Numerical study on the wavelength-dependence of light extraction efficiency in AlGaN-based ultraviolet light-emitting diodes

Wavelength-dependence of light extraction efficiency (LEE) in AlGaN-based ultraviolet (UV) light-emitting diode (LED) structures is numerically studied based on three-dimensional finite-difference time-domain methods. Due to strong UV light absorption in the p-GaN contact layer, LEE of the UV vertical LED structures remains to be only 6–7 % for the transverse-electric mode and 2–3 % for the transverse-magnetic mode, respectively. The effective LEE of UV LEDs is calculated by considering the optical polarization-dependent LEE, and is found to increase from 4 to 5.5 % as the wavelength increases from 260 to 360 nm. It is shown that the wavelength-dependence of LEE can partially explain the decrease in external quantum efficiency with decreasing wavelengths in AlGaN-based UV LEDs.