Current-induced Degradation Research Articles

Ultrafast, room temperature rejuvenation of SiC Schottky diodes from forward current-induced degradation

In this work, we demonstrate the rejuvenation of Ti/4H-SiC Schottky barrier diodes after forward current-induced degradation, at room temperature and in a few seconds, by exploiting the physics of high-energy electron interactions with defects. The diodes were intentionally degraded to a 42% decrease in forward current and a 9% increase in leakage current through accelerated electrical stressing. The key feature of our proposed rejuvenation process is very high current density electrical pulsing with low frequency and duty cycle to suppress any temperature rise. The primary stimulus is, therefore, the electron wind force, which is derived from the loss of the momentum of the high energy electrons upon collision with the defects. Such defect-specific or “just in location” mobilization of atoms allows a significant decrease in defect concentration, which is not possible with conventional thermal annealing that requires higher temperatures and longer times. We show evidence of rejuvenation with additional improvement in leakage current (16%) and forward current (38%) beyond the pristine condition. Transmission electron microscopy, geometric phase analysis, Raman spectroscopy, and energy dispersive x-ray-spectroscopy reveal the enhancement of defects and interfaces. The ultrafast and room temperature process has the potential for rejuvenating electronic devices operating in high power and harsh environmental conditions.

Self-Healing Ability of Perovskites Observed via Photoluminescence Response on Nanoscale Local Forces and Mechanical Damage.

The photoluminescence (PL) of metal halide perovskites can recover after light or current-induced degradation. This self-healing ability is tested by acting mechanically on MAPbI3 polycrystalline microcrystals by an atomic force microscope tip (applying force, scratching, and cutting) while monitoring the PL. Although strain and crystal damage induce strong PL quenching, the initial balance between radiative and nonradiative processes in the microcrystals is restored within a few minutes. The stepwise quenching-recovery cycles induced by the mechanical action is interpreted as a modulation of the PL blinking behavior. This study proposes that the dynamic equilibrium between active and inactive states of the metastable nonradiative recombination centers causing blinking is perturbed by strain. Reversible stochastic transformation of several nonradiative centers per microcrystal under application/release of the local stress can lead to the observed PL quenching and recovery. Fitting the experimental PL trajectories by a phenomenological model based on viscoelasticity provides a characteristic time of strain relaxation in MAPbI3 on the order of 10-100 s. The key role of metastable defect states in nonradiative losses and in the self-healing properties of perovskites is suggested.

Current-induced degradation behaviors of InGaN/GaN multiple quantum well UV photodetectors: Role of electrically active defects

To examine the critical role of electrically active defects and surface states in InGaN/GaN multiple quantum well (MQW) ultraviolet photodetectors (UV-PDs), the study of degradation mechanisms in such devices is very important. In this work, we have fabricated InGaN/GaN MQW UV-PDs with a thick passivation layer of Al 2 O 3 and studied their degradation behaviors by applying high current stress. The origin of degradation processes has been investigated intensively by employing different combined optical and electrical measurements. As a consequence of stress, we noticed that (i) the electroluminescence intensity decreases distinctly (∼ 48 %), suggesting that more of the charge carriers are captured by the newly induced defects in the active region; (ii) the open circuit voltage is mostly accountable for the degradation of photovoltaic properties in treated PDs; (iii) the parasitic current leakage paths increase significantly which in turn reduce the photocurrent generation process largely; (iv) within the temperature range of 100–440 K, the values of the ideality factor and barrier height are found to be always higher and lower in treated PDs, respectively, indicating the presence of generation-recombination centers caused by defects; (v) two major trap levels are identified in treated PDs via Laplace deep level transient spectroscopy analysis; and (vi) the responsivity in treated PDs decreases. The obtained results indicate that degradation is mainly associated with the newly generated defects, mostly Mg-related shallow acceptors, including Mg Ga and Mg-H 2 complexes, which can form the acceptor levels as a result of the breaking of Mg-H chemical complexes due to high heating levels during the stress treatment. • Degradation characteristics of InGaN/GaN MQW UV photodetectors are studied. • Two major trap levels are detected in stressed PDs via Laplace deep level transient spectroscopy analysis. • Newly induced defects in the active region play an important role in worsening the device performances. • Degradation is mostly associated with Mg-related shallow acceptors, including Mg Ga and Mg-H 2 chemical complexes.

Impact of current-induced degradation process on the electro-optical characteristics of InGaN/GaN multiple-quantum-well photodetectors fabricated on sapphire substrate

The impact of defects on the degradation behaviors of InGaN/GaN multiple-quantum-well photodetectors submitted to dc current stress has been intensively studied. The root mechanism for degradation has been studied employing combined electro-optical measurements. The collected results indicate that (i) stress can induce an increase in parasitic current leakage paths and trap-assisted tunneling in reverse and subturn-on forward bias ranges, respectively; (ii) during stress, the overall capacitance increases and localization improves in the apparent carrier concentration within the active region; (iii) stress causes a significant decrease in quantum well intensity and an increase in yellow luminescence; (iv) stress induces an increase in the external quantum efficiency due to broadening of the space-charge region; and (v) the detectivity of the device decreases after the stress treatment. These results suggest that degradation is largely attributed to the activation of initially inactive defects, mainly Mg–H, C-related, and VGa defects in the investigated devices, with consequent worsening of their performances.

Current-induced degradation process in (In)AlGaN-based deep-UV light-emitting diode fabricated on AlN/sapphire template

A comprehensive analysis of the degradation behavior of (In)AlGaN-based deep-ultraviolet light-emitting diode (DUV LED) stressed at a constant dc current of 60 mA has been presented. This work is based on combined X-ray diffraction (XRD), atomic force microscopy (AFM), electroluminescence (EL), cathodoluminescence (CL), current-voltage (I–V) and capacitance-voltage (C–V) characteristics. We used XRD and AFM data to investigate the structural properties of the epilayer. The EL spectrum shows two clear emission peaks at around 4.71 and 3.77 eV and a plateau region within 4.24 to 3.82 eV. To know the origin of the plateau region and the peak at 3.77 eV, we performed CL measurement. As a consequence of constant current stress, we obtained the following results: (1) a gradual degradation in EL power due to increase of Shockley–Read–Hall (SRH) recombination and the generation of new point defects in the active region; (2) a significant improvement in the leakage current, that is attributed to the enhance in trap assisted tunneling; and (3) a strong increment in the device capacitance in both reverse and forward bias regions, that is ascribed to the improvement in the net charge concentration and their redistribution in the active region of the LED.

The effect of pollutants on leakage current and power degradation of photovoltaic modules

The surface of photovoltaic (PV) modules exposed under sunlight are always covered with pollutants, which often lead to the increase of leakage current and potential induced degradation (PID). For investigating the indistinct mechanism and effect of pollutants on PV leakage current, activation energy, and power degradation, an experimental prototype was set up in an environmental chamber. Then different masses of pollutants were smeared on PV modules' surface to investigate their influence on leakage current. The polluted leakage current model was established by measuring the PV modules’ leakage current and calculating the activation energy with different humidity and pollutant mass. The experimental results indicate that the leakage current model proposed in this paper can predict the polluted leakage current, and the proposed pollutant correlation coefficient can reveal the degradation rate and guide for the economic operation of cleaning PV modules.

Current-induced degradation and lifetime prediction of 310 nm ultraviolet light-emitting diodes

The impact of operation current on the degradation behavior of 310 nm UV LEDs is investigated over 1000 h of stress. It ranges from 50 to 300 mA and corresponds to current densities from 34 to 201 A/cm2. To separate the impact of current from that of temperature, the junction temperature is kept constant by adjusting the heat sink temperature. Higher current was found to strongly accelerate the optical power reduction during operation. A mathematical model for lifetime prediction is introduced. It indicates that lifetime is inversely proportional to the cube of the current density, suggesting the involvement of Auger recombination.

Evaluation of impedance spectroscopy as a tool to characterize degradation mechanisms in silicon photovoltaics

Advancements in photovoltaic technologies are hindered by degradation mechanisms such as potential induced degradation (PID) and current-induced degradation (CID). In this work, impedance spectroscopy is used to examine passivated emitter and rear cell (PERC) silicon modules with PID and CID. A comparison between control and degraded modules is done to identify key differences in the impedance spectra and determine the extent of the degradation. PID was observed at the module level as a dramatic reduction in shunt resistance, with a small amount of spatial inhomogeneity present in the degradation. It was found that accurate characterization of CID via measurement of the minority carrier lifetime requires a high bias voltage at the module level that exceeds the capabilities of a standard impedance spectrometer. Because of this, CID was also examined at the cell level, where reductions in minority carrier lifetimes could be accurately measured. A correlation between the reduction in minority carrier lifetime due to CID and a reduction in the power conversion efficiency was observed. Thus the PID and CID mechanisms studied here induce unique changes in the impedance spectroscopy results, making them distinguishable and quantifiable. Finally, the ability to mitigate CID through the use of different silicon wafers and a current induced regeneration process was characterized by impedance spectroscopy.

Effect of Tariff Policy and Battery Degradation on Optimal Energy Storage

In the context of an increasing participation of renewable energy in the electricity market, demand response is a strategy promoted by electricity companies to balance the non-programmable supply of electricity with its usage. Through the use of differential electricity prices, a switch in energy consumption patterns is stimulated. In recent years, energy self-storage in batteries has been proposed as a way to take advantage of differential prices without a major disruption in daily routines. Although a promising solution, charge and discharge cycles also degrade batteries, thus expected savings in the energy bill may actually be non-existent if these savings are counterbalanced by the capacity lost by the battery. In this work a convex optimization problem that finds the operating schedule for a battery and includes the effects of current-induced degradation is presented. The goal is to have a tool that facilitates for a consumer the evaluation of the convenience of installing a battery-based energy storage system under different but given assumptions of electricity and battery prices. The problem is solved assuming operation of a commercial Li-ion under two very different yet representative electricity pricing policies.

Localization of current-induced degradation effects in (InAlGa)N-based UV-B LEDs

The degradation behavior of ultraviolet-B light emitting diodes (UV-B LEDs) emitting near 310 nm has been investigated and a method to localize the degradation effects is presented. Measurements of the electro-optical characteristics of UV-B LEDs, during a 200 h constant-current degradation study, showed an initial fast decrease in the optical power accompanied by a decrease in the drive voltage and an increase in the capacitance. Furthermore, by using a specially designed contact geometry, it was possible to separate the degradation of the electrical properties of the p-layers and p-contacts from the degradation of the active region and n-side of the LED heterostructure. Our investigations show that the initial changes in capacitance and voltage can be attributed to changes in the p-side and at the p-contact of the LED, which can be explained by an activation of Mg dopants.

(Invited) Current-Induced Degradation in Bulk GaN Vertical Schottky Diodes

The recent availability of high quality bulk GaN substrates with low threading dislocation density has made vertical power device structures an attractive possibility. Due to the low probability of a threading dislocation occurring within the active area of devices grown upon bulk GaN, reliability is driven by bulk or surface effects. Past work upon the reliability of Ni-GaN Schottky interfaces has suggested that interdiffusion of the Ni into the GaN can occur under thermal stress, adversely affecting the effective energy height of the barrier and increasing the ohmic nature of the interface. Conditions similar to such thermal stressing can be found at typical operating points in high current power devices used in power electronic applications. Our work examines the influence of high current density stress upon the reliability of vertical bulk GaN Schottky diodes. The vertical diodes studied were fabricated with Pd Schottky metallization with an Au ohmic overlayer. To study the effects of surface chemistry, reliability is compared between devices fabricated with different acidic and basic surface preparations, using HCl and KOH respectively. The fabricated devices were subject to life testing under varying levels of constant current density, up to 10 kA/cm^2. The lifetesting system was designed as a stress-measure-stress system, allowing for the evaluation of device parameters in-situ during testing. Electrical parameters indicating the state of the Schottky barrier were evaluated continuously during the measurement points of testing. In addition, a measurement of barrier inhomogeneity, evaluated using the Tung model, was also used as an indication of the condition of the Schottky interface. The microstructure of the interface before and after stress was examined using S/TEM imaging of representative lamellae samples of the stressed and unstressed devices. EDS imaging was used to determine the degree of diffusion between the Schottky metallization and the GaN substrate. Results of microstructure imaging are correlated with the electrical measurements taken to determine the responsible mechanisms for device degradation.

Current-induced and light-induced macroscopic changes in thin film solar cells: Device degradation mechanism

We report on the formation of large voids in hydrogenated polymorphous silicon (pm-Si:H) PIN solar cells upon light-soaking. We could monitor in situ, the formation of macroscopic bubbles and holes during current-induced degradation of the same devices using optical microscopy. Forward bias, leading to a current-injection of 300mA/cm2, was applied to hydrogenated amorphous silicon (a-Si:H) and pm-Si:H PIN solar cells and series of optical images were taken on the same spot at various steps of current-injection. During the current-injection, the pm-Si:H PIN solar cells experience significant topological changes, which we could not detect in a-Si:H PIN solar cells. These effects were further characterized by complementary ex-situ techniques such as SEM, AFM and spectroscopic ellipsometry.

Effect of Stray Current on Corrosion Behavior of Reinforcing Steel: Importance of Cell Geometry and Orientation with Respect to the Electrical Field

Stray current circulating in reinforced concrete structures may initiate corrosion or accelerate existing corrosion processes on embedded reinforcement. In some cases, the range of dangerous or unwanted interactions of stray currents under favorable conditions (environment), is much broader than is generally recognized. All these show that investigation of the effects of stray current on the corrosion behavior of steel is necessary and significant. In this work, the tested level of stray current was 3 mA/cm2, and the type of samples were reinforced mortar cubes (40 mm×40 mm×40 mm). To investigate the corrosion behavior of embedded steel undergoing stray current, the evaluation indicators adopted were OCP (Open Circuit Potential), Polarization resistance (Rp) derived through LPR (Linear Polarisation Resistance), and electrochemical parameters recorded through EIS (Electrochemical Impedance Spectroscopy) and PDP (Potentio-Dynamic Polarization). The recorded electrochemical response aimed to elucidate the importance of cell geometry i.e. the effect of steel orientation with respect to the electrical field (placed parallel or orthogonal to the current direction). It was found that the geometrical position of the steel bar is of significant importance and determines the level of stray current-induced degradation.

Simulation Study of Light-induced, Current-induced Degradation and Recovery on PERC Solar Cells

The way to permanently recover the well-known Light-Induced Degradation (LID) which affects the p-type Cz-Si PERC solar cells represents one of the main challenges of photovoltaic research. In this work we have set up a numerical simulations flow which allows us to reproduce the experimental measured values of figures of merit (FOMs) of four different Cz-PERC solar cells lots subjected to a degradation and two regeneration processes. The recombination centres in bulk and the Boron-Oxygen complexes (B-O) are modeled by means of two trap levels tuned on the basis of experimental data. From simulations we confirm that the FOM degradation levels off after 16hours and the regeneration process characterized by relatively long time process is preferred in terms of performance recovery. In addition, further cells with different passivation films are analyzed by adopting the same methodology.

Current-induced strength degradation of activated carbon spheres in carbon supercapacitors

Activated carbon microspheres (ACSs), which are prepared using hydrothermal synthesis and ammonia activation, are used as the active materials in the anode and cathode of electric double layer capacitors (EDLCs). The ACS-based EDLCs of symmetrical electrodes exhibit good stability and a high degree of reversibility over 2000 charge-discharge cycles for electric current up to 10 A g−1. The ACSs maintain a nongraphitized carbon structure after over 2000 charge-discharge cycles. Nanoindentation experiments are performed on the ACSs, which are electrochemically cycled in a voltage window of 0–1 V at three electric currents of 0.5, 5, and 10 A g−1. For the same indentation load, both the contact modulus and indentation hardness of the ACSs decrease with the increase of the electric current used in the electrical charging and discharging. These results suggest that there exists strength degradation introduced by the electric current. A larger electric current will cause more strength degradation than a smaller electric current.

Research on Electrical Efficiency Degradation Influenced by Current Crowding in Vertical Blue InGaN-on-SiC Light-Emitting Diodes

Current-induced electrical efficiency degradation (EED) is identified as a strong power conversion efficiency-limiting factor for vertical blue InGaN-on-SiC light-emitting diodes (LEDs). It is found that EED is caused by an increase in series resistance that follows current crowding. EED starts at the moderate-current domain ( ≥ 10-3 A) and limits the power conversion efficiency at the level of ≤ 75% in the high-current domain (>;1.0 A). By decreasing current spreading length, EED also causes the optical efficiency to degrade and stands for an important aspect of the vertical LED's performance.

High current-induced degradation of AlGaN ultraviolet light emitting diodes

Degradation under high current stress of AlGaN quantum well based light emitting diodes emitting at 285 and 310 nm has been studied using electroluminescence, time-resolved photoluminescence and current-voltage experimental techniques. The measurements have revealed that during aging decrease of the emission intensity is accompanied by increase of the tunneling current, increase of the nitrogen vacancy concentration and partial compensation of the p-doping. The main role in the device degradation has been ascribed to formation of tunneling conductivity channels, probably, via activation of the closed core screw dislocations with the help of nitrogen vacancies. Carrier lifetimes in the quantum wells and the p-cladding were found to be unaffected by the aging process, suggesting that the nonradiative recombination has a lesser influence on the device degradation.

Current-induced degradation of high performance deep ultraviolet light emitting diodes

Lifetime measurements on single-chip, packaged 285 nm light-emitting diodes (LEDs) performed under constant current injection at 20 and 75 mA, were compared to the performance of unbiased LEDs baked at the equivalent operating junction temperatures. The thermally stressed devices showed a lesser degradation than those electrically stressed, indicating that elevated temperature alone does not cause degradation. Despite a decay to less than half of the initial power under current injection, time-resolved photoluminescence of the active region exhibits little change, while capacitance-voltage measurements imply that the reduced efficiency and power decay originate from the generation of point defects near the p-side of the p-n junction.

A model for electric degradation of interconnect low-k dielectrics in microelectronic integrated circuits

The low-k dielectric used in interconnect systems of advanced microelectronic devices tends to degrade faster than gate oxide under electric field. The scaling down of the spacing between metal lines to a few tens of nanometers in emerging complementary metal oxide semiconductor technologies calls for re-examining and refining of existing degradation models for ensuring the reliability of future technology nodes without compromising performance. This paper suggests a simple model to explain the nature of the field- and current-induced degradation by taking the electron temperature into account. It is based on experimentally observed trapped charge and current versus time behavior under constant voltage stress. The model explains the low observed activation energy but predicts its increase at operating conditions. It suggests that the commonly used E model may be too conservative for the extrapolation of dielectric lifetime measured under accelerated test (high voltage) conditions to operating voltages. It also predicts that the use of the recently proposed E model is safe for reliability engineering purposes, although it does not describe the full degradation process complexity adequately.

Current-Induced Degradation of Nickel Ohmic Contacts to SiC

The stability of Ni ohmic contacts to p-type SiC under high current density was investigated. A test structure adapted from the four circular contacts method allowed for vertical stressing and the ability to extract a pre- and post-stressed specific contact resistance. The accuracy of the measured specific contact resistance was verified experimentally through comparisons with more widely used methods and the use of computer modeling. The growth of voids initially produced during the high-temperature ohmic contact anneal was found to be the degradation mechanism, effectively decreasing the area of the contact.