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.

Sepaktakraw-like catalyst Mn-doped CoP enabling ultrastable electrocatalytic oxygen evolution at 100 mA·cm^(-2) in alkali media

Seeking highly active,stable and low-cost electrocatalysts used as both cathode and anode in overall water splitting is very crucial for the sustainable utilization of resources.Herein,a highly efficient and long-term stable oxygen evolution reaction(OER)electrocatalyst Mn-doped CoP on foam Ni(MnCoP/NF)is synthesized by the one-step electrodeposition method.Owing to the synergetic effect among the Sepaktakraw-like morphology,the doped Mn element and the binder-free synthesis method,MnCoP/NF displays superior electrocatalytic activity and electrochemical stability toward OER.MnCoP/NF only requires an overpotential of 266 mV to deliver the current density of 10 mA·cm^(-2),demonstrating an excellent electrocatalytic activity even better than that of commercial catalysts of IrO_(2)/NF.And the retention rate of potential can still be maintained at 99.57%after the durability test as long as 240 h,indicating the prominent electrochemical stability of MnCoP/NF.Simultaneously,MnCoP/NF could be directly used as both cathode and anode in the two-electrode system for overall water splitting,exhibiting a low potential of 1.97 V for reaching 100 mA·cm^(-2).Impressive long-term stability of MnCoP/NF is also observed by limited activity decay after 240-h durability tests at 10 and 100 mA·cm^(-2).Thus,this study illustrates a feasible approach to the rational design of highly active and stable electrocatalyst and also provides valuable insights on the improved electrocatalytic performance of water splitting by Mn doping.