Numerical simulation of spatially nonuniform switching in silicon avalanche sharpening diodes

The process of spatially nonuniform switching in high-voltage silicon diodes operating in the delayed avalanche regime has been numerically simulated. The dependence of the transient process on the ratio between the total diode cross-section area and the area of the region where the switching takes place has been studied. The switching time (60?C70 ps) and qualitative form of the transient characteristic agree with the available experimental data. It is established that a rapid drop of the diode voltage begins after the ionization front has traveled over most of the base and then continues due to secondary avalanche breakdown of the base filled with free carriers. Thus the time of switching to the conducting state exhibits no direct correlation with the velocity of ionization front propagation.     

Addressing a model of multistreamer switching in high-voltage silicon <Emphasis Type="Italic">p-n</Emphasis> junctions above the Zener breakdown threshold

It is shown that a model of multistreamer switching from the blocking to conducting state in high-voltage diode structures cannot consistently explain the phenomenon of ultrafast switching of such silicon structures into the conducting state, which was experimentally observed in the rapid growth of the reverse bias voltage in strong (～1 MV/cm) electric fields.     

Phosphorene/ZnO Nano‐Heterojunctions for Broadband Photonic Nonvolatile Memory Applications

High‐performance photonic nonvolatile memory combining photosensing and data storage with low power consumption ensures the energy efficiency of computer systems. This study first reports in situ derived phosphorene/ZnO hybrid heterojunction nanoparticles and their application in broadband‐response photonic nonvolatile memory. The photonic nonvolatile memory consistently exhibits broadband response from ultraviolet (380 nm) to near infrared (785 nm), with controllable shifts of the SET voltage. The broadband resistive switching is attributed to the enhanced photon harvesting, a fast exciton separation, as well as the formation of an oxygen vacancy filament in the nano‐heterojunction. In addition, the device exhibits an excellent stability under air exposure compared with reported pristine phosphorene‐based nonvolatile memory. The superior antioxidation capacity is believed to originate from the fast transfer of lone‐pair electrons of phosphorene. The unique assembly of phosphorene/ZnO nano‐heterojunctions paves the way toward multifunctional broadband‐response data‐storage techniques.     

A magnetically controlled LED with S-shaped current-voltage characteristic

A p-i-n light-emitting diode (LED) structure with InGaAs/GaAs quantum wells has been manufactured by combining the vapor phase epitaxy and laser ablation methods. The obtained heterostructures exhibit a negative differential resistance and the magnetodiode effect at 77 K. The proposed LED structure admits (i) switching from the low- to high-resistance state by applied pulsed bias voltage and (ii) electroluminescence quenching by external magnetic field.     

A Piezoelectric-Driven Electrochromic/Electrofluorochromic Dual-Modal Display Device

Electrochromic (EC) reflective displays offer great advantages in delivering information and providing visual data, but are limited in dark environments. Reflective/emissive dual-modal displays capable of electrochemically-induced color and fluorescence change simultaneously are highly desirable, especially possessing rapid response speed as well as long-term durability. Herein, an electroactive fluorescent ionic liquid based on triphenylamine and imidazole (EFIL-TPA) has been synthesized for reflective/emissive dual-modal display. The resultant device exhibits outstanding electrochromic/electrofluorochromic (EC/EFC) performance with low driving voltage (below 1.0 V), fast switching speed (0.57–1.8 s), and remarkable cycling durability (91% retention for 10 000 cycles). A piezoelectric nanogenerator (PENG) driven EC/EFC integrated system is fabricated to harvest energy from human motion and visually drive the color/fluorescence change for human motion indication in both bright and dark environments. This innovative EC/EFC dual-modal display device based on EFIL-TPA supports a huge space for the development of self-powered human motion visualized indication in all-light conditions.     

Molecularly inherent voltage-controlled conductance switching

Molecular electronics has been proposed as a pathway for high-density nanoelectronic devices. This pathway involves the development of a molecular memory device based on reversible switching of a molecule between two conducting states in response to a trigger, such as an applied voltage. Here we demonstrate that voltage-triggered switching is indeed a molecular phenomenon by carrying out studies on the same molecule using three different experimental configurations-scanning tunnelling microscopy, crossed-wire junction, and magnetic-bead junction. We also demonstrate that voltage-triggered switching is distinctly different from stochastic switching, essentially a transient (time-dependent) phenomenon that is independent of the applied voltage.     

Fabrication of Al/MgO/C and C/MgO/InSe/C tunneling barriers for tunable negative resistance and negative capacitance applications

In this work, the design and characterization of magnesium oxide based tunneling diodes which are produced on Al and InSe films as rectifying substrates are investigated. It was found that when Al thin films are used, the device exhibit tunneling diode behavior of sharp valley at 0.15 V and peak to valley current ratio (PVCR) of 11.4. In addition, the capacitance spectra of the Al/MgO/C device show a resonance peak of negative capacitance (NC) values at 44.7 MHz. The capacitance and resistance–voltage characteristics handled at an ac signal frequency of 100 MHz reflected a build in voltage (V_bi) of 1.29 V and a negative resistance (NR) effect above 2.05 V. This device quality factor (Q)–voltage response is ~10⁴. When the Al substrate is replaced by InSe thin film, the tunneling diode valley appeared at 1.1 V. In addition, the PVCR, NR range, NC resonance peak, Q and V_bi are found to be 135, 0.94–2.24 and 39.0 MHz, ~10⁵ and 1.34 V, respectively. Due to the wide differential negative resistance and capacitance voltage ranges and due to the response of the C/MgO/InSe/C device at 1.0 GHz, these devices appear to be suitable for applications as frequency mixers, amplifiers, and monostable–bistable circuit elements (MOBILE).     

Ultrafast current switching using the tunneling-assisted impact ionization front in a silicon semiconductor closing switch

Ultrafast current switching in semiconductors, based on the mechanism of tunneling-assisted impact ionization front, has been experimentally implemented and theoretically studied. A voltage pulse with an amplitude of 220 kV and a front duration of 1 ns was applied to a semiconductor device containing 20 serially connected silicon diode structures. After switching, 150-to 160-kV pulses with a power of 500 MW, a pulse duration of 1.4 ns, and a front duration of 200–250 ps were obtained in a 50-Ω transmission line. The maximum current and voltage buildup rates amounted to 10 kA/ns and 500 kV/ns, respectively, at a switched current density of 13 kA/cm². The results of numerical simulation are presented, which show that the current switching is initiated at a threshold field strength of about 1 MV/cm in the vicinity of the p-n junction, where the tunneling-assisted impact ionization begins.     

ZVT interleaved boost converters for high-efficiency, high step-up DC-DC conversion

The narrow turn-off period of the conventional boost converters limits their applications in high step-up DC-DC conversion. The voltage gain is extended without an extreme duty-cycle by the winding-coupled inductor structure. However, the leakage inductance induces large voltage spikes when the switch turns off. An active-clamp circuit is introduced here to clamp the switch turn-off voltage spikes effectively and to recycle the leakage energy. Both the main switches and the auxiliary switches are ZVT during the whole switching transition. Meanwhile, the output diode reverse-recovery problem is alleviated because the leakage inductance of the coupled inductors is in series with the output diode. Furthermore, a family of ZVT interleaved boost converters for high efficiency and high step-up DC-DC conversion is deduced. The experimental results based on 40-380 V front-end applications verify the significant improvements in efficiency     

Device based on the coupling of an organic light-emitting diode with a photoconductive material

We have realized a device based on the coupling of an organic light-emitting diode (with tri(8-hydroxyquinoline)aluminium for light emission) as an input unit with a photoconductive material as an output unit. Various photoconductive materials like pentacene, Cu-phtalocyanine and fullerene were investigated under green light illumination with an emission peak at 550 nm. Photocurrent measurements versus light intensity and bias voltage (applied between two 50 μm distant indium-tin oxide bottom electrodes for the current to flow through the materials) were realized at room temperature a photocurrent gain around 4 is obtained when the materials are subjected to a luminance of about 5000 cd/m² and for bias voltage of − 50 V. Besides, it was shown that to obtain a device with a fast photocurrent response by switching the light off and on, it is necessary to apply a bias voltage higher than − 200 V in these conditions, the gain is multiplied by a factor of 3.     

Subnanosecond avalanche switching in high-voltage silicon diodes with abrupt and graded p-n junctions

The phenomenon of delayed avalanche breakdown in high-voltage silicon diodes has been studied for the first time using an experimental setup with specially designed resistive coupler as a part of a high-quality matched measuring tract. Three types of diode structures with identical geometric parameters and close stationary breakdown voltages within 1.1–1.3 kV have been studied, including p ⁺-n-n ⁺ structures with abrupt p-n junctions and two different p ⁺-p-n-n ⁺ structures with graded p-n junctions. Upon switching of all structures, a voltage step with an amplitude above 1 kV and a rise time of ～100 ps at a breakdown voltage of about 2 kV is formed in the load. However, switching to a state with low (～150 V) residual voltage has been observed only in the structures with an abrupt p-n junction, while the voltage in structures with graded junctions only decreased to a level of ～1 kV, which is close to the stationary breakdown voltage.     

Enhancing the photovoltaic effect in the infrared region by germanium quantum dots inserted in the intrinsic region of a silicon p-i-n diode with nanostructure

We show that a strong photovoltaic response in the infrared region of the solar spectrum (1.1–1.4 μm wavelength) is obtained by inserting a multilayer structure of germanium quantum dots and silicon spacer layers into the intrinsic region of a silicon p-i-n diode. The multilayer structure (active layer) is deposited on an n-type silicon wafer using the technique of ultra-high vacuum chemical vapor deposition. Reflection high-energy electron diffraction has been used to in situ monitor the transition from the two-dimensional to three-dimensional growth mode of germanium on silicon. The p-type layer of the diode is formed in situ by doping a layer of silicon with boron. Prototype solar cells have been fabricated in situ to measure the energy conversion efficiency. Photoluminescence spectroscopy has been used to probe the presence of any defect-related energy levels within the band gap, and the quality of the diode is determined from measurement of dark current. Scanning electron microscopy, atomic force microscopy, and transmission/scanning transmission electron microscopy have been used to characterize the structure of the active layer. It is demonstrated that by optimizing the structure of the active layer to minimize recombination of charge carriers in the quantum dots, a short-circuit current of 24 mA/cm² and an open-circuit voltage of 0.6 V could be achieved leading to an energy conversion efficiency of about 11.5% corresponding to an active layer with a thickness of 300 nm.     

A Pt/Ga/sub 2/O/sub 3/-ZnO/SiC Schottky diode-based hydrocarbon gas sensor

In this paper, a novel metal-reactive insulator-silicon carbide device with a catalytic layer for hydrocarbon gas-sensing is presented. This structure, employed as a Schottky diode, utilizes sol-gel prepared Ga/sub 2/O/sub 3/-ZnO layer as the reactive insulator. The sensor has been exposed to propene gas, which lowers the barrier height of the diode. The responses were stable and repeatable at operating temperatures between 300 and 600/spl deg/C. The response to propene in different ambients was examined. The effect of diode bias has been investigated by analyzing the sensors response to various propene concentrations when held at constant currents of 2 and 8 mA.     

Parameters of silicon carbide diode avalanche shapers for the picosecond range

Parameters of ultrafast avalanche switching of high-voltage diode structures based on 4H-SiC have been estimated theoretically. The calculation was carried out using the analytical theory of the impact ionization wave of the TRAPATT type, which makes it possible to determine the main characteristics of a wave for arbitrary dependences of the impact ionization coefficients and carrier drift velocity on electric field. It is shown that, for a high-voltage (1–10 kV) 4H-SiC structure, the time of switching from the blocking to the conducting state is ~10 ps, which is an order of magnitude shorter than that for a Si structure with the same stationary breakdown voltage, and the concentration of the electron-hole plasma created by the wave is two orders of magnitude higher. Picosecond switching times can be reached for 4H-SiC structures with a stationary breakdown voltage exceeding 10 kV.     

Ultralow voltage resonant tunnelling diode electroabsorption modulator

Embedding a double barrier resonant tunnelling diode (RTD) in a unipolar InGaAlAs optical waveguide gives rise to a very low driving voltage electroabsorption modulator (EAM) at optical wavelengths around 1550 nm. The presence of the RTD within the waveguide core introduces high non-linearity and negative differential resistance in the current-voltage (I-V) characteristic of the waveguide. This makes the electric field distribution across the waveguide core strongly dependent on the bias voltage: when the current decreases from the peak to the valley, there is an increase of the electric field across the depleted core. The electric field enhancement in the core-depleted layer causes the Franz-Keldysh absorption band-edge to red shift, which is responsible for the electroabsorption effect. High-frequency ac signals as low as 100 mV can induce electric field high-speed switching, producing substantial light modulation (up to 15 dB) at photon energies slightly lower than the waveguide core band-gap energy. The key difference between this device and conventional p-i-n EAMs is that the tunnelling characteristics of the RTD are employed to switch the electric field across the core-depleted region; the RTD-EAM has in essence an integrated electronic amplifier and, therefore, requires considerably less switching power.     

Concepts for diamond electronics

The present status in the development of diamond as electronic semiconductor material with wide band-gap (5.45 eV) is reviewed. Since diamond cannot be doped with shallow impurities, specific doping concepts and related diode and FET structures had to be developed, restricted to p-type boron doping. The results allow to predict that diamond high voltage switching diodes, high power RF FET sources and operation at high temperature will surpass the capability of devices designed in competing wide band-gap materials like SiC and GaN.     

Rapid thermal annealing of Ti Schottky contacts ton-GaAs

Ti Schottky contacts were formed onn-GaAs surfaces and were subjected to rapid thermal annealing (RTA) at various temperatures. Low temperature RTA (<500 °C) results in a reduction in the diode leakage currents and increase in the barrier voltage. High temperature RTA (>500 °C) results in progressive degradation of the diode parameters. The improvement in diode parameters is expected to be due to better adhesion of Ti Schottky contact resulting in a more intimate contact of the Schottky metal to the GaAs substrate.     

High-voltage GaAs diodes with subnanosecond gate voltage recovery

High-voltage GaAs switching diodes with subnanosecond characteristic times of reverse current decay on switching from forward to reverse bias were studied. The diode structures studied had impurity concentration profiles in the base region close to those of the charge-storage diodes and operated in the regimes corresponding to those employed in silicon-based high-voltage fast-recovery drift diodes. The application prospects of the proposed GaAs diodes are demonstrated, for example, in the devices generating pulses with a front width of several hundred picoseconds, a current of several hundred amperes, and a voltage of a several kiloelectronvolts at a frequency of up to several hundred kilohertz.     

Effects of dielectric thickness and contact area on current-voltage characteristics of thin film metal-insulator-metal diodes

Planar asymmetric Ni-NiO-Cr/Au thin film Metal-Insulator-Metal (MIM) tunnel diodes were fabricated for use in an ultra-sensitive infrared detector operating at room temperature. MIM diodes with contact areas of 100 μm² and 1 μm² were fabricated using standard Micro-Electro Mechanical Systems techniques. A linear relationship between the thickness of reactively sputtered Nickel Oxide (NiO) and the breakdown voltage was experimentally determined, and the diode performance was verified using a theoretical approach. Current-Voltage measurements of the MIM diode revealed an increase in the current from 1.5 nA to 0.8 mA, when the thickness of the dielectric and the contact area of the detector decreased. Also, the rectification ratios of the detectors were determined, exhibiting an asymmetry of 4.5 at 1 V and 6 at 0.2 V for detectors A and B, respectively. Further, the ratio was observed to be increasing with bias voltage suggesting a strong asymmetric behavior. The results are in agreement with the theoretical predictions confirming conduction via tunneling. The nonlinearity and asymmetry exhibited by these diodes suggests their viability in infrared applications.     

Electrohydrodynamic atomization approach to graphene/zinc oxide film fabrication for application in electronic devices

Graphene-based composites represent a new class of materials with potential for many applications. Metal, semiconductor, or any polymer properties can be tuned by attaching it to graphene. Here, a new route for fabrication of graphene based composites thin films has been explored. Graphene flakes (<4 layers) and a well-known semiconductor zinc oxide (ZnO) (<50 nm particle size) have been dispersed in N-methylpyrrolidone and ethanol, respectively. Thin film of graphene flakes is deposited and decorated with ZnO nanoparticles to fabricate graphene/ZnO composite thin film on silicon substrate by electro hydrodynamic atomization technique. Graphene/ZnO composite thin film has been characterized morphologically, structurally and chemically. To investigate electronic behavior of the composite thin film, it is deployed as cathode in a diode device i.e. indium tin oxide/poly (3,4-ethylenedioxythiophene) poly (styrenesulfonate)/polydioctylfluorene-benzothiadiazole/(graphene/ZnO). The J–V analysis of diode device has shown that at voltage of 1 V, the current density in organic structure is at low value of 4.69 × 10^?3 A/cm² and when voltage applied voltage is further increased; the device current density has increased by the order of 200 that is 1.034 A/cm² at voltage of 12 V.