Lateral Barrier Research Articles

Towards a better understanding of the highly overpressured Lower Triassic Bunter reservoir rocks in the Terschelling Basin

Abstract Large lateral variations in pore-fluid pressures and associated overpressures occur in the compartmentalized Lower Triassic Bunter reservoir rocks in the Terschelling Basin (northern Dutch offshore). This study describes the main controlling factors on the distribution of these overpressures by combining seismically derived structural interpretations with pressure data. The most important controlling factor is considered to be the presence and type of both lateral and vertical permeability barriers. Lateral permeability barriers are formed by Zechstein salt and faults. The most effective vertical permeability barrier for maintaining high overpressures is the Upper Triassic Röt evaporite. Overpressures of more than 30 MPa are observed in the Bunter compartments where the Röt is present and laterally continuous. Overpressures are lower than 15 MPa in compartments where the Röt was affected by Mid-Cimmerian erosion. Based on structural observations, it is concluded that the highly overpressured compartments became fully hydraulically restricted during the Late Jurassic and Early Cretaceous. Calculations show that subsequent sedimentary loading, during the Cretaceous and Cenozoic, was able to generate the observed overpressures.

A 1.9 kV/2.61 mΩ·cm2 Lateral GaN Schottky Barrier Diode on Silicon Substrate with Tungsten Anode and Low Turn-On Voltage of 0.35 V

In this letter, we report the achievement of a high-performance lateral GaN Schottky barrier diode (SBD) on a silicon substrate with a low turn- ON voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{ \mathrm{ON}}$ </tex-math></inline-formula> ) of 0.35 V and tungsten (W) as the anode. Non-field-plated lateral GaN SBDs with the anode–cathode distances ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {AC}}$ </tex-math></inline-formula> ) of 6, 10, 15, 20, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25~\mu \text{m}$ </tex-math></inline-formula> demonstrate the reverse breakdown voltages of 0.6, 1.1, 1.25, 1.5, and 1.9 kV with the differential specific ON-resistances ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text{ON}, \text {sp}}$ </tex-math></inline-formula> ) of 0.38, 0.72, 1.23, 1.87, and 2.61 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. The power figure-of-merit (FOM) is calculated to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {1}\times 10^{ {3}}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {1.7}\times {10}^{ {3}}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {1.3}\times {10}^{ {3}}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {1.2}\times {10}^{ {3}}$ </tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {1.4}\times {10}^{{3}}$ </tex-math></inline-formula> MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . To the best of our knowledge, this FOM of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1.7}\times {10}^{{3}}$ </tex-math></inline-formula> MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is the highest among all the lateral GaN SBDs on a Si substrate. Combined with the ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> current ON/OFF ratio at room temperature, the GaN SBD with the W anode shows a great promise for next-generation power electronics.

Field-Plated Lateral β-Ga2O3 Schottky Barrier Diode with High Reverse Blocking Voltage of More Than 3 kV and High DC Power Figure-of-Merit of 500 MW/cm2

In this letter, we report on demonstrating high-performance field-plated lateral <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Schottky barrier diode (SBD) on a sapphire substrate with a reverse blocking voltage of more than 3 kV and a low dc specific ON-resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{{ \mathrm{\scriptscriptstyle ON}, \text {sp}}}$ </tex-math></inline-formula> ) of 24.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at an anode–cathode spacing ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {AC}}$ </tex-math></inline-formula> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$24~\mu \text{m}$ </tex-math></inline-formula> . To the best of our knowledge, this lateral breakdown voltage (BV) >3 kV with dc power figure-of-merit (FOM) >370 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is the highest BV achieved among all the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> SBDs. Meanwhile, lateral <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> SBD with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {AC}} = \text {16}\,\,\mu \text{m}$ </tex-math></inline-formula> also demonstrates a high BV of 2.25 kV and low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{{ \mathrm{\scriptscriptstyle ON}, \text {sp}}} = \text {10.2}\,\,\text{m}\Omega \cdot $ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , yielding a record high dc power FOM of 500 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Combining with 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> high-current ON/OFF ratio, 1.15-eV Schottky barrier height and 1.25 ideality factor, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> SBD with field-plate structure shows its great promise for power electronics applications.

Potentially toxic elements in urban soil catenas of W-Mo (Zakamensk, Russia) and Cu-Mo (Erdenet, Mongolia) mining areas

The aim of this study was to characterize the conditions of the lateral migration of potentially toxic elements (PTEs) and to identify the zones of their accumulation in soil catenas of ore-mining landscapes in the cities of Zakamensk (Buryat Republic, Russia) and Erdenet (Mongolia) which are situated in the basin of the Selenga River. Eight soil catenas across the river valley with 31 pits in Zakamensk area and five catenas with 15 pits in Erdenet area were studied. Soil samples were collected in four landscape–geochemical positions: autonomous, on tops of the hills; trans-eluvial, on slopes of river valleys; trans-accumulative, at the footslopes; and superaqual, on the river floodplains. The total contents of 16 PTEs in the 148 samples were determined by mass spectrometry and by atomic emission spectrometry with inductively coupled plasma. It is found that the chemical composition of undisturbed soils is greatly affected by the widespread distribution of volcanic rocks enriched with W, Mo, Cd, Bi, and Sr in Zakamensk and with V, Co, Sr, and As in Erdenet. The difference between geochemical positions is relatively small. Under the influence of technogenic loads in the cities, the concentrations of PTE change along soil catenas increases by an order of magnitude. For chalcophile elements—Mo, Bi, Pb, Sb, and Cu in Zakamensk and Cu, Zn, Mo, Cd, Sn, and W in Erdenet—the type of their lateral distribution in the soil catenas changes because of the intense migration from the tailings and facilities with water and air flows. The accumulation of PTEs takes place on the chemisorptive (V, Co, Ba, As, Cr, and Ni), gley (Mo and Sb), organomineral (Sn), and alkaline (Sr and W) lateral geochemical barriers (LGBs) confined to subordinate positions. The artificial technological LGBs are formed due to the increased content of sand derived from the tailings by water erosion in Zakamensk and the input of silt particles windblown from the technogenic sources in Erdenet. This causes the rise in the concentrations of major ore elements (Mo, W, and Cu) and the accompanying elements (Pb, Bi, As, Sr, Cr, and Ni). The results of soil–geochemical studies using the catenary approach and concept of LGBs made it possible to understand the main features of migration and fixation of PTEs in soils of the mining centers. They indicate the formation of a system of LGBs with intensive accumulation of major ore elements and associated ones in the subordinate landscapes of Zakamensk and Erdenet.

Internal current amplification induced by dielectric hole trapping in monolayer MoS2 transistor

Carrier transport in layered transition-metal dichalcogenides is highly sensitive to surrounding charges because of the atomically thin thickness. By exploiting this property, we report a new internal current amplification mechanism through positive feedback induced by dielectric hole trapping in a MoS2 back-gate transistor on a tantalum oxide substrate. The device exhibits an extremely steep subthreshold slope of 17 mV/decade, which is strongly dependent on the substrate material and drain bias. The steep subthreshold slope is attributed to the internal current amplification arising from the positive feedback between hole generation in MoS2 triggered by large lateral electric field and Schottky barrier narrowing induced by localized hole trapping in tantalum oxide near the source contact.

Giant oscillations of the current in a dirty 2D electron system flowing perpendicular to a lateral barrier under magnetic field

The charge transport in a dirty 2-dimensional electron system biased in the presence of a lateral potential barrier under magnetic field is theoretically studied. The quantum tunneling across the barrier provides the quantum interference of the edge states localized on its both sides that results in giant oscillations of the charge current flowing perpendicular to the lateral junction. Our theoretical analysis is in a good agreement with the experimental observations presented in Ref.8. In particular, positions of the conductance maxima coincide with the Landau levels while the conductance itself is essentially suppressed even at the energies at which the resonant tunneling occurs and hence these puzzling observations can be resolved without taking into account the electron-electron interaction.

Structural Characterization of Ordered, Non-Close-Packed Functionalized Silica Nanoparticles on Gold Surfaces.

Nanostructured surfaces play an important role in modern science and technology. In particular, ordered arrangements of nonclose-packed nanoparticles created by self-assembly offer a versatile route to prepare systems, which can be used in various applications such as sensing, plasmonic devices or antireflection coatings. Self-assembly based systems are particularly appealing as preparation is rather simple. The ability of nanoparticle systems to form nonclosed packed monolayers by self-assembly depends on the balance of various energetic contributions in particular the adsorption energy, the lateral barrier for diffusion and the repulsion between particles. Even for simple model systems such as the monodispersed silica particles adsorbed on a bare gold surface investigated here, none of these quantities is easy to determine experimentally. To this end, we will report on a detailed characterization of the adsorption in particular with respect to the structural properties of the above-mentioned model system. Based on experimental results obtained by using quartz crystal microbalance with dissipation monitoring (QCM-D) as well as scanning electron microscopy (SEM) it is possible to determine the electrostatic pair potential from the lateral arrangement of the nano particles in the limit of low coverage.

Quantitative geometric description of fracture systems in an andesite lava flow using terrestrial laser scanner data

Permeability hosted in andesitic lava flows is dominantly controlled by fracture systems, with geometries that are often poorly constrained. This paper explores the fracture system geometry of an andesitic lava flow formed during its emplacement and cooling over gentle paleo-topography, on the active Ruapehu volcano, New Zealand. The fracture system comprises column-forming and platy fractures within the blocky interior of the lava flow, bounded by autobreccias partially observed at the base and top of the outcrop. We use a terrestrial laser scanner (TLS) dataset to extract column-forming fractures directly from the point-cloud shape over an outcrop area of ∼3090 m2. Fracture processing is validated using manual scanlines and high-resolution panoramic photographs. Column-forming fractures are either steeply or gently dipping with no preferred strike orientation. Geometric analysis of fractures derived from the TLS, in combination with virtual scanlines and trace maps, reveals that: (1) steeply dipping column-forming fracture lengths follow a scale-dependent exponential or log-normal distribution rather than a scale-independent power-law; (2) fracture intensities (combining density and size) vary throughout the blocky zone but have similar mean values up and along the lava flow; and (3) the areal fracture intensity is higher in the autobreccia than in the blocky zone. The inter-connected fracture network has a connected porosity of ∼0.5 % that promote fluid flow vertically and laterally within the blocky zone, and is partially connected to the autobreccias. Autobreccias may act either as lateral permeability connections or barriers in reservoirs, depending on burial and alteration history. A discrete fracture network model generated from these geometrical parameters yields a highly connected fracture network, consistent with outcrop observations.

Electronic properties and lateral inhomogeneous barrier heights of n-InP rods/p-Si heterojunction prepared by liquid phase epitaxy

In/n-InP/p-Si/Al heterojunction has been manufactured by depositing InP layer onto p-Si single crystal substrates by liquid phase epitaxy (LPE) technique. InP layers was found to grow as rods with cubic zinc blende crystal structure. The electrical properties have been investigated in terms of current–voltage (I–V) and capacitance–voltage (C–V) measurements. The most predominant conduction mechanisms in the device are elucidated from the I–V characteristics over the temperature range 300–425 K. Based on thermionic emission theory at V < 0.8, the junction main parameters namely; the ideality factor, barrier height and series resistance are calculated as a function of temperature (300–425 K). Analysis showed that the device has inhomogeneous barrier heights which were found to follow Gauss distribution. At voltages 0.8 ≤ V ≤ 2, the conduction is controlled by space charge limited current in which the total trap concentration is determined as 1.39 × 1019 cm− 3. The C–V measurements showed the abrupt nature of the junction. Based on these measurements, the built-in potential, carrier concentration and the width of the depletion region were obtained.

Graphene-Templated Supported Lipid Bilayer Nanochannels

The use of patterned substrates to impose geometrical restriction on the lateral mobility of molecules in supported lipid membranes has found widespread utility in studies of cell membranes. Here, we template-pattern supported lipid membranes with nanopatterned graphene. We utilize focused ion beam milling to pattern graphene on its growth substrate, then transfer the patterned graphene to fresh glass substrates for subsequent supported membrane formation. We observe that graphene functions as an excellent lateral diffusion barrier for supported lipid bilayers. Additionally, the observed diffusion dynamics of lipids in nanoscale graphene channels reveal extremely low boundary effects, a common problem with other materials. We suggest this is attributable to the ultimate thinness of graphene.

Bound states induced giant oscillations of the conductance in the quantum Hall regime

We theoretically studied the quasiparticle transport in a 2D electron gas biased in the quantum Hall regime and in the presence of a lateral potential barrier. The lateral junction hosts the specific magnetic field dependent quasiparticle states highly localized in the transverse direction. The quantum tunnelling across the barrier provides a complex bands structure of a one-dimensional energy spectrum of these bound states, , where py is the electron momentum in the longitudinal direction y. Such a spectrum manifests itself by a large number of peaks and drops in the dependence of the magnetic edge states transmission coefficient D(E ) on the electron energy E. E.g. the high value of D occurs as soon as the electron energy E reaches gaps in the spectrum. These peaks and drops of D(E) result in giant oscillations of the transverse conductance Gx with the magnetic field and/or the transport voltage. Our theoretical analysis, based on the coherent macroscopic quantum superposition of the bound states and the magnetic edge states propagating along the system boundaries, is in a good accord with the experimental observations found in Kang et al (2000 Lett. Nat. 403 59)

MBE grown GaN/AlGaN lateral Schottky barrier diodes for high frequency applications

The authors report the results of studies of lateral and vertical Schottky barrier diodes (SBD) based on molecular beam epitaxy (MBE) grown GaN/AlGaN heterostructures with two dimensional electron gas (2DEG) present at the heterostructure interface. The epilayers were grown by plasma assisted molecular beam epitaxy under metal-rich conditions on commercially available freestanding (0001) GaN substrates. Here, the authors present detailed results for two structures with electron sheet density (N2DEG) of 4.6 × 1012 and 1 × 1013 cm−2 and room temperature mobility of μ2DEG = 1925 cm2/V s and μ2DEG = 1760 cm2/V s, respectively. The processing of lateral and vertical Schottky barrier diodes was performed by laser writer using shallow mesas and Ni/Au metallization for Schottky barriers. The direct current electrical tests performed on lateral and vertical Schottky barrier diodes yielded a turn-on voltage of 0.6 and 1 V, respectively. For both cases, the reverse current registered in the experiment was very low and did not exceed 1 μA/mm for reverse voltage VR = −5 V while the breakdown voltage for both structures was approximately VB = −90 V, which is a good result for nonpassivated surface and anode/cathode distance of the order of a few micrometers. The comparison of current–voltage characteristics for lateral devices with different electron sheet densities shows significant disparity in differential resistances at on-state, which is attributed to the increase of ohmic contact resistance with aluminum mole fraction increase in the AlGaN epilayer. Lateral Schottky diodes demonstrated the low frequency noise amplitude comparable with that reported for regular GaN-based Schottky diodes of much larger area. Low frequency noise characterization on our SDBs is presented. Additionally, the authors present as an example our first result of 140 GHz radiation detection/rectification experiment done on the SBD grown by MBE on (0001) GaN/sapphire. The similar experiments on the SBD freestanding samples will be the subject of forthcoming studies.

Ultralow reverse leakage current in AlGaN/GaN lateral Schottky barrier diodes grown on bulk GaN substrate

We report on a study of AlGaN/GaN heterostructure lateral Schottky barrier diodes (L-SBDs) grown on a bulk GaN substrate. The L-SBDs exhibited an ultralow reverse leakage current below 10−6 A/cm2 without employing any extra treatments, which was over 4 orders of magnitude lower than that of a reference device on a sapphire substrate. The superior performance was attributed to the high crystalline quality of the heterostructure achieved by homoepitaxy. The comparison also revealed that the absence of high-density trap states in the homoepitaxial L-SBD grown on the bulk GaN substrate played a key role in achieving a low reverse leakage current.

Soil Elementary Processes In The Inundated Landscapes Of Uda River In Kharkov’s Range

Purpose. The soil elementary processes (SEP) in the inundated landscapes of Uda river in Kharkiv’s range are investigated. Methods. Complex field, chemical analytical techniques and methods of data processing (including interpolation methods, clustering, and so on). Results. With the method of expert’s estimations the intensity of the soil elementary processes is gave to assessment to the territory of the study. The acid-alkaline characteristics of soil genetic horizons of inundated landscapes of Uda river in Kharkiv’s range are evaluated. The presence of natural height valuable sorption and chemisorption lateral acid-alkaline geochemical barrier in the research area is suggested. Conclusions. The most common and severe elementary processes of soil formation floodplain landscapes p. Uda within Kharkiv is humus-ilyuvialny and clay-ilyuvialny processes related to illuvial accumulation processes, ie, dominated by the processes of accumulation of matter and energy, which is indicative of the presence of natural geochemical barrier, due to the peculiarities of the relief and the composition of the parent rocks

Management Opportunities Salinization Alluvial Soils in the Flood Plains of Environmental Management System of Urban Areas

Purpose. Assessment of soil salinity alluvial flood plains r. Uda within the city Kharkiv and defining features of the profile distribution hloryd-, hidrokarbonat- and carbonate- ions in the soil profile to create a cluster alluvial soils in the flood plains environmental management system of urban areas.Methods. Complex field, chemical-analytical, statistical (interpolation, clustering, and so on.). Results. The soil salinization processes of the alluvial soils in the inundated landscapes of Uda river in Kharkiv’s range are investigated. The acid-alkaline characteristics of soil genetic horizons are evaluated, and the profile distribution of chloride, hydrocarbonate and carbonate ions in the soils profile of the investigated alluvial soils are showed. The stages of profile migration of the corresponding ions in the study area are evaluated, as well as the degree of salinity of each genetic horizon of the studied soils profiles are assessed. The predominance of progressive chloride-soda salinization of the alluvial soils in the inundated landscapes of Uda river in Kharkiv’s range is determined. The presence of natural height valuable sorption and chemisorption radial, mechanical and lateral acid-alkaline geochemical barrier in the research area is suggested. Conclusions. Proposed use parameters salinization of soils on alluvial flood plains in the cluster system of environmental management of urban areas.

Barrier height fluctuations in InGaN polarization dipole diodes

We present an analysis of the effects of lateral barrier height fluctuations on the transport properties of an InGaN polarization dipole diode (PDD). Typical diode analysis proceeds by performing a linear fit to the data contained in a Richardson plot in order to extract the zero-bias barrier height (ϕB) and the Richardson constant (A*). The experimental PDD Richardson plot, however, is highly nonlinear and we attribute this to a spatially nonuniform distribution of barrier heights. After modeling the barrier height distribution using a Gaussian, we fit the Richardson data with a modified, second-order function from which we extract the Richardson constant, mean barrier height, and standard deviation simultaneously. We propose that the physical cause of the observed barrier height inhomogeneity in the PDD is statistical nanoscale fluctuations in indium composition.

Algal polysaccharides as matrices for the immobilization of urease in lipid ultrathin films studied with tensiometry and vibrational spectroscopy: Physical–chemical properties and implications in the enzyme activity

Currently, many biological substances extracted from algae have received special attention because of their intrinsic characteristics, which can be applied to different areas of biotechnology. Therefore, in the current study, exopolysaccharides (EPS) from the microalgae Cryptomonas tetrapirenoidosa were employed as an aqueous subphase of a monolayer formed by the lipid dioctadecyldimethylammonium bromide (DODAB). The primary objective of this approach was to evaluate whether EPS could serve as a matrix for the immobilization of the enzyme urease to produce biosensors for urea. After DODAB was spread on the EPS solutions, urease was injected into the aqueous subphase, and the surface was submitted to compression using lateral barriers. The monolayers were subsequently characterized by surface pressure-area isotherms and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The results indicated that EPS enhanced the adsorption of the enzyme on the lipid monolayer. The mixed films were later transferred to solid supports using the Langmuir–Blodgett (LB) technique and were characterized by transfer ratio, PM-IRRAS, quartz crystal microbalance, and atomic force microscopy. The immobilization of the enzyme on solid supports was fundamental for providing an ideal geometrical accommodation of urease because the interaction of EPS with urease in solution causes a decrease of the relative activity of urease. Therefore, these LB films are promising for the fabrication of future urea biosensors, the architecture of which can be manipulated and enhanced at the molecular level.

Stress-directed compositional patterning of SiGe substrates for lateral quantum barrier manipulation

While vertical stacking of quantum well and dot structures is well established in heteroepitaxial semiconductor materials, manipulation of quantum barriers in the lateral directions poses a significant engineering challenge. Here, we demonstrate lateral quantum barrier manipulation in a crystalline SiGe alloy using structured mechanical fields to drive compositional redistribution. To apply stress, we make use of a nano-indenter array that is pressed against a Si0.8Ge0.2 wafer in a custom-made mechanical press. The entire assembly is then annealed at high temperatures, during which the larger Ge atoms are selectively driven away from areas of compressive stress. Compositional analysis of the SiGe substrates reveals that this approach leads to a transfer of the indenter array pattern to the near-surface elemental composition, resulting in near 100% Si regions underneath each indenter that are separated from each other by the surrounding Si0.8Ge0.2 bulk. The “stress transfer” process is studied in detail using multiscale computer simulations that demonstrate its robustness across a wide range of applied stresses and annealing temperatures. While the “Si nanodot” structures formed here are not intrinsically useful as quantum structures, it is anticipated that the stress transfer process may be modified by judicious control of the SiGe film thickness and indenter array pattern to form more technologically useful structures.

Analysis of inhomogeneous device parameters using current–voltage characteristics of identically prepared lateral Schottky structures

We have identically fabricated 50 dots of Au/n-Si/Al Schottky structures and investigated the mean values of diode parameters from current-to-voltage (I–V) characteristics at 300 K. The values of diode parameters are determined from I–V characteristics, and Cheung and the modified Norde functions are varied from diode to diode although the Schottky structures are identically fabricated. The experimental values of ideality factor (n) and barrier height (ΦB) for 50 dots of the Au/n-Si/Al Schottky structures have ranged from 1.048 to 1.695 and from 0.708 to 0.807 eV, respectively. The interface state densities (N ss) are approximately obtained from 2 × 1013 to 2 × 1011 eV−1 cm−2 in the energy range from E c − 0.45 to E c − 0.75 eV, respectively. These findings can be referred to lateral barrier inhomogeneities of Schottky diodes. The distributions of all calculated parameters have been fitted by means of Gaussian function. The mean n and ΦB values have been found to be 1.316 ± 0.213 and 0.758 ± 0.030 eV, respectively. Furthermore, the value of lateral homogenous barrier height for 50 dots of Schottky structures is determined as 0.802 eV from the linear relationship between n and ΦB.

Theoretical study of the DC and transient characteristics of a lateral Schottky barrier photodiode for application as high‐speed photodetector

AbstractWe present a numerical characterization of a high‐speed high‐responsivity GaAs lateral Schottky barrier photodiode (LSBPD). The LSBPD is a planar structure composed of interdigitated Schottky barrier and ohmic contacts. A metal–semiconductor–metal (MSM) structure with identical geometry is simulated for comparison. The dark characteristics are found identical for the two devices. Under illumination, the LSBPD exhibited significantly superior responsivity compared with the MSM, while maintaining comparatively similar response time and 3 dB bandwidths. The results of the study indicate conclusively that the lateral Schottky barrier photodiode can provide an excellent alternative to the standard MSM photodetectors for high‐speed optoelectronic applications. Copyright © 2015 John Wiley &amp; Sons, Ltd.