Impact of gamma irradiation on operating 255 nm AlGaN UV LEDs: defect analysis via DLTS and admittance spectroscopy

We investigated the effects of gamma (γ) ray irradiation on 255 nm AlGaN UV LEDs under various stress conditions, including current stress and combined irradiation and current stress. Our results show that the LEDs are similarly impacted by all conditions, with powered devices exhibiting significant changes in both optical and electrical properties. Deep Level Transient Spectroscopy (DLTS) was used to analyze defects, revealing that γ-ray exposure and other stresses primarily affect the active region and p-side of the device. The observed effects are attributed to an increase in hole traps associated with gallium vacancy complexes at 0.67 eV and nitrogen vacancies associated with active regions (V_N traps) at 0.2 eV. These defect concentrations alter the effective carrier concentration, accelerating degradation under electrical stress. Our findings provide new insights into the radiation tolerance of 255 nm AlGaN UV LEDs under various stress conditions.