Investigation of the Purcell effect in GaN-based vertical LED structures using FDTD simulation

The spontaneous emission (SE) rate in GaN-based vertical light-emitting diode (LED) structures can be modified significantly depending on the local density of states near the high-reflectance mirror. In this study, this Purcell effect in vertical LED structures is investigated numerically using finite-difference time-domain simulation. The Purcell factor of vertical LED structures is found to vary periodically with the p-GaN thickness, while it is almost independent of the n-GaN thickness, indicating strong influence of the p-type electrode reflector on the SE modification. The peak of the Purcell factor is obtained to be as high as 1.5 at a properly chosen p-GaN thickness, which leads to substantial increase in the internal quantum efficiency (IQE) of LEDs. Since the influence of the Purcell factor on IQE becomes more conspicuous as IQE decreases, the Purcell effect of vertical LED structures is expected to mitigate the green-gap and the efficiency droop problems of current LED technologies.