Numerical investigation of light extraction efficiency in AlGaN deep ultraviolet light-emitting diodes

Light extraction efficiency (LEE) in AlGaN deep ultraviolet (UV) light-emitting diodes (LEDs) is investigated using finite-difference time-domain simulations. For flip-chip LED structures, LEE is obtained to be <;10% due to strong UV light absorption in the p-GaN layer. In addition, LEE of transverse-magnetic (TM) modes is found to be more than ten times smaller than that of transverse-electric (TE) modes, which explains the decreasing behavior of external quantum efficiency of UV LEDs with decreasing wavelengths.