a cavity with a single photon mode. The DQD is connected to two electron reservoirs, and the total system is under an external perpendicular magnetic field. The DQD system exhibits a complex multi-level energy spectrum. By varying the photon energy, several anti-crossings between photon dressed electron states of the DQD-cavity system are found at low strength of the magnetic field. The anti-crossings are identified as multiple Rabi resonances arising from the photon exchange between these states. As the results, a dip in the current is seen caused by the multiple Rabi resonances. By increasing the strength of the external magnetic field, a dislocation of the current dip to a lower photon energy is found and the current dip can be diminished. The interplay of the strength of the magnetic field and the geometry of the states the DQD system can weaken the multiple Rabi resonances in which the exchange of photon between the anti-crossings is decreased. We can therefore confirm that the electron transport behavior in the DQD-cavity system can be controlled by manipulating the external magnetic field and the photon cavity parameters.

Two-dimensional GaS/MoTe2 van der Waals heterostructures with tunable electronic and optical properties

Two-dimensional van der Waals heterostructures (vdWHs) based on transition metal dichalcogenides and gallium monochalcogenides have attracted widely attention for their distinctive physicochemical properties. Here, the GaS/MoTe2 vdWHs are constructed and their electronic structures, transport behaviors and optical properties are investigated via the first-principles calculations. The results demonstrated that the GaS/MoTe2 vdWHs are type-I semiconductors with direct bandgaps of 1.05 eV. The heterostructures have flexible tunability, compression strain and negative external electric field (Efield) can induce the conversion of type-I GaS/MoTe2 to type-II. The semiconductor-metal transition can be achieved under the control of strain and Efield. Current-voltage curves display that the current magnitude can reach the order of μA. Additionally, the absorption coefficients (∼105 cm-1) and adsorption ranges of the heterostructures are far greater than GaS and MoTe2 monolayers. Especially, the absorption intensity of GaS is significantly enhanced in the visible-light region. The work provides a significant theoretical guidance for the next generation optoelectronic materials, nanodevices applications and the design of GaS/MoTe2 vdWHs.

Effect of Ag+ doping and Ag addition on the thermoelectric properties of KSr2Nb5O15

The electron and phonon thermal transport behavior of Ag + doped KSr2Nb5O15 were discussed by using the first-principles calculations. The band gap was reduced after Ag+ doping, and the electrons near the Fermi level had stronger transition capability, which effectively increased the carrier concentration and electrical conductivity and reduced the thermal conductivity, thereby improving the ZT of the doped KSr2Nb5O15 from 0.6298 to 0.7214 (1200 K) under ideal conditions. In addition, the solid-state reaction method was used to prepare Ag nanoparticle added KSr2Nb5O15 samples, and their thermoelectric performance was tested. The experimental results and the calculated results showed a good consistent trend in which Ag improved the thermoelectric properties of KSr2Nb5O15. When the amount of addition of nanosized Ag was 20 wt%, the power factor and ZT of the material were the highest at 1073 K, which were 0.228 mW/(K2·m) and 0.1090, respectively. This research shows how to improve the thermoelectric performance of KSr2Nb5O15 ceramics and broaden their temperature range for application.

Interfacial‐Modulated Growth of Nanostructured Bi2Te3 Films for Enhancing Thermoelectric Performance

Growth Behavior of Layered Materials In article number 2200108, Zhiyu Hu and co-workers present layered hexagonal Bi2Te3 grown into nanopillars and nanoplates. Transport behavior of electrons and phonons at the interface indicates the potential to enhance the thermoelectric power factor while maintaining a small electronic thermal conductivity.

Electronic transport in organic photovoltaic materials subjected to dark and light irradiation conditions: A first principles study

Organic solar cell nanomaterials are molecular systems that have been recently incorporated in devices with remarkable properties and high efficiencies. A systematic theoretical study based on density functional theory and non-equilibrium Green’s functions was performed to elucidate the electron transport behavior on solar cell materials. The I−V profiles based on the transmission obtained from the electronic density revealed an appropriate performance in simulated conditions of sunlight irradiation, while in dark conditions such systems may behave as a diode. The current methodology may represent a tool to select and design high performance materials for the new generation of solar cell devices.

High-Temperature Electronic Transport Properties of PEDOT:PSS Top-Contact Molecular Junctions with Oligophenylene Dithiols

In this study, we investigated the high-temperature electronic transport behavior of spin-coated PEDOT:PSS top-contact molecular ensemble junctions based on self-assembled monolayers (SAMs) of oligophenylene dithiols. We observed irreversible temperature-dependent charge transport at the high-temperature regime over 320 K. The effective contact resistance and normalized resistance decreased with increasing temperature (320 to 400 K), whereas the tunneling attenuation factor was nearly constant irrespective of temperature change. These findings demonstrate that the high-temperature transport properties are not dominated by the integrity of SAMs in molecular junctions, but rather the PEDOT:PSS/SAMs contact. Transition voltage spectroscopy measurements indicated that the contact barrier height of the PEDOT:PSS/SAMs is lowered at elevated temperatures, which gives rise to a decrease in the contact resistance and normalized resistance. The high-temperature charge transport through these junctions is also related to an increase in the grain area of PEDOT cores after thermal treatment. Moreover, it was found that there was no significant change in either the current density or normalized resistance of the annealed junctions after 60 days of storage in ambient conditions.

Defect-control electron transport behavior of gallium nitride/silicon nonplanar-structure heterojunction

Compared with a traditional heterojunction, a nonplanar-structure heterojunction can reduce the problems caused by a lattice mismatch through a three-dimensional stress release mechanism, which will be helpful for promoting the performance and stability of related devices. In this paper, we report our study on the electron transport behavior of a gallium nitride (GaN)/silicon (Si) heterojunction with nonplanar-structure interface, which was prepared through growing GaN on a hierarchical structure, Si nanoporous pillar array (Si-NPA). To clarify the electron transport mechanism and promote the device performance, annealing treatment in ammonia atmosphere was carried out to as-prepared GaN/Si-NPA. The formation of the heterojunction was verified by the typical rectification behavior observed in both as-prepared and annealed samples. After annealing treatment, a lower turn-on voltage, a smaller reverse saturation current density, a larger forward current density and a higher reverse breakdown voltage were obtained, which indicate the promotion of the heterojunction performance. By comparatively studying the spectrum evolution of photoluminescence before and after annealing treatment, the underlying mechanism is clarified as the variation of the type and density of point defects such as gallium vacancy (V Ga), oxygen substitutional impurity (ON), and their complex defect V Ga−ON in GaN. The results illustrate an effective defect-control strategy for optimizing the performance of GaN/Si heterojunction optoelectronic devices.

Nonlocal thermoelectric resistance in vortical viscous transport

The pursuit for clearly identifiable signatures of viscous electron flow in the solid state systems has been a paramount task in the search of the hydrodynamic electron transport behavior. In this work, we investigate theoretically the nonlocal electric and thermal resistances for the generic non-Galilean-invariant electron liquids in the multiterminal Hall-bar devices in the hydrodynamic regime. The role of the device inhomogeneity is carefully addressed in the model of the disorder potential with the long-range correlation radius. We obtain analytic expressions for the thermoelectric resistances that are applicable in the full crossover regime from charge neutrality to high electron density. We show that the vortical component of the electron flow manifests in the thermal transport mode close to the charge neutrality where vorticity is already suppressed by the intrinsic conductivity in the electric current. This behavior can be tested by the high-resolution thermal imaging probes.

Intriguing heterophase domain patterns in correlated electron material via tip force engineering

Vanadium dioxide (VO2) is a compelling correlated electron material in advanced electronics and fundamental research, for its fascinating metal-insulator transition (MIT) and tunability by external stimuli. However, despite of its well-known strain sensitivity, the potential of local strain control of the heterophase domain patterning in VO2 remains largely unexamined. Here, we report that intriguing heterophase domain patterns can be mechanically created in VO2 platelets via tip pressing forces. Based on tip-domain and domain-domain interactions, letter-shaped patterns (e.g., ‘I’, ‘V’, ‘N’, ‘W’, ‘Y’, etc.) and geometry-shaped patterns (e.g., wedge, parallelogram, triangle, diamond, etc.) can be readily obtained. Moreover, the global and local electronic transport behaviors of VO2 platelets are sensitive to the induced heterophase domain patterns, based on which, device concepts like force-gate-transistors and anti-crosstalk devices are demoed. The feasible tip force control on the MIT heterophase structures of VO2 also paves a way to explore the phase transition physics of materials with a strong first-order feature.

Contact Conductance Governs Metallicity in Conducting Metal Oxide Nanocrystal Films

Although colloidal nanoparticles hold promise for fabricating electronic components, the properties of nanoparticle-derived materials can be unpredictable. Materials made from metallic nanocrystals exhibit a variety of transport behavior ranging from insulators, with internanocrystal contacts acting as electron transport bottlenecks, to conventional metals, where phonon scattering limits electron mobility. The insulator-metal transition (IMT) in nanocrystal films is thought to be determined by contact conductance. Meanwhile, criteria are lacking to predict the characteristic transport behavior of metallic nanocrystal films beyond this threshold. Using a library of transparent conducting tin-doped indium oxide nanocrystal films with varied electron concentration, size, and contact area, we assess the IMT as it depends on contact conductance and show how contact conductance is also key to predicting the temperature-dependence of conductivity in metallic films. The results establish a phase diagram for electron transport behavior that can guide the creation of metallic conducting materials from nanocrystal building blocks.

Realizing External Quantum Efficiency over 25% with Low Efficiency Roll-Off in Polymer-Based Light-Emitting Diodes Synergistically Utilizing Intramolecular Sensitization and Bipolar Thermally Activated Delayed Fluorescence Monomer

Realizing External Quantum Efficiency over 25% with Low Efficiency Roll-Off in Polymer-Based Light-Emitting Diodes Synergistically Utilizing Intramolecular Sensitization and Bipolar Thermally Activated Delayed Fluorescence Monomer

Accelerated Formation of 2D Ruddlesden-Popper Perovskite Thin Films by Lewis Bases for High Efficiency Solar Cell Applications.

Various types of 2D organic–inorganic perovskite solar cells have been developed and investigated due to better electron transport behavior and environmental stability. Controlling the formation of phases in the 2D perovskite films has been considered to play an important role in influencing the stability of perovskite materials and their performance in optoelectronic applications. In this work, Lewis base urea was used as an effective additive for the formation of 2D Ruddlesden—Popper (RP) perovskite (BA)2(MA)n−1PbnI3n+1 thin film with mixed phases (n = 2~4). The detailed structural morphology of the 2D perovskite thin film was investigated by in situ X-ray diffraction (XRD), grazing-incidence small-angle X-ray scattering (GISAXS) and photoluminescence mapping. The results indicated that the urea additive could facilitate the formation of 2D RP perovskite thin film with larger grain size and high crystallinity. The 2D RP perovskite thin films for solar cells exhibited a power conversion efficiency (PCE) of 7.9% under AM 1.5G illumination at 100 mW/cm2.

Scattering lifetime and high figure of merit in CsAgO predicted by methods beyond relaxation time approximation

The electronic transport behaviour of CsAgO has been discussed using the theory beyond relaxation time approximation from room temperature to 800 K. Different scattering mechanisms such as acoustic deformation potential scattering, impurity phonon scattering, and polar optical phonon scattering are considered for calculating carrier scattering rates to predict the absolute values of thermoelectric coefficients. The scattering lifetime is of the order of 10−14 s. The lattice thermal transport properties like lattice thermal conductivity and phonon-lifetime have been evaluated. The calculated lattice thermal conductivity equals 0.12 and 0.18 W mK−1 along ‘a’ and ‘c’ axes, respectively, at room temperature, which is very low compared to state-of-the-art thermoelectric materials. The anisotropy in the electrical conductivity indicates that the holes are favourable for the out-of-plane thermoelectrics while the electrons for in-plane thermoelectrics. The thermoelectric figure of merit for holes and electrons is nearly same with a value higher than 1 at 800 K for different doping concentrations. The value of the thermoelectric figure of merit is significantly higher than the existing oxide materials, which might be appealing for future applications in CsAgO.

Enhanced surface electron migration of porous and hollow SnO2/Zn2SnO4 heterostructures for efficient triethylamine-sensing performance

Porous and hollow SnO2/Zn2SnO4 composites with typical one-dimensional (1D) structure have been synthesized by adjusting the amounts of 2-methylimidazole zinc salt (ZIF-8) added in the precursor solution through a modified electrospinning technology. Compared with the gas-sensing performance of different samples detected in the normal condition, it is confirmed that the optimal working temperature can be markedly decreased from 260 to 120 °C under UV light irradiation, along with the substantially improved gas selectivity. In addition, SnO2/Zn2SnO4 heterostructures exhibit a higher response (increases from 1.7 to 2.8) and faster response/recovery times (decreases from 24/154 to 14/42 s) to triethylamine (TEA) than that of the pure SnO2. Significantly, the good practicality of gas sensors for food spoilage evaluation could be testified by effectively detecting the gas released during the putridity of prawns. UV light enhanced surface electron migration mainly contributes to the elevated synergistic effect between the formation of n-n heterojunction and tunable surface/interface electron transport behavior, as well as the adsorption and desorption of TEA molecules on the surface of the sensing materials.

Mechanisms of Scaling Effect for Emerging Nanoscale Interconnect Materials.

The resistivity of Cu interconnects increases rapidly with continuously scaling down due to scatterings, causing a major challenge for future nodes in M0 and M1 layers. Here, A Boltzmann-transport-equation-based Monte Carlo simulator, including all the major scattering mechanisms of interconnects, is developed for the evaluation of electron transport behaviors. Good agreements between our simulation and the experimental results are achieved for Cu, Ru, Co, and W, from bulk down to 10 nm interconnects. The line resistance values of the four materials with the inclusion of liner and barrier thicknesses are calculated in the same footprint for a fair comparison. The impact of high aspect ratio on resistivity is analyzed for promising buried power rail materials, such as Ru and W. Our results show that grain boundary scattering plays the most important role in nano-scale interconnects, followed by surface roughness and plasma excimer scattering. Surface roughness scattering is the origin of the resistivity decrease for high-aspect-ratio conductive rails. In addition, the grain sizes for the technical nodes of different materials are extracted and the impact of grain size on resistivity is analyzed.

MoS2/SnO2 heterojunction-based self-powered photodetector

A heterostructure of MoS2/SnO2 has been fabricated. A SnO2 film was deposited by Sn sputtering followed by oxidation of a Sn film in the ambient. Later, a MoS2 film was deposited on SnO2 by pulsed laser deposition. The built-in electric potential generated at the SnO2/MoS2 interface facilitates self-powered broadband photodetection ranging from the ultraviolet-visible to near-infrared (NIR) wavelength. Under NIR illumination, the device exhibits excellent photoresponse with a responsivity of 0.35 A W−1 and a detectivity of 1.25 × 1011 Jones at 0 V. Moreover, the device shows faster response with rise/fall times as 153/200 ms. The excellent performance of the device is attributed to the high electron transport behavior of SnO2 and a built-in electric field at the interface.

Discerning the biodegradation of binary dyes in microbial fuel cell: Interactive effects of dyes, electron transport behaviour, autocatalytic mechanism, and degradation pathways

This research presented the first attempt to investigate the effect of biodegradation of binary Acid Orange 7 (AO7) and Reactive Green 19 (RG19) on the performances of wastewater treatment and bioelectricity generation, using anti-gravity flow microbial fuel cell (AGF-MFC) system. The influences of initial dye concentration, substrate loading, sulphate concentration and application of quinones on system performances were comprehensively evaluated. The decolourization efficiencies of AO7 were higher than RG19 in binary solutions, at every tested concentrations. The addition of higher concentration of RG19 in binary solution was also found to have increased the overall performances of MFC, owing to electron mediating characteristics of its decolourized intermediates. However, the power density declined with the addition in dye concentration. Further increase of substrate loading by 3-folds (2.43 g/L) improved the decolourization efficiency approximately by 7%, but deteriorated power performance by 42%, to 63.40 ± 0.07 mW/m2. Increasing sulphate concentration from 20 to 400 mg/L had resulted in a high decolourization extent of binary dyes ascribed to sulphide-mediated dye degradation, whereas the power generation was reduced. The increase of sulphate to 800 mg/L led to decrease in decolourization and power density of the system. These outcomes deciphered the competitions of electrons between different electron acceptors in the anodic compartment. Moreover, the autocatalytic mechanism of RG19 decolourized intermediates, 1-amino-2-naphthol-3,6-disulphonate (1A2N36S) as electronophore was thoroughly unearthed. Detailed degradation pathways of dyes were proposed based on UV-Visible spectra and gas chromatograph-mass spectrometer (GC-MS) analyses.

Rare earth dysprosium nickelate nanospheres for the selective electrochemical detection of antipsychotic drug perphenazine in biological samples

Currently, perphenazine (PPZ) is widely used to treat the symptoms of schizophrenia, namely, a mental illness that reasons strong or improper emotions, loss of interest in life, and disturbed or abnormal thinking. In addition, the PPZ is exploited to control acute nausea and vomiting in adults, and it acts by reducing unusual excitement in the brain. Accordingly, we report a novel dysprosium nickelate (DyNiO3)-modified electrodes were used to detect PPZ. The DyNiO3 nanospheres were synthesized via the coprecipitation method. The excellent electron transport behavior and electrocatalytic activity of DyNiO3-modified screen-printed electrode (SPCE) were used in the electro-oxidation of PPZ. The constructed DyNiO3-500°C/SPCE sensor has a broad linear range and a low detection limit of 0.04–761.6 μM and 0.006 μM, respectively. The resultant-modified sensor demonstrates appreciable reproducibility, selectivity, repeatability, cyclic, and storage stability toward PPZ detection. The practicability of the reported fabricated electrode was investigated in human biological samples (urine and serum) spiked with PPZ, and the correlated recoveries were acceptable.