Effects of electrical stress on the characteristics and defect behaviors in GaN-based near-ultraviolet light emitting diodes

The degradation mechanism of GaN-based near-ultraviolet(NUV,320-400 nm)light emitting diodes(LEDs)with low-indium content under electrical stress is studied from the aspect of defects.A decrease in the optical power and an increase in the leakage current are observed after electrical stress.The defect behaviors are characterized using deep level transient spectroscopy(DLTS)measurement under different filling pulse widths.After stress,the concentration of defects with the energy level of 0.47-0.56 eV increases,accompanied by decrease in the concentration of 0.72-0.84 eV defects.Combing the defect energy level with the increased yellow luminescence in photoluminescence spectra,the device degradation can be attributed to the activation of the gallium vacancy and oxygen related complex defect along dislocation,which was previously passivated with hydrogen.This study reveals the evolution process of defects under electrical stress and their spatial location,laying a foundation for manufacture of GaN-based NUV LEDs with high reliability.

The reliability of AlGaN/GaN high electron mobility transistors under step-electrical stresses

In spite of their extraordinary performance, AlGaN/GaN high electron mobility transistors （HEMTs） still lack solid reliability. Devices under accelerated DC stress tests （off-state, VDS = 0 state, and on-state step-stress） are investigated to help us identify the degradation mechanisms of the AlGaN/GaN HEMTs. All our findings are consistent with the degradation mechanism based on crystallographic-defect formation due to the inverse piezoelectric effects in Ref. [1] （Joh J and del Alamo J A 2006 IEEE IDEM Tech. Digest p. 415）. However, under the on-state condition, the devices are suffering from both inverse piezoelectric effects and hot electron effects, and so to improve the reliability of the devices both effects should be taken into consideration.

Electrical stress and acid orange 7 synergistically clear the blockage of electron flow in the methanogenesis of low-strength wastewater

Energy recovery from low-strength wastewater through anaerobic methanogenesis is constrained by limited substrate availability.The development of efficient methanogenic communities is critical but challenging.Here we develop a strategy to acclimate methanogenic communities using conductive carrier(CC),electrical stress(ES),and Acid Orange 7(AO7)in a modified biofilter.The synergistic integration of CC,ES,and AO7 precipitated a remarkable 72-fold surge in methane production rate compared to the baseline.This increase was attributed to an altered methanogenic community function,independent of the continuous presence of AO7 and ES.AO7 acted as an external electron acceptor,accelerating acetogenesis from fermentation intermediates,restructuring the bacterial community,and enriching electroactive bacteria(EAB).Meanwhile,CC and ES orchestrated the assembly of the archaeal community and promoted electrotrophic methanogens,enhancing acetotrophic methanogenesis electron flow via a mechanism distinct from direct electrochemical interactions.The collective application of CC,ES,and AO7 effectively mitigated electron flow impediments in low-strength wastewater methanogenesis,achieving an additional 34%electron recovery from the substrate.This study proposes a new method of amending anaerobic digestion systems with conductive materials to advance wastewater treatment,sustainability,and energy self-sufficiency.

Internal Stress of Dense Refractory Castables During Unilateral Heating

The change of the internal stress of dense refractory castables during unilateral rapid heating was studied by the electric stress measurement. The results indicate that： （1） during rapid heating, the position near the heated surface is under compressive stress ; the closer the position to the heated surface, the larger the compressive stress; （2） the specimen bursts during the rapid heating; （3） the calculated stress of the structure at the burst moment shows that the compressive stress produced at the same depth as the cracking surface exceeds the ultimate strength of the structure.

A Bio-Physical Analysis of Extracellular Ion Mobility and Electric Field Stress

The electric field stress applied to the cell in the electric field will cause the biological effects of the cell on electromagnetic field. In this paper, the single-shell spherical cell is equated to dielectric spheres, and a biophysical method is used to solve the boundary value problem, and then Maxwell tensor analysis is used to discuss the electric field stresses affecting the applied electric field applied to the cells. The results of numerical analysis show that the ion mobility decreases nonlinearly with increasing frequency in the lower region of the applied electric field frequency, and increases with increasing equivalent dielectric constant at a certain frequency, and the magnitude of the electric field stress is almost independent of the frequency;as the frequency increases, the ion mobility tends to a minimum value and is almost independent of the equivalent dielectric constant, while the applied electric field frequency and the cell dielectric constant both affect the cell normal and the tangential stresses. Therefore, the frequency applied electric field and cell dielectric constant affect the extracellular ion mobility, electric field stress applied to the cell membrane by the electric field;the extracellular ion mobility caused by the electric field in the low frequency range is more pronounced than that in the high frequency, and electric field stress is the basic cause of cell deformation.

热应力与电-热复合应力下油纸绝缘老化特性的比较研究(英文)

During the operation of power transformer,its oil-paper insulation is continuously subjected to various stresses,c.g.,the thermal,electrical,mechanical,and chemical stresses,which cause insulation aging gradually.It has been considered that the combined thermal and electrical stresses are the most important and unavoidable factors that induce insulation materials aging.In this work,accelerated aging experiments of oil-impregnated pressboards under combined thermal(130℃) and electrical stresses(4 kV/mm) are performed,while the aging experiments under single thermal stress are also carried out at the corresponding temperature(130℃).The electrical and physic-chemical properties of oil,including dielectric losses factor tanδ,resistivity,acid value and pH value etc.,are measured during the aging process.Dissolved gasses in oil and polymerization degree of cellulose are also measured.The relationship between these properties of oil-paper insulation and aging time is investigated.The results show that dissolved gases in oil,resistivity,tanδof oil under combined thermal and electrical stresses are obviously different from that tinder thermal stress during aging process while some other properties show similar changing trend.For cellulose, compared with the single thermal aging results,it even shows a slower degradation rate in the presence of electrical stress.

Reliability analysis of GaN-based light emitting diodes for solid state illumination

In this paper, we have discussed the effect of electrical stress on GaN light emitting diode （LED）. With the lapse of time, the LED with an applied large current stress can reduce its current more than without such a stress under a large forward-voltage drop. Its scanning electron microscopy （SEM） image shows that there exist several pits on the surface of the p-metal. With an electrical stress applied, the number of pits greatly increases. We also find that the degradation of GaN LED is related to the oxidized Ni/Au ohmic contact to p-GaN. The electrical activation of H-passivated Mg acceptors is described in detail. Annealing is performed in ambient air for 10 min and the differential resistances at a forward-voltage drop of 5 V are taken to evaluate the activation of the Mg acceptors. These results suggest some mechanisms of degradation responsible for these phenomena, which are described in the paper.

Analysis of Capacitive Parasitism in PWM Inverter-Fed Motor

The effects of parasitic capacitance in induction motor system are unnoticed when it is fed from the AC line, but they are obvious when supplied directly from a PWM inverter. Consequently, many parasitic problems occur, such as motor to earth leakage current, bearing current, incoming line current distortion and uneven distribution of electrical stresses along the winding. On the basis of the uniform transmission line principle, a complete equivalent circuit of the PWM inverter fed motor system is presented, based on which all the capacitive parasitic problems mentioned above are analyzed and simulated by means of PSPICE. All the results are consistent with the existing ones.

THE BEHAVIOR OF TWO PARALLEL SYMMETRIC PERMEABLE CRACKS IN PIEZOELECTRIC MATERIALS

The behavior of two parallel symmetric cracks in piezoelectric materials under anti-plane shear loading was studied by the Schmidt method for the permeable crack face conditions. By using the Fourier transform, the problem can be solved with two pairs of dual integral equations in which the unknown variable is the jump of the diplacement across the crack surfaces. These equations were solved using the Schmidt method. The results show that the stress and the electric displacement intensity factors of cracks depend on the geometry of the crack. Contrary to the impermeable crack surface condition solution, it is found that the electric displacement intensity factors for the permeable crack surface conditions are much smaller than the results for the impermeable crack surface conditions.

ELECTRO-ELASTIC GREEN'S FUNCTIONS FOR APIEZOELECTRIC HALF-SPACE ANDTHEIR APPLICATION

In this paper, as is studied are the electro-elastic solutions for a piezoelectric halfspace subjected Io a line force, a line charge and a line dislocation, i. e.. Green sfunclions on the basis of Stroh formalism and the concept of analytical continuation,explicit expressions for Green's functions are derived. As a direct application of theresults obtained, an infinite piezoelectric solid containing a semi-infinite crack isexammed. Attention iffocused on the stress and electric displacement fields of a cracktip. The stress and electric displacement intensity .factors are given explicitly.

Effects of subconvulsive electrical stimulation to the hippocampus on emotionality and spatial learning and memory in rats

Objective To observe the effects of repeated subconvulsive electrical stimuli to the hippocampus on the emotional behavior and spatial learning and memory ability in rats.Methods One hundred and eight male Wistar rats were randomized into 3 groups. Animals in group SE (n = 42) were given subconvulsive electrical stimulation to the hippocampus through a constant pulsating current of 100 μA with an intratrain frequency of 25 Hz, pulse duration of 1 millisecond, train duration of 10 seconds and interstimulus interval of 7 minutes, 8 times a day, for 5 days. In the electrode control group or CE group (n = 33), animals were implanted with an electrode in the hippocampus, but were not stimulated. Group NC (n =33) animals received no electrode or any stimulation. The emotional behavior of experimental rats was examined by activity in an unfamiliar open field and resistance to capture from the open field, while the spatial learning and memory ability was measured during training in a Morris water maze.Results The stimulated rats tested 1 month after the last round of stimulation displayed substantial decreases in open field activity (scale: 10. 4±2. 3, P<0. 05) and increases in resistance to capture (scale: 2. 85±0. 56, P < 0. 01 ). The amount of time for rats in group SE to find the platform (latency) as a measurement for spatial bias was prolonged (29±7) seconds after 15 trials in the water maze, P<0. 05). The experimental rats swam aimlessly in all four pool quadrants during the probe trial in the Morris water maze.Conclusions Following repeated subconvulsive electrical stimuli to the hippocampus, rats displayed long-lasting significant abnormalities in emotional behavior, increased anxiety and defensiveness, enhanced ease to and delayed habituation to startlement, transitory spatial learning and memory disorder, which parallels many of the symptoms in posttraumatic stress disorder patients.