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PEDOT: PSS thin films are widely used as transparent coatings in flexible semiconductor devices including solar cells. However, they are not widely used as transparent coatings in combination with crystal substrates. This work shows the possibility of using PEDOT:PSS thin films as a frontal transparent conducting layer in hybrid organic-inorganic Schottky type heterojunctions of the PEDOT:PSS/n‑CdTe, which were prepared by deposition of PEDOT:PSS thin films (using the spin-coating method) on crystalline cadmium telluride substrates. The current-voltage (in a wide temperature range) and capacitance-voltage (at room temperature) characteristics of heterojunctions were measurement and analyzed. It has been established that PEDOT:PSS/n-CdTe heterojunctions have good diode properties with a high rectification ratio RR≈105, a potential barrier height φ0 = 0.95 eV, and series Rs = 91 Ohm and shunt Rsh = 5.7 × 107 Ohm resistances. Analysis of the forward branches of the I–V characteristics of heterojunctions showed that the dominant charge transfer mechanisms are determined by the processes of radiative recombination at low biases (3kT/e 1013 Jones) are very promising for further detailed analysis and improvement. The proposed concept of a hybrid organic-inorganic heterojunction also has potential for use in inexpensive γ- and X-ray detectors.

An analytical model of the channel electron energy distribution in an on-state GaN transistor has been proposed based on the assumption that drift velocities of channel electrons obey the two-dimensional Maxwell–Boltzmann distribution. The validity of such an assumption was confirmed by Monte Carlo simulation. It was found that there could be a larger number of high-energy channel electrons whose energy is higher than the intervalley energy between Γ 1 and Γ 2 valleys in a GaN transistor with a high electron temperature. The fraction of hot electrons with its energy higher than the intervalley energy between Γ 1 and Γ 2 valleys to the total channel electrons can easily reach 50% when the electron temperature is higher than 3000 K. Such an electron temperature in a GaN transistor had been determined in experiments. Thus, hot electrons in the Γ 1 valley can transit into Γ 2 valleys. It suggests that intervalley transitions could be one possible physical origin of the abrupt change in the source−drain current in GaN devices. The proposed model can well explain how an abrupt change in the source–drain current in GaN transistor experiments depends on the voltage-dependent gate, the trap, etc. [ABSTRACT FROM AUTHOR]

A photopolymer based Al/Norland Optical Adhesive 60 (NOA60)/p-Si MPS (metal-polymer-semiconductor) device was fabricated by a combination of vacuum evaporation and smear technique. The current transport properties of the device were investigated by using the forward bias current–voltage (I-V) characteristic in the temperature range of 80–300 K. The cross-sectional structure of polymer/semiconductor was revealed by the scanning electron microscope (SEM) image and it was seen that the NOA60 photopolymer was tidily coated on the p-Si surface. According to the I-V measurements at room temperature, the MPS device exhibits a good rectification ratio of 8140 at ± 1 V. The temperature-dependent I-V measurements (I-V-T) were analyzed based on the thermionic emission (TE) theory and an abnormal increase in zero-bias barrier height (BH) and a decrease in ideality factor (n) was observed with increasing temperature. Additionally, two different linear regions with distinct values from the theoretical value of the Richardson constant (A*) were observed in the conventional Richardson plot. Such deviations from the ideal TE theory have been attributed to the effect of BH inhomogeneities. Gaussian distribution (GD) of the BH model has applied the I-V-T results and the double GD BH with mean values of 0.75 ± 0.08 eV (80–140 K) and 1.02 ± 0.11 eV (140–300 K) were calculated. Moreover, the A* value of 31.4 A/cm2K2 was calculated close to the known value of p-Si from the modified Richardson plot. Thus, it has been concluded that the current transport of the Al/NOA60/p-Si MPS device can be explained by TE with a double GD BH model for a wide temperature region. [ABSTRACT FROM AUTHOR]

Coastal waters of Lake Superior are generally inhospitable to the establishment of invasive Dreissena spp. mussels (both Dreissena polymorpha and Dreissena bugensis). Dreissena have inhabited the Saint Louis River estuary (SLRE; largest commercial port in the Laurentian Great Lakes) for over three decades, but only in the last few years have small colonies been found in the Apostle Islands National Lakeshore (APIS, an archipelago situated 85 km to the east of SLRE) A 2017 survey determined a low abundance Dreissena spatial distribution in APIS, with the largest colonies on the north and west islands which suggested potential veliger transport from the SLRE via longshore currents. Our objective in this study was to determine if Dreissena veligers are transported by currents at low densities along the south shore of Lake Superior from the SLRE to APIS. To do so, we used both eDNA (water and passive substrate samples) and zooplankton collection methods at eight sites evenly spaced between the SLRE and APIS with three sampling times over five weeks. Dreissena veligers were consistently detected along the south shore, although at low abundances (veligers per m3 range = 0–690, median = 8), and for every 1 km increase in distance from the SLRE, both veliger counts and water eDNA copy numbers decreased on average by 5 and 7%, respectively. D. polymorpha (suited to estuary habitats) was detected two times more than D. bugensis (better suited to deep-lake habitats). There was not a trend in the veliger size distribution along the south shore, and temperature and calcium concentrations fluctuated around the threshold for Dreissena veliger and adult development, averaging 11.0°C and 14.8 ppm, respectively. Three zooplankton taxa representative of the estuary community–Daphnia retrocurva, Diaphanosoma birgei, and Mesocyclops copepodites–decreased as the distance from the SLRE increased mirroring Dreissena veliger abundance patterns. Findings represent multiple sources of evidence of a propagule “conveyor belt” for Dreissena along the south shore of Lake Superior. We conclude that veligers are functioning as a propagule, using coastal currents to spread from the point of invasion, thereby traversing coastal habitat previously reported as inhospitable to distant habitats suitable for colonization.

In this paper, a novel technique is presented to fabricate aligned polymer-wrapped semiconducting carbon nanotube (CNT)-based devices to overcome the issues that arise in randomly oriented CNT network devices. It is challenging to make the CNT-based devices with straight polymer-wrapped CNTs. Straight CNTs have better conductivity than the bended ones. Therefore, we have fabricated simple electrodes of a square pad with the conventional lithography process. Subsequently, dispersed single-walled CNTs (SWNT)-polyacrylonitrile is used to fabricate aligned nanofiber by an electrospinning system on the fabricated electrodes. The average diameter of the fabricated nanofiberr is found to be 100 nm. The current–voltage (I–V) characteristics are investigated for the fabricated devices. The I–V characteristics are similar to those of a back-to-back Schottky diode. The Schottky barrier height and ideality factor of the nanofiber devices are found to be 431 meV and 4.1, respectively. Therefore, the multiple current transport mechanisms (thermionic emission, tunneling, generation-recombination, and leakage) contribute to the current through the nanofiber device. Applications of the devices can include gas sensors, biosensors, and other CNT-based device electronics applications. [ABSTRACT FROM AUTHOR]

A n-4H SiC based diode is fabricated by an Au front metal contact to provide rectification at the metal-semiconductor (MS) junction, and a back ohmic contact is also obtained using Au metal with post-thermal heating. MS diode characteristics are investigated by current–voltage ( I - V ) measurements with a wide range of temperature from 80 K to 300 K. At each temperature, rectifying behavior is achieved and it is improved with an increase in temperature. Barrier height and ideality factor are calculated according to the thermionic emission (TE) model from linearity in the forward bias region of the ln I versus V plot. The experimental zero-bias barrier height ( Φ b 0 ) values are in a good agreement with literature, and at around room temperature the ideality factor (n ) reaches unity. At saturation regions in I - V curves, parasitic resistance values are derived by Ohm's law and the series resistance values are also reevaluated by Cheung's relation. Detailed I - V analysis is performed by modifying the TE model with an approximation of low barrier patches embedded in the main barrier height. Two linear relations in the characteristic plots of Φ b 0 and n indicate that double Gaussian distribution is a suitable current conduction model via localized barrier patches at low temperatures. Additionally, reverse bias current flow is analyzed under the dominant effect of Poole-Frenkel emission associated with the interfacial traps. According to the characteristic electric field-dependent current density plot, emission barrier height and relative dielectric constant for n-4H SiC are calculated. [ABSTRACT FROM AUTHOR]

TaOx is a promising candidate for random access memory formation. To provide the possibility of 3D integration, it is grown by the atomic layer deposition (ALD). Herein, such properties of the pristine TaOx grown by radical‐enhanced ALD (REALD) as oxygen vacancies concentration and the trap energy are evaluated to reveal whether it can replace more common ion‐sputtered TaOx both in filamentary and nonfilamentary resistive random access memory (ReRAM) stacks. For this purpose, charge transport mechanism in the TiN/TaOx/Pt stacks is analyzed. It is found that charge transport through TaOx is described by the phonon‐assisted tunneling between traps model. The thermal Wt = 0.85 eV and optical Wopt = 1.7 eV trap energies are determined. The trap concentration N = 1 × 1021 cm−3 found from transport corresponds well with the oxygen vacancy concentration, obtained by ab initio simulation of valence band X‐ray photoelectron spectrum. Derived parameters are typical for the ion‐sputtered TaOx. As a result, it can be considered to replace ion‐sputtered TaOx in the nonfilamentary bilayer stacks. Moreover, the observed properties explain the possibility to achieve electroforming‐free resistive switching in a single layer REALD grown TaOx‐based stack in combination with extracting Ta electrode. [ABSTRACT FROM AUTHOR]

MoN/n-Si semiconductor heterojunctions were fabricated by sputtering thin films of molybdenum nitride using the reactive magnetron sputtering in a universal vacuum system Leybold-Heraeus L560 on silicon substrates 5x5x0.3 mm in size, at a temperature of 473 K, with different surface treatment (growing nanowires using a chemical method). We have measured current-voltage (at different temperatures) and capacitance-voltage characteristics. It has been established that growing nanowires leads to some deterioration in the electrical properties and band parameters of MoN/n-Si heterojunctions; however, further digestion in HF positively affects the electrical properties and band parameters of heterostructures. The mechanisms of the current flow through heterojunctions do not change. It has been established that the electric current flowing through the studied heterostructures at small forward biases is caused by the generation-recombination processes in the region of the spatial nucleus; the main mechanism of the current transfer is the tunneling-recombination. The main mechanism of the current transport at reverse biases for MoN/n-Si heterostructures is tunneling through the space charge region. A detailed analysis of the capacitance-voltage characteristics of the MoN/n-Si heterostructures with surface treatment was carried out. It was shown that the series resistance for heterostructures with grown nanowires and etched in HF significantly affects their capacitance-voltage characteristics. The main photoelectric parameters of MoN/n-Si heterostructures with grown nanowires and etched in HF were determined, namely, the open circuit voltage Voc = 0:13 V, the short circuit current Isc = 0:54 mA/cm² at a light intensity of 80 mW/cm². [ABSTRACT FROM AUTHOR]

The paper studies peculiarities of current transport in Au/Pt/Ni/diamond Schottky diodes with the hysteresis in current–voltage (I-V) characteristics and the nonlinear dependence of the barrier height φ b on the applied voltage and proposes a method for determining basic parameters. Lateral diode structures were processed on boron-doped HPHT-diamond grown in the Fe-Al-B-C system and demonstrated barrier I-V characteristics with the exponential growth of the forward current of about eight orders of magnitude. It is shown that the voltage-dependent barrier height and hysteresis of the current-voltage characteristics can be explained by the presence of a thin dielectric gap at the metal-semiconductor interface and deep levels with lifetimes of the order of tens of seconds or more. Recharging of deep levels can significantly affect the parameters of the current-voltage characteristics. Three distinct regions were revealed. Excess current at zero voltage (region I) is related to deep-level recharge. Within regions II and III linear dependence of the φ b on the applied voltage was observed. A linear dependence of the φ b is related to the thermionic-field emission mechanism of current transport. Analysis of the temperature dependence I-V characteristics, capacitance-voltage (С-V) as well as frequency-capacitance (C-f) characteristics of arrays of HPHT diamond Schottky diodes yields information on the distribution of macro-defects, the state of the surface, and doping of the sub-surface region, which can be used for the improvement of the growth process and post-growth treatments for the development of diamond-based microelectronic devices. [Display omitted] • The use of boron-doped high-pressure high-temperature (HPHT) diamonds for developing Schottky barrier diodes is studied. • Peculiarities of current-voltage (I-V) characteristics of the Au/Pt/Ni/HPHT-diamond Schottky diodes are studied in detail. • The voltage-dependent barrier height and hysteresis in the I-V relate to a dielectric gap and deep-level slow states. [ABSTRACT FROM AUTHOR]

This paper investigates the stability problem of superconductors against quench. Numerical (Finite Element) simulations are applied to calculate the distribution of transient temperature, critical current density and transport current in the conductor cross section under a disturbance, here: flux flow losses. Contrary to standard stability models, focus of the paper is on situations very close to the superconducting/normal conducting phase transition. The obtained results demonstrate it is not realistic, even in thin films, to assume uniform conductor temperature under a disturbance. A method is suggested how to predict time and position of a quench when it is expected to occur in the conductor cross section. Quench starts always locally. Application of a microscopic stability model allows to describe continuous, not abrupt but very fast break-down of transport current in situations close to the phase transition. [ABSTRACT FROM AUTHOR]

Summary: Currents play critical roles in neurons. Direct observation of current flows in cells at nanometre dimensions and picoampere current resolution is still a daunting task. In this study, we investigated the current flows in hippocampal neurons, PC12 cells and astrocytes in response to voltages applied to the cell membranes using conductive atomic force microscopy (CAFM). The spines in the hippocampal neurons play crucial roles in nerve signal transfer. When the applied voltage was greater than 7.2 V, PC12 cells even show metallic nanowire‐like characteristics. Both the cell body and glial filaments of astrocytes yielded CAFM test results that reflect different electrical conductance. To our best knowledge, the electrical characteristics and current transport through components of cells (especially neurons) in response to an applied external voltage have been revealed for the first time at nanometre dimensions and picoampere current levels. We believe that such studies will pave new ways to study and model the electrical characteristics and physiological behaviours in cells and other biological samples. [ABSTRACT FROM AUTHOR]

The characteristics of a multistage electrohydrodynamic converter (EHDC) have been studied, and the results are presented in this paper. The diagram of an experimental installation is described; the pressure head, flow rate, and current characteristics are provided as a function of time and the EHDC supply voltage. The factors determining the EHDC parameters and the methods of their regeneration are determined. [ABSTRACT FROM AUTHOR]

The transport of an underdamped particle driven by an external force in a periodic asymmetric potential with color noises is investigated. The corresponding mathematical model is established. By the method of the numerical simulation, we present the movement of the steady current of underdamped particles. Different parameters have different influences on current transport, such as increasing or decreasing. It is shown that the cooperations among the external force and the noises parameter lead to the phenomena: when the external force is not zero, the large external force may cause the large current value or the absolute value of the current. The current value is due to the effect of the cooperations of external force and noise parameter. [ABSTRACT FROM AUTHOR]

In the present work, aluminum oxide (Al 2 O 3 ) thin films were deposited on p -type silicon substrates by thermal atomic layer deposition technique. The structural properties of as-deposited Al 2 O 3 thin films were characterized by grazing-incidence x-ray diffraction and it was determined that the films had an amorphous structure. Electrical transport mechanisms and dielectrical properties of the amorphous Al 2 O 3 thin films were then investigated by fabricating and characterizing Al/Al 2 O 3 / p -Si metal–oxide-semiconductor (MOS) capacitors by performing the dc current-voltage and frequency-dependent dielectric measurements. As a function of the applied gate electric fields, the current conduction in low electric fields consists of Schottky emission, but in relatively high electric fields current conduction is dominated by space-charge limited conduction. From the frequency-dependent dielectric measurements, the dielectric loss showed two peaks at the frequencies of 10 kHz and 0.7 MHz which evidence of the dielectric relaxation. The low and high frequency dielectric relaxation behaviors were attributed to space charge polarization and orientation-polarization of dipoles, respectively. It was concluded that defects related localized states in the Al 2 O 3 films may contribute to dielectric properties at high frequency. [ABSTRACT FROM AUTHOR]

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Zero bias conductance (ZBC) in ballistic voltage‐biased d‐wave superconductor/ferromagnet/d‐wave superconductor (DFD) junctions is studied theoretically, for various orientations of superconducting electrodes. We show that ZBC increases with exchange field h in the F barrier, up to some maximum value of h which is of the order of the pair potential in the superconducting electrodes. We find that for a given exchange field, ZBC monotonically decreases with temperature. When the exchange field h is smaller or of the order of the superconducting gap Δ, ZBC has a distinct kink at some characteristic temperature T*. It appears that for this temperature Δ(T*) = h. Thus, observing T* where the kink in the ZBC temperature dependence occurs provides a reliable measurement method to determine exchange fields of the order of the superconducting gap. [ABSTRACT FROM AUTHOR]

p-NiO/n-CdTe-photosensitive heterojunctions were prepared by the deposition of nickel oxide thin films onto n-type single-crystal CdTe substrates by DC reactive magnetron sputtering. The analysis of capacitance-voltage (C -- V) characteristics, measured at different frequencies of the small amplitude AC signal and corrected by the effect of the series resistance, provided evidence of the presence of electrically charged interface states, which significantly affect the measured capacitance. The dominant current transport mechanisms in the heterojunctions were determined at forward and reverse biases. Using "light" I -- V characteristics, we determined the open-circuit voltage Voc = 0.42 V, the short-circuit current Isc = 57.5 µA/cm², and the fill factor FF = 0.24 under white light illumination with the intensity of 80 mW/cm². [ABSTRACT FROM AUTHOR]

Current transport through a unique structure design employing high quality GaN based heterostructure with sharp interfaces has been investigated. A novel approach of structure design has been adopted to enhance the current transport in GaN heterostructures with a specific number of barrier layers of AlN which includes Single Barrier Heterostructure (SBH) and Double Barrier Heterostructure (DBH) devices. The high band gap AlN can act as a barrier for current conduction between GaN layers and help in effectively enhancing the current transport in the device through tunneling phenomena. A highly enhanced current transport in comparison with No Barrier Heterostructure (NBH) has been observed in SBH and a further improvement is perceived in DBH. Moreover, the phenomenon of current conduction is explained through drift-diffusion model, in which current enhancement upon subsequent addition of high bandgap barrier layer has resulted in localized high electric field and thus charge carrier velocity overshoots. Further, this has also been explained via quantum model, by interference of transmitted and reflected electron wave at interfaces. UV photodetectors using such heterostructure designs with and without AlN barrier layers in metal-semiconductor-metal geometry have been fabricated. The UV photodetection device developed using DBH yields photoresponsivity 80 times higher as compared to NBH device under UV illumination (325 nm). Employment of such structures will enable scaling up the production of highly efficient optoelectronic devices. [ABSTRACT FROM AUTHOR]

In this paper, we report on the fabrication of multi-layer bismuth selenide (Bi 2 Se 3 ) devices by lithography process and their electrical transport characteristics studied at room temperature. The observation of a non-linear current-voltage characteristic is analyzed with various current transport mechanisms such as Schottky barrier, space-charge limited conduction (SCLC), Fowler-Nordheim (F-N) tunneling and Poole-Frenkel (P-F) conduction. The F-N tunneling via field emission current induced in high-voltage was found to be the dominant conduction mechanism which could responsible for the nonlinear behavior as compared to SCLC and P-F conduction phenomena. The charge traps present in the Bi 2 Se 3 bulk causes SCLC and P-F conduction. A carrier mobility in Bi 2 Se 3 is extracted as ~ 1220 cm 2 V −1 s −1 . Our study further advances the understanding of the fundamental charge transport mechanisms appeared in Bi 2 Se 3 which will be an essential parameter in the development of various electronic applications such as resistive memory switching and sensing devices. [ABSTRACT FROM AUTHOR]

This paper presents a review of models of the current transport in different kind of heterojunctions (HJs) and their characteristics. In order to effectively deduce the dominant electron transport for the HJs based on ZnO or Zn1-xMgxO layers grown on Si substrate by MBE a comparison is performed - which type of the HJ exhibits better electrical properties. The current-voltage characteristics for the studied HJs were measured within 280-300 K. The transport properties of the HJs are explained in terms of Anderson model with reference to aforementioned current transport models. It is found, that the mechanisms of current transport for all of the studied HJs are similar. At a low forward voltage bias the tunneling current dominates while at medium voltage bias (0.5-1 V) multitunneling capture-emission prevails with the electron trap located at 0.1-0.25 eV below the bottom of a ZnO (Zn1-xMgxO) conduction band. Beyond this voltage bias space charge limited current governs the current transport. [ABSTRACT FROM AUTHOR]

It is fundamentally important to understand the nanoscale electronic properties of a single quantum dot (QD) contrary to an ensemble of QDs. Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM) are two important tools, which could be employed to probe surface potential, charging phenomena, and current transport mechanism of individual QD. We demonstrate the aforementioned characteristics of self-assembled Ge QDs, which was grown on Si substrates by solid source molecular beam epitaxy driven by the Stranski-Krastanov method. Study reveals that each Ge QD acts as charge storage node even at zero applied bias. The shape, size and density of QDs could be well probed by CAFM and KPFM, whereas QD facets could be better resolved by the conductive tip. The CAFM investigation further reveals that there exists a composition gradient within the QDs and Ge core can be charged more efficiently than the Si-Ge periphery at low level of bias. Schematic energy band diagram at the tip-sample contact is presented to explain the current transport mechanism, charging/discharging characteristics and the threshold voltages of I–V characteristics of the individual Ge QDs. [ABSTRACT FROM AUTHOR]

The transport mechanisms for metal-molecule-metal junction after break are analyzed. Theoretical expression for the threshold voltage for transmission from the direct tunneling current to the Fowler-Nordheim tunneling is obtained and analyzed. It is show that threshold voltage depends on the electrode metal work function and displacement. With the increase in displacement the threshold voltage quickly decreases. Differential resistances for the low and high voltage modes increase with increasing in the displacement, and in the Fowler-Nordheim tunneling mode the differential resistance increases when voltage is decrease. It is shown that for the cases commonly used metals (Ag, Au, Pt) the threshold voltage is linearly dependent on the work function of metals. [ABSTRACT FROM AUTHOR]

A pair of heterojunctions with different type of interlayer: n-ZnO/ZnCdO and n-ZnCdO/ZnO were grown by molecular beam epitaxy on p-Si substrate and investigated in the present work. At first, their electrical properties and parameters were discussed following current-voltage (I-V) characteristics measured over a wide range of temperatures from 40 K to 300 K. The analysis of I-V plots in log-log scale pointed out the presence of different carrier transport mechanisms: tunneling, multi-tunneling capture-emission and space-charge limited currents. Next, the capacitance-voltage characteristics were studied to determine the dopant concentration of the investigated junctions, along with the net doping profiles and their temperature dependence in the range of 40 K to 300 K. Finally, a deep level transient spectroscopy method was applied to characterise defects in the studied junctions. Donor-like traps were identified and their parameters, such as activation energy and capture cross section, were calculated. Furthermore, the influence of cadmium ions in ZnCdO interlayer of n-ZnO/ZnCdO/p-Si diode on the energy position of trap levels was noticed. Moreover, it was demonstrated that the interlayer type affects junction parameters, especially its built-in potential, as well as it modifies the current transport mechanisms in the intermediate range of voltage. [Display omitted] • Heterojunctions of n-ZnO/ZnCdO/p-Si and n-ZnCdO/ZnO/p-Si were grown by MBE. • The impact of interlayer type on current transport mechanisms was studied. • Temperature dependences of several junction parameters were discussed in details. • The presence of defects in heterojunctions was studied by DLTS. • First experimental proof for Cd Zn -V O -Zn i defect existence in ZnCdO was presented. [ABSTRACT FROM AUTHOR]

The article offers information on charge carriers in conjugated polyelectrolyte (CPE). Topics discussed include optoelectronic features of organic semiconductors with the ability of polyelectrolytes to modulate physical properties through electrostatic forces; injection barriers in organic optoelectronic devices; and the information on the Hall effect, Seebeck coefficient, field effect transistors (FETs), and ultraviolet photoelectron spectroscopy (UPS) measurements.

The paper describes the deep level transient spectroscopy (DLTS) measurements that were performed in order to investigate defects in p-Si/n-Zn 0.9 Mg 0.1 O/n-ZnO heterojunction (HJ). The HJ structure was grown by molecular beam epitaxy (MBE) technique on a p-type Si(111) substrate at 500 °C. The DLTS studies had been preceded by the current-voltage (I-V) and capacitance-voltage (C-V) measurements. The I-V measurements show the rectifying behavior of the HJ and indicate that the low forward bias (less than 0.6 V) mechanism of current transport is dominated by recombination-tunneling whereas at higher voltage space charge limited current (SCLC) governs the current transport. The I-V and C-V measurements yield donor concentration of N D = 5·10 15 cm −3 in the Zn 0.9 Mg 0.1 O layer. This value is two orders of magnitude less than the acceptor concentration, N A = 2·10 17 cm −3 in the Si substrate. Therefore it has been assumed that the depletion region extends mainly on the Zn 0.9 Mg 0.1 O side of the HJ and the DLTS signal has its origin in this layer and at the HJ interface. The DLTS measurements performed within the temperature range of 20–400 K revealed the presence of three electron traps, with activation energies of 0.06 eV, 0.38 eV, and 0.39 eV respectively. The latter two are ascribed to the defects in the Zn 0.9 Mg 0.1 O layer, while the trap with the activation energy of 0.06 eV is located either in the Zn 0.9 Mg 0.1 O layer or at the interface with Si. [ABSTRACT FROM AUTHOR]

This paper reports a complex analysis of structural, optical and electrical properties of Cu 2 ZnSnS 4 (CZTS) films, prepared by spin-coating of a sol-gel based on the low-cost and environmentally friendly solvent dimethyl sulfoxide (DMSO) and synthesized in low vacuum (0.1 Pa). The effect of a short-term low-temperature treatment in air and final annealing under low vacuum (0.1 Pa) on the synthesis of CZTS films was tested and analyzed. XRD and Raman spectra have shown the polycrystalline nature of obtained CZTS films with almost a pure kesterite phase content. The average size of crystallites D ~60 nm in the films was estimated. The value of the band gap E g ≈1.53 eV was determined from the analysis of optical characteristics. The analysis of electrical characteristics was carried out in the scope of the model of current transport in polycrystalline materials with electrically active grain boundaries. The determined values of the specific resistance ρ ≈2.38 Ω cm, the hole density p 0 ≈4.2×10 18 cm −3 and the effective mobility μ p ≈0.63 cm 2 /(V s) demonstrate that the CZTS films under investigation are prospective for the fabrication of highly efficient solar cells. [ABSTRACT FROM AUTHOR]

A simple approach, which can estimate the barrier height of non-Ohmic back contacts for CdS/CdTe solar cell by using its temperature dependent forward biased current-voltage data, is explained. The method involves modelling the forward J – V characteristics using a double exponential expression for the main junction and by a reverse biased Schottky barrier for the back contact. Cells processed with both CdCl 2 and MgCl 2 are compared, with the current transport phenomena in both kinds of cells also being analysed. Performance loss due to limitation of the forward bias hole current, and its dependence on the post-deposition chloride processing, is discussed. The forward current transport is mainly dominated by recombination at CdS/CdTe interfacial region with pronounced tunnelling effects. Classical Schottky-type conduction, as described by the Richardson-Schottky formula, is a good fit to the reverse biased current-voltage behaviour of an Au/CdTe junction above ∼240 K. Below this temperature, the current limiting effect due to the increasing contribution from interfacial defect states can be satisfactorily explained by Bardeen’s model for a modified Schottky type barrier at back contact interface. [ABSTRACT FROM AUTHOR]

p-Si/n-ZnInSe 2 hetero-junction diode was deposited by thermal evaporation of elemental evaporation sources on the 600 μm thick p-type (1 1 1) mono-crystalline Si wafers having the resistivity value of 1 - 3 (Ω.cm). Detailed electrical characterization of the hetero-junction was performed by the help of temperature dependent current-voltage measurements. The forward current-voltage behaviour of the hetero-junction diode was investigated under the evaluation of possible current transport mechanisms. In the studied temperature range, thermionic emission and space charge limited current were found to be predominant transport models for this hetero-junction. In addition, the parasitic resistance, ideality factor and barrier height were determined. The contribution of the p- and n-layer in the junction was studied under the spectral photo-response measurement. [ABSTRACT FROM AUTHOR]

Few fossil vertebrate skeletons are complete and fully articulated. Various taphonomic processes reduce the skeletal fidelity of decaying carcasses, the effects of most of which are reasonably well understood. Some fossil vertebrates, however, exhibit patterns of disarticulation and loss of completeness that are difficult to explain. Such skeletons are one of two variants. They are incomplete, often markedly so, but the preserved parts are highly articulated. Alternatively, they are complete, or nearly so, but articulation varies markedly between parts of the body. A characteristic feature is the absence of skeletal elements that, on the basis of their larger size and/or greater density, would be predicted to be present. Here we erect a model, termed “stick ‘n’ peel”, that explains how these distinctive patterns originate. The model emphasizes the role of decay products, especially fluids released from the carcass while resting on the sediment surface. These fluids permeate the sediment below and around the carcass. As a result, skeletal elements on the downward facing side of the carcass become adhered to the sediment surface, and are less likely to be remobilized as a result of current activity than others. The pattern of articulation and, especially, completeness is thus not what would be predicted on the basis of the size, shape and density of the skeletal elements. The effects of stick ‘n’ peel are difficult to predict a priori. Stick ‘n’ peel has been identified in vertebrate fossils in lacustrine and marine settings and is likely to be a common feature of the taphonomic history of many vertebrate assemblages. Specimens becoming adhered to the substrate may also explain the preservation in situ of the multi-element skeletons of invertebrates such as echinoderms, and integumentary structures such as hair and feathers in exceptionally preserved fossils. [ABSTRACT FROM AUTHOR]

This paper reports on the both possible applications of molybdenum oxide (MoO x) thin films in combination with hole or electron conducting CdTe. The high quality ohmic contancts and strongly rectifying photodiodes were prepared by the DC magnetron sputtering of MoO x thin films onto freshly cleaved p- and n-type CdTe single crystal substrates. The analysis of DC and AC electrical properties of the MoO x/ p-CdTe ohmic contact was carried out. The dominating current transport mechanisms through the MoO x/p-CdTe heterojunction at forward and reverse bias were determined. The unoptimized heterojunction photodiode showed promising rectifying and photoelectrical characteristics for practical application in the photoconductive mode. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Based on the results of investigations of charge transport in the "metal — p-Si" contacts with different thickness of polycrystalline p-Si layer the mechanisms of charge transport through such structures are shown. It is established that with increasing thickness of the layer of polycrystalline p-Si current transport mechanism changes from a double injection into the drift-diffusion. This change is due to an increase in the drift current component in the space charge zone of "metal — p-Si" contact, which arises as a result of increased surface density of scattering barriers, which are localized at the boundaries of neighboring silicon polycrystals.

This paper presents an understanding of the fundamental carrier transport mechanism in hydrogenated amorphous silicon (a-Si:H)-based n/p junctions. These n/p junctions are, then, used as tunneling and recombination junctions (TRJ) in tandem solar cells, which were constructed by stacking the a-Si:H-based solar cell on the heterojunction with intrinsic thin layer (HIT) cell. First, the effect of activation energy (Ea) and Urbach parameter (Eu) of n-type hydrogenated amorphous silicon (a-Si:H(n)) on current transport in an a-Si:H-based n/p TRJ has been investigated. The photoluminescence spectra and temperature-dependent current-voltage characteristics in dark condition indicates that the tunneling is the dominant carrier transport mechanism in our a-Si:H-based n/p-type TRJ. The fabrication of a tandem cell structure consists of an a-Si:H-based top cell and an HIT-type bottom cell with the a-Si:H-based n/p junction developed as a TRJ in between. The development of a-Si:H-based n/p junction as a TRJ leads to an improved a-Si:H/HIT-type tandem cell with a better open circuit voltage (Voc), fill factor (FF), and efficiency. The improvements in the cell performance was attributed to the wider band-tail states in the a-Si:H(n) layer that helps to an enhanced tunneling and recombination process in the TRJ. The best photovoltage parameters of the tandem cell were found to be Voc = 1430mV, short circuit current density = 10.51 mA/cm2, FF = 0.65, and efficiency = 9.75%. [ABSTRACT FROM AUTHOR]

In this paper, AlN thin films with two different thicknesses, i.e., 7 and 47 nm, were deposited at 200 °C on p-type Si substrates by plasma-enhanced atomic layer deposition using trimethylaluminum and ammonia. To investigate the electrical characteristics of these AlN films, MIS capacitor structures were fabricated and characterized using current–voltage and high-frequency (1 MHz) capacitance–voltage measurements. The results showed that the current transport mechanism under accumulation mode is strongly dependent on the applied electric field and thickness of the AlN film. Possible conduction mechanisms were analyzed, and the basic electrical parameters were extracted and compared for AlN thin films with different thicknesses. Compared with 7-nm-thick film, a 47-nm-thick AlN film showed a lower effective charge density and threshold voltage along with a higher dielectric constant. [ABSTRACT FROM AUTHOR]

We employed oxygen plasma treatment to improve the electrical properties in Cu/n-type Ge Schottky junctions and investigated temperature dependent current transport mechanism in the temperature range of 100–300 K. The Schottky barrier height increased commensurate with increasing temperature, which was attributed to barrier inhomogeneity. The inhomogeneity of the barrier was represented by a double Gaussian distribution, each one prevailing in a distinct temperature range: a high-temperature range from 220 to 300 K and a low-temperature range from 100 to 180 K. Modified Richardson plots revealed a Richardson constant of 160.0 Acm −2 K −2 for the high-temperature region (220–300 K), which is comparable to the theoretical value of 140.0 Acm −2 K −2 for n-type Ge. Reverse current analysis revealed that Poole–Frenkel and Schottky emissions were dominant in the lower and higher voltage regions, respectively. [ABSTRACT FROM AUTHOR]

The AlGaN-based ultraviolet light-emitting diodes (UV LEDs) with different Al composition in the multiple quantum well (MQW) active region are investigated numerically. It is manifest that the Al content significantly affects the polarization field in the MQWs, which further have great impact on the current transport mechanisms for different type UV LEDs. The energy band diagrams and electric field in MQWs are simulated to illustrate the devices' performance theoretically. [ABSTRACT FROM AUTHOR]

Quaternary semiconductor compound Cu 2 ZnSnS 4 (CZTS) is a promising non-toxic absorber material for solar cells made from earth abundant elements. In this study temperature dependencies ( T = 10–300 K) of current–voltage (J–V) characteristics and external quantum efficiency (EQE) spectra of CZTS monograin layer solar cells were measured in order to clarify current transport in CZTS that is still not fully understood. Three different temperature ranges can be distinguished from the temperature dependence of the series resistance ( R s ) obtained from J–V measurements and the effective bandgap energy ( E g ⁎ ) determined from the EQE spectra. Thermally activated conductivity, Mott's variable-range hopping conductivity, and very low temperature (< 40 K) blocking of the interface recombination were observed. [ABSTRACT FROM AUTHOR]

This paper reports comprehensive characterization of vertical GaN-on-GaN Schottky barrier diodes (SBDs) fabricated on free-standing GaN substrates. The GaN active layer properties are evaluated by atomic force microscopy (AFM), secondary-ion mass spectrometry (SIMS), micro-Raman spectroscopy, cathodoluminescence (CL), and deep-level transient Fourier spectroscopy (DLTFS). The GaN SBDs exhibit near-unity ideality factor (n = 1.1), promising Schottky barrier height (SBH) of Φ B = 0.82 eV, low turn-on voltage ∼0.56 V, leakage current density of J R < 5.5 × 10−6 Acm−2 at −100 V, breakdown voltage V BR < −200 V, and less interface state density (N SS < 5 × 1012 eV−1 cm−2) at the Ni/GaN Schottky contact. The forward and reverse current transport mechanisms of the SBD are identified by fitting analysis of measured J-V. Weak temperature dependence of Φ B and n is detected from I–V-T measurements. Similar traps at E C - 0.18 eV and E C - 0.56 are identified in the various SBDs from DLTFS, signifying that these traps are omnipresent defects in the epilayer. • Comprehensive characterizations are carried out for vertical GaN-on-GaN Schottky barrier diodes (SBDs). • Typical electrical characteristics of quasi-ideal vertical GaN-on-GaN SBDs are reported. • Various current transport mechanisms involved during forward and reverse characteristics of the SBD are identified. • The GaN active layer properties are evaluated by AFM, SIMS, micro-Raman spectroscopy, cathodoluminescence (CL). • Furthermore, traps in the GaN diodes are detected by deep level transient Fourier spectroscopy (DLTFS). [ABSTRACT FROM AUTHOR]

High contact resistance of the order of 10 −3 Ω cm 2 observed in p-type HgCdTe is one of the practical problems in the production of fine pitch high operating temperature and avalanche photodiode detector array. Electrical and compositional measurements on Au/p-HgCdTe are reported to understand the difficulties in reducing the contact resistance in HgCdTe detectors. Characterization of Au contacts on p-type Hg 1− x Cd x Te ( x =0.3) formed by electrode-less (electroless) process and current transport mechanism are discussed. SIMS depth profiling of interfacial layer formed by the reaction of gold chloride with HgCdTe have been analyzed. Extent of the interfacial layer containing Au, Te, O and Cl is found to increase with increasing deposition time. Effect of annealing on the migration of Au across the contact region and electrical characteristics are presented. Heavily doped HgCdTe region with N A =10 17 cm −3 is produced beneath the contact regions after annealing at 80 °C leading to an order of magnitude improvement in the specific contact resistance. These results are useful for the creation of Au/p-HgCdTe contacts in a controlled and reproducible manner. [ABSTRACT FROM AUTHOR]

This paper reports on the detail analysis of the DC electrical and photoelectrical properties of the high-efficient (η=8.01% under standard 100mW/cm2 AM1.5 illumination) small molecule bulk heterojunction (SM BHJ) solar cells p-DTS(FBTTh2)2/PC70BM. In this SM BHJ solar cell, the dark diode current is determined by the multistep tunnel-recombination via interface states at low forward bias (V<0.65V) and the interface state assisted thermionic emission at high forward bias (V>0.65V). The effect of illumination on the diode current was also quantitatively investigated. It was observed a reduced Shockley-Read-Hall recombination via interface states at large forward bias (from the maximum power point to the open-circuit conditions). The expression of the load I-V characteristic of the illuminated high-efficient SM BHJ solar cells was derived in the presence of the light dependent series and shunt resistance. [ABSTRACT FROM AUTHOR]

Abstract: Schottky interface properties of p-diamond (100) were investigated. Gold (Au), which is a representative noble metal, and tungsten carbide (WC), a carbide preformed metal, were selected as Schottky contact metals. When Au was used as the Schottky metal, Schottky properties were strongly related to the surface oxidation method. The Schottky barrier height was as high as >2eV. The distribution of the ideality factor became small when using the vacuum ultraviolet (VUV) light/ozone treatment for diamond surface oxidation, compared to the case of conventional wet-chemical oxidation treatment. However, for a WC Schottky contact, interface properties were insensitive to the surface oxidation method. This insensitivity was regarded as deriving from the formation of interfacial bonding between WC and diamond during metal deposition. Schottky barrier diodes (SBDs) prepared by the VUV light/ozone treatment showed good temperature stability with low reverse current of <1pA up to 550K. Through heating at higher temperatures of >600K, the ideality factor of Au SBD increased and the Schottky barrier height changed greatly. Oxygen termination dissociation was inferred to occur at the Au/diamond Schottky interface. WC SBD had better thermal stability than Au SBD because the interface was stabilized by interfacial bonding. [Copyright &y& Elsevier]