Search

The current voltage characteristics and the low-frequency noise in high voltage 4H-SiC junction barrier Schottky diodes irradiated with high energy (15MeV) protons were studied at different temperatures and irradiation doses Φ from 3 x 1012 cm-2 to 1 x 1014 cm-2. Irradiation led to the increase of the base resistance and the appearance of slow relaxation processes at small, V ≤ 0.2 V, and at rather high, V ≥ 2 V, forward voltages. The characteristic times of these relaxation processes ranged from ~1 µs to 10³s. The exponential part of the current-voltage characteristic was only weakly affected by irradiation. The temperature dependence of the base resistance changed expo-nentially with temperature with activation energy Ea ~ 0.6 eV, indicating that the Z1/2 level plays a dominant role in this process. The temperature increase also led to the increase of the ideality factor from 1.05 at 25 °C to 1.1 at 172 °C. At elevated temperatures and high forward voltages V > 2-4 V, the current voltage characteristics tend to be super-linear. It is concluded that at high voltages, the space charge limited current of majority carriers (electrons) and hole injection from the p-n regions play an important role in the formation of the current voltage characteristic. The frequency dependences of noise spectral density S of proton irradiated Schottky diodes have the unusual form of S ~ 1/f05. [ABSTRACT FROM AUTHOR]

We report on fabrication of MoS2 thin-film transistors (TFTs) and experimental investigations of their high-temperature current-voltage characteristics. The measurements show that MoS2 devices remain functional to temperatures of at least as high as 500 K. The temperature increase results in decreased threshold voltage and mobility. The comparison of the direct current (DC) and pulse measurements shows that the direct current sub-linear and super-linear output characteristics of MoS2 thin-films devices result from the Joule heating and the interplay of the threshold voltage and mobility temperature dependences. At temperatures above 450 K, a kink in the drain current occurs at zero gate voltage irrespective of the threshold voltage value. This intriguing phenomenon, referred to as a "memory step," was attributed to the slow relaxation processes in thin films similar to those in graphene and electron glasses. The fabricated MoS2 thin-film transistors demonstrated stable operation after two months of aging. The obtained results suggest new applications for MoS2 thin-film transistors in extreme-temperature electronics and sensors. [ABSTRACT FROM AUTHOR]

Schottky diodes with Ni/Au contact to the side of the two dimensional channel in GaN/AlGaN system were fabricated and studied. This kind of lateral heterodimensional diodes demonstrated the ideality factor n=1.2–1.25 and apparent barrier height φb=(0.59–0.63) eV. The noise measurements within the frequencies range from 1 Hz to 50 kHz showed that the diodes demonstrated the superposition of 1/f and generation recombination noise. In spite of extremely small area of lateral Schottky diodes, the amplitude of noise was similar or even smaller than that for AlGaN and GaN Schottky diodes with the regular contact. This makes GaN-based lateral Schottky diodes to be very promising devices for RF and terahertz applications. [ABSTRACT FROM AUTHOR]

Detection of terahertz radiation by GaAs transistor structures has been studied experimentally. The two types of samples under study included dense arrays of HEMTs and large-apertures detectors. Arrays consisted of parallel and series chains with asymmetric gate transistors for enhanced photoresponse on terahertz radiation. We investigated two types of wide-aperture detectors: grating gate detector, and single gate detector with bow-tie antenna. Wide-aperture detectors were symmetrical. Studies of transistor chains have shown that two essential features for this type of detector are the presence of asymmetry in the gate, and the type of connection between individual transistors themselves. Wide-aperture detectors have also been tested by narrow beams of terahertz radiation, which allows analyzing the role influence of individual parts of the detector for total sensitivity to terahertz excitation. The sensitivity and noise equivalent power of the detectors were evaluated. [ABSTRACT FROM AUTHOR]

We demonstrated selective gas sensing with MoS2 thin-film transistors using the change in the channel conductance, characteristic transient time, and low-frequency current fluctuations as the sensing parameters. The back-gated MoS2 thin-film field-effect transistors were fabricated on Si/SiO2 substrates and intentionally aged for a month to verify reliability and achieve better current stability. The same devices with the channel covered by 10 nm of Al2O3 were used as reference samples. The exposure to ethanol, acetonitrile, toluene, chloroform, and methanol vapors results in drastic changes in the source-drain current. The current can increase or decrease by more than two-orders of magnitude depending on the polarity of the analyte. The reference devices with coated channel did not show any response. It was established that transient time of the current change and the normalized spectral density of the low-frequency current fluctuations can be used as additional sensing parameters for selective gas detection with thin-film MoS2 transistors. [ABSTRACT FROM AUTHOR]

Owing to their ultimate surface-to-volume ratio two-dimensional (2D) van der Waals materials are candidates for flexible gas sensor applications. However, all demonstrated devices had relied on direct exposure of the active 2D channel to gases, which presents problems for their reliability and stability. We demonstrated, for the first time, selective gas sensing with molybdenum disulfide (MoS2) thin films transistors capped with a thin layer of hexagonal boron nitride ( $h$ -BN). The resistance change, \Delta R/R$ , was used as a sensing parameter to detect chemical vapors. It was found that h$ -BN dielectric passivation layer does not prevent gas detection via changes in the current in the MoS2 channel. The detection without direct contacting the channel with analyte molecules was achieved with \Delta R/R . In addition, we show that the use of $h$ -BN cap layers (thickness $H \sim 10$ nm) improves sensor stability and prevents degradation due to environmental and chemical exposure. [ABSTRACT FROM PUBLISHER]

Spatially resolved x-ray fluorescence (XRF) based analysis employing incident beam sizes in the low micrometer range (μ XRF) is widely used to study lateral composition changes of various types of microstructured samples. However, up to now the quantitative analysis of such experimental datasets could only be realized employing adequate calibration or reference specimen. In this work, we extent the applicability of the so-called reference-free XRF approach to enable reference-free μ XRF analysis. Here, no calibration specimen are needed in order to derive a quantitative and position sensitive composition of the sample of interest. The necessary instrumental steps to realize reference-free μ XRF are explained and a validation of ref.-free μ XRF against ref.-free standard XRF is performed employing laterally homogeneous samples. Finally, an application example from semiconductor research is shown, where the lateral sample features require the usage of ref.-free μ XRF for quantitative analysis. [ABSTRACT FROM AUTHOR]

The degradation of organic pollutants by transition metal activated peroxymonosulfate (PMS) has important application value in the field of advanced oxidation. MnO2/SiC composite catalyst was prepared by hydrothermal method on the surface of silicon carbide (SiC), which was used to activate PMS to degrade and remove methylene blue (MB) from water. The results show that MnO2 is uniformly attached to the surface of SiC in the form of particles, and the removal rate of MB by MnO2/SiC-PMS system reaches 99% within 40 min. The MnO2/SiC-PMS system can achieve high degradation efficiency of MB over a wide pH range (5.0~9.0), while 5 mmol/L Cl- and NO3- had no significant effect on the MnO2/SiC-PMS system. Phosphate and bicarbonate have quenching effect on oxidative free radicals, leading to a decrease in the degradation efficiency of MB in the MnO2/SiC PMS system. The results of free radical quenching experiments indicate that plays a major role in the MnO2/SiC-PMS system. In addition, MnO2/SiC has good recyclability. [ABSTRACT FROM AUTHOR]

The design of semiconductor-based heterojunction structures can be turned useful to raise the efficiency of nuclear micro-batteries. In this study, we have investigated a micro-power alphavoltaic battery by using a lab-made software. The nuclear battery consists of an In0.49Ga0.51P/GaAs heterostructure irradiated by americium-241 (Am241) alpha particles with an average kinetic energy of 5.485 MeV. The alphavoltaic battery exhibits an overall active area of 1 cm². Based on a comprehensive analytical model, the device current density-voltage J(V) and output electric power P(V) characteristics are simulated extracting the energy conversion efficiency. The model takes into account the reflection of the incident alpha particles, the ohmic losses, the effect of the boundary between the two layers, and the depletion region borders. Different values of the radioisotope apparent activity density, the emitter and base dopant concentrations, and the surface recombination velocities in both the front and back layers are considered during the simulations to optimize the battery performance. The present study reports that by irradiating by a 2.4 mCi/cm² Am241 source, the obtained energy conversion efficiency of the battery can reach 10.31% with a maximum output power density of 16.07 μW/cm². Therefore, In0.49Ga0.51P/GaAs heterostructure coupled with Am241 seems a promising design for long- term energy supply in harsh environments. [ABSTRACT FROM AUTHOR]

We report on a design of fin-shaped channel GaN/AlGaN field-effect transistors developed for studying resonant terahertz plasma oscillations. Unlike common two dimensional FinFET transistor design, the gates were deposited only to the sides of the two dimensional electron gas channel, i.e., metal layers were not deposited on the top of the AlGaN. This side gate configuration allowed us to electrically control the conductivity of the channel by changing its width while keeping the carrier density and mobility virtually unchanged. Computer simulations and analytical model describe well the general shape of the characteristics. The side gate control of the channel width of these transistors allowed us to eliminate the so-called oblique plasma wave modes and paves the way towards future terahertz detectors and emitters using high quality factor plasma wave resonances. [ABSTRACT FROM AUTHOR]

Reliable and controllable growth of two-dimensional (2D) hexagonal boron nitride (h-BN) is essential for its wide range of applications. Substrate engineering is one of the critical factors that influence the growth of the epitaxial h-BN films. Here, we report the growth of monolayer h-BN on Ni (111) substrates incorporated with oxygen atoms via molecular beam epitaxy. It was found that the increase of incorporated oxygen concentration in the Ni substrate through a pretreatment process prior to the h-BN growth step would have an adverse effect on the morphology and growth rate of 2D h-BN. Under the same growth condition, h-BN monolayer coverage decreases exponentially as the amount of oxygen incorporated into Ni (111) increases. Density functional theory calculations and climbing image nudged elastic band (CI-NEB) method reveal that the substitutional oxygen atoms can increase the diffusion energy barrier of B and N atoms on Ni (111) thereby inhibiting the growth of h-BN films. As-grown large-area h-BN monolayer films and fabricated Al/h-BN/Ni (MIM) nanodevices were comprehensively characterized to evaluate the structural, optical and electrical properties of high-quality monolayers. Direct tunneling mechanism and high breakdown strength of ∼11.2 MV cm−1 are demonstrated for the h-BN monolayers grown on oxygen-incorporated Ni (111) substrates, indicating that these films have high quality. This study provides a unique example that heterogeneous catalysis principles can be applied to the epitaxy of 2D crystals in solid state field. Similar strategies can be used to grow other 2D crystalline materials, and are expected to facilitate the development of next generation devices based on 2D crystals. [ABSTRACT FROM AUTHOR]

We present the study of the SiGe quantum ring (QR) modeled by an anharmonic axially symmetric potential with a centrifugal core in the effective mass approximation. We show how the femtosecond laser pulses (FLPs) can be used efficiently for controlling the induced current and magnetic field. We have compared the strength of induced currents and magnetic fields with and without pulsed laser which shows a substantial change. The spin-orbit interaction (SOI) and Zeeman energy show a massive impact on the generation and enhancement of these induced current and magnetic fields. These induced currents and magnetic fields have many applications in interdisciplinary areas. We have shown that the SOI presence with the FLP fields while competing with the confinement strength lowers the strength of the induced current and field. [ABSTRACT FROM AUTHOR]

Comparison of optical power, external quantum efficiency in InGaN/GaN UV LEDs at room temperature and liquid nitrogen temperature is carried out. The spectral densities of the current low-frequency noise have been investigated. The mechanisms of carrier transport, the formation of low-frequency noise, and the dependences of the rates of radiative and nonradiative recombination at room and nitrogen temperatures are considered. [ABSTRACT FROM AUTHOR]

High-density integration of ferroelectric field-effect transistors (FeFETs) is hindered by factors such as interfacial states, short-channel effects, and ferroelectricity degradation in ultrathin films. Accordingly, the introduction of two-dimensional (2D) materials could effectively solve these problems. However, most current studies focus on the replacement of Si-based channels with 2D channels. Little progress has been made in addressing issues caused by bulk-phase ferroelectric gate layers, such as the unavoidable rough interfaces and the fading of ferroelectricity in ultrathin films. Herein, the 2D ferroelectric material In2Se3 is introduced as the gate dielectric. Combined with 2D insulating h-BN and 2D channel MoS2, an all-van der Waals (vdW) stacking FeFET is fabricated to provide a straight solution for the abovementioned issues. First, the robust ferroelectric phase of In2 Se3 is verified in an ultrathin film case and a high-temperature case, which is outstanding among recently reported 2D ferroelectrics. Second, device-level out-of-plane ferroelectric polarization switching is achieved in the cross-structure device. Based on these results, In2 Se3 is adopted as the ferroelectric gate dielectric to fabricate all-vdW stacking FeFETs. The subsequent transistor performance measurement on the fabricated FeFETs indicates that the ferroelectric polarization of the In2 Se3 layer plays a dominating role in forming a counterclockwise hysteresis loop. Further pulse response measurements manifest the feasibility of nonvolatile channel conductance tuning of these devices with a proper pulse design. Our findings suggest that In2Se3 is a suitable 2D ferroelectric gate material and that all-vdW stacking FeFETs based on 2D ferroelectrics are promising in the application of high-density memory. [ABSTRACT FROM AUTHOR]

The influence of proton irradiation at high temperatures ("hot" irradiation) on the capacitance–voltage and current–voltage characteristics of semiconductor devices based on silicon carbide has been studied for the first time. The experiments were performed on commercial high-voltage integrated 4H-SiC Schottky diodes with a blocking voltage of 1700 V, which were irradiated by 15-MeV protons at temperatures within 20–400°C. It is established that the most sensitive parameter determining the degree of radiation-induced damage is the ohmic resistance of the base, which monotonically increases with irradiation dose D. Under "hot" irradiation conditions, the radiation resistance of diodes is significantly higher as compared to that observed in the case of low-temperature ("cold") irradiation. It is concluded that an increase in the temperature is accompanied by a decrease in the rate of formation of deep defect centers in the upper half of the bandgap of silicon carbide. [ABSTRACT FROM AUTHOR]

Effect of irradiation with 0.9 MeV electrons on the parameters of 4H-SiC Schottky diodes with a limiting blocking voltage Ub = 600 and 1700 V was studied for the first time in the range of operating temperatures Ti (23 and 175°C). The range of fluences Φ was 1 × 1016–2 × 1016 cm–2 for devices with Ub = 600 V and 5 × 1015–1.5 × 1016 cm–2 for devices with Ub = 1700 V. Irradiation at room temperature increases significantly the differential resistance of the base of the diodes. Irradiation with the same doses at Ti = 175°C—i.e. at limiting operating temperature of devices, does not affect practically the parameters of current–voltage characteristics. Nevertheless, the DLTS spectra demonstrate a significant increase in the concentration of deep levels in the upper half of the band gap not only after irradiation at room temperature, but also after irradiation at Ti = 175°C. [ABSTRACT FROM AUTHOR]

The effect of proton irradiation (proton energy 15 MeV) on the parameters of high-voltage 4H-SiC integrated Schottky diodes (JBS) was studied for the first time in the operating temperature range Ti (23 and 175°C). The blocking voltage of the diodes under study, Ub, was 600 and 1700 V. For devices with Ub = 600 V, the fluence range was 5 × 1013–1 × 1014 cm–2; for devices with Ub = 1700 V, the fluence range was 3 × 1013–6 × 1013 cm–2. An increase in the irradiation temperature leads to a noticeable decrease in the effect of irradiation on the current–voltage characteristics of the diodes. The effect of annealing on the current-voltage characteristics of irradiated devices is studied. [ABSTRACT FROM AUTHOR]

Abstract: JBS diodes based on 4H-SiC irradiated with electrons and protons are studied. This is carried out by using the methods of capacitance-voltage and current-voltage characteristics. It is concluded that, for both kinds of irradiation, deep centers are formed in the upper half of the band gap of silicon carbide. This leads to a sharp decrease in the concentration of ionized carriers in the conduction band and to an exponential increase in the resistance of the base regions of the structures under study. [ABSTRACT FROM AUTHOR]

Solid-state magnetic field sensors are important for applications in commercial electronics and fundamental materials research. Most magnetic field sensors function in a limited range of temperature and magnetic field, but Hall sensors in principle operate over a broad range of these conditions. Here, we evaluate ultraclean graphene as a material platform for high-performance Hall sensors. We fabricate micrometer-scale devices from graphene encapsulated with hexagonal boron nitride and few-layer graphite. We optimize the magnetic field detection limit under different conditions. At 1 kHz for a 1 μm device, we estimate a detection limit of 700 nT Hz -1/2 at room temperature, 80 nT Hz -1/2 at 4.2 K, and 3 μT Hz -1/2 in 3 T background field at 4.2 K. Our devices perform similarly to the best Hall sensors reported in the literature at room temperature, outperform other Hall sensors at 4.2 K, and demonstrate high performance in a few-Tesla magnetic field at which the sensors exhibit the quantum Hall effect.

Film structures based on Si1–xGex (0 < x < 1) solid solutions are currently obtained by chemical-vapor-deposition methods. For device application of the obtained structures, it is necessary to know the electrical properties of the material synthesized under different conditions. In this work, we carry out galvanomagnetic studies of the electrical conductivity in porous and solid Si1–xGex films, as well as the concentration and mobility of the majority charge carriers in them at a temperature of 30–300 K. It is shown that, as in pure silicon and germanium of comparable porosity, the electrical conductivity in the studied samples can be considered as in a medium with voids. It is established that the type of majority charge carriers in the alloy is determined by the type of silicon substrate used. This is practically important for creating both arms of a thermoelectric converter, which makes the method for producing Si1–xGex(0 < x < 1) alloy promising for device applications, in particular in thermoelectric converters and lithium-ion batteries. [ABSTRACT FROM AUTHOR]

NH- ÎĽ LED, namely a micro light-emitting diode structure with nano-holes dug all the way through the active region, is designed to make silver nanoparticles in extremely close contact with the quantum wells for improving the coupling between the localized surface plasmon and the quantum wells (LSP-QWs coupling) and thus enhancing the optical properties of the ÎĽ LED. The experimental results show that, thanks to this deep nanohole structure, the LSP-QWs coupling can be realized effectively, which ultimately increases the optical performance of the ÎĽ LED. The internal quantum efficiency of the NH- ÎĽ LED filled with silver nanoparticles is increased by 12%, and the final optical output power is also enhanced. We have further carried out a comparison study which measures the transient lifetime of two different types of ÎĽ LEDs, and the results provide convincing evidence for the existence of the ultra close range LSP-QWs coupling effect. [ABSTRACT FROM AUTHOR]

In this article, we study 1 / f γ , γ ≈ 1 electrical noise in amorphous phase-change materials. Given the relevance of noise in recent applications, it is necessary to gain a deeper perspective on its nature in phase-change semiconductors, a promising class of materials. Electron conduction is envisaged in terms of an envelope function and a field-dependent Bloch wave function; the electron transport across the structure is modeled as driven phase oscillators under a weak field and obeys a Kuramoto-type equation. Its solutions naturally divide into a phase-synchronized group and phase-desynchronized oscillators. The former is comprised by long-lived pairs or aggregates and are responsible for 1 / f , γ = 1 noise. We identify the dividing frequency between γ = 1 noise and γ ≠ 1 noise. The phase-desynchronized carriers generate γ ≠ 1 noise and are single carriers, not aggregates, and are short-lived. We apply our analysis to recent experiments. [ABSTRACT FROM AUTHOR]

The excrescent electromagnetic (EM) radiation exposure in the air threatens human health and electronic equipment due to the abuse of EM waves in wireless telecommunication technology and electronic applications. Consequently, electromagnetic interference (EMI) shielding materials are provided to solve the EM waves pollution problem. In particular, the appearance of one-dimensional (1D) metallic, magnetic, and dielectric nanofillers will extremely reduce the density of EMI composite and enhance EMI protection performance because they can easily assemble to form complete two-dimensional (2D) or three-dimensional (3D) EMI network based on their high aspect ratio, large specific surface area, and additional attenuated sites. This review focuses on the EMI shielding composites with 1D metallic, magnetic, and dielectric nanofillers, which could be constructed in the final form of membrane- or aerogel/sponge-like shielding materials. According to the structural features, 1D metallic, magnetic, and dielectric nanofillers are classified into nanowires, nanorods, nanospindles, nanochains, nanofibers, nanotubes, nanorings, nanocoils, and quasi-one-dimensional (1D) van der Waals materials. Accordingly, the fabricated routes, shielding performances, and EM waves attenuation mechanism of the 1D metallic, magnetic, and dielectric nanofiller-based composites are summarized. It is found that the dominant shielding mechanism of most of the 1D metal-based EMI composites is reflection loss, while that of 1D magnetic and dielectric nanomaterials-based EMI composites is absorption loss caused by interfacial polarization, natural resonance, eddy current, and multiple scattering. Finally, the challenges and prospects of 1D nanofiller-based composites with a tunable architecture and composition are put forward, aiming to give a guideline for the next generation of high-performance EMI shielding materials. [ABSTRACT FROM AUTHOR]

Integration of nanolayered metal chalcogenides with wide-bandgap semiconductors forming pn heterojunction leads to the way of high-performance photodetection. This work demonstrates the fabrication of a few nanometer thick Molybdenum diselenide (MoSe2)/Mg-doped Gallium Nitride (p-GaN) heterostructure for light detection purposes. The device exhibits low noise broadband spectral response from ultraviolet to near-infrared range (300â€"950 nm). The band-alignment and the charge transfer at the MoSe2/p-GaN interface promote self-powered photodetection with high photocurrent to dark current ratio of 2000 and 1000 at 365 nm and 640 nm, respectively. A high responsivity of 130 A Wâˆ'1, detectivity of 4.8 × 1010 Jones, and low noise equivalent power of 18 fW/Hz1/2 at 365 nm is achieved at an applied bias of 1 V. Moreover, the transient measurements reveal a fast rise/fall time of 407/710 ÎĽ sec for the fabricated device. These outcomes exemplify the viability of MoSe2/p-GaN heterostructure for high-speed and low-noise broadband photodetector applications. [ABSTRACT FROM AUTHOR]

We introduce in the many-body GW scheme the modulation of the screened Coulomb interaction W arising from the macroscopic dielectric response in the infrared. We derive expressions for the polaron binding energies, the renormalization of the effective masses and for the electron and hole relaxation times. Electron and hole mobilities are then obtained from the incorporation of appropriate scattering rules. Zinc-blende GaN and orthorhombic MAPbI3 are used as test beds finding fair agreement with results from rigorous electron-phonon coupling approaches. Although limited to polar phonons, our method has a negligible computational cost. [ABSTRACT FROM AUTHOR]

Electron spin qubits are a promising platform for quantum computation. Environmental noise impedes coherent operations by limiting the qubit relaxation (T1) and dephasing (Tϕ) times. There are multiple sources of such noise, which makes it important to devise experimental techniques that can detect the spatial locations of these sources and determine the type of source. In this paper, we propose that anisotropy in T1 and Tϕ with respect to the direction of the applied magnetic field can reveal much about these aspects of the noise. We investigate the anisotropy patterns of charge noise, evanescent-wave Johnson noise, and hyperfine noise in hypothetical devices. It is necessary to have a rather well-characterized sample to get the maximum benefit from this technique. The general anisotropy patterns are elucidated. We calculate the expected anisotropy for a particular model of a Si/SiGe quantum dot device. [ABSTRACT FROM AUTHOR]

The effect of annealing on the parameters of 4H-SiC Schottky diodes irradiated with electrons at a high temperature is studied for the first time. The electron energy is 0.9 MeV, irradiation is carried out at temperatures of 23, 300, and 500°C with fluences Φ in the 1 × 1016–1.3 × 1017 cm–2 range. The results of annealing samples irradiated at high temperatures differ qualitatively from the results of annealing samples irradiated with the same fluence at room temperature. The results indicate that, under high-temperature ("hot") irradiation, the spectrum of radiation-induced defects introduced in SiC differs significantly from the spectrum of defects introduced at room temperature. The effect of reverse annealing, when the resistance of the base of the diode does not fall but increases as a result of annealing, was discovered for large values of Φ at irradiation temperatures of 300 and 500°C. [ABSTRACT FROM AUTHOR]

Strain engineering as one of the most powerful techniques for tuning optical and electronic properties of Ill-nitrides requires reliable methods for strain investigation. In this work, we reveal, that the linear model based on the experimental data limited to within a small range of biaxial strains (< 0.2%), which is widely used for the non-destructive Raman study of strain with nanometer-scale spatial resolution is not valid for the binary wurtzite-structure group-III nitrides GaN and AlN. Importantly, we found that the discrepancy between the experimental values of strain and those calculated via Raman spectroscopy increases as the strain in both GaN and AlN increases. Herein, a new model has been developed to describe the strain-induced Raman frequency shift in GaN and AlN for a wide range of biaxial strains (up to 2.5%). Finally, we proposed a new approach to correlate the Raman frequency shift and strain, which is based on the lattice coherency in the epitaxial layers of superlattice structures and can be used for a wide range of materials. [ABSTRACT FROM AUTHOR]

Nonlinear oscillations in micro- and nanoelectromechanical systems have emerged as an exciting research area in recent years due to their promise in realizing low-power, scalable, and reconfigurable mechanical memory and logic devices. Here, we report ultralow-power mechanical memory operations utilizing the nonlinear oscillation regime of GaN microcantilevers with embedded piezotransistive AlGaN/GaN heterostructure field effect transistors as highly sensitive deflection transducers. Switching between the high and low oscillatory states of the nonlinear oscillation regime was demonstrated using a novel phase-controlled opto-mechanical excitation setup, utilizing a piezo actuator and a pulsed laser as the primary and secondary excitation sources, respectively. Laser-based photoacoustic excitation was amplified through plasmonic absorption in Au nanoparticles deposited on a transistor. Thus, the minimum switching energy required for reliable memory operations was reduced to less than a picojoule (pJ), which translates to one of the lowest ever reported, when normalized for mass. [ABSTRACT FROM AUTHOR]

In this paper, a junction-less charge plasma (CP) double-drift region (DDR) impact avalanche transit time (IMPATT) diode structure has been proposed for realizing a high-power and efficient terahertz (THz) source. A comprehensive two-dimensional (2-D) self-consistent quantum drift-diffusion (SCQDD) model has been developed by the author to study the static and THz performance of 4H-SiC based CP-DDR source designed to operate at 1.0 THz. Comparative studies on the DC and THz performance of the proposed device and conventionally doped vertical DDR IMPATT device reveal that the proposed CP-DDR can be the potential alternative of the conventional DDRs (C-DDRs), especially at the THz regime. The proposed THz CP-DDR source can be exclusively preferable over its conventional counterparts due to its easier and less complicated fabrication steps as well as equivalent performance capability with respect to the THz C-DDR sources. [ABSTRACT FROM AUTHOR]

Defects can significantly modify the electro-optical characteristics of InGaN light-emitting diodes (LEDs); however, modeling the impact of defects on the electrical characteristics of LEDs is not straightforward. In this paper, we present an extensive investigation and modeling of the impact of defects on the electrical characteristics of InGaN-based LEDs, as a function of the thickness of the quantum well (QW). First, we demonstrate that the density of defects in the active region of III-N LEDs scales with increasing thickness of the InGaN QW. Since device layers with high indium content tend to incorporate more defects, we ascribed this experimental evidence to the increased volume of defects-rich InGaN associated to thicker InGaN layers. Second, we demonstrate that the current–voltage characteristics of the devices are significantly influenced by the presence of defects, especially in the sub turn-on region. Specifically, we show that the electrical characteristics can be effectively modeled in a wide current range (from pA to mA), by considering the existence of trap-assisted tunneling processes. A good correspondence is obtained between the experimental and simulated electrical characteristics (I–V), by using—in the simulation—the actual defect concentrations/activation energies extracted from steady-state photocapacitance, instead of generic fitting parameters. [ABSTRACT FROM AUTHOR]

This work presents an useful tool for constructing the solution of steady-state heat transfer problems, with temperature-dependent thermal conductivity, by means of the solution of Poisson equations. Specifically, it will be presented a procedure for constructing the solution of a nonlinear second-order partial differential equation, subjected to Robin boundary conditions, by means of a sequence whose elements are obtained from the solution of very simple linear partial differential equations, also subjected to Robin boundary conditions. In addition, an a priori upper bound estimate for the solution is presented too. Some examples, involving temperature-dependent thermal conductivity, are presented, illustrating the use of numerical approximations. [ABSTRACT FROM AUTHOR]

Achieving high interface thermal conductance is one of the biggest challenges in the nanoscale heat transport of GaN-based devices such as light emitting diodes (LEDs), and high electron mobility transistors (HEMTs). In this work, we experimentally measured thermal boundary conductance (TBC) at interfaces between GaN and the substrates with AuSn alloy as a commonly-used adhesive layer by time-domain thermoreflectance (TDTR). We find that the TBCs of GaN/Ti/AuSn/Ti/Si, GaN/Ti/AuSn/Ti/SiC, and GaN/Ti/AuSn/Ti/diamond, are 16.5, 14.8, and 13.2 MW·m−2·K−1 at room temperature, respectively. Our measured results show that the TBC of GaN/Ti/AuSn/Ti/SiC interface is inferior to the TBC of pristine GaN/SiC interface, due to the large mismatch of phonon modes between AuSn/Ti and substrates, shown as the difference of Debye temperature of two materials. Overall, we measured the TBC at interface between GaN and thermal conductive substrates, and provided a guideline for designing the interface between GaN and substrate at HEMT from a thermal management point of view. [ABSTRACT FROM AUTHOR]

This work investigates the intrinsic degradation mechanism of InGaN/GaN UVA (320–400 nm) light emitting diodes (LEDs) after swift heavy ion irradiation from the defect aspect using temperature-dependent low frequency noise measurement. The UVA LEDs were exposed to 1423 MeV Ta ions with a fluence of 108–1010 ions cm−2. The optical power decreases and the leakage current increases evidently after irradiation. The defect behaviors were characterized to analyze the degradation mechanism. It is indicated that the ∼0.2 eV energy level defect decreases, and the defect with an energy level of about 0.65 eV increases with the increasing fluence, resulting in device degradation. Combining the defect energy level and the decreased yellow luminescence in the photoluminescence spectrum, the possible defect transform process is the newly created N interstitial atoms fill in the intrinsic VGa and form NGa after irradiation. [ABSTRACT FROM AUTHOR]

In this work, we studied the impact of post-metallization annealing (PMA) on interfacial and bulk dielectric properties of AlSiO/β-Ga2O3 metal–oxide–semiconductor capacitors (MOSCAPs). Annealing at 300 °C improved the reverse operational stability within the test operation range from −10 V to −42 V. The near-interface fast and slow traps were both suppressed by PMA at 300 °C and 350 °C, leading to a negligible flat-band voltage hysteresis. The low gate leakage region was extended from 3.7 MV cm−1 to 4 MV cm−1 and the breakdown strength was improved from 7.8 MV cm−1 to 8.2 MV cm−1 for AlSiO/β-Ga2O3 MOSCAPs with PMA at 300 °C compared with not-annealed samples. The superior operational reliability demonstrated in this work is useful for future high-performance and reliable MOS-based Ga2O3 transistors. [ABSTRACT FROM AUTHOR]

Semiconductors have been used in solar energy conversion for decades based on the photovoltaic effect. An important challenge of photovoltaics is the undesired heat generated within the device. An alternative approach is thermionics, which uses the thermal excitation of electrons from an emitter to a collector across a vacuum gap. If the emitter is a p-type semiconductor, the photogeneration-induced quasi-Fermi level splitting can reduce the effective barrier for electron emission—a mechanism used by a photon enhanced thermionic emission device. Here, we evaluate the prospects of this alternative solar conversion technology considering different semiconductor materials and thermionic device configurations. We also reveal that whether such a device operates in the photon enhanced or purely thermionic mode, depends on the complex interplay among materials properties, device physics and solar concentration level. A semiconductor thermionic device, which utilises thermally excited electrons, is considered as an alternative in solar conversion technology, yet its working mechanism is not clear. Here, the authors reveal that whether such a device operates in the photon enhanced or purely thermionic mode, greatly depends on the material properties and device physics. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of post-deposition annealing (PDA) temperature on H2S gas sensing and low-frequency noise characteristics of In2O3 gas sensors. In2O3 thin-films are deposited using the radio frequency (RF) sputtering method at an RF power of 150 W and post-annealed at various temperatures (200, 300, and 400 °C). The response of the In2O3 gas sensor to H2S decreases with increasing PDA temperature due to the increase of grain size. However, the In2O3 post-annealed at 200 °C shows the largest 1/f noise since the damaged sensing material-substrate interface is not fully recovered by the PDA. The sensors post-annealed at a higher temperature (300 °C and 400 °C) recover the damaged interface. Thanks to its moderate response and noise level, the sensor post-annealed at 300 °C shows the largest signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

Gallium Nitride (GaN) remarkably shows high electron mobility, wide energy band gap, biocompatibility, and chemical stability. Wurtzite structure makes topmost Gallium atoms electropositive, hence high ligand binding ability especially to anions, making it usable as humidity sensor due to water self-ionization phenomenon. In this work, thin-film GaN based humidity sensor is fabricated through pulse modulated DC magnetron sputtering. Interdigitated electrodes (IDEs) with 100 μm width and spacing were inkjet printed on top of GaN sensing layer to further enhance sensor sensitivity. Impedance, capacitance, and current response were recorded for humidity and bio-sensing applications. The sensor shows approximate linear impedance response between 0 and 100% humidity range, the sensitivity of 8.53 nF/RH% and 79 kΩ/RH% for capacitance and impedance, and fast response (Tres) and recovery (Trec) time of 3.5 s and 9 s, respectively. The sensor shows little hysteresis of < 3.53% with stable and wide variations for accurate measurements. Especially, it demonstrates temperature invariance for thermal stability. Experimental results demonstrate fabricated sensor effectively evaluates plant transpiration cycle through water level monitoring by direct attachment onto leaves without causing any damage as well as freshness level of meat loaf. These properties of the proposed sensor make it a suitable candidate for future electronics providing a low-cost platform for real time monitoring applications. [ABSTRACT FROM AUTHOR]

Variable-period oscillations (VPOs) in various optical spectra in sub-bandgap long wavelength region, including reflection, transmission, absorption, and even luminescence spectra, are a frequently observed phenomenon in various semiconducting and dielectric films. These functional films include nitrides, oxides, silicides, sulfides, and perovskites. Although the phenomenon is widely known to be caused by optical interference, a generalized analytical model for it has not yet been established, probably due to both varying oscillation period and amplitude. In this article, we attempt to develop such a model by introducing a new concise dispersion of the sub-bandgap refractive index, i.e. containing a frictional component. In particular, we show that the VPOs in the reflectance and corresponding transmission shall have reverse maxima and minima in intensity, giving a self-consistent explanation to the existing experimental results in literature. Furthermore, the present analytical method is proven to be accurate for finding optical constants and thicknesses of films. Finally, the rationality of the new dispersion is further argued in terms of a generalized refractive index of crystal with lattice anomalies (e.g. defected and strained lattice), which was derived by Gonçalves et al from the fractional Drude–Lorentz model. In addition, the equivalency between the VPOs and Newton's rings in energy space is discussed based on the present model. [ABSTRACT FROM AUTHOR]

In this paper, we give a systematical description of Ni|6H-SiC Schottky diode by current–voltage I(V) characteristics at room temperature and capacitance–voltage C(V) characteristics at various frequencies (10–800 kHz) and various temperatures (77–350 K). The I(V) characteristics show a double-barrier phenomenon, which gives a low and high barrier height ( = 0.91 eV, = 1.55 eV), with a difference of Δϕbn = 0.64 eV. Also, low ideality factor nL = 1.94 and high ideality factor nH = 1.22 are obtained. The C–V–T measurements show that the barrier height ϕbn decreases with decreasing of temperature and gives a temperature coefficient α = 1.0 × 10–3 eV/K and ϕbn (T = 0 K) = 1.32 eV. Deep-level transient spectroscopy (DLTS) has been used to investigate deep levels in the Ni|6H-SiC Schottky diode. The traps signatures such as activation energies Ea = 0.50 ± 0.07 eV, capture cross-section σ = 1.8 × 10–20 cm2, and defect concentration NT = 6.2 × 1013 cm–3 were calculated from Arrhenius plots. [ABSTRACT FROM AUTHOR]