Spatially resolved degradation effects in UVB LEDs stressed by constant current operation

InAlGaN-based UVB light-emitting diodes with an emission wavelength of 310 nm were operated at an elevated nominal current density of 200 A/cm(2) and a heatsink temperature of 29 ?. The spatial intensity distributions of the electroluminescence and photoluminescence were measured before, during, and after dc stress. A decreasing homogeneity of the spatial intensity distributions with operation time was observed. It is concluded that the current density distribution changes during operation. Furthermore, the active region degrades more rapidly in the areas of higher current density. By quantitatively evaluating the current density distribution, it is proposed that a decreasing radiative recombination efficiency of the active region is causing the decrease in the total optical power of the LEDs during operation.