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.