Diode Breakdown Research Articles

Avoiding avalanche breakdown in planar GaN Gunn diodes by means of a substrate contact

Abstract Impact ionization originated by the buffer leakage current, together with high electric fields ( > 3 MV cm−1) at the anode corner of the isolating trenches, has been identified as the failure mechanism of shaped planar GaN Gunn diodes when biased above 20 V, so that no evidence of Gunn oscillations in fabricated devices has been observed yet. In order to avoid the avalanche, we propose the addition of a Schottky substrate terminal, which, by means of Monte Carlo simulations, has been confirmed to be able to suppress such not-desired leakage current when applying a negative substrate bias. When the substrate bias is positive, impact ionization is also reduced due to the lower electric field at the hotspot, but a vertical cathode-substrate current degrades the device operation. In order to avoid such current, we propose the use a MIS configuration for the substrate contact, which is the optimal solution.

Performance limiting inhomogeneities of defect states in ampere-class Ga2O3 power diodes

Impacts of spatial charge inhomogeneities on carrier transport fluctuations and premature breakdown were investigated in Schottky ampere-class Ga2O3 power diodes. Three prominent electron traps were detected in Ga2O3 epilayers by a combination of the depth-resolved capacitance spectroscopy profiling and gradual dry etching. The near-surface trap occurring at 1.06 eV below the conduction band minimum (EC), named E3, was found to be confined within a 180 nm surface region of the Ga2O3 epilayers. Two bulk traps at EC − 0.75 eV (E2*) and at EC − 0.82 eV (E2) were identified and interconnected with the VGa- and FeGa-type defects, respectively. In the framework of the impact ionization model, employing the experimental trap parameters, the TCAD simulated breakdown characteristics matched the experimental breakdown properties well, consistently with inverse proportionality to the total trap densities. In particular, the shallowest distributed E3 trap with the deepest level is responsible for higher leakage and premature breakdown. In contrast, Ga2O3 Schottky diodes without E3 trap exhibit enhanced breakdown voltages, and the leakage mechanism evolves from variable range hopping at medium reverse voltages, to the space-charge-limited conduction at high reverse biases. This work bridges the fundamental gap between spatial charge inhomogeneities and diode breakdown features, paving the way for more reliable defect engineering in high-performance Ga2O3 power devices.

Drain-Induced Multifunctional Ambipolar Electronics Based on Junctionless MoS2.

Applying a drain bias to a strongly gate-coupled semiconductor influences the carrier density of the channel. However, practical applications of this drain-bias-induced effect in the advancement of switching electronics have remained elusive due to the limited capabilities of its current modulation known to date. Here, we show strategies to largely control the current by utilizing drain-bias-induced carrier type switching in an ambipolar molybdenum disulfide (MoS2) field-effect transistor with Pt bottom contacts. Our CMOS-compatible device architecture, incorporating a partially gate-coupled p-n junction, achieves multifunctionality. The ambipolar MoS2 device operates as an ambipolar transistor (on/off ratios exceeding 107 for both NMOS and PMOS), a rectifier (rectification ratio of ∼3 × 106), a reversible negative breakdown diode with an adjustable breakdown voltage (on/off ratio exceeding 109 with a maximum current as high as 10-4 A), and a photodetector. Finally, we demonstrate a complementary inverter (gain of ∼24 at Vdd = 1.5 V), which is highly facile to fabricate without the need for complex heterostructures and doping processes. Our study provides strategies to achieve high-performance ambipolar MoS2 devices and to effectively utilize drain bias for electrical switching.

Improved electrical performance of InAlN/GaN high electron mobility transistors with forming gas annealing

The surface electronic states and defects of gallium nitride based high-electron-mobility transistors (HEMTs) play a critical role affecting channel electron density, electron mobility, leakage current, radio frequency (RF) power output and power added efficiency of devices. This article demonstrates the improved surface properties of InAlN/GaN HEMTs through forming gas (FG) annealing, resulting in a significantly improved electrical properties. The X-ray photoelectron spectra reveals a reduction of surface native oxide after FG H2/N2 annealing whereby the amount of Ga–O bonds is decreased. Compared with N2 annealing, an on-resistance of 1.68 Ω·mm, a subthreshold swing of 118 mV/dec, a transconductance peak of 513 mS/mm, a gate diode breakdown voltage of surpassing 42 V, and a high current/power gain cutoff frequency (fT/fmax) of 165/165 GHz are achieved by the 50-nm InAlN/GaN HEMT on Si substrate.

Subnanosecond switching of GaAs diode due to impact ionization in collapsing bipolar Gunn domains

Subnanosecond switching of high-voltage GaAs diodes initiated by a steep reverse voltage ramp (≥1 kV/ns) is investigated experimentally and numerically. The triggering occurs at the voltage Um which exceeds stationary breakdown voltage Ub, similar to delayed impact ionization breakdown in Si picosecond-range high-voltage diodes known as silicon avalanche sharpening (SAS) diodes. Despite this similarity, we argue that the triggering mechanism of GaAs diodes is qualitatively different and is based on negative differential electron mobility in GaAs. Spatial patterns of recombination emission indicate formation of narrow conducting channels. Numerical simulations reveal the spontaneous appearance of high-field (∼400 kV/cm) bipolar Gunn domains in these channels. The agreement of experiments and simulations demonstrates that impact ionization within collapsing Gunn domains is responsible for a rapid increase of nonequilibrium carrier concentration and subnanosecond switching of the reversely biased GaAs diode to the conducting state with low (<100 V) residual voltage. In particular, the proposed mechanism explains why GaAs diodes exhibit subnanosecond switching at moderate overvoltage ratio Um/Ub ≈ 1.5 smaller than typical overvoltage Um/Ub ≈ 2 required for switching Si diodes, and the origin of anomalous delay of several nanoseconds that is experimentally observed in such regimes.

A Deep Learning-Monte Carlo Combined Prediction of Side-Effect Impact Ionization in Highly Doped GaN Diodes

The existence of leakage current pathways leading to the appearance of impact ionization and the potential device breakdown in planar Gunn GaN diodes is analyzed by means of a combined Monte Carlo (MC)-deep learning approach. Front-view (lateral) MC simulations of the devices show the appearance of a high-field hotspot at the anode corner of the etched region, just at the boundaries between the dielectric, the GaN-doped layer, and the buffer. Thus, if the isolation created by the etched trenches is not complete, a relevant hot carrier population within the buffer is observed at sufficiently high applied voltages, provoking the appearance of a very significant number of impact ionizations and the consequent avalanche process before the onset of Gunn oscillations. A neural network trained from MC simulations allows predicting with extremely good precision the breakdown voltage of the diodes depending on the doping of the GaN active layer, the permittivity of the isolating dielectric, and the lattice temperature. Low doping, high temperature, and high permittivity provide larger operational voltages, which implies a tradeoff with the conditions required to achieve terahertz (THz) Gunn oscillations at low voltages.

Interface engineering of p-type quaternary metal oxide semiconductor interlayer-embedded β-Ga2O3 Schottky barrier diode

Here, we propose a p-type copper aluminum oxide (p-CuAlO2) interlayer for the high breakdown and low leakage current of β-Ga2O3 Schottky barrier diodes (SBDs). The XPS and TEM analysis was employed to confirm the surface elemental compositions, chemical states, and microstructural properties of RF sputtered p-CuAlO2 thin films on β-Ga2O3. The electrical and carrier transport properties of Pt/β-Ga2O3 SBD and Pt/p-CuAlO2/β-Ga2O3 heterojunction (HJ) were studied by using current-voltage (I–V) and capacitance-voltage (C–V) measurements. In comparison to the SBD, the HJ displayed superior rectifying behavior, lower reverse leakage current, lower on-resistance, and a larger turn-on voltage. Higher barrier height (BH) was attained for the HJ compared to the SBD, which enabled the p-CuAlO2 interlayer to alter the barrier height. The reverse breakdown voltage of HJ increased by nearly 300 V compared to SBD and reached a maximum of 922 V. The BH values were extracted from the I–V, Hernandez, Cheung's, Mikhelashvili, Norde's, Chot, and surface potential methods found the values are comparable with one another, which indicates their steadiness and validity. The energy distribution profile of the interface state density (NSS) of the HJ decreases compared to the SBD, which indicates that the p-CuAlO2 interlayer facilitated the reduction of NSS of the Pt/β-Ga2O3 SBD interface. The forward log(I)-log(V) plot of the SBD and HJ reveals the ohmic nature at low voltage regions and space-charge limited conduction at higher voltage regions. Results reveal that the reverse leakage current conduction mechanism of the SBD and HJ showed that the Poole-Frenkel conduction mechanism is found to be governed in the lower voltage region, whereas the Schottky conduction mechanism is found to be directed in the higher voltage region, respectively. These outcomes point out that the p-CuAlO2 is a high potential candidate material for forming a heterojunction with β-Ga2O3.

Transients in solar photovoltaic systems during lightning strikes to a transmission line

With the rapid growth of solar energy generation, lightning hazards to photovoltaic (PV) plants have received attention increasingly. Many PV plants are built in the transmission corridor, leading to an increased occurrence of lightning damages. These damages are caused by lightning strikes to the transmission line nearby, which have not been well addressed in the literature. This paper investigates the transient behaviors of a practical PV plant when a nearby transmission line is struck by lightning. Three types of lightning damages are investigated, namely failure of PV inverters, breakdown of bypass diodes, and arcing between metallic parts. Both bypass diode breakdown and arcing-related incidents in the PV systems have not been analyzed systemically in the literature. In this paper, the numerical results of lightning transients are presented. The simulated induced voltage is consistent with the observed result in the practical plant. Several protection measures against lightning to the PV systems are proposed to achieve better protection performance.

PIC-MCC Investigation on the Influences of Gas Medium and Flashover on the Multipacting Cathode Operation

In this article, the influences of outgassing and flashover on the performance of a novel multipacting cathode are numerically investigated by using particle in cell-Monte Carlo collision (PIC-MCC) method, including the conditions of weak, medium, and strong outgassing. The numerical results demonstrate that under the condition of weak outgassing (0.1 Torr), multipacting is hardly influenced by gas ionization. Multipacting dominates the entire physical process. Due to the further improved output current by additional electrons generated from ionization, the weak outgassing can help cathode performance enhancement. Under the condition of medium outgassing (1 Torr), gas ionization first boosts multipacting developing and then tends to suppress multipacting process. During the initial stage, multipacting dominates the entire physical process. When multipacting tends to saturate, gas ionization will dominate the whole physical process. The rapidly increased output current will finally decrease gap voltage and induce the diode breakdown. Under the condition of strong outgassing (1 atm), multipacting is suppressed by gas ionization from beginning to end. Gas ionization dominates the whole physical process all the time. The strong effect of ionization collision will finally induce streamer discharge and diode breakdown.

TCAD Investigation of Differently Doped DLC Passivation for Large-Area High-Power Diodes

An electroactive passivation for high-voltage diodes with bevel termination has been investigated based on diamondlike carbon (DLC) films. Variations of the DLC properties, i.e., conductivity and geometry, have been investigated by experiments and numerical simulations to the purpose of gaining an insight on their influence on the diode leakage current and breakdown voltage. The role played by the DLC/Si interface has been investigated by characterizing metal–DLC–Si devices. Both boron and nitrogen doping have been investigated, and a TCAD setup has been provided accounting for the main transport features of the DLC material with different doping configurations. A significant polarization effect has been observed in the DLC material, which improves the DLC performance as a passivation material. High-voltage diodes have been characterized and simulated with different DLC layers on top of the bevel termination in order to identify the role played by conductivity and polarization on the blocking state. The correlation of leakage current and voltage breakdown with the DLC doping and thickness is provided and explained by the TCAD simulation results.

Influence of the DLC Passivation Conductivity on the Performance of Silicon High-Power Diodes Over an Extended Temperature Range

The diamond-like carbon (DLC) is important for passivation of junction termination in high power devices due to its excellent electrical, mechanical, and thermal properties. While the role of conductivity and polarization of the DLC layer on the blocking capability of a p-n junction has been explained recently, the thermal behavior still needs to be addressed. For this purpose, the diode leakage current was measured on large area power diodes with negative bevel coated by the DLC in a typical industrial range between 300 and 413 K. An unusual deviation from the expected Arrhenius law was experimentally observed. A predictive TCAD model, which incorporates the effect of the DLC layer, has been developed to study the impact of the DLC layer parameters on diode thermal performance. Both the electrostatic features and charge transport mechanisms through and along the DLC/Silicon interface have been modeled over a wide range of temperatures. Different DLC/Silicon doping combinations have been analyzed to explain the main effects determining the temperature dependence of diode leakage current and breakdown voltage. A complete validation of the TCAD approach has been achieved.

Simple Adaptive Rectifier with High Efficiency over a Range of 21 dBm Input Power for RF Energy Harvesting Applications

This paper presents a novel simple adaptive and efficient rectifier for Radio Frequency (RF) energy harvesting applications. Traditional rectifiers have maximum RF-DC Power Conversion Efficiency (PCE) over a narrow range of RF input power due to diode breakdown voltage restrictions. The proposed adaptive design helps to extend the PCE over a wider range of RF input power at 2.45GHz using a simple design. Two alternative paths arecontrolled depending on the RF input power level. Low input power levels activate the first path connected to a single rectifier; low power levels make the diode operate below its breakdown voltage and therefore avoiding PCE degradation. High input power levels activate the second path dividing it into three rectifiers. This keeps input power at each rectifier at a low power level to avoid exceeding the diode break down voltage. Simulated PCE of this work is kept above 50% over a range of 21.4 dBm input power from -0.8dBm to 20.6dBm.

Self-Adaptive Rectenna with High Efficiency over a Wide Dynamic Range for RF Energy Harvesting Applications

This paper presents a novel simple adaptive and efficient rectenna with automatic power distribution to achieve high radio frequency-direct current (RF-DC) power conversion efficiency (PCE) over a wide range of RF input power. This design employs two rectifier paths operating at low and high-power levels, respectively. Automatic power distribution method exploits the power-dependent input impedance of the rectifier and routes the RF input power into the assigned path according to the input power level. A distinctive enhancement in the rectifier dynamic range is achieved when dividing the high path power equally into two or more parallel diode cells, which helps the high path to camouflage the diode breakdown voltage in case of high input power level. The proposed adaptive design applies two different rectifier topologies, one by using shunt diode topology and the other by using voltage doubler topology at 2.45 GHz. Simulated PCE of this work is kept above 50% over a range of 25.1 dBm from -5.7 to 19.4 dBm of RF input power using shunt diode topology and over a range of 30 dBm from -6.3 to 23.7 dBm of RF input power using voltage doubler topology.

Diagnostic Devices for Remote Controller of Synchronous Machines

In this paper, the prerequisites of creating a device for diagnosing the breakdown of the rectifier diodes and discharge thyristor of the brushless exciter of the synchronous machine without the need for its disassembly are considered. The processes occurring in the exciter and its rotating rectifier are analyzed. Requirements for the system of diagnosis of the exciter are formulated. The results of laboratory experiments performed are shown, the possibility of providing diagnostics (detection of breakdown) of rotary elements of the exciter (diodes, discharging thyristors) before starting the machine by applying a 220 V 50 Hz voltage to the exciter’ excitation winding are shown. It is shown that the damage of the exciter elements located on the rotor can be detected by analyzing the EMF of the excitation winding of the exciter, for which it must be powered from a source with high output resistance (a gyrator with the active elements was used in the experiment). An electrical circuit diagram of a system for diagnosing the elements of the exciter located on the rotor, which is made on the basis of a single-crystal microcontroller and allows to detect the breakdown of the diodes of the rotary rectifier or the discharge circuit on the stopped machine (before starting). In addition, during machine startup, the proposed system captures the firing voltage of the discharge circuit, and during operation – measures the voltage at the output of the rotary rectifier. The data transmission from the exciter rotor, on which the proposed system is installed, is carried out by the use of an air transformer by the method of back-scattering

In situ thermal runaway of Si-based press-fit diodes monitored by infrared thermography

Overvoltage is one of the main causes that lead to the failure of electronic devices. This makes fundamental to understand the electrical and thermal mechanisms engaged in the process. In this work, the influence of the semiconductor technology on the thermal runaway involved in the dielectric breakdown of commercial press-fit diodes, operating in reverse conditions, has been studied. Infrared thermography has been used to monitor the temperature evolution before, during and after the failure. Schottky and Metal oxide semiconductor devices, based on Si, have been evaluated following this methodology. The current flowing through the diode causes its temperature to rise, which increases the current with a further increase in temperature that triggers the avalanche process. The diode configuration conditions the heating associated with the spark appearing during the breakdown. This process is faster for Schottky diodes than for Metal oxide semiconductors, leading to higher temperatures. Besides, mechanical breaking is observed in the semiconductor due to the stresses generated during the fast heating-cooling processes after the different breakdowns events. The reached temperatures are enough to melt the solder that creates an electrical path, which short-circuits the diodes and leads to their final failure. These differences in the failure behavior must be taken into account to choose the adequate technology in practical applications.

On the Role of Interface States in AlGaN/GaN Schottky Recessed Diodes: Physical Insights, Performance Tradeoff, and Engineering Guidelines

In this paper, the impact of donor and acceptor states at the Schottky interface of fully recessed AlGaN/GaN Schottky diode is physically modeled using device TCAD and detailed experiments. This allowed us to develop physical insights into recessed AlGaN/GaN diode's reverse breakdown, reverse leakage, and ON-state performance as a function of interface states and provided design guidelines to engineer fully recessed AlGaN/GaN Schottky diode for the maximum reverse breakdown and least reverse leakage without compromising its ON-state performance. It has been observed that donor states are responsible for high reverse leakage and reduced breakdown performance in Schottky diodes. On the other hand, the presence of acceptor states at the interface improves the diode leakage and breakdown voltage. Experiments involve a number of dry and wet surface treatments to: 1) validate computational findings and 2) find ways to cure or passivate donor states affected Schottky interface/recessed region. The introduction of acceptor traps at the Schottky interface has been proposed and experimentally verified using the Fluorine implant to cure donor state-affected Schottky interface, which improves the breakdown and reverse leakage characteristics significantly.

BMAG interlock troubleshooting of Varian clinac IX linear accelerator

Through the analysis of 3 maintenance of Bmag interlocking fault of Varian Clinac IX Linear Accelerator, it is found that the full wave rectifier diode breakdown in the bend magnet power supply, the improper setting of the bend magnet interlock, and the failure of the modulator CB3 air switch can cause the bmag interlocking. Through the replacement of accessories, adjustment parameters, etc., so that the fault is resolved. Key words: Linear accelerator; Bend magnet power; Current alarm; Voltage alarm

Effect of cathode and anode materials on the high-energy electron beam in the nanosecond-pulse breakdown in gas-filled diodes

High-energy electron beam can be generated during the breakdown process in a gas diode at elevated pressures. The design of electrodes in the gas diode affects the parameters of these electron beams. In this paper, investigation on parameters of the runaway electron beam (REB) in air and nitrogen excited by nanosecond pulsed generators are presented. Experiments were carried out with gas diodes by using cathode and anode made of different materials, including stainless steel, aluminum, copper and titanium. Experimental results show that, in the case of nanosecond-pulse breakdown, the cathode material significantly affects the amplitude of the REB current pulse when either pressure or gap spacing are small. When the pressure is low, the REB current is highest for the stainless steel cathode due to its small electron work function. However, the REB current for the aluminum, copper and titanium cathodes is higher than that of stainless steel cathode at atmospheric pressure because of the Malter effect on their surfaces. The dependence of the amplitude of the REB current on the anode foils is investigated by using aluminum, titanium, copper and tantalum. The experimental results show that the atomic number of the metal, as well as mass mean free path of the electron in it contribute to the amplitude of the REB current pulse. Based on the REB currents of different anode foils, energy distribution of runaway electrons is estimated. Electron distribution with an average energy of ~55 keV is obtained when the amplitude of the applied voltage pulse across the discharge gap is 110 kV. The results may contribute to the design of the gas diode for the generation of high-energy electron beams in nanosecond-pulse breakdown.

Enhanced radio frequency rectifier with a power splitting/combining topology for wireless energy transfer and harvesting

Power splitting of the input radio frequency (RF) signal is used to improve the efficient power range of a RF rectifier. Direct current (dc) power at the output of every rectifying branch is then combined over a resistive load and thus resulting in a single dc output. The enhancement in efficient power range, over which the power conversion efficiency (PCE) remains ≥ 50%, is determined to be 2.8 dB. The article starts by a theoretical analysis that addresses the negative effects of the diode's breakdown voltage, formulates an equation that predicts the maximum output dc voltage at saturation, and introduces a method that can improve the PCE of a typical shunt-type diode rectifier at low power levels. As a result, a rectifying system is designed and tested as a proof of concept. The proposed circuit, with the enhanced power range, is designed to operate within the power span from -10 dBm up until 10 dBm. Such system is suitable for operation in RF wireless energy transfer and energy harvesting applications.

Demonstration of a 9 kV reverse breakdown and 59 mΩ-cm2 specific on-resistance AlGaN/GaN Schottky barrier diode

Al0.26Ga0.74N/GaN on SiC lateral Schottky diodes were fabricated with variable anode-to-cathode spacing and were analyzed for blocking and on-state device performance. On-chip normally-on High Electron Mobility Transistor (HEMT) structures were also fabricated for a comparison of blocking characteristics. The Schottky diode displayed an ideality factor of 1.59 with a Ni/AlGaN zero bias barrier height of 1.18 eV and a flat band barrier height of 1.59 eV. For anode-to-cathode spacings between 10 and 100 μm, an increase in median breakdown voltages from 529 V to 8519 V and median specific on-resistance (Ron-sp) from 1.5 to 60.7 mΩ cm2 was observed with an increase in spacing. The highest performing diode had a lateral figure of merit of 1.37 GW/cm2 corresponding to a breakdown voltage upwards of 9 kV and a Ron-sp of 59 mΩ cm2. This corresponds to the highest Schottky diode breakdown voltage reported thus far with an Al0.26Ga0.74N/GaN lateral structure.